Precisely controllable microwave-driven reconstruction of Ni-Co-Fe trimetallic needle structures on nitrogen-doped carbon as bifunctional oxygen catalysts for Zn–air batteries

Zinc–air batteries (ZABs) are regarded as promising options for sustainable energy storage due to their high specific energy density, cost-effectiveness, and environmental friendliness. However, their scalability is rendered challenging because of high overpotential, slow kinetics in the bifunctional oxygen evolution reaction/oxygen reduction reaction, and instability in alkaline environments. Herein, we report the development of a highly active bifunctional oxygen catalyst, denoted as TON@NC (trimetallic oxide needles on nitrogen-doped carbon), which consists of Ni-Co-Fe oxide nanoneedles uniformly anchored on a nitrogen-doped carbon network. The synthesis of TON@NC is implemented by a hydrothermal process that creates hydroxide, followed by thermal heating using microwaves. The optimized TON@NC catalyst retains its desirable structural porosity and exhibits exceptional bifunctional oxygen catalytic performance owing to well-designed oxygen vacancies and suitable crystallite sizes. TON@NC demonstrates enhanced performance in oxygen catalytic reactions, with a half-wave potential of 0.78 V and an active potential of 1.49 V in alkaline environments, outperforming carbon-based precious metal catalysts. Furthermore, ZABs employing TON@NC as the air cathode show remarkable cycling stability over 300 h and an outstanding output power density of 100.5 mW cm⁻². This facile and adaptable synthetic strategy can accelerate the development of porous hybrids composed of precisely engineered nitrogen-doped carbon backbones combined with advanced multi-metallic catalysts for energy storage applications. Microwave-assisted reconstruction strategy is devised to fabricate a highly active bifunctional oxygen catalyst, named as TON@NC, in which Ni-Co-Fe trimetallic oxide needles are anchored on nitrogen-doped carbon network structures. TON@NC demonstrates highly enhanced oxygen catalytic reactions, with a half-wave potential of 0.78 V and an active potential of 1.49 V in alkaline environments, while ZABs employing TON@NC as the air cathode show remarkable cycling stability over 300 h and an outstanding output power density of 100.5 mW cm⁻².