Spinel-Type (FeCoCrMnZn)O High-Entropy Oxide: Facile Preparation and Supercapacitor Performance.

High-entropy oxides (HEOs) have attracted more and more attention because of their unique structures and potential applications. In this work, (FeCoCrMnZn)O HEO powders were synthesized via a facile solid-state reaction route. The confirmation of phase composition, the observation of microstructure, and the analysis of crystal structure, distribution of elements, and valences of elements were conducted by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS), respectively. Furthermore, a (FeCoCrMnZn)O/nickel foam ((FeCoCrMnZn)O/NF) electrode was prepared via a coating method, followed by the investigation of its supercapacitor performance. The results show that, after calcining (FeCoCrMnZn)O powders at 900 °C for 2 h, a single spinel structure (FCC, Fd-3m, = 0.8399 nm) was obtained with uniform distribution of Fe, Co, Cr, Mn, and Zn elements, the typical characteristic of a high-entropy oxide. In addition, the mass specific capacitance of the (FeCoCrMnZn)O/NF composite electrode was 340.3 F·g (with 1 M KOH as the electrolyte and 1 A·g current density), which indicates that the (FeCoCrMnZn)O HEO can be regarded as a prospective candidate for an electrode material in the field of supercapacitor applications.