Switch of the Rate-Determining Step of Water Oxidation by Spin-Selected Electron Transfer in Spinel Oxides

The 3d transition-metal oxides are a class of promising catalysts for the oxygen evolution reaction (OER) in alkaline media. Manganese-based spinel oxides usually do not show impressive OER performance, and their activity is generally lower than the counterparts containing cobalt. The OER activity and the electronic structure of spinel oxides ZnMn2O4, ZnCo2O4, and the cobalt-substituted ZnMn2O4 were investigated. It has been found that compared to ZnCo2O4, the lower activity of ZnMn2O4 arises from the limitation of spin-selective electron transfer and orbital symmetry restrictions between adsorption of the oxygen species onto the conduction band and the electron transfer from the conduction band to the valence band. The substitution of cobalt into ZnCo2O4 alleviates the spin incompatibility and enables the increase in OER activity.