Interface and Phase Synergy in Hierarchically Porous Co@(Co–Mn)3O4–x for High-Efficiency and Durable Rechargeable Zn–Air Batteries

The development of highly active and durable bifunctional electrocatalysts remains a key challenge in advancing rechargeable Zn–air battery technology. In this work, we report a synergistically integrated metal cluster on an oxide catalyst, Co@(Mn0.6Co0.4)3O4–x, to address this issue. The catalyst was synthesized through the hydrogen reduction of a spinel-structured (Mn0.4Co0.6)3O4 precursor. The reduction process yields a finely tuned multiphase composition, consisting of metallic Co and oxygen-deficient (Mn0.6Co0.4)3O4–x spinel, while resulting in a nanomicro porous architecture. This engineered structure provides synergistic benefits: (1) metallic Co enhances electrical conductivity, (2) oxygen-deficient spinel domains create abundant active sites, and (3) the hierarchical porous framework improves mass transport. As a result, Co@(Mn0.6Co0.4)3O4–x exhibits high bifunctional oxygen activity with a low overpotential, 460.5 mV at 10 mA cm–2 for the oxygen evolution reaction (OER), and a favorable four-electron oxygen reduction reaction (ORR) pathway (n = ∼3.94). It also shows a low bifunctional ΔE of 0.97 V and robust stability. In actual applications, the Co@(Mn0.6Co0.4)3O4–x cathode-based Zn–air battery demonstrates an open-circuit voltage of 1.48 V and a peak power density of 299.9 mW cm–2, with long-term discharge for 98 h and stable cycling over 460 cycles. Further analysis reveals that in primary battery mode, cathode performance degradation is largely due to ZnO accumulation on the cathode surface. In contrast, in rechargeable mode, the reversible Zn/ZnO conversion limits ZnO buildup. The high cycling durability is attributed to the strong structural stability of Co@(Mn0.6Co0.4)3O4–x. These findings highlight the importance of interface engineering and phase synergy in the optimization of multifunctional air electrodes for next-generation Zn–air batteries.