CeO2-Induced Interfacial Co2+ Octahedral Sites and Oxygen Vacancies for Water Oxidation

Electrocatalytic oxygen evolution reaction (OER) is a key process in electrochemical energy conversion and storage. Cobalt-containing spinel oxides are promising candidates for OER, but suffer from cation deficiency during OER, because of the high stability and reversibility of the spinel structure. Herein, we combine catalytically inactive CeO₂ and spinel structure Co₃O₄ (CeO₂/Co₃O₄) by a built-in p–n heterojunction. The strongly coupled p–n heterojunction interface allows a rapid interfacial charge transfer from CeO₂ to Co₃O₄, which leads to a high concentration of oxygen vacancies and the generation of Co²⁺ octahedral (Co²⁺(O_h)) sites from the reduction of Co³⁺(O_h) at the CeO₂/Co₃O₄ interface. Consequently, the CeO₂/Co₃O₄ interface with the optimal ratio of Ce/Co exhibits high OER activity with an overpotential of only 265 mV at the current density of 10 mA cm^–2, a Tafel slope of 68.1 mV dec^–1, and long-term durability in an alkaline medium.