Porous carbon nanosheets integrated with graphene-wrapped CoO and CoNx as efficient bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries.

Abstract

The development of advanced bifunctional oxygen electrocatalysts for the oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) is crucial for the practical application of zinc-air batteries (ZABs). Herein, porous carbon nanosheets integrated with abundant graphene-wrapped CoO and CoNx (CoO/CoNx-C) were successfully fabricated through a simple one-step pyrolysis. With convenient porous channel and large accessible surface, abundant CoO/CoNx species and graphene wrapping structure, CoO/CoNx-C exhibited a half-wave potential of 0.844 V in ORR and an overpotential of 384 mV (@10 mA cm^-2) in OER in the alkaline environment and presented a negative shift of 9 mV in ORR after 8000 cycles and positive shift of 19 mV in OER after 2000 cycles. Electrochemical acid-washing and comparison analysis revealed that the ORR activity mainly originated from CoO nanoparticles, while CoNx species were greatly responsible for OER catalysis. Furthermore, the as-prepared CoO/CoNx-C endowed the rechargeable liquid and solid ZABs with superior power density (161 mW cm^-2 for liquid ZABs and 137 mW cm^-2 for solid ZABs) and long-term stability (stable in 1000 h charge/discharge tests) compared to commercial catalysts. This work provides a feasible strategy for cobalt/carbon hybrid materials as advanced bifunctional electrocatalysts for ZABs.