Bifacially coated trimetallic oxide nanoparticles on N-doped hollow carbon spheres synthesized via rapid thermal manufacturing as bifunctional electrocatalysts for long-lifetime zinc–air batteries

Nanostructuring of multi-transition metal oxides and doped carbon supports is a promising strategy to achieve efficient and durable bifunctional electrocatalysts for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) in rechargeable zinc–air batteries (ZABs). However, fabricating nanostructured catalysts involves high-cost, time-consuming, and energy-inefficient processes, while the substantial overpotential, instability, and sluggish kinetics of ORR/OER pose significant bottlenecks. Herein, a rational strategy using an ultrafast thermal process is devised to fabricate trimetallic (Co, Fe, Ni) oxide nanoparticles inside and outside of N-doped hollow carbon spheres (TMO@N-HCS) as high-performance bifunctional electrocatalysts. The N-HCS, prepared by polymerization and thermal decomposition of polypyrrole optimally confines the growth of TMO nanoparticles through a capillary-force-driven fuel melting–diffusion strategy during the combustion-driven nanostructured recombination. The bifacially deposited TMO on N-HCS leads to superior ORR/OER activity due to the enhanced electron transport and diverse oxidation states for synergistic electrochemical activity, while the intrinsically porous nature improves electrolyte/catalyst contacts and provides abundant active sites. ZABs with TMO@N-HCS demonstrate a high open-circuit voltage (1.41 V), power density (106 mW cm −2 ), and excellent cycling stability (>350 h), surpassing Pt/C + Ir/C. This study inspires scalable fabrication routes of nanostructured non-noble metal electrocatalysts for metal–air batteries, fuel cells, and water splitting. • Bifacially coated trimetallic oxide nanoparticles on N-doped hollow carbon spheres (TMO@N-HCS). • Scalable ultrafast thermal process is devised to fabricate TMO@N-HCS as bifunctional electrocatalysts. • TMO@N-HCS achieves half-wave (ORR) and active (OER) potentials of 0.78 and 1.47 V. • Intrinsically porous nature improves electrolyte/catalyst contacts and active sites accessibility. • Zinc-air batteries with TMO@N-HCS show 350 h stability, 1.41 V OCV, 106 mW cm −2 power density.