Failure Mechanism and Regeneration Strategy of Hygroscopic Ionic Liquids for Aluminium Electrodeposition

Abstract Chloroaluminic acid ionic liquids (ILs), e.g., 1-ethyl-3-methylimidazolium chloride-aluminium chloride (EMIC-AlCl3), are recognized as promising green and low-carbon solvent for aluminium (Al) electrodeposition, because of their relatively high conductivity, low viscosity, and good stability. Nevertheless, electrodeposition of Al must be carried out under dry conditions with inert gas shielding, limited by the hygroscopic behavior of ILs in air atmosphere. Otherwise, the electrolyte will be a failure, thus impeding the development of Al electrodeposition from the ILs. To explore a possible method for the electrolyte regeneration, herein, the effect of water content on Al electrodeposition in the EMIC-AlCl3 ILs was investigated systematically. The results demonstrated that the electrical conductivity was gradually reduced with the increase of water content, leading to the elevated cell voltage and decreased current efficiency during Al electrodeposition. In addition, water adsorption may also change the coordination structure of electrochemical active species in EMIC-AlCl3, thereby influencing the electrodeposition behavior of Al along with deposit properties. All of these have a negative impact on Al electrodeposition. Detailed spectroscopic analysis combined with density functional theory calculation were conducted to clarify the failure mechanism of ILs electrolyte in humid environment, and meanwhile an effective strategy was proposed for the electrolyte regeneration.