The electrodeposition of aluminum (Al) has been extensively investigated for a range of emerging applications in electrical, electronic, and automotive industries due to its excellent corrosion and wear tolerance. One highly prospective process is the Al electrodeposition from an electrolytic bath comprised of an air and moisture-stable ionic liquid, such as 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl), and an aluminum precursor, which is normally aluminum chloride (AlCl_3). Recent spectroscopic studies have shown that Al deposition results from electrochemical reduction of chloroaluminate complexes. In general, the chloroacidity determines reactivity and electrochemistry in the ionic liquid electrolyte. However, the Al deposition chemistry has been complicated by the chemical nature of different chloroaluminate complexes species, their chemical equilibria, and interconversion. The [AlCl_4]~-, [Al_2Cl_7]~1, and Cl~- are the main anions in the solution of alkylimidazolium chloride and AlCl_3. More complicated anions such as [Al_3Cl_(10)]~1, [Al_4Cl_(13)]~-, and [Al_2OCl_5]~-, have also been detected when the AlCl_3 concentration is high.
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