Unveiling the potential of (CoFeNiMnCr)3_3O4_4 high-entropy oxide synthesized from CoFeNiMnCr high-entropy alloy for efficient oxygen-evolution reaction

Electrochemical water-splitting is a promising green technology for the production of hydrogen. One of the bottlenecks, however, is the oxygen evolution half-reaction (OER), which could be overcome with the development of a suitable electrocatalyst. Recently, non-noble metal, high-entropy oxides (HEO) have been investigated as potential OER electrocatalysts, but complex synthesis approaches that usually produce the material in powder form limit their wider utilization. Here, an innovative synthesis strategy of formulating a nanostructured (CoFeNiMnCr)$_3$O$_4$ HEO thin film on a CoFeNiMnCr high entropy alloy (HEA) using facile electrochemical and thermal treatment methods is presented. The CoFeNiMnCr HEA serves as exceptional support to be electrochemically treated in an ethylene glycol electrolyte with ammonium fluoride to form a rough and microporous structure with nanopits. The electrochemically treated CoFeNiMnCr HEA surface is more prone to oxidation during a low-temperature thermal treatment, leading to the growth of a spinel (CoFeNiMnCr)$_3$O$_4$ HEO thin film. The (CoFeNiMnCr)$_3$O$_4$ HEO exhibits a superior overpotential of 341 mV at 10 mA cm$^{−2}$ and a Tafel slope of 50 mV dec$^{−1}$ along with remarkable long-term stability in alkaline media. The excellent catalytic activity and stability for the OER can serve as a promising platform for the practical utilization of (CoFeNiMnCr)$_3$O$_4$ HEO