Self-Standing Metal Organic Framework–Carbon Nanofiber Composites as Bifunctional Electrocatalysts for Rechargeable Zinc-Air Batteries

Abstract

Metal-organic framework (MOF)–carbon composite materials are promising candidates for use as electrocatalysts in zinc-air batteries (ZAB). Electrospun carbon nanofibers (CNFs) are particularly advantageous as conductive substrates due to their porous and binder-free architecture. However, achieving stable and efficient dispersion of MOFs on CNFs remains a significant challenge. In this study, we present the synthesis of a composite electrode comprising of nickel-based metal-organic framework decorated over cobalt oxide-embedded carbon nanofibers (NM@CCNF), designed as a self-standing bifunctional electrocatalyst for rechargeable ZABs. The NM@CCNF features a unique open flower petal-like morphology providing abundant active sites for oxygen reduction (ORR) and oxygen evolution reactions (OER). Electrochemical testing demonstrated that NM@CCNF exhibited a low potential gap (ΔE) between the ORR and OER of 0.794 V, surpassing individual noble metal catalysts and rivaling benchmark Pt/C and IrO₂ combinations. The assembled ZAB demonstrated a high specific capacity of 830 mA h g _Zn⁻¹, and a peak power density of 77.36 mW cm⁻². Long-term cycling stability tests over 200 cycles showed minimal voltage degradation, indicating excellent durability and rechargeability. Post-mortem analysis confirmed the reversible formation of ZnO during operation, validating the battery's rechargeability. These findings highlight the potential of NM@CCNF as a promising candidate for next-generation energy storage systems.