Electrodeposited NiFeCoMoW High-Entropy Alloys with Nanoscale Amorphous Structure as Effective Hydrogen Evolution Electrocatalysts

The growing demand for hydrogen and the effectiveness of alkaline anion exchange membrane (AEM) electrolyzers has led to an increased interest in finding lower cost alternatives to traditional noble metal electrocatalysts for the hydrogen evolution reaction (HER). High-entropy alloy (HEA) electrocatalysts have received significant attention due to their properties such as high configurational entropy and high lattice distortion which can help promote electrocatalytic reactions. In this work, an aqueously electrodeposited and structurally amorphous NiFeCoMoW HEA was synthesized and investigated for its HER performance. The importance of factors such as surface morphology, chemical composition, and microstructure on the electrochemical activity and stability was also explored. Increased electrochemical activity was observed in the HEA compared to electrodeposited binary alloys, owing to a larger number of active sites with differing electronic structures and adsorption energies. NiFeCoMoW HEAs electrodeposited at a pH of 5 exhibited the smallest Tafel slope of all the tested samples with an average Tafel slope of 83 mV/dec. Meanwhile, the lowest overpotential for 10 mA/cm 2 GA of 171 mV was observed in the samples prepared at pH 6, which possessed a higher roughness factor (RF). These results highlight the potential of using HEAs for electrocatalytic applications and demonstrate aqueous electrodeposition as a simple, inexpensive, and scalable synthesis method to produce effective HEA electrocatalysts.