Trifunctional electrocatalyst of N-doped graphitic carbon nanosheets encapsulated with CoFe alloy nanocrystals: The key roles of bimetal components and high-content graphitic-N

Abstract A robust trifunctional electrocatalyst based on N-doped graphitic carbon nanosheets encapsulated with CoFe alloy nanocrystals (CoFe@NC/NCHNSs) is synthesized, which exhibits a positive half-wave potential (E1/2) of 0.92 V for oxygen reduction reaction (ORR), and low overpotentials of 285 mV and 120 mV at 10 mA cm−2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The superior trifunctional electrocatalytic performance can be accredited to the synergetic effect of the rich CoFe alloy sites and the high-content doping of graphitic N, as evidenced with theoretical calculations and experimental results. The introduction of Co and Fe species in the synthesis of the CoFe@NC/NCHNSs catalyst plays the important roles of both anchoring N in the carbon matrix and generating graphitic N species, which critically promote the formation of high-content graphitic-N and therefore further boost the electrocatalytic activity. Impressively, with the as-prepared trifunctional catalyst, the assembled liquid Zn-air batteries and water electrolyzers exhibit excellent catalytic activity and durability, and the solid-state Zn-air batteries show a high-power density up to 125 mW cm−2, demonstrating a great potential of this kind of devices for practical applications.