
==== Front
Nat Commun
Nat Commun
Nature Communications
2041-1723
Nature Publishing Group UK London

39251585
51871
10.1038/s41467-024-51871-z
Article
Cr dopant mediates hydroxyl spillover on RuO2 for high-efficiency proton exchange membrane electrolysis
Shen Yu 1
http://orcid.org/0000-0002-5596-0776
Zhang Xiao-Long 2
Qu Ming-Rong 2
Ma Jie 1
http://orcid.org/0000-0002-2301-7601
Zhu Sheng zhusheng@shiep.edu.cn

13
Min Yu-Lin minyulin@shiep.edu.cn

13
http://orcid.org/0000-0002-7805-803X
Gao Min-Rui mgao@ustc.edu.cn

2
http://orcid.org/0000-0003-3732-1011
Yu Shu-Hong shyu@ustc.edu.cn

2
1 https://ror.org/02w4tny03 grid.440635.0 0000 0000 9527 0839 Shanghai Key Laboratory of Materials Protection and Advanced Materials in Electric Power, College of Environmental and Chemical Engineering, Shanghai University of Electric Power, Shanghai, China
2 https://ror.org/04c4dkn09 grid.59053.3a 0000 0001 2167 9639 Division of Nanomaterials & Chemistry, Hefei National Research Center for Physical Sciences at the Microscale, New Cornerstone Science Laboratory, Department of Chemistry, University of Science and Technology of China, Hefei, China
3 https://ror.org/05d8cac05 Shanghai Institute of Pollution Control and Ecological Security, Shanghai, China
9 9 2024
9 9 2024
2024
15 78614 2 2024
19 8 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
Simultaneously improving the activity and stability of catalysts for anodic oxygen evolution reaction (OER) in proton exchange membrane water electrolysis (PEMWE) remains a notable challenge. Here, we report a chromium-doped ruthenium dioxide with oxygen vacancies, termed Cr0.2Ru0.8O2-x, that drives OER with an overpotential of 170 mV at 10 mA cm−2 and operates stably over 2000 h in acidic media. Experimental and theoretical studies show that the synergy of Cr dopant and oxygen vacancy induces an unconventional dopant-mediated hydroxyl spillover mechanism. Such dynamic hydroxyl spillover from Cr dopant to Ru active site changes the rate-determining step from OOH* formation to O2 formation and thus greatly improves the OER performance. Moreover, the Cr dopant and oxygen vacancy also play a crucial role in stabilizing surface Ru and lattice oxygen in the Ru-O-Cr structural motif. When assembled into the anode of a practical PEMWE device, Cr0.2Ru0.8O2-x enables long-term durability of over 200 h at an ampere-level current density and 60 degrees centigrade.

Developing highly active and stable anode catalysts for green hydrogen production is crucial but challenging. Here, the authors report a Cr0.2Ru0.8O2-x catalyst with an unconventional dopant-mediated hydroxyl spillover mechanism for high-efficiency proton exchange membrane water electrolysis.

Subject terms

Electrocatalysis
Electrocatalysis
Hydrogen fuel
https://doi.org/10.13039/501100001809 National Natural Science Foundation of China (National Science Foundation of China) 22293044 U1932213 Yu Shu-Hong issue-copyright-statement© Springer Nature Limited 2024
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pmcIntroduction

Proton exchange membrane water electrolysis (PEMWE) for green hydrogen production using renewable electricity from wind and solar power is regarded as an effective way to resolve the current global energy and environmental crisis1–3. The major bottleneck of PEMWE is the anodic oxygen evolution reaction (OER) with sluggish four-electron transfer kinetics4–10. Developing anode catalysts with high activity and durability in corrosive acidic media under oxidizing potential is crucial for improving the efficiency of PEMWE11–16. For decades, iridium (Ir) and its oxides have been considered the only practical OER catalysts in PEMWE due to their robust stability17–20. However, the extreme scarcity and relatively low activity hampered their large-scale industrial application21–24. Recently, ruthenium (Ru) based catalysts, especially RuO2, have attracted intensive attention owing to their lower price (~1/10 the price of Ir) and higher intrinsic activity. Unfortunately, the long-term stability of Ru-based catalysts remains a formidable challenge7,14–16,25,26.

Theoretically, the acidic OER activity and stability of RuO2 are a couple of contradiction based on the conventional mechanisms, namely adsorbate evolution mechanism (AEM) and lattice oxygen oxidation mechanism (LOM)27–29. In AEM, the overpotential is thermodynamically limited to a ceiling of 370 mV due to the scaling relationship between the adsorption energies of OOH* versus OH*, while the crystal structure of catalyst, in principle, remains intact during OER, leading to good stability. As to LOM, the participation of lattice oxygen in reaction can enable a much lower overpotential. However, such structural perturbation also contributes to the collapse of structure, thus undermining the stability. Moreover, RuO2 has been widely observed to undergo over-oxidation of Ru species to dissolvable RuO4 and demetallation of surface Ru under OER potentials30–33. To improve the activity and stability simultaneously, various strategies have been exploited for the modification of RuO2, including morphology tuning34–36, hetero structuring37–40, element doping41–49, defect engineering50–52, and others. Recent work has described that cation doping together with oxygen vacancies could greatly enhance the OER performance of RuO2 by synergistically regulating the chemical environment of Ru centers53–55. However, the dopant/host interaction, especially the dynamic adsorption/desorption behavior of oxygenated intermediates between them, and the underlying mechanism that boosts acidic OER have not been fully elucidated.

Herein, we develop a Cr-doped rutile RuO2 with oxygen vacancies (Cr0.2Ru0.8O2-x) as a high-performing anode catalyst in PEMWE. Operando and ex-situ spectroscopies reveal that the dopant/host interaction can improve OER kinetics via a dynamic dopant-mediated hydroxyl spillover mechanism, by which OH* adsorbed on Cr dopant can be transferred to adjacent Ru active site to generate OOH* during OER, thereby increasing the OOH* coverage on the catalyst surface. Computational studies confirm that Cr dopant and oxygen vacancy synergistically modulate the adsorption of oxygenated intermediates and the hydroxyl spillover from Cr to Ru is energetically favorable. The crucial role of Cr dopant and oxygen vacancy in stabilizing surface Ru and lattice oxygen in the Ru-O-Cr structural motif is also demonstrated. Consequently, Cr0.2Ru0.8O2-x requires an overpotential of only 170 mV at 10 mA cm−2 and operates steadily for 2000 h. In a practical PEMWE device, Cr0.2Ru0.8O2-x exhibits durability of over 200 h at 1 A cm−2 and 60 °C. Our findings unveil that dopant-mediated hydroxyl spillover is a promising strategy for the design of anode catalyst in highly efficient PEMWE.

Results

Synthesis and characterization of Cr0.2Ru0.8O2-x

The Cr0.2Ru0.8O2-x catalyst was synthesized via a simple and scalable sol-gel method (Fig. 1a). Briefly, the metal ion precursors were first gelated to produce a liquogel. After an air annealing treatment, the liquogel was activated and transformed to metal oxides powder. The obtained powder was then acid-leached to remove unstable species and form the final catalyst. For comparison, catalysts with different Cr: Ru mole ratios and annealing temperatures were also synthesized using the same method.Fig. 1 Synthesis scheme and physical characterizations of Cr0.2Ru0.8O2-x.

a Schematic synthesis of Cr0.2Ru0.8O2-x. b XRD patterns and c Raman spectra of Cr0.2Ru0.8O2-x, homemade RuO2, and commercial RuO2. d TEM image and diameter distribution (inset) of Cr0.2Ru0.8O2-x. e HADDF-STEM images of Cr0.2Ru0.8O2-x under low and high (inset) magnifications. f Corresponding fast Fourier transform pattern of inset in (e). g EDS mapping of Cr0.2Ru0.8O2-x.

In Fig. 1b, the X-ray diffraction (XRD) pattern shows that the crystalline phase of Cr0.2Ru0.8O2-x matched the rutile-structured RuO2 without phase segregation. We noted that the diffraction peaks of homemade RuO2 were shifted to lower angles than those of commercial RuO2, presumably owing to the lattice expansion induced by the formation of oxygen vacancies56,57, an important attribute in lowering the OER activation energy and stabilizing the intermediates during the reaction11. With the increased amount of Cr dopant, the diffraction peaks were gradually shifted to higher angles, suggesting a lattice contraction due to the smaller atomic radius of Cr (1.27 Å) compared to Ru (1.32 Å) (Supplementary Fig. 1). Cr0.2Ru0.8O2-x, homemade RuO2, and commercial RuO2 present the same characteristic Raman peaks at 521, 638, and 705 cm−1, corresponding to the Ru-O vibrational modes of Eg, A1g, and B2g, respectively (Fig. 1c), which confirms the incorporation of Cr in RuO2. Transmission electron microscopy (TEM) and high-angle annular dark-field scanning TEM (HAADF-STEM) images (Fig. 1d and Supplementary Fig. 2) of Cr0.2Ru0.8O2-x clearly show an interconnected and uniformly sized nanoparticles morphology with an average diameter of ~6.5 nm (inset in Fig. 1d), slightly smaller than that of homemade RuO2 (Supplementary Fig. 3a). Each nanoparticle exhibits good crystallinity and well-resolved lattice fringes corresponding to the (110) planes of rutile RuO2 (Figs. 1e, f), testifying the lattice contraction caused by the incorporation of Cr (Supplementary Figs. 3b–d), in agreement with the XRD analysis. The lattice contraction represents a shortened interatomic Ru-Cr distance in Cr0.2Ru0.8O2-x, which potentially contributes to promote dopant/host interaction. Energy-dispersive spectroscopic (EDS) mapping images display the homogenous distribution of Ru, Cr, and O elements throughout the catalyst (Fig. 1g and Supplementary Figs. 4, 5). The co-existence of Ru and Cr was also evidenced by the electron energy-loss spectroscopy (EELS) analysis of two randomly selected regions in a single nanocrystal (Supplementary Fig. 6). Brunauer-Emmett-Teller (BET) adsorption/desorption isotherms disclose that the Cr0.2Ru0.8O2-x nanoparticles possess a relatively high surface area of 40.0 m2 g−1 (Supplementary Fig. 7). The overall Ru percentages and Cr/Ru mole ratios of different catalysts were further determined by inductively coupled plasma mass spectrometry (ICP-MS) (Supplementary Fig. 8 and Supplementary Table 1).

Electronic properties of Cr0.2Ru0.8O2-x

The local structure and chemical states of Ru, Cr, and O in Cr0.2Ru0.8O2-x were investigated by X-ray photoelectron spectroscopy (XPS) (Supplementary Fig. 9). Given that the Ru 3d region is overlapped with C 1 s peak of adventitious carbon, we calibrated all the binding energies based on the lattice oxygen signal centered at 529.8 eV and analyzed the Ru 3p region instead38,58. Figure 2a shows the doublet peaks of Cr 2p3/2 and 2p1/2 orbitals of Cr0.2Ru0.8O2-x. The Cr 2p3/2 spectrum could be fitted with the peaks at 576.0 and 577.9 eV, ascribable to Cr3+-O and Cr3+-OH59,60. For Ru 3p3/2, the fitted peaks at 463.1 and 465.1 eV could be assigned to Ru4+ and Ru3+, respectively (Fig. 2b)50,61. Compared to homemade RuO2, Cr0.2Ru0.8O2-x exhibited a lower integral area ratio of Ru4+ and Ru3+ peaks (Ru4+/Ru3+), implying that Ru species in Cr0.2Ru0.8O2-x possess a slightly lower oxidation state than that in homemade RuO2. As the content of Cr dopant increased from 0% to 40%, the Ru4+/Ru3+ value decreased from 2.09 to 1.35 (Supplementary Fig. 10a), which exhibited a good linear relationship (Supplementary Fig. 11a), suggesting that Cr doping increased the concentration of Ru3+ species. In Fig. 2c, the O 1 s spectrum of Cr0.2Ru0.8O2-x could be deconvoluted into three peaks located at 529.8, 531.1, and 533.0 eV, corresponding to lattice oxygen (OL), oxygen vacancies (OV), and surface-adsorbed hydroxyl species (OHad), respectively53–55. We noted that the proportion of surface oxygen vacancies and lattice oxygen (OV/OL) increased markedly after doping (Supplementary Fig. 10b). A higher OV/OL ratio implies preferential adsorption of water at the intrinsic OV sites due to the decrease of steric hindrance54,62, which pertains to optimizing the adsorption of oxygenated intermediates. Moreover, a linear trend was also found between the OV/OL value and the doping ratio (Supplementary Fig. 11b), indicating that more oxygen vacancies were induced by the incorporation of Cr. The electron paramagnetic resonance (EPR) spectra confirmed the higher OV concentration in Cr0.2Ru0.8O2-x compared with that in homemade RuO2 (Supplementary Fig. 12)63. According to the neutrality principle, oxygen vacancies will be formed to maintain the electrostatic balance when a lower valence cation dopant (Cr3+) is incorporated into the host metal ions (Ru4+) in the oxide, and the valence of the host metal ions (Ru4+) will be reduced correspondingly64,65.Fig. 2 Electronic structure characterizations of Cr0.2Ru0.8O2-x.

a Cr 2p core level XPS spectra of Cr0.2Ru0.8O2-x. b Ru 3p3/2 and c O 1 s core level XPS spectra of Cr0.2Ru0.8O2-x and homemade RuO2. d Normalized Ru K-edge XANES spectra and e Ru K-edge FT-EXAFS spectra of Cr0.2Ru0.8O2-x, RuO2 and Ru foil. f Ru K-edge WT-EXAFS spectra of Cr0.2Ru0.8O2-x and RuO2. g Normalized Cr K-edge XANES and h Cr K-edge FT-EXAFS spectra of Cr0.2Ru0.8O2-x, Cr2O3, and Cr foil. i Cr K-edge WT-EXAFS spectra of Cr0.2Ru0.8O2-x and Cr2O3.

We further employed X-ray absorption spectroscopy (XAS) to evaluate the valence state and coordination environment of Ru and Cr sites in Cr0.2Ru0.8O2-x. Figure 2d depicts the Ru K-edge X-ray absorption near-edge structure (XANES) spectrum of Cr0.2Ru0.8O2-x, along with Ru foil and commercial RuO2 as references. The absorption edge of Cr0.2Ru0.8O2-x was found to be slightly shifted to lower energy compared with that of commercial RuO2 (inset in Fig. 2d), hinting at a relatively lower Ru oxidation state in Cr0.2Ru0.8O2-x, consistent with the XPS results. The Fourier-transformed extended X-ray absorption fine-structure (FT-EXAFS) spectrum of Cr0.2Ru0.8O2-x at the Ru K-edge showed a prominent peak at ~1.50 Å affiliated with the first Ru-O coordination shell, identical to that of RuO2 (Fig. 2e). Quantitative FT-EXAFS fitting yielded a Ru coordination number of 5.67 (Supplementary Fig. 13 and Supplementary Table 2), attributing to the presence of oxygen vacancies, which serve as the nucleophilic sites in promoting O-O bond formation66. We also analyzed the XANES and EXAFS spectra of Cr0.2Ru0.8O2-x and reference samples at the Cr K-edge, showing that the oxidation state of Cr in Cr0.2Ru0.8O2-x was very close to Cr2O3 of +3 (Fig. 2g). Additionally, the distinct FT-EXAFS spectrum compared with that of the Cr2O3 or Cr reference revealed that no obvious Cr2O3 or Cr metal nanoparticles were formed in Cr0.2Ru0.8O2-x (Fig. 2h), indicating the incorporation of Cr inside the RuO2 lattice, in agreement with the HAADF-STEM results. The wavelet transform (WT) EXAFS spectra confirmed that the Cr dopants were uniformly distributed in the RuO2 matrix (Figs. 2f, i, and Supplementary Fig. 14).

Electrocatalytic performance in solution and PEMWE

The OER catalytic activity of Cr0.2Ru0.8O2-x was assessed using the rotating disk electrode (RDE) method in 0.1 M HClO4. Linear sweep voltammetry (LSV) of Cr0.2Ru0.8O2-x exhibits an overpotential of 170 ± 6 mV at 10 mA cm−2 (Fig. 3a, Supplementary Figs. 15–17 and Supplementary Note 1), outperforming that of homemade RuO2 (260 ± 10 mV) and commercial RuO2 (330 ± 13 mV). The Tafel slope of Cr0.2Ru0.8O2-x in the second region was 75.3 mV dec-1 (Fig. 3b), much smaller than that of homemade RuO2 (118.9 mV dec-1) and commercial RuO2 (127.3 mV dec-1), suggesting a possible change in the rate-determining step (RDS) at high overpotential67,68. Electrochemical impedance spectroscopy (EIS) shows the lowest charge-transfer resistances (Rct) for Cr0.2Ru0.8O2-x, indicating a superior charge transfer and enhanced OER kinetics (Supplementary Fig. 18)34,46,49. The electrochemically active surface areas (ECSA) of different catalysts were also calculated by estimating the double-layer capacitance (Cdl) from the cyclic voltammogram (CV) curves in the non-Faradaic region (Fig. 3c, Supplementary Fig. 19 and Supplementary Note 2). Cr0.2Ru0.8O2-x exhibits the largest ECSA (220.3 cm2) compared with that of homemade RuO2 (115.7 cm2) and commercial RuO2 (39.4 cm2) (Supplementary Table 3). Figure 3d compares several important performance metrics of different studied catalysts (Supplementary Table 4 and Supplementary Notes 3–5). Cr0.2Ru0.8O2-x yields a turnover frequency (TOF) of 0.127 ± 0.010 s-1, which is 9.1 and 25.4 folds greater than that of homemade RuO2 and commercial RuO2, respectively. Additionally, the specific activities of Cr0.2Ru0.8O2-x normalized by the Ru loading mass, the BET surface area, or the ECSA were also much higher than those of homemade RuO2 and commercial RuO2. Overall, the Cr0.2Ru0.8O2-x catalyst exhibits the highest intrinsic activity, possibly caused by a different OER mechanism. We further utilized in-situ gas chromatography (GC) to analyze the O2 gas produced from the Cr0.2Ru0.8O2-x decorated carbon paper electrode at 10, 100, 200, and 500 mA cm−2 (Supplementary Fig. 20). The quantified O2 amount at these current densities all matched well with the theoretical values, representing an average Faradaic efficiency (FE) of 99.8 ± 0.3% (Supplementary Fig. 21 and Supplementary Note 6), indicating that the O2 formation through the four-electron transfer during OER is the only reaction pathway over Cr0.2Ru0.8O2-x.Fig. 3 OER performance.

a LSV curves and b Tafel plots of Cr0.2Ru0.8O2-x, homemade RuO2, and commercial RuO2 on a 0.196 cm2 electrode (100% iR correction, where R was determined to be 28.5 ± 0.4 Ω). c Cdl plots of Cr0.2Ru0.8O2-x, homemade RuO2, and commercial RuO2. d Radar diagram of some major OER performance metrics of Cr0.2Ru0.8O2-x, homemade RuO2, and commercial RuO2. e Chronopotentiometry curves of Cr0.2Ru0.8O2-x, homemade RuO2, and commercial RuO2 at a constant current density of 10 mA cm−2. f Polarization curves of the PEMWE device with Cr0.2Ru0.8O2-x and commercial RuO2 as anode catalysts at 60 °C. g Chronopotentiometry curves of the PEMWE device with Cr0.2Ru0.8O2-x and commercial RuO2 as anode catalysts operated at 1 A cm−2 and 60 °C. Insets show photographs of the PEMWE device.

Next, we investigated the acidic OER stability of Cr0.2Ru0.8O2-x by employing the accelerated degradation tests (ADT). After 5000 cycles, the LSV curve of Cr0.2Ru0.8O2-x experienced a minor shift, with the overpotential at 10 mA cm−2 increased by mere 5 mV (Supplementary Fig. 22). In contrast, the homemade RuO2 displayed a pronounced positive shift of 81 mV, while the commercial RuO2 almost lost its OER activity entirely. Additionally, the chronopotentiometry (CP) curves of Cr0.2Ru0.8O2-x shows that the overpotential at 10 mA cm−2 increased 26 mV after 2000 h (Fig. 3e), representing a degradation rate of 13 μV h−1. In stark contrast, the activity of homemade RuO2 and commercial RuO2 decayed rapidly within 120 h and 30 h, respectively. At a higher current density of 100 mA cm−2, Cr0.2Ru0.8O2-x also demonstrated superior stability with an additional overpotential of 96 mV for over 300 h (Supplementary Fig. 23). The metal dissolution during CP test at 10 mA cm−2 was checked by ICP-MS (Supplementary Fig. 24). It shows that the concentrations of Ru and Cr in the electrolyte were 168 and 91 ppb after 2000 h stability test, corresponding to the mass loss of ~1.67% with Ru and ~7.79% with Cr over their stoichiometric loadings in Cr0.2Ru0.8O2-x (Supplementary Note 7). Accordingly, the stability number (S-number) of Cr0.2Ru0.8O2-x at 2000 h was determined to be 1.1 × 106 noxygen nRu-1 (Supplementary Note 8), 35.5 times as that of homemade RuO2 at 100 h (3.1 × 104 noxygen nRu-1). These results place Cr0.2Ru0.8O2-x among the most active and stable Ru-based catalysts documented in acidic electrolyte (Supplementary Table 5).

Encouraged by the three-electrode test results, we further assembled a PEMWE device with Cr0.2Ru0.8O2-x as anode catalyst using deionized water as feed at 60 °C (Supplementary Fig. 25). The polarization curves in Fig. 3f show that Cr0.2Ru0.8O2-x requires a cell voltage of 1.77 V at 1 A cm−2, which is 260 mV lower than that of commercial RuO2. More impressively, Cr0.2Ru0.8O2-x can be operated steadily at 1 A cm−2 over 200 h, with potential increase of only 64 mV, which is in stark contrast with the commercial RuO2 that deactivated within mere 5 h (Fig. 3g). Subsequent structural characterizations of the used Cr0.2Ru0.8O2-x catalyst revealed that the structure, morphology and composition were well preserved (Supplementary Fig. 26). The performance of Cr0.2Ru0.8O2-x in PEMWE surpasses most Ru-based catalysts reported previously and even some Ir-based catalysts (Supplementary Table 6), demonstrating its prospect for industrial-scale water electrolysis.

Structure-stability relationship

To detect the structural evolution of Cr0.2Ru0.8O2-x, we performed a separate CP test in 0.1 M HClO4 electrolyte for 300 h at 10 mA cm−2. The surface structure and morphology of the catalyst after OER were found to be nearly unchanged from the pristine state (Supplementary Figs. 27, 28). We noted that the lattice spacing of Cr0.2Ru0.8O2-x after OER was slightly increased (Supplementary Figs. 28b, e), probably because the mass loss of Cr was more than that of Ru during the reaction, giving rise to a decrease of Cr doping in Cr0.2Ru0.8O2-x. Nevertheless, such slight lattice expansion caused by the surface metal dissolution seemed to not affect the OER performance, showing the robustness of Cr0.2Ru0.8O2-x against structural perturbation. Intriguingly, the Raman spectrum exhibits a new vibration peak of Cr-OH at ~800 cm−1 after OER (Supplementary Fig. 29a)69,70, indicating that Cr dopant may serve as a Lewis acid site to dynamically split water molecules and capture hydroxyl species during the reaction59. To verify the existence of Cr-OH, the Raman spectra were recorded after another CP test in D2O supported 0.1 M HClO4 electrolyte for 3 h at 10 mA cm−2. In the deuterium isotopic measurement, the peak of Cr-OH at ~800 cm−1 was shifted to lower wavenumbers of ~580 cm−1 (Supplementary Fig. 29b), in accordance with the expected shifts from the mass formula (γ = 72.76%) (Supplementary Note 9), confirming that the peak at ~800 cm−1 belongs to the Cr-OH vibration on Cr0.2Ru0.8O2-x.

We also analyzed the chemical states of Ru, Cr, and O in Cr0.2Ru0.8O2-x before and after OER by XPS (Supplementary Fig. 30a) to demonstrate the over-oxidation and dissolution resistance of Cr0.2Ru0.8O2-x. The slightly decreased area ratio of Ru4+/Ru3+ together with the positive shift of Cr3+-O after stability test revealed that Cr dopants donate partial electrons to Ru active sites in the Ru-O-Cr structural motif to prevent Ru over-oxidation (Supplementary Figs. 30b, c)43. Noticeably, the contribution of Cr3+-OH to the Cr 2p3/2 peak increased compared with that of the pristine sample, confirming the capture of OH* on Cr dopants from water proposed by the Raman results. The O 1 s (Supplementary Fig. 30d) and EPR (Supplementary Fig. 31) spectra show that the OV/OL ratio was significantly reduced after OER. We thus surmise that, with the presence of Cr dopant and oxygen vacancy, the formation energy of oxygen vacancy was raised and the O–O coupling from lattice oxygen via LOM was inhibited. These observations provide a preliminary explanation for the stability of the Cr0.2Ru0.8O2-x catalyst.

OER enhancement mechanism

Our Raman and XPS analysis on Cr0.2Ru0.8O2-x revealed the capture of hydroxyl species on Cr dopants from water. We thus speculated that the surface Cr dopants could participate in the catalytic OER pathway and enhance the kinetics. To this end, we carried out quasi in-situ XPS to probe the variation in adsorbed hydroxyl species on Cr dopants from open-circuit potential (OCP) to 1.8 V. Results show that the area ratio of Cr3+-OH in Cr 2p3/2 peak displays an opposite trend to the LSV curve with the increase of anodic potential (Fig. 4a, b). In the pre-catalysis stage (< 1.3 V), the Cr3+-OH ratio was maintained at a high level and hardly decreased. However, when OER commenced, the Cr3+-OH ratio declined rapidly as the current intensity increased, indicating the accelerated participation of OH* on Cr dopants in the reaction. Operando surface-enhanced Raman scattering (SERS) was applied to investigate the dynamic surface structural evolution (Supplementary Figs. 32–34). For Cr0.2Ru0.8O2-x, the vibration peak area of Cr-OH at ~800 cm−1 presents a similar decreasing tendency with increasing potential (Fig. 4c, d), affirming the involvement of Cr dopants in OER. In addition to the vibration peaks of Ru-O bands appears at 521, 638, and 705 cm−1 throughout the potential interval, a new Raman peak at ~720 cm−1 could be deconvoluted above 1.4 V, assignable to the generation of Ru-OOH intermediates38,71. These OOH* species gradually enriched on the Ru sites as the potential increased (1.3-1.6 V) and then deprotonated to form O2 at high overpotential (> 1.6 V), when the OER proceeds much more rapidly, resulting in a “volcano curve” of surface coverage. In contrast, the amount of Ru-OOH on homemade RuO2 kept on increasing during OER, with a slower growth rate than that of Cr0.2Ru0.8O2-x (Fig. 4d and Supplementary Fig. 35). We noted that the decrement of Cr-OH combined with the intensified enrichment of Ru-OOH suggest a different mechanism in which OOH* on active site can be converted from O* via the dynamic adsorption of OH* desorbed from adjacent dopant. To further corroborate the source and amount of Ru-OOH on Cr0.2Ru0.8O2-x, operando SERS were performed on Cr2O3 (Supplementary Fig. 36a). As the potential increased, the peak area of Cr-OH initially unchanged and then slightly increased at high overpotential, indicating that OH* adsorbed on Cr site should not be oxidized to O* or OOH* and thus tends to act as a provenance to form Ru-OOH, consistent with the LSV curve of Cr2O3 within the same potential range (Supplementary Fig. 36b). The operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) spectra (Supplementary Figs. 37, 38) of Cr0.2Ru0.8O2-x show an apparent signal peak at ~1230 cm−1 above 1.4 V, corresponding to the generation of OOH*, which can be regarded as Ru-OOH since the formation of Cr-OOH is excluded by the operando SERS and LSV results on Cr2O3. Compared with homemade RuO2, Cr0.2Ru0.8O2-x shows stronger peak intensities of OOH*. Moreover, the peak area variation with increasing potential (Supplementary Fig. 39) exhibits a similar trend as that of Ru-OOH measured by operando SERS. These findings together evidence the faster generation of Ru-OOH on Cr0.2Ru0.8O2-x.Fig. 4 Quasi in situ XPS, operando SERS, and operando DEMS measurements understanding the mechanism on Cr0.2Ru0.8O2-x catalyst during OER.

a Quasi in situ XPS spectra of Cr 2p3/2 for Cr0.2Ru0.8O2-x under applied potentials from OCP to 1.8 V. b Area ratio of Cr3+-OH and OER current (without iR correction) as a function of applied potential for Cr0.2Ru0.8O2-x. c Operando SERS spectra of Ru-O and Cr-OH bands for Cr0.2Ru0.8O2-x under applied potentials from OCP to 1.8 V. d Normalized peak areas of Cr-OH and Ru-OOH as a function of applied potential for Cr0.2Ru0.8O2-x and homemade RuO2. e Operando DEMS measurements for Cr0.2Ru0.8O2-x. Top: CV cycles (without iR correction); middle: DEMS signals of 32O2 (16O + 16O) and 34O2 (16O + 18O) collected during CV cycles; bottom: signal intensity ratio of 34O2:32O2. f Schematic illustration of dopant-mediated hydroxyl spillover mechanism on Cr0.2Ru0.8O2-x for acidic OER.

We used 18O isotope-labeled operando differential electrochemical mass spectrometry (DEMS) to study the OER mechanism on Cr0.2Ru0.8O2-x (Supplementary Fig. 40), following a test protocol45,54. First, we labeled the catalyst with 18O by operating CP test. We then detected the isotope signal of evolved O2 by scanning CV in H216O electrolyte. If OER occurs through LOM pathway, 34O2 can be produced by the combination of 18O labeled lattice oxygen and 16O in water, thus the signal ratio of 34O2/32O2 would be significantly higher than the natural abundance determined 34O2/32O2 (Supplementary Note 10) and gradually decrease as the reaction proceeds due to the consumption of labeled 18O in lattice. In contrast, in AEM pathway, 34O2 can only be generated from 18O and 16O in water because lattice oxygen does not participate in OER, therefore the 34O2/32O ratio would be identical to the natural abundance determined 34O2/32O2 and remain constant. As Fig. 4e shows, the 34O2/32O2 ratio was maintained at around 0.4% during OER, suggesting the OER mechanism on Cr0.2Ru0.8O2-x is similar to AEM rather than LOM72–74.

In light of the above analysis, we propose a mechanism with dopant-mediated hydroxyl spillover on Cr0.2Ru0.8O2-x catalyst for acidic OER (Fig. 4f), which is different from conventional AEM and LOM (Supplementary Figs. 41a, b). Dual-site oxide path mechanism (OPM) (Supplementary Fig. 41c) can also be excluded because distinctive OOH* intermediates involved in the AEM-like OER were detected in both operando SERS and operando ATR-SEIRAS measurements. It has been recognized that rutile RuO2 follows AEM in acidic media, with the attack and oxidation of water on O* to form OOH* as the RDS45,53–55. Our modified OER mechanism involves the accelerated formation and increased coverage of OOH* intermediates on the catalyst surface via the dynamic hydroxyl spillover from dopant (Cr) to the adjacent active site (Ru), which lowers the energy barrier of RDS in conventional AEM and greatly improves the OER activity. Apart from the structural integrity inherited from AEM, the lowered energy barrier of RDS under the modified mechanism mitigates the over-oxidation of Ru active sites, thus the OER stability is also improved.

Furthermore, our quasi in-situ XPS analysis exhibits that the peak of Cr3+-O shifted continuously towards higher binding energy when the applied potential increased from OCP to 1.8 V (Fig. 4a), confirming that Cr dopants protect Ru active sites from over-oxidation by donating electrons to Ru. The area ratio of Ru4+/Ru3+ increased in the pre-catalysis stage due to the oxidizing potential, suggesting an activation of Ru sites prior to OER (Supplementary Figs. 42a, 43a)43. The Ru4+/Ru3+ value then restored to its original level at low overpotential and stayed nearly constant at high overpotential, confirming the stable Ru chemical state during OER. Additionally, the OV/OL ratio initially decreased and then showed little changes at high overpotential (Supplementary Figs. 42b, 43b), indicating the crucial role of oxygen vacancy in stabilizing the Ru-O-Cr structural motif.

To better understand the OER mechanism and the source of boosted activity and stability, density functional theory (DFT) calculations were performed. Based on the XRD and HAADF-STEM observations, we constructed three models, including perfect RuO2 (RuO2), Cr-doped RuO2 (Cr-RuO2), and Cr-doped RuO2 with oxygen vacancy (Cr-RuO2-OV) on RuO2 (110) surface (Supplementary Figs. 44-47 and Supplementary Data 1), to investigate the synergistic effect of Cr dopant and oxygen vacancy. We first calculated the Gibbs free energies for RuO2 (AEM) and Cr-RuO2-OV (AEM and dopant-mediated hydroxyl spillover mechanism) to confirm the favorable OER pathway (Fig. 5a, Supplementary Figs. 48, 49 and Supplementary Note 11). In AEM pathway, the formation of OOH* from O* is the RDS for both RuO2 and Cr-RuO2-OV, and the limiting free energy barrier for Cr-RuO2-OV (1.90 eV) is even higher than that for RuO2 (1.87 eV). Nevertheless, when taking the dopant-mediated hydroxyl spillover into account, the RDS for Cr-RuO2-OV changes from OOH* formation to O2 formation, and the limiting free energy barrier decreased drastically to 1.76 eV, in line with the Tafel analysis (Fig. 3b), suggesting that the OER activity of RuO2 can be indeed enhanced by activating OH* at adjacent doping sites. Besides, the OH* deprotonation energy (1.82 eV) on Cr site of Cr-RuO2-OV is much higher than the spillover energy (1.07 eV) from Cr to Ru (Fig. 5b), corroborating that OH* on Cr cite tends to spillover to Ru site rather than to be oxidized to O*. The projected density of states (PDOS) reveals that the introduction of Cr dopant and oxygen vacancy pushes the Ru d-band center (εRu) close to the Fermi level, moving from −3.38 eV (RuO2) to −3.17 eV (Cr-RuO2), then to −3.07 eV (Cr-RuO2-OV) (Fig. 5c). The up-shift of Ru d-band center increases the binding strength between Ru active sites and oxygenated intermediates, which is deleterious to the OER activity due to the scaling relationship in conventional AEM, explaining the higher limiting free energy barrier for Cr-RuO2-OV compared to RuO2 following AEM pathway. However, the enhanced binding strength of oxygen species on Ru site would accelerate the hydroxyl adsorption from adjacent Cr dopant to form Ru-OOH. Meanwhile, the presence of oxygen vacancy significantly down-shifts the Cr d-band center (εCr) from −3.36 eV (Cr-RuO2) to −4.20 eV (Cr-RuO2-OV), indicating much weaker adsorption and more difficult deprotonation of OH* on Cr site, conducive to the efficient hydroxyl desorption. Therefore, we theoretically validated that Cr dopant and oxygen vacancy synergistically modulate the adsorption of oxygenated intermediates and the hydroxyl spillover from Cr to Ru is energetically favorable.Fig. 5 DFT calculations.

a Free energy profiles of RuO2 and Cr-RuO2-OV with different OER pathways. b OH* deprotonation energy on Cr site of Cr-RuO2-OV. Insets show the optimized structures in the corresponding steps. The silver, red, golden, and white balls represent Ru, O, Cr, and H atoms, respectively. c PDOS of Ru 4d and Cr 3d-bands for RuO2, Cr-RuO2, and Cr-RuO2-OV; corresponding d-band centers are denoted by dashed lines. d Vacancy formation energies of surface Ru and lattice oxygen for RuO2, Cr-RuO2, and Cr-RuO2-OV.

The vacancy formation energies of surface Rucus (ΔEVRu) and Olat (ΔEVO) for different models were also calculated (Supplementary Figs. 50, 51 and Supplementary Note 11). Figure 5d shows that ΔEVRu increases from 1.68 eV for RuO2 to 2.53 eV for Cr-RuO2, indicating that surface Ru can be stabilized by Cr dopant. With the presence of oxygen vacancy, ΔEVRu decreases to 2.04 eV for Cr-RuO2-OV due to lower overall Ru-O chelation number, which, however, is still 0.36 eV higher than that for RuO2, suggesting a more stable surface Ru in Cr-RuO2-OV than in RuO2. The ΔEVO values for RuO2, Cr-RuO2 and Cr-RuO2-OV were calculated to be 3.55, 3.63 and 3.75 eV, respectively, manifesting that both Cr dopant and oxygen vacancy can stabilize surface lattice oxygen in the Ru-O-Cr structural motif. Our DFT results thus predict the enhanced OER stability of Cr0.2Ru0.8O2-x, agreeing with experimental observations.

Discussion

In summary, we report a Cr0.2Ru0.8O2-x catalyst that exhibits boosted OER activity and stability in acidic electrolyte. Experimental and theoretical studies show that the synergy of Cr dopant and oxygen vacancy induces an unconventional dopant-mediated hydroxyl spillover mechanism. Such dynamic hydroxyl spillover from Cr dopant to Ru active site changes the RDS from OOH* formation to O2 formation and thus greatly improves the OER performance. Moreover, the Cr dopant and oxygen vacancy also play a crucial role in stabilizing surface Ru and lattice oxygen in the Ru-O-Cr structural motif. Benefiting from the dopant-mediated hydroxyl spillover, a practical PEMWE device assembled with Cr0.2Ru0.8O2-x as anode catalyst performs steadily over 200 h at 1 A cm−2 and 60 °C. This work offers a prospective catalyst design concept through tuning OER mechanism for the future development of PEMWE.

Methods

Chemicals

Ruthenium chloride trihydrate (RuCl3·3H2O, ≥ 98%), Chromic chloride hexahydrate (CrCl3·6H2O, ≥ 99%), ruthenium oxide (RuO2, ≥ 99.95%), chromium oxide (Cr2O3, ≥ 99%) and deuterium oxide (D2O, 99.9 atom % D) were purchased from Adamas Reagent Co., Ltd. Citric acid monohydrate (C6H8O7·H2O, ≥ 99.7%), ethanol (C2H5OH, ≥ 99.7%), sodium hydroxide (NaOH, ≥ 96%), nitric acid (HNO3, 65 ~ 68%), hydrochloric acid (HCl, 36% ~ 38%), and perchloric acid (HClO4, 70 ~ 72%) were purchased from Sinopharm Chemical Reagent Co., Ltd. Nafion solution (5 wt%) was purchased from DuPont Co. 18O water (H218O, ≥ 97%) was purchased from Macklin Biochemical Co., Ltd. All chemical reagents were used as received without further purification.

Synthesis of Cr0.2Ru0.8O2-x

In a typical process, 100 mg of RuCl3·3H2O and 26 mg of CrCl3·6H2O were mixed with 10 mL of ethanol to form a homogeneous solution. 10 mL of 1 M C6H8O7·H2O in ethanol was added dropwise into the solution under vigorous stirring. The solution was then aged overnight and dried at 120 °C to produce a brown liquogel. Next, the liquogel was annealed in air at 650 °C for 3 h. After cooling to room temperature, the powder was careful grinded and immersed in 1 M HCl for 12 h. Finally, the sample was washed three times with ethanol and deionized water, respectively, and dried in vacuum at 60 °C to obtain Cr0.2Ru0.8O2-x. Catalysts with different Cr/(Cr+Ru) mole ratios (0, 0.05, 0.1, 0.3, 0.4) and annealing temperatures (350, 450, 550, 750 °C) were also prepared following the same process.

Characterizations

XRD patterns were recorded on a Bruker D8 Advance diffractometer with Cu Kα radiation. Raman spectra were captured by a LabRAM HR Evolution spectrometer with an excitation laser of 633 nm. TEM and HRTEM were performed on a JEM-2100F transmission electron microscope under an accelerating voltage of 200 kV. HAADF-STEM, EDS mapping and EELS analysis were carried out on a JEM-ARM 200 F aberration-corrected transmission electron microscope at 200 kV. The N2 adsorption isotherms and BET surface areas were obtained by a Micromeritics ASAP 2460 system. ICP-MS was measured on a PerkinElmer NexION 300X spectrometer. For ICP sample preparation, 2 mg of sample was mixed with 10 mL of 10 M NaOH in a digestion tank, followed by heating at 220 °C in a microwave digester for 30 minutes. After cooling, 10 mL of HNO3 was added to the digestion tank, followed by heating at 180 °C for 15 minutes. After complete digestion, the solution was diluted to a desired concentration by water. EPR was conducted on a Bruker A300 instrument at 77 K. XPS data were collected on a Thermo ESCALAB 250XI spectrometer equipped with a monochromatic Al Kα X-ray source (1486.6 eV). XAS data were gathered at the beamline 1W1B station in the Beijing Synchrotron Radiation Facility.

Electrochemical measurements

All the electrochemical measurements were performed in a standard three-electrode cell connected to a BioLogic SP300 workstation under room temperature. Hg/Hg2SO4 (saturated K2SO4) electrode and graphite rod were served as the reference and counter electrodes, respectively. The reference electrode was calibrated in a three-electrode system consisted of Pt foils as both working electrode and counter electrode in H2-saturated 0.1 M HClO4 electrolyte (pH = 1 ± 0.02), which was freshly prepared by diluting 1.66 mL of HClO4 into 200 mL of DI water. Potentials measured were calibrated to reversible hydrogen electrode (RHE) by the following equation: E(RHE) = E(Hg/Hg2SO4) + 0.059 pH + 0.656 V. To prepare the working electrode, 5 mg of catalyst was dispersed in a mixture solution containing 950 μL of isopropanol and 50 μL of Nafion solution, followed by ultrasonicating in ice water for 1 h to form the catalyst ink, of which 20 μL was poured on a pre-polished RDE with a glassy carbon disk (Pine, 5 mm in diameter) and dried naturally before use, resulting in the catalyst loading of ~0.5 mg cm−2. The RDE tests were run in 100 mL of O2-saturated 0.1 M HClO4 electrolyte. LSV curves were recorded at a scan rate of 5 mV s-1 and a rotating speed of 1600 rpm to remove O2 bubbles formed on the catalyst surface. EIS measurements were performed by applying a sinusoidal voltage of 5 mV with an amplitude at 1.4 V versus RHE over a frequency range from 100 kHz to 100 mHz. To estimate the Cdl values, cyclic voltammograms were measured at different scan rates in the potential region of 0.997–1.097 V versus RHE. The ADT experiments were carried out by potential cycling between 1.1–1.5 V versus RHE at a scan rate of 100 mV s-1. The CP data were collected using catalyst decorated carbon paper with a loading mass of ~1.5 mg cm−2 and an effective area of 1 cm2 as working electrode in 100 mL of 0.1 M HClO4 solution. All the LSV and CP curves measured in three-electrode system were corrected by 100% iR correction.

PEMWE device measurements

A catalyst-coated membrane (CCM) method was used to prepare the membrane electrode assembly (MEA). Cr0.2Ru0.8O2-x or commercial RuO2 was used as the anode catalyst, while commercial Pt/C (40 wt%) was used as the cathode catalyst. The catalysts were first dispersed in a mixture of isopropanol, DI water and Nafion solution, followed by ultrasonicating to form a homogeneous ink. The anode and cathode ink were sprayed onto two pieces of polytetrafluoroethylene (PTFE), respectively. A Nafion 115 membrane with an effective area of 4 cm2 was placed in between the two pieces of catalyst-coated PTFE, and then hot pressed at 135 °C under a pressure of 2 T for 5 min to obtain the MEA. The anode and cathode catalysts loading were controlled at ~3 mg cm−2 and ~1 mg cm−2, respectively.

The PEMWE device consists of a Ti bipolar plate at the anode and a graphite bipolar plate at the cathode with serpentine flow channels on both sides. The MEA was sandwiched between a Ti wafer as the anodic porous transport layer (PTL) and a carbon paper as the cathodic gas diffusion layer (GDL). For the PEMWE test, the device temperature was set at 60 °C, and the pre-heated DI water was fed as reactant into the anode under a flow rate of 40 mL min−1. The steady-state polarization curves were collected at a galvanostatic mode from 0 to 2 A cm−2. The durability of the catalyst was evaluated by measuring CP at 1 A cm−2. All the data of PEMWE were displayed as raw data without iR correction.

Quasi-in situ XPS measurements

Quasi-in situ XPS measurements were performed using a Thermo ESCALAB 250 XI electron spectrometer connected to an Ar-filled glove box through a vacuum channel. To avoid air exposure, OER under different potentials was carried out in a standard three-electrode cell in Ar atmosphere. Hg/Hg2SO4 (saturated K2SO4) electrode, graphite rod and catalyst decorated carbon paper were served as the reference electrode, counter electrode, and working electrode respectively. After reaction, the catalysts were collected and dried in the glove box, and then transferred to the analysis chamber through the vacuum channel for further XPS measurements.

Operando SERS measurements

The operando SERS measurements were carried out on a LabRAM HR Evolution spectrometer equipped with a 50× microscope objective and an excitation laser of 633 nm. The Raman spectra were collected at 20 s exposure time averaged over 15 exposures. The electrochemical cell was homemade by Teflon and a quartz plate was employed as the window to cross the laser. A saturated Ag/AgCl electrode and a Pt wire were served as the reference electrode and the counter electrode respectively. The working electrode was prepared by drop-casting the catalysts ink onto a pre-roughened Au disk electrode with a diameter of 5 mm and a loading of ~0.5 mg cm−2. The electrolyte (O2-saturated 0.1 M HClO4) was pumped through the cell with a chamber volume of ~7.5 mL using a metering pump.

Operando ATR-SEIRAS measurements

The operando ATR-SEIRAS measurements were performed on a SHIMADZU IRTracer-100 Fourier transform infrared spectrometer equipped with a mercury cadmium telluride (MCT) detector cooled by liquid nitrogen. The IR spectra were acquired at a resolution of 4 cm−1 with unpolarized IR radiation. The catalysts ink was dripped onto an Au-coated Si prism as working electrode with an effective central diameter of 6 mm and a loading of ~0.5 mg cm−2, which was then assembled in a spectroelectrochemical cell. A saturated Ag/AgCl electrode and a Pt plate served as the reference electrode and the counter electrode respectively. The electrolyte used in the measurement was 10 mL of 0.1 M HClO4, which was continuously purged with O2 during the experiment. All spectra were shown in the absorbance unit as -log(I/I0), where I and I0 represent the intensities of the reflected radiation for sample and reference single-beam spectra, respectively.

Operando DEMS measurements

Operando DEMS measurements were conducted on a Linglu QMG 250 differential electrochemical mass spectrometer equipped with a high vacuum chamber connected to a molecular pump. An electrochemical cell was linked to the vacuum chamber through a cold trap cooled with dry ice to intercept the water vapor into the mass spectrometer. For gas-liquid separation, the working electrode was prepared by sputtering Au onto a 50 μm thick porus PTFE membrane with a pore size of 0.2 μm and a porosity of 85%, followed by drop-casting the catalysts ink onto the Au with an effective central diameter of 1 cm and a loading of ~0.5 mg cm−2. A saturated Ag/AgCl electrode and a graphite stick were served as the reference electrode and the counter electrode respectively. Catalysts were first labeled with 18O in 5 mL of H218O supported 0.1 M HClO4 electrolyte by operating CP test at 10 mA cm−2 for 30 min. Next, electrodes and cell were rinsed with H216O to remove surface adsorbed H218O. Last, the above catalysts were carried out four times of CV cycles in 10 mL of normal H216O supported 0.1 M HClO4 electrolyte. The gaseous products of different molecular weights generated during OER were monitored in real time by the mass spectrometer. Data were averaged every twenty points to yield a smoother mass signal, and m/z 34/32 signals were calculated with the fitting data.

DFT calculations

The Vienna ab initio simulation package (VASP)75,76 code based on density functional theory (DFT) was adopted for the computational simulations. Perdew-Burke-Ernzerhof (PBE) functional within the generalized gradient approximation (GGA) was used to model the exchange-correlation energy77. The ionic cores were described by projector-augmented wave (PAW) pseudopotentials78,79 with an energy cutoff of 450 eV. Grimme’s DFT-D3 method was incorporated to implement the Van der Waals correction. Geometry optimizations were performed with the force convergency smaller than 0.05 eV Å−1. The adsorption energies on different structures were evaluated with the energy convergency smaller than 10−5 eV. Monkhorst-Pack80 k-points of 3 × 3 × 1 was applied for all the calculations. The solvation effect was considered using the implicit solvation model implemented in VASPsol with the dielectric constant of 78.5 for water81. Due to the strong correlation of d electrons in Cr, a U–J value of 3.7 eV was adopted82. Spin-polarization effect was also considered.

Supplementary information

Supplementary Information

Peer Review File

Description of Additional Supplementary Files

Supplementary Data 1

Source data

Source Data

Supplementary information

The online version contains supplementary material available at 10.1038/s41467-024-51871-z.

Acknowledgements

This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grants XDB0450402), the National Key Research and Development Program of China (2018YFE0202201, 2021YFA0715700), the National Natural Science Foundation of China (Grants 22075174, 22293044, U1932213), the Major Basic Research Project of Anhui Province (2023z04020009), and the New Cornerstone Investigator Program.

Author contributions

S.Z. conceived the original idea and project design. S.Z., Y.L.M., M.R.G., and S.H.Y. supervised the project. Y.S. and J.M. performed the catalyst synthesis, characterization, electrochemical measurements, and related data processing. X.L.Z. helped the theoretical calculations. M.R.Q. assisted in the data analysis. S.Z. and M.R.G. wrote the manuscript. All the authors commented on the results and approved the final version of the manuscript.

Peer review

Peer review information

Nature Communications thanks the anonymous reviewers for their contribution to the peer review of this work. A peer review file is available.

Data availability

Source data are provided with this paper.

Competing interests

The authors declare no competing interests.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

These authors contributed equally: Yu Shen, Xiao-Long Zhang, Ming-Rong Qu, Jie Ma.
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