Electrochemical impedance spectroscopy and Raman spectroscopy studies on electrochemical interface between Au(111) electrode and ethaline deep eutectic solvent

Abstract Deep eutectic solvents (DESs) are promising candidate electrolytes in electrochemical fields due to their excellent properties. In this work, cyclic voltammetry, electrochemical impedance spectroscopy and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) have been employed to explore the potential-dependent innermost layer structure in electrical double layer at Au(111) electrode in ethaline DES (choline chloride and ethylene glycol in a 1:2 molar ratio). It is found that chloride anions adsorption on Au(111) surface gives rise to the lifting of Au(111)-(√3 × 22) reconstruction and the abrupt increase of differential capacitance. When the potential shifts positively, a disorder-order phase transition of chloride anion adsorbate is revealed. When the potential shifts negatively, choline cations and ethylene glycol molecules adsorb on Au(111) surface with weak interaction detected by SHINERS technique. This work provides new insight into the potential-dependent adsorption and phase transition behaviors of innermost layer structure in electrical double layer in ethaline DES.