Facile synthesis of high-entropy (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4 nanopowders and their electrochemical properties as supercapacitor electrode

High-entropy oxide (HEO) nanopowders are expected to have unique electrochemical energy storage properties due to their unique structural characteristic and tailorable chemical composition. However, HEO nanopowders are difficult to be prepared because of severe grain coarsening and particle agglomeration in high temperature calcination. In this study, a polyacrylamide gel method was presented to prepare high-entropy (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4 nanopowders. The mole ratio of acrylamide/metal cations (A/M) had a significant influence on the average particle size of HEO nanopowder, which was decreased with the increase of A/M mole ratio. Electrochemical tests demonstrated that as-prepared HEO nanopowders had a specific capacitance of 384 F/g at a current density of 1 A/g, which was remained 57 % as the current density was increased to 20 A/g. Furthermore, a relatively high capacitance retention of 60 % was obtained after 2000 charge-discharge cycles at 5 A/g. In addition, a HEO//activated carbon asymmetric supercapacitor was assembled, which achieved an energy density of 24 Wh/kg at a power density of 746 W/kg. This study presents a simple and cost-effective method to prepare HEO electrode material for supercapacitors.