Co/Co2P Nanoparticles Encapsulated within Hierarchically Porous Nitrogen, Phosphorus, Sulfur Co-doped Carbon as Bifunctional Electrocatalysts for Rechargeable Zinc-Air Batteries

Developing high performance nonprecious metal-based electrocatalysts has become a critical first step towards commercial applications of metal-air batteries. Herein, nanocomposites based on Co/Co2P nanoparticles encapsulated within hierarchically porous N, P, S co-doped carbon are prepared by controlled pyrolysis of zeolitic imidazolate frameworks (ZIF-67) and poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS). The resulting Co/Co2P@NPSC nanocomposites exhibit apparent oxygen reduction reaction (ORR) and evolution reaction (OER) catalytic performance, and are used as the reversible oxygen catalyst for zinc-air batteries (ZABs). Density functional theory (DFT) calculations exhibit that Co2P could provide active sites for the ORR and promote the conversion between the adsorbed intermediates, and porous N,P,S co-doped carbon with Co2P nanoparticles also improves the exposure of actives sites and endows charge transport. Liquid-state ZABs with Co/Co2P@NPSC as the cathode catalysts demonstrate the greater power density of 198.1 mW cm(-2) and a long cycling life of 50 h at 10 mA cm(-2), likely due to the encapsulation of Co/Co2P nanoparticles by the carbon shell. Solid-state ZABs also display a remarkable performance with a high peak power density of 74.3 mW cm(-2). Therefore, this study indicates the meaning of the design and engineering of hierarchical porous carbon nanomaterial as electrocatalyst for rechargeable metal-air batteries.