The role of reducibility vis-à-vis oxygen vacancies of doped Co3O4/CeO2 in the oxygen evolution reaction

Abstract

Electrochemical water splitting, which is a highly promising and environmentally friendly technology for H₂ fuel production, faces significant hurdles due to the sluggish kinetics of the oxygen evolution reaction. Co -based oxides have garnered significant attention as alternative catalysts for the oxygen evolution reaction owing to the Co²⁺/Co³⁺ redox couple. Enhancing the challenging Co²⁺ → Co³⁺ oxidation process can further improve the catalytic oxygen evolution reaction. The aim of our work was to design a Co₃O₄-based catalyst to enhance reactivity by increasing the number of Co³⁺ active sites, serving as an excellent platform for facilitating the oxygen evolution reaction. To drive the effectiveness of the catalyst, in this study, we synthesized Co₃O₄ anchored on CeO₂ (Co₃O₄/CeO₂). The kinetics and efficacy of the oxygen evolution reaction catalysed by Co₃O₄/CeO₂ was significantly improved by aliovalent doping of Sr into Ce sites and Cu into Co sites. The reducible nature of Ce stimulates the formation of Co³⁺ ions, resulting in an increased production of intermediate –OOH species, thus expediting the reaction. The transformation of Co²⁺ to Co³⁺ consequently leads to an increase in anion vacancies, which, in turn, promotes the adsorption of more intermediate species at the active site. The Sr- and Cu-doped Co₃O₄/CeO₂ catalyst exhibited a high current density of 200 mA cm⁻² at 580 mV and a low overpotential of 297 mV at 10 mA cm⁻². The study functions as a key indicator to establish a connection between oxygen vacancies and metal oxidation states in order to investigate the mechanistic aspects of the oxygen evolution reaction on mixed metal oxides. Moreover, this study is expected to pave the way for the development of innovative oxygen evolution reaction catalysts with reducible supports, thus offering a new pathway for their design.