High energy density liquid state asymmetric supercapacitor devices using Co–Cr–Ni–Fe–Mn high entropy alloy

Abstract

For satisfying the ever-growing need in novel material search for energy storage applications, high entropy alloys (HEAs) have been explored recently. A simple induction melting method was used to synthesize the CoCrNiFeMn bulk HEA sample that was later ball-milled to obtain nanoparticles. The dimension reduction provided an increased surface area for sample usage in supercapacitor applications. The highest specific capacitance of 386.66 F g⁻¹ was obtained at 5 mV s⁻¹ in an aqueous 3 M KOH electrolyte in a three-electrode system. We also studied the contribution of d-band electrons from the metals for electrochemical interaction in the system through DFT calculations. The liquid state CoCrNiFeMn//activated carbon (AC) asymmetric supercapacitor (ASC) device was fabricated, and the energy stored was used to glow a 1.5 V LED device. The energy density of the ASC device was 21 W h kg⁻¹ at a power density of 307 W kg⁻¹, which is one of the first reports on HEA-based liquid-state asymmetric devices.