The electrodeposition of cobalt, iron, antimony and their aluminum alloys from acidic aluminum chloride 1-methyl-3-ethylimidazolium chloride room-temperature molten salt.

摘要

The electrodeposition of cobalt, iron, antimony, and their aluminum alloys was investigated in the room-temperature molten salt, aluminum chloride-1-methyl-3-ethylimidazolium chloride (AlCl{dollar}sb3{dollar}-MeEtimCl). Solutions of Co(II), Fe(II), and Sb(III) were prepared by controlled-potential coulometric anodization of the respective metal in Lewis acidic melt. The plating and stripping of these metals was investigated using cyclic voltammetry, rotating disk and rotating ring-disk electrode voltammetry, controlled potential coulometry, and potential step chronoamperometry. Bulk deposits of the pure and aluminum-alloyed metals were analyzed using scanning electron microscopy, energy dispersive x-ray spectroscopy, atomic absorption spectroscopy, and x-ray diffraction methods.; The underpotential co-deposition of aluminum was observed during the electrodeposition of cobalt and iron; however, this phenomenon did not occur during the electrodeposition of antimony. The results of this investigation suggest that both a positive work function difference between the transition metal and aluminum and the mutual solubility of these components determine whether or not the co-deposition of aluminum takes place.; Two electroanalytical techniques were developed for the analysis of co-deposited aluminum alloys: the first was based on anodic linear sweep voltammetry at a rotating-ring-disk electrode. The second was derived from the transition metal ion concentration changes observed during bulk deposition experiments. In the first technique, an alloy deposit was stripped from the disk electrode while the ring potential was held at a value where only one of the ions oxidized from the alloy could be reduced. In the second technique, the concentration of transition metal ions was monitored in an undivided cell with an anode made from the depositing metal. The co-deposition of aluminum was signalled by an increase in the transition metal ion concentration. The alloy composition data resulting from both techniques were in excellent agreement with that obtained from the analysis of partial currents by means of sampled-current voltammetry.; Chronoamperometry was used to study the nucleation of antimony and iron on glassy carbon substrates. The electrodeposition of these metals was found to involve three-dimensional nucleation with hemispherical diffusion-controlled growth of the nuclei. Comparison of the experimental dimensionless current-time transients with theoretical transients indicated that the nucleation of iron followed a progressive mechanism whereas the nucleation of antimony followed a progressive mechanism at a finite number of active sites. Analysis of the potential dependence of the nucleation rate according to the Atomistic Theory of Nucleation suggested that active sites on the glassy carbon substrate act as critical nuclei.; The formal potentials of the Co(II)/Co, Fe(II)/Fe, and Sb(III)/Sb couples were found to be: 0.86 {dollar}pm{dollar} 0.02, 0.52 {dollar}pm{dollar} 0.01, and 1.02 {dollar}pm{dollar} 0.03 V, respectively, in the 60.0-40.0 m/o AlCl{dollar}sb3{dollar}-MeEtimCl molten salt at 25{dollar}spcirc{dollar}C. The diffusion coefficients of cobalt(II), iron(II), and antimony(III) were found to be: {dollar}(3.4pm0.1)times10sp{lcub}-7{rcub}{dollar}; {dollar}(2.6times0.3)times10sp{lcub}-6{rcub}{dollar}; and {dollar}(1.1pm0.1)times10sp{lcub}-6{rcub}{dollar} {dollar}rm cmsp2 ssp{lcub}-1{rcub},{dollar} respectively.