Room-Temperature Electrodeposition of Aluminum via Manipulating Coordination Structure in AlCl₃ Solutions

The coordination mechanism of chloroaluminate species in aluminum chloride (AlCl₃) solutions in γ-butyrolactone (GBL) is investigated using electrochemical, spectroscopic, and computational methods. The liquid-state ²⁷Al NMR spectroscopy shows a sequence of new species generated in the AlCl₃-GBL solutions with increasing AlCl₃/GBL ratio. Ab initio molecular dynamics simulation reveals the dynamic coordination process between GBL and AlCl₃, and the resultant chloroaluminate species are identified as [AlCl₂·(GBL)₂]⁺, AlCl₄^-, AlCl₃·GBL, and Al₃Cl₁₀^-. The species are further confirmed by surface enhanced Raman spectroscopy combined with calculated Raman spectra from methods based on density functional theory. Electrochemical deposition of Al is achieved from the AlCl₃-GBL solution containing Al₃Cl₁₀^-, which is one of the few noneutectic electrolytes for room-temperature Al deposition reported to date.