Co2P Nanoparticles Encapsulated in N-Doped Carbon Nanotubes as a Bifunctional Oxygen Catalyst for a High-Performance Rechargeable Zn–Air Battery

Abstract

A significant but challenging task is the development of a rechargeable Zn–air battery bifunctional catalyst. Here, a supramolecular self-assembly of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (P123) was designed to construct Co2P nanoparticles encapsulated in N-doped carbon nanotubes (Co2P@NCNT-x). The results show that P123 is an important factor in the formation of N-doped carbon nanotubes coated with Co2P nanoparticles. The Co2P@NCNT-4 catalyst exhibits the maximum limiting diffusion current density (5.2 mA·cm–2 under 808.9 hPa) and a more positive onset potential (0.90 V vs RHE) and half-wave potential (0.84 V vs RHE) due to the greater specific surface area and higher graphitization degree. Its potential gap is only 0.87 V versus RHE which is between the half-wave potential of the oxygen reduction reaction and the Ej = 10 of the oxygen evolution reaction. The Co2P@NCNT-4-based rechargeable Zn–air battery shows the highest peak power density (217 mW·cm–2), the highest specific capacity (831.25 mA h·gZn–1 at 10 mA·cm–2), and remarkable cycle stability. This preparation method can provide ideas for designing other transition metal phosphide catalysts in the future.