Understanding the Effect of Nickel Doping in Cobalt Spinel Oxides on Regulating Spin State to Promote the Performance of the Oxygen Reduction Reaction and Zinc-Air Batteries

Metal-doped cobalt spinel oxides are considered to be effective materials to improve the oxygen reduction reaction (ORR) performance. However, the doping sites of nickel in Co3O4 spinel (octahedral sites or tetrahedral sites) remain controversial, leading to a poor understanding of the effects of nickel. Herein, directionally introducing nickel into the octahedral sites of Co3O4 (NiOh-Co3O4) is proposed by exploiting the different redox capabilities of different nickel sources, which yields an encouraging ORR and rechargeable Zn-air battery performance. Magnetic measurements and theoretical calculations reveal that the nickel occupied at the octahedral site can effectively promote the spin-state transition from low spin to higher spin states for cobalt ions and the hybridization of Co 3d-O 2p electrons, resulting in the optimization of the adsorption strength for the oxygen intermediates, thus improving the oxygen catalytic activity of NiOh-Co3O4.