Effect of hydrogen bond donor molecules ethylene glycerol and lactic acid on electrochemical interfaces in choline chloride based-deep eutectic solvents

Choline chloride (ChCl)-based-deep eutectic solvents (DESs) are widely used in electrochemical fields. In this work, the effect of two types of hydrogen bond donor (HBD) molecules, ethylene glycerol and lactic acid (LA), on electrochemical interfaces between the Au electrode and DESs has been investigated by employing voltammetry and electrochemical impedance spectroscopy. The anodic dissolution and passivation behaviors of the Au electrode are revealed in both ethaline and ChCl:LA. In ChCl:LA, the anodic dissolution of Au is slowed down, and the passivation film is relatively dense and stable due to the existence of the carboxyl group in HBD molecule LA. In the double layer region, the lifting and formation of Au(111) surface reconstruction and a disorder-order phase transition of the chloride ion adlayer were observed in the two DESs. Moreover, compared with ethaline, an extra pair of current peaks appears in ChCl-LA possibly due to the adsorption and desorption of LA on the Au(111) surface, which might imply the stronger interaction of LA with the Au electrode in ChCl:LA. HBD LA could even have marked an impact on the disorder-order phase transition of the chloride ion adlayer. The above results provide new insight into the significant effect of HBD molecules on the anodic dissolution and the passivation of the Au electrode and the electrochemical behaviors in the double layer region.