Cation-substitution-tuned oxygen electrocatalyst of spinel cobaltite McO₂O₄ (M = Fe, Co, and Ni) hexagonal nanoplates for rechargeable Zn-air batteries

The spinel cobalt oxide (Co₃O₄) nanoplate exposed with hexagonal {111} facets is demonstrated to be a highly active catalyst, while the effect of cation substitution on the oxygen electrocatalysis is still unclear. Herein, the electrocatalytic activity of cation-substituted spinel cobaltite MCo₂O₄ (M = Fe, Co, and Ni) nanoplates with the {111} facets is investigated systematically by experiments and theoretical calculations. For both oxygen reduction and evolution reactions, Ni-substituted Co₃O₄ hexagonal nanoplates show the best activity. It is mainly attributed to the increased surface energy per unit area and the enhanced oxygen species absorption ability, which are also evidenced by density functional theory calculations. Moreover, the three kinds of MCo₂O₄ nanoplates are applied in Zn-air batteries and the corresponding electrochemical performance is tested. Among the three batteries, NiCo₂O₄ hexagonal nanoplates also enable the highest peak power density of 110.3 mW cm⁻² and the most stable discharge-charge voltage profiles for 50 cycles, indicating that NiCo₂O₄ nanoplates are the promising catalyst for further Zn-air battery applications. Besides, this work illustrates that the substitution of Co by Ni or Fe can remarkably change the electronic structural states, thus tuning the electrochemical properties of the hexagonal Co₃O₄ nanoplates.