Electrodeposition of Cu-Al Alloys and Underpotential Deposition of Al onto Cu Single Crystals from a Room-Temperature Chloroaluminate Molten Salt

摘要

Onto Cu(111), Cu(100) and Cu(110) faces, were investigated in the Lewis acidic aluminum chloride/1-methyl-3-ethyl-imidazolium chloride. It was shown that it is possible to produce Cu-Al alloy deposits at potentials positive of that corresponding to the electrodeposition of bulk Al (approx approx 0 V). For a 0.05 mol dm(-3) solution of Cu(I), the onset of the Al codeposition process was found to occur at around 0.30 V versus the Al(III)/Al couple; however, a limiting current for the reduction of Cu(I) to pure Cu metal can be observed in the 0.60 V to 0.30 V potential interval in this solution. The Cu-Al alloy composition was found to be independent of the Cu(I) concentration, reaching a maximum value of 43 atomic percent (a/o) Al at 0 V. X-ray diffraction studies indicated that Cu-Al deposits containing about 7.2 a/o Al retained the fcc Cu structure; however, deposits containing 12.8 a/o Al were two-phase with the second phase tentatively identified as martensitic beta'-Cu_3Al. This phase appears to form before fcc Cu becomes saturated with Al. Cyclic voltammograms recorded onto Cu(111), Cu(100) and Cu(110) clearly indicate that UPD of Al commences at about 0.3 V vs. Al. On the (111) face of Cu UPD takes place through two sharp and separated peaks, indicating formation of two different adsorbed structures, with the second peak corresponding to the formation of a monolayer of Al. Surface alloying of Cu with Al was detected at potentials of the first peak (approx approx 0.25 vs. Al).