Scalable exothermic synthesis of sprout-like Ni-Co-Fe trimetallic oxide nanoparticles anchored on N-doped carbon nanotubes as bifunctional oxygen catalysts for zinc-air batteries

Zn-air batteries (ZABs) offer a high specific energy density, cost-effectiveness, and eco-friendliness. Hence, they are attractive candidates for use as sustainable energy-storage devices. However, their practical applications are limited by their high bifunctional oxygen evolution reaction/oxygen reduction reaction (OER/ORR) overpotential and sluggish kinetics. To address these limitations, in this study, a highly active bifunctional oxygen catalyst, TNPs@N-CNT, is developed, in which Ni-Co-Fe trimetallic nanoparticles are anchored on N-doped carbon networks. TNPs@N-CNT is synthesized via the thermally driven combustion of collodion fuel. The carbonization of melamine foam containing pyridinic N in TNPs@N-CNT enhances the ORR and affords a high catalytic surface area and high electrical conductivity. Morphological studies and chemical characterization aid in finely tuning the thermal processing conditions, affording a TNPs@N-CNT suitable for charge transfer. TNPs@N-CNT shows enhanced ORR activity (half-wave potential = 0.62 V and onset potential = 1.49 V) in alkaline media. A ZAB with TNPs@N-CNT as the air cathode exhibits an output power density of 90 mW cm-2 and excellent cycling stability for over 200 h, outperforming previously reported carbon-supported preciousmetal catalysts. This tunable and scalable fabrication strategy could promote the development of novel mesoporous structures combined with high-efficiency multi-metallic catalysts for applications in energy-storage systems.