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

Promoting the initially deficient but cost-effective catalysts to high-performing competitors is of significance in developing better catalysts. Spinel zinc cobalt oxide (ZnCo 2 O 4 ) 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 2g 6 e g 0 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 ZnCo 2 O 4 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 ZnCo 2 O 4 , while not working for Co 3 O 4 . The activity of the best spin-state-engineered ZnCo 2 O 4 outperforms other typical Co-based oxides. Our work pinpoints the critical influence of the spinel composition on the splitting energy of the metals and further on the feasibility of spin state engineering.