Electrochemistry of aluminium in room temperature A1C13-TMPAC molten salts.

Abstract

Aluminium can be electrodeposited on tungsten, aluminium, platinum, nickel and glassy carbon from 2: 1 A1C13-TMPAC (trimethylphenylammonium chloride) molten salts at room temperature. The A1C13-TMPAC melts diluted with 1,2-dichlorobenzene of had a beneficial effect on increasing aluminium deposition and stripping currents by decreasing viscosity and increasing the conductivity of the melt. The reductions of A12C17 ions were quasi-reversible and diffusion controlled, The irreversibility of the reductions was due to the relatively low conductivity and high viscosity of the melts. The aluminium deposition was associated with the reduction of the resulting product A1C14 ions following the locally changing acidity of the melts, and a corrosion reaction between fresh aluminium deposits and the melt. The mechanism for aluminium electrodeposition from 2: 1 A1C13-TMPAC was realised likely similar to that for the acidic A1C13- BPC melts. The bulk depositions of aluminium on all electrode except platinum involved three-dimensional instantaneous nucleation process followed by hemispherical diffusion-controlled growth of the developing nuclei. On platinum the nucleation process was characteristic of instantaneous at short time and then tended to progressive. The phenomena of aluminium UPD were found on all electrodes but not on aluminium itself, highly dependent upon substrates, and involved alloying effects on metal substrates. The UPD layers on the surface of the electrodes corresponded to about 2 -- 10 aluminium monolayer equivalents. The UPD was surface constrained on tungsten, whereas were diffusion controlled on nickel and platinum. The processes on tungsten and platinum were under the limitation of kinetics. On nickel and platinum, the electrodes and the nickel and platinum components in fresh deposits were likely to react with A12C17 and Cl' ions in the melt to form corresponding metal complexes. 11 The passivation phenomena were observed to occur on all electrodes. These could resulted from a black layer formed by AIC13 precipitates. Particularly, on aluminium the stripping of aluminium was involved in an active dissolution-passivation process.