Electrochemical Hydrogen Evolution Reaction Evaluation of CoNi(Cr/V) Medium-Entropy Alloys in an Acidic Environment

Developing nonprecious metal-based electrocatalysts with outstanding performance has been the focal point of the scientific community for the past decade. Multiprinciple element medium- and high-entropy alloys have recently been known to exhibit a range of superior mechanical, physical, electrocatalytic, and anticorrosive properties, which are superior to traditional alloys. In this study, the electrocatalytic properties of equiatomic single-phase medium-entropy alloy electrodes with equiatomic compositions CoNiCr, CoNiV, and CoNi(Cr/V) are investigated for the hydrogen evolution reaction in 0.5 M H₂SO₄ at room temperature. Electrochemical measurements revealed operational overpotentials of 50 and 228 mV at current densities of 10 and 100 mA/cm² with a Tafel slope of 46 mV/dec for the CoNi(Cr/V) alloy, while CoNiCr and CoNiV exhibited Tafel slopes of 78 and 82 mV/dec, respectively. The long-term durability of all specimens in the acidic phase was further tested at room temperature using cyclic voltammetry degradation and chronoamperometry methods, and it was found that all samples exhibited good stability with a shift in overpotential of just 6 mV@50 mA/cm² after 2000 cycles and stable multistep current density values for 20 h. X-ray photoelectron spectroscopy analysis showed an increase in the surface oxidation number of Ni and Co through Cr and V doping, which is in agreement with the higher electrocatalytic activity of the CoNi(Cr/V) alloy. The spin-polarized first-principles calculations within the context of the plane wave self-consistent field method were performed to evaluate the mechanism of electrochemical experimental results.