Engineering High-Spin State Cobalt Cations in Spinel Zinc Cobalt Oxide for Spin Channel Propagation and Active Site Enhancement in Water Oxidation

Spinel zinc cobalt oxide (ZnCo₂O₄) is not considered as a superior catalyst for the electrochemical oxygen evolution reaction (OER), which is the bottleneck reaction in water-electrolysis. Herein, taking advantage of density functional theory (DFT) calculations, we find that the existence of low-spin (LS) state cobalt cations hinders the OER activity of spinel zinc cobalt oxide, as the t_2g⁶e_g⁰ configuration gives rise to purely localized electronic structure and exhibits poor binding affinity to the key reaction intermediate. Increasing the spin state of cobalt cations in spinel ZnCo₂O₄ is found to propagate a spin channel to promote spin-selected charge transport during OER and generate better active sites for intermediates adsorption. The experiments find increasing the calcination temperature a facile approach to engineer high-spin (HS) state cobalt cations in ZnCo₂O₄, while not working for Co₃O₄. The activity of the best spin-state-engineered ZnCo₂O₄ outperforms other typical Co-based oxides.