Temperature-regulated reversible transformation of spinel-to-oxyhydroxide active species for electrocatalytic water oxidation

Abstract

The electrocatalytic oxygen evolution reaction (OER) is a strong electrooxidation process and usually drives the self-oxidation of the anode material. Thus, exploring a facile and efficient strategy to regulate the active species of electrocatalytic materials during the OER process is critical, but it still remains a challenge. Here, the active species of NiCo₂O₄ for the OER is found to be NiCo₂O₄ at room temperature, and Ni(Co) oxyhydroxides at 45 °C. In situ Raman and online X-ray absorption spectroscopy data reveal that the reversibly mutual transformation of the active species between NiCo₂O₄ and oxyhydroxides can be induced by regulating the temperature. Density functional theory calculations suggest that NiOOH has high activity and different rate-limiting steps toward the OER, compared with NiCo₂O₄. Both the temperature-induced change in the active species and accelerated kinetics lead to the improved activity of NiCo₂O₄ at 45 °C. This work may provide a new insight into both understanding and regulating the active species of OER materials.