Optimizing Silver Incorporation in MnO x Air Cathodes to Balance Power Density and Cycling Stability in Rechargeable Zn-Air Batteries

Abstract

Rechargeable Zn-air batteries (ZABs) require air cathodes that simultaneously deliver high power output and durable bifunctional oxygen electrocatalysis. Herein, we systematically investigate the effect of controlled Ag incorporation into MnO x catalysts supported on carbon paper (CP) to elucidate the interplay between conductivity, catalytic reversibility, and long-term stability. Three binderless electrodes CP/MnO x , CP/MnO x Ag 0.03 , and CP/MnO x Ag 0.05 were evaluated through polarization, power density, galvanostatic cycling (300 cycles at 2 mA cm -2 ), and electrochemical impedance spectroscopy (EIS) before and after cycling. Increasing Ag loading significantly enhances electronic conductivity and charge-transfer kinetics, leading to improved instantaneous performance, with CP/MnO x Ag 0.05 delivering the highest current density (80.5 mA cm -2 ) and power density (39.1 mW cm -2 ). However, long-term cycling reveals a distinct optimum at moderate Ag loading. CP/MnO x Ag 0.03 exhibits the lowest voltage gap (1.09 V) and highest roundtrip efficiency (50.6%) after 300 cycles, outperforming both pristine MnO x and the CP/MnO x Ag 0.05 electrode. EIS shows that while higher Ag content stabilizes interfacial conductivity, excessive Ag disrupts the balance between oxygen reduction and evolution reactions, resulting in increased polarization growth during cycling. In contrast, moderate Ag incorporation preserves Mn redoxactive sites and maintains more symmetric ORR/OER kinetics, ensuring superior bifunctional reversibility and durability. These results demonstrate that maximizing peak power density does not necessarily yield optimal rechargeable performance; instead, achieving a balanced synergy between conductive additives and redox-active oxide centers is critical. This work establishes a composition-dependent design strategy for bifunctional air cathodes, highlighting optimal Ag loading as a key parameter for developing efficient and durable rechargeable Zn–air batteries.