Nanoflower‐Like High‐Entropy Co‐Fe‐Cr‐Mo‐Mn Spinel for Oxygen Evolution

Abstract Oxygen evolution reaction (OER) is the key anode reaction of electrolytic water. To improve the slow OER kinetics, we synthesize nanoflower‐like Co−Fe‐Cr−Mo‐Mn high‐entropy spinel (HES) nanosheets on nickel foam (NF) by one‐step solvothermal method, which exhibit an overpotential (η 10 ) of only 188 mV at 10 mA cm −2 , much lower than bimetallic CoFeO x /NF (233 mV), trimetallic CoFeCrO x /NF (211 mV), and tetrametallic CoFeCrMoO x /NF (200 mV). The OER overpotential decreases with the increase of the number of metals, indicating that the formation of HES has a positive effect on the improvement of electrocatalytic performance, since the synergistic effect between different metals enhances the charge transfer rate and decreases reaction barrier. In‐situ Raman spectra demonstrate that the formation of γ‐NiOOH on the HES surface is a crucial active species for the OER. This work demonstrates a simple and efficient synthesis method to prepare nanoflower‐like high‐entropy electrocatalysts for efficient OER electrocatalysis.