Co/Co3O4 Heterojunctions Encased in Porous N-Doped Carbon Nanocapsules for High-Performance Cathode of Rechargeable Zinc–Air Batteries

A long-term goal of rechargeable zinc-air batteries (ZABs) has always been to design bifunctional electrocatalysts that are robust, effective, and affordable for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). It has become a feasible method to construct metal/metal oxide interfaces to achieve superior electrocatalytic performance for ORR and OER by enhanced charge transfer. In this study, Co/Co₃O₄ heterojunctions were successfully prepared and encased in porous N-doped mesoporous carbon (Co/Co₃O₄@NC) via a simple condensation-carbonization-etching method. The extensive specific surface area of Co/Co₃O₄@NC facilitates effective interaction between the electrolyte and the catalyst, thereby enabling sufficient exposure of active sites for the ORR and the OER, consequently enhancing the rate of transport of active species. The well-designed Co/Co₃O₄@NC delivers superior ORR catalytic activity with a half-wave potential of 0.82 V (vs RHE) and a low overpotential of 347 mV at 10 mA cm^-2 for OER in alkaline solution. The power density of Co/Co₃O₄@NC-based alkaline aqueous ZAB (156.5 mW cm^-2) is superior to the commercial Pt/C + IrO₂-based alkaline aqueous ZAB, and the cycling stability of ZAB is up to 220 h. In addition, Co/Co₃O₄@NC-based ZAB shows a high power density (50.1 mW cm^-2). The construction of metal/metal oxide heterojunction encased in N-doped mesoporous carbon provides a novel route for the design of bifunctional electrocatalysts for high-performance ZABs.