High entropy spinel metal oxide (CoCrFeMnNi)<inf>3</inf>O<inf>4</inf> nanoparticles as a high-performance supercapacitor electrode material

High entropy spinel oxides (HEO) are a new type of material stabilized by contributions from configurational entropy, and they are expected to show interesting electrochemical energy storage properties. In this study, the first spinel (CrMnFeCoNi)3O4 HEO nanoparticle-based supercapacitor electrode material is synthesized using a reverse co-precipitation approach. The X-ray diffraction analysis confirmed the phase-pure spinel structure. The X-ray photoelectron spectroscopy is used to identify the oxidation states of the cations in spinel HEO. Scanning electron microscopy and electron dispersive X-ray spectroscopy revealed smooth spherical morphology with uniform distribution of cations in HEO nanoparticles. Electrochemical energy storage properties were further studied on spinel HEO-based supercapacitor electrode material. The HEO electrode showed capacitance of 239 F g−1 and specific energy of 24.1 Wh kg−1 at a current density of 0.5 A g−1. A rate capability of 38% is observed from 0.5 to 25 A g−1. Capacitance retention is found to be 76% after 1000 cycles. The columbic efficiency is remained 86% for 1000 cycles which indicates that HEO has good charge-discharge reversibility. The solution resistance (Rs) and a charge transfer (Rct) of HEO electrodes are found to be 0.96 Ω and 1.56 Ω, respectively. This is the first report on the deployment of pristine spinel-type HEO nanoparticles in supercapacitors, and it opens up possibilities for further exploration of other HEOs.