Nonmetallic Phosphorus-Driven Oxygen Vacancy and Electronic Structure Modulation Enhancing Bifunctional Catalytic Activity of Cobalt-Based Spinel Air Electrode for Rechargeable Zn–Air Batteries

Zinc-air batteries (ZABs) have great promise for sustainable energy storage. However, the energy conversion efficiency is limited by the lack of cost-effective bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a nonmetallic phosphorus doping strategy in the B-site of MnCo2O4 spinel catalyst via a scalable self-propagating combustion synthesis is developed for ZABs. The optimized MnCo1.90P0.10O4-δ catalyst exhibits exceptional bifunctional activity at 0.1 M KOH, achieving a positive half-wave potential of 0.80 V vs RHE for ORR alone with superior long-term stability (91.92% current density retention after 15000s), and an overpotential of 430 mV at 10 mA cm-2 for OER, which is comparable to commercial Pt/C-RuO2 catalysts. Moreover, when the MnCo1.90P0.10O4-δ applied as the air electrode of ZABs, the ZABs enable a high peak power density of 152 mW cm-2 and stable cycling over 120 h at 10 mA cm-2. Interestingly, phosphorus doping significantly increases the oxygen vacancy concentration and optimizes the Co3+/Co2+ ratio with elevated eg orbital occupancy, synergistically enhancing O2 activation and charge transfer, alongside a 2.5-fold increase in surface area (from 6.88 to 17.25 m2 g-1). This study indicates the critical role of electronic vacancy synergy in boosting bifunctional oxygen electrocatalysis, providing a generalizable strategy for spinel-type transition metal oxides in ZABs.