High-Entropy Alloy Al0.2Co1.5CrFeNi1.5Ti0.5 Prepared from High-Entropy Oxide (Al0.2Co1.5CrFeNi1.5Ti0.5)3O4 by a Deoxidation Process via a CaH2-Assisted Molten Salt Method

Abstract

High-entropy alloys (HEAs) have attracted a great deal of research interest these days because of their attractive properties. Low-temperature chemical synthesis methods are being developed to obtain nanoscale HEAs with low energy consumption. In this study, we prepared HEA Al0.2Co1.5CrFeNi1.5Ti0.5 nanoparticles from high-entropy oxide (HEO) (Al0.2Co1.5CrFeNi1.5Ti0.5)3O4 by a deoxidation process via a CaH2-assisted molten salt method at 600 °C. X-ray diffraction measurements demonstrated that the oxide precursor and the reduced product have single-phases of spinel structure and face-centered cubic structures, indicating the formation of HEO and HEA, respectively. The HEA nanoparticles exhibited superior catalytic performance in the liquid-phase hydrogenation of p-nitrophenol at room temperature with little leaching of the component elements. Scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDX) exhibited a good distribution of constituent elements over the HEA nanoparticles in a micro-sized range. However, transmission electron microscopy (TEM) with EDX revealed a slight deviation of elemental distributions of Al and Ti from those of Co, Cr, Fe, and Ni in a nano-sized range, probably due to the incomplete reduction of aluminum and titanium oxides. The elemental homogeneity in the HEA nanoparticles could be improved by taking advantage of the HEO precursor with homogeneous elemental distributions, but the experimental results suggested the importance of the total reduction of oxide precursors to prepare homogeneous HEAs from HEOs.