Activating and stabilizing Co sites in CoP for triggering oxygen electrocatalysis in zinc-air battery

Catalysts with high activity and corrosion-resistance are desirable for oxygen reduction and evolution reactions (ORR/OER) in rechargeable zinc-air batteries (ZABs). Herein, via an etching-phosphating-annealing strategy, CoP is in situ formed in hollow carbon-nanobox, both of which are wrapped by a thin nitrogen-doped carbon layer (CoP/HNBs@NCL). Tannic acid etches ZIF-67 nanobox to release Co2+ and 2-methylimidazole to generate hollow structure. As-marked CoP/HNBs@NCL-2 (271.9 m2 g−1) exhibits robust activities towards ORR (half-wave potential of 0.88 V) and OER (overpotential of 0.36 V), which outperforms many non-precious metal catalysts due to the strong interactions between CoP and N-species and the smooth mass transfer via the porous hollow structure. Even at high potentials (OER), HNBs@NCL framework can still relieve the leaching of Co species (leaching ratio of 15.5 % after 6 h) to obtain high corrosion resistance and stability. Theoretical calculations reveal that N atoms enhance the electron delocalization degree of Co sites in CoP to lower energy barriers and balance adsorption free-energies of O-intermediates to enhance oxygen electrocatalysis. Notably, ZAB with CoP/HNBs@NCL-2 air-electrode exhibits high peak power density (139.8 mW cm−2) and charge–discharge cycling stability (132 h). This work presents a reliable protocol to design hollow electrocatalysts with desirable bifunctional activity and stability for ZABs.