Pyridinic-N exclusively enriched CNT-encapsulated NiFe interfacial alloy nanoparticles on knitted carbon fiber cloth as bifunctional oxygen catalysts for biaxially flexible zinc–air batteries

Abstract

The electrocatalytic oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are the core reactions in reversible zinc–air batteries but are kinetically challenging because of their complex multi-electron transfer process. In this case, the exploration and rational design of non-precious bifunctional oxygen electrocatalysts with dense active sites and optimized electronic structures can facilitate favorable 4e⁻ transfer. In this study, we report a highly reversible bifunctional electrocatalyst for flexible Zn–air batteries featuring pyridinic-N exclusively enriched carbon-nanotube-encased nickel–iron (NiFe) interfacial alloy nanoparticles derived from an LDH template on knitted carbon fiber cloth. The NiFe nanoparticles were catalytically released from NiFe-MOFs to form CNT tentacles when pyrolyzed in an inert atmosphere. XPS and XAS studies revealed the dominant presence of pyridinic-N, which reduces electron localization around NiFe centers and improves the interaction with oxygenated species. As a result, NiFe–N-CNT-KCC catalysts exhibited a low operating overpotential (η₁₀) of 173 mV for the OER and a half-wave potential (E_1/2) of 0.87 V for the ORR, which are superior to benchmark electrocatalysts. As an air cathode for zinc–air batteries, the NiFe–N-CNT-KCC-based battery showed an excellent electrochemical performance, with an open circuit voltage (OCV) of 1.55 V, high power density of 153 mW cm⁻², excellent specific capacity of 793.2 mA h g⁻¹, and long-term stability. Impressively, a solid-state flexible zinc–air battery with the NiFe–N-CNT-KCC cathode showed an admirable rate performance and exceptional mechanical stability under arbitrary bending and twisting conditions, showing great potential for practical implementation in next-generation high-power and high-energy-density batteries wearable applications.