Medium-Entropy Co–Fe–Cr–Mo Spinel Nanoflowers as Electrocatalysts for Oxygen Evolution

Oxygen evolution reaction (OER) plays an important role in many electrocatalysis-related fields. However, the slow kinetics of the OER seriously hinders energy efficiency. Here, we synthesize flower-like Co–Fe–Cr–Mo medium-entropy spinel (MES) nanosheets on nickel foam (NF) using one-step solvothermal method for the OER. Due to high stability and compositional diversity, the CoFeCrMoOx/NF catalyst exhibits excellent electrocatalytic OER performance with an overpotential of only 196 mV at 10 mA cm–2 in 1.0 M KOH solution, much lower than CoFeCrMnOx/NF, CoFeCrCeOx/NF, CoFeCrSnOx/NF, CoFeCrAlOx/NF, and commercial IrO2 catalysts, reflecting that the formation of flower-like MES has a positive effect on the improvement of OER performance. The introduction of Mo increases active sites, promotes electron transfer, accelerates the adsorption and desorption of the OER intermediates, reduces the energy barrier, and thus improves the performance of the OER. In situ Raman spectra indicate that the surface CoOOH and FeOOH species are important active components for the OER.