Synthesis and characterization of individual high-entropy alloy particles for electrocatalytic water oxidation.

High-entropy alloys (HEAs) have attracted considerable attention as promising catalysts. Despite a rapidly growing number of publications in this area, characterization of HEA electrocatalytic activity and stability remains challenging. In this paper, we report rapid and scalable microwave-shock assisted synthesis of FeCoNiCuMnCr HEA and its characterization at a single particle level. HEA particles synthesized on HOPG without additional reagents or pre-/post-treatments exhibited a significant activity toward water oxidation in 0.1 M NaOH. Individual micrometer-sized FeCoNiCuMnCr HEA particles were imaged by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) to show the uniform distribution of all six metals, and the potential dependence of the oxygen evolution reaction (OER) at its surface was probed by scanning electrochemical microscopy (SECM). Significant variations in onset potential of OER on different HEA particles were observed; however, no obvious correlation with the particle size was found. The HEA stability was confirmed by SEM/EDS imaging of the same FeCoNiCuMnCr particle after several hours of OER experiments and also by voltammetry and XRD analysis.