Effectively engineering in situ coupled cobalt-cobalt phosphide nanoparticles with nitrogen-doped carbon materials for advanced bifunctional oxygen electrocatalysts in rechargeable Zn-air batteries

Constructing efficient and inexpensive bifunctional catalysts with oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) is urgently requisite for advanced Zn-air batteries. Herein, a composite material consisting of cobalt-cobalt phosphide nanoparticles in situ coupled with N-doped carbon (Co-Co2P @ NC) is conveniently engineered via a facile all-in-one carbonization/phosphorization process. Specifically, Co-Co2P @ NC implements unprecedented bifunctional catalytic activities with a positive ORR half-wave potential of 0.858 V and a low OER potential of 1.598 V at 10 mA cm−2, outperforming the benchmark catalysts and is on a par with recently reported non-precious metal-based catalysts. These impressive electrocatalytic performances are attributable to the synergistic coupling effects between metallic Co, Co2P and NC, extraordinary specific surface area, rich active species and conductive carbon frameworks. Prominently, a rechargeable aqueous ZAB with Co-Co2P @ NC as an air cathode catalyst delivers an ultra-long term cycling stability of more than 2000 h (over continuous 6000 cycles) with a small change of charge-discharge voltage gap from 0.841 V to 0.890 V at 2 mA cm−2. Beyond that, both button-like and foldable quasi-solid-state ZABs also exhibit admirable performance even under the limited electrolyte condition, evidently indicating the wide adaptability and feasibility in practical energy conversion and storage.