Mg²⁺ ion-powered hybrid supercapacitor with β-MnO<inf>2</inf> as a cathode and α-Fe<inf>2</inf>O<inf>3</inf> as an anode

Abstract

Commercial electrochemical supercapacitors are expensive, toxic, and have inadequate energy density at a high power density. To overcome above complications, researchers are focusing on aqueous magnesium-ion-based supercapacitors via bivalent Mg2+ ions. Herein, the facile hydrothermal method was employed for the synthesis of the β-MnO2 and α-Fe2O3 electrodes, which are confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) techniques. We fabricated a Mg2+-based hybrid supercapacitor (Mg-HSC) with β-MnO2 as a cathode, α-Fe2O3 as an anode, and 1 M MgSO4 as an electrolyte; β-MnO2 exhibited a specific capacitance of 1867 F/g while α-Fe2O3 showed 1896 F/g. The good performance is attributed to small ions of Mg2+ and its bivalent nature. The Mg-HSC exhibited excellent specific capacitance of 230.0 F/g at 1 A/g current density in a wide voltage range of 0 to 1.7 V. The Mg-HSC showed 82.1 Wh/kg energy density at 6153.8 W/kg power density. Moreover, this configured device showed superior long-term cycling stability with capacitance retention of >96.2% over 5000 cycles at 15 A/g current density. The facile synthesis method of electrode materials and the bivalent MgSO4 yield into the high-performance hybrid supercapacitor which can compete with current electrochemical energy storage devices.