α-MnO₂@ZIF-67 as bifunctional electrocatalyst for air cathode in high performance rechargeable zinc-air batteries

The development of cost-effective solutions and highly efficient electrocatalysts for both oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) is crucial for Zn-air batteries. With rapid advancement in metal organic frameworks derived advanced infrastructures, a unique composite is designed from ZIF-67 and MnO2 nanowires through simple wet chemical and pyrolysis approach. The pyrolysis of MnO2@ZIF-67 results in the formation of Co2O3 nanoparticles evenly distributed within the MnO2 nanowires. The composite with 3 wt % loading of MnO2 nanowires represented the most efficient activity as electrocatalysts for ORR and OER, owing to the enhanced surface area and more exposed active sites. It exhibits half-wave potential of 0.85 V for the ORR and a low potential of 1.67 V for the OER generating a standard current density of 10 mA/cm2. The 3 wt % MnO2@ZIF-67 based primary and rechargeable Zn-air battery device was assembled and cycled to demonstrate superior performance as bifunctional electrocatalyst for zinc air battery device with an open circuit potential of 1.28 V, power density of 203.4 mW/cm2, discharge specific capacity of 812.3 mAh/g, and high electrochemical stability for up to 200 h, offering inexpensive, and eco-friendly paradigm to systematically design microporous electrocatalysts for zinc-air batteries.