The oxygen evolution reaction has an important role in many alternative-energy schemes because it supplies the protons and electrons required for converting renewable electricity into chemical fuels1,2,3. Electrocatalysts accelerate the reaction by facilitating the required electron transfer4, as well as the formation and rupture of chemical bonds5. This involvement in fundamentally different processes results in complex electrochemical kinetics that can be challenging to understand and control, and that typically depends exponentially on overpotential1,2,6,7. Such behaviour emerges when the applied bias drives the reaction in line with the phenomenological Butler–Volmer theory, which focuses on electron transfer8, enabling the use of Tafel analysis to gain mechanistic insight under quasi-equilibrium9,10,11 or steady-state assumptions12. However, the charging of catalyst surfaces under bias also affects bond formation and rupture13,14,15, the effect of which on the electrocatalytic rate is not accounted for by the phenomenological Tafel analysis8 and is often unknown. Here we report pulse voltammetry and operando X-ray absorption spectroscopy measurements on iridium oxide to show that the applied bias does not act directly on the reaction coordinate, but affects the electrocatalytically generated current through charge accumulation in the catalyst. We find that the activation free energy decreases linearly with the amount of oxidative charge stored, and show that this relationship underlies electrocatalytic performance and can be evaluated using measurement and computation. We anticipate that these findings and our methodology will help to better understand other electrocatalytic materials and design systems with improved performance.
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We thank HZB for synchrotron radiation beamtime and the High-Performance Computing Center Stuttgart (HLRS) for access to the HazelHen and Hawk supercomputers as part of the ECHO project. Part of this work was carried out at Petra III (beamline P64) and we thank V. Murzin, A. Tayal and W. Caliebe for assistance and acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for access. We thank M. Hashagen, J. Allan and F. Girgsdies for BET and X-ray diffraction measurements and A. Müller-Kauke for inductively coupled plasma–optical emission spectrometry measurements. Financial support from the German Research Foundation (DFG) under Priority Program 1613 and Grant STR 596/11-1 is acknowledged. P.S. acknowledges partial funding by the DFG under Germany’s Excellence Strategy – EXC 2008/1 – 390540038 (zum Teil gefördert durch die Deutsche Forschungsgemeinschaft (DFG) im Rahmen der Exzellenzstrategie des Bundes und der Länder – EXC 2008/1 – 390540038).
The authors declare no competing interests.
Peer review information Nature thanks Shannon Boettcher and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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The SI pdf contains Supplementary Methods, Supplementary Discussion, Supplementary Figures 1 to 22, Supplementary Tables 1 to 7, and references. The text and display items present an extended discussion on methodology of the employed techniques, additional characterization, and results from additional materials, including Cl treatment.
ca. 5 ps water dynamics on surface with 0/4 ML θh+.
ca. 5 ps water dynamics on surface with 1/4 ML θh+.
ca. 5 ps water dynamics on surface with 1/2 ML θh+.
ca. 5 ps water dynamics on surface with 3/4 ML θh+.
ca. 5 ps water dynamics on surface with 4/4 ML θh+.
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Nong, H.N., Falling, L.J., Bergmann, A. et al. Key role of chemistry versus bias in electrocatalytic oxygen evolution. Nature 587, 408–413 (2020). https://doi.org/10.1038/s41586-020-2908-2