An In Situ Scanning Tunneling Microscopy Study on the Electrochemical Interface between Au(111) and Ethaline Deep Eutectic Solvent

Deep eutectic solvents (DESs) possess excellent properties that make them promising candidates for electrolytes in electrochemical fields. However, information about the electrical double layer, particularly the potential-dependent innermost layer structure and electrode surface structure, is still lacking. In this work, we investigated the Au(111) surface structure and adsorption behaviors of DES components on a Au(111) surface in ethaline (choline chloride and ethylene glycol in a 1 : 2 molar ratio) by using in situ scanning tunneling microscopy and cyclic voltammetry. The surface reconstruction of Au(111) and its lifting are disclosed, and the potential-dependent adsorption behavior of chloride ions is analyzed with emphasis on their strong interactions with the Au surface. The results provide new insights into the electrical double layer structure in ethaline DES with atomic-level resolution.