Uniform copper-cobalt phosphides embedded in N-doped carbon frameworks as efficient bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries.

The development of efficient and abundant transition metal bifunctional electrocatalysts is crucial in sustainable energy utilization. Copper-cobalt bimetallic composites exhibit excellent electrochemical performance but the agglomeration of nanoparticles and phase separation cannot be avoided in high temperature pyrolysis. Herein, Cu(ii) ions are introduced into Co-based zeolitic imidazolate frameworks (ZIF-67) by a polymer-coating method to synthesize copper-cobalt bimetallic composite phosphides (CuCoP). After further pyrolysis and phosphidation, the uniform CuCoP nanoparticles are embedded into N-doped carbon frameworks (CuCoP-NC) derived from organic ligands. CuCoP-NC possesses unique hollow structure, rich pores in the carbon framework and large specific surface areas. At an optimal carbonization temperature of 700 °C, CuCoP-NC-700 exhibits admirable electrocatalytic performance such as high onset potentials (0.978 V vs. reversible hydrogen potential (RHE) in alkaline media and 0.801 V vs. RHE in acidic media), large limiting current densities, long-term stability and eximious resistance to methanol poisoning towards the oxygen reduction reaction (ORR) in both alkaline and acidic media and a low overpotential of 337 mV at 10 mA cm-2 towards the oxygen evolution reaction (OER). Moreover, CuCoP-NC-700 is assembled into a Zn-air battery and presents a higher power density (116.5 mW cm-2) and stability compared to Pt/C.