Cobalt Phosphide Coupled with Heteroatom-Doped Nanocarbon Hybrid Electroctalysts for Efficient, Long-Life Rechargeable Zinc-Air Batteries

Metal phosphides and heteroatom-doped carbons have been regarded as promising candidates as bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). However, both have suffered from stability issues during repeated ORR and OER operations in zinc-air batteries (ZABs). Herein, this study reports a versatile cobalt-based hybrid catalyst with a 1D structure by integrating the metal-organic framework-derived conversion approach and an in situ crosslinking method. Among them, the 1D hybrid catalyst composed of ultrasmall cobalt phosphide nanoparticles supported by nitrogen-, sulfur-, phosphorus-doped carbon matrix shows remarkable bifunctional activity close to that of the benchmark precious-metal catalysts along with an excellent durability in the full potential range covering both the OER and ORR. The overall overpotential of the rechargeable ZABs can be greatly reduced with this bifunctional hybrid catalyst as an air-electrode, and the cycling stability outperforms the commercial Pt/C catalyst. It is revealed that the cobalt phosphide nanoparticles are in situ converted to cobalt oxide under the accelerated conditions during OER (and/or ORR) of the ZABs and reduces the anodic current applied to the carbon. This contributes to the stability of the carbon material and in maintaining the high initial catalytic properties of the hybrid catalyst.