Electronic Synergy in NiCo-Embedded Nitrogen-Doped Hollow Mesoporous Carbon Spheres for Bifunctional Oxygen Catalysis and Zinc–Air Batteries

Abstract

Rechargeable zinc–air batteries (ZABs) are promising candidates for sustainable energy storage; however, their performance is severely limited by sluggish oxygen reduction and evolution (ORR/OER) kinetics. Here, a hard-templating etching strategy was employed to construct nitrogen-doped hollow mesoporous carbon spheres embedded with NiCo nanoparticles (NiCo@N-HMCS). The hollow nanostructure, together with a strong electronic coupling between NiCo alloys and N-doped carbon, provides abundant accessible active sites, optimized charge transfer, and robust structural stability. As a result, NiCo@N-HMCS delivers remarkable bifunctional electrocatalytic activity in alkaline media, with a half-wave potential of 0.84 V for the oxygen reduction reaction and an overpotential of 330 mV at 10 mA cm⁻² for the oxygen evolution reaction. When applied in ZABs, the catalyst delivers a high open-circuit voltage of 1.56 V, a peak power density of 185.53 mW cm⁻², and durable cycling over 300 h. The flexible ZAB configuration also delivers a power density of 79.06 mW cm⁻² and stable operation of 120 h. This study demonstrates a robust platinum-group-metal-free strategy for advancing next-generation rechargeable and flexible energy storage systems.