Unveiling the pH-dependent structure-activity relationship of Co-based catalysts toward oxygen evolution reaction
Creators
- 1. Electrochemistry Laboratory, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
- 2. Photon Science Division, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
- 3. Laboratory for High Performance Ceramics, Empa - Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland
- 4. Institute for Physical Molecular Sciences, ETH Zürich, CH-8093 Zürich, Switzerland
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Description
Co-based catalysts are promising candidates to replace the Ir/Ru-based oxides for the oxygen evolution reaction (OER) in an acidic environment. However, both the reaction mechanism and the active species in an acidic environment remain unclear. In this study, by combining surface-sensitive soft X-ray adsorption spectroscopy (sXAS) characterization with electrochemical analysis, we unveil the truly active Co species for acidic OER. Surfaces composed of only high-spin CoII are found to be not active due to their unfavorable deprotonation to form CoIII-OH species. In contrast, we show that the presence of low-spin CoIII is essential to promote surface reconstruction and catalysis of OER. The correlation between OER activity and Co oxidation/spin state represents a breakthrough in the structure-activity relationship of Co-based catalysts for acidic OER, which interestingly does not hold in the alkaline and neutral environments. These findings not only help to design efficient acidic OER catalysts, but also deepen the understanding of the reaction mechanism.