Highly efficient heterogeneous thermal catalysis for noble-metal-free hydrogen production from formic acid

Domain: physics
Published: 2025-12-27
Editorial outcome: major_revision

Abstract
Hydrogen extraction from liquid hydrogen carriers is a promising strategy to address hydrogen storage and transportation challenges for a hydrogen economy. We report a novel heterogeneous catalytic architecture, Ni(Mn)-O-P/GaN nanowires, for efficient, selective, and ultra-stable hydrogen evolution from formic acid (FA). The catalyst achieves a high activity of 29.92 mol H2·g-1·h-1 with nearly 100% selectivity and a high turnover frequency (TOF) of 31,019.2 h-1 at 150 °C. It exhibits exceptional stability over 4000 hours under fluctuated temperatures (55-75 °C) with a turnover numbers (TONs) of 5,023,060, integrable with low-grade industrial waste heat. In-situ characterizations, isotope experiments, and density functional theory calculations collectively reveal that the synergy between Ni(Mn)-O-P and GaN are favorable for the O-H dissociation of FA with an interesting H-exchange mechanism with H2O while inhibiting the undesired FA dehydration and coking formation. An industrial prototype test validates practical on-demand hydrogen production using waste heat.

Introduction
Green hydrogen (H2) is emerged as a disruptive renewable energies carrier owing to its high energy density (142 MJ/kg) and zero emission1. However, the unique physicochemical properties of H2, such as low boiling point (−253 °C), low molecular weight (2 g/mol), and inflammability, pose insurmountable challenges for its storage, transportation, and distribution2. Conventional gas compression and cryogenic liquefaction methods can’t meet the massive demand for H2 from different economic sectors, remaining the bottleneck of the eventual success in establishing an H2 economy3. Liquid hydrogen carriers (LHCs) present a revolutionary strategy to address the issues above by employing well-established infrastructures of liquid fuels4,5. Critically, the thermal catalysis of on-demand hydrogen extraction from LHCs shows great promise for global decarbonization by synergizing industrial waste heat (which accounts for nearly 60% of the total global energy consumption) with renewable energies.

Among a variety of LHCs, formic acid (FA) has attracted global attention due to its non-toxicity, low flammability, and high hydrogen density6,7. Moreover, FA can be produced from CO2 hydrogenation or partial oxidation of biomass, thus promising a sustainable loop for green H28–11. Since the pioneering study in the 1960s12, homogeneous catalysts have been extensively explored for FA dehydrogenation with high activity, some of which even delivered high turnover numbers (TONs) of over a million13–15. However, organic solvents or base additives are often indispensable to accelerate the reaction kinetics, which increases the complexity and cost of the system16. Meanwhile, homogeneous catalysts are not industrially conducive to producing H2 from FA owing to their vulnerability and limited reusability. In stark contrast, heterogeneous catalysis holds grand promise for practically producing H2 from FA owing to its superior reusability, robustness, and scalability17,18. Thus far, a number of supported metals heterogeneous catalysts, including single atom catalysts19–21, metal nanoparticles (NPs)22–25, a combination of single atoms and clusters26, and multimetallic alloy27,28 have been used for FA decomposition. However, although some studies have reported the use of earth-rich metals as catalysts in both homogeneous and heterogeneous systems29, H2 production from FA is highly dependent on noble metals, which are limited by their high cost and low abundance13,30. Meanwhile, noble metals are easily deactivated because of their CO sensitivity and severe coke formation during thermal catalysis of LHCs31–34. In addition, the undesired dehydration reaction would limit the practical application of thermal catalysis of FA decomposition due to the resultant toxic impurities (HCOOH→CO↑+H2O)35,36. In this context, it is imperative to explore a noble-metal-free heterogeneous catalytic architecture for highly efficient, selective, and stable FA decomposition into H2. The pursuit of an ideal solid support to work in synergy with rational catalytic centers is critical yet remains a grand challenge.

1-dimensional (1D) GaN nanowires (NWs) are an emerging support for assembling a new-generation heterogeneous catalytic architecture because of the unique geometric and electronic properties37,38. First, the well-defined 1D morphology with ultrahigh surface area is geometrically favorable for efficient exposure of active sites. Second, the surface of GaN with polar variability can be precisely engineered at the atomic level to tailor chemical reactions by cooperating with appropriate co-catalysts39,40. In this study, an unprecedented heterogeneous catalytic architecture was proposed for thermal catalysis of FA decomposition by rationally coupling Ni(Mn)–O–P with GaN NWs (Fig. 1). The as-prepared heterogeneous catalyst shows a considerable activity of 29.92 mol H2·g-1·h-1 with a high selectivity of nearly 100% from FA decomposition under 150 °C. Benefitting from the high atom efficiency of the catalyst, a high turnover frequency (TOF) of 31019.2 h-1 was obtained for Ni(Mn)–O–P/GaN NWs. Of note, the catalyst exhibits an ultra-long-term operation over 4000 hours with high TONs of 5,023,060 mole H2 under fluctuating temperatures ranging from 55 to 75 °C. It thus shows desired flexibility to utilize different industrial waste heat for H2 extraction from FA on demand, which is verified by an industrial-scale pilot system in the scenario of steam power generation. As studied by the comprehensive in situ spectroscopic characterizations, isotope labeling experiments, and density functional theory (DFT) calculations, the integrated Ni(Mn)-O-P/GaN NWs is beneficial for water-assisted activation of the O–H bond of FA to lower the energy barrier of FA dehydrogenation through an interesting H-exchange mechanism (HCOO-H + HO-H ⇋ HCOO-H + HO-H ) while suppressing the undesired FA dehydration (HCOOH→H2O+CO↑), thus simultaneously enhancing the activity and selectivity. Furthermore, the introduction of Ni(Mn)-O-P over GaN NWs imparts the catalyst with the distinctive CO-insensitive and anti-coking properties, thus resulting in superior stability. Overall, this work illustrates the scientific and technical feasibility of on-demand H2 extraction from FA powered by low-grade industrial waste heat, showing significant potential for employing LHCs to address the growing demand for green H2 across multiple industrial sectors.

Results
Materials growth and characterizations
The epitaxial GaN NWs were employed as scaffolds to assemble a new heterogeneous catalytic architecture for H2 evolution from FA by coupling with Mn-doped Ni-O-P (Please see “Methods” Section and Figs. S1–S3 in Supplementary Information). As characterized by scanning electron microscope (SEM), GaN NWs exhibited lengths ranging from 500 to 700 nm with diameters in the range of 50 to 80 nm (Fig. S4). The 1D morphology of GaN NWs can maximize the number of catalytic sites. As seen from Figs. 2a, S5, the decoration of Ni(Mn)-O-P nanoclusters did not alter the overall morphology of 1D NWs. High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) image (Fig. S6) showed that Ni(Mn)-O-P species were randomly distributed on the GaN NWs surface with a diameter ranging from 27.4–92.9 nm. High-Resolution Scanning Transmission Electron Microscopy (HR-STEM) image (Fig. 2b) showed the lattice spacing of 0.26 nm, which was attributed to the (002) plane of GaN41,42, indicating the growth direction of the nanowires along the c-axis. It is consistent with the X-ray Diffraction (XRD) patterns (Fig. S7) and Raman spectra43 (Fig. S8). The lattice spacing of 0.24 nm and 0.206 nm could be indexed to the (111) plane of NiO and the (212) plane of NiP. However, no XRD diffraction peaks of Ni(Mn)-O-P were observed, possibly due to its low loading content (0.23 μmol·cm-2 as measured by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)). Energy-dispersive X-ray Spectroscopy (EDS) mapping images (Figs. 2c, S9) and Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) (Fig. 2d, e) further confirmed the success in anchoring Ni(Mn)-O-P nanoclusters onto the GaN NWs surface. Moreover, Mn is highly dispersed across the as-prepared Ni(Mn)-O-P.

The assembled Ni(Mn)-O-P was further investigated by X-ray Photoelectron Spectroscopy (XPS) characterizations (Fig. S10). A positive binding energy shift of 0.23 eV was observed for Ga 2p over Ni(Mn)-O-P/GaN NWs compared to pristine GaN NWs (Fig. S11b). Additionally, the N 1s peak of pristine GaN at 397.26 eV is shifted to 397.56 eV upon the decoration of Ni(Mn)-O-P (Fig. S11c). These results evidenced the electronic interaction between GaN NWs and Ni(Mn)-O-P. The existence of Ni-O-P was further validated with a clear indicator of Ni-O, Ni-P and P-O interaction (Figs. 2f, S11d, Table S1). Of note, the doping of Mn leads to a substantial decrease in the binding energy of Ni and O. It is indicative of the electron redistribution from the doped Mn sites to the Ni and O sites (Fig. 2f, g), which significantly affects FA decomposition as studied below.

The catalytic activity of formic acid decomposition
The reaction was conducted in a sealed stainless temperature-programmed chamber under atmospheric argon (Fig. S12). 1 mL of neat FA (>99.9%) was used as the feedstock if not specifically noted. As seen from Figs. 3a, S13, the influence of co-catalysts on FA dehydrogenation is significant. Particularly, the H2 activity of Ni-O/GaN NWs reaches 0.88 mol·g-1·h-1. The introduction of phosphorus can further improve the activity up to 3.20 mol·g-1·h-1, even surpassing some noble metals tested (Table S2, Figs. S14, S15). More interestingly, the doping of secondary transition metals, i.e., Cr, Fe, Cr, Mn further enables a significant enhancement in the activity of FA dehydrogenation. Among them, Ni(Mn)-O-P/GaN NWs deliver an optimal activity of 11.55 mol·g-1·h-1, which is nearly 2 orders of magnitude higher than that of the commercial Pt/C catalyst (Fig. S16). The activity is closely related to the doping amount of Mn in the Ni(Mn)-O-P, showing a volcano trend as the Mn content increases (Fig. 3b). Compared with pure GaN NWs, the selectivity of H2 was sharply improved from 49% up to 99% by loading Ni(Mn)-O-P nanoclusters (Fig. 3c). Without GaN, Ni(Mn)-O-P was nearly inactive for FA decomposition, suggesting the critical synergy of GaN with Ni(Mn)-O-P in H2 production from FA (Fig. S17). More interestingly, compared to neat FA decomposition, the introduction of water (1 mL HCOOH+200 μL H2O) resulted in an observable enhancement in H2 activity with a high value of 29.92 mol·g-1·h-1 (Figs. 3d, S18), the underlying cause will be studied below. Of note, CO2 was produced from formic acid dehydrogenation at a stoichiometric H2/CO2 ratio of 1/1. This finding indicates negligible formic acid dehydration (Fig. S19). The temperature-dependent activity of Ni(Mn)-O-P/GaN NWs for water-assisted FA decomposition was next studied (Fig. 3e). The reaction can readily occur under 60 °C with H2 activity of 3.79 mol·g-1·h-1, which is superior to most of the reported catalysts under comparable conditions (Table S3, Fig. 3f). A considerable TOF of 3,932.68 h-1 was obtained due to the combined effect of high intrinsic activity and high atom efficiency of the catalyst. As expected, the activity was rapidly enhanced by increasing the reaction temperature, reaching 29.92 mol·g-1·h-1 with a high TOF of 31,019.2 h-1 at 150 °C. From the perspective of practical applications, such a broad reactive temperature range is flexible for directly utilizing industrial waste heat from various sources with different grades to extract H2 from FA on demand.

Long-term stability was tested to assess the viability of using Ni(Mn)-O-P/GaN NWs for heterogeneous catalysis of H2 production from FA over fluctuating temperatures. As shown in Fig. 3g, the optimized Ni(Mn)-O-P/GaN NWs demonstrated an exceptional stability of over 4000 h with benchmark TONs of 5,023,060 mole H2. After the 4000 h test, the hydrogen activity only decreased by ~10% (Fig. S20). The Transmission Electron Microscope (TEM) images and XPS spectra show that the morphological and valence state of the nanoclusters remain stable and do not undergo significant change during the reaction. (Fig. S21). In sharp contrast, noble metals such as Ir, Pd, and Pt showed obvious activity degradation after 200 h of operation under identical conditions (Fig. S22). Herein, the exceptional stability of Ni(Mn)-O-P/GaN NWs can be attributed to their CO insensitivity and superior anti-coking property as revealed by spectroscopic characterizations and density functional theory calculations below.

Reaction mechanism
To unravel the reaction mechanism at the molecular level, in situ Fourier Transform Infrared Spectroscopy (FTIR), and electron paramagnetic resonance (EPR) characterizations were collectively carried out to investigate the key intermediates of FA decomposition. As shown in Fig. S23, the in situ FTIR characteristic peaks of HCOO* at 1363 cm-1, 1585 cm-1, and 2940 cm-1 were observed for both Ni(Mn)-O-P/GaN NWs and bare GaN NWs, which results from the O–H dissociation of FA (HCOOH→HCOO*+*H)44–48. It should be noted that the accumulation rate of HCOO* over Ni(Mn)-O-P/GaN far outperforms that over pure GaN (Fig. S24), corroborating the synergistic effect between Ni(Mn)-O-P and GaN in promoting the O–H dissociation of FA, which aligns with the in situ EPR characterizations49,50 (Fig. 4a). Notably, upon the addition of water, in situ FTIR spectral shifts were observed during the reaction (Fig. 4b). Typically, the asymmetric stretching vibration of HCOO* in HCOOH/H2O system exhibited an obvious redshift, which is indicative of the water-assisted stabilization of the HCOO* intermediate arising from the O-H dissociation of HCOO-H51,52. By contrast, the carbonyl stretching band of HCOOH was shifted from 1742 cm-1 downward to 1780 cm-1 when water was introduced into neat FA, further suggesting the activation of HCOOH with H2O51,52. Meanwhile, as studied by Nuclear Magnetic Resonance Spectroscopy (NMR) characterizations, the adsorbed water was dissociated into H*+*OH (in a terminal hydroxyl configuration) over the Ni(Mn)-O-P/GaN interface53,54 (Fig. 4c). It is energetically favorable for FA dehydrogenation through an interesting H-exchange mechanism while inhibiting the undesired FA dehydration, which was verified by Gas chromatography-mass spectrometry (GC–MS) measurement (Figs. 4d, e, S25), both HD and D2 were produced from when DCOOD and H2O were used as feedstock. Meanwhile, trace amounts of DCOOD and DCOOH/HCOOD were detected in the mixture of HCOOH and D2O. These results validated the H exchange between FA and H2O (HCOO-H + HO-H ⇋ HCOO-H + HO-H ). The kinetic isotope effect (KIE) was then studied. As shown in Fig. 4f, the KIE ratios of (HCOOH+H2O)/(DCOOD+H2O) and (HCOOH+H2O)/(HCOOH+D2O) are greater than 1, indicating that H2O can promote the dehydrogenation of FA in the kinetics. These findings signify that the O-H cleavage of HCOOH is likely to be the rate-determining step (RDS) of FA decomposition, which can be facilitated by H2O.

Temperature-programmed H2 desorption (TPD) characterizations were further conducted to gain more insights into the reaction mechanism. As demonstrated in Fig. 4g, h, the desorption temperature of H2 can be reduced from 289 °C over bare GaN NWs downward to 279 °C over Ni(Mn)-O-P/GaN NWs. It is indicative of the readily desorption of H2, which is favorable for H2 extraction from FA over the Ni(Mn)-O-P/GaN interface. Meanwhile, the decorated Ni(Mn)-O-P facilitates the desorption of CO from the GaN surface, which is a clear indicator of the CO-insensitivity property of the catalyst, thus facilitating stability. Moreover, during the long-term heterogeneous catalysis of H2 extraction from FA, no carbon species were obviously detected on the surface of Ni(Mn)-O-P/GaN NWs after stability testing, as characterized by the Raman spectroscopy technique (Fig. 4i). In contrast, the progressive changes in the C 1s spectra (Figure S26), combined with Raman spectroscopy (Fig. 4i), demonstrate the evolution of coking over Pd/GaN NWs after 200 h of thermal catalysis of FA decomposition. The results above reveal the superiority of Ni(Mn)-O-P/GaN NWs for highly efficient and ultra-stable H2 production from FA.

Theoretical calculations
DFT calculations were performed to study the origin of the outstanding activity, selectivity, and stability (Fig. S27). The electronic properties of Ni(Mn)-O-P/GaN are first elucidated. As indicated by charge transfer analysis (Figs. 5a, S28), Ni(Mn)-O-P clusters deliver 0.623 e to GaN, which is much less than that Ni-O and Ni-O-P and the presented pattern is consistent with the XPS results (Fig. 2f). Density of states (DOS) calculations revealed that the introduction of phosphorus and manganese helps to increase the electron occupation near the Fermi level, and the significant interfacial charge redistribution was mediated through the Ni 3d orbitals (Figs. 5b, S29). Meanwhile, the highest occupied molecular orbital (HOMO) orbitals on the Ni(Mn)-O-P surface are concentrated near Mn atoms, suggesting that Mn sites are most likely active sites for efficient FA dehydrogenation (Fig. S30). These changes in electronic properties all indicate that the introduction of Ni(Mn)-O-P has created an excellent interface environment for the dehydrogenation of FA.

DFT calculations were further conducted to gain more insights into water-assisted FA decomposition at the molecular level. The OH adsorption energies over different catalytic interfaces were first calculated (Fig. S31). As shown in Fig. 5c, Ni(Mn)-O-P/GaN exhibits stronger *OH affinity at POx moieties with a relatively high ΔEads of −4.19 eV compared to Ni-O-P/GaN (−1.92 eV). The oxygen center in the adsorbed OH on Ni(Mn)-O-P/GaN shows a reduced charge compared to the Ni-O-P/GaN counterpart, indicating the introduction of Mn has enhanced the electronegativity of the nanoparticles. (Fig. S32). Furthermore, compared to Ni-O/GaN and Ni-O-P/GaN, HCOOH is thermodynamically favored to be absorbed on Ni(Mn)-O-P*OH/GaN (Fig. S33). It is noteworthy that the O–H bond of HCOOH is extended over Ni(Mn)-O-P while the C–O bond is shortened, indicating the activation of the O–H bond as well as the stabilization of C–O bond (Table S4). Hence, the Ni(Mn)-O-P/GaN interface facilitates the selective FA dehydrogenation into H2 while inhibiting the undesired dehydration.

The dehydrogenation step of FA decomposition over Ni-O/GaN, Ni-O-P/GaN and Ni(Mn)-O-P/GaN was then calculated (Figs. 5d, S34–S36). It was discovered that, for Ni-O/GaN, the O–H cleavage of HCOO-H (HCOOH→HCOO*+*H) was identified to be RDS in the intermediate (IM1) with a high energy barrier of 2.56 eV, which can be significantly lowered to 0.96 eV by doping with phosphorous. More critically, upon the incorporation of Mn in Ni-O–P, the detached H atoms readily migrated to the Mn sites with a further reduced energy barrier of 0.89 eV. It is thus rationalized that Ni(Mn)-O-P works in synergy with GaN to promote the O–H dissociation of HCOOH, which is in excellent agreement with in situ FTIR and EPR spectroscopic characterizations above. Consequently, the RDS was switched from the O–H dissociation over Ni-O/GaN into H*+H*→*H2 over Ni(Mn)-O-P/GaN with a significantly lowered energy barrier of 1.12 eV. For comparison, the energy state of *HCOOH→HCO*+*OH, a key step in FA dehydration, was also investigated. As seen from Figs. 5e, S37, the energy barrier of *HCOOH→HCO*+*OH at the Ni(Mn)-O-P/GaN interface is as high as 2.02 eV. It is much higher than that of *HCOOH→HCOO*+H* (0.89 eV), thus preventing the undesired FA dehydration. As a consequence, the synergy between Ni(Mn)-O-P and GaN not only enhances the activity by lowering the energy barrier of FA dehydrogenation but also improves the selectivity by inhibiting the undesired dehydration. Moreover, the key step of coking formation, i.e., *CO→*C conversion, is thermodynamically disfavored with an exceptionally high Gibbs free energy (ΔG) of 7.68 eV over the Ni(Mn)-O-P/GaN interface (Fig. 5f), suggesting the superior anti-coking property. The results above provide solid computational evidence to support the exceptional activity, selectivity, and stability of hydrogen production from FA over Ni(Mn)-O-P/GaN, which is well consistent with spectroscopic characterizations.

Industrial prototype test
To evaluate the eventual viability of using industrial waste heat to extract H2 from FA over Ni(Mn)-O-P/GaN NWs, an industrial-scale pilot system was designed for FA decomposition using simulated industrial exhaust gas by heating air (Fig. 6a). As shown in Fig. 6b, H2 activity can reach 3.06 mol·g-1·h-1 by purging with hot air at 60 °C. As calculated by the software of ChemSep, in the steam turbine power generation scenario, with the output of 13 kW of useful work, 24.3 kW of low-grade waste heat can be utilized for thermal catalysis of H2 production from FA. 47.52 kmol of H2 per hour can be achieved (equal to 95.42 kg/h). The endeavor above illustrates the feasibility of using Ni(Mn)-O-P/GaN NWs for on-demand H2 production from liquid hydrogen carriers powered by industrial heat waste.

Methods
Assembly of GaN-supported metals
MBE growth of GaN onto a 4-inch Si wafer. GaN nanowires (NWs) were epitaxially synthesized on a 4-inch Si(111) substrate using a SVTA molecular beam epitaxy (MBE) system. The setup included a dual-filament Knudsen cell for the gallium source (Ga purity: 99.99999%), a standard Knudsen cell for magnesium (Mg purity: 99.9999%), and a Veeco Unibulb radio frequency (RF) nitrogen plasma source (N2 purity: 99.9999%). During deposition, the nitrogen plasma was maintained with a steady N2 flow rate of 1.0 sccm and an RF power of 400 W, yielding a GaN NW growth rate of 300 nm/h. All nanowires were fabricated under nitrogen-rich conditions, with a III/V ratio fixed at 0.2. Prior to growth, the silicon wafer was degassed in the chamber at 900 °C for 30 min. This was followed by a 60-s surface nitridation at 800 °C to form a thin SixNy layer that promotes subsequent GaN nucleation. An unintentionally doped n-type GaN NW layer was first deposited at 700 °C, after which Mg-doped p-GaN NWs were grown at 600 °C. To modulate the nanowire diameter during p-GaN deposition, the temperature of the Mg cell was systematically increased from 230 °C to 270 °C. The final structure consists of a p–n double-layer GaN nanowire array.

Deposition of metals. The deposition of metals onto 1D GaN was conducted in a sealed quartz chamber (0.44 L) under illumination by a 300 W Xenon lamp. GaN NWs supported by a Si wafer were placed at the bottom of the chamber. A solution comprising 60 mL of methanol-water mixture (volume ratio of CH3OH/H2O=1/5) along with the requisite amount of the precursors of various metals (NiCl2 (99.99% metals basis), MnSO4 (99.99% metals basis), CoCl2·6H2O (99.99% metals basis), CrCl2·6H2O (99.5% metals basis), FeCl3·6H2O (99.99% metals basis) Shanghai Aladdin Biochemical Technology Co., Ltd. NaPH2O2, H2IrCl6·6H2O (≥98% metals basis) Beijing InnoChem Science & Technology Co., Ltd. H2PtCl6-6H2O (99.95% metals basis), Shanghai Titan Technology Co. Ltd. K2PdCl4 (Pd≥26.3%), Na3RhCl6 (Rh 17.1%), Shanghai Meryer Biochemical Technology Co. Ltd. RuCl3 (97%), Shanghai Bidepharm Technology Co. Ltd. HAuCl4·4H2O (48～50% metals basis), Shanghai Chemiejoy Biotechnology Co. Ltd.) in varying proportions was introduced into the container. Subsequently, the chamber was evacuated and purged with argon gas, followed by illumination with a 300 W xenon lamp irradiation for 30 minutes. Finally, the wafer was thoroughly rinsed with distilled water and dried prior to use. Distilled water was used throughout the entire research.

Characterization
XRD analysis was performed using a Bruker D8 Advance diffractometer. The Ni(Mn)-O-P content on 1D GaN supported by Si was quantified through ICP-AES using an AGILENT 730 instrument. SEM characterization was carried out with a Quattro ESEM (FEI). TOF-SIMS characterizations were conducted using a TOF.SIMS 5-100 instrument (ION-TOF GmbH, Germany). Raman spectra were recorded using a HORIBA LabRAM HR Evolution spectrometer (Japan) with a spectral range of 200–2100 nm and a focal length of 800 mm. XPS measurements were conducted on an ESCALAB 250xi system equipped with a non-monochromatic aluminum anode, with the C 1s peak at 284.8 eV serving as the calibration reference. STEM images were performed on a Thermo Fisher Scientific Talos F200X S/TEM system operating at 200 kV, which was also equipped with a Super-X EDS detector. TEM images were obtained using a JEOL 2100F microscope. TPD measurements were carried out on a Quantachrome Autosorb-iQ-C chemisorption analyzer. FTIR spectroscopy was conducted on a PerkinElmer Frontier FTIR spectrometer equipped with an MCT detector and a detachable 10 cm gas cell. EPR spectroscopy was conducted on a Bruker A300 instrument (Germany), EPR spectra were obtained on solution samples (100 mM), and the quantitative results of free radicals were obtained using the standard DPPH. GC-MS measurements were obtained using TRACE 1300, ISQ 7000, Thermo Scientific. The NMR spectra were recorded on a Bruker AVANCE III 400 WB spectrometer.

Performance evaluation
Activity measurement. The decomposition of FA was conducted in a 0.25 L stainless-steel reactor (Model BS250, Shanghai LABE Instrument Co., Ltd.). The catalyst, with a loading density of approximately 0.24 mg·cm-2 (covering an area of ~0.3 cm2), was placed at the bottom of the reactor. After introducing 1 mL of liquid FA (Shanghai Aladdin Biochemical Technology Co., Ltd., UltraPure ChromTM, for HPLC, 99.9%), the reactor was evacuated and flushed with argon to ensure an inert atmosphere. The reaction system was heated using a programmed ramp-up protocol at a rate of 5 °C·min-1, followed by maintaining the desired reaction temperature for 1 h. Product analysis was performed using a gas chromatograph (GC-9080, Sun Corporation) equipped with a thermal conductivity detector (TCD). The rates of product evolution, turnover frequency (TOF), turnover number (TON), and selectivity were determined using the following formulas:

H2 evolution rate = Product yield per unit area of catalyst per hour (mol·cm-2·h-1) / Mass of catalyst per unit area (g·cm-2) (1)

Mass of catalyst per unit area = L × ν × 6.1 g·cm-3 × 1 cm2 (2)

Where the L is the length of GaN NWs, and the ν is denoted as the fill factor. According to the top-view SEM image of GaN NWs supported by Si (Fig. S4), the average L was estimated to be ~570 nm. By taking the density of GaN (6.1 g·cm-3) into the calculation, the catalyst mass per unit area is thus estimated to be 0.24 mg. The weight of Ni(Mn)-O-P was not taken into consideration owing to its trace amount (<0.01 mg·cm-2).

TOF = H2 production amount (μmol) / (Ni Content of immobilized Ni nanoparticles (μmol) × Reaction time (h)) (3)

TON = H2 production amount (μmol) / Ni Content of immobilized Ni nanoparticles (μmol) (4)

The optimal content of Ni over GaN NWs/Si was determined to be 0.23 μmol·cm-2, measured by ICP-AES.

Selectivity = H2 yield amount (μmol) / (H2 yield amount (μmol) + CO2 yield amount (μmol)) × 100% (5)

Durability test. A Ni(Mn)-O-P/GaN NWs wafer (≈0.3 cm2) was fixed at the bottom of the chamber. The reaction was operated for 24 h. After 1 cycle, the chamber was thoroughly purged with argon to completely replace the atmosphere, followed by the injection of 1 mL of FA. H2 was periodically measured using GC to test the catalytic activity.

Computational methods
DFT calculations. Density functional theory (DFT)55 calculations were performed using the Vienna Ab Initio Simulation Package 6.1.0 (VASP 6.1.0)56,57. The interaction between valence electrons and ionic cores was treated with the projector-augmented wave (PAW) method58. Exchange-correlation effects within the Kohn-Sham framework59 were described using the Perdew-Burke-Ernzerhof (PBE) functional under the generalized gradient approximation (GGA)60. A plane-wave basis set with a kinetic energy cutoff of 400 eV was used to expand the wavefunctions. For slab calculations, a 2×2×1 Gamma scheme k-point grid was employed to sample the Brillouin zone61. Geometry optimization was carried out with convergence thresholds set to 0.02 eV/Å for atomic forces and 10-4 eV for total energy.

Based on experimental identification of the m-plane of GaN, a GaN (100) surface was modeled using a 4×3 supercell consisting of four atomic layers to represent pristine GaN accurately. Ni-O/GaN, Ni-O-P/GaN, Ni(Mn)-O-P/GaN configurations were then generated by placing Ni6O9, Ni6O6P3, NiMnO6P1 clusters on the GaN (100) surface. To prevent interference from periodic images, a vacuum layer of at least 25 Å was applied perpendicular to the surface for all slab models, and in all three dimensions for nanoclusters. During structural relaxation, the bottom two layers of GaN were fixed in their bulk positions for slab simulations. The Gibbs free energy of adsorption (ΔG) was calculated using the following equation:

ΔG = Ead + ΔZPE - TΔS (6)

where Ead is the adsorption energy defined by:

Ead = E surface+adsorbate - E surface - E adsorbate (7)

ΔZPE and ΔS are the changes in zero-point energy and entropy during adsorption62,63.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The researchers investigated a precious metal-free heterogeneous catalytic system consisting of Ni(Mn)-O-P/GaN-NWs for the production of hydrogen (H2) from formic acid (FA) by making use of industrial waste heat. Their newly designed architecture showed a record TON of 5,023,060 moles of H2 per mole of Ni(Mn)-O-P running long-term operations of more than 4000 hours with temperatures ranging between 328 K and 348 K. With combined in-situ spectroscopy, isotopic labeling, and DFT calculations, the researchers could show that the interplay between Ni(Mn)-O-P and GaN facilitates the dehydrogenation of formic acid via an interesting hydrogen exchange mechanism with water. It was also shown that the developed architecture is CO insensitive and that anti-coking properties of the Ni(Mn)-O-P/GaN provide enormous stability. The stability exceeded by far that of known advanced noble metals.\nThe researchers also demonstrated the technical feasibility of on-demand H2 production from FA using low-grade industrial waste heat. Overall, this study demonstrated the importance of LHC-mediated hydrogen storage systems for the chemical transformation and for tackling climate change.\nI think the idea and technical implementation of the project involving hydrogen release from formic acid is fantastic. The catalytic system works very efficiently at moderate temperatures and is also highly selective. I am particularly impressed by the stability of the noble metal-free catalyst. The interpretation of the results using DFT calculations is also convincing and explains the measurement data.\nPerhaps the authors could point out, for the sake of completeness, that there have been successful experiments in homogeneous catalytic processes for the release of hydrogen from formic acid that have worked without noble metal complexes (e.g., with iron complexes). See ref DOI: 10.1126/science.1206613 and others.", "reviewer_2": "In the manuscript titled \"Highly Efficient, Selective, and Ultra-Stable Heterogeneous Thermal Catalysis for Noble-Metal-Free Hydrogen Production from Formic Acid\" Qiu et al. introduce a novel catalytic structure that combines manganese-doped nickel-phosphorus oxide with gallium nitride nanowires to facilitate efficient hydrogen production from formic acid. The catalyst reportedly achieves a record-high hydrogen output of nearly 30 mol H₂ per gram of catalyst per hour, with nearly 100% selectivity and a high turnover frequency at 150°C. Additionally, it demonstrates impressive stability, operating for over 4,000 hours under fluctuating temperatures and producing more than 5 million moles of hydrogen, which suggests potential for industrial waste heat utilization.\nHowever, some aspects of the results presented do not sufficiently substantiate the conclusions drawn, and comparisons between parameters appear somewhat inconsistent. Specifically, the thermal stability tests involve variations in reaction temperature up to three times, and the evaluation of industrial waste heat is somewhat vague, leading to results that may be challenging to reproduce and interpret robustly. Moreover, there are several inconsistencies throughout the manuscript that should be addressed before considering it for publication.\nGiven these concerns and the points outlined above, I recommend that the manuscript be rejected for publication in Nature Communications.\nTypos:\nFig. S6 HADDF-STEM image and diameter distribution of Ni(Mn)-O-P/GaN NWs. Please correct it.\nLine 172. The selectivity of N2 was sharply 173 improved from 49% up to 99% by loading Ni(Mn)-O-P nanoclusters. Please correct it by H2 selectivity.\n1. Although the introduction is well written, a real comparison with the most recent results obtained for the dehydrogenation of formic acid in liquid media is lacking. (Nature Communications | (2024) 15:8189,\n2. Furthermore, the authors claim in the introduction that “First, the well-defined 1D morphology with ultrahigh surface area is geometrically favorable for efficient exposure of active sites.” However, throughout the manuscript, neither the textural properties of the catalytic system nor the exposure of active sites have been evaluated. The evaluation of the specific surface area by BET analysis, as well as the exposed metal surface area by H2 chemisorption, should be performed on the catalyst.\n3. According to the deconvolution of the Ni 2p spectrum (XPS), for the different nickel species deposited on GaN, and although the authors have not added a table with the quantitative values obtained from the deconvolution for each species, (it should be added and discussed). It can be observed that the majority species in all cases is nickel oxide, a fact that also agrees with the binding energy in the O 1s spectrum, Figure 2g and h. However, the authors have found a lattice spacing of 0.28 nm, which they have assigned to Ni-P species, which are in the minority. How do the authors explain this fact? Have they performed TEM microscopy analysis of the reduced catalyst? How do these nanoclusters evolve when exposed to reducing atmospheres at high temperatures? A more detailed explanation should be added to the manuscript.\n4. The authors demonstrate the electronic interaction between GaN and Ni(Mn)-O-P by positive shifting (0.23 eV) in the Ga 2p and N 1s peaks. The authors should add the carbon 1s (C1s) spectrum of both materials to demonstrate the positive shifting, Figure 11S.\n5. The term \"Turnover Frequency\" (TOF) is typically used to evaluate a catalyst's activity under steady-state, continuous flow conditions where the reaction rate is constant over time. In batch reactions, the reaction rate and catalyst activity can vary significantly during the process due to factors like substrate depletion, product accumulation, temperature changes, and catalyst deactivation. Because of these dynamic changes, it is challenging to accurately determine a consistent TOF in batch conditions. Instead, activity is usually assessed using initial rate measurements or total turnover numbers over the entire reaction period, which do not directly reflect the catalyst's intrinsic activity at any specific moment.\n6. The authors conclude from Figure 3a, “Particularly, the H2 activity of NiOx/GaN NWs reaches 0.88 mol∙gcat-1∙h-1, even surpassing state-of-the-art noble metals tested.” However, they do not show the metal dispersion and exposure of the active phase in each of the different catalysts, so making comparisons between them is totally unfair and adds no scientific value.\n7. According to the unit of measurement of catalytic activity used by the authors for the conversion of formic acid to hydrogen, Figure S12. How do the authors control agitation within the batch reactor, with such a small volume of formic acid in such a large reactor? Have the authors evaluated the possible diffusion problems that the reactor could present?\n8. Why do the authors compare the catalytic results obtained in terms of TOF, assuming nickel loading as the only active phase, Figure S13? If in Figure 3c, the authors demonstrate that GaN exhibits catalytic activity on its own. Similarly, to rule out that the different transition metals used to dope the Ni-O-P nanoclusters, Figure 3a, do not exhibit intrinsic catalytic activity, a nickel-free blank should be tested and included.\n9. Similarly, the authors claims: “Without GaN, Ni(Mn)-O-P was practically inactive for FA decomposition, suggesting the critical synergy of GaN with Ni(Mn)-O-P in the production of H2 from FA (Fig. S14).” However, they show in the in-situ FTIR test that GaN alone is active at 60ºC. Once again, to prove this conclusion, a blank using GaN must be tested and demonstrated.\n10. Authors should add the assignments of all peaks appearing in the chromatogram in Figure S16, in addition to the subscripts a, b, and c used.\n11. Why has the reaction temperature been modified in the thermal stability test? Why do they start the test at 55°C, then raise it to 75°C, and then lower it back to 65°C? In my opinion, the thermal stability results for the catalyst are inconclusive and therefore cannot be compared with the literature. A thermal stability test without changing the temperature should be performed.\n12. The benchmarking of catalysts performed by the authors in Figure 3g is meaningless based on the way in which the authors calculate the TOF. For a real comparison with the published results, the authors should express the activity in terms of H2 evolution rate.\n13. Did the authors find leaching of the Ni(Mn)-O-P nanocluster after the stability test?\n14. In Figure S18, the authors should invert the x-axis (Wavenumbers).\n15. The authors claim in line 213 that “As shown in Fig. S18, the in situ DRIFTS characteristic peak,” however, in Figure S18, the authors refer to the test as in situ FTIR and present the results in transmittance. Is it a DRIFTS or FTIR test? Check it also in the experimental section.\n16. If measured under diffusion conditions rather than transmittance, the results must be expressed in Kubelba-Munt.\n17. Authors should include the experimental data from the H-NMR test. Why did they evaluate a mixture of sodium formate and formic acid in this test? This will cause a shift in the proton peaks due to the low electronegativity compared to that of the proton. All the peaks exhibited on the H-NMR spectra should be assigned.\n18. The authors claim, “In contrast, as an evident indicator of coking, graphic carbon was obviously observed on the Pd/GaN NWs surface by XPS (Fig. S22) characterizations after 200 hours of thermal catalysis of FA decomposition.” However, they do not show the C 1s peak of the catalysts before reaction, nor do they provide a quantitative analysis to demonstrate an increase in surface carbon concentration. This sentence is meaningless and should be removed from the text.\nFor this reason, the work might not be published in Nature communications.", "reviewer_3": "This manuscript reports manganese-doped nickel-phosphorus oxide supported on GaN nanowires as a catalyst for hydrogen production from formic acid. The authors claim record activity, selectivity, and stability, supported by spectroscopic characterization, DFT modeling, and a limited pilot-scale demonstration. While the topic is timely and the approach of developing noble-metal-free catalysts is potentially impactful, the current version of the manuscript suffers from major shortcomings in scientific rigor, data clarity, experimental methodology, and overall presentation. In its current form, the manuscript cannot be recommended for publication.\n1. The authors claim that the TOF for their catalyst is better than that of state-of-the-art homogeneous and heterogeneous catalysts. However, this statement is not correct as most homogeneous catalytic systems outperform significantly and show very high TOFs in comparison. (see Advanced Energy Materials 2022, 12, 2103799 and Energy & Fuels 2023, 37, 17075-17093)\n2. The significance of the manuscript primarily hinges on the performance of the catalysts. However, there are substantial errors in the calculation of product yields, TONs, and TOFs. Accurate recalculation can reveal that the overall performance of the catalyst may remain mediocre. Furthermore, the calculation of TOF is based on artificially low catalyst loading, resulting in inflated activity figures.\n3. The calculation of the H2 evolution rate does not seem to be appropriate. The authors have carried out thermal catalysis, and therefore, the overall catalyst weight has to be considered instead of metal deposition, if they need to provide the yield per gram of catalyst (molH2 gcat−1 h−1). If not, it is advisable to provide the yield values per active site instead.\n4. No information was provided about the flow rate of formic acid or the catalyst amount used in long-term stability tests (4000 h). The number 5,023,060 mole H2 is not logical without the reaction details.\n5. The selectivity of the catalysts remains >99% despite the significant changes in the morphology of the catalysts. This seems highly unlikely in heterogeneous catalysts. The authors need to provide more detailed characterization to support these results.\n6. The authors have not provided formic acid conversion values. CO2 selectivity and yields are neglected. It is important to check the mass balance of the reaction.\n7. Catalyst performance was presented as H2 evolution rate per gram of catalyst. This comparison is not ideal as noble metals, with high atomic mass, obviously show a low evolution rate.\n8. The manuscript contains repeated grammatical and presentation errors, undermining its professional standard. Examples include mislabeling \"N2\" instead of \"H2,\" incorrect or ambiguous references to photocatalyst mass, incomplete figure captions, etc.\n9. The authors could clarify where to source or how to purify formic acid to have >99.9% purity."}, "author_response": "Response Letter\nManuscript ID: NCOMMS-25-55883A\nTitle: “Highly Efficient, Selective, and Ultra-Stable Heterogeneous Thermal\nCatalysis for Noble-Metal-Free Hydrogen Production from Formic Acid”\nWe thank the reviewer a lot for the constructive comments that helped us to improve the quality\nof the manuscript. We have meticulously addressed all the referee’s concerns, and as such,\ncompleted a comprehensive revision of the manuscript. The change has been highlighted by the\nyellow background.\nReviewer #1\n:\nThe researchers investigated a precious metal-free heterogeneous catalytic system consisting of\nNi(Mn)-O-P/GaN-NWs for the production of hydrogen (H ) from formic acid (FA) by making use\n2\nof industrial waste heat. Their newly designed architecture showed a record TON of 5,023,060\nmoles of H per mole of Ni(Mn)-O-P running long-term operations of more than 4000 hours with\n2\ntemperatures ranging between 328 K and 348 K. With combined in-situ spectroscopy, isotopic\nlabeling, and DFT calculations, the researchers could show that the interplay between Ni(Mn)-O-\nP and GaN facilitates the dehydrogenation of formic acid via an interesting hydrogen exchange\nmechanism with water. It was also shown that the developed architecture is CO insensitive and\nthat anti-coking properties of the Ni(Mn)-O-P/GaN provide enormous stability. The stability\nexceeded by far that of known advanced noble metals.\nThe researchers also demonstrated the technical feasibility of on-demand H production from FA\n2\nusing low-grade industrial waste heat. Overall, this study demonstrated the importance of LHC-\nmediated hydrogen storage systems for the chemical transformation and for tackling climate\nchange.\nI think the idea and technical implementation of the project involving hydrogen release from\nformic acid is fantastic. The catalytic system works very efficiently at moderate temperatures and\nis also highly selective. I am particularly impressed by the stability of the noble metal-free catalyst.\nThe interpretation of the results using DFT calculations is also convincing and explains the\nmeasurement data.\nPerhaps the authors could point out, for the sake of completeness, that there have been successful\nexperiments in homogeneous catalytic processes for the release of hydrogen from formic acid that\nhave worked without noble metal complexes (e.g., with iron complexes). See ref DOI:\n10.1126/science.1206613 and others.\nResponse We thank the reviewer a lot for the positive comments and constructive suggestions.\nBased on the valuable comments, we have included the related research with regard to\nhomogeneous hydrogen production from formic acid without noble metal complexes in the revised\nmanuscript as follows: “although some studies have reported the use of earth-rich metals as\ncatalysts in both homogeneous and heterogeneous systems29, H production from FA are highly\n2\ndependent on noble metals, which are limited by their high cost and low abundance13,30.”\n(Please see Page 3-4 in the Manuscript)\nReviewer #2\nIn the manuscript titled “Highly Efficient, Selective, and Ultra-Stable Heterogeneous Thermal\nCatalysis for Noble-Metal-Free Hydrogen Production from Formic Acid” Qiu et al. introduce a\nnovel catalytic structure that combines manganese-doped nickel-phosphorus oxide with gallium\nnitride nanowires to facilitate efficient hydrogen production from formic acid. The catalyst\nreportedly achieves a record-high hydrogen output of nearly 30 mol H per gram of catalyst per\n2\nhour, with nearly 100% selectivity and a high turnover frequency at 150 ℃. Additionally, it\ndemonstrates impressive stability, operating for over 4,000 hours under fluctuating temperatures\nand producing more than 5 million moles of hydrogen, which suggests potential for industrial\nwaste heat utilization.\nHowever, some aspects of the results presented do not sufficiently substantiate the conclusions\ndrawn, and comparisons between parameters appear somewhat inconsistent. Specifically, the\nthermal stability tests involve variations in reaction temperature up to three times, and the\nevaluation of industrial waste heat is somewhat vague, leading to results that may be challenging\nto reproduce and interpret robustly. Moreover, there are several inconsistencies throughout the\nmanuscript that should be addressed before considering it for publication.\nGiven these concerns and the points outlined above, I recommend that the manuscript be rejected\nfor publication in Nature Communications.\nResponse We greatly appreciate the referee for the positive comments “introduce a novel\ncatalytic structure that combines manganese-doped nickel-phosphorus oxide with gallium\nnitride nanowires to facilitate efficient hydrogen production from formic acid. The catalyst\nreportedly achieves a record-high hydrogen output of nearly 30 mol H per gram of catalyst\n2\nper hour, with nearly 100% selectivity and a high turnover frequency at 150 ℃. Additionally,\nit demonstrates impressive stability, operating for over 4,000 hours under fluctuating\ntemperatures and producing more than 5 million moles of hydrogen, which suggests\npotential for industrial waste heat utilization.” More importantly, we thank the referee a lot for\nthe constructive suggestions that helped us to improve the quality of the manuscript. We have done\nour best to address the referee’s concerns. Please see the details below.\nComment 1 Typos:\n(1) Fig. S6 HADDF-STEM image and diameter distribution of Ni(Mn)-O-P/GaN NWs. Please\ncorrect it.\n(2) Line 172. The selectivity of N was sharply improved from 49% up to 99% by loading Ni(Mn)-\nhas been revised to: “HAADF-STEM image and diameter distribution of Ni(Mn)-O-P/GaN NWs”.\nThe sentence has been corrected to: “Compared with pure GaN NWs, the selectivity of H was\n2\nsharply improved from 49% up to 99% by loading Ni(Mn)-O-P nanoclusters (Fig. 3c).” in the\nrevised manuscript. We appreciate the careful review again.\n(Please see Page 8 in the Manuscript, and Page 11 in the Supplementary Information)\nComment 2 Although the introduction is well written, a real comparison with the most recent\nresults obtained for the dehydrogenation of formic acid in liquid media is lacking. (Nature\nCommunications | (2024) 15:8189,\nResponse We thank the reviewer very much for bringing this important literature to our attention.\nWe have included the discussion about the most recent results obtained for the dehydrogenation\nof formic acid in liquid media in the revised Introduction section (ref [26]): “Thus far, a number\nof supported metals heterogeneous catalysts, including single atom catalysts19-21, metal\nnanoparticles (NPs)22-25, combination of single atoms and clusters26, and multi-metallic alloy27,28\nhave been used for FA decomposition.”, Fig 3g and Table S3:\nTable S3 Summary of state-of-the-art catalysts for HCOOH decomposition toward H .\nCatalyst T (℃) Stability (h) Ref\n(h-1) (mmol·g -1·h-1)\ncat\n150 31019.2 29920\nThis\nNi(Mn)-O-P/GaN NWs ~4000\nwork\n60 3932.68 3790\nCo-SAs/NPs@NC 100 62.6 5 [1]\nNi Pd Ups T 954.3 3 [2]\n0.4 0.6 Room\nAg–Pd core–shell\nT ＜200 ＜10 [3]\nRoom\nnanocatalyst\nPd/C ZnCl 50 76 [4]\nvin. 2\nPdAg/SBA-15-Amine 70 65 [5]\nTi C T MXenes 80 365 [6]\n3 2 x\n[FeCl(PP )]BF 80 9425 16 [7]\n3 4\nCo-N-C(SAC)-1000 100 1053.6 120 [8]\nPt-Mo/NC 115 ~2200 11441.5 50 [9]\n0.07\nPd-PCN-350R 120 65.2 360 [10]\n*Unit Conversion and Notes\nAll comparisons are assumed to be for ideal gases under standard conditions, the unit is unified through the\nfollowing formula: 1 mLH = 0.0446 mmolH ; 1 mol -1 = 1/M g -1, M (g/mol) is the relative atomic mass\n2 2 cat cat cat cat\nof the catalyst; 1 h-1(TOF) = 3600 s-1(TOF)\n[1] Co-SAs/NPs@NC: 1403.8 mL·g −1·h−1 = 62.6 mmol·g −1·h−1\ncat cat\n[8] Co-N-C(SAC)-1000: 23.6 L·g -1h-1 = 1053.6 mmol·g −1·h−1\nCo Co\n[9] Pt-Mo/NC0.07: 0.62 mol mol −1 s−1 = 11441.5 mmol·g −1·h−1\nHCOOH Pt Pt\n[10] Pd-PCN-350R: 1.46 L g −1·h−1 = 65.2 mmol·g −1·h−1\ncat cat\nFig. 3 Performance of heterogeneous thermal catalysis of FA decomposition. (g) Performance\ncomparison of state-of-the-art thermal catalysts of FA decomposition.\n(Please see Page 3, 9 in the Manuscript, and Page 4 in the Supplementary Information)\nComment 3 Furthermore, the authors claim in the introduction that “First, the well-defined 1D\nmorphology with ultrahigh surface area is geometrically favorable for efficient exposure of\nactive sites.” However, throughout the manuscript, neither the textural properties of the catalytic\nsystem nor the exposure of active sites have been evaluated. The evaluation of the specific surface\narea by BET analysis, as well as the exposed metal surface area by H chemisorption, should be\n2\nperformed on the catalyst.\nResponse We sincerely thank the reviewer for this critical and constructive comment. We fully\nagree with the reviewer that the textual properties and active site exposure are crucial to support\nour claim. Based on the referee’s valuable comment, BET analysis and H chemisorption test were\n2\nperformed on the catalyst. As measured by BET characterization, 1D GaN NWs demonstrated\nhigh surface area (158.06 m2·g-1). It is conducive to the dispersion of active sites, which can be\nverified by the H chemisorption (Dispersion of exposed metals is 50.80%). (Fig. R1)”\nspecies deposited on GaN, and although the authors have not added a table with the quantitative\nvalues obtained from the deconvolution for each species, (it should be added and discussed). It can\nbe observed that the majority species in all cases is nickel oxide, a fact that also agrees with the\nbinding energy in the O 1s spectrum, Fig. 2g and h. However, the authors have found a lattice\nspacing of 0.28 nm, which they have assigned to Ni-P species, which are in the minority. How do\nthe authors explain this fact? Have they performed TEM microscopy analysis of the reduced\ncatalyst? How do these nanoclusters evolve when exposed to reducing atmospheres at high\ntemperatures? A more detailed explanation should be added to the manuscript.\nResponse We are grateful to the reviewer for this insightful comment.\nBased on the referee’s valuable comment, we have included the quantitative values of Ni species\nin the revised manuscript (Table S1). It can be seen that Ni-O species are indeed predominant on\nthe catalyst surface.\nTable S1 Inverse convolution quantitative value of Ni 2p\nXPS environment Ratio (%)\nNi-O 71.3\nNi(Mn)-O-P/GaN NWs Ni-P 8.9\nNi-Pox 19.8\nNi-O 76.0\nNi-O-P/GaN NWs Ni-P 6.5\nNi-Pox 17.5\nNi-O/GaN NWs\nNi-O 100\nIn the previous manuscript, lattice fringe of Ni-P was preferentially shown to highlight the\nsuccessful incorporation of P. In fact, the lattice spacing of Ni-O (0.24 nm) are broadly observed\nin the as-prepared catalyst. Based on the referee’s comment, we have updated the STEM image\n(Fig.2b) to comprehensively present the structural information of the catalyst in the revised\nmanuscript as follows: “High-Resolution Scanning Transmission Electron Microscopy (HR-\nSTEM) image (Fig. 2b) showed the lattice spacing of 0.26 nm which was attributed to the (002)\nplane of GaN42,43, indicating the growth direction of the nanowires along the c-axis. It is consistent\nwith the X-ray Diffraction (XRD) patterns (Fig. S7) and Raman spectra44 (Fig. S8). The lattice\nspacing of 0.24 nm and 0.206 nm could be indexed to the (111) plane of NiO and (212) plane of\nNiP.”\nFig. 2 Assembly and characterization of Ni(Mn)-O-P/GaN NWs. (b) HR-STEM images of\nNi(Mn)-O-P/GaN NWs.\nFurthermore, we thank the reviewer for raising this important question regarding the\nevolution of nanoclusters during the reaction. In this study, the reaction was conducted below\n150 °C in an atmosphere consisting of formic acid vapor diluted in argon. In response to the\nreviewer’s' concern, we have provided morphological and valence state information of the\nnanoparticles after stability test. As characterized by TEM and XPS techniques (Fig. S21), it is\ndiscovered that the nanoclusters remain stable and do not undergo significant change during the\nreaction.\nFig. S21 (a) HAADF-TEM image of Ni(Mn)-O-P/GaN NWs after stability test and (b) High-\nresolution XPS spectra of Ni 2p of Ni(Mn)-O-P/GaN NWs before and after stability test.\nWe hope that this explanation can well address the reviewer’s concern.\n(Please see Page 6-7 in the Manuscript, Page 2 and 26 in the Supplementary Information)\nComment 5 The authors demonstrate the electronic interaction between GaN and Ni(Mn)-O-P by\npositive shifting (0.23 eV) in the Ga 2p and N 1s peaks. The authors should add the carbon 1s (C\n1s) spectrum of both materials to demonstrate the positive shifting, Fig. S11.\nResponse We thank the reviewer again. Based on the referee’s comment, C 1s spectrum of both\nmaterials has been included to demonstrate the positive shifting (Fig. S11a)\nFig. S11 High-resolution XPS spectra of (a) C 1s of bare GaN NWs, Ni-O/GaN NWs, Ni-O-P/GaN\nNWs and Ni(Mn)-O-P/GaN NWs\n(Please see Page 16 in the Supplementary Information)\nComment 6 The term “Turnover Frequency” (TOF) is typically used to evaluate a catalyst’s\nactivity under steady-state, continuous flow conditions where the reaction rate is constant over\ntime. In batch reactions, the reaction rate and catalyst activity can vary significantly during the\nprocess due to factors like substrate depletion, product accumulation, temperature changes, and\ncatalyst deactivation. Because of these dynamic changes, it is challenging to accurately determine\na consistent TOF in batch conditions. Instead, activity is usually assessed using initial rate\nmeasurements or total turnover numbers over the entire reaction period, which do not directly\nreflect the catalyst's intrinsic activity at any specific moment.\nResponse We thank the reviewer for raising this important concern regarding to Turnover\nFrequency (TOF) in catalytic studies. We fully acknowledge the reviewer’s concern that reaction\nconditions in a batch reactor are dynamic, and the theoretically defined TOF is most precise under\nsteady-state, continuous-flow conditions.\nHowever, we would like to respectfully clarify and justify our use of TOF in this context. Based\non previous studies [Nature 2023, 613, 66; Nat. Catal. 2023, 6, 987; Nat. Commun. 2025, 16, 1002.\nNat. Commun. 2024, 15, 7393; PNAS, 2022, 119, e2121174119; Angew Chem Int. Edit. 2024,\ne202400011; Angew. Chem. Int. Edit. 2025, e202511886.], TOF and TON were also broadly used\nin batch reactor conditions. Considering that, compared with Ni(Mn)-O-P/GaN NWs/Si wafer (Fig.\nS13), the catalytic capabilities of pure GaN NWs/Si wafer and Mn-O-P/GaN NWs/Si wafer for H\n2\nare extremely limited (< 4.5%), it is rationalized that nickel is the active site of the reaction. From\non, TOF and TON are calculated from the nickel loadings calculated by inductively coupled\nplasma atomic emission spectrometry (ICP-AES):\nH production amount (μmol)\nNi Content of immobilized Ni nanoparticles (μmol)  Reaction time (h)\nH production amount (μmol)\nNi Content of immobilized Ni nanoparticles (μmol)\nThe optimal content of Ni over GaN NWs/Si was determined to be 0.23 μmol·cm-2 measured by\nICP-AES.\nFig. S13 The activity of FA decomposition of Ni(Mn)-O-P/GaN NWs and various Ni-free\ncatalysts at 150 °C.\nWe hope this clarification addresses the reviewer's concern.\n(Please see Page 20 in the Manuscript and Page 18 in the Supplementary Information)\nComment 7 The authors conclude from Fig. 3a, “Particularly, the H activity of NiO /GaN\n2 x\nNWs reaches 0.88 mol∙g -1∙h-1, even surpassing state-of-the-art noble metals tested.”\ncat\nHowever, they do not show the metal dispersion and exposure of the active phase in each of the\ndifferent catalysts, so making comparisons between them is totally unfair and adds no scientific\nvalue.\nResponse: We sincerely thank the reviewer for this important comment. Based on the reviewer’s\ncomment, we have shown the metal dispersion and exposure of the active phase in each of the\ndifferent catalysts to make the comparison as fair as possible (Table S2 and Fig. S14).\nFig.S14 HAADF-STEM image and diameter distribution of (a) Rh/GaN NWs, (b) Pd/GaN NWs,\n(c) Pt/GaN NWs, (d) Ru/GaN NWs, (e) Au/GaN NWs, and (f) Ir/GaN NWs.\nTable S2 The loaded amount of different cocatalysts on GaN surface\nCatalysts Ni Rh Pd Pt Ru Au Ir\nloaded amount(µmol·cm-2) 0.230 0.078 0.035 0.038 0.021 0.113 0.086\nBased on the results of ICP, the TOF was calculated and the results were shown in Fig. S15. To\nmake the conclusion more rigorous, the sentence has been changed to “As seen from Fig. 3a and\nS13, the influence of co-catalysts on FA dehydrogenation is significant. Particularly, the H activity\n2\nof Ni-O/GaN NWs reaches 0.88 mol∙g -1∙h-1. The introduction of phosphorus can further improve\ncat\nthe activity up to 3.20 mol∙g -1∙h-1, even surpassing some noble metals tested (Table S2, Fig. S14\ncat\nand S15).”in the revised manuscript.\nFig. S15 The TOF of FA decomposition of various catalysts at 150 °C.\n(Please see Page 7-8 in the Manuscript, Page 3, 19-20 in Supplementary Information)\nComment 8 According to the unit of measurement of catalytic activity used by the authors for the\nconversion of formic acid to hydrogen, Fig. S12. How do the authors control agitation within the\nbatch reactor, with such a small volume of formic acid in such a large reactor? Have the authors\nevaluated the possible diffusion problems that the reactor could present?\nResponse: We thank the reviewer again. We agree with the referee that the diffusion problem may\naffect the reaction. However, in this study, formic acid was evaporated at first, followed by\ndehydrogenation to produce via a gas-solid reaction process. Further, the reactor was not equipped\nwith a stirrer. Therefore, agitation was not provided. Based on the referee’s suggestion, we will\nfurther improve the diffusion issue by optimizing the chamber design.\nComment 9 Why do the authors compare the catalytic results obtained in terms of TOF, assuming\nnickel loading as the only active phase, Fig. S13 (Fig. S16 in revised Supplementary\nInformation)? If in Fig. 3c, the authors demonstrate that GaN exhibits catalytic activity on its\nown. Similarly, to rule out that the different transition metals used to dope the Ni-O-P nanoclusters,\nFig. 3a, do not exhibit intrinsic catalytic activity, a nickel-free blank should be tested and included.\nResponse We thank the reviewer for this insightful comment. The TOF was calculated based on\nNi loading because the intrinsic activity of bare GaN NWs was negligible compared to that of\nNi(Mn)-O-P/GaN NWs. In the revised manuscript, we have included the “Evolution rate” in Fig.\n3c, which confirmed that its contribution to the overall activity is approximately only 4.4% of that\nof the Ni(Mn)-O-P/GaN NWs.\nFig. 3 Performance of heterogeneous thermal catalysis of FA decomposition. (c) The activity\nof FA decomposition over GaN NWs and Ni(Mn)-O-P/GaN NWs at 150 °C.\nBased on the referee's comment, a nickel-free blank was tested. The catalytic activity of the nickel\nfree catalyst for formic acid dehydrogenation did not show significant improvement compared to\nbare GaN NWs, indicating that nickel is the primary active species for the reaction. (Fig. S13)\nFig. S13 The activity of FA decomposition of Ni-O-P/GaN NWs and various Ni-free catalysts at\n150 °C.\n(Please see Page 9 in the Manuscript, Page 18 in the Supplementary Information)\nComment 10 Similarly, the authors claims: “Without GaN, Ni(Mn)-O-P was practically\ninactive for FA decomposition, suggesting the critical synergy of GaN with Ni(Mn)-O-P in\nthe production of H from FA (Fig. S14 (Fig.S18 in revised Supplementary Information)).”;\nthis conclusion, a blank using GaN must be tested and demonstrated.\nResponse We sincerely thank the reviewer for raising this important concern. Based on the\nreferee’s comment, a blank using GaN was tested. As mentioned in Comment 9, we have added\nthe activity of GaN NWs in the revised Manuscript (Fig. 3c). It was found that the activity of bare\nGaN NWs was two orders of magnitude lower than that of Ni(Mn)-O-P/GaN NWs. Moreover, in-\nsitu FTIR characterization showed that the characteristic peak signals of HCOO* over bare GaN\nNWs, which are much weaker than that of Ni(Mn)-O-P/GaN NWs (Fig. S23, 24). Based on the\ndiscussion above, it is rationalized that the synergy between Ni(Mn)-O-P and GaN NWs is critical\nfor achieving the distinct activity.\nFig. 3 Performance of heterogeneous thermal catalysis of FA decomposition. (c) The activity\nof FA decomposition over GaN NWs and Ni(Mn)-O-P/GaN NWs at 150 °C.\nFig. S23 In-situ FTIR characterizations of FA decomposition over Ni(Mn)-O-P/GaN NWs (left)\nand GaN NWs (right) under 60 °C.\nFig. S24 Diagram of the signal slopes of FTIR spectra for HCOO* arising from the O-H\ndissociation of HCOO-H.\n(Please see Page 9 in the Manuscript, Page 28-29 in the Supplementary Information)\nComment 11 Authors should add the assignments of all peaks appearing in the chromatogram in\nFig. S16 (Fig.S20 in revised Supplementary Information), in addition to the subscripts a, b, and\nc used.\nResponse We thank the reviewer for this suggestion. Based on the referee’s suggestion, we have\nadded the assignments of all peaks in the chromatogram (Fig. S20). Different types of\nchromatographic columns were labeled accordingly in the legend.\nFig. S20 GC spectra of different products of thermo-catalytic FA decomposition in one hour over\nthe tested Ni(Mn)-O-P/GaN NWs after 4000 hours of long-term operation. (a) Flame ionization\ndetector 1, (b) Flame ionization detector 2 and (c) thermal conductivity detector\n(Please see Page 25 in the Supplementary Information)\nComment 12 Why has the reaction temperature been modified in the thermal stability test? Why\ndo they start the test at 55 ℃, then raise it to 75 ℃, and then lower it back to 65 ℃? In my opinion,\nthe thermal stability results for the catalyst are inconclusive and therefore cannot be compared with\nthe literature. A thermal stability test without changing the temperature should be performed.\nResponse We appreciate the reviewer’s comment regarding the temperature variations in the long-\nterm stability test. Herein, the varied temperatures (55 °C → 75 °C → 65 °C) were employed to\nsimulate the temperature fluctuations that often occur during real industrial operation, aiming to\ntest the practical viability of the as-designed catalyst for formic acid dehydrogenation using\nindustrial heat waste. This approach allows us to rigorously evaluate the catalyst's resilience and\nstability under more realistic and potentially harsh conditions, rather than under idealized constant\ntemperatures. Each temperature stage was maintained for an extended period (1000-2000 hours)\nto ensure a meaningful assessment of stability at each condition. We believe this method provides\na more comprehensive and industrially relevant demonstration of the catalyst's robust stability\ncompared to a single fixed-temperature test.\nComment 13 The benchmarking of catalysts performed by the authors in Fig. 3g is meaningless\nbased on the way in which the authors calculate the TOF. For a real comparison with the published\nresults, the authors should express the activity in terms of H evolution rate.\n2\nrate was used to express the activity. Please see the change in the revised Fig. 3g.\nFig. 3 Performance of heterogeneous thermal catalysis of FA decomposition. (g) Performance\ncomparison of state-of-the-art thermal catalysts of FA decomposition.\n(Please see Page 9 in the Manuscript)\nComment 14 Did the authors find leaching of the Ni(Mn)-O-P nanocluster after the stability test?\nResponse We thank the reviewer a lot. Leaching of the Ni(Mn)-O-P nanocluster was not evidently\nobserved after the stability. As shown in Fig. S21a, the nanoclusters remained attached to the\nsurface of GaN NWs even after a 4000 h stability test. Moreover, Through ICP-AES testing, we\ndid not detect leached nanoclusters in the reactants.\nFig. S21 (a) HAADF-TEM image of Ni(Mn)-O-P/GaN NWs after stability test\n(Please see Page 26 in the Supplementary Information)\nComment 15 In Fig. S18 (Fig. S23 in revised Supplementary Information), the authors should\ninvert the x-axis (Wavenumbers).\nResponse We thank the reviewer very much. Based on the referee’s comment, the x-axis\n(Wavenumbers) in Fig. 4b and S23 has been inverted in the revised manuscript:\nFig. 4 In-situ spectroscopic characterizations of heterogeneous catalysis of FA decomposition\nover Ni(Mn)-O-P/GaN NWs. (b) In-situ FTIR characterizations of neat formic acid and water-\nassisted FA decomposition over Ni(Mn)-O-P/GaN NWs under 60 °C.\nFig. S23 In-situ FTIR characterizations of FA decomposition over Ni(Mn)-O-P/GaN NWs (left)\nand GaN NWs (right) under 60 °C.\n(Please see Page 12 in the Manuscript, Page 28 in the Supplementary Information)\nComment 16 The authors claim in line 213 that “As shown in Fig. S18 (Fig.S22 in revised\nSupplementary Information), the in situ DRIFTS characteristic peak”; however, in Fig. S18\n(Fig.S22 in revised Supplementary Information), the authors refer to the test as in situ FTIR\nand present the results in transmittance. Is it a DRIFTS or FTIR test? Check it also in the\nexperimental section.\nResponse We thank the reviewer for bringing this issue to our attention. As matter of fact, the\nmeasurement was performed using in situ FTIR spectroscopy. Based on the referee’s, we have\nrevised the related demonstration through the entire manuscript. “To unravel the reaction\nmechanism at the molecular level, in-situ Fourier Transform Infrared Spectroscopy (FTIR), and\nelectron paramagnetic resonance (EPR) characterizations were collectively carried out to\ninvestigate the key intermediates of FA decomposition.”\n(Please see Page 10 in the Manuscript)\nComment 17 If measured under diffusion conditions rather than transmittance, the results must\nbe expressed in Kubelba-Munt.\nResponse We thank the reviewer again. As clarified in our response to Comment 16, the spectra\nwere acquired in transmission mode using in situ FTIR. Therefore, the data is appropriately\npresented in transmittance.\nComment 18 Authors should include the experimental data from the H-NMR test. Why did they\nevaluate a mixture of sodium formate and formic acid in this test? This will cause a shift in the\nproton peaks due to the low electronegativity compared to that of the proton. All the peaks\nexhibited on the H-NMR spectra should be assigned.\nResponse We thank the referee for bringing this error to our attention and we sincerely apologize\nfor the mistake. The reaction system does not contain sodium formate. We have thoroughly\ncorrected this mistake in the revised manuscript. The H-NMR spectrum has been revised; the\nlegend has also been updated accordingly.\nFig. 4 (c) 1H-NMR spectra of the mixture of HCOOH+ H O over Ni(Mn)-O-P/GaN NWs.\n2\n(Please see Page 12 in the Manuscript)\nComment 19 The authors claim, “In contrast, as an evident indicator of coking, graphic carbon\nwas obviously observed on the Pd/GaN NWs surface by XPS (Fig. S22 (Fig.S26 in revised\nSupplementary Information)) characterizations after 200 hours of thermal catalysis of FA\ndecomposition.”; However, they do not show the C 1s peak of the catalysts before reaction, nor do\nthey provide a quantitative analysis to demonstrate an increase in surface carbon concentration.\nThis sentence is meaningless and should be removed from the text.\nResponse We appreciate the reviewer’s valuable comment. As suggested, we have included the C\n1s spectra of the fresh Pd/GaN NWs catalyst (0 h) alongside with the spectra after 200 h of reaction\n(Fig.S26). It is clearly seen that compared to the fresh catalyst, the used catalysts show a significant\nincrease in surface carbon concentration, indicating the accumulation of coke. Based on the\nreferee’s valuable comment, in the revised manuscript, we have provided a quantitative analysis\nto demonstrate an increase in surface carbon concentration (Fig. S26b) as below: “In contrast, the\nprogressive changes in the C 1s spectra (Fig. S26), combined with Raman spectroscopy (Fig. 4i),\ndemonstrate the evolution of coking over Pd/GaN NWs after 200 h of thermal catalysis of FA\ndecomposition.”\nFig. S26 (a) High-resolution XPS spectra of C 1s of Pd/GaN NWs after 200 h of stability testing\nand (b) quantitative analysis of C 1s peak.\n(Please see Page 11 in the Manuscript, Page 31 in the Supplementary Information)\nReviewer #3\n:\nThis manuscript reports manganese-doped nickel-phosphorus oxide supported on GaN nanowires\nas a catalyst for hydrogen production from formic acid. The authors claim record activity,\nselectivity, and stability, supported by spectroscopic characterization, DFT modeling, and a limited\npilot-scale demonstration. While the topic is timely and the approach of developing noble-metal-\nfree catalysts is potentially impactful, the current version of the manuscript suffers from major\nshortcomings in scientific rigor, data clarity, experimental methodology, and overall presentation.\nIn its current form, the manuscript cannot be recommended for publication.\nResponse We thank the reviewer a lot for the positive comments and constructive suggestions.\nWe have carefully responded to the reviewers' comments as below.\nComment 1 The authors claim that the TOF for their catalyst is better than that of state-of-the-art\nhomogeneous and heterogeneous catalysts. However, this statement is not correct as most\nhomogeneous catalytic systems outperform significantly and show very high TOFs in comparison.\n(see Advanced Energy Materials 2022, 12, 2103799 and Energy & Fuels 2023, 37, 17075-17093)\nResponse We thank the reviewer for bringing this important reference to our attention. Based on\nthe referee’s comment, we have updated the claim about TOF to make the demonstration more\nscientifically as below: “The as-designed Ni(Mn)-O-P/GaN NWs delivers an impressive hydrogen\nproduction activity of 29.92 mol H ·g -1·h-1 with nearly 100% selectivity and a high turnover\n2 cat\nfrequency (TOF) of 31,019.2 h-1 at 150 °C, outperforming most of heterogeneous catalysts.” and\n“Benefitting from the high atom efficiency of the catalyst, a record-high TOF of 31019.2 h-1 was\nobtained for Ni(Mn)-O-P/GaN NWs, far outperforming most of heterogeneous catalysts.”\n(Please see Page 2, 4 in the Manuscript)\nComment 2 The significance of the manuscript primarily hinges on the performance of the\ncatalysts. However, there are substantial errors in the calculation of product yields, TONs, and\nTOFs. Accurate recalculation can reveal that the overall performance of the catalyst may remain\nmediocre. Furthermore, the calculation of TOF is based on artificially low catalyst loading,\nresulting in inflated activity figures.\nResponse We thank the reviewer for this critical comment. With due respect, the method of TOF\nhas been broadly in previous studies [Nature 2023, 613, 66; Nat. Catal. 2023, 6, 987; Nat. Commun.\n2025, 16, 1002. Nat. Commun. 2024, 15, 7393; PNAS, 2022, 119, e2121174119; Angew Chem Int.\nEdit. 2024, e202400011; Angew. Chem. Int. Edit. 2025, e202511886.]. It is scientific to validate\nthe superior product yield, TONs, and TOFs of this catalyst:\nProduct yield per unit area of catalyst per hour (mol∙cm-2∙h-1)\nH evolution rate= (1)\nMass of catalyst per unit area=L  ν  6.1 g·cm-3 ×1 cm2 (2)\nWhere the L is the length of GaN nanowires, and the ν is denoted as the fill factor. According to\nthe top-view SEM image of 1D GaN nanowires supported by Si (Fig. S4), the average L was\nestimated to be ~570 nm. By taking the density of GaN (6.1 g·cm-3) into the calculation, the\ncatalyst mass per unit area is thus estimated to be 0.24 mg. The weight of Ni(Mn)-O-P was not\ntaken into consideration owing to their trace amount (<0.01 mg∙cm-2).\nFig. S4 The 45o-tilted SEM image of GaN NWs vertically aligned on a Si (111) wafer. The inset\nimage is the top view.\nConsidering that, compared with Ni(Mn)-O-P/GaN NWs/Si wafer (Fig. S13), the catalytic\ncapabilities of pure GaN NWs/Si wafer and Mn-O-P/GaN NWs/Si wafer for H are extremely\n2\nlimited (< 4.5%), it is rationalized that nickel is the active site of the reaction. Thus, TOF and\nTON are calculated based on the nickel loading amount as measured by inductively coupled\nplasma atomic emission spectrometry (ICP-AES):\nH production amount (μmol)\nNi Content of immobilized Ni nanoparticles (μmol)  Reaction time (h)\nH production amount (μmol)\nNi Content of immobilized Ni nanoparticles (μmol)\nThe optimal content of Ni over GaN NWs/Si was determined to be 0.23 μmol·cm-2 measured by\nICP-AES.\nIt is worth noting that, compared with highly dispersed homogeneous catalysts of active metals\nand single-atom catalysts, the TON and TOF calculated by ICP are underestimated, because ‘the\nsurface-active Ni is much less than the total Ni deposition’. This was also confirmed through the\nchemical pulse adsorption of H (Fig. R1, the dispersion of Ni was 50.80%)\nFig. S13 The activity of FA decomposition of Ni(Mn)-O-P/GaN NWs and various Ni-free\ncatalysts at 150 °C.\nFig.R1 Pulsed chemical adsorption of H over Ni(Mn)-O-P/GaN NWs.\n2\n(Please see Page 20 in the Manuscript, Page 9, 18 in the Supplementary Information)\nComment 3 The calculation of the H evolution rate does not seem to be appropriate. The authors\n2\nhave carried out thermal catalysis, and therefore, the overall catalyst weight has to be considered\ninstead of metal deposition, if they need to provide the yield per gram of catalyst (molH g -1 h-\n2 cat\n1). If not, it is advisable to provide the yield values per active site instead.\nResponse We thank the reviewer again. With due respect, we would like to clarify that the\nevolution rate was calculated based on the total mass of GaN plus Ni(Mn)-O-P rather than on the\nmass of the deposited metal. Please see below the calculation methods in detail.\nProduct yield per unit area of catalyst per hour (mol∙cm-2∙h-1)\nH evolution rate= (1)\nMass of catalyst per unit area=L  ν  6.1 g·cm-3 ×1 cm2 (2)\nWhere the L is the length of GaN nanowires, and the ν is denoted as the fill factor. According to\nthe top-view SEM image of 1D GaN nanowires supported by Si (Fig. S4), the average L was\nestimated to be ~570 nm. By taking the density of GaN (6.1 g·cm-3) into the calculation, the\ncatalyst mass per unit area is thus estimated to be 0.24 mg. The weight of Ni(Mn)-O-P was not\ntaken into consideration owing to their trace amount (<0.01 mg∙cm-2).\nFig. S4 The 45o-tilted SEM image of GaN NWs vertically aligned on a Si (111) wafer. The inset\nimage is the top view.\n(Please see Page 20 in the Manuscript and Page 9 in the Supplementary Information)\nWe hope this response can well address the reviewer’s concern.\nComment 4 No information was provided about the flow rate of formic acid or the catalyst amount\nused in long-term stability tests (4000 h). The number 5,023,060 mole H is not logical without\n2\nthe reaction details.\nResponse We thank the reviewer very much. In this study, the reaction was conducted in a batch\nreactor. Based on the referee’s valuable comment, we have elaborated the reaction details in the\nrevised manuscript as follows: “A Ni(Mn)-O-P/GaN NWs wafer (≈0.3 cm2) was fixed at the\nbottom of the chamber. The reaction was operated for 24 h. After 1 cycle, the chamber was\nthoroughly purged with argon to completely replace the atmosphere, followed by injection of 1\nmL of FA. H was periodically measured using GC to test the catalytic activity.”\n2\n(Please see Page 20 in the Manuscript)\nComment 5 The selectivity of the catalysts remains 99% despite the significant changes in the\nmorphology of the catalysts. This seems highly unlikely in heterogeneous catalysts. The authors\nneed to provide more detailed characterization to support these results.\nResponse We thank the reviewer for the crucial comments. Based on the referee’s comment, we\nhave provided supplementary high-resolution TEM images of the post-reaction catalyst in the\nrevised supporting information (Fig. S21). It is discovered that although some variations in surface\nmorphology occurred after 4000 hours of test, the nanowire structure was preserved after 4000 h\nof long-term operation. This can well explain the performance degradation after the long-term\nstability test. We have elaborated the discussion as below: “After the 4000 h test, the hydrogen\nactivity only decreased by ~10% (Fig. S20). The Transmission Electron Microscope (TEM)\nimages and XPS spectra show that morphological and valence state of the nanoclusters remain\nstable and do not undergo significant change during the reaction. (Fig. S21)”\nFig. S21 (a) HAADF-TEM image of Ni(Mn)-O-P/GaN NWs after stability test and (b) High-\nresolution XPS spectra of Ni 2p of Ni(Mn)-O-P/GaN NWs before and after stability test.\n(Please see Page 9 in the Manuscript and Page 26 in the Supplementary Information)\nComment 6 The authors have not provided formic acid conversion values. CO selectivity and\n2\nyields are neglected. It is important to check the mass balance of the reaction.\nResponse We thank the reviewer for this valuable comment. Based on the referee’s comment,\nunder the optimized conditions, the conversion rate of formic acid (1mL) at 150℃ for 1 hour is\nabout 5%.\nAs reported [Nature Catal. 2021, 4, 193; Nature Commun. 2024, 15, 8189; Nature Commun. 2023,\n14, 7518], thermal decomposition of formic acid can proceed via two different pathways (HCOOH\n→H + CO ; HCOOH→H O + CO). Based on the referee’s valuable comment, the yield of CO\n2 2 2 2\nfrom formic acid dehydrogenation was measured by the gas chromatography equipped with a TCD\ndetector (Shimadzu GC 2014). It was found that CO was produced from formic acid\n2\ndehydrogenation at a nearly stoichiometric CO /H ratio of 1/1 without detection of CO. This\n2 2\nfinding indicates the negligible formic aid dehydration. Based on the reviewer’s comment, we\nhave added the ratio of H and CO in the revised Manuscript and Supplementary Information\n2 2\nalong with the following statement: “Of note, CO was produced from formic acid\n2\ndehydrogenation at a stoichiometric H /CO ratio of 1/1 without detection of CO. This finding\n2 2\nindicates the negligible formic acid dehydration (Fig. S17).”\nFig. S17 GC spectra of the gas reaction mixture for measuring the ratio of H : CO of FA\n2 2\ndecomposition used HCOOH + H O over Ni(Mn)-O-P/GaN NWs. Experimental conditions:1 mL\n2\n(Please see Page 8 in the Manuscript, Page 22 in the Supplementary Information)\nComment 7 Catalyst performance was presented as H evolution rate per gram of catalyst. This\n2\ncomparison is not ideal as noble metals, with high atomic mass, obviously show a low evolution\nrate.\nResponse We thank the referee again. As responded in Comment 2 and Comment 3, the H\n2\nevolution rate was calculated based on the total mass of for the deposited metal plus GaN NWs,\nrather than being calculated solely based on the atomic weight of the loaded metal. Please see the\ncalculation method in Equation below:\nProduct yield per unit area of catalyst per hour (mol∙cm-2∙h-1)\nH evolution rate= (1)\nMass of catalyst per unit area=L  ν  6.1 g·cm-3 ×1 cm2 (2)\nWhere the L is the length of GaN nanowires, and the ν is denoted as the fill factor. According to\nthe top-view SEM image of 1D GaN nanowires supported by Si (Fig. S4), the average L was\nestimated to be ~570 nm. By taking the density of GaN (6.1 g·cm-3) into the calculation, the\ncatalyst mass per unit area is thus estimated to be 0.24 mg. The weight of Ni(Mn)-O-P was not\ntaken into consideration owing to their trace amount (<0.01 mg∙cm-2).\n(Please see Page 20 in the Manuscript)\nComment 8 The manuscript contains repeated grammatical and presentation errors, undermining\nits professional standard. Examples include mislabeling “N ” instead of “H ”, incorrect or\n2 2\nambiguous references to photocatalyst mass, incomplete figure captions, etc.\nResponse We thank the reviewer very much for the critical comments. Based on the referee’s\ncomments, we have carefully gone through the manuscript and have revised the grammatical and\npresentation errors in the revised manuscript.\nComment 9 The authors could clarify where to source or how to purify formic acid to have 99.9%\npurity.\nResponse We thank the reviewer a lot again. Formic acid with high purity was purchased from\nthe company and used for the reaction without further purification. To address the referee’s\nconcern, we have elaborated the formic acid information in the revised manuscript as follows: “FA\n(Shanghai Aladdin Biochemical Technology Co., Ltd., UltraPureChromTM, for HPLC, 99.9%)”.\n(Please see Page 19 in the Manuscript)\nManuscript ID: NCOMMS-25-55883B\nTitle: “Highly Efficient Heterogeneous Thermal Catalysis for Noble-Metal-\nFree Hydrogen Production from Formic Acid”\nWe thank the reviewer a lot for the constructive comments that helped us to improve the quality\nof the manuscript. We have meticulously addressed the referee’s concern.\nReviewer #3\n:\nComment 1 Most of the concerns were addressed, but a TON of 5,023,060 over 4000 hours\nsuggested an average TOF of 1256, which is far away from 31,000. This means the catalyst loses\nit activity quickly. The authors may wish to provide further comments.\nResponse We sincerely thank the reviewer for this comment. The TOF of ~31,000 was measured\nat 150°C, while the average TOF of 1256 under stability test (55–75°C) is consistent in magnitude\nwith the activity measured at corresponding temperatures. This does not indicate rapid deactivation.\n1"}, {"round": 2, "reviewer_comments": {"reviewer_1": "In my opinion, the authors have done an excellent job of revising the manuscript. This applies to the criticism, requests for changes, and additions made by all three reviewers.\nAdequate responses were provided for both the actual manuscript and the supporting materials. The same applies to supplementary experiments and recalculations of data.\nI would now be happy to approve the publication of this work.", "reviewer_2": "I would like to thank the authors for all the revisions made to the previous version of the manuscript to enhance its quality.\nAfter satisfactorily addressing all the issues raised and implementing all the necessary modifications throughout the manuscript, I consider that the manuscript is now ready for publication.", "reviewer_3": "Most of the concerns were addressed, but a TON of 5,023,060 over >4000 hours suggested an average TOF of <1256, which is far away from 31,000. This means the catalyst loses it activity quickly. The authors may wish to provide further comments."}, "author_response": "Manuscript ID: NCOMMS-25-55883B\nTitle: “Highly Efficient Heterogeneous Thermal Catalysis for Noble-Metal-\nFree Hydrogen Production from Formic Acid”\nWe thank the reviewer a lot for the constructive comments that helped us to improve the quality\nof the manuscript. We have meticulously addressed the referee’s concern.\nReviewer #3\n:\nComment 1 Most of the concerns were addressed, but a TON of 5,023,060 over 4000 hours\nsuggested an average TOF of 1256, which is far away from 31,000. This means the catalyst loses\nit activity quickly. The authors may wish to provide further comments.\nResponse We sincerely thank the reviewer for this comment. The TOF of ~31,000 was measured\nat 150°C, while the average TOF of 1256 under stability test (55–75°C) is consistent in magnitude\nwith the activity measured at corresponding temperatures. This does not indicate rapid deactivation.\n1"}]

Decision letter