Hierarchical engineering of alfa-MnO2 nanowires on ZIF-67 nanoparticles as a bifunctional electrocatalytic air cathode for zinc–air batteries

The development of cost-effective, high-performance bifunctional electrocatalysts is a critical challenge in advancing next-generation rechargeable zinc-air batteries (ZABs). In this work, we introduce a hierarchically structured composite, α-MnO?@ZIF-67, synthesized via in-situ growth followed by pyrolysis, to address the intrinsic limitations of pristine ZIF-67, such as deeply buried active sites and poor conductivity. The incorporation of α-MnO? nanowires into the ZIF-67 framework not only prevents the collapse and agglomeration of the porous structure during thermal treatment but also significantly enhances the exposure of active sites, promotes charge transport, and facilitates ion diffusion through an interconnected mesoporous network.

The optimized 3 wt. % α-MnO?@ZIF-67 composite exhibits remarkable bifunctional electrocatalytic activity, delivering a half-wave potential (E1/2) of 0.85 V for the oxygen reduction reaction (ORR) and a low overpotential of 1.67 V at 10 mA/cm² for the oxygen evolution reaction (OER). These values surpass those of both the bare ZIF-67 and commercial Pt/C and RuO? catalysts. When employed as the air cathode in a Zn-air battery, the composite enables a high open-circuit voltage of 1.28 V, a peak power density of 203.4 mW/cm², and a specific discharge capacity of 812.3 mAh/gZn, alongside long- term stability over 200 hours of continuous cycling.

This study highlights the structural and electrochemical synergy between MnO? nanowires and ZIF- derived frameworks in tuning porosity, conductivity, and bifunctional catalytic behavior. The MnO? scaffold serves as both a structural spacer and an electron-conducting backbone, activating the full potential of ZIF-67 as a low-cost, durable electrocatalyst. The proposed strategy opens promising avenues for rationally engineering MOF-based heterostructures for advanced metal–air battery applications.