Hydroxy functionalized ionic liquids as promising electrolytes for supercapacitor study of α-Fe2O3 thin films

Abstract

Herein, we are exploring hydroxy functionalized ionic liquids (HFILs) as electrolytes in electrochemical studies of Fe2O3 thin films in aqueous medium. The thin films are deposited by simple and cost effective successive ionic layer adsorption and reaction (SILAR) method at room temperature. Four HFILs, [HEMIM][Cl], [TEHEA][Cl], [(EtOH)NH3][Ac] and [(EtOH)3NH][Ac] are synthesized and their aqueous solutions have been studied as electrolytes. Syntheses of ILs are confirmed by NMR spectra whereas the structural and surface properties of Fe2O3 thin film is determined by X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDAX) and Brunauer–Emmett–Teller (BET) analysis. XRD pattern confirms the rhombohedral phase of α-Fe2O3 (hematite). Electrochemical performance of Fe2O3 electrode in 0.1 M HFILs is investigated with cyclic voltammetry (CV), galavanostatic charge/discharge (GCD) analysis and electrochemical impedance spectroscopy (EIS). Fe2O3 electrode exhibited good capacitive nature in all HFILs, however, [HEMIM][Cl] conferred highest specific capacitance of 124 Fg−1 at 4.0 mA cm−2 current density amongst the studied HFILs. Good cycle stability and up to 91% retention of capacitance over 1000 cycles is availed with [HEMIM][Cl]. Such promising results are strongly emphasizing the possible utilization of HFILs as environmental benign media in supercapacitor application.