Durable acidic water oxidation ruthenium based electrocatalyst by fluorination induced symmetry breaking

Domain: physics
Published: 2025-11-25
Editorial outcome: major_revision

Abstract
Ru–based materials exhibit high electrocatalytic activity for the acidic oxygen evolution reaction, but they are prone to transform into soluble RuO4 species via traditional lattice oxygen mechanism at high oxidation potentials, resulting in rapid inactivation. Herein, density functional theory calculations predict that the F induced symmetry–breaking can alter the oxygen evolution reaction route of RuO2 from the lattice oxygen mechanism route to the stable adsorption evolution mechanism pathway. Consequently, we fabricate an efficient F–RuO2/FC electrocatalyst by substituting a portion of O in RuO2 with F. Specifically, it can operate continuously for over 1440 h (2 months) at 100, 500 and 1000 mA cm–2 when using F–RuO2/FC as anode electrocatalyst in proton exchange membrane water electrolyzer. Detailed in situ experiments demonstrate that the adsorption of intermediates is impacted by the presence of F in RuO2, thus forcing the oxygen evolution reaction to proceed via the adsorption evolution mechanism. This study provides experimental and theoretical insights for customizing stable Ru–based electrocatalysts for water splitting and beyond.

Introduction
Hydrogen energy has received considerable attentions in scientific research and industry attributed to its environmentally friendly and sustainable characteristics over the past decades1–4. Electrocatalytic water splitting based on polymer electrolyte membrane (PEM) is considered a promising strategy for hydrogen production due to their minimal gas crossover, large current density, and high gas purity5–8. Regrettably, the demanding acidic environment and large oxidation potential make it necessary to use corrosion–resistant yet expensive iridium (Ir) (~US$140 g–1) as anode electrocatalysts in practical industrial applications9–11. It is predicted that the requirement for Ir in all proposed PEM electrolyzers is ninefold the current global output for 2030 in the Net Zero Emissions Scenario, undoubtedly exacerbating the critical situation of low iridium reserves12. Therefore, the construction of robust Ir–free OER electrocatalysts is highly desired yet challenging for PEM electrolyzers.

Ruthenium (Ru), as an acidic OER electrocatalyst, is anticipated to supplant Ir because of its elevated electrocatalytic activity, greater earth abundance, and economical cost (~US$16 g–1)13–15. However, the characteristics of thermodynamic instability under acidic OER conditions severely limit their industrialization process, primarily due to the fact that traditional Ru–based materials tend to follow the lattice oxygen mechanism (LOM) that lattice oxygen (OL) is participates in the reaction process, which inevitably leads to structural collapse16,17. Initially, researchers sought to enhance the OER performance of Ru–based materials by introducing oxygen vacancy (OV)18. Regrettably, it has been argued that the generated OV leads to the exposure of Ru, which tends to over–oxidize to form soluble high valence Rux>4, ultimately compromising stability19. Therefore, several schools of thought believe that making the formation energy of OV higher than the redox H2O/O2 energy may be a promising strategy to break the stability bottleneck of Ru–based materials20,21. As so far, numerous feasible approaches have been reported to significantly enhance the formation energy of OV, including heterometal doping (Sn–RuO222, Ni–RuO223, Ta/RuO224), interface engineering (Co–Ru@RuO29:125, GB–RuO226), strain regulation (Li–RuO227, RuSn0.5O228), high–entropy compounds (M–RuIrFeCoNiO29), anion regulation (LD–B/RuO230, Ru/Se–RuO231, RuO2–Cl32) and so on. Among these, the electronegativity and electron affinity of anions are more conducive to optimizing the adsorption/desorption behavior of reaction intermediates on the electrocatalyst surface33. Nevertheless, most recently reported anion–modulated catalysts for OER have predominantly focused on performance enhancement while neglecting the intrinsic connection between the reaction mechanism and microstructure, which impedes the in–depth understanding of highly efficient electrocatalysts. Fundamentally, the intrinsic properties of materials overwhelmingly depend on their crystal symmetry and atomic arrangement. The defects in a lattice may reduce its crystal symmetry, which is named the symmetry–breaking effect34–38. Consequently, it is reasonable to speculate that the energy barrier for O escape can be regulated to suppress the participation of OL in the OER process by breaking the symmetry of the octahedral configuration. Simultaneously, the reconfigured electrons on Ru will alter the adsorption of intermediates, thus forcing the Ru–based materials from the inherent LOM pathway toward a more robust and stable route.

Herein, the acidic OER mechanism of RuO2, predicted by using density functional theory (DFT), has been successfully switched by highly electronegative F–induced symmetry–breaking. As a result, the optimized F–RuO2/FC exhibits robust OER performance with low overpotential and long–term stability in acidic media. In addition, only cell voltages as low as 1.58, 1.70, 1.89, and 2.05 V are required to reach current densities of 500, 1000, 2000, and 3000 mA cm–2, respectively, in a scalable PEM water electrolysis (PEMWE) device. It is worth noting that it can operate stably for up to 1440 h (2 months) at 100, 500, and 1000 mA cm–2. In situ experiments demonstrate that the reaction mechanism follows the adsorption evolution mechanism (AEM) pathway when part O in RuO2 is replaced by F, ensuring long–lasting stability. This work pioneers a fresh horizon for constructing robust catalysts in the electrochemical field by F–anion–induced symmetry–breaking.

Results
Theoretical simulations

The widely recognized acidic OER mechanism on RuO2 is LOM pathway, in which O interacts with water–oxygen (OW) to facilitate the formation of O–O intermediate species, concurrently creating OV (Fig. 1a). The generated OV can also serve as active site to accelerate the OER process, ultimately leading to structural collapse and leaching of metal Ru, thus presenting rapid deactivation. In contrast, converting the traditional LOM pathway to a more stable AEM route by anion–induced symmetry–breaking may be a feasible strategy to improve the stability of Ru–based materials (Fig. 1b). Evidently, the oxygen involved comes from water rather than OL, thereby ensuring robust structural integrity during the OER process. Subsequently, DFT simulations were used to accelerate the discovery of high–performance electrocatalysts, thus M–RuO2 (M=F, S, Se, P, N, Cl, and Br) was constructed to evaluate their OER performance. According to the results, a more energy–favorable structural model was adopted for subsequent calculations (Supplementary Figs. 1–7 and Supplementary data 1). The Gibbs free energy of rate–determining step (RDS) for F–RuO2 is 1.80 eV, lower than that of N–RuO2 (1.83 eV), S–RuO2 (1.86 eV), P–RuO2 (2.60 eV), Se–RuO2 (2.76 eV), Cl–RuO2 (3.16 eV), Br–RuO2 (4.28 eV) and RuO2 (1.89 eV) (Fig. 1c and Supplementary Figs. 8–15). In addition, the observed hydrogen bonds between H and adjacent O indicate a low value of the calculated enthalpy change, which serves to stabilize OOH adsorption at the coordinatively unsaturated Ru site on the F–RuO2 (110) surface (Supplementary Fig. 16). The charge distinction for the two O species adsorbed on F–Ru and O–Ru is about 0.06 e, which demonstrates the improved O atom binding on F–RuO2 (110), thereby fostering the genesis of O−O coupling and ultimately leading to the production of molecular O (Supplementary Fig. 17). Furthermore, the electron localization function (ELF) of the *OOH adsorbed on F–RuO2 surfaces shows a higher ELFmax value than RuO2, which indicates an enhanced covalent bond of OOH intermediate induced by the stronger interaction of *OOH on the F–RuO2 (Supplementary Fig. 18). Moreover, the limiting potential for OER on the F–RuO2 (110) surface was estimated at 1.80 V, representing a reduction of approximately 0.11 V compared to RuO2 and implying enhanced OER activity (Supplementary Fig. 19). The outcomes of the calculations revealed that the d–band structure of Ru and the 2p–band structure of O undergo modulation due to the incorporation of F (Fig. 1d). Density of states (DOS) indicates that O 2p band center moves from –2.96 eV (RuO2) to –3.23 eV with the introduction of F, signifying an elevated formation energy for OV, which consequently suppresses the dissolution of Ru in acidic media. Notably, a decrease of the Ru d–band center relative to fermi energy level (Ef) is observed after the partial substitution of O with F, potentially influencing the adsorption/desorption of intermediates on the catalyst surface39. Therefore, compared with the traditional RuO2 following LOM route, the introduction of F gives RuO2 more energy advantages on the AEM path (Supplementary Fig. 20). Furthermore, similar phenomena have been observed on (111) and (100) planes of F–RuO2 and RuO2, proving its universality (Supplementary Fig. 21).

To further assess the stability of F–RuO2, the enthalpy of F within bulk C–centered orthorhombic structure was used to compute their chemical potential, indicating resistance to the detachment of F from RuO2 (Supplementary Fig. 22). Additionally, the enthalpy change for subsurface oxygen loss was calculated in Supplementary Figs. 23–30. The enthalpy change of subsurface O loss on the F–RuO2 was significantly higher than that of RuO2 modified by other anions, indicating that symmetry breaking also affects the stability of OV in RuO2 (Fig. 1e). The examination of the enthalpy change associated with the demetallation process of the surface Ru atom from both RuO2 (110) and F–RuO2 (110) was evaluated to further investigate the stability (Supplementary Fig. 31). It can be found that the energy expenditure for Ru demetallation elevated from 1.72 to 2.52 eV after the symmetry of octahedral configuration in RuO2 is broken by partial substitution of O with F, indicating increased stability of the surface Ru in F–RuO2 compared to RuO2. It is clear that the Gibbs free energy of the RDS varies with symmetry breaking in an inverted volcano shape (Fig. 1f and Table S1). In contrast, the enthalpy change related to subsurface oxygen loss displays a volcano–shaped profile as a function of symmetry breaking. Note of that F–RuO2 is located at the bottom/top of the volcano due to the presence of high electronegativity but small atomic radius F, which induce slight symmetry breaking in the octahedral configuration of RuO2, consequently reducing the reaction energy barrier and enhancing its stability.

Catalyst synthesis and characterization

Of the candidate electrocatalysts predicted by theoretical calculations, F–RuO2 was considered to be the most promising for OER activity and stability. Therefore, the spherical FC and RuCl3 were ultrasonicated at room temperature (25 °C) and then dried to obtain FC supported RuCl3 (RuCl3/FC) (Supplementary Figs. 32, 33). Subsequently, the F–RuO2/FC was successfully achieved by heat treating the RuCl3/FC at 400 °C in air for 4 h. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization revealed that the spherical FC emerged with abundant pore structures (Supplementary Fig. 34). However, the intact spherical can be maintained for FC without the addition of RuCl3, indicating that the presence of Ru will accelerate the local pyrolysis of FC and thus lead to a rich pore structure (Supplementary Fig. 35). Therefore, the pyrolysis temperature and time of FC will be ameliorated once Ru is present, thus the specific surface area of F–RuO2/FC can be significantly enhanced as evidenced by N2 absorption–desorption isotherm (Supplementary Figs. 36, 37). In addition, long–range ordered atomic arrangements were successfully detected using a spherical aberration–corrected high–angle annular dark–field scanning TEM (AC–HAADF–STEM) (Fig. 2a). The well–defined lattice spacings (0.22 and 0.18 nm) of (020) and (211) planes for RuO2 unequivocally indicate the presence of lattice strain compared to RuO2, which maybe caused by symmetry breaking due to introduction of heterogeneous atoms (Fig. 2b). The fast Fourier transform (FFT) pattern, inset in Fig. 2b, reveals the exposed (020) and (211) planes along the [102] zone axis of F–RuO2/FC. To confirm the heterogeneous atoms in F–RuO2/FC, STEM energy dispersive spectrometer (STEM–EDS) elemental mappings were conducted in Fig. 2c. In addition to the uniformly distributed Ru and O elements, conspicuous F signals can be observed, suggesting that the lattice strain in F–RuO2/FC may be caused by the incorporation of F. Subsequently, geometrical phase analysis (GPA) was performed to evaluate the strain level and distribution in the F–RuO2/FC. Evidently, the reduced and enhanced strain can be observed along the horizontal (εxx) and vertical (εyy) direction, respectively (Fig. 2d, e). The strain profiles of line1 and line2 acquired from strain mappings further confirm that the compressive stress is predominantly along the εxx direction and the tension stress along the εyy direction (Fig. 2f)40. To investigate the critical insight of chemical distributions for F–RuO2/FC, time of flight secondary ion mass spectrometry (TOF–SIMS) analysis was performed in Fig. 2g. The element intensity versus sputter time reveals that the concentration of O– is notably greater than that of Ru+, being consistent with the characteristics of RuO2. In addition, the detected RuF– signals indicate that F indeed replaces part of O and then bonds with Ru during the heat treatment process. Two–dimensional (2D) TOF–SIMS elemental mappings also confirm the presence of significant RuF– species alongside the abundant Ru and O species (Fig. 2h). Clearly, the distribution of Ru and O signals throughout the space in three–dimensional (3D) TOF–SIMS views indicates that the predominant species is RuO2, consistent with the AC–HAADF–STEM analysis (Fig. 2i). The uniform distribution of RuF– signals throughout the entire 3D space further confirm the partial substitution of O by F, thus leading to the formation of Ru–F bonds. X–ray diffraction (XRD) with Rietveld refinement was conducted to obtain the detailed unit cell parameter (Fig. 2j and Table S2). The sharp diffraction peaks correspond to the tetragonal RuO2 with the space group P42/mnm, indicating that the adsorbed RuCl3 on the surface of FC gradually crystallizes into RuO2 during the heat treatment process. The presence of Ru accelerates the local pyrolysis of FC and resulting in F occupying part of the position of O in F–RuO2/FC (inset in Fig. 2j). The F elements were removed by calcining the FC at 400 °C for 12 h (denoted as (F)C) (Supplementary Fig. 38). Subsequently, M–RuO2/(F)C was successfully prepared by adsorption of RuCl3 on the (F)C combined with heat treatment process (Supplementary Figs. 39–46). Furthermore, the Baur distortion index (Di) was employed to quantify the asymmetry of virtual octahedral units within the RuO2 crystal structure:

Di = 1/6 Σ i=1 to 6 |bi – b| (1)

where bi and b represent the individual bond length and the average of six bond lengths, respectively41. Notably, the Di, based on the Rietveld refinement of XRD patterns results, were increase in the order F<N<S<P<Se<Cl<Br, indicating an increase of octahedral symmetry breaking degree, consistent with DFT predictions (Supplementary Fig. 47 and Table S3–S8).

Subsequently, Raman spectra were carried out in Fig. 3a, where the typical peaks at 506.8, 622.2, and 693.4 cm–1 are attributable to the vibration modes of Eg, A1g, and B2g for Ru–O bonds, respectively42. Compared to RuO2, a noticeable red shift can be observed in the vibration peaks of F–RuO2/FC, which may be caused by the shortened Ru–O bond owing to the partial substitution of O by the highly electronegative F (Fig. 3a). Therefore, F–RuO2/FC, F 1s XPS spectra at 684.3 eV, corresponding to the Ru–F bond (Fig. 3b). Furthermore, the F content in F–RuO2/FC is 4.3 at%, which can be confirmed by EDS, XPS, and Raman analysis (Supplementary Figs. 48–54 and Table S9, S10)44,45. Additionally, O 1s XPS peaks of RuO2 are located at 529.0, 530.0, and 531.7 eV, corresponding to OL, OV, and surface–adsorbed H2O, respectively (Fig. 3c)46,47. Evidently, a notable shift of the O species toward higher binding energy can be observed in F–RuO2/FC due to the presence of high electronegativity F results in an altered electronic interaction between Ru and O43. Compared with RuO2, Ru 3p XPS peaks for F–RuO2/FC are negative shift of 0.35 eV, revealing a lower valence state than Ru4+ (Fig. 3d). Furthermore, X–ray absorption near–edge structure (XANES) and extended X–ray absorption fine structure (EXAFS) was executed to scrutinize the electronic structure. The lower absorption energy for F–RuO2/FC compared to RuO2 suggests that the average valence state of Ru in F–RuO2/FC is below +4, which is attributed to the partial substitution of O by highly electronegative F (Fig. 3e). The chemical structure and coordination environment of the F–RuO2/FC was analyzed by Fourier transform of the EXAFS (FT–EXAFS) spectra, where the peak at ~1.42 Å in F–RuO2/FC can be attributed to Ru–O or Ru–F coordination environment (denote as Ru–O/F) (Fig. 3f and Supplementary Fig. 55). Obviously, the diminished intensity of Ru–O/F bonds for F–RuO2/FC as opposed to RuO2 suggests that the introduction of F leads to an unsaturated coordination environment (Table S11). In addition, charge density difference and Bader charge analysis also reveals that the valence state of Ru (+1.34) in F–RuO2 decreases with increasing surrounding electron density, attributing to the electron density surrounding Ru was readjusted as a result of the octahedral symmetry breakdown induced by the highly electronegative F, potentially altering the adsorption of intermediates on RuO2 and thereby switching the reaction route (Fig. 3g–j).

Evaluation of electrocatalytic activity

To verify the prediction of DFT calculation, the catalytic activities of various catalysts towards water oxidation were evaluated using a representative three–electrode setup in 0.5 M H2SO4 (Fig. 4a and Supplementary Fig. 56). Notably, the F–RuO2/FC exhibit a lower overpotential (192, 243, and 296 mV) than those of RuO2/C (230, 306, and 370 mV) and RuO2 (270, 357, and 428 mV) for achieving a current density of 10, 50, and 100 mA cm–2 (Fig. 4a). The rapid OER kinetics of F–RuO2/FC is evidenced by a low Tafel slope value of 41.6 mV dec–1 compared to RuO2/C (69.7 mV dec–1) and RuO2 (76.0 mV dec–1) (Fig. 4b). The OER activities of overpotential and Tafel slope for various catalysts are visually presented in Fig. 4c, where F–RuO2/FC exhibit the smallest overpotential and the Tafel slope value, exhibiting competitive activity among the Ru–based catalysts reported recently (Table S12). Furthermore, electrochemically active surface area (ECSA), which is related to the electrochemical double–layer capacitances (Cdl), was conducted to evaluate the OER activity (Supplementary Fig. 57). The F–RuO2/FC (29.3 mF cm–2) exhibit higher Cdl values compared to RuO2/C (15.6 mF cm–2) and RuO2 (8.9 mF cm–2). Remarkably, the high turnover frequency (TOF) of F–RuO2/FC further confirming that the incorporation of F in RuO2 produced more active sites (Supplementary Fig. 58). In addition, durability is also a crucial factor in assessing their potential for practical application. Therefore, chronopotentiometry tests were performed in Supplementary Fig. 59, where the stability of RuO2/C and RuO2 can be observed to be similar, suggesting that the contribution of existing C towards stability is negligible. Importantly, F–RuO2/FC can operate continuously for over 60 h with slightly dissolution of Ru, indicating that the partial substitution of O by F in RuO2 can significantly improve stability even under harsh acidic conditions (Supplementary Fig. 60). Moreover, the flat polarization curve and fleeting stability prove that FC is inert for OER (Supplementary Fig. 61). It is noteworthy that the activity and stability are closely resemble that of RuO2 when it is mechanically mixed with FC, confirming that the enhanced OER performance of F–RuO2/FC is not caused by the FC substrate (Supplementary Figs. 62, 63). In addition, the lower OER performance demonstrate its sensitivity to the fluorine doping level (Supplementary Fig. 64). Specifically, the Di remains largely unchanged at low F doping levels, while the TOF decreases significantly, suggesting that low F doping primarily affects the number of active sites rather than the Di (Supplementary Figs. 51a, 65). Conversely, as the F doping levels increase, Di increases while TOF decreases, demonstrating that excessive symmetry breaking degrades OER performance (Supplementary Fig. 51b). Similarly, the heat treatment time will also affect the OER activity and stability of F–RuO2 (Supplementary Figs. 66–69). Furthermore, the sharply reduced activity and stability of RuO2/(F)C prove that F is decisive for improving the OER performance of RuO2 (Supplementary Figs. 70, 71). As predicted by the DFT, the RDS energy barrier of OER and the enthalpy change caused by O loss will undergo significant changes when O was replaced by S, Se, P, N, Cl, Br, suggesting that the symmetry–breaking induced by different anions result in varied performance (Supplementary Figs. 72, 73).

Encouraged by the efficient OER performance, F–RuO2/FC and Pt/C were utilized as the anode and cathode electrocatalysts, respectively, to evaluate their practical application potential in the PEMWE device. Specifically, to deliver current densities of 500, 1000, 2000, and 3000 mA cm–2, F–RuO2/FC||PEM||Pt/C cell requires voltage as low as 1.58, 1.70, 1.89 and 2.05 V, respectively, which are lower than those of RuO2||PEM||Pt/C (1.61, 1.78, 2.10 and 2.42 V) and RuO2/(F)C||PEM||Pt/C (1.70, 1.96, 2.44 and 2.86 V) (Fig. 4d and Supplementary Fig. 74a). Subsequently, the chronopotentiometry test was carried out to evaluate the stability of F–RuO2/FC in the PEMWE device (Fig. 4e). Excitingly, the F–RuO2/FC–based cell can operate stably for 2 months even at 100, 500 and 1000 mA cm–2, far surpassing RuO2||PEM||Pt/C and RuO2/(F)C||PEM||Pt/C, indicating the promising potential for practical applications (Supplementary Fig. 74b, c). Notably, after long–term PEMWE testing, the morphology, chemical states, and crystal structure of F–RuO2/FC remain largely unchanged, in sharp contrast to the severely degraded RuO2/(F)C, proving long–lasting stability (Supplementary Figs. 75–77)48,49. Apparently, F–RuO2/FC present a larger current density and longer stability, exhibiting competitive performance among the recently reported PEM electrocatalysts (Table S13).

Mechanism studies

To investigate the underlying mechanism during the OER process, in situ characterizations were conducted in Fig. 5. Note of that the diffraction peak intensity does not decrease significantly as the potential range from 1.0 to 1.5 V by in situ electrochemical XRD testing, implying the structure of F–RuO2/FC remain intact during a wide range of potential tests (Fig. 5a). More importantly, the well–preserved diffraction peak in the situ monitoring for up to 60 minutes suggests that the O in F–RuO2/FC may not participate in the OER process, thus deviating from the traditional LOM route (Supplementary Fig. 78). Therefore, the dynamic evolution of the surface structure during the OER process is monitored by in situ electrochemical Raman spectroscopy (Fig. 5b). Clearly, the vibrational peaks corresponding to Ru–O bonds (Eg, A1g, and B2g) are evidently present across the entire potential window, suggesting that the structure of F–RuO2/FC is not greatly damaged, consistent with the results of in situ XRD. Significantly, a Raman peak emerges gradually at ~731 cm–1 with the applied potential increases, compared with RuO2/C, attributed to the formation of Ru–OOH intermediates in the AEM pathway (Supplementary Fig. 79)50. As shown in Fig. 5c, the corresponding contour plots exhibit significantly enhanced vibration signals of B2g for Ru–OOH intermediates except for the predominant feature signals of Ru–O bonds, proving that the reaction intermediates in the AEM pathway are indeed captured.

To further elucidate the actual OER route, in situ attenuated total reflectance infrared (ATR–IR) spectroscopy was carried out to detect the reaction intermediates. As shown in Supplementary Fig. 80, two absorption peaks attributed to the *OO intermediate formed during the LOM pathway are detected, indicating that RuO2/C follow the conventional LOM pathway during the acidic OER process51. Conversely, in situ ATR–IR spectroscopy of F–RuO2/FC showed a sharp characteristic peak appear at 1237 cm–1, belonging to the stretching vibration of surface–adsorbed *OOH intermediates, evidencing the dominance of the AEM pathway (Fig. 5d)52. Obviously, the signals of *OOH intermediates gradually appear and are significantly enhanced with the increase of potential, indicating that the incorporation of F can force the reaction mechanism of RuO2 from the traditional LOM to AEM, thus ensuring long–lasting stability even at high applied potential. Additionally, F–RuO2/FC show clearly pH–independence, suggesting the significant suppression of the LOM pathway and the dominant role of the AEM pathway (Supplementary Fig. 81)53,54. Furthermore, the reaction intermediate signals of *OOH in the AEM pathway and *OO in the LOM pathway were simultaneously detected during the OER process of N–RuO2/(F)C and S–RuO2/(F)C, but the signals of *OOH are disappeared across the entire potential window of P–RuO2/(F)C, Se–RuO2/(F)C, Cl–RuO2/(F)C and Br–RuO2/(F)C (Supplementary Fig. 82)55. Subsequently, operando differential electrochemical mass spectrometry (DEMS) was performed on 18O isotope–labeled F–RuO2/FC using linear sweep voltammograms (LSV) in H216O–0.5 M H2SO4 (Supplementary Fig. 83a). As shown in Fig. 5e, the mass signals of 32O2 and 34O2 were detected without 36O2 products, suggesting the non–participation of OL in the OER process56. The mass signals of 32O2 gradually increase and present a constant ratio (34O2:32O2) with the occurrence of OER, further demonstrating the dominant AEM pathway (Supplementary Fig. 83b, c). Therefore, it can be concluded that the LOM pathway that OL is involved in the OER process, including a labeled 18O and an ambient O (16O) from the electrolyte, resulting in the instability surface of the RuO2 and consequently generating 16O18O species (Fig. 5f). Based on the DFT computations and detailed experimental characterization, the F induced symmetry–breaking in octahedral configuration of RuO2 improves the interaction between adsorbent and the electrocatalysts surface, alters the OER route to follow the AEM pathway, and ultimately enhancing the electrocatalytic performance.

In summary, a highly efficient acidic OER electrocatalyst has been predicted by DFT calculation, which uses F to replace partial O in RuO2 to break the symmetry of the octahedral configuration and thus switch the reaction path. The improved O species adsorption and attenuated demetallation process of Ru improve the OER intrinsic activity and resistance to solvation. As a validation, to deliver the current density of 10, 50, and 100 mA cm–2, only overpotentials of 192, 243, and 296 mV need to be provided for F–RuO2/FC in acidic conditions. More importantly, the cell voltage of 1.58, 1.70, 1.89 and 2.05 V can drive current densities up to 500, 1000, 2000, and 3000 mA cm–2, respectively, simultaneously continuously operating at 100, 500 and 1000 mA cm–2 for 2 months in a PEMWE device. Detailed in situ experiments reveal that the F–induced symmetry–breaking ensures the structural stability of RuO2 during the OER process and changes their traditional OER mechanism from LOM to AEM, thus greatly enhancing the stability. This study offers a fresh perspective for altering the reaction mechanism of OER electrocatalysts based on anion–induced symmetry–breaking to realize efficient performance.

Methods
Chemicals

Ruthenium (III) chloride (RuCl3, 97%) was obtained from Shanghai Xihang New Materials Technology Co., Ltd. Fluorocarbon (FC) was purchased from Wenzhou Bangxinyuan Technology Co., Ltd. Melamine (CH6N6, 99%), selenium (Se, 99.99%), isopropyl alcohol (C3H8O, 99.5%), Nafion (5 wt%) and VC–X72 carbon were obtained from Meryer. Manganese dioxide (MnO2, 99%), sulfur (S, 99.99%), ruthenium (IV) oxide (RuO2, 99.9%), polyvinyl chloride ((C2H3Cl)n, K–value 68–65) and sodium hypophosphite (NaPO2H2, 99%) were obtained from Aladdin. Hexabromobenzene (C6Br6, 99%) was obtained from Macklin. Pt/C (20 wt%) and Nafion 115 membrane (diameter: 3 cm, thickness: 127 μm) were obtained from Sinero. Ethanol (C2H6O, 99.7 wt%) was purchased from Anhui Ante Food Co., Ltd. Sulfuric acid (H2SO4, 95.0–98.0 wt%) was obtained from Zhejiang Zhongxing Chemical Reagent Co., Ltd. Reagents were used directly without further purification, and all experiments utilized deionized water (18 MΩ cm–1).

Preparation of F–RuO2/FC

10 mg of FC and 5.2 mg of RuCl3 were added to ethanol and sonicated homogeneously at ambient temperature (25 °C). Subsequently, the homogeneous solution was dried at 80 °C to yield RuCl3/FC. At last, the RuCl3/FC was annealed at 400 °C for 4 h in an air atmosphere (denoted as F–RuO2/FC). In the preparation of RuO2/C, FC was replaced by VC–X72 carbon.

Preparation of RuO2/(F)C

The synthesis condition of RuO2/(F)C is the same as F–RuO2/FC, except that the FC used for RuO2/(F)C was pre–annealed in air at 400 °C for 12 h to remove F (denoted as (F)C).

Preparation of M–RuO2/(F)C (M=N, S, P, Se, Cl and Br)

The M–RuO2/(F)C electrocatalyst was synthesized by vapor transport method, where the anion sources and RuO2/(F)C (mass ratio 1:2) were placed in a quartz tube as shown in Supplementary Fig. 84. To obtain M–RuO2/(F)C, the RuO2/(F)C was annealed at 400 °C for 1 h (heating rate: 5 °C min–1), while the anion sources were simultaneously heated to their respective target temperatures. In addition, melamine, sulfur powder, sodium hypophosphite, selenium powder, a mixture of polyvinyl chloride and manganese dioxide, and hexabromobenzene were used as anion sources, releasing anions under heat treatment at the target temperatures specified in Table S14, respectively.

Preparation of electrolyte

13.8 mL of sulfuric acid was slowly added to deionized water and diluted to a final volume of 500 mL in a volumetric flask. After thorough mixing, the resulting homogeneous solution was the final 0.5 M H2SO4 electrolyte with a pH of 0.3 ± 0.01. The prepared electrolyte was stored in a sealed container under dry conditions at room temperature (25 °C).

Electrochemical measurements

A CHI1100D workstation (CHI Instruments, Inc., Shanghai) was employed to assess the OER activity of the electrocatalysts within a standard three–electrode system. Then 2.0 mg of catalyst was added to 200 μL of a solution comprising Nafion (5 μL) and isopropyl alcohol (195 μL), and the ink was prepared by ultrasonic at 25 °C. The content of Ru is 14.71 wt%, as determined by inductively coupled plasma atomic emission spectroscopy (ICP–AES) measurements. For the preparation of the working electrode (0.196 cm2, Gaoss Union), 10 μL of ink was dripped onto a glassy carbon electrode and dried at 25 °C. The loading amount of Ru on working electrode is 75 μg cm–2, based on the calculation (10 μL × 10 μg μL–1 × 14.71 wt%)/0.196 cm2. The counter electrode and reference electrode used in the OER tests were graphite rod and saturated calomel electrode (SCE). Therein, the calibration of the reference electrode was periodically performed in an H2–saturated 0.5 M H2SO4 electrolyte using a three–electrode system with a Pt wire served as both the working and counter electrodes. All OER polarization curves (95% iR compensation) are averages of the multiple test results collected at a scan rate of 5 mV s–1. The resistance of the electrolyte was determined using iR correction.

Structure Characterizations

A FEI Tecnai F20 instrument was employed to acquire the scanning electron microscope (SEM) images of the catalysts. The microscopic morphology was examined through transmission electron microscope (TEM) imaging using a HITACHI HT700 operated at 100 kV. The surface chemical composition of the catalysts was investigated by X–ray photoelectron spectroscopy (XPS), with data acquired using a Kratos Axis Supra instrument. A FEI Talos F200S microscope operating at 200 kV was employed to characterize of microstructure and elemental composition by acquiring high–resolution transmission electron microscope (HRTEM) and energy dispersive X–ray spectroscopy (EDS) data.

Calculation of the turnover frequency (TOF)

Based on the condition that each Ru atom on the electrode was considered as an active site, the TOF were calculated according to Eq. (2):

TOF = Number of O2 per second / Number of active Ru sites (2)

The number of oxygen per second was obtained from the LSV curves based on Eq. (3):

Number of O2 per second = (jJjA) / (4e * 96453.8 C mol–1) (3)

where J is the geometric current.

The number of active Ru sites can be calculated following Eq. (4):

Number of active Ru sites = (mcat × Ru wt%) / 101.07 g mol–1 × 6.023 × 1023 (4)

Where mcat is the mass of catalysts loaded on the work electrode.

In situ XRD tests

In situ XRD measurements were carried out in a representative three–electrode setup. The electrodes were assembled in a in situ electrolytic cell and then tested on the Bruker D8 ADVANCE X–ray with the potential range from 1.0 to 1.5 V versus reversible hydrogen electrode (vs. RHE). The voltage and current of the tubes used are 45 kV and 200 mA.

In situ ATR–IR tests

A professionally customized three–electrode reaction cell was used for the In situ ATR–IR measurements (Supplementary Fig. 85). ATR–IR spectra were collected using unpolarized IR radiation on a PerkinElmer Frontier FT–IR spectrometer that was equipped with a built–in mercury–cadmium–telluride (MCT) detector and operated at a resolution of 4 cm−1. Following data acquisition, all spectral data were converted to absorbance units. This conversion was based on the formula -log (I/I0), with I and I0 denoting the reflected radiation intensity from the sample and reference spectra, respectively.

In situ Raman tests

A Renishaw InVia Raman spectrometer equipped with 50× objective and 532 nm laser was employed for in situ electrochemical Raman measurements. The experiments were conducted in a standard three–electrode setup, comprising a catalyst–loaded L–shaped Au working electrode, a Pt wire counter electrode and an Ag/AgCl reference electrode. The in situ Raman spectra were ultimately collected while applying a constant potential ranging from 1.0 to 1.7 V (vs. RHE) to the working electrode.

PEMWE tests

A Nafion 115 membrane (N115, DuPont, geometric area: 1 × 1 cm2) with a thickness of 127 μm was used to construct the membrane electrode assembly (MEA). F–RuO2/FC and commercial Pt/C (20 wt%) were used as the anode and cathode, respectively. The N115 membrane was pretreated prior to MEA preparation with sequential 1 h treatments at 80 °C in 5 wt% H2O2 solution and 5 wt% dilute H2SO4, each interspersed with a 0.5 h deionized water rinse. The catalyst ink was formulated with a solution of isopropyl alcohol and deionized water in a 2:1 volume ratio serving as the dispersion medium, with Nafion ionomer (5 wt%) added (25 wt% relative to the catalyst) before ultrasonication. Then, the prepared ink was sprayed onto the both sides of Nafion 115 membrane to get the catalyst–coated membrane (CCM), achieving noble metal loadings of 2 mg cm–2 for anode and 0.5 mg cm–2 for cathode. Subsequently, the CCM was sandwiched between porous Pt–plated Ti foam gas diffusion layer (GDL) and assembled into the PEM cell. Last, 5 Nm torque was applied on PEM cell for sealing. All performance evaluations, conducted without iR correction, were carried out in a PEM cell at 80 °C under ambient pressure, where the stability of F–RuO2/FC was evaluated by chronopotentiometry at 100, 500 and 1000 mA cm–2.

DFT calculations

DFT calculations were conducted using the Vienna ab initio simulation package (VASP), which employed the projector augmented wave (PAW) method to simulate the electron–ions interactions57,58. The exchange–correction interactions were described by the generalized gradient approximation (GGA) of the Perdew–Burke–Ernzerhof (GGA–PBE)59. The RuO2 (110) facet was selected because it exposes fully coordinated bridged Ru sites and coordination unsaturated sites with quintuple coordination that bind to triple–coordinated O for better identification of the active site60–62. Additionally, this surface is known to exhibit the most favorable thermodynamic free energy during most synthesis processes, as established in prior studies63. The cutoff energy was set as 400 eV during the structural optimization of all slab models. During the structural optimization calculations, the atoms in the bottom two layers were fixed and other layers of atom were allowed to relax. The vacuum layer above the surface is at least 15 Å, and the calculation module was placed in a 6.2146 × 12.6698 × 21.7973 Å lattice. The k–points (Monkhorst–Pack mesh) during the structural optimization and electronic structure–involved calculations were set to 4×2×1 and 5×5×1, respectively.

The Gibbs free energy change during OER was calculated by ΔG=ΔE+ΔZPE – TΔS, where the ΔE is the energy change of intermediates adsorbed on catalysts surface based on the DFT calculations, ΔZPE and ΔS is the change in zero–point energy and entropy, respectively, T is room temperature (298.15 K). The free energy of (H++ e–) at standard conditions was assumed as the energy of 1/2 H2. Namely, G(H++e–)=1/2G(H2).

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This work presents a strategy utilizing F-induced symmetry breaking to inhibit structural degradation of RuO₂, achieving 2-month stability under industrial-grade current densities of 1000 mA cm-2. However, the conclusion regarding the switchable reaction mechanism from the LOM to the AEM, driven by the F-doping, lacks sufficient evidence from appropriate control experiments and theoretical calculations. In addition, relevant literatures on anionic doping in RuO2 have not been adequately referenced and compared (B-RuO2, Angew. Chem. Int. Ed. 2024, 63 (50), e202411603, DOI: 10.1002/anie.202411603; Cl-RuO2, Angew. Chem. Int. Ed. 2025, 64, e202420860, DOI: 10.1002/anie.202420860), which makes it difficult to assess the novelty and innovation of this work. Therefore, in its present form, I consider that the manuscript cannot meet the high standards of Nature Communications.\n1. The authors claim that RuO2 is widely recognized to follow the LOM mechanism, however, the theoretical calculations of OER activity in RuO2 presented in this work focus solely on the AEM pathway. In other words, the barriers calculated does not correspond to the lowest energy barrier for RuO2-based catalysts. In addition, there is a lack of systematic investigation into the differences in energy barriers between the LOM and AEM pathways in RuO2-based catalysts, as well as the effect of anionic doping.\n2. Another point of concern is the authors' statement: \"As predicted by DFT, a marked decline in OER activity and stability was observed when O was replaced by S, Se, and P…..\" (Line 192-193, Page 9). How does the DFT calculation predict stability degradation following the doping of S, P, or Se?\n3. The concept of symmetry breaking lacks a clear definition or quantitative indicators. It should not only be supported by theoretical calculations but also validated through experimental evidence. Additionally, doping any element could lead to structural changes in RuO2, making the selection of the dopant particularly crucial. The authors chose S/P/Se as dopants, which belong to different periods and main groups compared to F, raising ambiguity, as it would be more straightforward to compare fluorine with elements from the same period (such as C, N, or B). The extent of symmetry breaking induced by F (which may be insufficient) and S (which may be excessive) could deviate from the optimal range needed for maximum OER activity, suggesting that the actual peak performance might lie in dopant systems not yet explored.\n4. The use of carbon support for the PEMWE test is confusing, as carbon supports are inherently unstable under acidic OER conditions, particularly at high potentials. If this material is ever going to be used in an electrolyzer, it should also be possible to use it in an unsupported manner. In addition, it would be beneficial to include characterization of the carbon support after long-term PEMWE testing.\n5.The introduction fails to adequately review current modification strategies for RuO2 and lacks a comparison of anion dopants with other alternatives, such as metal dopants, overlooking a critical analysis of how anion dopants can address the existing stability challenges.\n6. The absence of in-situ experiments for undoped RuO2 and S/P/Se-doped RuO2 limits the validation of the proposed switchable reaction mechanism, particularly regarding the effects of F doping.\n7. The manuscript lacks detailed synthetic protocols for S/P/Se-RuO₂ materials, with some descriptions remaining ambiguous (e.g., \"Concurrently, M–RuO2/(F)C...heat treatment process\"). Additionally, there is no quantification of noble metal mass loading in any of the electrochemical measurements. These insufficient experimental details hinder the accurate evaluation of the OER performance of the catalysts.", "reviewer_2": "The manuscript describes the modelling, fabrication, characterization and electrochemical testing of anion doped ruthenium oxide catalysts for oxygen evolution reaction (OER) in acidic electrolyte. The manuscript is well structured and logically organized. The champion fluorine doped ruthenium oxide shows impressive activity and robustness towards OER. The manuscript could be accepted with the following minor aspects having been addressed.\n1. As the dopant is essential to break the symmetry and induce electrocatalytic activity, the nature of the dopant is important information. What is the dopant level of the fluorine doped ruthenium oxide and did the author observe any dopant level dependent activity towards OER?\n2. There has been debate on the true active site of the anion doped metal oxide as OER electrocatalyst and whether the active site could be preserved after long-term test. It is suggested that the author provide more material characterization data to show the structural properties.\n3. To further prove the stability of the electrocatalysts, the leaching of ruthenium from the electrocatalysts with and without dopant can be monitored and compared.\n4. Are the identified intermediates in the in-situ IR/Raman spectroscopy characterizations unique to the fluorine doped ruthenium oxide or they are generally observed for ruthenium oxide. The information is useful for the discussion of role of dopant/asymmetry on the reaction mechanism.\n5. It is suggested that the scale bars could be added to the images, such as Figure 2d, e, h, i.\n6. The experimental details on the fabrication of anion doped ruthenium oxide samples, PEM water electrolyzers, in-situ testing (e.g., Raman spectroscopy), could be provided for the audience.\n7. Is it very obvious that the electrocatalyst is iridium–free as no iridium has been used in this work? The authors could consider an alternative manuscript title.\n8. The authors should double check the wordings, such as absorb/adsorb, figure numbers.", "reviewer_3": "In this manuscript, the authors endeavor to markedly enhance the stability of Ru-based catalysts via fluorine doping strategies. However, further supplementation and refinement are required regarding the microscopic mechanism of symmetry breaking, the comprehensiveness of experimental validation, and the depth of comparison with state-of-the-art research. It is recommended that the authors strengthen the correlation between theoretical calculations and experimental characterizations, while clearly articulating the positioning of innovation points within the existing framework to elevate the novelty and persuasiveness of the manuscript.\n1. The introduction does not adequately address current approaches to resolving stability issues in ruthenium-based catalysts (e.g., heterometal doping, interface engineering, strain regulation, high-entropy compounds, etc.). Literature searches indicate that these strategies have achieved substantial advancements. It is advised to incorporate relevant references to bolster the comprehensiveness of the discussion.\n2. The specific mechanism by which F-induced symmetry breaking suppresses LOM lacks sufficient detail. Existing studies (e.g., 10.1002/anie.202420848, 10.1038/s41467-024-49281-2) demonstrate that lattice symmetry breaking inhibits OLE participation through elongation of Ru-O bond lengths and reduced covalency. Further elucidation of the effects of F doping on electronic structures and reaction pathways using DFT calculations is warranted.\n3. In Figure 1, the authors focus solely on the F-RuO2(110) surface without explaining the rationale for selecting this orientation (e.g., exposed crystal surfaces, reactive site distributions). Comparative analysis of other crystal faces (e.g., (100), (111)) is recommended to validate the universality of the findings.\n4. In Figure 1, the authors state that F-RuO2 is positioned at the bottom of the volcano inversion diagram; however, the introduction of F only induces a slight symmetry breaking. Further validation is required to confirm whether this conclusion aligns with the simulation results for other halogens (e.g., Cl and Br), thereby avoiding overinterpretation of a single data point. Additionally, more detailed information should be provided to compare the local structural changes in RuO₂ after substitution by different elements (e.g., bond lengths, bond angles).\n5. In Figure 1, the authors do not address potential overlooked factors in the DFT simulations (e.g., solvent effects, zero-point energy corrections). It is recommended to include a critical evaluation of the model's assumptions, such as whether the effect of octahedral distortion on oxygen vacancy (OV) formation energy has been overestimated.\n6. In Figure 1, the authors briefly describe the mechanism by which F suppresses Ru dissolution (e.g., O-2p band center shift). It is suggested to integrate Bader charge analysis to elucidate how F enhances stability through electronic structure regulation and discuss its applicability under various acidic conditions.\n7. In Figures 2-3, the lattice strain mechanism induced by F is insufficiently explained. The interaction between the F-O bond and Ru-O bond should be clarified using DFT calculations.\n8. In Figure 3, the Ru valence states predicted by DFT (e.g., average oxidation state reduced to +3.5) should be quantitatively correlated with experimental data (e.g., XPS Ru 3p peak negative shift). The original paper only provides a qualitative description of \"electron density adjustment.\" It is recommended to quantify the polarization effect of F on Ru charge using Bader charge analysis and compare it with relevant experimental characterization results (e.g., XPS and EXAFS).\n9. In Figure 4, the authors do not explicitly clarify whether resistance voltage drop (iR) correction has been applied to the overpotential (η). In acidic electrolytes, electrode interface impedance (R_total) may lead to an overestimation of η, particularly when the catalyst exhibits poor conductivity (e.g., RuO₂-based materials).\n10. In Figure 4, the author merely claims that \"F introduces more active sites,\" which lacks robust and direct evidence.\n11. The comparison between DFT predictions and experimental results remains superficial (e.g., only \"symmetry breaking\" is mentioned), and the adsorption energy or reaction pathway of key intermediates has not been quantitatively validated. It is recommended to include in the supplementary material a correlation between the ΔG* (OER steps) calculated via DFT and the Tafel slope measured experimentally to establish a clear theory-experiment mapping.\n12. In Figure 5, no explicit correlation mechanism linking F doping with the AEM path has been established, and there is a lack of DFT transition state analysis or EXAFS surface coordination verification.\n13. Inferring from XRD structural stability that O does not participate in the reaction involves a logical leap; oxygen isotope tracking data should be incorporated for validation.\n14. It is suggested that the conclusion propose additional research directions, such as investigating the impact of other halogens (Cl, Br) or non-elemental doping on symmetry breaking and OER properties, as well as exploring the potential characteristics and performance of the catalyst under reaction conditions.\n15. The description of the DFT calculation method omits several critical details, including the model size, whether atoms are fixed, how the adsorption site is determined, and how free energy is calculated and corrected. It is recommended that the authors consult relevant literature to provide a comprehensive description to ensure the reproducibility of the computational results."}, "author_response": "Responses to Reviewers\nDear Reviewers,\nThank you for your precious time to constructive comments on our manuscript titled “Ultradurable acidic water oxidation iridium–free electrocatalyst by fluorination induced symmetry–breaking” (Manuscript ID: NCOMMS-25-10822) for Nature Communications. We sincerely appreciate your opinions and confirmation of our work. Accordingly, we have made the corresponding response and revision based on those comments. For other concerns on our work, we have also supplied the corresponding response.\nReviewer #1\nGeneral Comment: This work presents a strategy utilizing F–induced symmetry breaking to inhibit structural degradation of RuO₂, achieving 2–month stability under industrial–grade current densities of 1000 mA cm–2. However, the conclusion regarding the switchable reaction mechanism from the LOM to the AEM, driven by the F–doping, lacks sufficient evidence from appropriate control experiments and theoretical calculations. In addition, relevant literatures on anionic doping in RuO\n2\nhave not been adequately referenced and compared (B–RuO , Angew. Chem. Int. Ed. 2024, 63 (50),\n2\ne202411603, DOI: 10.1002/anie.202411603; Cl–RuO , Angew. Chem. Int. Ed. 2025, 64,\n2\ne202420860, DOI: 10.1002/anie.202420860), which makes it difficult to assess the novelty and innovation of this work. Therefore, in its present form, I consider that the manuscript cannot meet the high standards of Nature Communications.\n[Author’s Response]: Thank you very much for your constructive comments. We highly appreciate that you strictly point out our deficiency in this work and we are truly sorry that our work did not supply a satisfying interpretation and explanation to demonstrate our research. By following your suggestions, we rechecked our manuscript and made the corresponding improvement.\nIn the revised manuscript, we elaborated in detail from both computational and experimental perspectives that the symmetry breaking induced by F leads to the transformation of the OER mechanism from LOM to AEM. The specific description is as follows:\nThe desirable Gibbs free energy of rate–determining step (RDS) for F–RuO is 1.80 eV, lower than\n2\nthat of S–RuO (1.86 eV), P–RuO (2.60 eV), Se–RuO (2.76 eV), N–RuO (1.83 eV), Cl–RuO (3.16\n2 2 2 2 2\neV), Br–RuO (4.28 eV) and RuO (1.89 eV) (Fig. 1c). Notably, a decrease of the Ru d–band center\n2 2\nrelative to fermi energy level (E) is observed after the partial substitution of O with F, potentially\nf\ninfluencing the adsorption/desorption of intermediates on the catalyst surface (Fig. 1d).[36] Therefore,\ncompared with the traditional RuO following LOM route, the introduction of F gives RuO more\n2 2\nenergy advantages on the AEM path (Supplementary Fig. 20). [Page 4, Line 19–21 and Page 5,\nLine 13–17]\nFigure 1. DFT calculations. (c) Gibbs free energy diagram for different catalysts. (d) DOS of Ru 3d and O 2p for F–RuO2; corresponding d–band centers are denoted by white lines.\nSupplementary Fig. 20. Calculated free energy evolution of OER via LOM on F–RuO2, S–RuO2, P–RuO2, Se–RuO2, RuO2, N–RuO2, Cl–RuO2 and Br–RuO2 under electrode potential of 0 V.\nAs shown in Fig. 3g–j, charge density difference and Bader charge analysis also reveals that the\nvalence state of Ru (+1.34) in F–RuO decreases with increasing surrounding electron density,\n2\nattributing to the electron density surrounding Ru was readjusted as a result of the octahedral\nsymmetry breakdown induced by the highly electronegative F, potentially altering the adsorption of\nintermediates on RuO and thereby switching the reaction route. [Page 9, Line 4–8]\nTo investigate the underlying mechanism during the OER process, in situ characterizations were\nconducted in Fig. 5. Note of that the diffraction peak intensity does not decrease significantly as the\npotential range from 1.0 to 1.5 V by in situ electrochemical XRD testing, implying the structure of\nF–RuO /FC remain intact during a wide range of potential tests (Fig. 5a). More importantly, the well–\n2\npreserved diffraction peak in the situ monitoring for up to 60 minutes suggests that the O in F–\nRuO /FC may not participate in the OER process, thus deviating from the traditional LOM route\n2\n(Supplementary Fig. 68). [Page 11, Line 9–15]\nFigure 5. Mechanism explorations. (a) In situ XRD patterns, (b) in situ Raman spectra and (c) corresponding contour plots, (d) in situ ATR–IR spectra of F–RuO2/FC. (e) DEMS signals of 32O2, 34O2, and 36O2 from the gaseous products for 18O–labeled F–RuO2/FC catalysts in H2 16O aqueous H2SO4 electrolyte during three times of LSV cycles.\nSupplementary Fig. 68. In situ XRD patterns of F–RuO2/FC within 60 min.\nTo verify this conjecture, the dynamic evolution of the surface structure during the OER process is\nmonitored by in situ electrochemical Raman spectroscopy (Fig. 5b). Surprisingly, a new Raman peak\nemerges gradually at ~731 cm–1 with the applied potential increases, compared with RuO /C,\n2\nattributed to the formation of Ru–OOH intermediates in the AEM pathway (Supplementary Fig.\n69).[44] As shown in Fig. 5c, the corresponding contour plots exhibit significantly enhanced vibration\nsignals of B for Ru–OOH intermediates except for the predominant surface feature signals of Ru–\n2g\nO bonds, proving that the reaction intermediates in the AEM pathway are indeed captured. [Page 11,\nLine 18–23]\nSupplementary Fig. 69. In situ Raman spectra of RuO2/C.\nTo further elucidate the actual OER route, in situ attenuated total reflectance infrared (ATR–IR)\nspectroscopy was carried out to detect the reaction intermediates. As shown in Supplementary Fig.\n70, two absorption peaks attributed to the *OO intermediate formed during the LOM pathway are\ndetected, further indicating that RuO /C follow the conventional LOM pathway during the acidic\n2\ncharacteristic peak appear at 1237 cm–1, belonging to the stretching vibration of surface–adsorbed\n*OOH intermediates, evidencing the dominance of the AEM pathway (Fig. 5d).[46] Obviously, the\nsignals of *OOH intermediates gradually appear and are significantly enhanced with the increase of\npotential, indicating that the incorporation of F can force the reaction mechanism of RuO from the\n2\ntraditional LOM to AEM, thus ensuring exceptional stability even at high applied potential.\nAdditionally, F–RuO /FC shows clearly pH–independence, suggesting the significant suppression of\n2\nthe LOM pathway and the dominant role of the AEM pathway (Supplementary Fig. 71).[47, 48] [Page\n12, Line 1–12]\nSupplementary Fig. 70. In situ ATR–IR spectra of RuO2/C.\nSupplementary Fig. 71. OER polarization curves of F–RuO2/FC in various pH–H2SO4 electrolytes.\nFinally, the oxygen isotope tracking experiment was carried out to verify the suppressed LOM process,\nthat is, whether lattice oxygen was involved in the reaction. Operando differential electrochemical\nmass spectrometry (DEMS) was performed on 18O isotope–labelled F–RuO /FC using linear sweep\n2\nvoltammograms (LSV) in H 16O 0.5 M H SO (Supplementary Fig. 73a). As shown in Fig. 5e, the\n2 2 4\nmass signals of 32O and 34O were detected without 36O products, suggesting the non–participation\n2 2 2\nof O in the OER process.[50] The mass signals of 32O gradually increase and present a constant ratio\nL 2\n(32O :34O ) with the occurrence of OER, further demonstrating the dominant AEM pathway\n2 2\n(Supplementary Fig. 73b, c). [Page 12, Line 16–21]\nSupplementary Fig. 73. (a) Schematic illustration of the operando DEMS device. (b) DEMS signals of 32O2 (16O + 16O) were collected during the LSV cycle. (c) Ratio of 34O2:32O2 within the LSV range.\nFigure 5. Mechanism explorations. (e) DEMS signals of 32O2, 34O2, and 36O2 from the gaseous products for 18O–labeled F–RuO2/FC catalysts in H2 16O aqueous H2SO4 electrolyte during three times of LSV cycles.\nBased on your suggestions, we have conducted an in–depth discussion on the current modification\nstrategies of RuO (including anion doping) in the introduction part of the revised manuscript and\n2\ncarried out a performance comparison in the performance part, as follows:\nAs so far, numerous feasible approaches have been reported to significantly enhance the formation\nenergy of O , including heterometal doping (SnRuO [21], Ni–RuO [22], Ta /RuO [23]), interface\nV X 2 1 2\nengineering (Co–Ru@RuO 9:1[24], GB–RuO [25]), strain regulation (Li RuO [26], RuSnO [27]),\n2 2 0.52 2 X\nhigh–entropy compounds (M–RuIrFeCoNiO [28]), anion regulation (LD–B/RuO [29], Ru/Se–RuO [30],\n2 2 2\nRuO –Cl[31]) and so on. Among these, the superior electronegativity and electron affinity of anions\n2\nare more conducive to optimizing the adsorption/desorption behavior of reaction intermediates on the\nelectrocatalyst surface.[32] Nevertheless, most recently reported anion–modulated catalysts for OER\nhave predominantly focused on performance enhancement while neglecting the intrinsic connection\nbetween the reaction mechanism and microstructure, which impedes the in–depth understanding of\nhighly efficient electrocatalysts. [Page 3, Line 5–14]\n[21] Shi, Z. et al. Customized reaction route for ruthenium oxide towards stabilized water oxidation in high–performance PEM\nelectrolyzers. Nat. Commun. 14, 843 (2023). [Page 16, Line 14–15]\n[22] Wu, Z. Y. et al. Non–iridium–based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane\nwater electrolysis. Nat. Mater. 22, 100–108 (2023). [Page 16, Line 16–17]\n[23] Shim, J. et al. Atomically dispersed high-valent d0–metal breaks the activity–stability trade–off in proton exchange membrane\nwater electrolysis. J. Am. Chem. Soc. 147, 16179–16188 (2025). [Page 16, Line 18–19]\n[24] Chen, J. et al. Cobalt–doped Ru@RuO2 core–shell heterostructure for efficient acidic water oxidation in low–Ru–loading proton\nexchange membrane water electrolyzers. J. Am. Chem. Soc. 147, 8720–8731 (2025). [Page 16, Line 20–22]\n[25] He, W. et al. Grain–boundary–rich RuO2 porous nanosheet for efficient and stable acidic water oxidation. Angew. Chem. Int. Ed.\n63, e202405798 (2024). [Page 16, Line 23–24]\n[26] Qin, Y. et al. RuO2 electronic structure and lattice strain dual engineering for enhanced acidic oxygen evolution reaction\nperformance. Nat. Commun. 13, 3784 (2022). [Page 16, Line 25–26]\n[27] Xu, Y. et al. Strain–modulated Ru–O covalency in Ru–Sn oxide enabling efficient and stable water oxidation in acidic solution.\nAngew. Chem. Int. Ed. 136, e202316029 (2024). [Page 16, Line 27–28]\n[28] Hu, C. et al. Misoriented high–entropy iridium ruthenium oxide for acidic water splitting. Sci. Adv. 9, eadf9144 (2023). [Page 16,\nLine 29–30]\n[29] Chen, G. et al. A long–range disordered RuO2 catalyst for highly efficient acidic oxygen evolution electrocatalysis. Angew. Chem.\nInt. Ed. 63, e202411603 (2024). [Page 17, Line 1–2]\n[30] Huang, K. et al. Ru/Se–RuO2 composites via controlled selenization strategy for enhanced acidic oxygen evolution. Adv. Funct.\nMater. 33, 2211102 (2023). [Page 17, Line 3–4]\n[31] Chen, J. et al. Chloride residues in RuO2 catalysts enhance its stability and efficiency for acidic oxygen evolution reaction. Angew.\nChem. Int. Ed. 137, e202420860 (2025). [Page 17, Line 5–6]\n[32] Liu, Y. et al. Shining light on anion–mixed nanocatalysts for efficient water electrolysis: fundamentals, progress, and perspectives.\nNano–Micro lett. 14, 43 (2022). [Page 17, Line 7–8]\n[36] Li, L. et al. Lanthanide–regulating Ru–O covalency optimizes acidic oxygen evolution electrocatalysis. Nat. Commun. 15, 4974\n(2024). [Page 17, Line 15–16]\n[44] Li, W. Q. et al. Identification of the molecular pathways of RuO2 electroreduction by in–situ electrochemical surface–enhanced\nRaman spectroscopy. J. Catal. 400, 367–371 (2021). [Page 18, Line 1–2]\n[45] Gou, W. et al. Oxygen spillover from RuO2 to MoO3 enhances the activity and durability of RuO2 for acidic oxygen evolution.\nEnergy Environ. Sci. 17, 6755–6765 (2024). [Page 18, Line 3–4]\n[46] Jin, H. et al. Dynamic rhenium dopant boosts ruthenium oxide for durable oxygen evolution. Nat. Commun. 14, 354 (2023). [Page\n18, Line 5–6]\n[47] Shi, Z. et al. Confined Ir single sites with triggered lattice oxygen redox: toward boosted and sustained water oxidation catalysis.\nJoule 5, 2164–2176 (2021). [Page 18, Line 7–8]\n[48] Wu, L. et al. Role of interfacial water in improving the activity and stability of lattice–oxygen–mediated acidic oxygen evolution\non RuO2. Angew. Chem. Int. Ed. e202420848 (2025). [Page 18, Line 9–10]\n[50] Han, X. et al. Defect engineering of RuO2 aerogels for efficient acidic water oxidation. ACS Mater. Lett. 6, 748–7755 (2024).\n[Page 18, Line 13–14]\nApparently, F–RuO /FC present a larger current density and longer stability, outperforming most of\n2\nthe recently reported PEM electrocatalysts (Fig. 4f and Table S4). [Page 11, Line 5–7]\nFigure 4. Electrochemical activity studies. (f) Comparison of the stability between F–RuO2/FC and recently reported PEM\nelectrocatalysts.\nTable S4. Summary of the reported PEMWE activity and stability using different Ru–based OER electrocatalysts.\nCatalyst Activity (V) Stability (month) Ref.\n1.45 V@100 mA cm–2 2.00@100 mA cm–2\nF–RuO2/FC 1.58 V@500 mA cm–2 2.00@500 mA cm–2 This work\n1.70 V@1000 mA cm–2 2.00@1000 mA cm–2\nSnRuOX 1.57 V@1000 mA cm–2 1.81@1000 mA cm–2 Nat. Commun. 14, 842 (2023)\nNi–RuO2 1.78 V@500 mA cm–2 1.39@200 mA cm–2 Nat. Mater. 22, 100–108 (2023)\nRuO2/MoO3–SO4 1.75 V@1000 mA cm–2 0.21@150 mA cm–2 Angew. Chem. Int. Ed. 63, e202413653 (2024)\nNd0.1RuOx/CC 1.60 V@50 mA cm–2 0.07@10 mA cm–2 Adv. Funct. Mater. 33, 2213304 (2023)\nRuO2/BNNS / 0.28@200 mA cm–2 Angew. Chem. Int. Ed. 136, e202402018 (2024)\nNb0.1Ru0.9O2 1.69 V@1000 mA cm–2 0.14@300 mA cm–2 Joule 7, 558–573 (2023)\n(Ru–W)Ox 1.62 V@1000 mA cm–2 0.42@500 mA cm–2 Adv. Mater. 35, 2305939 (2023)\nIn–RuO2/G / 0.49@100 mA cm–2 Angew. Chem. Int. Ed. 136, e202316903 (2024)\n1.58 V@500 mA cm–2\nPb–RuO2\n1.67 V@1000 mA cm–2\n0.35@500 mA cm–2 Nat. Commun. 15, 9774 (2024)\nRuFe/CF 1.90 V@1000 mA cm–2 0.35@200 mA cm–2 Adv. Mater. 36, 2312369 (2024)\nCr0.6Ru0.4O2 1.54 V@1000 mA cm–2 0.49@300 mA cm–2 J. Am. Chem. Soc. 146, 32049–32058 (2024)\nCr0.2Ru0.8O2–x 1.77 V@1000 mA cm–2 0.28@1000 mA cm–2 Nat. Commun. 15, 7861 (2024)\nMnRuOx–300 1.73 V@500 mA cm–2 0.11@100 mA cm–2 Angew. Chem. Int. Ed. 63, e202405641 (2024)\nBa0.3(SO4)δW0.2Ru0.5O 1.54 V@500 mA cm–2\n0.42@500 mA cm–2 Nat. Commun. 14, 8093 (2023)\n2–δ 1.68 V@1000 mA cm–2\nRuCoOx 1.53 V@100 mA cm–2 0.01@100 mA cm–2 J. Am. Chem. Soc. 145, 17995–18006 (2023)\nInSnRuO2–450 1.59 V@100 mA cm–2 0.28@50 mA cm–2 Adv. Mater. 2414579 (2024)\nZnRuOx 1.68 V@1000 mA cm–2 0.17@200 mA cm–2 J. Am. Chem. Soc. 146, 15515–15524 (2024)\nW0.2Er0.1Ru0.7O2–δ / 0.17@100 mA cm–2 Nat. Commun. 11, 5368 (2020)\nSS Pt–RuO2 HNSs / 0.14@100 mA cm–2 Sci. Adv. 8, eabl9271 (2022)\nEr–RuOx 1.59 V@1000 mA cm–2 0.14@1000 mA cm–2 Nat. Commun. 15, 4974 (2024)\nRu0.8Sb0.2O2 1.64 V@1000 mA cm–2 0.69@1000 mA cm–2 J. Am. Chem. Soc. 146, 23146–23157 (2024)\nLD–B/RuO2 1.63 V@1000 mA cm–2 0.42@250 mA cm–2 Angew. Chem. Int. Ed. e202411603 (2024)\nPtCo–RuO2/C 2.00 V@4400 mA cm–2 0.03@1000 mA cm–2 Energy Environ. Sci. 146, 1119–1130 (2022)\nRuO2/D–TiO2 1.74 V@1500 mA cm–2 0.14@200 mA cm–2 ACS Catal. 12, 9437–9445 (2022)\nGB/RuO2 1.54 V@1000 mA cm–2 0.14@100 mA cm–2 Angew. Chem. Int. Ed. e202411603 (2024)\nRu/Ti4O7 1.69 V@500 mA cm–2 0.42@500 mA cm–2 Nat. Commun. 15, 2728 (2024)\nTa1/RuO2 1.80 V@3500 mA cm–2 0.90@500 mA cm–2 J. Am. Chem. Soc. 147, 16179–16188 (2025)\nCo–Ru@RuO2 9:1 1.58 V@1000 mA cm–2 0.27@500 mA cm–2 J. Am. Chem. Soc.147, 8720–8731 (2025)\nM–RuIrFeCoNiO2 / 0.69@500 mA cm–2 Sci. Adv. 9, eadf9144 (2023)\nRuO2–Cl 1.54 V@1000 mA cm–2 0.69@600 mA cm–2 Angew. Chem. Int. Ed. 64, e202420860 (2025)\n1. The authors claim that RuO is widely recognized to follow the LOM mechanism, however, the\n2\ntheoretical calculations of OER activity in RuO presented in this work focus solely on the AEM\n2\npathway. In other words, the barriers calculated does not correspond to the lowest energy barrier for\nRuO –based catalysts. In addition, there is a lack of systematic investigation into the differences in\n2\nenergy barriers between the LOM and AEM pathways in RuO –based catalysts, as well as the effect\n2\nof anionic doping.\n[Author’s Response]: Thank you for your constructive feedback, which have helped us significantly\nimprove the quality of our manuscript. As requested, M–RuO (M = F, S, Se, P, N, Cl, and Br) was\n2\nconstructed to evaluate their OER performance. The desirable Gibbs free energy of rate–determining\nstep (RDS) for F–RuO is 1.80 eV, lower than that of S–RuO (1.86 eV), P–RuO (2.60 eV), Se–\n2 2 2\nRuO (2.76 eV), N–RuO (1.83 eV), Cl–RuO (3.16 eV), Br–RuO (4.28 eV) and RuO (1.89 eV)\n2 2 2 2 2\n(Fig. 1c). Compared with the traditional RuO following LOM route, the introduction of F gives RuO\n2 2\nmore energy advantages on the AEM path (Supplementary Fig. 20). Apparently, with the increase\nof the degree of symmetry–breaking, the energy barriers of RDS in the AEM pathway are elevated\nand the energy barriers of the RDS in the LOM pathway are decreased, the situation of the OER\nmechanism is not consistent at different anion doping, and the weaker symmetry breaking is more\nfavorable to the AEM. [Page 4, Line 19–22 and Page 5, Line 15–17]\nFigure 1. DFT calculations. (c) Gibbs free energy diagram for different catalysts.\nSupplementary Fig. 20. Calculated free energy evolution of OER via LOM on F–RuO2, S–RuO2, P–RuO2, Se–RuO2, RuO2, N–RuO2, Cl–RuO2 and Br–RuO2 under electrode potential of 0 V.\n2. Another point of concern is the authors' statement: \"As predicted by DFT, a marked decline in OER\nactivity and stability was observed when O was replaced by S, Se, and P…..\" (Line 192-193, Page 9).\nHow does the DFT calculation predict stability degradation following the doping of S, P, or Se?\n[Author’s Response]: We sincerely appreciate your thorough review and insightful comments on\nour manuscript. In response to your concerns, we have supplemented additional data and revised the\nmanuscript where appropriate, as follows:\nAs predicted by the DFT, the RDS energy barrier of OER (Fig. 1c) and the enthalpy change caused\nby O loss (Fig. 1e) will undergo significant changes when O was replaced by S, Se, P, N, Cl, Br,\nsuggesting that the symmetry–breaking induced by different anions result in varied performance\n(Supplementary Fig. 64, 65). [Page 4, Line 19–22 and Page 5, Line 23–Page 6, Line 2 and Page\n10, Line 16–19]\nFigure 1. DFT calculations. (c) Gibbs free energy diagram for different catalysts.\nFigure 1. DFT calculations. (e) Calculated enthalpy changes for subsurface oxygen loss of various catalysts.\nSupplementary Fig. 64. (a) OER polarization curves, (b) Tafel plots, and (c) chronopotentiometry tests of N–RuO2/(F)C, S–\nRuO2/(F)C, P–RuO2/(F)C, Se–RuO2/(F)C, Cl–RuO2/(F)C and Br–RuO2/(F)C.\nSupplementary Fig. 65. Gibbs free energy of RDS versus Tafel slope.\n3. The concept of symmetry breaking lacks a clear definition or quantitative indicators. It should not\nonly be supported by theoretical calculations but also validated through experimental evidence.\nAdditionally, doping any element could lead to structural changes in RuO , making the selection of\n2\nthe dopant particularly crucial. The authors chose S/P/Se as dopants, which belong to different periods\nand main groups compared to F, raising ambiguity, as it would be more straightforward to compare\nfluorine with elements from the same period (such as C, N, or B). The extent of symmetry breaking\ninduced by F (which may be insufficient) and S (which may be excessive) could deviate from the\noptimal range needed for maximum OER activity, suggesting that the actual peak performance might\nlie in dopant systems not yet explored.\n[Author’s Response]: Thank you for your guidance on our manuscript, which help to improve the\nquality of our work. According to your suggestion, the concept of symmetry–breaking is clearly\ndefined in our revised manuscript, and as follows:\nFundamentally, the intrinsic properties of materials overwhelmingly depend on their crystal\nsymmetry and atomic arrangement. The structural modifications at atomic scale may reduce its crystal\nsymmetry, which is named the symmetry breaking effect.[33–35] [Page 3, Line 14–16]\n[33] Gao, F. et al. Symmetry–breaking induced piezocatalysis of Bi2S3 nanorods and boosted by alternating magnetic field. Appl. Catal.\nB–Environ. 316, 121664 (2022). [Page 17, Line 9–10]\n[34] Nguyen, Q. N., Wang, C., Shang, Y., Janssen, A. & Xia, Y. Colloidal synthesis of metal nanocrystals: from asymmetrical growth\nto symmetry breaking. Chem. Rev. 123, 3693–3760 (2023). [Page 17, Line 11–12]\n[35] Cao, P. et al. Breaking symmetry for better catalysis: insights into single–atom catalyst design. Chem. Soc. Rev. 54, 3848–3905\n(2025). [Page 17, Line 13–14]\nTo address your concerns, we condected comprehensive characterization of the symmetry breaking\nof F–RuO\n2\n/FC. The result of analysis revealing that the partial substitution of O by F in RuO\n2\nleads\nto symmetry breaking, causing slight distortion of the octahedral configuration and changes in\nintrinsic properties. The detailed analysis is presented below:\nFirstly, to verify the lattice strain mechanism induced by F, long–range ordered atomic arrangements\nwere successfully detected using a spherical AC–HAADF–STEM (Fig. 2a). The well–defined lattice\nspacings (0.22 and 0.18 nm) of (020) and (211) planes for RuO unequivocally indicate the presence\n2\nof lattice strain compared to RuO , which may be caused by symmetry breaking due to introduction\n2\nof heterogeneous atoms (Fig. 2b). The fast Fourier transform (FFT) pattern, inset in Fig. 2b, reveals\nthe exposed (020) and (211) planes along the [102] zone axis of F–RuO /FC. To confirm the\n2\nheterogeneous atoms in F–RuO /FC, STEM energy dispersive spectrometer (STEM–EDS) elemental\n2\nmappings were conducted in Fig. 2c. In addition to the uniformly distributed Ru and O elements,\nconspicuous F signals can be observed, suggesting that the lattice strain in F–RuO /FC may be caused\n2\nby the incorporation of F. [Page 7, Line 1–11]\nFigure 2. Structural characterizations. (a, b) spherical aberration–corrected HAADF–STEM images, (c) STEM–EDS elemental\nmappings of F–RuO2/FC. Inset in (b) is the FFT pattern of F–RuO2/FC.\nSecondly, geometrical phase analysis (GPA) was performed to evaluate the strain level and\ndistribution in the F–RuO /FC. Evidently, the reduced and enhanced strain can be observed along the\n2\nhorizontal (Ꜫ ) and vertical (Ꜫ ) direction, respectively (Fig. 2d, e). The strain profiles of line1 and\nxx yy\nline2 acquired from strain mappings further confirm that the compressive stress is predominantly\nalong the Ꜫ direction and the tension stress along the Ꜫ direction (Fig. 2f).[37] [Page 7, Line 11–\nxx yy\n15]\nFigure 2. Structural characterizations. Strain mappings of F–RuO2/FC along (d) Ꜫxx and (e) Ꜫyy direction from GPA and (f) line\nprofiles of strain along the dotted white lines in (d) and (e).\n[37] Wu, G. et al. In–plane strain engineering in ultrathin noble metal nanosheets boosts the intrinsic electrocatalytic hydrogen\nevolution activity. Nat. Commun. 13, 4200 (2022). [Page 17, Line 17–18]\nThirdly, to investigate the critical insight of chemical distributions for F–RuO /FC, TOF–SIMS\n2\nanalysis was performed in Fig. 2g. The element intensity versus sputter time reveals that the\nconcentration of O– is notably greater than that of Ru+, being consistent with the characteristics of\nRuO . In addition, the detected RuF– signals indicate that F indeed replaces part of O and then bonds\n2\nwith Ru during the heat treatment process. Two–dimensional (2D) TOF–SIMS elemental mappings\nalso confirm the presence of significant RuF– species alongside the abundant Ru and O species (Fig.\n2h). Clearly, the distribution of Ru and O signals throughout the space in three–dimensional (3D)\nTOF–SIMS views indicates that the predominant species is RuO , consistent with the AC–HAADF–\nfurther confirms the partial substitution of O by F, thus leading to the formation of Ru–F bonds. [Page\n7, Line 15–Page 8, Line 2]\nFigure 2. Structural characterizations. (g) TOF–SIMS depth analysis of Ru+, O–, and RuF– for F–RuO2/FC and (h) corresponding\n2D elemental mapping images and (i) 3D render overlay images.\nNext, XRD with Rietveld refinement was conducted to obtain the detailed unit cell parameter (Fig.\n2j and Table S2). The sharp diffraction peaks correspond to the tetragonal RuO with the space group\n3 2\nduring the heat treatment process. The presence of Ru accelerates the local pyrolysis of FC and\nresulting in F occupying part of the position of O in F–RuO /FC (inset in Fig. 2j). [Page 8, Line 2–\n2\n7]\nFigure 2. Structural characterizations. (j) XRD pattern of F–RuO2/FC. Inset in (j) is structural model of F–RuO2/FC.\nTable S2. Refined parameters of F–RuO2/FC.\nF–RuO2/FC X Y Z\nRu0 0.500000 0.500000 0.500000\nRu1 0.000000 0.000000 0.000000\nO2 0.694330 0.694330 0.000000\nO3 0.194330 0.805670 0.500000\nO4 0.239972 0.225644 –9.999990\nF1 0.805670 0.194330 0.500000\na = 4.5436 Å, b = 4.5436 Å, c = 3.1397 Å, space grpup P42/mnm, Rwp = 6.12%, Rp = 4.70%, Chi2 = 8.977\nFinally, compared to RuO , a noticeable red shift can be observed in the vibration peaks of F–\nhighly electronegative F (Fig. 3a).[39] Therefore, F 1s XPS spectra of F–RuO /FC present a wider\n2\npeak than that of FC, corresponding to the C–F and Ru–F species (Fig. 3b). Additionally, O 1s XPS\npeaks of RuO are located at 529.0, 530.0, and 531.7 eV, corresponding to O , O , and surface–\nadsorbed H O, respectively (Fig. 3c).[40, 41] Evidently, a notable shift of the oxygen species towards\n2\nhigher binding energy can be observed in F–RuO /FC due to the presence of high electronegativity F\n2\nresults in an altered electronic interaction between Ru and O.[39] [Page 8, Line 8–17]\nFigure 3. Electronic structure investigation. (a) Raman spectra of F–RuO2/FC and RuO2. (b) F 1s XPS spectra of F–RuO2/FC and\nFC. (c) O 1s XPS spectra of F–RuO2/FC and RuO2.\n[39] Xiao, K., Wang, Y., Wu, P., Hou, L. & Liu, Z. Q. Activating lattice oxygen in spinel ZnCo2O4 through filling oxygen vacancies\nwith fluorine for electrocatalytic oxygen evolution. Angew. Chem. Int. Ed. 62, e202301408 (2023). [Page 17, Line 21–23]\n[40] Liu, Z. et al. Optimal geometrical configuration of cobalt cations in spinel oxides to promote oxygen evolution reaction. Angew.\nChem. Int. Ed. 59, 4736–4742 (2020). [Page 17, Line 24–25]\n[41] Xue, J. Y. et al. Engineering multiphasic MoSe2/NiSe heterostructure interfaces for superior hydrogen production electrocatalysis.\nAppl. Catal. B–Environ. 312, 121434 (2022). [Page 17, Line 26–27]\nTo comprehensively explore the practical peak performance, as requested, N–RuO /(F)C\n2\nelectrocatalyst was synthesized using N as dopant (Supplementary Fig. 58). Compared to F–\nRuO /FC, the activity and stability of N–RuO /(F)C showed markedly reduced, which is consistent\n2 2\nwith the results predicted by DFT calculation (Supplementary Fig. 64 and Fig. 1c, e, and f).\nFigure 1. DFT calculations. (c) Gibbs free energy diagram for different catalysts. (e) Calculated enthalpy changes for subsurface\noxygen loss of various catalysts.\nFigure 1. DFT calculations. (f) Reaction free energy (RDS) and subsurface O loss enthalpy change volcano against the symmetry–\nbreaking.\nSupplementary Fig. 58. (a) SEM image, (b) TEM image, (c) XRD pattern, (d) N 1s XPS spectrum, (e) STEM image, and (f) STEM–\nEDS elemental mappings of N–RuO2/(F)C.\nSupplementary Fig. 64. (a) OER polarization curves, (b) Tafel plots, and (c) chronopotentiometry tests of N–RuO2/(F)C, S–\nRuO2/(F)C, P–RuO2/(F)C, Se–RuO2/(F)C, Cl–RuO2/(F)C and Br–RuO2/(F)C.\n4. The use of carbon support for the PEMWE test is confusing, as carbon supports are inherently\nunstable under acidic OER conditions, particularly at high potentials. If this material is ever going to\nbe used in an electrolyzer, it should also be possible to use it in an unsupported manner. In addition,\nit would be beneficial to include characterization of the carbon support after long–term PEMWE\ntesting.\n[Author’s Response]: Thank you for the comments. The C–F bond, recognized as one of the\nstrongest single bonds, endows fluorinated materials with high thermal and chemical stability (Nat.\nMater. 9, 119–133 (2024)). This unique feature of strong bonding, high electronegativity, and\nstability makes fluorinated materials widely applicable in the field of energy materials (Energy\nEnviron. Sci. 16, 1907–1942 (2023)).\nTo investigate the stability of carbon support, the F–RuO /FC electrocatalyst after long–term\nlargely unchanged, proving exceptional stability (Supplementary Fig. 66, 67).[42, 43] [Page 11, Line\n3–5]\nSupplementary Fig. 66. (a) SEM images of the cross section of MEA before and after CP test. (b) SEM image and (c) TEM image\nof F–RuO2/FC after CP test of PEMWE.\nSupplementary Fig. 67. (a) F 1s XPS spectrum, (b) O 1s XPS spectrum, (c) Ru 3p XPS spectrum and (d) XRD pattern of F–RuO2/FC\nafter CP test of PEMWE.\n[42] O'Hagan, D. Understanding organofluorine chemistry. an introduction to the C–F bond. Chem. Soc. Rev. 37, 308–319 (2008).\n[Page 17, Line 28–29]\n[43] Wang, T. et al. Recent advances in fluorine–doped/fluorinated carbon–based materials for supercapacitors. Energy Storage Mater.\n30, 367–384 (2020). [Page 17, Line 30–31]\n5. The introduction fails to adequately review current modification strategies for RuO and lacks a\n2\ncomparison of anion dopants with other alternatives, such as metal dopants, overlooking a critical\nanalysis of how anion dopants can address the existing stability challenges.\n[Author’s Response]: Thanks for your kind suggeation. Based on your consideration, the current\nmodification strategies for RuO and the stability challenges associated with anion doping are\n2\nthoroughly discussed in the introduction section of our revised manuscript, and as follows:\nAs so far, numerous feasible approaches have been reported to significantly enhance the formation\nenergy of O , including heterometal doping (SnRuO [21], Ni–RuO [22], Ta /RuO [23]), interface\nV X 2 1 2\nengineering (Co–Ru@RuO 9:1[24], GB–RuO [25]), strain regulation (Li RuO [26], RuSnO [27]),\n2 2 0.52 2 X\nhigh–entropy compounds (M–RuIrFeCoNiO [28]), anion regulation (LD–B/RuO [29], Ru/Se–RuO [30],\n2 2 2\nRuO –Cl[31]) and so on. Among these, the superior electronegativity and electron affinity of anions\n2\nare more conducive to optimizing the adsorption/desorption behavior of reaction intermediates on the\nelectrocatalyst surface.[32] Nevertheless, most recently reported anion–modulated catalysts for OER\nhave predominantly focused on performance enhancement while neglecting the intrinsic connection\nbetween the reaction mechanism and microstructure, which impedes the in–depth understanding of\nhighly efficient electrocatalysts. [Page 3, Line 5–14]\n[21] Shi, Z. et al. Customized reaction route for ruthenium oxide towards stabilized water oxidation in high–performance PEM\nelectrolyzers. Nat. Commun. 14, 843 (2023). [Page 16, Line 14–15]\n[22] Wu, Z. Y. et al. Non–iridium–based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane\nwater electrolysis. Nat. Mater. 22, 100–108 (2023). [Page 16, Line 16–17]\n[23] Shim, J. et al. Atomically dispersed high–valent d0–metal breaks the activity–stability trade–off in proton exchange membrane\nwater electrolysis. J. Am. Chem. Soc. 147, 16179–16188 (2025). [Page 16, Line 18–19]\n[24] Chen, J. et al. Cobalt–doped Ru@RuO2 core–shell heterostructure for efficient acidic water oxidation in low–Ru–loading proton\nexchange membrane water electrolyzers. J. Am. Chem. Soc. 147, 8720–8731 (2025). [Page 16, Line 20–22]\n[25] He, W. et al. Grain–boundary–rich RuO2 porous nanosheet for efficient and stable acidic water oxidation. Angew. Chem. Int. Ed.\n63, e202405798 (2024). [Page 16, Line 23–24]\n[26] Qin, Y. et al. RuO2 electronic structure and lattice strain dual engineering for enhanced acidic oxygen evolution reaction\nperformance. Nat. Commun. 13, 3784 (2022). [Page 16, Line 25–26]\n[27] Xu, Y. et al. Strain–modulated Ru–O covalency in Ru–Sn oxide enabling efficient and stable water oxidation in acidic solution.\nAngew. Chem. Int. Ed. 136, e202316029 (2024). [Page 16, Line 27–28]\n[28] Hu, C. et al. Misoriented high–entropy iridium ruthenium oxide for acidic water splitting. Sci. Adv. 9, eadf9144 (2023). [Page 16,\nLine 29–30]\n[29] Chen, G. et al. A long–range disordered RuO2 catalyst for highly efficient acidic oxygen evolution electrocatalysis. Angew. Chem.\nInt. Ed. 63, e202411603 (2024). [Page 17, Line 1–2]\n[30] Huang, K. et al. Ru/Se–RuO2 composites via controlled selenization strategy for enhanced acidic oxygen evolution. Adv. Funct.\nMater. 33, 2211102 (2023). [Page 17, Line 3–4]\n[31] Chen, J. et al. Chloride residues in RuO2 catalysts enhance its stability and efficiency for acidic oxygen evolution reaction. Angew.\nChem. Int. Ed. 137, e202420860 (2025). [Page 17, Line 5–6]\n[32] Liu, Y. et al. Shining light on anion–mixed nanocatalysts for efficient water electrolysis: fundamentals, progress, and perspectives.\nNano–Micro lett. 14, 43 (2022). [Page 17, Line 7–8]\n6. The absence of in–situ experiments for undoped RuO and S/P/Se–doped RuO limits the validation\n2 2\nof the proposed switchable reaction mechanism, particularly regarding the effects of F doping.\n[Author’s Response]: We deepest gratitude goes to you for your thoughtful suggestion that have\nhelped improve our manuscript substantially. To further investigate the switchable reaction\nmechanism, in situ ATR–IR spectroscopy was performed on RuO /C, S–RuO /(F)C, P–RuO /(F)C\n2 2 2\nand Se–RuO /(F)C. As shown in Supplementary Fig. 70, two absorption peaks attributed to the *OO\n2\nintermediate formed during the LOM pathway are detected, further indicating that RuO /C follow the\n2\nconventional LOM pathway during the acidic OER process.[45] [Page 12, Line 1–4]\nSupplementary Fig. 70. In situ ATR–IR spectra of RuO2/C.\nFurthermore, the reaction intermediate signals of *OOH in the AEM pathway and *OO in the LOM\npathway were simultaneously detected during the OER process of S–RuO /(F)C, but the signals of\n2\n*OOH are disappeared across the entire potential window of P–RuO /(F)C and Se–RuO /(F)C\n2 2\n(Supplementary Fig. 72b-d).[49] Remarkably, in situ ATR–IR spectroscopy of F–RuO /FC showed\n2\na sharp characteristic peak appear at 1237 cm–1, belonging to the stretching vibration of surface–\nadsorbed *OOH intermediates, evidencing the dominance of the AEM pathway (Fig. 5d).[46] Based\non the above analysis, it can be concluded that the symmetry breaking in octahedral configuration of\nRuO induced by different anion dopants enables controllable switching of reaction mechanisms,\n2\nverifying the feasibility of the symmetry–breaking strategey. [Page 12, Line 5–7 and Line 12–15]\nSupplementary Fig. 72. In situ ATR–IR spectra of (b) S-RuO2/(F)C, (c) P-RuO2/(F)C, and (d) Se-RuO2/(F)C.\nFigure 5. Mechanism explorations. (d) In situ ATR–IR spectra of F-RuO2/FC.\n[45] Gou, W. et al. Oxygen spillover from RuO2 to MoO3 enhances the activity and durability of RuO2 for acidic oxygen evolution.\nEnergy Environ. Sci. 17, 6755–6765 (2024). [Page 18, Line 3–4]\n[46] Jin, H. et al. Dynamic rhenium dopant boosts ruthenium oxide for durable oxygen evolution. Nat. Commun. 14, 354 (2023). [Page\n18, Line 5–6]\n[49] Xu, J. et al. IrOx·nH2O with lattice water–assisted oxygen exchange for high–performance proton exchange membrane water\nelectrolyzers. Sci. Adv. 9, eadh1718 (2023). [Page 18, Line 11–12]\n7. The manuscript lacks detailed synthetic protocols for S/P/Se-RuO materials, with some\n2\ndescriptions remaining ambiguous (e.g., \"Concurrently, M–RuO /(F)C...heat treatment process\").\nmeasurements. These insufficient experimental details hinder the accurate evaluation of the OER\nperformance of the catalysts.\n[Author’s Response]: Thank you for your careful review of our manuscript. we have provided a\ndetailed description of the synthesis process of M–RuO and the loading of noble metal during the\n2\ntesting process as follows:\nPreparation of RuO /(F)C. The synthesis condition of RuO /(F)C is the same as F–RuO /FC, except\n2 2 2\nthat the FC used for RuO /(F)C was pre–annealed in air at 400 °C for 12 h to remove F (denoted as\n2\n(F)C). [Page 14, Line 3–4]\nPreparation of M–RuO /(F)C (M = N, S, P, Se, Cl and Br). The M–RuO /(F)C electrocatalyst was\n2 2\nsynthesized by vapor transport method, where the anion–donating powder and RuO /(F)C (mass ratio\n2\n1:2) were placed at the upstream and downstream positions of a quartz tube, respectively. The anion–\ndonating powder and RuO /(F)C were heated to the target temperature and 400 °C respectively at a\n2\nheating rate of 5 ℃ min–1 in an Ar atmosphere and maintained for 1 h to obtain M–RuO /(F)C. In\n2\naddition, melamine, sulfur powder, sodium hypophosphite, selenium powder, a mixture of polyvinyl\nchlorid and manganese dioxide, and hexabromobenzene were unsed as anion sources, releasing\nanions under heat treatment at 450 °C, 150 °C, 300 °C, 500 °C, 450 °C, and 350 °C, respectively.\n[Page 14, Line 5–12]\nElectrochemical measurements. Then 2.0 mg of catalyst was added into the solution containing 195\nμL of isopropyl alcohol and 5 μL of Nafion, and the ink was prepared by ultrasonic at ambient\ntemperature. Next, the ink was vertically dripped on the glassy carbon electrode (0.196 cm2) to obtain\nthe work electrode (loading amount: ~75 mg ). [Page 14, Line 14–17]\nRu\nPEMWE tests. After ultrasonication for 1 h, the prepared ink were spray onto the both sides of\nNafion 115 membrane to get the catalyst–coated membrane (CCM), achieveing noble matal loadings\nof 2 mg cm–2 for anode and 0.5 mg cm–2 for cathode. [Supplementary Information Page 3, Line 1–\n4]\nReviewer #2\nGeneral Comment: The manuscript describes the modelling, fabrication, characterization and\nelectrochemical testing of anion doped ruthenium oxide catalysts for oxygen evolution reaction (OER)\nin acidic electrolyte. The manuscript is well structured and logically organized. The champion\nfluorine doped ruthenium oxide shows impressive activity and robustness towards OER. The\nmanuscript could be accepted with the following minor aspects having been addressed.\n[Author’s Response]: We thank you for the highly positive recommendation. We especially\nappreciate your comments and advices, which help us to further improve the quality of our work.\nAccording to your suggestions, we have carefully revised our manuscript.\n1. As the dopant is essential to break the symmetry and induce electrocatalytic activity, the nature of\nthe dopant is important information. What is the dopant level of the fluorine doped ruthenium oxide\nand did the author observe any dopant level dependent activity towards OER?\n[Author’s Response]: Thanks you for your valuable suggestions. Based on your considerations, the\ncontent of F in F–RuO /FC was characterized by SEM–EDS. Apparently, the content of F in F–\n2\nactivity and stability demonstrate its sensitivity to the fluorine doping level (Supplementary Fig. 50).\n[Page 10, Line 8–10]\nSupplementary Fig. 48. SEM–EDS spectra of (a) F–RuO2/FC–300 °C, (b) F–RuO2/FC, and (c) F–RuO2/FC–500 °C.\nSupplementary Fig. 50. (a) OER polarization curves and (b) chronopotentiometry tests of F–RuO2/FC–300 °C and F–RuO2/FC–500 °C.\n2. There has been debate on the true active site of the anion doped metal oxide as OER electrocatalyst\nand whether the active site could be preserved after long–term test. It is suggested that the author\nprovide more material characterization data to show the structural properties.\n[Author’s Response]: Thanks very much for your insightful comment. We have fully considered\nyour question, and explain as follows:\nThe flat polarization curve and fleeting stability prove that FC is inert for OER (Supplementary Fig.\n43). It is noteworthy that the activity and stability are closely resemble that of RuO when it is\n2\nmechanically mixed with FC, confirming that the unequivocally demonstrates that the F–modified\nRu consititutes the true active sites (Supplementary Fig. 44, 45). [Page 10, Line 5–8]\nSupplementary Fig. 43. (a) OER polarization curve and (b) chronopotentiometry test of FC.\nSupplementary Fig. 44. (a, b) SEM images of RuO2+FC.\nSupplementary Fig. 45. (a) OER polarization curve and (b) chronopotentiometry test of RuO2+FC.\nNext, the F elements were removed by calcining the FC at 400 °C for 12 h (denoted as (F)C). The\nsharply reduced activity and stability of RuO /(F)C prove that F is decisive for improving the OER\n2\nperformance of RuO\n2\n(Supplementary Fig. 55–57). [Page 10, Line 12–14]\nSupplementary Fig. 55. (a) SEM image and (b) F 1s XPS spectrum of (F)C.\nSupplementary Fig. 56. (a) SEM image and (b) XRD pattern of RuO2/(F)C.\nSupplementary Fig. 57. (a) OER polarization curve and (b) chronopotentiometry test of RuO2/(F)C.\nImportantly, the signal of Ru–F species remained detectable in the F 1s XPS spectra of F–RuO /FC\n2\nafter long–term testing, coupled with negligible changes in both crystalline structure and surface\nchemical states, which confirms the complete preservation of active sites as well as the excellent OER\nstability of F–RuO /FC electrocatalyst (Supplementary Fig. 66, 67). [Page 11, Line 3–5]\nof F–RuO2/FC after CP test of PEMWE.\nSupplementary Fig. 67. (a) F 1s XPS spectrum, (b) O 1s XPS spectrum, (c) Ru 3p XPS spectrum and (d) XRD pattern of F–RuO2/FC\nafter CP test of PEMWE.\n3. To further prove the stability of the electrocatalysts, the leaching of ruthenium from the\nelectrocatalysts with and without dopant can be monitored and compared.\n[Author’s Response]: Thank you very much for your professional comment. As your proposal, a\ntime tracking experiment was performed to monitor the dissolution of Ru in the stability test\n(Supplementary Fig. 42). Surprisingly, F–RuO /FC can operate continuously for over 60 h with\n2\nslightly dissolution of Ru, indicating that the partial substitution of O by F in RuO can significantly\n2\nimprove stability even under harsh acidic conditions. [Page 10, Line 2–5]\nSupplementary Fig. 42. The total Ru dissolution in the electrolyte during chronopotentiometry test of (a) F–RuO2/FC and (b) RuO2/C.\n4. Are the identified intermediates in the in–situ IR/Raman spectroscopy characterizations unique to\nthe fluorine doped ruthenium oxide or they are generally observed for ruthenium oxide. The\ninformation is useful for the discussion of role of dopant/asymmetry on the reaction mechanism.\n[Author’s Response] Thank you for underlining the deficiency. To address your concern, in situ\ncharacterizations were performed on RuO /C. Obviously, the Raman spectra of RuO /C showed no\n2 2\nvibration signals of Ru–OOH intermediates, and the distinct stretching vibration of the *OO\nintermediate were detected in in situ ATR–IR spectroscopy, suggesting the RuO /C follow the LOM\n2\npathway during the OER process (Supplementary Fig. 69, 70). [Page 11, Line 18–21 and Page 12,\nLine 2–4]\nSupplementary Fig. 69. In situ Raman spectra of RuO2/C.\nSupplementary Fig. 70. In situ ATR–IR spectra of RuO2/C.\n5. It is suggested that the scale bars could be added to the images, such as Figure 2d, e, h, i.\n[Author’s Response]: Thanks you for your detailed review and feedback. According to your\nsuggeation, the scale bars have been added to the Figure 2d, e, h and i in our revised manuscript.\nFigure 2. Structural characterizations. Strain mappings of F–RuO2/FC along (d) Ꜫxx and (e) Ꜫyy direction from GPA.\nFigure 2. Structural characterizations. TOF–SIMS depth analysis of (h) corresponding 2D elemental mapping images and (i) 3D\nrender overlay images.\n6. The experimental details on the fabrication of anion doped ruthenium oxide samples, PEM water\nelectrolyzers, in–situ testing (e.g., Raman spectroscopy), could be provided for the audience.\n[Author’s Response]: Thanks for your constructive suggeation. As suggested, we have described in\ndetail the synthesis process, PEMWE tests, and in situ Raman tests of M–RuO in the experimental\n2\nsection as follows:\nPreparation of RuO /(F)C. The synthesis condition of RuO /(F)C is the same as F–RuO /FC, except\n2 2 2\nthat the FC used for RuO /(F)C was pre–annealed in air at 400 °C for 12 h to remove F (denoted as\n2\n(F)C). [Page 14, Line 3–4]\nPreparation of M–RuO /(F)C (M = N, S, P, Se, Cl and Br). The M–RuO /(F)C electrocatalyst was\n2 2\nsynthesized by vapor transport method, where the anion–donating powder and RuO /(F)C (mass ratio\n2\n1:2) were placed at the upstream and downstream positions of a quartz tube, respectively. The anion–\ndonating powder and RuO /(F)C were heated to the target temperature and 400 °C respectively at a\n2\nheating rate of 5 ℃ min–1 in an Ar atmosphere and maintained for 1 h to obtain M–RuO /(F)C. In\n2\naddition, melamine, sulfur powder, sodium hypophosphite, selenium powder, a mixture of polyvinyl\nchlorid and manganese dioxide, and hexabromobenzene were unsed as anion sources, releasing\nanions under heat treatment at 450 °C, 150 °C, 300 °C, 500 °C, 450 °C, and 350 °C, respectively.\n[Page 14, Line 5–12]\nPEMWE tests. The membrane electrode assembly (MEA) was obtained by Nafion 115 with a\ngeometric area of 1 × 1 cm2. Commercial Pt/C (20 wt%) and F–RuO /FC were used as the cathode\n2\nand anode, respectively. To prepare anode and cathode ink, the catalysts were dispersed into the\nsolution containing isopropyl alcohol and deionized water with a volume ratio of 2:1, and then the\nNafion ionomer (5 wt%) was added (25 wt% relative to both F–RuO /FC and Pt/C). After\n2\nultrasonication for 1 h, the prepared ink were spray onto the both sides of Nafion 115 membrane to\nget the catalyst–coated membrane (CCM), achieveing noble matal loadings of 2 mg cm–2 for anode\nand 0.5 mg cm–2 for cathode. Subsequently, the CCM was sandwiched between porous Pt–plated Ti\nfoam gas diffusion layer (GDL) and assembled into the PEM cell. Last, 5 N m torque was applied on\nPEM cell for sealing. During the tests, the PEM cell was operated at 80 °C to obtain polarization\ncurve. The stability of F–RuO /FC was evaluated by chronopotentiometry at current density of 100,\n2\n500 and 1000 mA cm–2. [Supplementary Information Page 2, Line 35–Page 3, Line 7]\nIn situ Raman tests. A Renishaw InVia Raman spectrometer equipped with 532 nm laser and 50×\nobjective was employed for in situ electrochemical Raman measurements. The experiments were\nconducted in a professionally customized in situ Raman reaction cell with a standard three–electrode\nsetup, where the catalyst–coated L–shaped Au gold, Pt wire, and Ag/AgCl electrode were used as the\nworking electrode, counter electrode, and reference electrode, respectively. The in situ Raman spectra\nwere ultimately collected while applying a constant potential to the working electrode within the\npotential range from 1.0 to 1.7 V vs. RHE. [Supplementary Information Page 2, Line 28–34]\n7. Is it very obvious that the electrocatalyst is iridium–free as no iridium has been used in this work?\nThe authors could consider an alternative manuscript title.\n[Author’s Response]: Thanks for the valuable suggestion. Based on your suggestions, we have\nrevised the title to “Ultradurable acidic water oxidation ruthenium–based electrocatalyst by\nfluorination induced symmetry–breaking” in the revised version. [Page 1, Line 1–2]\n8. The authors should double check the wordings, such as absorb/adsorb, figure numbers.\n[Author’s Response]: Thank you for your careful checks, we feel sorry for our carelessness. We\nhave thoroughly checked the wording throughout the manuscript, which confirmed that the correct\nterms are used in the appropriate context and ensured that all figure numbers are accurate and\nconsistent.\nReviewer #3\nGeneral Comment: In this manuscript, the authors endeavor to markedly enhance the stability of\nRu–based catalysts via fluorine doping strategies. However, further supplementation and refinement\nare required regarding the microscopic mechanism of symmetry breaking, the comprehensiveness of\nexperimental validation, and the depth of comparison with state–of–the–art research. It is\nrecommended that the authors strengthen the correlation between theoretical calculations and\nexperimental characterizations, while clearly articulating the positioning of innovation points within\nthe existing framework to elevate the novelty and persuasiveness of the manuscript.\n[Author’s Response]: Thank you for the kind support of our work. Your comments have been very\nhelpful for us to further improve the quality of our work. According to your comments, we have made\nthe necessary revision of the manuscript. We hope that the revised manuscript will address all your\ncomments on this work.\n1. The introduction does not adequately address current approaches to resolving stability issues in\nruthenium–based catalysts (e.g., heterometal doping, interface engineering, strain regulation, high–\nentropy compounds, etc.). Literature searches indicate that these strategies have achieved substantial\nadvancements. It is advised to incorporate relevant references to bolster the comprehensiveness of\nthe discussion.\n[Author’s Response]: Thanks for your valuable suggestions. Based on your consideration, we have\ncomprehensively discussed currently available feasible strategies for addressing the stability of\nruthenium–based catalysts in our revised manuscript, and as follows:\nAs so far, numerous feasible approaches have been reported to significantly enhance the formation\nenergy of O , including heterometal doping (SnRuO [21], Ni–RuO [22], Ta /RuO [23]), interface\nV X 2 1 2\nengineering (Co–Ru@RuO 9:1[24], GB–RuO [25]), strain regulation (Li RuO [26], RuSnO [27]),\n2 2 0.52 2 X\nhigh–entropy compounds (M–RuIrFeCoNiO [28]), anion regulation (LD–B/RuO [29], Ru/Se–RuO [30],\n2 2 2\nRuO –Cl[31]) and so on. Among these, the superior electronegativity and electron affinity of anions\n2\nare more conducive to optimizing the adsorption/desorption behavior of reaction intermediates on the\nelectrocatalyst surface.[32] [Page 3, Line 5–11]\n[21] Shi, Z. et al. Customized reaction route for ruthenium oxide towards stabilized water oxidation in high–performance PEM\nelectrolyzers. Nat. Commun. 14, 843 (2023). [Page 16, Line 14–15]\n[22] Wu, Z. Y. et al. Non–iridium–based electrocatalyst for durable acidic oxygen evolution reaction in proton exchange membrane\nwater electrolysis. Nat. Mater. 22, 100–108 (2023). [Page 16, Line 16–17]\n[23] Shim, J. et al. Atomically dispersed high–valent d0–metal breaks the activity–stability trade–off in proton exchange membrane\nwater electrolysis. J. Am. Chem. Soc. 147, 16179–16188 (2025). [Page 16, Line 18–19]\n[24] Chen, J. et al. Cobalt–doped Ru@RuO2 core–shell heterostructure for efficient acidic water oxidation in low–Ru–loading proton\nexchange membrane water electrolyzers. J. Am. Chem. Soc. 147, 8720–8731 (2025). [Page 16, Line 20–22]\n[25] He, W. et al. Grain–boundary–rich RuO2 porous nanosheet for efficient and stable acidic water oxidation. Angew. Chem. Int. Ed.\n63, e202405798 (2024). [Page 16, Line 23–24]\n[26] Qin, Y. et al. RuO2 electronic structure and lattice strain dual engineering for enhanced acidic oxygen evolution reaction\nperformance. Nat. Commun. 13, 3784 (2022). [Page 16, Line 25–26]\n[27] Xu, Y. et al. Strain–modulated Ru–O covalency in Ru–Sn oxide enabling efficient and stable water oxidation in acidic solution.\nAngew. Chem. Int. Ed. 136, e202316029 (2024). [Page 16, Line 27–28]\n[28] Hu, C. et al. Misoriented high–entropy iridium ruthenium oxide for acidic water splitting. Sci. Adv. 9, eadf9144 (2023). [Page 16,\nLine 29–30]\n[29] Chen, G. et al. A long–range disordered RuO2 catalyst for highly efficient acidic oxygen evolution electrocatalysis. Angew. Chem.\nInt. Ed. 63, e202411603 (2024). [Page 17, Line 1–2]\n[30] Huang, K. et al. Ru/Se–RuO2 composites via controlled selenization strategy for enhanced acidic oxygen evolution. Adv. Funct.\nMater. 33, 2211102 (2023). [Page 17, Line 3–4]\n[31] Chen, J. et al. Chloride residues in RuO2 catalysts enhance its stability and efficiency for acidic oxygen evolution reaction. Angew.\nChem. Int. Ed. 137, e202420860 (2025). [Page 17, Line 5–6]\n[32] Liu, Y. et al. Shining light on anion–mixed nanocatalysts for efficient water electrolysis: fundamentals, progress, and perspectives.\nNano–Micro lett. 14, 43 (2022). [Page 17, Line 7–8]\n2. The specific mechanism by which F–induced symmetry breaking suppresses LOM lacks sufficient\ndetail. Existing studies (e.g., 10.1002/anie.202420848, 10.1038/s41467-024-49281-2) demonstrate\nthat lattice symmetry breaking inhibits OLE participation through elongation of Ru–O bond lengths\nand reduced covalency. Further elucidation of the effects of F doping on electronic structures and\nreaction pathways using DFT calculations is warranted.\n[Author’s Response]: We appreciate your expert suggestions, which will contribute to the refinement\nof our work. In the revised manuscript, we elucidate the details of the F–induced symmetry breaking\nsuppression of LOM from both computational and experimental perspectives. Meanwhile, the effects\nof F doping on electronic structures and reaction pathways was further clarified using DFT\ncalculations. The specific description is as follows:\nThe desirable Gibbs free energy of rate–determining step (RDS) for F–RuO is 1.80 eV, lower than\n2\nthat of S–RuO (1.86 eV), P–RuO (2.60 eV), Se–RuO (2.76 eV), N–RuO (1.83 eV), Cl–RuO (3.16\n2 2 2 2 2\neV), Br–RuO (4.28 eV) and RuO (1.89 eV) (Fig. 1c). Notably, a decrease of the Ru d–band center\n2 2\nrelative to fermi energy level (E) is observed after the partial substitution of O with F, potentially\nf\ninfluencing the adsorption/desorption of intermediates on the catalyst surface (Fig. 1d).[36] Therefore,\ncompared with the traditional RuO following LOM route, the introduction of F gives RuO more\n2 2\nenergy advantages on the AEM path (Supplementary Fig. 20). [Page 4, Line 19–22 and Page 5,\nLine 13–17]\nFigure 1. DFT calculations. (c) Gibbs free energy diagram for different catalysts. (d) DOS of Ru 3d and O 2p for F–RuO2; corresponding d–band centers are denoted by white lines.\nSupplementary Fig. 20. Calculated free energy evolution of OER via LOM on F–RuO2, S–RuO2, P–RuO2, Se–RuO2, RuO2, N–RuO2, Cl–RuO2 and Br–RuO2 under electrode potential of 0 V.\nAs shown in Fig. 3g–j, charge density difference and Bader charge analysis also reveals that the\nvalence state of Ru (+1.34) in F–RuO decreases with increasing surrounding electron density,\n2\nattributing to the electron density surrounding Ru was readjusted as a result of the octahedral\nsymmetry breakdown induced by the highly electronegative F, potentially altering the adsorption of\nintermediates on RuO and thereby switching the reaction route. [Page 9, Line 4–8]\nTo investigate the underlying mechanism during the OER process, in situ characterizations were\nconducted in Fig. 5. Note of that the diffraction peak intensity does not decrease significantly as the\npotential range from 1.0 to 1.5 V by in situ electrochemical XRD testing, implying the structure of\nF–RuO /FC remains intact during a wide range of potential tests (Fig. 5a). More importantly, the\n2\nwell–preserved diffraction peak in the situ monitoring for up to 60 minutes suggests that the O in F–\nRuO /FC may not participate in the OER process, thus deviating from the traditional LOM route\n2\n(Supplementary Fig. 68). [Page 11, Line 9–15]\nFigure 5. Mechanism explorations. (a) In situ XRD patterns, (b) in situ Raman spectra and (c) corresponding contour plots, (d) in situ ATR–IR spectra of F–RuO2/FC. (e) DEMS signals of 32O2, 34O2, and 36O2 from the gaseous products for 18O–labeled F–RuO2/FC catalysts in H2 16O aqueous H2SO4 electrolyte during three times of LSV cycles.\nSupplementary Fig. 68. In situ XRD patterns of F–RuO2/FC within 60 min.\nTo verify this conjecture, the dynamic evolution of the surface structure during the OER process is\nmonitored by in situ electrochemical Raman spectroscopy (Fig. 5b). Surprisingly, a new Raman peak\nemerges gradually at ~731 cm–1 with the applied potential increases, compared with RuO /C,\n2\nattributed to the formation of Ru–OOH intermediates in the AEM pathway (Supplementary Fig.\n69).[44] As shown in Fig. 5c, the corresponding contour plots exhibit significantly enhanced vibration\nsignals of B for Ru–OOH intermediates except for the predominant surface feature signals of Ru–\n2g\nO bonds, proving that the reaction intermediates in the AEM pathway are indeed captured. [Page 11,\nLine 18–23]\nSupplementary Fig. 69. In situ Raman spectra of RuO2/C.\nTo further elucidate the actual OER route, in situ attenuated total reflectance infrared (ATR–IR)\nspectroscopy was carried out to detect the reaction intermediates. As shown in Supplementary Fig.\n70, two absorption peaks attributed to the *OO intermediate formed during the LOM pathway are\ndetected, further indicating that RuO /C follow the conventional LOM pathway during the acidic\n2\ncharacteristic peak appear at 1237 cm–1, belonging to the stretching vibration of surface–adsorbed\n*OOH intermediates, evidencing the dominance of the AEM pathway (Fig. 5d).[46] Obviously, the\nsignals of *OOH intermediates gradually appear and are significantly enhanced with the increase of\npotential, indicating that the incorporation of F can force the reaction mechanism of RuO from the\n2\ntraditional LOM to AEM, thus ensuring exceptional stability even at high applied potential.\nAdditionally, F–RuO /FC shows clearly pH–independence, suggesting the significant suppression of\n2\nthe LOM pathway and the dominant role of the AEM pathway (Supplementary Fig. 71).[47, 48] [Page\n12, Line 1–12]\nSupplementary Fig. 70. In situ ATR–IR spectra of RuO2/C.\nSupplementary Fig. 71. OER polarization curves of F–RuO2/FC in various pH–H2SO4 electrolytes.\nFinally, the oxygen isotope tracking experiment was carried out to verify the suppressed LOM process,\nthat is, whether lattice oxygen was involved in the reaction. Operando differential electrochemical\nmass spectrometry (DEMS) was performed on 18O isotope–labelled F–RuO /FC using linear sweep\n2\nvoltammograms (LSV) in H 16O 0.5 M H SO (Supplementary Fig. 73a). As shown in Fig. 5e, the\n2 2 4\nmass signals of 32O and 34O were detected without 36O products, suggesting the non–participation\n2 2 2\nof O in the OER process.[50] The mass signals of 32O gradually increase and present a constant ratio\nL 2\n(32O :34O ) with the occurrence of OER, further demonstrating the dominant AEM pathway\n2 2\n(Supplementary Fig. 73b, c). [Page 12, Line 16–21]\nSupplementary Fig. 73. (a) Schematic illustration of the operando DEMS device. (b) DEMS signals of 32O2 (16O + 16O) were collected during the LSV cycle. (c) Ratio of 34O2:32O2 within the LSV range.\nFigure 5. Mechanism explorations. (e) DEMS signals of 32O2, 34O2, and 36O2 from the gaseous products for 18O–labeled F–\nRuO2/FC catalysts in H2 16O aqueous H2SO4 electrolyte during three times of LSV cycles.\n[36] Li, L. et al. Lanthanide–regulating Ru–O covalency optimizes acidic oxygen evolution electrocatalysis. Nat. Commun. 15, 4974\n(2024). [Page 17, Line 15–16]\n[44] Li, W. Q. et al. Identification of the molecular pathways of RuO2 electroreduction by in–situ electrochemical surface–enhanced\nRaman spectroscopy. J. Catal. 400, 367–371 (2021). [Page 18, Line 1–2]\n[45] Gou, W. et al. Oxygen spillover from RuO2 to MoO3 enhances the activity and durability of RuO2 for acidic oxygen evolution.\nEnergy Environ. Sci. 17, 6755–6765 (2024). [Page 18, Line 3–4]\n[46] Jin, H. et al. Dynamic rhenium dopant boosts ruthenium oxide for durable oxygen evolution. Nat. Commun. 14, 354 (2023).\n[Page 18, Line 5–6]\n[47] Shi, Z. et al. Confined Ir single sites with triggered lattice oxygen redox: toward boosted and sustained water oxidation catalysis.\nJoule 5, 2164–2176 (2021). [Page 18, Line 7–8]\n[48] Wu, L. et al. Role of interfacial water in improving the activity and stability of lattice–oxygen–mediated acidic oxygen evolution\non RuO2. Angew. Chem. Int. Ed. e202420848 (2025). [Page 18, Line 9–10]\n[50] Han, X. et al. Defect engineering of RuO2 aerogels for efficient acidic water oxidation. ACS Mater. Lett. 6, 748–7755 (2024).\n[Page 18, Line 13–14]\n3. In Figure 1, the authors focus solely on the F–RuO (110) surface without explaining the rationale\n2\nfor selecting this orientation (e.g., exposed crystal surfaces, reactive site distributions). Comparative\nanalysis of other crystal faces (e.g., (100), (111)) is recommended to validate the universality of the\nfindings.\n[Author’s Response]: Thanks for your kind suggestion. The RuO (110) facet was selected because\n2\nit exposes fully coordinated bridged Ru sites and coordination unsaturated sites with quintuple\ncoordination that bind to triple–coordinated oxygen for better identification of the active site.[4-6]\nAdditionally, this surface is known to exhibit the most favorable thermodynamic free energy during\nmost synthesis processes, as established in prior studies.[7] [Supplementary Information Page 3,\nLine 11–15]\nAs requested, AEM and LOM pathway on different planes ((111) and (100)) of F–RuO₂ and RuO₂\nwere carried out in Supplementary Fig. 21. Apparently, similar phenomena have been observed on\ndifferent planes ((111) and (100)) of F–RuO₂ and RuO₂, proving its universality. [Page 5, Line 17–\n19]\nSupplementary Fig. 21. Calculated Gibbs free energy evolution of OER via (a, b) AEM and (c, d) LOM on (a, c) F–RuO2 and (b, d)\nRuO2.\n[4] Sun, Q. et al. Effect of a humid environment on the surface structure of RuO2(110). Phys. Rev. B 67, 205424 (2003).\n[Supplementary Information Page 82, Line 7–8]\n[5] Abbott, D. F. et al. Oxygen reduction on nanocrystalline ruthenia–local structure effects. RSC Adv. 5, 1235–1243 (2014).\n[Supplementary Information Page 82, Line 9–10]\n[6] Rao, R. R. et al. Operando identification of site–dependent water oxidation activity on ruthenium dioxide single–crystal surfaces.\nNat. Catal. 3, 516–525 (2020). [Supplementary Information Page 82, Line 11–12]\n[7] Latimer, A. A. et al. A theoretical study of methanol oxidation on RuO2(110): bridging the pressure gap. ACS Catal. 7, 4527–4534\n(2017). [Supplementary Information Page 82, Line 13–14]\n4. In Figure 1, the authors state that F–RuO is positioned at the bottom of the volcano inversion\n2\ndiagram; however, the introduction of F only induces a slight symmetry breaking. Further validation\nis required to confirm whether this conclusion aligns with the simulation results for other halogens\n(e.g., Cl and Br), thereby avoiding overinterpretation of a single data point. Additionally, more\ndetailed information should be provided to compare the local structural changes in RuO after\n2\nsubstitution by different elements (e.g., bond lengths, bond angles).\n[Author’s Response]: Thank you for your honest advice. We deeply agree with this view, so that the\nmodels of Cl–RuO and Br–RuO were constructed using Cl and Br as dopants, respectively.\n2 2\nAccording to the DFT calculation analysis, compare to F–RuO , the incorporation of Cl or Br induces\n2\nmore pronounced symmetry–breaking in the octahedral configuration of RuO (Fig. 1f and Table\nFigure 1. DFT calculations. (f) Reaction free energy (RDS) and subsurface O loss enthalpy change volcano against the symmetry–\nbreaking.\nTable S1. Bond angle of different catalysts.\nCatalysts Bond angle\nF–RuO2 91.4\nRuO2 90.0\nN–RuO2 95.1\nS–RuO2 126.7\nP–RuO2 127.1\nSe–RuO2 131.5\nCl–RuO2 135.4\nBr–RuO2 140.0\n5. In Figure 1, the authors do not address potential overlooked factors in the DFT simulations (e.g.,\nsolvent effects, zero–point energy corrections). It is recommended to include a critical evaluation of\nthe model's assumptions, such as whether the effect of octahedral distortion on oxygen vacancy (O )\nV\nformation energy has been overestimated.\n[Author’s Response]: Thank you for your professional comment. The Gibbs free energy change\nduring OER was calculated by ΔG = ΔE + ΔZPE – TΔS, where the ΔE is the energy change of\nintermediates adsorbed on catalysts surface based on the DFT calculations, ΔZPE and ΔS is the\nchange in zero–point energy and entropy, respectively, T is room temperature (298.15 K). According\nto your suggestion, we have included consideration of solvent effects in the model construction when\nrecalculating the octahedral distortion on the O formation energy by including a Water Bi–layer\nV\nwater model to represent the interaction between the solvent water and the model surface (Fig. 1e and\nSupplementary Fig. 23–30). [Page 5, Line 22–Page 6, Line 2]\nFigure 1. DFT calculations. (e) Calculated enthalpy changes for subsurface oxygen loss of various catalysts.\nSupplementary Fig. 23. Atomistic structures showing the detachment of subsurface O from F–RuO2(110) surface. The grey, red,\nblue and white balls represent Ru, O, F and H atoms, respectively.\nSupplementary Fig. 24. Atomistic structures showing the detachment of subsurface O from N–RuO2(110) surface. The grey, red,\npink and white balls represent Ru, O, N and H atoms, respectively.\nSupplementary Fig. 25. Atomistic structures showing the detachment of subsurface O from S–RuO2(110) surface. The grey, red,\nyellow and white balls represent Ru, O, S and H atoms, respectively.\nSupplementary Fig. 26. Atomistic structures showing the detachment of subsurface O from P–RuO2(110) surface. The grey, red,\norange and white balls represent Ru, O, P and H atoms, respectively.\nSupplementary Fig. 27. Atomistic structures showing the detachment of subsurface O from Se–RuO2(110) surface. The grey, red,\ngreen and white balls represent Ru, O, Se and H atoms, respectively.\nSupplementary Fig. 28. Atomistic structures showing the detachment of subsurface O from Cl–RuO2(110) surface. The grey, red,\ncyan and white balls represent Ru, O, Cl and H atoms, respectively.\nSupplementary Fig. 29. Atomistic structures showing the detachment of subsurface O from Br–RuO2(110) surface. The grey, red,\nbrown and white balls represent Ru, O, Br and H atoms, respectively.\nSupplementary Fig. 30. Atomistic structures showing the detachment of subsurface O from RuO2(110) surface. The grey, red, and\nwhite balls represent Ru, O and H atoms, respectively.\n6. In Figure 1, the authors briefly describe the mechanism by which F suppresses Ru dissolution (e.g.,\nO–2p band center shift). It is suggested to integrate Bader charge analysis to elucidate how F enhances\nstability through electronic structure regulation and discuss its applicability under various acidic\nconditions.\n[Author’s Response]: Thank you for your valuable suggestions. In fact, charge density difference\nand Bader charge were presented in Fig. 3g–j. The valence state of Ru (+1.34) in F–RuO decreases\n2\nwith increasing surrounding electron density, attributing to the electron density surrounding Ru was\nreadjusted as a result of the octahedral symmetry breakdown induced by the highly electronegative\nF, potentially altering the adsorption of intermediates on RuO and thereby switching the reaction\n2\nroute (Fig. 3g–j). [Page 9, Line 4–8]\nFigure 3. Electronic structure investigation. Electron density difference of (g) F–RuO2/FC and (h) RuO2. The blue and yellow shaded area mean the electron density accumulation and donation and the isosurface value is 0.065 e/Å3. Bader charge analysis for Ru (grey), F (blue), and O (red) sites of (i) F–RuO2/FC and (j) RuO2.\nAdditionally, F–RuO /FC shows clearly pH–independence, suggesting the significant suppression of\n2\nthe LOM pathway and the dominant role of the AEM pathway (Supplementary Fig. 71).[47, 48] [Page\n12, Line 10–12]\nSupplementary Fig. 71. OER polarization curves of F–RuO2/FC in various pH–H2SO4 electrolytes.\n[47] Shi, Z. et al. Confined Ir single sites with triggered lattice oxygen redox: toward boosted and sustained water oxidation catalysis.\nJoule 5, 2164–2176 (2021). [Page 18, Line 7–8]\n[48] Wu, L. et al. Role of interfacial water in improving the activity and stability of lattice–oxygen–mediated acidic oxygen evolution\non RuO2. Angew. Chem. Int. Ed. e202420848 (2025). [Page 18, Line 9–10]\n7. In Figures 2–3, the lattice strain mechanism induced by F is insufficiently explained. The\ninteraction between the F–O bond and Ru–O bond should be clarified using DFT calculations.\n[Author’s Response]: Thanks for your carefully reading of our manuscript. We will systematically\naddress your questions through the following two sections:\nPart I: To address your concerns, we condected comprehensive characterization of the crystal\nstructure of F–RuO /FC using advanced techniques including spherical aberration–corrected high–\n2\nangle annular dark–field scanning transmission electron microscopy (AC–HAADF–STEM), time of\nflight secondary ion mass spectrometry (TOF–SIMS) and X–ray diffraction (XRD) with Rietveld\nrefinement. The result of analysis revealing that the partial substitution of O by F in RuO , inducing\n2\nslight distortion in the octahedral configuration. The detailed analysis is presented below:\nFirstly, to verify the lattice strain mechanism induced by F, long–range ordered atomic arrangements\nwere successfully detected using a spherical AC–HAADF–STEM (Fig. 2a). The well–defined lattice\nspacings (0.22 and 0.18 nm) of (020) and (211) planes for RuO unequivocally indicate the presence\n2\nof lattice strain compared to RuO , which may be caused by symmetry breaking due to introduction\n2\nof heterogeneous atoms (Fig. 2b). The fast Fourier transform (FFT) pattern, inset in Fig. 2b, reveals\nthe exposed (020) and (211) planes along the [102] zone axis of F–RuO /FC. To confirm the\n2\nheterogeneous atoms in F–RuO /FC, STEM energy dispersive spectrometer (STEM–EDS) elemental\n2\nmappings were conducted in Fig. 2c. In addition to the uniformly distributed Ru and O elements,\nconspicuous F signals can be observed, suggesting that the lattice strain in F–RuO /FC may be caused\n2\nby the incorporation of F. [Page 7, Line 1–11]\nFigure 2. Structural characterizations. (a, b) spherical aberration–corrected HAADF–STEM images, (c) STEM–EDS elemental\nmappings of F–RuO2/FC. Inset in (b) is the FFT pattern of F–RuO2/FC.\nSecondly, geometrical phase analysis (GPA) was performed to evaluate the strain level and\ndistribution in the F–RuO /FC. Evidently, the reduced and enhanced strain can be observed along the\n2\nhorizontal (Ꜫ ) and vertical (Ꜫ ) direction, respectively (Fig. 2d, e). The strain profiles of line1 and\nxx yy\nline2 acquired from strain mappings further confirm that the compressive stress is predominantly\nalong the Ꜫ direction and the tension stress along the Ꜫ direction (Fig. 2f).[37] [Page 7, Line 11–\nxx yy\n15]\nFigure 2. Structural characterizations. Strain mappings of F–RuO2/FC along (d) Ꜫxx and (e) Ꜫyy direction from GPA and (f) line\nprofiles of strain along the dotted white lines in (d) and (e).\nThirdly, to investigate the critical insight of chemical distributions for F–RuO /FC, TOF–SIMS\n2\nanalysis was performed in Fig. 2g. The element intensity versus sputter time reveals that the\nconcentration of O– is notably greater than that of Ru+, being consistent with the characteristics of\nRuO . In addition, the detected RuF– signals indicate that F indeed replaces part of O and then bonds\n2\nwith Ru during the heat treatment process. Two–dimensional (2D) TOF–SIMS elemental mappings\nalso confirm the presence of significant RuF– species alongside the abundant Ru and O species (Fig.\n2h). Clearly, the distribution of Ru and O signals throughout the space in three–dimensional (3D)\nTOF–SIMS views indicates that the predominant species is RuO , consistent with the AC–HAADF–\nfurther confirms the partial substitution of O by F, thus leading to the formation of Ru–F bonds. [Page\n7, Line 15–Page 8, Line 2]\nFigure 2. Structural characterizations. (g) TOF–SIMS depth analysis of Ru+, O–, and RuF– for F–RuO2/FC and (h) corresponding\n2D elemental mapping images and (i) 3D render overlay images.\nFinally, XRD with Rietveld refinement was conducted to obtain the detailed unit cell parameter (Fig.\n2j and Table S2). The sharp diffraction peaks correspond to the tetragonal RuO with the space group\n3 2\nduring the heat treatment process. The presence of Ru accelerates the local pyrolysis of FC and\nresulting in F occupying part of the position of O in F–RuO /FC (inset in Fig. 2j). [Page 8, Line 2–\n2\n7]\nFigure 2. Structural characterizations. (j) XRD pattern of F–RuO2/FC. Inset in (j) is structural model of F–RuO2/FC.\nTable S2. Refined parameters of F–RuO2/FC.\nF–RuO2/FC X Y Z\nRu0 0.500000 0.500000 0.500000\nRu1 0.000000 0.000000 0.000000\nO2 0.694330 0.694330 0.000000\nO3 0.194330 0.805670 0.500000\nO4 0.239972 0.225644 –9.999990\nF1 0.805670 0.194330 0.500000\na = 4.5436 Å, b = 4.5436 Å, c = 3.1397 Å, space grpup P42/mnm, Rwp = 6.12%, Rp = 4.70%, Chi2 = 8.977\nPart II: It is worth noting that the F–O bond mentioned by the reviewers is not covered in this\nmanuscript. To avoid ambiguity, we clearly defined the descriptions of Ru–O or Ru–F bonds and\nclarified their interactions in our revised manuscript, and as follows:\nThe chemical structure and coordination environment of the F–RuO /FC was analyzed by Fourier\n2\ntransform of the EXAFS (FT–EXAFS) spectra, where the peak at ~1.42 Å in F–RuO /FC can be\n2\nattributed to Ru–O or Ru–F coordination environment (denote as Ru–O/F) (Fig. 3f and\nSupplementary Fig. 38). [Page 8, Line 22–Page 9, Line 2]\nFigure 3. Electronic structure investigation. (f) EXAFS of F–RuO2/FC, Ru foil and RuO2.\nSupplementary Fig. 38. (a, c) R space and (b, d) inverse FT–EXAFS results of Ru K–edge for (a, b) F–RuO2/FC and (c, d) RuO2.\nCompared to RuO , a noticeable red shift can be observed in the vibration peaks of F–RuO /FC,\n2 2\nwhich may be caused by the shortened Ru–O owing to the partial substitution of O by the highly\nelectronegative F (Fig. 3a).[39] Therefore, F 1s XPS spectra of F–RuO /FC present a wider peak than\n2\nthat of FC, corresponding to the C–F and Ru–F species (Fig. 3b). Additionally, O 1s XPS peaks of\nRuO are located at 529.0, 530.0, and 531.7 eV, corresponding to O , O , and surface–adsorbed H O,\nrespectively (Fig. 3c).[40, 41] Evidently, a notable shift of the O species towards higher binding energy\ncan be observed in F–RuO /FC due to the presence of high electronegativity F results in an altered\n2\nelectronic interaction between Ru and O.[39] [Page 8, Line 8–17]\nFigure 3. Electronic structure investigation. (a) Raman spectra of F–RuO2/FC and RuO2. (b) F 1s XPS spectra of F–RuO2/FC and\nFC. (c) O 1s XPS spectra of F–RuO2/FC and RuO2.\nIn addition, the valence state of Ru (+1.34) in F–RuO 2 decreases with increasing surrounding electron\ndensity, attributing to the electron density surrounding Ru was readjusted as a result of the octahedral\nsymmetry breakdown induced by the highly electronegative F, potentially altering the adsorption of\nintermediates on RuO and thereby switching the reaction route (Fig. 3g–j). [Page 9, Line 4–8]\n[37] Wu, G. et al. In–plane strain engineering in ultrathin noble metal nanosheets boosts the intrinsic electrocatalytic hydrogen\nevolution activity. Nat. Commun. 13, 4200 (2022). [Page 17, Line 17–18]\n[39] Xiao, K., Wang, Y., Wu, P., Hou, L. & Liu, Z. Q. Activating lattice oxygen in spinel ZnCo2O4 through filling oxygen vacancies\nwith fluorine for electrocatalytic oxygen evolution. Angew. Chem. Int. Ed. 62, e202301408 (2023). [Page 17, Line 21–23]\n[40] Liu, Z. et al. Optimal geometrical configuration of cobalt cations in spinel oxides to promote oxygen evolution reaction. Angew.\nChem. Int. Ed. 59, 4736–4742 (2020). [Page 17, Line 24–25]\n[41] Xue, J. Y. et al. Engineering multiphasic MoSe2/NiSe heterostructure interfaces for superior hydrogen production electrocatalysis.\nAppl. Catal. B–Environ. 312, 121434 (2022). [Page 17, Line 26–27]\n8. In Figure 3, the Ru valence states predicted by DFT (e.g., average oxidation state reduced to +3.5)\nshould be quantitatively correlated with experimental data (e.g., XPS Ru 3p peak negative shift). The\noriginal paper only provides a qualitative description of \"electron density adjustment.\" It is\nrecommended to quantify the polarization effect of F on Ru charge using Bader charge analysis and\ncompare it with relevant experimental characterization results (e.g., XPS and EXAFS).\n[Author’s Response]: Thank you for your guidance on our manuscript, which help to improve the\nquality of our work. According to your suggestiions, X–ray photoelectron spectroscopy (XPS) was\nperformed on F–RuO /FC. Compared with RuO , Ru 3p XPS peaks for F–RuO /FC are negative shift\n2 2 2\nof 0.35 eV, revealing a lower valence state than Ru4+ (Fig. 3d). Furthermore, X–ray absorption near–\nedge structure (XANES) showed a lower absorption energy for F–RuO /FC compared to RuO\n2 2\nsuggests that the average valence state of Ru in F–RuO /FC is below +4, which is attributed to the\n2\npartial substitution of O by highly electronegative F (Fig. 3e). In addition, charge density difference\nand Bader charge analysis also reveals that the valence state of Ru (+1.34) in F–RuO decreases with\n2\nincreasing surrounding electron density, which is consistent with the results from XPS and XANES\nanalyses (Fig. 3g–j). [Page 8, Line 17–22 and Page 9, Line 4–8]\nFigure 3. Electronic structure investigation. (d) Ru 3p XPS spectra of F–RuO2/FC and RuO2.\nFigure 3. Electronic structure investigation. Ru K–edge (e) XANES of F–RuO2/FC Ru foil and RuO2.\nFigure 3. Electronic structure investigation. Electron density difference of (g) F–RuO2/FC and (h) RuO2. The blue and yellow shaded area mean the electron density accumulation and donation and the isosurface value is 0.065 e/Å3. Bader charge analysis for Ru (grey), F (blue), and O (red) sites of (i) F–RuO2/FC and (j) RuO2.\n9. In Figure 4, the authors do not explicitly clarify whether resistance voltage drop (iR) correction\nhas been applied to the overpotential (η). In acidic electrolytes, electrode interface impedance\n(R_total) may lead to an overestimation of η, particularly when the catalyst exhibits poor conductivity\n(e.g., RuO –based materials).\n2\n[Author’s Response]: Thank you for your scrutiny of our manuscript. According to your\nconsideration, we define the detail electrochemical measurements process in methods section, in\nwhich 95% iR compensation have been implemented on the LSV polarization curves.\nElectrochemical measurements. All polarization curves (95% iR compensation) are averages of the\nmultiple test results at 5 mV s–1. [Page 14, Line 18–19]\n10. In Figure 4, the author merely claims that \"F introduces more active sites,\" which lacks robust\nand direct evidence.\n[Author’s Response]: Thanks for your perceptive observations regarding this study. To strengthen\nthis conclusion, this intrinsic activity of individual Ru sites was evaluated through the calculations of\nturnover frequency (TOF) (Supplementary Fig. 40). Notable, the F–RuO /FC displays high intrinsic\n2\nactivity compare to RuO /C and RuO , demonstrating that F as a dopant effectively introduces more\n2 2\nactive sites. [Page 9, Line 21–22]\nCalculation of the turnover frequency (TOF). At first, each Ru atom on the electrode was\nconsidered as an active site in the calculation process. The TOF of F–RuO /FC, RuO /C and RuO\n2 2 2\nwere calculated according to equation (1).\nTOF =\nNumber of O2 per second\n(1)\nNumber of active Ru sites\nThe number of oxygen per second was obtained from the LSV curves according to equation (2).\nNumber of O per second = (|J|A)( )( )( )( ) (2)\n2\ns 96453.8 C 4e 1 mol O2\nin which J is the geometric current.\nThe number of active Ru sites can be calculated following equation (3).\nNumber of active Ru sites = mcat×Ru wt% × 6.023 × 1023 (3)\n101.07 g mol−1\nWhere m is the mass of catalysts loaded on the work electrode. [Supplementary Information\ncat\nPage 2, Line 8–17]\nSupplementary Fig. 40. TOF of F–RuO2/FC, RuO2/C, and RuO2.\n11. The comparison between DFT predictions and experimental results remains superficial (e.g., only\n\"symmetry breaking\" is mentioned), and the adsorption energy or reaction pathway of key\nintermediates has not been quantitatively validated. It is recommended to include in the\nsupplementary material a correlation between the ΔG* (OER steps) calculated via DFT and the\nTafel slope measured experimentally to establish a clear theory–experiment mapping.\n[Author’s Response]: Thank you very much for the insightful and constructive comments, which\nhave inspired us to futher refine our research work. As your suggestion, the Tafel slope of\nelectrocatalysts were calculated base on LSV, which displaying a positive correlation with the Gibbs\nfree energy of rate–determining step (RDS) (Supplementary Fig. 65).\nSupplementary Fig. 65. Gibbs free energy of RDS versus Tafel slope.\n12. In Figure 5, no explicit correlation mechanism linking F doping with the AEM path has been\nestablished, and there is a lack of DFT transition state analysis or EXAFS surface coordination\nverification.\n[Author’s Response]: We sincerely appreciate your valuable feedback, which has helped us improve\nthe manuscript. As shown in Fig. 5f, the LOM pathway that O is involved in the OER process,\nL\nincluding a labeled 18O and an ambient O (16O) from the electrolyte, resulting in the instability surface\nof the RuO and consequently generating 16O18O specie. Based on the DFT computations and detailed\n2\nexperimental characterization, the F induced symmetry–breaking in octahedral configuration of RuO\n2\nimproves the interaction between adsorbent and the electrocatalysts surface, alters the OER route to\nfollow the AEM pathway, and ultimately enhancing the electrocatalytic performance. [Page 12, Line\n21–Page 13, Line 4]\nFigure 5. Mechanism explorations. (f) Schematic illustration of the mechanism transformation from LOM to AEM caused by F–\nmediated symmetry breaking on RuO2.\nThe chemical structure and coordination environment of the F–RuO /FC was analyzed by Fourier\n2\ntransform of the EXAFS (FT–EXAFS) spectra, where the peak at ~1.42 Å in F–RuO /FC can be\n2\nattributed to Ru–O or Ru–F coordination environment (denote as Ru–O/F) (Fig. 3f and\nSupplementary Fig. 38). [Page 8, Line 22–Page 9, Line 4]\nFigure 3. Electronic structure investigation. (f) EXAFS of F–RuO2/FC, Ru foil and RuO2.\nSupplementary Fig. 38. (a, c) R space and (b, d) inverse FT–EXAFS results of Ru K–edge for (a, b) F–RuO2/FC and (c, d) RuO2.\nObviously, the diminished intensity of Ru–O/F bonds for F–RuO /FC as\n2\nopposed to RuO suggests that the introduction of F leads to an unsaturated coordination environment\n2\n(Table S3). [Page 8, Line 22–Page 9, Line 4]\nFigure 3. Electronic structure investigation. (f) EXAFS of F–RuO2/FC, Ru foil and RuO2.\nSupplementary Fig. 38. (a, c) R space and (b, d) inverse FT–EXAFS results of Ru K–edge for (a, b) F–RuO2/FC and (c, d) RuO2.\nTable S3. Structural parameters obtained from the curve–fitting analysis of the Ru K–edge EXAFS spectra.\nSample Shell N R(Å) σ2(10-3 Å2) R factor\nF–RuO2/FC Ru–O(F) 5.7 1.95 5.85 0.017\nRuO2 Ru–O 6.0 1.96 2.44 0.015\nNote:\nN is the coordination number.\nR is interatomic distance (the bond length between central atoms and surrounding coordination atoms).\nσ2 is Debye–Waller factor (a measure of thermal and static disorder in absorber–scatterer distances).\nR factor is residual factor.\n13. Inferring from XRD structural stability that O does not participate in the reaction involves a\nlogical leap; oxygen isotope tracking data should be incorporated for validation.\n[Author’s Response]: Thank you for your professional suggestions. In the original manuscript,\nwe have already conducted O–isotope tracking experiments, which are described as follows:\nOperando differential electrochemical mass spectrometry (DEMS) was performed on 18O isotope–\nlabelled F–RuO /FC using linear sweep voltammograms (LSV) in H 16O 0.5 M H SO\n2 2 2 4\n(Supplementary Fig. 73a). As shown in Fig. 5e, the mass signals of 32O and 34O were detected\n2 2\nwithout 36O products, suggesting the non–participation of O in the OER process. The mass signals\nof 32O gradually increase and present a constant ratio (32O :34O ) with the occurrence of OER, further\n2 2 2\ndemonstrating the dominant AEM pathway (Supplementary Fig. 73b, c). [Page 12, Line 16–21]\nSupplementary Fig. 73. (a) Schematic illustration of the operando DEMS device. (b) DEMS signals of 32O2 (16O + 16O) were\ncollected during the LSV cycle. (c) Ratio of 34O2:32O2 within the LSV range.\nFigure 5. Mechanism explorations. (e) DEMS signals of 32O2, 34O2, and 36O2 from the gaseous products for 18O–labeled F–\nRuO2/FC catalysts in H2 16O aqueous H2SO4 electrolyte during three times of LSV cycles.\n14. It is suggested that the conclusion propose additional research directions, such as investigating\nthe impact of other halogens (Cl, Br) or non–elemental doping on symmetry breaking and OER\nproperties, as well as exploring the potential characteristics and performance of the catalyst under\nreaction conditions.\n[Author’s Response]: Thanks for your kind suggestion. Based on your consideration, the models of\nCl–RuO and Br–RuO were constructed using Cl and Br as dopants, respectively. According to the\n2 2\nDFT calculation analysis, compare to F–RuO , the incorporation of Cl or Br leads to a higher reaction\n2\nenergy barrier and a lower formation energy of O for RuO , indicating that excessive symmetry\nV 2\nbreaking also affects the activity and stability of RuO (Fig. 1c, e, and f). [Page 4, Line 19–21 and\nFigure 1. DFT calculations. (c) Gibbs free energy diagram for different catalysts. (e) Calculated enthalpy changes for subsurface\noxygen loss of various catalysts.\nFigure 1. DFT calculations. (f) Reaction free energy (RDS) and subsurface O loss enthalpy change volcano against the symmetry–\nbreaking.\nSubsequently, Cl–RuO /(F)C and Br–RuO /(F)C were synthesized in Supplementary Fig. 62, 63.\n2 2\nPreparation of RuO /(F)C. The synthesis condition of RuO /(F)C is the same as F–RuO /FC, except\n2 2 2\nthat the FC used for RuO /(F)C was pre–annealed in air at 400 °C for 12 h to remove F (denoted as\n2\n(F)C). [Page 14, Line 3–4]\nPreparation of M–RuO /(F)C (M = N, S, P, Se, Cl and Br). The M–RuO /(F)C electrocatalyst was\n2 2\nsynthesized by vapor transport method, where the anion–donating powder and RuO /(F)C (mass ratio\n2\n1:2) were placed at the upstream and downstream positions of a quartz tube, respectively. The anion–\ndonating powder and RuO /(F)C were heated to the target temperature and 400 °C respectively at a\n2\nheating rate of 5 ℃ min–1 in an Ar atmosphere and maintained for 1 h to obtain M–RuO /(F)C. In\n2\naddition, melamine, sulfur powder, sodium hypophosphite, selenium powder, a mixture of polyvinyl\nchlorid and manganese dioxide, and hexabromobenzene were unsed as anion sources, releasing\nanions under heat treatment at 450 °C, 150 °C, 300 °C, 500 °C, 450 °C, and 350 °C, respectively.\n[Page 14, Line 5–12]\nSupplementary Fig. 62. (a) SEM image, (b) TEM image, (c) XRD pattern, (d) Cl 2p XPS spectrum, (e) STEM image, and (f) STEM–\nEDS elemental mappings of Cl–RuO2/(F)C.\nSupplementary Fig. 63. (a) SEM image, (b) TEM image, (c) XRD pattern, (d) Br 3d XPS spectrum, (e) STEM image, and (f) TEM–\nEDS elemental mappings of Br–RuO2/(F)C.\nThe activity and stability of Cl–RuO /(F)C and Br–RuO /(F)C showed markedly reduced compared\n2 2\nto F–RuO /FC, which is consistent with the results predicted by DFT calculations (Supplementary\nSupplementary Fig. 64. (a) OER polarization curves, (b) Tafel plots, and (c) chronopotentiometry tests of N–RuO2/(F)C, S–\nRuO2/(F)C, P–RuO2/(F)C, Se–RuO2/(F)C, Cl–RuO2/(F)C and Br–RuO2/(F)C.\n15. The description of the DFT calculation method omits several critical details, including the\nmodel size, whether atoms are fixed, how the adsorption site is determined, and how free energy is\ncalculated and corrected. It is recommended that the authors consult relevant literature to provide a\ncomprehensive description to ensure the reproducibility of the computational results.\n[Author’s Response]: We sincerely appreciate your valuable suggestions. The comprehensive DFT\ncalculation details were added to the methods section in our revised manuscript.\nDFT calculations were conducted using the Vienna ab initio simulation package (VASP), which\nemployed the projector augmented wave (PAW) method to simulate the electron–ions interactions.[1,\n2] The exchange–correction interactions were described by the generalized gradient approximation\n(GGA) of the Perdew–Burke–Ernzerhof (GGA–PBE).[3] The RuO (110) facet was selected because\n2\nit exposes fully coordinated bridged Ru sites and coordination unsaturated sites with quintuple\ncoordination that bind to triple–coordinated O for better identification of the active site.[4–6]\nAdditionally, this surface is known to exhibit the most favorable thermodynamic free energy during\nmost synthesis processes, as established in prior studies.[7] The cutoff energy was set as 400 eV during\nthe structural optimization of all slab models. During the structural optimization calculations, the\natoms in the bottom two layers were fixed and other layers of atoms were allowed to relax. The\nvacuum layer above the surface is at least 15 Å, and the calculation module was placed in a 6.2146\nÅ × 12.6698 Å × 21.7973 Å lattice. The k–points (Monkhorst–Pack mesh) during the structural\noptimization and electronic structure–involved calculations were set to 4 × 2 × 1 and 5 × 5 × 1,\nrespectively.\nThe Gibbs free energy change during OER was calculated by ΔG = ΔE + ΔZPE – TΔS, where the\nΔE is the energy change of intermediates adsorbed on catalysts surface based on the DFT\ncalculations, ΔZPE and ΔS is the change in zero-point energy and entropy, respectively, T is room\ntemperature (298.15 K). The free energy of (H+ + e–) at standard conditions was assumed as the\nenergy of 1/2 H . Namely, G(H+ + e–) = 1/2G(H ). G(OH–) = G(H O) – 1/2G(H ). [Supplementary\n2 2 2 2\nInformation Page 3, Line 8–25]\n[1] Kresse, G. & Furthmüller, J. Efficiency of ab–initio total energy calculations for metals and semiconductors using a plane–wave\nbasis set. Comput. Mater. Sci. 6, 15–50 (1996). [Supplementary Information Page 82, Line 2–3]\n[2] Blöchl, P. E. Projector augmented–wave method. Phys. Rev. B 50, 17953–17979 (1994). [Supplementary Information Page 82,\nLine 4]\n[3] Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).\n[Supplementary Information Page 82, Line 5–6]\n[4] Sun, Q. et al. Effect of a humid environment on the surface structure of RuO2(110). Phys. Rev. B 67, 205424 (2003).\n[Supplementary Information Page 82, Line 7–8]\n[5] Abbott, D. F. et al. Oxygen reduction on nanocrystalline ruthenia–local structure effects. RSC Adv. 5, 1235–1243 (2014).\n[Supplementary Information Page 82, Line 9–10]\n[6] Rao, R.R. et al. Operando identification of site-dependent water oxidation activity on ruthenium dioxide single–crystal surfaces.\nNat. Catal. 3, 516–525 (2020). [Supplementary Information Page 82, Line 11–12]\n[7] Latimer. A A, et al. A theoretical study of methanol oxidation on RuO2(110): bridging the pressure gap. ACS Catal. 7, 4527–4534\n(2017). [Supplementary Information Page 82, Line 13–14]\n------------------------------------\nIn the end, we would like to thank for the precious time of the reviewers and the editor. We sincerely\nwish that our point-to-point response and the revised manuscript have addressed your concerns and\nsatisfy your requirements for publications. We would be grateful if we have the chance to share our\nwork with readers of Nature Communications.\nXiaoqing Huang\nResponse to Reviewers\nTo Reviewer 1:\nGeneral comment: The author provided some new materials in response to my questions, but most of my\ndoubts remain unresolved.\n[Author’s Response]: We appreciate your precious time for reviewing our revised manuscript. During\nthe revision process, we have indeed addressed all your concerns in detail. As you requested, we have\ncarried out the following experiments to address your comments point-to-point.\n1. Comment: First, the concept of symmetry breaking lacks a clear definition, along with quantitative\nmetrics to measure its extent. The authors define symmetry breaking as \"the structural modifications at\natomic scale that reduce its crystal symmetry\". However, this definition remains somewhat generalized\nand does not provide a clear method for quantifying the degree of symmetry breaking based on\nexperimental evidence. Generally, any elemental doping or substitution will introduce atomic-scale\nstructural modifications, which inherently trigger symmetry breaking.\n[Author’s Response]: Thanks for your perceptive observations and constructive feedback on this study.\nAccording to the literature (Proc. Natl. Acad. Sci. 93, 14256–14259 (1996); Science 177, 393-396 (1972)),\nsymmetry breaking is a fundamental concept in physics, referring to the phenomenon where a system with\noriginally high symmetry undergoes a reduction in its degree of symmetry due to the emergence of\nasymmetric factors. Considering Wang et al.'s (Appl. Catal. B–Environ. 316, 121664 (2022)) recent\napplication of the symmetry–breaking effect to materials chemistry and their clear definition, that is,\ndefects in a crystal lattice lower the lattice's symmetry, which is known as the symmetry–breaking effect,\nwe have thoroughly revised our manuscript.\nMoreover, the Baur distortion index (D), proposed by Li et al. (Nature 620, 328–335 (2023)), is used to\ni\nquantify the asymmetry or distortion in the virtual octahedral units of crystal structures. Therefore, the\nBaur distortion index (D) was employed to quantify the degree of symmetry breaking of virtual octahedral\ni\nunits within the RuO crystal structure:\n2\n𝐷 = 1 ∑6 ( |𝑏𝑖−𝑏̅| )\n𝑖 6 𝑖=1 𝑏̅\nwhere 𝑏 and 𝑏̅ represent the individual bond length and the average of six bond lengths, respectively.[41]\n𝑖\nBased on the Rietveld refinement of XRD patterns results (Fig. 2j and Supplementary Fig. 40c, 41c, 42c,\n43c, 44c and 45c), the octahedral structural units of F–RuO /FC, N–RuO (F)C, S–RuO (F)C, P–\n2 2 2\nRuO (F)C, Se–RuO (F)C, Cl–RuO (F)C and Br–RuO (F)C are depicted in Supplementary Fig. 46 and\n2 2 2 2\nTable S2–S8. The calculated D were increase in the order F < N < S < P < Se < Cl < Br, indicating an\ni\nincrease of octahedral distortion degree, consistent with DFT predictions. [Page 8, Line 8–16]\nWe agree with the reviewer's point that any elemental doping or substitution will introduce atomic–scale\nstructural modifications, which inherently trigger symmetry breaking. Recently, Dai et al. also reviewed\ncurrent symmetry–breaking methods (Chem. Soc. Rev. 54, 3848–3905 (2025)), including doping—\nintroducing heteroatoms (such as non–metals or metallic heteroatoms) and surface modification and defect\nengineering—introducing defect sites (e.g.,vacancies and lattice distortions) or modifying surfaces with\nspecific functional groups. Therefore, in this study, the introduction of heteroatoms F, N, S, P, Se, Cl, and\nBr as asymmetric elements into the RuO crystal structure can be categorized as a non–metal doping\n2\nstrategy to achieve symmetry breaking.\nSupplementary Fig. 46. The metal–nonmetal bond length of F–RuO2, N–RuO2, S–RuO2, P–RuO2, Se–RuO2, Cl–RuO2 and Br–RuO2\ncrystal structure. The calculated distortion indexes are indicated.\nFigure 2. Structural characterizations. (j) XRD pattern of F–RuO2/FC. Inset in (j) are the structural model of F–RuO2/FC.\nSupplementary Fig. 40. (c) XRD pattern of N–RuO2/(F)C.\nSupplementary Fig. 41. (c) XRD pattern of S–RuO2/(F)C.\nSupplementary Fig. 42. (c) XRD pattern of P–RuO2/(F)C.\nSupplementary Fig. 43. (c) XRD pattern of Se–RuO2/(F)C.\nSupplementary Fig. 44. (c) XRD pattern of Cl–RuO2/(F)C.\nSupplementary Fig. 45. (c) XRD pattern of Br–RuO2/(F)C.\nTable S2. Refined parameters of F–RuO2/FC.\nF–RuO2/FC X Y Z\nRu0 0.48485 0.51515 0.50000\nRu1 0.01756 -0.01756 -0.00000\nO2 0.69389 0.69616 0.00000\nO3 0.19451 0.80549 0.50000\nO4 0.30384 0.30611 -0.00000\nF1 0.80534 0.19466 0.50000\na = 4.50909 Å, b = 4.50909 Å, c = 3.11133 Å, space grpup P42/mnm, Rwp = 5.59%, Chi2 = 7.53\nTable S3. Refined parameters of N–RuO2/(F)C.\nN–RuO2/(F)C X Y Z\nRu0 0.50883 0.49117 0.50000\nRu1 -0.01173 0.01173 -0.00000\nO2 0.69264 0.69243 0.00000\nO3 0.19586 0.80414 0.50000\nO4 0.30757 0.30736 -0.00000\nN1 0.80683 0.19317 0.50000\na = 4.52037 Å, b = 4.52037 Å, c = 3.12181 Å, space grpup P42/mnm, Rwp = 5.05%, Chi2 = 6.58\nTable S4. Refined parameters of S–RuO2/(F)C.\nS–RuO2/(F)C X Y Z\nRu0 0.48556 0.51444 0.50000\nRu1 0.01766 -0.01766 -0.00000\nO2 0.68746 0.69669 0.00000\nO3 0.20040 0.79960 0.50000\nO4 0.30330 0.31254 -0.00000\nS1 0.80561 0.19439 0.50000\na = 4.48394 Å, b = 4.48394 Å, c = 3.11028 Å, space grpup P42/mnm, Rwp = 6.44%, Chi2 = 8.25\nTable S5. Refined parameters of P–RuO2/(F)C.\nP–RuO2/(F)C X Y Z\nRu0 0.48025 0.51975 0.50000\nRu1 0.02406 -0.02406 -0.00000\nO2 0.68849 0.69716 0.00000\nO3 0.19748 0.80252 0.50000\nO4 0.30284 0.31151 -0.00000\nP1 0.80241 0.19759 0.50000\na = 4.50192 Å, b = 4.50192 Å, c = 3.10770 Å, space grpup P42/mnm, Rwp = 4.53%, Chi2 = 3.74\nTable S6. Refined parameters of Se–RuO2/(F)C.\nSe–RuO2/(F)C X Y Z\nRu0 0.47722 0.52278 0.50000\nRu1 0.03359 -0.03359 0.00000\nO2 0.68462 0.69946 -0.00000\nO3 0.19975 0.80025 0.50000\nO4 0.30055 0.31538 0.00000\nSe1 0.80428 0.19572 0.50000\na = 4.49913 Å, b = 4.49913 Å, c = 3.10685 Å, space grpup P42/mnm, Rwp = 4.46%, Chi2 = 3.72\nTable S7. Refined parameters of Cl–RuO2/(F)C.\nCl–RuO2/(F)C X Y Z\nRu0 0.47924 0.52077 0.50000\nRu1 0.02721 -0.02721 -0.00000\nO2 0.68822 0.69910 0.00000\nO3 0.19879 0.80120 0.50000\nO4 0.30090 0.31178 -0.00000\nCl1 0.80563 0.19437 0.50000\na = 4.49933 Å, b = 4.49933 Å, c = 3.10890 Å, space grpup P42/mnm, Rwp = 6.20%, Chi2 = 6.45\nTable S8. Refined parameters of Br–RuO2/(F)C.\nBr–RuO2/(F)C X Y Z\nRu0 0.47220 0.52780 0.50000\nRu1 0.03881 -0.03881 -0.00000\nO2 0.68573 0.70042 0.00000\nO3 0.19902 0.80098 0.50000\nO4 0.29958 0.31427 -0.00000\nBr1 0.80468 0.19532 0.50000\na = 4.50267 Å, b = 4.50267 Å, c = 3.10783 Å, space grpup P42/mnm, Rwp = 4.78%, Chi2 = 3.56\n[41] Najarian, A. M. et al. Homomeric chains of intermolecular bonds scaffold octahedral germanium perovskites. Nature 620, 328–335\n(2023). [Page 18, Line 11–12]\n2. Comment: Current experimental evidence confirms the successful doping of elements, such as N, S, P,\nSe, Cl and Br into RuO . However, there is no definitive experimental data demonstrating how these\n2\ndopants specifically change the degree of symmetry breaking.\n[Author’s Response] Thanks for your exceptional insights that fundamentally improved our work. Due\nto the combined influence of electronegativity, atomic radius, and so on, the introduction of different\nheteroatoms causes changes in structural parameters like bond length, thus breaking the symmetry of the\noriginal structure. Thus, XRD Rietveld refinement was conducted to obtain the octahedral structure units\nof F–RuO₂/FC, N–RuO₂(F)C, S–RuO₂(F)C, P–RuO₂(F)C, Se–RuO₂(F)C, Cl–RuO₂(F)C, and Br–\nRuO₂(F)C (Supplementary Fig. 40c, 41c, 42c, 43c, 44c and 45c, 46 and Table S2–S8). Subsequently,\nthe Baur distortion index (D) was employed to quantify the symmetry breaking degree of virtual\ni\noctahedral units within the RuO crystal structure:\n2\n𝐷 = 1 ∑6 ( |𝑏𝑖−𝑏̅| )\n𝑖 6 𝑖=1 𝑏̅\nwhere 𝑏 and 𝑏̅ represent the individual bond length and the average of six bond lengths, respectively.[41]\n𝑖\n[Page 8, Line 8–13]\nAs evidenced by the computational results based on the Rietveld refinement of XRD patterns results, a\npositive correlation exists between the D and octahedral distortion severity, with elevated D values\ni i\ndirectly correspond to both increased structural distortion and enhanced octahedral symmetry breaking.\nTherefore, incorporation of F, N, S, P, Se, Cl and Br elements into RuO enables controlled symmetry\n2\nbreaking through modulation of the bond length in the octahedral coordination environment.\nSupplementary Fig. 46. The metal–nonmetal bond length of F–RuO2, N–RuO2, S–RuO2, P–RuO2, Se–RuO2, Cl–RuO2 and Br–RuO2\ncrystal structure. The calculated distortion indexes are indicated.\nFigure 2. Structural characterizations. (j) XRD pattern of F–RuO2/FC. Inset in (j) are the structural model of F–RuO2/FC.\nSupplementary Fig. 40. (c) XRD pattern of N–RuO2/(F)C.\nSupplementary Fig. 41. (c) XRD pattern of S–RuO2/(F)C.\nSupplementary Fig. 42. (c) XRD pattern of P–RuO2/(F)C.\nSupplementary Fig. 43. (c) XRD pattern of Se–RuO2/(F)C.\nSupplementary Fig. 44. (c) XRD pattern of Cl–RuO2/(F)C.\nSupplementary Fig. 45. (c) XRD pattern of Br–RuO2/(F)C.\nTable S2. Refined parameters of F–RuO2/FC.\nF–RuO2/FC X Y Z\nRu0 0.48485 0.51515 0.50000\nRu1 0.01756 -0.01756 -0.00000\nO2 0.69389 0.69616 0.00000\nO3 0.19451 0.80549 0.50000\nO4 0.30384 0.30611 -0.00000\nF1 0.80534 0.19466 0.50000\na = 4.50909 Å, b = 4.50909 Å, c = 3.11133 Å, space grpup P42/mnm, Rwp = 5.59%, Chi2 = 7.53\nTable S3. Refined parameters of N–RuO2/(F)C.\nN–RuO2/(F)C X Y Z\nRu0 0.50883 0.49117 0.50000\nRu1 -0.01173 0.01173 -0.00000\nO2 0.69264 0.69243 0.00000\nO3 0.19586 0.80414 0.50000\nO4 0.30757 0.30736 -0.00000\nN1 0.80683 0.19317 0.50000\na = 4.52037 Å, b = 4.52037 Å, c = 3.12181 Å, space grpup P42/mnm, Rwp = 5.05%, Chi2 = 6.58\nTable S4. Refined parameters of S–RuO2/(F)C.\nS–RuO2/(F)C X Y Z\nRu0 0.48556 0.51444 0.50000\nRu1 0.01766 -0.01766 -0.00000\nO2 0.68746 0.69669 0.00000\nO3 0.20040 0.79960 0.50000\nO4 0.30330 0.31254 -0.00000\nS1 0.80561 0.19439 0.50000\na = 4.48394 Å, b = 4.48394 Å, c = 3.11028 Å, space grpup P42/mnm, Rwp = 6.44%, Chi2 = 8.25\nTable S5. Refined parameters of P–RuO2/(F)C.\nP–RuO2/(F)C X Y Z\nRu0 0.48025 0.51975 0.50000\nRu1 0.02406 -0.02406 -0.00000\nO2 0.68849 0.69716 0.00000\nO3 0.19748 0.80252 0.50000\nO4 0.30284 0.31151 -0.00000\nP1 0.80241 0.19759 0.50000\na = 4.50192 Å, b = 4.50192 Å, c = 3.10770 Å, space grpup P42/mnm, Rwp = 4.53%, Chi2 = 3.74\nTable S6. Refined parameters of Se–RuO2/(F)C.\nSe–RuO2/(F)C X Y Z\nRu0 0.47722 0.52278 0.50000\nRu1 0.03359 -0.03359 0.00000\nO2 0.68462 0.69946 -0.00000\nO3 0.19975 0.80025 0.50000\nO4 0.30055 0.31538 0.00000\nSe1 0.80428 0.19572 0.50000\na = 4.49913 Å, b = 4.49913 Å, c = 3.10685 Å, space grpup P42/mnm, Rwp = 4.46%, Chi2 = 3.72\nTable S7. Refined parameters of Cl–RuO2/(F)C.\nCl–RuO2/(F)C X Y Z\nRu0 0.47924 0.52077 0.50000\nRu1 0.02721 -0.02721 -0.00000\nO2 0.68822 0.69910 0.00000\nO3 0.19879 0.80120 0.50000\nO4 0.30090 0.31178 -0.00000\nCl1 0.80563 0.19437 0.50000\na = 4.49933 Å, b = 4.49933 Å, c = 3.10890 Å, space grpup P42/mnm, Rwp = 6.20%, Chi2 = 6.45\nTable S8. Refined parameters of Br–RuO2/(F)C.\nBr–RuO2/(F)C X Y Z\nRu0 0.47220 0.52780 0.50000\nRu1 0.03881 -0.03881 -0.00000\nO2 0.68573 0.70042 0.00000\nO3 0.19902 0.80098 0.50000\nO4 0.29958 0.31427 -0.00000\nBr1 0.80468 0.19532 0.50000\na = 4.50267 Å, b = 4.50267 Å, c = 3.10783 Å, space grpup P42/mnm, Rwp = 4.78%, Chi2 = 3.56\n[41] Najarian, A. M. et al. Homomeric chains of intermolecular bonds scaffold octahedral germanium perovskites. Nature 620, 328–335\n(2023). [Page 18, Line 11–12]\n3. Comment: The authors propose that the doping amount of F in RuO is controlled by the annealing\n2\ntemperature. However, numerous studies have demonstrated that annealing temperature, even without any\nelemental doping, can significantly alter the intrinsic structure of RuO , such as the strength of Ru-O\n2\nbonds and structural stability. These structural changes, in turn, influence both the catalytic activity and\nstability (Nat. Commun. 2025, 16, 801, DOI: 10.1038/s41467–025–56188–z). Therefore, the approach of\nusing annealing temperature to control the F doping amount lacks sufficient rigor and needs further\nclarification.\n[Author’s Response]: Thanks for the valuable suggestion. According to the literature provided by the\nreviewers (Nat. Commun. 16, 801 (2025)), the work of Shao et al. indicates that modulating the annealing\ntemperature can induce a structural transformation in the electrocatalyst from amorphous (h–RuO ) to\nX\nhighly crystalline RuO (anh–RuO ), thereby significantly enhancing its catalytic performance.\n2 2\nRegrettably, although the heat treatment process substantially enhances the stability of anh–RuO (550\nX\nh@1 A cm–2) relative to h–RuO (<1 min@ 1 A cm–2), it still performs considerably worse than the F–\nX\nRuO /FC (1440 h@1 A cm–2) reported in our work (Fig. 4e).\nTo investigate the influence of heat treatment temperature on the intrinsic structure of RuO in this work,\n2\ndifference in activity and stability exists between RuO (F)C and F–RuO /FC across various heat treatment\n2 2\ntemperatures, underscoring the impact of F–doping levels on stability. [Page 10, Line 22–Page 11, Line\n1]\nSupplementary Fig. 67. (a) XRD pattern, (b) OER polarization curve and (c) chronopotentiometry test of RuO2/(F)C–300 °C and\nRuO2/(F)C–500 °C.\nSubsequently, we investigated the influence of heat treatment temperature on the F–doping level from\nmultiple perspectives, as detailed below:\nFirstly, F 1s XPS spectra were employed to further elucidate fluorine incorporation at various calcination\ntemperatures (Fig. 3b and Supplementary Fig. 51). Obviously, the signal of Ru–F changed significantly\nwith calcination temperature, indicating that the heat treatment process can indeed regulate the content of\nF.\nFigure 3. Electronic structure investigation. (b) F 1s XPS spectra of F–RuO2/FC and FC.\nSupplementary Fig. 51. F 1s XPS spectra of (a) F–RuO2/FC–300 °C and (b) F–RuO2/FC–500 °C.\nSecondly, EDS analysis indicates that the content of F in F–RuO /FC varies with the calcination\n2\ntemperature, which is consistent with the conclusion of XPS analysis (Supplementary Fig. 50).\nSupplementary Fig. 50. EDS spectra of (a) F–RuO2/FC–300 °C, (b) F–RuO2/FC, and (c) F–RuO2/FC–500 °C.\nThirdly, Raman spectra were carried out in Fig. 3a, where the typical peaks at 506.8, 622.2, and 693.4\ncm–1 are attributable to the vibration modes of E , A , and B for Ru–O bonds, respectively. Compared\ng 1g 2g\nto RuO , a distinct red shift can be observed in the vibration peaks of F–RuO /FC at various calcination\n2 2\ntemperatures, which may be caused by the shortened Ru–O bond owing to the partial substitution of O by\nthe highly electronegative F (Supplementary Fig. 52). [Page 8, Line 22–Page 9, Line 1]\nFigure 3. Electronic structure investigation. (a) Raman spectra of F–RuO2/FC and RuO2.\nSupplementary Fig. 52. Raman spectra of (a) F–RuO2/FC–300 °C and (b) F–RuO2/FC–500 °C.\nFinally, abundant literature also confirms that varying the annealing temperature allows for effective\ncontrol over the content of incorporated non-metallic elements (Nat. Nanotechnol. 10, 444–452 (2015);\nAngew. Chem. Int. Ed. 63, e202412825 (2024)).\nBased on the above analysis, controlling the annealing temperature can indeed affect the doping amount\nin RuO , thereby influencing the catalytic performance.\n2\n4. Comment: The newly added [Page 14, Lines 14–15] states: \"Next, the ink was vertically dripped on the\nglassy carbon electrode (0.196 cm²) to obtain the work electrode (loading amount: ~75 mg Ru).\" The high\nloading of Ru seems to exaggerate the OER activity. A comparison with previous studies should be\nprovided and summarized.\n[Author’s Response]: Thank you for pointing out this mistake, and we sincerely apologize for the\noversight. The correct Ru loading amount on the working electrode (75 μg cm–2) has been update in the\nRu\nelectrochemical measurements section of the revised manuscript as following:\nElectrochemical measurements. Then 2.0 mg of catalyst was added into the 200 μL of a solution\ncontaining 195 μL of isopropyl alcohol and 5 μL of Nafion, and the ink was prepared by ultrasonic at\nambient temperature. Inductively coupled plasma atomic emission spectroscopy (ICP–AES) suggested\nthat the content of Ru is 14.71 wt% (w ). To prepare the working electrode, 10 μL of ink was vertically\nRu\ndripped on the glassy carbon electrode with a geometric area of 0.196 cm2 (loading amount: ~75 μg\nRu\ncm–\n2). [Page 15, Line 3–8]\nIn detail, the loading amount of Ru (𝑚 ) on the working electrode was calculated by the following\n𝑅𝑢\nequation:\n𝑚 = \nm𝑙𝑜𝑎𝑑𝑖𝑛𝑔 × 𝑤𝑅𝑢\n𝑅𝑢 𝑆\nWhere m is the mass of the catalyst dripped on the working electrode and S is the geometric area of\nloading\nglassy carbon electrode.\nTherefore, the OER activities of overpotential and Tafel slope for various catalysts are visually presented\nin Fig. 4a–c, where F–RuO /FC exhibit the smallest overpotential and the Tafel slope value,\n2\noutperforming most of the Ru–based catalysts reported recently (Table S10). [Page 9, Line 22–Page 10,\nLine 6]\nFigure 4. Electrochemical activity studies. (a) OER polarization curves and (b) Tafel plots of F–RuO2/FC, RuO2/C, and RuO2. (c)\nHistogram of overpotentials at 10 mA cm–2 and Tafel slopes of F–RuO2/FC, RuO2/C, and RuO2.\nTable S10. Comparison of the Ru loading amount and OER performance of F–RuO2/FC with recently reported OER electrocatalysts in a\nthree–electrode setup.\nLoading Activity (at Tafel slope\nCatalyst Electrolyte Ref.\namount of Ru 10 mA cm–2) (mV dec–1)\nF–RuO2/FC 0.5 M H2SO4 75 μg cm–2 192 mV 41.6 This work\nJ. Am. Chem. Soc. 147, 4159–4166\nPd@RuO2 0.5 M H2SO4 200 μg cm–2 189 mV 65.2\n(2025)\nGB–V–RuO2 0.5 M H2SO4 697 μg cm–2 159 mV 58.5 Nat. Commun. 16, 4482 (2025)\nJ. Am. Chem. Soc. 147, 24392–\nRu–γ–MnO2 0.1 M HClO4 12 μg cm–2 246 mV 57.0\n24402 (2025)\nRuO2@COF–O(3) 0.5 M H2SO4 212 μg cm–2 218 mV 64.3 Adv. Mater. 37, 2417374 (2025)\nAngew. Chem. Int. Ed. 137,\nGa–RuO2 0.5 M H2SO4 57 μg cm–2 218 mV 60.5\ne202413334 (2025)\niGa0.2Ru0.7O2 1.0 M HClO4 4000 μg cm–2 188 mV 33.9 Nat. Commun. 16, 3976 (2025)\nh–ATO/RuO2 0.5 M H2SO4 180 μg cm–2 216 mV 60.0 Nat. Commun. 16, 337 (2025)\nRuFe@CF 0.5 M H2SO4 823 μg cm–2 188 mV 80.3 Adv. Mater. 36, 2312369 (2024)\nIr–RuO2 0.5 M H2SO4 625 μg cm–2 167 mV 48.2 Nat. Commun. 15, 10315 (2024)\nInSnRuO2 0.5 M H2SO4 200 μg cm–2 183 mV 49.8 Adv. Mater. 36, 2414579 (2024)\nPb–RuO2 0.5 M H2SO4 436 μg cm–2 188 mV 58.6 Nat. Commun. 15, 9774 (2024)\nM–RuIrFeCoNiO2 0.5 M H2SO4 1377 μg cm–2 189 mV 49.0 Sci. Adv. 9, eadf9144 (2023)\nRu/TiOX 0.5 M H2SO4 71 μg cm–2 174 mV 45.6 Nat. Commun. 14, 7644 (2023)\nSnRuOX 0.5 M H2SO4 15 μg cm–2 194 mV 38.2 Nat. Commun. 14, 843 (2023)\nLi0.52RuO2 0.5 M H2SO4 637 μg cm–2 156 mV 83.3 Nat. Commun. 13, 3784 (2022)\nC–RuO2–RuSe–5 0.5 M H2SO4 306 μg cm–2 212 mV 49.5 Chem 8, 1673–1687 (2022)\nAngew. Chem. Int. Ed. 61,\nRuO2–WC NPs 0.5 M H2SO4 22 μg cm–2 347 mV 75.7\ne202202519 (2022)\nSS Pt–RuO2 HNSs 0.5 M H2SO4 306 μg cm–2 260 mV 51.0 Sci. Adv. 8, eabl9271 (2022)\n5. Comment: Additional, [Page 14, Lines 9–12]: \"In addition, melamine, …… at 450 °C, 150 °C, 300 °C,\n500 °C, 450 °C, and 350 °C, respectively\". The repetition of 450 °C appears to be an error. Such\ninconsistencies may undermine the rigor of the manuscript.\n[Author’s Response]: Thank you for your thorough review of our manuscript. To address your concern,\nwe have further clarified and elaborated on the synthesis process for the M–RuO /(F)C (M = N, S, P, Se,\nsources and RuO /(F)C were placed in separate tube furnaces located upstream and downstream of the\n2\nquartz tube for heat treatment. This configuration facilitates sufficient anion release from the anion sources\nat different target temperatures (Table S12). [Page 14, Line 16–Page 15, Line 1]\nSupplementary Fig. 80. Schematic diagram of the heat treatment synthesis process for M–RuO2/(F)C (M = N, S, P, Se, Cl and Br) using\ntube furnace.\nTable S12. Target temperature under heat treatment of different anion sources.\nAnion sources Target temperature (℃)\nmelamine 450\nsulfur powder 150\nsodium hypophosphite 300\nselenium powder 500\na mixture of polyvinyl chloride and manganese dioxide 450\nhexabromobenzene 350\n6. Comment: The PEM tests lack control samples (RuO₂, RuO₂/(F)C) for comparison, which are crucial\nfor enabling readers to more effectively assess the catalytic performance.\n[Author’s Response]: We sincerely appreciate your insightful feedback, as it has provided important\nguidance for enhancing our work. According to your suggestion, RuO and RuO /(F)C were employed as\n2 2\nanode catalysts for the PEM electrolyzer, and their respective electrochemical performances were\nsystematically evaluated. Specifically, to deliver current densities of 500, 1000, 2000, and 3000 mA cm–\n2, higher cell voltages of RuO ||PEM||Pt/C (1.61, 1.78, 2.10 and 2.42 V) and RuO /(F)C||PEM||Pt/C (1.70,\n2 2\n1.96, 2.44 and 2.86 V) were required compare with F–RuO /FC (1.58, 1.70, 1.89 and 2.05 V)\n2\n(Supplementary Fig. 70a). Notably, both RuO ||PEM||Pt/C and RuO /(F)C||PEM||Pt/C exhibit\n2 2\nsignificantly lower stability than that of F–RuO /FC, and the severe degradation of RuO /(F)C underscores\n2 2\nthe pivotal role of F in catalytic stability (Supplementary Fig. 70b, c and Supplementary Fig. 71). [Page\n11, Line 8–16]\nSupplementary Fig. 70. (a) Polarization curves of PEM electrolyzer using RuO2/(F)C and RuO2 as anode. Chronopotentiometry tests of\nPEM electrolyzer using (b) RuO2||Pt/C and (c) RuO2/(F)C||Pt/C as electrocatalysts.\nSupplementary Fig. 71. (a) SEM images of the cross section of MEA before and after CP test. (b) SEM image and (c) TEM image of\nRuO2/(F)C after CP test of PEMWE.\nGeneral comment: In summary, this manuscript does not provide sufficient evidence to demonstrate clear\ndifferences in the degree of symmetry breaking across various anionic dopants. Therefore, this work far\ncan not meet the high standards of Nature Communications.\n[Author’s Response]: Thank you very much for your constructive comments. We highly appreciate that\nyou strictly point out our deficiency in this work and we are truly sorry that our work did not supply a\nsatisfying interpretation and explanation to demonstrate our research. To address your concerns, we have,\naccording to the literature (Nature 620, 328–335 (2023)), employed the Baur distortion index to quantify\nthe observed differences in the degree of symmetry breaking among the various anionic dopants.\n------------------------------------\nIn the end, we would like to thank for the precious time of the reviewers and the editor. We sincerely wish\nthat our point-to-point response and the revised manuscript have addressed your concerns and satisfy your\nrequirements for publications. We would be grateful if we have the chance to share our work with readers\nof Nature Communications.\nXiaoqing Huang\nResponse to Reviewers\nDear Reviewer,\nThank you for your continued guidance and the valuable time you have dedicated to our manuscript titled\n“Ultradurable acidic water oxidation ruthenium–based electrocatalyst by fluorination induced\nsymmetry–breaking” (Manuscript ID: NCOMMS-25-10822B-Z) for Nature Communications. We\nare greatly encouraged by your positive recognition of our previous revisions. Regarding the final point\nraised, we have given it in-depth consideration and provided a detailed explanation below. We sincerely\nhope these revisions have adequately addressed your concern and further improved the quality of the\nmanuscript.\nReviewer #1\n1. Comment: In the revised manuscript, the authors have made efforts to improve the quality of the\npresented research. However, the reviewer raises a final concern regarding how to distinguish the effects\nof doping amount from the type of doping element on the Baur distortion indices.\n[Author’s Response]: Thank you for acknowledging our efforts in previous revisions and for raising this\ncritical concern about attributing the distinction between the effects of dopant type and doping amount on\nthe Baur distortion indices (D). We fully agree that addressing this point is essential to solidify the\ni\nscientific rigor of our conclusions. Motivated by this question, we conducted an in–depth investigation. It\nwas revealed that the type of doping element is the key factor driving the change of D, whereas the doping\ni\namount modulates the OER performance mainly through affecting the number of active sites and D.\nThis\ni\nconclusion is drawn from the following analysis:\nThe effect of doping element type: Evidently, M–RuO (M = F, N, S, P, Se, Cl and Br) shows varying\ni\ndoping element type critically determines the D.\ni\nSupplementary Fig. 46. EDS spectra of (a) N–RuO2/(F)C, (b) S–RuO2/(F)C, (c) P–RuO2/(F)C, (d) Se–RuO2/(F)C, (e) Cl–RuO2/(F)C and\n(f) Br–RuO2/(F)C.\nSupplementary Fig. 52. EDS spectra of (a) F–RuO2/FC–300 °C, (b) F–RuO2/FC, and (c) F–RuO2/FC–500 °C.\nSupplementary Fig. 47. The metal–nonmetal bond length of F–RuO2, N–RuO2, S–RuO2, P–RuO2, Se–RuO2, Cl–RuO2 and Br–RuO2\ncrystal structure. The calculated distortion indexes are indicated.\nThe effect of doping amount: Taking F doping as an example, at low doping levels (Supplementary Fig.\n52a), the D remains largely unchanged (Supplementary Fig. 50a, 51a, and Table S9), while the TOF\ni\ndecreases significantly (Supplementary Fig. 64), suggesting that low F doping primarily affects the\nnumber of active sites rather than the D. Conversely, as the F doping levels increase (Supplementary Fig.\ni\n52c), D increases while TOF decreases (Supplementary Fig. 50b, 51b, 64 and Table S10), demonstrating\ni\nthat excessive symmetry breaking degrades OER performance (Supplementary Fig. 63) [Page 10, Line\n20–Page 11, Line 1].\nSupplementary Fig. 50. XRD patterns of (a) F–RuO2/FC–300 °C and (b) F–RuO2/FC–500 °C.\nSupplementary Fig. 51. The metal–nonmetal bond length of (a) F–RuO2/FC–300 °C and (b) F–RuO2/FC–500 °C crystal structure. The\ncalculated distortion indexes are indicated.\nTable S9. Refined parameters of F–RuO2/FC–300 °C.\nF–RuO/FC–300 °C X Y Z\nRu1 0.01696 -0.01656 0.00000\nO2 0.69389 0.69616 0.00000\nO3 0.19322 0.80779 0.50000\nO4 0.30384 0.30611 -0.00000\nF1 0.80894 0.19002 0.50000\na = 4.48250 Å, b = 4.48250 Å, c = 3.11133 Å, space grpup P42/mnm, R = 5.16%, Chi2 = 7.36\nwp\nTable S10. Refined parameters of F–RuO2/FC–500 °C.\nF–RuO/FC–500 °C X Y Z\nRu1 0.01298 0.01297 0.00000\nO2 0.69602 0.69649 0.00000\nO3 0.19388 0.80445 0.50000\nO4 0.80428 0.19361 0.50000\nF1 0.30704 0.30674 0.00000\nF2 0.30679 0.30661 0.00000\na = 4.48250 Å, b = 4.48250 Å, c = 3.12181 Å, space grpup P42/mnm, R = 4.32%, Chi2 = 2.95\nwp\nSupplementary Fig. 64. TOF of F–RuO2/FC–300 °C and F–RuO2/FC–500 °C.\nSupplementary Fig. 63. (a) OER polarization curves and (b) chronopotentiometry tests of F–RuO2/FC–300 °C and F–RuO2/FC–500 °C.\n------------------------------------\nIn the end, we extend our sincere appreciation to the editor and reviewers for the precious time and the\nvaluable feedback throughout the review process. We sincerely wish that the revised manuscript and our\nresponse have adequately addressed your concerns and meet the high standards for publication. We would\nbe grateful if we have the chance to share our work with readers of Nature Communications.\nXiaoqing Huang"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The author provided some new materials in response to my questions, but most of my doubts remain unresolved.\n1. First, the concept of symmetry breaking lacks a clear definition, along with quantitative metrics to measure its extent. The authors define symmetry breaking as \"the structural modifications at atomic scale that reduce its crystal symmetry\". However, this definition remains somewhat generalized and does not provide a clear method for quantifying the degree of symmetry breaking based on experimental evidence. Generally, any elemental doping or substitution will introduce atomic-scale structural modifications, which inherently trigger symmetry breaking.\n2. Current experimental evidence confirms the successful doping of elements, such as N, S, P, Se, Cl and Br into RuO2. However, there is no definitive experimental data demonstrating how these dopants specifically change the degree of symmetry breaking.\n3. The authors propose that the doping amount of F in RuO2 is controlled by the annealing temperature. However, numerous studies have demonstrated that annealing temperature, even without any elemental doping, can significantly alter the intrinsic structure of RuO2, such as the strength of Ru-O bonds and structural stability. These structural changes, in turn, influence both the catalytic activity and stability (Nat. Commun. 2025, 16, 801, DOI：10.1038/s41467-025-56188-z). Therefore, the approach of using annealing temperature to control the F doping amount lacks sufficient rigor and needs further clarification.\n4. The newly added [Page 14, Lines 14–15] states: \"Next, the ink was vertically dripped on the glassy carbon electrode (0.196 cm²) to obtain the work electrode (loading amount: ~75 mg Ru).\" The high loading of Ru seems to exaggerate the OER activity. A comparison with previous studies should be provided and summarized.\n5. Additional, [Page 14, Lines 9–12]: \"In addition, melamine, …… at 450 °C, 150 °C, 300 °C, 500 °C, 450 °C, and 350 °C, respectively\". The repetition of 450 °C appears to be an error. Such inconsistencies may undermine the rigor of the manuscript.\n6. The PEM tests lack control samples (RuO₂, RuO₂/(F)C) for comparison, which are crucial for enabling readers to more effectively assess the catalytic performance.\nIn summary, this manuscript does not provide sufficient evidence to demonstrate clear differences in the degree of symmetry breaking across various anionic dopants. Therefore, this work far can not meet the high standards of Nature Communications.", "reviewer_2": "The authors have addressed the comments in the revised manuscript. The manuscript is now acceptable to the journal.", "reviewer_3": "The authors considered the suggestions of the reviewers and made comprehensive revisions to the manuscript. I think this manuscript has now met the requirements for publication."}, "author_response": "Response to Reviewers\nTo Reviewer 1:\nGeneral comment: The author provided some new materials in response to my questions, but most of my\ndoubts remain unresolved.\n[Author’s Response]: We appreciate your precious time for reviewing our revised manuscript. During\nthe revision process, we have indeed addressed all your concerns in detail. As you requested, we have\ncarried out the following experiments to address your comments point-to-point.\n1. Comment: First, the concept of symmetry breaking lacks a clear definition, along with quantitative\nmetrics to measure its extent. The authors define symmetry breaking as \"the structural modifications at\natomic scale that reduce its crystal symmetry\". However, this definition remains somewhat generalized\nand does not provide a clear method for quantifying the degree of symmetry breaking based on\nexperimental evidence. Generally, any elemental doping or substitution will introduce atomic-scale\nstructural modifications, which inherently trigger symmetry breaking.\n[Author’s Response]: Thanks for your perceptive observations and constructive feedback on this study.\nAccording to the literature (Proc. Natl. Acad. Sci. 93, 14256–14259 (1996); Science 177, 393-396 (1972)),\nsymmetry breaking is a fundamental concept in physics, referring to the phenomenon where a system with\noriginally high symmetry undergoes a reduction in its degree of symmetry due to the emergence of\nasymmetric factors. Considering Wang et al.'s (Appl. Catal. B–Environ. 316, 121664 (2022)) recent\napplication of the symmetry–breaking effect to materials chemistry and their clear definition, that is,\ndefects in a crystal lattice lower the lattice's symmetry, which is known as the symmetry–breaking effect,\nwe have thoroughly revised our manuscript.\nMoreover, the Baur distortion index (D), proposed by Li et al. (Nature 620, 328–335 (2023)), is used to\ni\nquantify the asymmetry or distortion in the virtual octahedral units of crystal structures. Therefore, the\nBaur distortion index (D) was employed to quantify the degree of symmetry breaking of virtual octahedral\ni\nunits within the RuO crystal structure:\n2\n𝐷 = 1 ∑6 ( |𝑏𝑖−𝑏̅| )\n𝑖 6 𝑖=1 𝑏̅\nwhere 𝑏 and 𝑏̅ represent the individual bond length and the average of six bond lengths, respectively.[41]\n𝑖\nBased on the Rietveld refinement of XRD patterns results (Fig. 2j and Supplementary Fig. 40c, 41c, 42c,\n43c, 44c and 45c), the octahedral structural units of F–RuO /FC, N–RuO (F)C, S–RuO (F)C, P–\n2 2 2\nRuO (F)C, Se–RuO (F)C, Cl–RuO (F)C and Br–RuO (F)C are depicted in Supplementary Fig. 46 and\n2 2 2 2\nTable S2–S8. The calculated D were increase in the order F < N < S < P < Se < Cl < Br, indicating an\ni\nincrease of octahedral distortion degree, consistent with DFT predictions. [Page 8, Line 8–16]\nWe agree with the reviewer's point that any elemental doping or substitution will introduce atomic–scale\nstructural modifications, which inherently trigger symmetry breaking. Recently, Dai et al. also reviewed\ncurrent symmetry–breaking methods (Chem. Soc. Rev. 54, 3848–3905 (2025)), including doping—\nintroducing heteroatoms (such as non–metals or metallic heteroatoms) and surface modification and defect\nengineering—introducing defect sites (e.g.,vacancies and lattice distortions) or modifying surfaces with\nspecific functional groups. Therefore, in this study, the introduction of heteroatoms F, N, S, P, Se, Cl, and\nBr as asymmetric elements into the RuO crystal structure can be categorized as a non–metal doping\n2\nstrategy to achieve symmetry breaking.\nSupplementary Fig. 46. The metal–nonmetal bond length of F–RuO2, N–RuO2, S–RuO2, P–RuO2, Se–RuO2, Cl–RuO2 and Br–RuO2\ncrystal structure. The calculated distortion indexes are indicated.\nFigure 2. Structural characterizations. (j) XRD pattern of F–RuO2/FC. Inset in (j) are the structural model of F–RuO2/FC.\nSupplementary Fig. 40. (c) XRD pattern of N–RuO2/(F)C.\nSupplementary Fig. 41. (c) XRD pattern of S–RuO2/(F)C.\nSupplementary Fig. 42. (c) XRD pattern of P–RuO2/(F)C.\nSupplementary Fig. 43. (c) XRD pattern of Se–RuO2/(F)C.\nSupplementary Fig. 44. (c) XRD pattern of Cl–RuO2/(F)C.\nSupplementary Fig. 45. (c) XRD pattern of Br–RuO2/(F)C.\nTable S2. Refined parameters of F–RuO2/FC.\nF–RuO2/FC X Y Z\nRu0 0.48485 0.51515 0.50000\nRu1 0.01756 -0.01756 -0.00000\nO2 0.69389 0.69616 0.00000\nO3 0.19451 0.80549 0.50000\nO4 0.30384 0.30611 -0.00000\nF1 0.80534 0.19466 0.50000\na = 4.50909 Å, b = 4.50909 Å, c = 3.11133 Å, space grpup P42/mnm, Rwp = 5.59%, Chi2 = 7.53\nTable S3. Refined parameters of N–RuO2/(F)C.\nN–RuO2/(F)C X Y Z\nRu0 0.50883 0.49117 0.50000\nRu1 -0.01173 0.01173 -0.00000\nO2 0.69264 0.69243 0.00000\nO3 0.19586 0.80414 0.50000\nO4 0.30757 0.30736 -0.00000\nN1 0.80683 0.19317 0.50000\na = 4.52037 Å, b = 4.52037 Å, c = 3.12181 Å, space grpup P42/mnm, Rwp = 5.05%, Chi2 = 6.58\nTable S4. Refined parameters of S–RuO2/(F)C.\nS–RuO2/(F)C X Y Z\nRu0 0.48556 0.51444 0.50000\nRu1 0.01766 -0.01766 -0.00000\nO2 0.68746 0.69669 0.00000\nO3 0.20040 0.79960 0.50000\nO4 0.30330 0.31254 -0.00000\nS1 0.80561 0.19439 0.50000\na = 4.48394 Å, b = 4.48394 Å, c = 3.11028 Å, space grpup P42/mnm, Rwp = 6.44%, Chi2 = 8.25\nTable S5. Refined parameters of P–RuO2/(F)C.\nP–RuO2/(F)C X Y Z\nRu0 0.48025 0.51975 0.50000\nRu1 0.02406 -0.02406 -0.00000\nO2 0.68849 0.69716 0.00000\nO3 0.19748 0.80252 0.50000\nO4 0.30284 0.31151 -0.00000\nP1 0.80241 0.19759 0.50000\na = 4.50192 Å, b = 4.50192 Å, c = 3.10770 Å, space grpup P42/mnm, Rwp = 4.53%, Chi2 = 3.74\nTable S6. Refined parameters of Se–RuO2/(F)C.\nSe–RuO2/(F)C X Y Z\nRu0 0.47722 0.52278 0.50000\nRu1 0.03359 -0.03359 0.00000\nO2 0.68462 0.69946 -0.00000\nO3 0.19975 0.80025 0.50000\nO4 0.30055 0.31538 0.00000\nSe1 0.80428 0.19572 0.50000\na = 4.49913 Å, b = 4.49913 Å, c = 3.10685 Å, space grpup P42/mnm, Rwp = 4.46%, Chi2 = 3.72\nTable S7. Refined parameters of Cl–RuO2/(F)C.\nCl–RuO2/(F)C X Y Z\nRu0 0.47924 0.52077 0.50000\nRu1 0.02721 -0.02721 -0.00000\nO2 0.68822 0.69910 0.00000\nO3 0.19879 0.80120 0.50000\nO4 0.30090 0.31178 -0.00000\nCl1 0.80563 0.19437 0.50000\na = 4.49933 Å, b = 4.49933 Å, c = 3.10890 Å, space grpup P42/mnm, Rwp = 6.20%, Chi2 = 6.45\nTable S8. Refined parameters of Br–RuO2/(F)C.\nBr–RuO2/(F)C X Y Z\nRu0 0.47220 0.52780 0.50000\nRu1 0.03881 -0.03881 -0.00000\nO2 0.68573 0.70042 0.00000\nO3 0.19902 0.80098 0.50000\nO4 0.29958 0.31427 -0.00000\nBr1 0.80468 0.19532 0.50000\na = 4.50267 Å, b = 4.50267 Å, c = 3.10783 Å, space grpup P42/mnm, Rwp = 4.78%, Chi2 = 3.56\n[41] Najarian, A. M. et al. Homomeric chains of intermolecular bonds scaffold octahedral germanium perovskites. Nature 620, 328–335\n(2023). [Page 18, Line 11–12]\n2. Comment: Current experimental evidence confirms the successful doping of elements, such as N, S, P,\nSe, Cl and Br into RuO . However, there is no definitive experimental data demonstrating how these\n2\ndopants specifically change the degree of symmetry breaking.\n[Author’s Response] Thanks for your exceptional insights that fundamentally improved our work. Due\nto the combined influence of electronegativity, atomic radius, and so on, the introduction of different\nheteroatoms causes changes in structural parameters like bond length, thus breaking the symmetry of the\noriginal structure. Thus, XRD Rietveld refinement was conducted to obtain the octahedral structure units\nof F–RuO₂/FC, N–RuO₂(F)C, S–RuO₂(F)C, P–RuO₂(F)C, Se–RuO₂(F)C, Cl–RuO₂(F)C, and Br–\nRuO₂(F)C (Supplementary Fig. 40c, 41c, 42c, 43c, 44c and 45c, 46 and Table S2–S8). Subsequently,\nthe Baur distortion index (D) was employed to quantify the symmetry breaking degree of virtual\ni\noctahedral units within the RuO crystal structure:\n2\n𝐷 = 1 ∑6 ( |𝑏𝑖−𝑏̅| )\n𝑖 6 𝑖=1 𝑏̅\nwhere 𝑏 and 𝑏̅ represent the individual bond length and the average of six bond lengths, respectively.[41]\n𝑖\n[Page 8, Line 8–13]\nAs evidenced by the computational results based on the Rietveld refinement of XRD patterns results, a\npositive correlation exists between the D and octahedral distortion severity, with elevated D values\ni i\ndirectly correspond to both increased structural distortion and enhanced octahedral symmetry breaking.\nTherefore, incorporation of F, N, S, P, Se, Cl and Br elements into RuO enables controlled symmetry\n2\nbreaking through modulation of the bond length in the octahedral coordination environment.\nSupplementary Fig. 46. The metal–nonmetal bond length of F–RuO2, N–RuO2, S–RuO2, P–RuO2, Se–RuO2, Cl–RuO2 and Br–RuO2\ncrystal structure. The calculated distortion indexes are indicated.\nFigure 2. Structural characterizations. (j) XRD pattern of F–RuO2/FC. Inset in (j) are the structural model of F–RuO2/FC.\nSupplementary Fig. 40. (c) XRD pattern of N–RuO2/(F)C.\nSupplementary Fig. 41. (c) XRD pattern of S–RuO2/(F)C.\nSupplementary Fig. 42. (c) XRD pattern of P–RuO2/(F)C.\nSupplementary Fig. 43. (c) XRD pattern of Se–RuO2/(F)C.\nSupplementary Fig. 44. (c) XRD pattern of Cl–RuO2/(F)C.\nSupplementary Fig. 45. (c) XRD pattern of Br–RuO2/(F)C.\nTable S2. Refined parameters of F–RuO2/FC.\nF–RuO2/FC X Y Z\nRu0 0.48485 0.51515 0.50000\nRu1 0.01756 -0.01756 -0.00000\nO2 0.69389 0.69616 0.00000\nO3 0.19451 0.80549 0.50000\nO4 0.30384 0.30611 -0.00000\nF1 0.80534 0.19466 0.50000\na = 4.50909 Å, b = 4.50909 Å, c = 3.11133 Å, space grpup P42/mnm, Rwp = 5.59%, Chi2 = 7.53\nTable S3. Refined parameters of N–RuO2/(F)C.\nN–RuO2/(F)C X Y Z\nRu0 0.50883 0.49117 0.50000\nRu1 -0.01173 0.01173 -0.00000\nO2 0.69264 0.69243 0.00000\nO3 0.19586 0.80414 0.50000\nO4 0.30757 0.30736 -0.00000\nN1 0.80683 0.19317 0.50000\na = 4.52037 Å, b = 4.52037 Å, c = 3.12181 Å, space grpup P42/mnm, Rwp = 5.05%, Chi2 = 6.58\nTable S4. Refined parameters of S–RuO2/(F)C.\nS–RuO2/(F)C X Y Z\nRu0 0.48556 0.51444 0.50000\nRu1 0.01766 -0.01766 -0.00000\nO2 0.68746 0.69669 0.00000\nO3 0.20040 0.79960 0.50000\nO4 0.30330 0.31254 -0.00000\nS1 0.80561 0.19439 0.50000\na = 4.48394 Å, b = 4.48394 Å, c = 3.11028 Å, space grpup P42/mnm, Rwp = 6.44%, Chi2 = 8.25\nTable S5. Refined parameters of P–RuO2/(F)C.\nP–RuO2/(F)C X Y Z\nRu0 0.48025 0.51975 0.50000\nRu1 0.02406 -0.02406 -0.00000\nO2 0.68849 0.69716 0.00000\nO3 0.19748 0.80252 0.50000\nO4 0.30284 0.31151 -0.00000\nP1 0.80241 0.19759 0.50000\na = 4.50192 Å, b = 4.50192 Å, c = 3.10770 Å, space grpup P42/mnm, Rwp = 4.53%, Chi2 = 3.74\nTable S6. Refined parameters of Se–RuO2/(F)C.\nSe–RuO2/(F)C X Y Z\nRu0 0.47722 0.52278 0.50000\nRu1 0.03359 -0.03359 0.00000\nO2 0.68462 0.69946 -0.00000\nO3 0.19975 0.80025 0.50000\nO4 0.30055 0.31538 0.00000\nSe1 0.80428 0.19572 0.50000\na = 4.49913 Å, b = 4.49913 Å, c = 3.10685 Å, space grpup P42/mnm, Rwp = 4.46%, Chi2 = 3.72\nTable S7. Refined parameters of Cl–RuO2/(F)C.\nCl–RuO2/(F)C X Y Z\nRu0 0.47924 0.52077 0.50000\nRu1 0.02721 -0.02721 -0.00000\nO2 0.68822 0.69910 0.00000\nO3 0.19879 0.80120 0.50000\nO4 0.30090 0.31178 -0.00000\nCl1 0.80563 0.19437 0.50000\na = 4.49933 Å, b = 4.49933 Å, c = 3.10890 Å, space grpup P42/mnm, Rwp = 6.20%, Chi2 = 6.45\nTable S8. Refined parameters of Br–RuO2/(F)C.\nBr–RuO2/(F)C X Y Z\nRu0 0.47220 0.52780 0.50000\nRu1 0.03881 -0.03881 -0.00000\nO2 0.68573 0.70042 0.00000\nO3 0.19902 0.80098 0.50000\nO4 0.29958 0.31427 -0.00000\nBr1 0.80468 0.19532 0.50000\na = 4.50267 Å, b = 4.50267 Å, c = 3.10783 Å, space grpup P42/mnm, Rwp = 4.78%, Chi2 = 3.56\n[41] Najarian, A. M. et al. Homomeric chains of intermolecular bonds scaffold octahedral germanium perovskites. Nature 620, 328–335\n(2023). [Page 18, Line 11–12]\n3. Comment: The authors propose that the doping amount of F in RuO is controlled by the annealing\n2\ntemperature. However, numerous studies have demonstrated that annealing temperature, even without any\nelemental doping, can significantly alter the intrinsic structure of RuO , such as the strength of Ru-O\n2\nbonds and structural stability. These structural changes, in turn, influence both the catalytic activity and\nstability (Nat. Commun. 2025, 16, 801, DOI: 10.1038/s41467–025–56188–z). Therefore, the approach of\nusing annealing temperature to control the F doping amount lacks sufficient rigor and needs further\nclarification.\n[Author’s Response]: Thanks for the valuable suggestion. According to the literature provided by the\nreviewers (Nat. Commun. 16, 801 (2025)), the work of Shao et al. indicates that modulating the annealing\ntemperature can induce a structural transformation in the electrocatalyst from amorphous (h–RuO ) to\nX\nhighly crystalline RuO (anh–RuO ), thereby significantly enhancing its catalytic performance.\n2 2\nRegrettably, although the heat treatment process substantially enhances the stability of anh–RuO (550\nX\nh@1 A cm–2) relative to h–RuO (<1 min@ 1 A cm–2), it still performs considerably worse than the F–\nX\nRuO /FC (1440 h@1 A cm–2) reported in our work (Fig. 4e).\nTo investigate the influence of heat treatment temperature on the intrinsic structure of RuO in this work,\n2\ndifference in activity and stability exists between RuO (F)C and F–RuO /FC across various heat treatment\n2 2\ntemperatures, underscoring the impact of F–doping levels on stability. [Page 10, Line 22–Page 11, Line\n1]\nSupplementary Fig. 67. (a) XRD pattern, (b) OER polarization curve and (c) chronopotentiometry test of RuO2/(F)C–300 °C and\nRuO2/(F)C–500 °C.\nSubsequently, we investigated the influence of heat treatment temperature on the F–doping level from\nmultiple perspectives, as detailed below:\nFirstly, F 1s XPS spectra were employed to further elucidate fluorine incorporation at various calcination\ntemperatures (Fig. 3b and Supplementary Fig. 51). Obviously, the signal of Ru–F changed significantly\nwith calcination temperature, indicating that the heat treatment process can indeed regulate the content of\nF.\nFigure 3. Electronic structure investigation. (b) F 1s XPS spectra of F–RuO2/FC and FC.\nSupplementary Fig. 51. F 1s XPS spectra of (a) F–RuO2/FC–300 °C and (b) F–RuO2/FC–500 °C.\nSecondly, EDS analysis indicates that the content of F in F–RuO /FC varies with the calcination\n2\ntemperature, which is consistent with the conclusion of XPS analysis (Supplementary Fig. 50).\nSupplementary Fig. 50. EDS spectra of (a) F–RuO2/FC–300 °C, (b) F–RuO2/FC, and (c) F–RuO2/FC–500 °C.\nThirdly, Raman spectra were carried out in Fig. 3a, where the typical peaks at 506.8, 622.2, and 693.4\ncm–1 are attributable to the vibration modes of E , A , and B for Ru–O bonds, respectively. Compared\ng 1g 2g\nto RuO , a distinct red shift can be observed in the vibration peaks of F–RuO /FC at various calcination\n2 2\ntemperatures, which may be caused by the shortened Ru–O bond owing to the partial substitution of O by\nthe highly electronegative F (Supplementary Fig. 52). [Page 8, Line 22–Page 9, Line 1]\nFigure 3. Electronic structure investigation. (a) Raman spectra of F–RuO2/FC and RuO2.\nSupplementary Fig. 52. Raman spectra of (a) F–RuO2/FC–300 °C and (b) F–RuO2/FC–500 °C.\nFinally, abundant literature also confirms that varying the annealing temperature allows for effective\ncontrol over the content of incorporated non-metallic elements (Nat. Nanotechnol. 10, 444–452 (2015);\nAngew. Chem. Int. Ed. 63, e202412825 (2024)).\nBased on the above analysis, controlling the annealing temperature can indeed affect the doping amount\nin RuO , thereby influencing the catalytic performance.\n2\n4. Comment: The newly added [Page 14, Lines 14–15] states: \"Next, the ink was vertically dripped on the\nglassy carbon electrode (0.196 cm²) to obtain the work electrode (loading amount: ~75 mg Ru).\" The high\nloading of Ru seems to exaggerate the OER activity. A comparison with previous studies should be\nprovided and summarized.\n[Author’s Response]: Thank you for pointing out this mistake, and we sincerely apologize for the\noversight. The correct Ru loading amount on the working electrode (75 μg cm–2) has been update in the\nRu\nelectrochemical measurements section of the revised manuscript as following:\nElectrochemical measurements. Then 2.0 mg of catalyst was added into the 200 μL of a solution\ncontaining 195 μL of isopropyl alcohol and 5 μL of Nafion, and the ink was prepared by ultrasonic at\nambient temperature. Inductively coupled plasma atomic emission spectroscopy (ICP–AES) suggested\nthat the content of Ru is 14.71 wt% (w ). To prepare the working electrode, 10 μL of ink was vertically\nRu\ndripped on the glassy carbon electrode with a geometric area of 0.196 cm2 (loading amount: ~75 μg\nRu\ncm–\n2). [Page 15, Line 3–8]\nIn detail, the loading amount of Ru (𝑚 ) on the working electrode was calculated by the following\n𝑅𝑢\nequation:\n𝑚 = \nm𝑙𝑜𝑎𝑑𝑖𝑛𝑔 × 𝑤𝑅𝑢\n𝑅𝑢 𝑆\nWhere m is the mass of the catalyst dripped on the working electrode and S is the geometric area of\nloading\nglassy carbon electrode.\nTherefore, the OER activities of overpotential and Tafel slope for various catalysts are visually presented\nin Fig. 4a–c, where F–RuO /FC exhibit the smallest overpotential and the Tafel slope value,\n2\noutperforming most of the Ru–based catalysts reported recently (Table S10). [Page 9, Line 22–Page 10,\nLine 6]\nFigure 4. Electrochemical activity studies. (a) OER polarization curves and (b) Tafel plots of F–RuO2/FC, RuO2/C, and RuO2. (c)\nHistogram of overpotentials at 10 mA cm–2 and Tafel slopes of F–RuO2/FC, RuO2/C, and RuO2.\nTable S10. Comparison of the Ru loading amount and OER performance of F–RuO2/FC with recently reported OER electrocatalysts in a\nthree–electrode setup.\nLoading Activity (at Tafel slope\nCatalyst Electrolyte Ref.\namount of Ru 10 mA cm–2) (mV dec–1)\nF–RuO2/FC 0.5 M H2SO4 75 μg cm–2 192 mV 41.6 This work\nJ. Am. Chem. Soc. 147, 4159–4166\nPd@RuO2 0.5 M H2SO4 200 μg cm–2 189 mV 65.2\n(2025)\nGB–V–RuO2 0.5 M H2SO4 697 μg cm–2 159 mV 58.5 Nat. Commun. 16, 4482 (2025)\nJ. Am. Chem. Soc. 147, 24392–\nRu–γ–MnO2 0.1 M HClO4 12 μg cm–2 246 mV 57.0\n24402 (2025)\nRuO2@COF–O(3) 0.5 M H2SO4 212 μg cm–2 218 mV 64.3 Adv. Mater. 37, 2417374 (2025)\nAngew. Chem. Int. Ed. 137,\nGa–RuO2 0.5 M H2SO4 57 μg cm–2 218 mV 60.5\ne202413334 (2025)\niGa0.2Ru0.7O2 1.0 M HClO4 4000 μg cm–2 188 mV 33.9 Nat. Commun. 16, 3976 (2025)\nh–ATO/RuO2 0.5 M H2SO4 180 μg cm–2 216 mV 60.0 Nat. Commun. 16, 337 (2025)\nRuFe@CF 0.5 M H2SO4 823 μg cm–2 188 mV 80.3 Adv. Mater. 36, 2312369 (2024)\nIr–RuO2 0.5 M H2SO4 625 μg cm–2 167 mV 48.2 Nat. Commun. 15, 10315 (2024)\nInSnRuO2 0.5 M H2SO4 200 μg cm–2 183 mV 49.8 Adv. Mater. 36, 2414579 (2024)\nPb–RuO2 0.5 M H2SO4 436 μg cm–2 188 mV 58.6 Nat. Commun. 15, 9774 (2024)\nM–RuIrFeCoNiO2 0.5 M H2SO4 1377 μg cm–2 189 mV 49.0 Sci. Adv. 9, eadf9144 (2023)\nRu/TiOX 0.5 M H2SO4 71 μg cm–2 174 mV 45.6 Nat. Commun. 14, 7644 (2023)\nSnRuOX 0.5 M H2SO4 15 μg cm–2 194 mV 38.2 Nat. Commun. 14, 843 (2023)\nLi0.52RuO2 0.5 M H2SO4 637 μg cm–2 156 mV 83.3 Nat. Commun. 13, 3784 (2022)\nC–RuO2–RuSe–5 0.5 M H2SO4 306 μg cm–2 212 mV 49.5 Chem 8, 1673–1687 (2022)\nAngew. Chem. Int. Ed. 61,\nRuO2–WC NPs 0.5 M H2SO4 22 μg cm–2 347 mV 75.7\ne202202519 (2022)\nSS Pt–RuO2 HNSs 0.5 M H2SO4 306 μg cm–2 260 mV 51.0 Sci. Adv. 8, eabl9271 (2022)\n5. Comment: Additional, [Page 14, Lines 9–12]: \"In addition, melamine, …… at 450 °C, 150 °C, 300 °C,\n500 °C, 450 °C, and 350 °C, respectively\". The repetition of 450 °C appears to be an error. Such\ninconsistencies may undermine the rigor of the manuscript.\n[Author’s Response]: Thank you for your thorough review of our manuscript. To address your concern,\nwe have further clarified and elaborated on the synthesis process for the M–RuO /(F)C (M = N, S, P, Se,\nsources and RuO /(F)C were placed in separate tube furnaces located upstream and downstream of the\n2\nquartz tube for heat treatment. This configuration facilitates sufficient anion release from the anion sources\nat different target temperatures (Table S12). [Page 14, Line 16–Page 15, Line 1]\nSupplementary Fig. 80. Schematic diagram of the heat treatment synthesis process for M–RuO2/(F)C (M = N, S, P, Se, Cl and Br) using\ntube furnace.\nTable S12. Target temperature under heat treatment of different anion sources.\nAnion sources Target temperature (℃)\nmelamine 450\nsulfur powder 150\nsodium hypophosphite 300\nselenium powder 500\na mixture of polyvinyl chloride and manganese dioxide 450\nhexabromobenzene 350\n6. Comment: The PEM tests lack control samples (RuO₂, RuO₂/(F)C) for comparison, which are crucial\nfor enabling readers to more effectively assess the catalytic performance.\n[Author’s Response]: We sincerely appreciate your insightful feedback, as it has provided important\nguidance for enhancing our work. According to your suggestion, RuO and RuO /(F)C were employed as\n2 2\nanode catalysts for the PEM electrolyzer, and their respective electrochemical performances were\nsystematically evaluated. Specifically, to deliver current densities of 500, 1000, 2000, and 3000 mA cm–\n2, higher cell voltages of RuO ||PEM||Pt/C (1.61, 1.78, 2.10 and 2.42 V) and RuO /(F)C||PEM||Pt/C (1.70,\n2 2\n1.96, 2.44 and 2.86 V) were required compare with F–RuO /FC (1.58, 1.70, 1.89 and 2.05 V)\n2\n(Supplementary Fig. 70a). Notably, both RuO ||PEM||Pt/C and RuO /(F)C||PEM||Pt/C exhibit\n2 2\nsignificantly lower stability than that of F–RuO /FC, and the severe degradation of RuO /(F)C underscores\n2 2\nthe pivotal role of F in catalytic stability (Supplementary Fig. 70b, c and Supplementary Fig. 71). [Page\n11, Line 8–16]\nSupplementary Fig. 70. (a) Polarization curves of PEM electrolyzer using RuO2/(F)C and RuO2 as anode. Chronopotentiometry tests of\nPEM electrolyzer using (b) RuO2||Pt/C and (c) RuO2/(F)C||Pt/C as electrocatalysts.\nSupplementary Fig. 71. (a) SEM images of the cross section of MEA before and after CP test. (b) SEM image and (c) TEM image of\nRuO2/(F)C after CP test of PEMWE.\nGeneral comment: In summary, this manuscript does not provide sufficient evidence to demonstrate clear\ndifferences in the degree of symmetry breaking across various anionic dopants. Therefore, this work far\ncan not meet the high standards of Nature Communications.\n[Author’s Response]: Thank you very much for your constructive comments. We highly appreciate that\nyou strictly point out our deficiency in this work and we are truly sorry that our work did not supply a\nsatisfying interpretation and explanation to demonstrate our research. To address your concerns, we have,\naccording to the literature (Nature 620, 328–335 (2023)), employed the Baur distortion index to quantify\nthe observed differences in the degree of symmetry breaking among the various anionic dopants.\n------------------------------------\nIn the end, we would like to thank for the precious time of the reviewers and the editor. We sincerely wish\nthat our point-to-point response and the revised manuscript have addressed your concerns and satisfy your\nrequirements for publications. We would be grateful if we have the chance to share our work with readers\nof Nature Communications.\nXiaoqing Huang\nResponse to Reviewers\nDear Reviewer,\nThank you for your continued guidance and the valuable time you have dedicated to our manuscript titled\n“Ultradurable acidic water oxidation ruthenium–based electrocatalyst by fluorination induced\nsymmetry–breaking” (Manuscript ID: NCOMMS-25-10822B-Z) for Nature Communications. We\nare greatly encouraged by your positive recognition of our previous revisions. Regarding the final point\nraised, we have given it in-depth consideration and provided a detailed explanation below. We sincerely\nhope these revisions have adequately addressed your concern and further improved the quality of the\nmanuscript.\nReviewer #1\n1. Comment: In the revised manuscript, the authors have made efforts to improve the quality of the\npresented research. However, the reviewer raises a final concern regarding how to distinguish the effects\nof doping amount from the type of doping element on the Baur distortion indices.\n[Author’s Response]: Thank you for acknowledging our efforts in previous revisions and for raising this\ncritical concern about attributing the distinction between the effects of dopant type and doping amount on\nthe Baur distortion indices (D). We fully agree that addressing this point is essential to solidify the\ni\nscientific rigor of our conclusions. Motivated by this question, we conducted an in–depth investigation. It\nwas revealed that the type of doping element is the key factor driving the change of D, whereas the doping\ni\namount modulates the OER performance mainly through affecting the number of active sites and D.\nThis\ni\nconclusion is drawn from the following analysis:\nThe effect of doping element type: Evidently, M–RuO (M = F, N, S, P, Se, Cl and Br) shows varying\ni\ndoping element type critically determines the D.\ni\nSupplementary Fig. 46. EDS spectra of (a) N–RuO2/(F)C, (b) S–RuO2/(F)C, (c) P–RuO2/(F)C, (d) Se–RuO2/(F)C, (e) Cl–RuO2/(F)C and\n(f) Br–RuO2/(F)C.\nSupplementary Fig. 52. EDS spectra of (a) F–RuO2/FC–300 °C, (b) F–RuO2/FC, and (c) F–RuO2/FC–500 °C.\nSupplementary Fig. 47. The metal–nonmetal bond length of F–RuO2, N–RuO2, S–RuO2, P–RuO2, Se–RuO2, Cl–RuO2 and Br–RuO2\ncrystal structure. The calculated distortion indexes are indicated.\nThe effect of doping amount: Taking F doping as an example, at low doping levels (Supplementary Fig.\n52a), the D remains largely unchanged (Supplementary Fig. 50a, 51a, and Table S9), while the TOF\ni\ndecreases significantly (Supplementary Fig. 64), suggesting that low F doping primarily affects the\nnumber of active sites rather than the D. Conversely, as the F doping levels increase (Supplementary Fig.\ni\n52c), D increases while TOF decreases (Supplementary Fig. 50b, 51b, 64 and Table S10), demonstrating\ni\nthat excessive symmetry breaking degrades OER performance (Supplementary Fig. 63) [Page 10, Line\n20–Page 11, Line 1].\nSupplementary Fig. 50. XRD patterns of (a) F–RuO2/FC–300 °C and (b) F–RuO2/FC–500 °C.\nSupplementary Fig. 51. The metal–nonmetal bond length of (a) F–RuO2/FC–300 °C and (b) F–RuO2/FC–500 °C crystal structure. The\ncalculated distortion indexes are indicated.\nTable S9. Refined parameters of F–RuO2/FC–300 °C.\nF–RuO/FC–300 °C X Y Z\nRu1 0.01696 -0.01656 0.00000\nO2 0.69389 0.69616 0.00000\nO3 0.19322 0.80779 0.50000\nO4 0.30384 0.30611 -0.00000\nF1 0.80894 0.19002 0.50000\na = 4.48250 Å, b = 4.48250 Å, c = 3.11133 Å, space grpup P42/mnm, R = 5.16%, Chi2 = 7.36\nwp\nTable S10. Refined parameters of F–RuO2/FC–500 °C.\nF–RuO/FC–500 °C X Y Z\nRu1 0.01298 0.01297 0.00000\nO2 0.69602 0.69649 0.00000\nO3 0.19388 0.80445 0.50000\nO4 0.80428 0.19361 0.50000\nF1 0.30704 0.30674 0.00000\nF2 0.30679 0.30661 0.00000\na = 4.48250 Å, b = 4.48250 Å, c = 3.12181 Å, space grpup P42/mnm, R = 4.32%, Chi2 = 2.95\nwp\nSupplementary Fig. 64. TOF of F–RuO2/FC–300 °C and F–RuO2/FC–500 °C.\nSupplementary Fig. 63. (a) OER polarization curves and (b) chronopotentiometry tests of F–RuO2/FC–300 °C and F–RuO2/FC–500 °C.\n------------------------------------\nIn the end, we extend our sincere appreciation to the editor and reviewers for the precious time and the\nvaluable feedback throughout the review process. We sincerely wish that the revised manuscript and our\nresponse have adequately addressed your concerns and meet the high standards for publication. We would\nbe grateful if we have the chance to share our work with readers of Nature Communications.\nXiaoqing Huang"}, {"round": 3, "reviewer_comments": {"reviewer_1": "The authors have revised the manuscript appropriately. The current version of the manuscript can be accepted for publication."}, "author_response": ""}]

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