Fe-Cu Alloy-Based Flexible Electrodes from Ethaline Ionic Liquid

The effective implementation of energy storage systems within flexible structures has recently become of particular interest. Here, the fabrication of inexpensive flexible electrodes via a number of straightforward methods formed the motivation for this research. Thin film-based Fe-Cu alloys were cathodically electrodeposited on a graphite substrate. As ionic liquids consist purely of ions (not solvent), they have recently been used in some electrochemical applications. In this study, therefore, Fe-Cu alloy coatings were prepared from an ethaline ionic liquid containing iron and copper salts. The electrochemical behaviour of Fe-Cu alloy films was determined by scanning between − 1.0 V and − 0.3 V in 1 M KOH at various scan rates ranging from 5 mV s⁻¹ to 200 mV s⁻¹. These films were characterised in terms of their structural and morphological properties by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and x-ray diffraction (XRD). Formation of iron and copper alloy was differentiated depending on applied potential. The supercapacitive ability of Fe-Cu-coated film observed in 1 M KOH electrolyte demonstrated a specific capacitance of 304 F g⁻¹ at a scan rate of 5 mV s^-1. The reaction between the alloy and the electrolyte was mainly controlled by a surface-controlled reaction. An asymmetric supercapacitor was constructed with an Fe-Cu-coated graphite negative electrode and a non-woven graphite positive electrode. Four asymmetric supercapacitors were connected in series and used to light up a blue light-emitting diode. This study shows that ethaline ionic liquid is a promising medium for the preparation of alloy-based electrodes in energy storage applications.