Anchoring NiCo2O4 nanowhiskers in biomass-derived porous carbon as superior oxygen electrocatalyst for rechargeable Zn-air battery

Abstract

Nonprecious bifunctional electrocatalysts with low cost and efficient catalytic activities in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desired to promote the commercialization of metal-air batteries. Herein, NiCo2O4 nanowhiskers embedded into biomass-derived porous carbon (NCO@HHPC) is proposed and fabricated by a facile one-step hydrothermal strategy. In this composite, NiCo2O4 nanowhiskers shows low degree of crystallinity, providing rich ORR and OER catalytic active sites. The conductive carbon framework shows hierarchically porous microstructure, acting as host for anchoring NiCo2O4 nanowhiskers, improving the electronic conductivity and supplying fast transport channels for O2 diffusion and electrolyte infiltration. With optimized composition, the NCO@HHPC-0.5 (containing 0.5 mmol Co(NO3)2·6H2O in precursor) exhibits an excellent bifunctional activity toward ORR and OER. Notably, the corresponding bifunctional activity parameter (ΔE) is as low as 0.78 V, outperforming most state-of-the-art reported nonprecious bifunctional electrocatalysts. Moreover, the assembled rechargeable Zn-air battery achieves superior over-length cycling stability and reversibility with a narrow voltage gap increasing of 0.08 V over 1460 cycles (487 h) at 10 mA cm−2.