Co2P@N,P-Codoped Carbon Nanofiber as a Free-Standing Air Electrode for Zn–Air Batteries: Synergy Effects of CoNx Satellite Shells

Here, a free-standing electrode composed of cobalt phosphides (Co₂P) supported by cobalt nitride moieties (CoN_x) and an N,P-codoped porous carbon nanofiber (CNF) in one-step electrospinning of environmentally friendly benign phosphorous precursors is reported. Physiochemical characterization revealed the symbiotic relationship between a Co₂P crystal and surrounding nanometer-sized CoN_x moieties embedded in an N,P-codoped porous carbon matrix. Co₂P@CNF shows high oxygen reduction reaction and oxygen evolution reaction performance owing to the synergistic effect of Co₂P nanocrystals and the neighboring CoN_x moieties, which have the optimum binding strength of reactants and facilitate the mass transfer. The free-standing Co₂P@CNF air-cathode-based Zn-air batteries deliver a power density of 121 mW cm^-2 at a voltage of 0.76 V. The overall overpotential of Co₂P@CNF-based Zn-air batteries can be significantly reduced, with low discharge-charge voltage gap (0.81 V at 10 mA cm^-2) and high cycling stability, which outperform the benchmark Pt/C-based Zn-air batteries. The one-step electrospinning method can serve as a universal platform to develop other high-performance transition-metal phosphide catalysts benefitting from the synergy effect of transition nitride satellite shells. The free-standing and flexible properties of Co₂P@CNF make it a potential candidate for wearable electronic devices.