Self-reconstruction of highly active NiCo2O4 with triple-continuous transfer of electrons, ions, and oxygen for Zn-air batteries

The prohibitive cost and scarcity of the noble-metal catalysts needed for catalyzing the oxygen reduction/evolution reaction (ORR/OER) in the Zn–air battery (ZAB) limit the commercialization of this clean energy technology. Herein, a noble-metal-free spinel-type NiCo2O4 electrocatalyst with high activity and 3D porous structure is rationally designed by duplexing interface engineering concept through an adaptive combination of surfactant assistance and electrochemical reconstruction processes, resulting in co-enhanced behaviors of overall oxygen electrochemistry in ZABs. As expected, the conventional three-phase electrochemical interface could be expanded into 3D networks in whole air electrode, which allows the 3D triple-continuous passage of electrons, ions, and oxygen, thus boosting the oxygen electrochemistry of OER (1.62 V at Ej = 10) and ORR (0.79 V at E1/2) in 0.1 M KOH electrolyte. Moreover, the ZAB with the as-prepared electrocatalyst demonstrates a low potential gap of 0.77 V and impressive long-term reversibility over 600 h at 5 mA cm−2, surpassing most previous reports. Such superiority is ascribed, in part, to the self-reconstruction of NiOOH-NiCo2O4 interfacial layer with 3D networks during the OER process as observed by in-situ Raman, ex-situ XPS, and SEM, which contributes additionally to the high activity and durability of the air electrode by enhancing the charge and mass transfer in ZABs.