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

[Display omitted] •CoP NPs encapsulated in porous walls of hollow nanobox are wrapped by carbon layer.•Porous hollow structure creates abundant active sites and mass transfer pathways.•N atom elevates electron delocalization degree of Co atom to boost ORR/OER activity.•Coated carbon-layer protects CoP from fast corrosion to gain high ORR/OER stability.•The assembled Zn-air battery exhibits high power density and rechargeability (132 h). 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.