Coordination Tuning in Cobalt Selenites for Electrocatalytic Water Oxidation

Cobalt-based materials have been considered as the most promising cheap electrocatalysts for water oxidation. The coordination structure of Co affects the catalytic performance significantly. However, the internal causes remain elusive because of the lack of rational design of Co-based materials with clear and singular coordination geometry. Herein, two crystalline cobalt selenites were designed with isolated octahedral or tetrahedral Co centers. It was found that the intrinsically better performance of the octahedral Co site originated from its splitting energy of the 3d orbitals. This splitting accounts for the faster construction of Co IV species, the higher concentration of Co IV species, and the stronger oxidative ability of Co IV species in the selenite with octahedral Co sites. Therefore, how the coordination structure of Co centers regulates the water oxidation performance was revealed in a straightforward manner based on the designed analogous selenites.