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

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 (η10) of only 188 mV at 10 mA cm−2, much lower than bimetallic CoFeOx/NF (233 mV), trimetallic CoFeCrOx/NF (211 mV), and tetrametallic CoFeCrMoOx/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. Nanoflower‐like high‐entropy CoFeCrMoMnOx/NF spinel catalyst exhibits outstanding electrocatalytic OER activity with an ultralow overpotential of 188 mV, surpassing most multicomponent electrocatalysts reported previously due to the synergistic effect between different metal elements. In‐situ Raman spectra illustrate that the formation of γ‐NiOOH on the high‐entropy spinel surface is a crucial active species for the OER.