Surface electron-hole rich species active in the electrocatalytic water oxidation

Velasco-Vélez, J-J; Carbonio, EA; Chuang, C-H; Hsu, C-J; Lee, J-F; Arrigo, R; Hävecker, M; Wang, R; Plodinec, M; Wang, FR; Centeno, A; Zurutuza, A; Falling, LJ; Mom, RV; Hofmann, S; Schlögl, R; Knop-Gericke, A; Jones, TE

Abstract

Iridium and ruthenium and their oxides/hydroxides are the best candidates for the oxygen evolution reaction under harsh acidic conditions owing to the low overpotentials observed for Ru- and Ir-based anodes and the high corrosion resistance of Ir-oxides. Herein, by means of cutting edge operando surface and bulk sensitive X-ray spectroscopy techniques, specifically designed electrode nanofabrication and ab initio DFT calculations, we were able to reveal the electronic structure of the active IrOx centers (i.e., oxidation state) during electrocatalytic oxidation of water in the surface and bulk of high-performance Ir-based catalysts. We found the oxygen evolution reaction is controlled by the formation of empty Ir 5d states in the surface ascribed to the formation of formally IrV species leading to the appearance of electron-deficient oxygen species bound to single iridium atoms (μ1-O and μ1-OH) that are responsible for water activation and oxidation. Oxygen bound to three iridium centers (μ3-O) remains the dominant species in the bulk but do not participate directly in the electrocatalytic reaction, suggesting bulk oxidation is limited. In addition a high coverage of a μ1-OO (peroxo) species during the OER is excluded. Moreover, we provide the first photoelectron spectroscopic evidence in bulk electrolyte that the higher surface-to-bulk ratio in thinner electrodes enhances the material usage involving the precipitation of a significant part of the electrode surface and near-surface active species.

• Journal Article Type: Article
• Online Publication Date: Aug 6, 2021
• Publication Date: Aug 18, 2021
• Deposit Date: Aug 16, 2021
• Publicly Available Date: Aug 16, 2021
• Journal: Journal of the American Chemical Society
• Print ISSN: 0002-7863
• Volume: 143
• Issue: 32
• Pages: 12524-12534
• DOI: https://doi.org/10.1021/jacs.1c01655
• Publisher URL: https://doi.org/10.1021/jacs.1c01655
• Related Public URLs: http://pubs.acs.org/journal/jacsat/about.html
• Additional Information: Additional Information : ** Article version: VoR ** From Crossref journal articles via Jisc Publications Router ** Licence for VoR version of this article starting on 06-08-2021: https://creativecommons.org/licenses/by/4.0/ **Journal IDs: pissn 0002-7863; eissn 1520-5126 **History: issued 06-08-2021; published_online 06-08-2021; Funders : Engineering and Physical Sciences Research Council (EPSRC);Engineering and Physical Sciences Research Council Doctoral Training Award;Bundesministerium für Bildung und Forschung;Deutscher Akademischer Austauschdienst;Ministry of Science and Technology, Taiwan;Ministry of Education and Science of the Russian Federation;Engineering and Physical Sciences Research Council; Projects : EP/M506485/1;EP/K016636/1;BMBF-05K14EWA;57218279;57392335;RFMEFI61614X0007;104-2112-M-032-005-MY2;105-2911-I-032-501; Grant Number: EP/K016636/1; Grant Number: EP/M506485/1; Grant Number: BMBF-05K14EWA; Grant Number: 57218279; Grant Number: 57392335; Grant Number: RFMEFI61614X0007; Grant Number: 104-2112-M-032-005-MY2; Grant Number: 105-2911-I-032-501