Understanding the nature of active sites is central to controlling (electro)catalytic activity. Here we employed surface X-ray scattering coupled with density functional theory and surface-enhanced infrared absorption spectroscopy to examine the oxygen evolution reaction on RuO2 surfaces as a function of voltage. At 1.5 VRHE, our results suggest that there is an –OO group on the coordinatively unsaturated ruthenium (RuCUS) site of the (100) surface (and similarly for (110)), but adsorbed oxygen on the RuCUS site of (101). Density functional theory results indicate that the removal of –OO from the RuCUS site, which is stabilized by a hydrogen bond to a neighbouring –OH (–OO–H), could be the rate-determining step for (100) (similarly for (110)), where its reduced binding on (100) increased activity. A further reduction in binding energy on the RuCUS site of (101) resulted in a different rate-determining step (–O + H2O – (H+ + e−) → –OO–H) and decreased activity. Our study provides molecular details on the active sites, and the influence of their local coordination environment on activity.
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The data supporting the findings of this study are available in the paper and its Supplementary Information. Extra data are available from the corresponding authors on reasonable request.
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This work was supported in part by the Toyota Research Institute through the Accelerated Materials Design and Discovery programme. We thank B. Han for transmission electron microscopy characterization of RuO2 nanoparticles and J. Corchado-Garcia for help during the CTR data collection. This work was supported in part by the Skoltech-MIT Center for Electrochemical Energy and the Cooperative Agreement between the Masdar Institute, UAE and the Massachusetts Institute of Technology, USA (grant no. 02/MI/MIT/CP/11/07633/GEN/G/00). The work by H.Y. was supported by US Department of Energy (DOE), Basic Energy Sciences (BES), Materials Sciences and Engineering Division, and the work by H.Z. and the use of the Advanced Photon Source were supported by DOE, BES, Scientific User Facility Division (SUFD) under contract no. DE-AC02-06CH11357. The work by A.M. was supported by DOE, BES, SUFD under contract no. DE-AC02-76SF00515. A.F.P. acknowledges the Danish Ministry for Higher Education and Science for an EliteForsk travel grant and the Strategic Research’s project NACORR (grant no. 12-133817). This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant no. ACI-154856283. This research also used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the US DOE under contract no. DE-AC02-05CH11231. T.V. and N.B.H acknowledge support through V-Sustain: the VILLUM Centre for the Science of Sustainable Fuels and Chemicals (grant no. 9455) from VILLUM FONDEN. I.E.L.S acknowledges the Peabody Visiting Associate Professorship, awarded by the Department of Mechanical Engineering at Massachusetts Institute of Technology.
The authors declare no competing interests.
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Rao, R.R., Kolb, M.J., Giordano, L. et al. Operando identification of site-dependent water oxidation activity on ruthenium dioxide single-crystal surfaces. Nat Catal 3, 516–525 (2020). https://doi.org/10.1038/s41929-020-0457-6
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