The Aluminum Electrode in AlCl[sub 3]-Alkali-Halide Melts

Abstract

REDUCTION OF C1 ON C 1161Studies of the mechanism of chlorine evolution on graphite (9) in molten lithium chloride suggests, as the rate determining step, the combination of chlorine atoms on a surface with appreciable coverage. In fact, when scanning the rotating carbon electrode from the region of chlorine evolution to more cathodic potentials, one indeed observes, up to overvoltages of 250 mV, a lower Tafel slope which changes to 2RT/F at higher overvoltages probably indicating the change from an intermediate to low coverage. On the anodic going sweep, this low coverage is maintained until reaching anodic potentials. Thus, we can conclude that the chlorine reduction on vitreous carbon in AlCls-KC1-NaC1 melts occurs according to path 1 with step la being most probably rate determining at higher polarizations with a low chlorine coverage on the electrode.

Anodic Dissolution of Aluminum in the Aluminum Chloride-1-Ethyl-3-methylimidazolium Chloride Ionic Liquid

“…These sharp decreases in current were attributed to a passivation-like process occurring on the Al electrode surface. 10 The onset of this passivation process is potential-dependent at a given temperature, with passivation occurring sooner when the overpotential is larger. Thus, the oxidation of Al appears to involve two distinct mechanisms depending on the overpotential/anodic dissolution rate.…”

“…Because of contributions to the net current density from the back reaction, i.e., Eq. 1, it was necessary to construct graphs of log j k versus η, i.e., classical Tafel plots, to determine the exchange current density, j 0 , by extrapolation of the linear portions of these graphs to η = 0 log j k = log j 0 + α a Fη/2.303RT [10] Examples of these graphs with the extrapolated anodic Tafel lines are shown in Figs. 8 and 9.…”

“…8 Others have reported the formation of a passive layer of AlCl 3 (s), which results in a limiting current governed by the diffusion of reacting ions to the electrode surface. 10 In a recent article, 14 we reported the anodic dissolution of Al in the Lewis neutral LiAlBr 4 -NaAlCl 4 -KAlCl 4 (30-50-20 m/o) haloaluminate molten salt as a function of temperature. This investigation was carried out by using rotating disk electrode voltammetry at a miniature Al electrode.…”

“…2,[8][9][10][11][12] But only few such investigations have been undertaken in the related room-temperature ionic liquids, e.g., AlCl 3 -EtMeImCl 13 and AlCl 3 -BuMeImCl, 7 with the former study conducted in the basic (Cl − -rich) ionic liquid. However, the kinetics and mechanistic aspects of the anodization reaction remain unclear.…”

Indirect Methods of Determination of K:Al Mole Ratio in Molten Chloroaluminates

“…Speciation of aluminum in chloroaluminate melts was characterized employing a variety of structural and electrochemical methods of analysis (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). It was found that AlCl 4 -, Al 2 Cl 7 -, Al 3 Cl 10 , Cl -and Me + ionic species can exist in these media and their content depends on the melt composition.…”