Plasma nitrided CoCrFeNiMn high entropy alloy coating as a self-supporting electrode for oxygen evolution reaction

Abstract

Noble metal electrocatalytic electrodes used in water electrolysis for hydrogen production are expensive and non-noble metal nanoparticle catalysts are not conducive to large-scale production. In this paper, the CoCrFeNiMn high entropy alloy (HEA) coating was prepared by high-velocity oxygen fuel (HVOF) spraying on the surface of stainless steel as a self-supporting oxygen evolution electrode, and the electrocatalytic activity of the electrode was further improved by plasma nitriding. The results show that the CoCrFeNiMn coating is mainly composed of FCC solid solution phase and MnCr2O4 spinel phase, and the thickness of the coating is approximately 100 μm. After nitriding, the surface of the coating is reshaped from the original semi-molten morphology to cauliflower-like structure, and the N atoms are mainly enriched in the MnCr2O4 phase. In addition, the binding energies of Co, Cr, and Ni to O in the nitrided coating decrease by 0.7 eV, while the binding energies of Fe and Mn to O are not significantly affected. The overpotential of the nitrided CoCrFeNiMn coating decreases from 363 mV to 309 mV at the current density of 10 mA cm−2, and it has a smaller Tafel slope and charge transfer resistance, and larger double-layer capacitance compared to the CoCrFeNiMn coating. Both the CoCrFeNiMn coated electrodes with and without nitriding show good long-term stability during the 60 h stability test. The high entropy alloy coating coupled with plasma nitriding technique provides a new research idea for the eletrocatalytic field of the water splitting.