Oxygen-deficient VOx integrated cobalt‑nitrogen codoped carbon emerging as a sustainable bifunctional catalyst for efficient zinc–air batteries

Abstract

Improving zinc-air batteries (ZABs) appeals for materials that hasten the two primary electrochemical reactions, especially OER and ORR. There has been significant efforts to construct non-precious metal dual functional catalysts as noble-metal catalyst alternatives. However, for these catalysts, reaching the performance levels required for ZAB commercialisation still remains an elusive goal. In this work, an interconnected oxygen-deficient vanadium oxide (VO_x) in proximity to (Co/Fe)-N-C sites evolving as a sustainable and efficient catalyst for ZABs has been presented. Among the synthesized materials, Co-N-C/VO_x@NC demonstrates superior bifunctional ORR/OER activity at ZAB air-electrode evidenced by its lower voltage gap between ORR and OER compared to Fe-N-C/VO_x@NC. According to theoretical simulations, the spectacular bifunctional performance of Co-N-C/VO_x@NC was attributed to escalated charge-transfer across the active sites and favourable d-band centre alignment which improves the adsorption energy of oxygenated intermediates facilitating the reaction kinetics. Under practical ZABs operating conditions, Co-N-C/VO_x@NC air electrode achieved a peak power density of 155 mW cm⁻², outperforming other catalysts and furthermore yielding a specific capacity of 869.2 mAh g⁻¹, exceeding that of PtRu/C by 1.8 % and Fe-N-C/VO_x@NC by 22.5 % under similar operating conditions. Co-N-C/VO_x@NC batteries performed well after 35 h of uninterrupted operation at 5 mA cm⁻², unlike PtRu/C batteries, which degraded after 600 cycles.