Engineering high-spin state cobalt cations in spinel ZnCo2O4 for spin channel propagation and electrocatalytic activity enhancement in Li-O2 battery

Abstract

Spinel zinc cobalt oxide (ZnCo2O4) is considered as the promising electrocatalyst for the electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, theoretical calculations uncovered that the presence of low-spin (LS) state cobalt cations impedes the electrocatalytic activity of ZnCo2O4 because the t2g6eg0 configuration yields purely localized electronic structure with poor binding affinity with reaction intermediate. By regulating the spin state of cobalt cations in ZnCo2O4, spin-selected charge transfer is boosted during ORR/OER processes due to the propagated spin channel, thus causing abundant active sites for intermediates adsorption. Experimental results show that increasing calcination temperature during the synthesis process is an operable method to fabricate high-spin (HS) cobalt cations in ZnCo2O4. And the Li-O2 battery with ZnCo2O4 containing high-spin cobalt cations shows remarkably low overpotential of only 0.45 V and excellent durability of more than 800 h. This work underlines the critical role of the electron spin state in facilitating oxygen redox reactions on transition metal oxides.