The interface of a 1 : 2 molar choline chloride/ethylene glycol deep eutectic solvent with a glassy carbon electrode has been investigated by polarization modulation reflection-absorption spectroscopy (PM-IRRAS). Temporal spectral changes at open circuit potential show the experiments to be surface sensitive and indicate slow adsorption of electrolyte molecules on the electrode surface. In situ spectroelectrochemical PM-IRRAS measurements reveal characteristic potential-dependent changes of band intensities and wavenumber-shifts in the surface spectra. The potential dependent spectral changes are discussed in terms of adsorption, reduction, desorption and reorientation of choline cations at the interface. Analogies are drawn to the ionic layer structure proposed for the architecture of electrode/ionic liquid interfaces. The results show that in situ PM-IRRAS is generally applicable to glassy carbon electrodes and to electrode interfaces with deep eutectic solvents.

Deep eutectic electrolytes have been suggested as alternatives to classical room temperature ionic liquids and been used for the electrodeposition of metals. We have investigated the electrodeposition of zinc from a Lewis-basic choline chloride/ethylene glycol deep eutectic solvent containing ZnCl₂. Raman spectroscopy confirmed the presence of the [ZnCl₄]²⁻ ion in the electrolyte that was examined by cyclic voltammetry at static and rotating glassy carbon disk electrodes. The formation of a dissolved, intermediate reducible zinc species Z during the cathodic sweep is proposed to account for the unusual zinc electrodeposition behavior observed in the deep eutectic electrolyte in agreement with the effect of rotation rate, cathodic switching potential and potential sweep rate on the deposition current in RDE voltammetry. The zinc electrodeposition behavior with sodium ethoxide added to the deep eutectic solvent supports the suggestion that Z is a complex of Zn²⁺ and deprotonated components of the solvent. The absence of a current plateau in RDE experiments with ethoxide containing electrolyte is thought to be the result of a potential dependent blocking of the reduction of Z by a layer adsorbed on the electrode.

The study underscores the development of an efficient electrochemical process for anodic H₂O₂production in continuous flow by investigating electrochemical cell setup, electrolyte flow type and rate, as well as electrolyte composition.