Co ₂ P@N,P-Codoped Carbon Nanofiber as a Free-Standing Air Electrode for Zn-Air Batteries: Synergy Effects of CoN _x Satellite Shells

Here, a free-standing electrode composed of cobalt phosphides (Co ₂ P) 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 Co ₂ P crystal and surrounding nanometer-sized CoN _x moieties embedded in an N,P-codoped porous carbon matrix. Co ₂ P@CNF shows high oxygen reduction reaction and oxygen evolution reaction performance owing to the synergistic effect of Co ₂ P nanocrystals and the neighboring CoN _x moieties, which have the optimum binding strength of reactants and facilitate the mass transfer. The free-standing Co ₂ P@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 Co ₂ P@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 Co ₂ P@CNF make it a potential candidate for wearable electronic devices.