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

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.