Synergistic electrode design for efficient CO_2 electrolysis to multicarbon products at elevated temperatures

Domain: physics
Published: 2026-02-12
Editorial outcome: minor_revision

Abstract
Electrocatalytic CO2 reduction reaction (CO2RR) technology holds significant industrial potential. However, when faced with elevated-temperature environments caused by industrial-scale operations, the fundamental understanding of temperature-dependent CO2RR behavior in flow cells remains elusive. This study points out that elevated-temperature operation (>333 K) presents both challenges and opportunities for multi-carbon (C2+) production. While elevated temperature enhances reaction kinetics and reduces thermodynamic energy barriers, it simultaneously induces reconstruction of Cu-based catalyst, accelerates gas diffusion electrode flooding, and promotes *CO desorption together with hydrogen evolution reaction, collectively suppressing C2+ product formation and compromising long-term reactor stability. Through rational design of hydrophobic-enhanced Pd-Cu2O/polytetrafluoroethylene (PTFE)/Ag tandem electrodes, we overcome these challenges. Leveraging thermal reduced C-C coupling barriers, the optimized electrode achieves >70% Faradaic efficiency of C2+ across industrially relevant current densities (200–1000 mA cm−2) at 348 K. This strategy converts elevated temperature adversity into a kinetic and thermodynamic advantage, boosting C2+ cathodic energy efficiency by 1.3 times compared to ambient operation, establishing a promising paradigm for industrially viable CO2 electrolysis.

Introduction
Electrocatalytic CO2 reduction to C2+ products offers a promising route for sustainable chemical synthesis and carbon emission mitigation1–3. Advances in electrocatalyst design, microenvironment engineering, and reactor optimization have enhanced C2+ production efficiency in ambient-temperature systems4–6. Nevertheless, when electrolyzers are scaled up and operated under industrial conditions, heat from Joule heating due to ohmic resistance, and limited heat dissipation collectively elevate electrode surface temperatures (Fig. 1a)7,8. Strikingly, scaling electrode areas from 4 cm2 to 25 cm2 rapidly elevates cell temperature to 353 K or induces violent boiling (Fig. 1b, Supplementary Fig. 1 and Supplementary Note 1), exceeding thermal limits of ion-exchange membranes and causing system failure. This demonstrates that elevated-temperature operation is unavoidable in industrial scaling. Understanding temperature impacts on CO2RR systems, including reactor integrity and reaction pathways, is essential for industrial implementation9,10.

Current understanding of temperature effects originates from H-cell studies, which provide preliminary insights into product selectivity and intermediate adsorption/desorption11–13. Koper et al. proposed that a slight increase in temperature promotes the formation of C2+ products, while excessive elevation accelerates the formation of the competing HER14. However, elevated temperature alters CO2 solubility, water vapor pressure, and electrolyte conductivity, there-by fundamentally reconstructing the reaction microenvironments15,16. Consequently, investigating temperature effects in H-cells is substantially hindered by the coupled influences of kinetic and mass transport changes, making it challenging to infer purely thermodynamic or intrinsic kinetic effects. Gas diffusion electrodes (GDEs) with stable gas–liquid–solid interfaces effectively mitigate mass transport limitations. Compared to membrane electrode assembly (MEA) electrolyzers, the flow-cell configuration offers a key advantage for fundamental research by enabling independent and precise thermal management and potential measurement of the cathode. Moreover, it avoids complications such as membrane degradation and water evaporation at elevated temperature, which are commonly encountered in MEA electrolyzers, thereby enabling a rigorous assessment of thermal impacts on reaction thermodynamics and kinetics17–19. Previous studies in flow cells demonstrate temperature-enhanced kinetics for C2+ products, exemplified by reduced overpotentials for CO and H2 evolution on silver catalysts from 291 to 343 K20, while mechanistic work reveals that temperature-dependent *COOH/*H adsorption competition dictates CO/H2 selectivity21.

Despite these advances for C2+ products, premature *CO desorption and accelerated hydrogen evolution reaction (HER) kinetics severely impede C-C coupling at elevated temperatures, limiting C2+ formation on Cu catalysts (Fig. 1c). Takanabe et al. demonstrate that temperatures exceeding 333 K significantly reduce the selectivity of C2+ products22. Han et al. Further confirms that lower operating temperature (270 K, −3 °C) favors C-C coupling and hydrogenation pathways of *CH-COH intermediates on Cu-based catalysts23, suggesting incompatibility between C2+ production conditions and industrial elevated-temperature environments. Additionally, elevated temperature may compromise the stability of both catalysts and GDEs in flow cells. Therefore, prior strategies have focused on circumventing, rather than addressing, the elevated-temperature challenge, for example, by lowering operating temperature via heat exchange and electrolyzers' cooling. Thus far, maintaining a high Faradaic efficiency (FE) for C2+ products in elevated-temperature flow cells remains a critical scientific challenge and a technological bottleneck urgently demanding resolution (Fig. 1d)13,14,16,23–31. Consequently, a comprehensive understanding of the adverse effects of elevated temperature on CO2RR in flow cells, together with the development of corresponding mitigation strategies, is essential for industrial implementation.

To bridge these gaps, we systematically investigate the effect of temperature (298–348 K) on CO2RR in flow cells. Experimental results reveal that elevated temperature induced dynamic restructuring of Cu-based catalysts, accelerated GDEs flooding due to increased water vapor pressure, and enhanced *CO desorption and HER kinetics. Therefore, elevated temperature inhibits the formation of C2+ products and indirectly promotes product loss in flow cells. To address these challenges, we engineered hydrophobic-enhanced Pd-Cu2O/PTFE/Ag tandem electrodes that achieve >70% FE of C2+ across 200–1000 mA cm−2 at 348 K and exhibit stable operation for extended periods (Fig. 1d). Operando Raman spectroscopy and density functional theory (DFT) calculations confirm that strengthened *CO adsorption and reduced C-C coupling energy barriers synergistically promote the formation of C2+ at elevated temperature. These strategies convert elevated-temperature challenges into opportunities, increasing cathodic energy efficiency (CEE) by 1.3 times compared to room-temperature operation. Preliminary techno-economic analysis (TEA) indicates that this strategy not only significantly reduces electricity consumption but also eliminates approximately 14.9% of cooling-related operating costs (Fig. 1e, Supplementary Fig. 2, Supplementary Note 2 and Supplementary Table 1 to 2). This work provides essential guidance for the scale-up and practical application of CO2 electrolysis technology.

Results
We systematically investigated the effect of temperature on CO2RR in a flow cell by simultaneously examining catalyst structure, three-phase interface stability, and key reaction intermediates and pathways, all of which collectively govern CO2RR activity. Given that ion exchange membranes are typically operated below 353 K, we investigated the impact of temperature on CO2RR within a safer range of 298-348 K32,33. To maintain a stable CO2RR interfacial temperature, both the flow cell and catholyte were heated to simulate the elevated temperature environment encountered in flow cell (Supplementary Fig. 3 and Supplementary Note 3). The flow cell temperature was monitored using two K-type thermocouples and infrared thermal imaging technology. Measurements commenced only after the temperature had reached the set-point and remained stable for 5 min.

The impact of temperature toward the catalyst structure
Cu is widely employed for C2+ production owing to its efficient C-C coupling capability, yet concerns persist regarding its structural vulnerability under industrial elevated-temperature industrial operation34,35. X-ray diffraction (XRD) analysis reveals distinct thermal oxidation pathways in magnetron-sputtered Cu electrodes (Fig. 2a). The as-synthesized electrodes exhibit characteristic Cu(111) and (200) diffraction peaks36,37. After immersion in 348 K 1.0 M KOH electrolyte, a new peak emerges at 36.5° corresponding to Cu2O(111), confirming surface oxidation38,39. Subsequent CO2RR operation restores the original Cu phase, demonstrating electrochemical reduction reversibility. X-ray photoelectron spectroscopy (XPS) verified this phenomenon (Supplementary Fig. 4a), i.e., Cu was oxidized in 348 K electrolyte, as evidenced by a distinct Cu(II) signal at 935 eV40. Cu LMM Auger electron spectroscopy (AES) confirms increased relative ratios of Cu(I) and Cu(II) signals at elevated temperature (Supplementary Fig. 4b)41. To eliminate environmental interference and probe dynamic redox behavior of the Cu electrode, electrochemical in situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements were conducted (Supplementary Fig. 5). Upon electrochemical reduction, the Cu K-edge XANES spectra (Fig. 2b and Supplementary Fig. 6a) confirm dominant Cu(0) states, matching the Cu foil references. However, once electrochemical control is removed, rapid surface oxidation occurs, as evidenced by a distinct Cu-O coordination peak at 1.6 Å in the EXAFS spectra (Fig. 2c, Supplementary Fig. 6b, and Supplementary Table 3)42. In addition to changes in chemical state, scanning electron microscope (SEM) images reveal that operating at the elevated temperature (348 K) caused slight morphological changes in Cu nanoparticles (Fig. 2d).

Therefore, elevated-temperature (348 K) electrolyte immediately affects the structure of Cu catalysts, but continuous electrochemical stimulation masks the effects of elevated-temperature oxidation, so this dynamic oxidation-reduction process is easily overlooked during the CO2RR. Critically, elevated-temperature-induced oxidation alters CO2RR pathways. As the temperature increased from 298 K to 348 K, the FE of CH4 increased from 3.4% to 20.8%, while the FE of C2H4 decreased from 30.2% to 17.6% at −200 mA cm−2, concomitant with accelerated HER (Supplementary Fig. 7). During the 6-hour stability test (Supplementary Fig. 8), the FE of C2H4 and CH4 remained nearly constant at 298 K. Conversely, at 348 K, Cu oxidation and surface restructuring shifted selectivity toward CH4.

In contrast, the elevated-temperature-induced dynamic oxidation-reduction process shows a different pattern on Cu2O. Cu2O undergoes no further oxidation in 348 K electrolyte, and its morphology remains unchanged (Fig. 2e). XRD analysis confirms the absence of elevated-temperature-induced crystal structure alteration (Supplementary Fig. 9); the weak diffraction peaks at 44° and 51° are ascribed to electrochemically reduced Cu(0) (111) and (200) facets43. XPS shows a slight decrease in the Cu(I)/Cu(0) ratio after electrochemical reduction at 348 K (Supplementary Fig. 10). Notably, XANES spectra reveal that a metallic Cu phase forms during the prolonged electrochemical reduction reaction (Fig. 2f and Supplementary Fig. 11). When electrochemical control is removed, the metallic Cu is re-oxidized to Cu2O (Fig. 2g). This result confirms that the Cu2O crystal structure is unaffected by the elevated temperature, yet the metallic Cu generated during CO2RR is still oxidized, just like the Cu electrode mentioned above. In contrast, as the temperature increased from 298 K to 348 K, the Cu2O electrode exhibited no appreciable changes in the distribution of carbon products (Supplementary Fig. 12), apart from a drastic increase in the FE of H2. Operando surface-enhanced Raman spectroscopy (SERS) revealed the temperature dependence of product selectivity on Cu and Cu2O electrodes (Supplementary Figs. 13–17 and Supplementary Notes 4–7), that elevated‑temperature‑induced structural changes in Cu significantly promote the activation of interfacial water. Under the combined effects of low *CO coverage and excessive protonation, the product selectivity shifts from C2+ to CH4. In contrast to Cu, Cu2O maintains its structural integrity at 348 K and, crucially, preserves its favorable interfacial water structure. Therefore, in subsequent research, selecting Cu2O as the subject of study can effectively avoid the adverse effects arising from structural changes in the catalyst induced by elevated temperatures. While Cu2O nanocubes demonstrate superior structural stability relative to metallic Cu at elevated temperature, their CO2RR performance at 348 K remains severely compromised. This performance degradation points to additional elevated-temperature barriers beyond structural preservation.

The impact of temperature toward the GDE
Beyond catalyst instability, elevated temperatures compromise electrode integrity by disrupting the gas-liquid equilibrium. Product distribution analysis on the Cu2O electrodes shows a sharp rise in the FE of H2 and a simultaneous drop in the FE of CO and C2+ when the temperature increases from 298 K to 348 K (Supplementary Fig. 12). This anomalous enhancement in HER does not stem from catalyst degradation but from catastrophic flooding of the GDE, a direct consequence of elevated water vapor pressure that destabilizes the three-phase boundary (Fig. 3a). In the flow cell configuration, the three-phase interface separates the CO2 feed from the electrolyte via the catalyst layer. The short gas diffusion path greatly enhances mass transfer efficiency from the CO2 feed to the catalyst-electrolyte interface, enabling high current densities. However, this design also renders the cathode susceptible to flooding44. When the hydrophobic GDE structure is compromised during electroreduction, electrolyte infiltrates the catalyst layer, the GDE, and the gas channel, blocking CO2 access to active sites. At elevated temperature, the electrolyte’s saturated vapor pressure rises; water vapor formation accelerates flooding, further diminishing the population of active sites for CO2RR. The remaining sites in contact with the electrolyte continue to drive the hydrogen evolution reaction.

The Cu layer formed by magnetron sputtering is highly dense and therefore hydrophobic, effectively preventing water vapor intrusion at elevated-temperature conditions (Supplementary Fig. 18a and Supplementary Note 8). In contrast, most Cu-based composite catalysts must be sprayed onto the GDE in the powder form; their high porosity compromises hydrophobicity and renders them more susceptible to flooding at elevated temperature (Supplementary Fig. 18b). The electrochemical in situ reconstruction of Cu2O is largely independent of H2 evolution; at 298 K the FE of H2 actually decreases when the current density is raised to −600 mA cm−2 (Fig. 3b). However, as the temperature rises further, the FE of H2 increases sharply, indicating that elevated temperatures disrupts CO2 transport and suppresses C2+ products formation (Fig. 3c and Supplementary Fig. 19). Damage to the three-phase interface also leads to product loss; the total FE falls to only 88.5%, of which H2 accounts for 74.9%. Thus, the electrode structure is more vulnerable at elevated temperatures and high current densities. Cyclic voltammetry (CV) in non-Faradaic regions shows that the Cdl value of Cu2O increases with temperature, giving a larger electrochemical active surface area (ECSA) at 348 K (Fig. 3d and Supplementary Table 4)45. In the flow cell, however, the ECSA encompasses both CO2RR and HER active sites; higher temperature therefore intensifies flooding and enlarges the HER-active area (Supplementary Fig. 20). After a 6-h stability test, the gas-solid-liquid interface is almost completely destroyed and H2 becomes the predominated reduction product (Supplementary Fig. 21).

Hydrophobic polytetrafluoroethylene (PTFE) particles were introduced into the catalyst layer to suppress water vapor intrusion (Supplementary Fig. 22)46. The Cdl value of Cu2O/PTFE remains nearly constant with increasing temperature, indicating that PTFE effectively stabilizes the three-phase interface at elevated temperature (Supplementary Fig. 23). Electrochemical impedance spectroscopy (EIS) shows that while elevated temperature lowers the interfacial charge transfer resistance, the insulating PTFE induces a slight increase in this value (Fig. 3e). The thickness (δ) of the CO2 diffusion layer on the catalyst was fitted at different temperatures (Supplementary Table 5). For Cu2O, δ decreased from 4.51 to 3.54 as temperature rose, consistent with water vapor instructions shortening reducing the CO2 diffusion path (Supplementary Fig. 24). In contrast, the almost unchanged δ for Cu2O/PTFE confirm that a stable three-phase interface that is insensitive to temperature. Consequently, PTFE effectively inhibits water flooding and limit the FE of H2 to only 13.0% at 348 K, even at −600 mA cm−2 (Fig. 3f). Thus, the shift of CO2RR products toward H2 on Cu2O at elevated temperature is mainly attributable to thermally accelerated water flooding that impedes CO2 diffusion. The PTFE not only mitigates flooding but also ensures robust GDE operation at elevated temperatures. Nevertheless, the FE of H2 on Cu2O/PTFE remains higher at 348 K than at 298 K (Supplementary Fig. 25), indicating that intrinsic kinetic limitations, beyond flooding, also contribute to suppressed C2+ formation.

The impact of temperature toward the C2+ product
The efficiency of C-C coupling is a key determinant of C2+ yield. Even with PTFE-stabilized GDE operation, elevated temperatures suppress C-C coupling, as evidenced by reduced C2+ FE and concomitant promotion of H2 and CO generation (Supplementary Fig. 25 and Fig. 4a). Investigating the temperature effect on C-C coupling therefore requires suppressing competitive hydrogen evolution and preventing *CO desorption. Although the Cu2O/PTFE electrode remains structurally stable at elevated temperatures, temperature rise still enhances its HER. The same trend was observed on magnetron-sputtered Cu electrodes. To further suppress H2 reduction, we coated an Ag layer onto the Cu2O/PTFE electrode, creating a spatially separated tandem architecture (Supplementary Fig. 26 and Supplementary Note 9)47. The Ag catalyst layer suppresses water dissociation and effectively reduces CO2 to CO, increasing the local *CO concentration while inhibiting *H adsorption on Cu2O surface (Fig. 4a and Supplementary Fig. 27)31,48 The CO2RR activity tests show that the Cu2O/PTFE/Ag tandem structure lowers the FE of H2 from 22.5% to 7.2% at 348 K and −200 mA cm−2 (Fig. 4b). In previous studies, Ag serves as a *CO generator, and higher *CO coverage can lower the C-C coupling barrier. However, Cu2O/PTFE/Ag exhibits a higher FE of CO than Cu2O/PTFE at both 298 K and 348 K (Supplementary Fig. 28 and Fig. 4b), indicating that the abundant *CO produced by Ag is not efficiently spilled over to Cu2O for coupling but is instead desorbed and vented. This suggests that the *CO-adsorption capability of Cu2O is equally critical; its capacity as a *CO receiver dictates the amount of *CO available for C-C coupling49. Because local *CO concentration and pH scale with current density, the *CO coverage at −200 mA cm−2 is lower than that at higher current densities, and the higher C-C coupling barriers yield lower FE of C2+. Moreover, Cu2O/PTFE/Ag shows a higher FE of CO at 348 K than at 298 K, confirming that elevated temperature not only fails to promote C-C coupling but also accelerates *CO desorption.

Recently, Xu et al. showed that alkali metal cations modulate both the activation enthalpy of reaction and the enthalpy of CO2 adsorption50. The CO2RR tests in electrolytes containing different alkali metal cations reveal that larger cations suppress water dissociation more effectively, with the FE of H2 following the order Li+ > Na+ > K+ > Cs+ (Supplementary Fig. 29). Conversely, larger cation weakens *CO adsorption, so the FE of CO increases in the order Li+ < Na+ < K+ < Cs+. As the temperature rises, the FEs of H2 and CO increase in all alkali metal cation-containing electrolytes, confirming that elevated temperatures accelerate *CO desorption. Cs+, which exhibits the weakest *CO binding, gives the highest FE of CO. These results demonstrate that the interfacial *CO adsorption capacity governs C-C coupling efficiency at elevated temperature (Supplementary Note 10). Therefore, converting the inherently adverse elevated temperature environment into a beneficial one hinges on suppressing *CO desorption. Because Pd possesses a markedly stronger *CO binding energy than Cu, highly dispersed Pd was deposited onto Cu2O via chemical reduction to stabilize *CO intermediates at elevated temperatures (Fig. 4a)51,52. Elemental maps confirm the uniform distribution of Pd across the Cu2O surface, and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) further verifies its atomic-level dispersion (Supplementary Fig. 30). At 298 K, the CO2RR tests show that Pd incorporation lowered the FE of CO and promoted the C-C coupling, yielding 53.1% FE of C2+ at −200 mA cm−2 (Supplementary Fig. 31). However, Pd also strongly binds *H, enhancing water dissociation and increasing the FE of H253. When the temperature is raised to 348 K, H2 becomes the dominant side product (Fig. 4c). To balance these competing effects, Pd and Ag were co-incorporated into the Cu2O/PTFE electrode. In the resulting Pd-Cu2O/PTFE/Ag architecture, Pd selectively suppresses *CO desorption, while Ag inhibits HER and continuously supplies *CO. The presence of Pd and Ag is confirmed by XRD and XPS spectra (Supplementary Fig. 32), and SEM imaging reveals in the Pd-Cu2O/PTFE/Ag electrode (Supplementary Fig. 33). Leveraging this synergy, the Pd-Cu2O/PTFE/Ag electrode delivers a C2+ FE to 60.2% at −200 mA cm−2 and 298 K (Supplementary Fig. 34). Pd strengthens *CO adsorption on Cu2O sites fed by Ag, and the additional thermal energy at elevated temperature further increases the probability of C-C coupling. Consequently, the Pd-Cu2O/PTFE/Ag electrode achieves a C2+ FE of 72.6% at −200 mA cm−2 upon raising the electrolyte temperature to 348 K (Fig. 4d and Supplementary Fig. 35). Optimization of Pd loading reveal that 0.7 wt% Pd provided optimal *CO and *H adsorption, maximizing FE of C2+ products while minimizing FE of H2 (Supplementary Fig. S36). The low loading and high dispersion of Pd prevent its aggregation during prolonged elevated-temperature electroreduction, thereby maintaining the structural function (Supplementary Figs. 37 and 38). Notably, elevated temperatures simultaneously suppresses CO/H2 generation and enhances C-C coupling at low current densities (Fig. 4e), overcoming the CO2 concentration limitation inherent to low current density operation. Benefiting from robust interfacial water management, the Pd-Cu2O/PTFE/Ag electrode remains stable during a 48-h test at 348 K (Supplementary Fig. 39). Furthermore, the elevated temperature accelerates CO2RR kinetics and lowers the required overpotential (Supplementary Fig. 40), thereby improving cathodic energy efficiency (CEE). Assisted by the elevated temperature, the Pd-Cu2O/PTFE/Ag electrode delivers a CEE of 48.9% at −200 mA cm−2 (Fig. 4f), 1.3-fold higher than at room temperature (37.7%) and 5.5-fold higher than the initial Cu2O/PTFE (8.9%)54. These results confirm that elevated temperature can promote C-C coupling under controlled conditions. Thus, by synergistically optimizing interfacial water management, strengthening *CO adsorption, and facilitating C-C coupling, the hydrophobic-enhanced Pd-Cu2O/PTFE/Ag electrode surmounts elevated-temperature limitations and achieves optimal C2+ production in flow cells at 348 K (Fig. 4g and Supplementary Table 6).

Mechanistic studies
Complementing our experimental observations of *CO desorption, Operando SERS provides direct evidence for interfacial intermediate dynamics in flow cells. Because the Ag tandem layer functions solely as a CO generator while C-C coupling occurs exclusively on Cu2O or Pd-Cu2O surfaces, the electrodes for Operando SERS measurements were fabricated without Ag layers to avoid interference from its strong surface-enhanced Raman scattering effect (Supplementary Fig. 41 and Supplementary Note 11). Raman spectra (Fig. 5a) reveal that at 298 K, when the Cu2O/PTFE electrode potential is lowered to -0.6 V (vs. RHE), characteristic peaks emerge at 2030-2090 cm−1, assigned to *CO atop stretching vibrations (*COatop)55. These signals indicate that *CO intermediate adsorbs predominantly atop Cu atoms and participates in C-C coupling. The concurrent appearance of a peak at 360 cm−1 (assigned to Cu-CO stretching) confirms strong potential-dependent Cu-CO interactions (Supplementary Fig. 42a). At 348 K, the disappearance of the *COatop peak signals (Fig. 5b) signifies suppressed C-C coupling56. The peak at 360 cm−1 now emerges only at higher potentials (Supplementary Fig. 42b), demonstrating that elevated temperature weakens Cu-CO binding and promotes *CO desorption. Collectively, these results underscore that catalyst-specific *CO adsorption strength is critical for C2+ formation. Depositing Pd onto Cu2O strengthens Cu-CO interactions; both the Cu-CO (360 cm−1) and *COatop peaks intensify at lower potentials at 298 K (Supplementary Fig. 42c and Fig. 5c), confirming Pd-enhanced *CO binding57. Importantly, Pd mitigates the elevated-temperature limitation; *COatop signals intensify at low potentials at 348 K (Fig. 5d), suggesting that elevated temperature accelerates localized *CO conversion, thereby facilitating low-potential C-C coupling. Additionally, the Pd-induced enhanced interfacial electric field strengthens the adsorption and activation of CO2−, thereby indirectly facilitating the protonation process of CO2−, evidenced by an enhanced CO2− peaks at 700 cm−1 and 1530–1560 cm−1 at low potentials (Supplementary Fig. 42d and Supplementary Note 12).

To quantify the temperature-dependent adsorption energetics inferred from Raman spectra, DFT calculations were employed to model *CO binding on Cu2O and Pd-Cu2O. The Cu2O (100) surface and atomically dispersed Pd on Cu2O (100) (denoted Pd-Cu2O (100)) served as models (Supplementary Data 1). The adsorption energy calculations reveal that both *CO and *H binding weaken monotonically with temperature (Supplementary Fig. 43 and Fig. 5e), promoting *CO desorption and impeding subsequent C-C coupling, consistent with experimental results. Although *CO binding on Pd-Cu2O remains temperature-dependent, Pd-Cu2O exhibits stronger CO absorption than Cu2O across the entire temperature range. This enhancement arises from the increased density of states near the Fermi level in Pd 4d orbitals, which upshifts the d-band center of Cu2O. Projected crystal orbital Hamiltonian population (pCOHP) analysis further reveals stronger Pd-C bonding, confirming the higher *CO adsorption energy (Supplementary Fig. 44). Given the critical role of surface *CO coverage in C-C coupling, we further examined the asymmetric *CO-COH coupling pathway under varying coverages58–60. Increasing *CO coverage on Cu2O from 1/18 ML to 5/18 ML (Supplementary Fig. 45 and Fig. 5f) progressively lowers the coupling barrier from 1.715 eV to 1.011 eV. This aligns with electrochemical observations. Higher current densities raise *CO coverage, reduce the C-C coupling barrier, and enhance the FE of C2+ products. At identical *CO coverage (5/18 ML), Pd-Cu2O exhibits a lower C-C coupling barrier than Cu2O (1.011 eV vs. 0.947 eV), rationalizing its superior C2+ FE at low current densities. Crucially, although elevated temperature promotes intermediate desorption, it simultaneously reduces C-C coupling barriers (Fig. 5g)61. Raising the temperature from 298 K to 348 K decreases the *OCCOH formation barrier by 0.124 eV for Cu2O and by 0.136 eV for Pd-Cu2O, underscoring the thermodynamic advantage of elevated temperature C-C coupling.

The influence of elevated temperature on C2+ production can be summarized as follows: (i) Elevated temperature accelerates *H and *CO desorption from the Cu2O surface, leading to substantial H2 and CO formation; (ii) Introducing an Ag tandem layer suppresses *H participation and continuously generates CO intermediates that migrate to the Cu2O surface. Although the locally high CO concentration facilitates the C-C coupling, weak *CO adsorption on Cu2O limits its ability to effectively capture and convert the migrated CO at elevated temperature; (iii) Incorporating Pd significantly strengthens the *CO adsorption on Cu2O, enabling localized accumulation of *CO and promoting the *OCCOH generation and subsequent C2+ formation. Additionally, Pd site mitigates *CO desorption at elevated temperature, leveraging the reduced C-C coupling barrier to further enhanced C2+ yields. Consequently, the Pd-Cu2O/PTFE/Ag electrode demonstrates significantly enhanced CO2RR activity at elevated temperature (Supplementary Note 13).

Methods
Chemicals and materials
Copper nitrate (Cu(NO3)2·3H2O, 98%), Sodium hydroxide (NaOH, 96%), L(+)-Ascorbic acid (99%), L-cysteine (98%), Sodium borohydride (NaBH4, 96%), and isopropanol (IPA) (C3H8O, 99%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Potassium chloropalladite (K2PdCl4, 98%) was purchased from Shanghai Acmec Biochemical Technology Co., Ltd. Ag nanoparticles were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Polytetrafluoroethylene (PTFE, particle size: 200 nm) was purchased from Shanghai Macklin Biochemical Technology Co., Ltd. GDL (YLS-30T) and Nafion (5.0 wt%, DuPont 520) were purchased from Suzhou Sinero Technology Co., Ltd. All chemicals were analytical grade and used without additional purification. The ultrapure water used in the experiments was deionized water (DI) with a resistivity of 18.2 MΩ·cm.

Fabrication of the Cu2O catalyst
Cu2O nanocube particles were prepared by a wet chemical method. First, 120.0 mg Cu(NO3)2·3H2O was added to 90.0 mL DI and stirred for 5 min. Subsequently, 200.0 mg NaOH, which had been dissolved in 5.0 ml DI, was added under stirring conditions to form a blue precursor solution. Finally, L(+)-Ascorbic acid dissolved in 5.0 mL DI was slowly dripped into the precursor solution and stirred vigorously for 60 min until the solution turned orange. The product was collected, washed with DI water and ethanol three times by centrifugation, and dried in a vacuum oven at 60 °C for 12 h. The final product was Cu2O nanocube particles with a size of about 200 nm.

Fabrication of the Pd-Cu2O catalyst
The above-prepared 70.0 mg Cu2O was added to 70.0 mL ethanol and dispersed by sonication for 1 h. Subsequently, 1.2 mg of L-cysteine was added and sonication was continued for 30 min. A certain volume (2.0 mL, 4.0 mL, and 6.0 mL) of K2PdCl4 precursor solution (0.01 mol·L−1) was added to the mixed solution under high-speed stirring conditions. The amount of Pd added was varied by changing the volume. After 60 min of stirring, 1.42 mg NaBH4 dissolved in 1.25 mL DI was added to the mixed solution and stirred continuously for 60 min. The products were collected and washed by centrifugation with DI water and ethanol. The Pd-Cu2O composites were obtained after drying in a vacuum oven for 12 h. All samples labeled Pd-Cu2O represent samples of 4.0 mL of K2PdCl4 precursor solution added, and 0.7 wt% Pd was obtained by inductively coupled plasma optical emission spectrometer (ICP-OES) testing.

Preparation of Cu2O electrodes
All electrodes were prepared by the spraying method. 20.0 mg Cu2O was dispersed in 2.0 mL of isopropanol, and 50 μL of Nafion solution was added as a binder. Dispersing was carried out under ultrasonic conditions for 1 h to form a homogeneous ink. The GDE was placed on a heater at 70 °C and sprayed with a spray gun fitted with ink. The quality of the catalyst was determined by weighing the change in mass of the GDE before and after spraying. The loading of Cu2O was controlled to be 1.0 mg·cm−2 by spraying several times. Finally, the Cu2O electrode was cut to 2.5 cm × 1.0 cm for testing.

Preparation of Cu2O/PTFE electrodes
Cu2O/PTFE electrodes were prepared in a similar manner to that described above. 20.0 mg of Cu2O and 50 μL Nafion were added to 2.0 mL IPA to make solution A. 10.0 mg of polytetrafluoroethylene (PTFE) powder was added to 2.0 mL IPA to make solution B. Solution A and solution B, after ultrasonication for 60 min, were mixed, and ultrasonication was continued for another 30 min to form ink. The steps for spraying were the same as described above.

Preparation of Cu2O/PTFE/Ag electrodes
A total of 10.0 mg of Ag and 50 μL Nafion were added to 2.0 mL IPA and sonicated for 30 min to form inks. Spraying of Ag was continued on Cu2O/PTFE electrodes to obtain Cu2O/PTFE/Ag electrodes. The loading of Ag was controlled to be 1.0 mg cm−2.

Preparation of Pd-Cu2O/PTFE/Ag electrodes
The Pd-Cu2O/PTFE/Ag electrode was prepared in the same way as the Cu2O/PTFE/Ag electrodes, but the Cu2O was replaced with Pd-Cu2O.

Preparation of Cu electrodes
Cu electrodes were prepared using a magnetron sputtering system (MSP-300B). A Cu layer with a thickness of about 400 nm was sputtered on carbon paper at a rate of 1 Å/sec.

Product analysis and performance evaluation for CO2RR
All electrocatalytic CO2 reduction reaction (CO2RR) measurements were tested on a CHI 760e electrochemical workstation with three electrodes. The flow cell reactor consisted of a cathodic gas runner plate, a cathodic flow chamber, and an anodic flow chamber. The volume of the cathode flow chamber is 0.7 cm3, and the reaction area is 1.0 cm2. The components are separated by PTFE gaskets. The cathode was a prepared gas diffusion electrode (2.5 cm × 1.0 cm), and the anode was IrO2/Ti (2.0 cm × 2.0 cm). Fresh 1.0 M KOH (pH = 13.7 ± 0.1) was used as the cathodic and anodic electrolyte. The electrolytes were all transported to the flow cell by a peristaltic pump at a flow rate of 13.0 mL min−1 and separated by an anion exchange membrane (3.0 cm × 3.0 cm, 130 μm). The anion exchange membrane was repeatedly flushed with pure water prior to use. CO2 (Messer gas, 99.99%) controlled by a mass flow controller (MFC) was delivered to the cathode gas flow channel plate. The gas flow rate at the outlet during the reaction was controlled to 30.0 mL·min−1 and monitored using a digital flowmeter. The product was collected after operating for 30 min in constant current mode. The gas phase products of CO2RR were analyzed using an online gas chromatograph. The chromatograph (PerkinElmer Clarus 680) was equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID). Ar (Messer gas, 99.999%) was used as carrier gas. The liquid phase products were analyzed using 1H nuclear magnetic resonance (1H NMR) spectroscopy on an Advance III 500-MHz Unity plus spectrometer (Bruker). A mixture of 500 μL of liquid phase product with 100 μL of DMSO was diluted to 100 ppm with D2O for testing. A saturated Ag/AgCl electrode was used as the reference electrode and was calibrated in H2-saturated 0.5 M H2SO4 (pH = 0) prior to testing. A Pt electrode and a graphite rod were employed as the working electrode and counter electrode, respectively. Cyclic voltammetry (CV) was conducted at a scan rate of 1 mV s⁻¹, and the potential at zero current was taken as the calibrated EAg/AgCl. No IR compensation was employed for all electrochemical tests. All the potentials used were based on the reversible hydrogen electrode (RHE) using the following equation (Eq. 1):

ERHE = EAg/AgCl + 0.059 × pH + 0.198 V (1)

Characterization
Scanning electron microscope (SEM) was performed on a HITACHI S-4800. X-ray photoelectron spectroscopy (XPS) measurements were conducted on a Thermo Scientific ESCALAB 250Xi instrument. Contact angle measurements were performed on a Dataphysics OCA 20. High-resolution transmission electron microscope (HRTEM) measurements were carried out on a FEI Talos F200s electron microscope. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) was captured using a JEOL Grand ARM 300F with double Cs correctors at an acceleration voltage of 300 kV. Inductively coupled plasma optical emission spectroscopy (ICP-OES) measurements were carried out by Thermo Fisher iCap 7000. The electrochemical surface area (ECSA) of the electrode was quantified by measuring its double-layer capacitance (Cdl). CV was performed at various scan rates within a potential window where no Faradaic processes occur. The value of Cdl was then obtained by fitting the slope of the plot of the charging current against the CV scan rate. Electrochemical impedance spectra (EIS) measurements were carried out in the frequency range from 0.1 Hz to 100 kHz at 0 V (vs. RHE) with an amplitude of 10 mV. The resistance of the flow cell was measured using EIS under open circuit potentials (0.62 ± 0.03 Ω). The room temperature in the experiment was consistently maintained at 298 K (25 °C).

In situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies were carried out using the Rapid XAFS HE (Anhui Absorption Spectroscopy Analysis Instrument Co., Ltd.) by transmission mode at 20 kV and 20 mA. A Si (553) spherically bent crystal analyzer (SBCA) with a radius of curvature of 500 mm served as the monochromator, thereby ensuring a diffraction geometry approaching a 90-degree backscatter angle at the absorption edge. After monochromatization, the X-rays pass through the sample and were collected using a high-energy-resolution silicon drift detector (SDD) to obtain the X-ray intensity. In measurements, a custom-made cell was utilized (The volume of the chamber is approximately 15.0 cm3), the samples were uniformly dispersed on carbon paper and immersed in a 0.5 M KHCO3 electrolyte (pH = 6.7 ± 0.1) saturated with CO2 gas. A saturated Ag/AgCl electrode and a Graphite rod electrode were used as the reference and counter electrodes, respectively. The XAFS data were acquired in transmission mode. During the XAFS measurements, the position of the absorption edge (E0) was calibrated using a standard Cu foil, and all data were collected within a single time period.

Operando surface-enhanced Raman spectroscopy (SERS) was carried out using a Horiba LabRAM HR Evolution Raman microscope in a modified flow cell (The configuration was identical to that of the flow cells used in electrochemical testing). The volume of the cathode flow chamber is 8.0 cm3, and the reaction area is 0.5 cm2. The electrolytes were all transported to the flow cell by a peristaltic pump at a flow rate of 13.0 mL min−1 and separated by an anion exchange membrane (3.0 cm × 1.5 cm, 130 μm). A saturated Ag/AgCl electrode and a IrO2/Ti electrode (2.0 cm × 1.0 cm) were used as the reference and counter electrodes, respectively. 1.0 M KOH (pH = 13.7 ± 0.1) was used as the electrolyte, and CO2 gas is continuously passed into the cathode. A 632.8 nm excitation laser was used. The signals were recorded at different applied potentials, using a 60-second integration and by averaging two scans.

Performance evaluation for CO2RR
The thickness of the diffusion layer δ can be determined as follows:

δ = sqrt(3RdDdCd) (2)

where Rd and Cd are the equivalent resistance and capacitance of the diffusion layer, and the values are obtained from the equivalent circuit fitting of EIS. D0 is the diffusion coefficient of CO2 in the electrolyte, which is affected by temperature changes62,63. D0 at different temperatures is calculated by the following equation:

D0 = (1.43 × 10−4 × T1.75) / (p × (VA1/3 + VB1/3)2 × sqrt(1/MA + 1/MB)) (3)

where T is the thermodynamic temperature (298 K, 323 K, and 348 K), p is the pressure (Pa), MA and MB are the molecular weight of H2O and CO2, and VA and VB are the molar volumes of H2O and CO2. The D0 values at 298 K, 323 K, and 348 K are 0.1574, 0.1776, and 0.1986 cm2·s−1, respectively62.

FE for each product was calculated based on the following equation:

FE = (zi × xi × F) / Q × 100% (4)

where zi is the number of electrons transferred for product, xi is the number of moles of the product, F is Faraday’s constant and Q is the total charge passed during electrolysis.

CEE for C2+ product was calculated based on the following equation:

CEE = (Σ FEi × (1.23 − Ei)) / (1.23 − Ecathode) (5)

where FEi is the FE for each C2+ product. Ei is the thermodynamic reduction potential of each C2+ product, Eethylene = 0.06 V vs RHE, Eethanol = 0.08 V vs. RHE, En-propanol = 0.10 V vs. RHE, and Eacetate = 0.12 V vs. RHE for the CO2RR64,65. Ecathode is the measured potential values in the experiment.

DFT calculations
In this work, all density functional theory (DFT) calculations were performed using the plane-wave code QUANTUM ESPRESSO66–68. The exchange-correlation potential was approximated with the Perdew−Burke−Ernzerhof functional69,70. The interaction between the cores and the valence electrons was represented with the projector augmented wave approach71, kinetic energy cutoff for wavefunctions and charge density were 50 and 500 Ry, respectively. The convergence criteria for electronic structure iterations and force on each atom during structure relaxation were set to 10−8 Ry and 5×10−4 Ry/Bohr, respectively. The 3×3 Cu2O(100) were modeled by two-layer slab with a 15 Å vacuum region to avoid interactions between periodic images. We sample the Brillouin zone with a 3×3×1 Γ-centered Monkhorst-Pack k-points for geometry optimizations. Gaussian smearing with a width of 10−3 Ry was used. For all the calculations, the van der Waals (vdW) interactions are described with the DFT-D3 method in Grimme’s scheme72. The transition states were determined using the climbing image nudged elastic band (CI-NEB) approach. The TS structure was optimized using quasi-Newton algorithm, and the TS were converged to a residual force smaller than 0.05 eV/Å. Additional, on-site Coulomb repulsion between the Cu 3d orbitals were chosen as U = 6.0 eV was adopted. One of the surface Cu atom in the unit cell was substituted by Pd atom, which was used as the model of Pd/Cu2O catalyst. Atomic coordinates of computational models for Cu2O (100) and Pd-Cu2O (100) are shown in Supplementary Data 1.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The authors present a significant and comprehensive study addressing a critical, yet frequently overlooked challenge in the industrial scaling of CO2 electrolysis: the detrimental effects of intrinsic Joule heating. They provide an understanding of why elevated temperatures suppress multicarbon (C2+) product formation, encompassing catalyst structure, the triple-phase interface, and key reaction intermediates. Furthermore, they have designed a tandem electrode (Pd-Cu2O/PTFE/Ag) to overcome these challenges. The work is strengthened by a technoeconomic analysis (TEA) that underscores the advantages of C2+ production under elevated-temperature conditions. This research may promote researchers' attention to the elevated-temperature environment in electrocatalytic systems and open new paradigms for the design of electrocatalytic systems. Several aspects require clarification and modification. I recommend publication in Nature Communications after minor revisions.\n1. The authors propose that the Ag tandem layer effectively suppresses H2 evolution and functions as a CO generator. However, the electrocatalytic CO2RR performance data for Ag is only provided at 348 K. Data at 298 K is absent, making it impossible to assess the influence of temperature variations on Ag's performance.\n2. As correctly noted by the authors, C2+ production at elevated temperature is governed by the Pd-Cu2O interface, which motivated the removal of the Ag layer for the operando SERS measurements. To rigorously validate the rationale behind this experimental design, it is imperative to provide operando Raman spectra of the complete Pd-Cu2O/PTFE/Ag electrode.\n3. Although the authors demonstrate improved stability for the Pd-Cu2O/PTFE/Ag electrode compared to the initial Cu2O electrode at 348 K, the provided stability test data is limited to 12 hours. While extended electrolysis at elevated temperature is challenging, I strongly recommend that the authors endeavor to prolong the stability test duration to better assess the system's potential for industrial implementation.\n4. To conclusively determine whether Pd atoms agglomerate during the elevated-temperature electroreduction process, it is necessary to provide AC-HAADF-STEM images of the electrode after the stability test for direct comparison with the fresh catalyst.\n5. The catalyst cost in the TEA calculations should be re-evaluated. The utilization of Pd and Ag will undoubtedly increase the catalyst cost, and a more detailed cost breakdown is warranted.\n6. There is a spelling error in Supplementary Fig. 1. The authors need to rigorously check the grammar and figures in the manuscript.", "reviewer_2": "What are the noteworthy results?\nNumerous studies exist on the temperature dependence of CO₂ electrolysis, but many point out negative effects at high temperatures, such as decreased selectivity for C₂+ products like ethylene due to increased temperatures near the catalyst caused by overvoltage. In this study, while confirming such negative high-temperature effects for conventional Cu and Cu₂O catalysts, the authors prevented flooding near the catalyst even at high temperatures by adding PTFE to the catalyst substrate. Furthermore, by adding Pd to the catalyst to prevent CO desorption accelerated at high temperatures and supporting Ag near the Cu₂O catalyst to enhance CO supply to the Cu₂O surface, the authors developed a novel CO₂RR catalyst that maintains selectivity for C₂+ products even at elevated temperatures (348 K) through sophisticated catalyst design, and demonstrated its effectiveness. Furthermore, the authors were successful in enhances selectivity for C₂+ products at high temperatures while simultaneously reducing the overpotential for CO₂ reduction, demonstrating the benefits of operating CO₂ electrolysis reactors at elevated temperatures within the limits of membrane durability. Such discussion was supported by extensive experimental and computational data.\n\nWill the work be of significance to the field and related fields? How does it compare to the established literature? If the work is not original, please provide relevant references.\nThese results provide valuable insights into temperature control, which can be a bottleneck in operating CO₂ electrolysis reactors, and offer a positive message for the social implementation of CO₂ electrolysis. Particularly noteworthy is that the study not only points out the negative effects of C₂+ compound formation under high temperatures but also demonstrates a pathway to overcoming these challenges through appropriate catalyst and peripheral structure control. However, while the research results highlighted in this paper are useful for researchers involved in CO2 electrolysis, there is concern that the content is too specialized to appeal to a broader audience.\n\nDoes the work support the conclusions and claims, or is additional evidence needed?\nAre there any flaws in the data analysis, interpretation and conclusions? Do these prohibit publication or require revision?\nIncluding supplementary materials, the content of this paper is highly comprehensive, and it is judged that sufficient data is provided to support the conclusions. While the Abstract and Discussion sections are very clear and easy to understand, the main text presents numerous data sets obtained by varying electrode structures and operating conditions such as temperature and current density. The organization of these data is insufficient, making the authors' arguments difficult to fully grasp. As a result, readers tend to become confused when reading the text.\nAdditionally, the abstract states “boosting C2+ cathodic energy efficiency (CEEC2+) by 1.3 times,” but reviewers could not understand how the figure 1.3 was derived. The potential ratio between 298K and 348K shown in Fig. 4h is smaller than 1.3. Does including Faradic efficiency in the calculation yield 1.3?\n\nIs the methodology sound? Does the work meet the expected standards in your field?\nIs there enough detail provided in the methods for the work to be reproduced?\nIncluding the supplementary materials, sufficient information is provided for researchers in related fields to reproduce the experimental results. While it certainly contains high-level experimental results and discussion among the numerous papers published on CO₂ electrolysis, opinions may differ on whether it constitutes an outstanding paper in the field.", "reviewer_3": "The authors have performed an extensive study with very interesting results. The work is significant to the field as it shows how some limitations of temperature on CO2RR on Cu could be overcome. However, I still have some questions to clarify their results:\nFigure 1b in the introduction. Is this your experimental data or how did you come up with this figure?\n“Han et al. confirms that lower operating temperature (270 K) favor C-C coupling and hydrogenation pathways of *CH-COH intermediates on Cu-based catalysts,[21] suggesting incompatibility between C2+ production conditions and industrial elevated-temperature environments (Fig. 1c)” -> the literature shows other results where C-C coupling is enhanced at (slightly) elevated temperatures (for example reference 11 by Vos, or Zong et al where it stays reasonably stable https://doi.org/10.1115/1.4046552). This should be addressed in the introduction instead of selectively only mentioning reference 21. (moreover, the results in reference 21 could be influenced by not taking into account the temperature dependance of the reference electrode).\nHow have the points in figure 1D been chosen? Because some of the references (and also this study) also show data for C2+ production at other temperatures which are not added to this figure. Moreover, it might be confusing that in this figure the references numbers of the SI are used and not of the main text.\nFor the equations in the SI, especially for the diffusion layer thickness and the diffusion coefficient, do the authors have references for these equations and can they show which values they have used in their calculations?\nFor the techno-economic analysis, what are the input parameters (FE and cell voltage) based on? I suspect it is based on your own experimental data, but could you make it transparent where these numbers come from? Same holds for other input parameters such as the COP=3 for the cooling system energy efficiency ratio and some of the references costs that are mentioned. Could the authors make transparent where these numbers come from?\nIs there a specific reason the authors state all temperatures in Kelvin and not in degrees Celcius? The later could make it a bit more intuitive which temperatures are used.\nIn Figure 2a and S3a the authors say that the Cu oxidizes after immersion in the heated electrolyte. But doesn’t this also happen when the Cu is immersed in room temperature electrolyte? In other words, this is not a fair comparison of the effect of temperature on the state of the Cu and one needs to have a reference experiment with room temperature electrolyte. Otherwise this statement: “Therefore, elevated-temperature (348 K) electrolyte immediately affects the structure of Cu catalysts” can not be made.\nIt is interesting that the FE towards methane increases with temperature on Cu. This is different than observed in H-cell configurations previously (see for example the cited papers from Ahn and Vos, ref 16 and 11 respectively and the previously mentioned paper by Zong et al https://doi.org/10.1115/1.4046552). Do the authors have an explanation for this?\nThe authors hypothesize that the enhancement in HER is due to flooding of the GDE. But is there any experimental evidence for this or is this merely a hypothesis?\nFor Figure S11, it would give more information about the effect of temperature when the contact angles are measured after CO2RR at the different temperatures, to see if temperature actually has an influence on the contact angle or not.\nThe caption of Figure S13 is not clear, which catalyst is this and at which temperature has CO2RR been performed?\n“with the FE of H2 following the order Li+> Na+> K+> Cs+ (Supplementary Fig. S20)” Can you really say this? I hardly see an effect on the FE towards H2 and the largest shifts are in the FE towards CO and ethylene, but for H2 the FE is very similar, especially between Na, K and Cs.\nAt room temperature, in literature it is often observed that the C2+ formation is enhanced going from Li<Na<K<Cs. However, this is contradictory to what you explain where you say larger cations weaken *CO adsorption. How do you explain this?\nLine 261 has a typo, namely 209 K.\nSupplementary Figure S17 is mentioned in the text but does not see the most relevant in the context of the main text, so maybe extend why this figure is included. Same for Figure S18, this figure is not exactly related to the main text as in the main text it refers to the tandem catalyst while Figure S18 shows the product distribution on pure Ag.\nMoreover in line 227 the authors refer to Figure S19 but they should also refer to Figure 4d. The authors should make sure that all Figure references in the main text are appropriate and complete.\nFor figure S22, it might be interesting to also place the results without Pd here so it is easier to compare the effect of the Pd, without scrolling to the different figures. This would enhance the message and would make it easier for the audience to observe the results.\nIt would nice to look at the effect of temperature on the Pd-Cu2O/PTFE/Ag electrode, by plotting this in one figure so it is more clear. Maybe more a general comment, the paper shows the effect of temperature on the CO2RR with different catalysts, but the authors choose to mostly plot the effect of current density at a certain temperature in their graphs. Why do the authors not plot the effect of temperature in one graphs so that this effect is more clear for the audience, without having to compare different figures?\nFor the CEE calculations the Ecathode is used. Do the authors report these somewhere for the different experiments?\n“Additionally, Pd promotes CO2 protonation, which is commonly rate-limiting step of CO2RR, evidenced by an enhanced CO2- peak at 700 cm-1 at low potentials (Supplementary Fig. S29d).” Could the authors explain why a CO2- band shows that CO2 protonation is promoted, because there is no protonation needed to for CO2-\nIn general the authors have performed an extensive study with very interesting results. They claim they have delineated the three primary challenges encountered under industrially relevant elevated-temperature (>333 K) operation in flow cells: (i) dynamic reconstruction of Cu catalysts, (ii) accelerated GDE flooding caused by increased vapor pressure, and (iii) detrimental *CO desorption coupled with enhanced HER and transformed these challenges into opportunities. I agree they have come up with solutions for challenge III. For challenge II they also show a solution, however, the problem could be investigated in more detail there. And for challenge I, based on their data I’m not convinced what the effect of the temperature is on the dynamic reconstruction. Moreover, how is this reconstruction actually addressed later in this manuscript?"}, "author_response": "We would like to express our sincerest gratitude to all reviewers for their invaluable feedback, which has proved instrumental in enhancing the quality of our work. We have responded to each of the points raised in a meticulous and methodical manner. The comments of the reviewers are presented in Blue font, while our responses are in Black font. Furthermore, the revised text in the Manuscript and Supplementary Information is highlighted in Yellow. Please find below our detailed responses to each point raised.\n[... detailed point-by-point responses to Reviewers 1, 2, and 3 ...]"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have revised the manuscript carefully to address the comments from reviewers. I recommend this manuscript to be published on Nature Communications.", "reviewer_2": "The authors provided sufficient information to make me convince that the manuscript is worth publication.", "reviewer_3": "I thank the authors for their in-dept discussion on the points I raised earlier. With their clear and elaborate answers all my questions are answered and I recommend publication in Nature Communications. I only have a few minor things left which could improve the manuscript slightly; (I’ll only refer to the number and not copy your answers to keep a good overview).\n3; Maybe it would be good to add the references to figure 1D together with a short explanation that you take the highest FE and the FE at the highest temperature from these studies.\nIn general the authors answer with very long discussions in their rebuttal which make things clear to the reviewers, but I do not always see changes in the manuscript or SI which would also make this clear to the reader. Of course in this case the rebuttal would also be published so it is not necessary to copy the entire discussion, but for a few points I think it would be nice if the authors can add a short summary of their discussion in the rebuttal also to the manuscript or the SI. Especially for the discussions of points 13 and 21."}, "author_response": "We are deeply grateful for your positive comments and recommendation of acceptance for publication. We have fully considered your suggestions and made corresponding revisions. We have added references to Fig. 1d and specified in the caption that “The highest FE and the FE at the highest temperature from these studies”. Additionally, in the previous revision, to avoid overcomplicating the discussion and to maintain focus on the core findings of the study, we retained part of the extended discussion only in the Response Letter. Following your advice, we have now incorporated the key discussions related to “Comment 13” and “Comment 21” into the Supplementary Information as Supplementary Note 10 and Supplementary Note 13, respectively."}]

Decision letter