Sputter-Deposited High Entropy Alloy Thin Film Electrocatalyst for Enhanced Oxygen Evolution Reaction Performance.

Thin film catalysts, giving a different morphology, provide a significant advantage over catalyst particles for the gas evolution reaction. Taking the advantages of sputter deposition, a high entropy alloy (HEA) thin film electrocatalyst is hereby reported for the oxygen evolution reaction (OER). The catalyst characteristics are investigated not only in its as-deposited state, but also during and after the OER. For comparison, unary, binary, ternary, and quaternary thin film catalysts are prepared and characterized. The surface electronic structure modification due to the addition of a metal is studied experimentally and theoretically using density functional theory calculation. It is demonstrated that sputtered FeNiMoCrAl HEA thin film exhibits OER performance superior to all the reported HEA catalysts with robust electrocatalytic activity having a low overpotential of 220 mV at 10 mA cm -2 , and excellent electrochemical stability at different constant current densities of 10 and 100 mA cm -2 for 50 h. Furthermore, the microstructure transformation is investigated during the OER, which is important for the understanding of the OER mechanism provided by HEA electrocatalyst. Such a finding will contribute to future catalyst design.