Journal
ACS CATALYSIS
Volume 12, Issue 6, Pages 3256-3268Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.1c05169
Keywords
Co oxide; electrocatalysis; oxygen evolution reaction; surface restructuring; structure-activity relationship; surface X-ray diffraction; model catalysts
Categories
Funding
- Agence Nationale de la Recherche (ANR)
- Deutsche Forschungsgemeinschaft (DFG) via project EC-MEC [ANR15-CE30-0024-01, DFG 284207613]
- German Federal Ministry of Education and Research (BMBF) [05K19FK3]
- DFG [431791331, SFB 1452, 214951840, 453560721, 431733372, FOR 1878 funCOS]
- project CALIPSOplus under EU Framework Program for Research and Innovation HORIZON 2020 [730872]
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Co oxides and oxyhydroxides have been extensively studied as electrocatalysts for the oxygen evolution reaction. This study focuses on epitaxial spinel-type Co3O4 films and reveals that the average thickness of the skin layer on the Co3O4 surface correlates with the reactivity of the oxygen evolution reaction. Increasing the thickness of the skin layer enhances the reactivity, and there is a proportional relationship between the number of reaction centers in the skin layer and the activity of the oxygen evolution reaction.
Co oxides and oxyhydroxides have been studied extensively in the past as promising electrocatalysts for the oxygen evolution reaction (OER) in neutral to alkaline media. Earlier studies showed the formation of an ultrathin CoOx(OH)(y) skin layer on Co3O4 at potentials above 1.15 V vs reversible hydrogen electrode (RHE), but the precise influence of this skin layer on the OER reactivity is still under debate. We present here a systematic study of epitaxial spinel-type Co3O4 films with defined (111) orientation, prepared on different substrates by electrodeposition or physical vapor deposition. The OER overpotential of these samples may vary up to 120 mV, corresponding to two orders of magnitude differences in current density, which cannot be accounted for by differences in the electrochemically active surface area. We demonstrate by a careful analysis of operando surface X-ray diffraction measurements that these differences are clearly correlated with the average thickness of the skin layer. The OER reactivity increases with the amount of formed skin layer, indicating that the entire three-dimensional skin layer is an OER-active interphase. Furthermore, a scaling relationship between the reaction centers in the skin layer and the OER activity is established. It suggests that two lattice sites are involved in the OER mechanism.
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