Dynamic Restructuring of Carbon Nanotube-Supported High-Entropy Alloys Enabling Efficient Oxygen Electrocatalysis

Oxygen electrocatalysis, mainly including the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), is a cornerstone in rechargeable metal-air batteries. However, these reactions are sluggish due to the four-electron transfer process and the linear scaling relationship of the intermediate binding strength. Herein, we have rationally developed a hybrid composite consisting of high-entropy alloy nanoparticles (NPs) encapsulated in carbon nanotubes (CNTs) to significantly improve the electrocatalytic performance. In situ spectroscopy investigations and theoretical calculations disclose that high-entropy alloys undergo dynamic reconstruction to form MOOH and M-OH (M represents metallic elements) as the authentic active species in the ORR and OER processes, respectively. Specifically, Fe, Co, Mn, and Cu regulate the charge transfer between the Ni-O bonds in MOOH for the OER, while the high-entropy effect and surface-absorbed OH groups coregulate the d-band center of surface Co for the efficient ORR. Accordingly, the as-developed FeCoNiMnCu@CNTs exhibits activity for both ORR and OER, with an ultralow voltage gap of 0.626 V between the half-wave potential of ORR and the OER potential at 10 mA cm^-2. Moreover, Zn-air batteries with FeCoNiMnCu@CNTs exhibit a power density of 131.3 mW cm^-2 and robust stability.