Single Crystalline CoNi Selenite for Investigating a Metal Synergic Effect in Electrocatalytic Water Oxidation

Bimetallic-based materials have been considered as prominent electrocatalysts for water oxidation. However, ambiguous concepts about the real active center widely exist in bimetallic electrocatalysts. Here, we prepared CoNi selenite single crystals with nondifferential distribution of Co and Ni metal centers. Compared with traditional solid solutions, single crystals provide an appealing platform to investigate the metal synergic effect in electrocatalytic water oxidation. On the basis of detailed spectral and electrochemical studies, it has been confirmed that Co promotes the formation of high-valent Ni species as the real active sites for water oxidation. Since there are sustained debates on the evolution of active sites in bimetallic materials for water oxidation, the findings in this work are of importance to understand the insights of water oxidation and are valuable in the rational design of functional bimetallic electrocatalysts.