Design and synthesis of low Pt-loaded Mn-ZIF-67 derived bifunctional electrocatalyst for oxygen electrode in metal–air batteries

Abstract

Rechargeable zinc–air batteries emerged as viable green energy storage solution due to their high theoretical energy density (1085 kW h/kg), low cost and environmental compatibility. However, the sluggish ORR and OER kinetics limit the performance and efficiency of RZABs. Noble metal-based electrocatalysts have the potential to improve redox reactions, but they are scarce and unstable. To mitigate this issue, this study introduces a noble metal-loaded, transition metal-based electrocatalyst derived from ZIF67. After pyrolysis, a nanoporous carbon structure with well-dispersed nanoparticles was obtained. The resulting Pt@MnCo/NC catalyst exhibits a halfwave potential of 0.86 V with a limiting current density of 5 mA/cm², surpassing the commercially available Pt/C electrocatalyst (0.84 V and 3.24 mA/cm²). It demonstrates a low overpotential of 0.34 V, significantly lower than commercial RuO₂ (0.57 V) and potential gap (ΔE) of 0.71 V, establishing it as an efficient bifunctional electrocatalyst. The catalyst maintains stability even after 1000 CV cycles. This improved performance is attributed to the synergistic effect of metal alloys and the nanoporous carbon network, which together increase the surface area of electrocatalyst and provide electrochemically active sites for oxygen reactions.