Facile synthesis of CoPNC-encapsulated Co2P nanoparticles as a bifunctional electrocatalyst for Zn–air batteries

Abstract

Coupling oxygen evolution reaction (OER) highly active transition metal compounds (TMCs) with oxygen reduction reaction (ORR) highly active metal-nitrogen-doped carbon (MNC) has become an important strategy to prepare bifunctional electrocatalysts for rechargeable Zn-air batteries. In this study, a cobalt–nitrogen–phosphorus-doped carbon-coated cobalt phosphide nanocomposite (Co₂P@CoPNC) was simply prepared using cobalt chloride, phytic acid (PA), commercial melamine foam (MF), and polyvinyl alcohol (PVA) as Co, P, N, and C sources, followed by high-temperature annealing and acid etching. The characterization results showed that the P had a stronger binding energy with Co but weaker binding energy with C than N at high temperature, leading to the embedding of Co₂P nanoparticles in the CoPNC matrix. Moreover, the P source could also induce numerous macropores and defects for the nanocomposite, resulting in its superior ORR–OER bifunctional electrocatalytic performance than Co@CoNC and NPC catalysts. Its half-wave potential for the ORR (E_1/2) and OER overpotential at 10 mA cm⁻² (η₁₀) could reach up to 0.80 V and 0.38 V, respectively, achieving a total overpotential of 0.81 V for the bifunctional catalyst. The prepared bifunctional electrocatalyst was further evaluated in rechargeable Zn-air batteries.