Co2P nanoparticles supported on cobalt-embedded N-doped carbon materials as a bifunctional electrocatalyst for rechargeable Zn-air batteries

Reversible oxygen electrodes with high efficiencies for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great significance for a variety of energy conversion devices, such as fuel cells and metal-air batteries. Herein, Co2P nanoparticles supported on cobalt-embedded N-doped carbon materials (Co2P/Co–N–C) have been prepared by pyrolysis of cobalt zeolitic imidazolate framework and phosphating post treatment. The optimal Co2P/Co–N–C composite shows excellent bifunctional electrocatalytic activities for both OER (the potential of 1.65 V at 10 mA cm−2) and ORR (half-wave potential of 0.82 V). As a practical demonstration, Co2P/Co–N–C catalyst is used as an air electrode in liquid Zn-air battery, which displays a large open-circuit voltage of 1.50 V, a high peak-power density of 158 mW cm−2 and excellent reversibility of over 205 h at 5 mA cm−2. Moreover, the flexible Zn-air battery with Co2P/Co–N–C exhibits a high open-circuit voltage of 1.46 V and the good flexibility with different angles. This work provides inspiration to explore new strategies for electrochemical energy conversion and storage.