Effects of Electrochemical Oxygen Reduction on Aluminum Electrodeposition from 1-ethyl-3-methylimidazolium Chloride and Acetamide Electrolytes

Aluminum (Al) electrodeposition from non-aqueous solutions has attracted significant attention for applications such as surface coating films, Al recycling, and Al-based secondary batteries. For practical use, it is desirable that Al electrolytes be handled in a dry air environment, similar to the conditions used in lithium-ion battery manufacturing. In such systems, understanding the effects of oxygen is critical for achieving high-quality Al films, extending electrolyte lifetime, and ensuring long-term battery performance. In our recent work, we evaluated two representative Al electrolytes (1-ethyl-3-methylimidazolium chloride (EMIC)–AlCl 3 ionic and an acetamide (AcAm)–AlCl 3 ) for Al electrodeposition under dry air, where oxygen is present. While the AcAm–AlCl 3 system yielded uniform Al films, the EMIC–AlCl 3 system resulted in non-uniform deposits and exhibited decreased current efficiency. However, the exact mechanism underlying the difference in Al electrodeposition behavior between these two electrolytes remains unclear. In this study, we investigated the cause of the Al electrodeposition failure in the EMIC–AlCl 3 electrolyte in the presence of oxygen. The results indicated that neither oxygen concentration nor electrochemical oxygen reduction was the direct cause of the Al electrodeposition failure. Instead, a by-product derived from the reaction between electrochemically reduced oxygen and the EMI + inhibited Al electrodeposition.