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

Abstract

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.