Electrodeposition of Gallium and Indium from Non-aqueous Electrolytes

Abstract

In this work, we studied the electrodeposition of gallium and indium from 1,2-dimethoxyethane (DME)-based and dimethyl sulfoxide (DMSO)-based electrolytes, respectively.1,2 Cyclic voltammetry in combination with rotating (ring) disk electrode and electrochemical quartz-crystal microbalance were used to identify the redox chemistry and electrodeposition behavior of both metals. Scanning electron microscopy (SEM) was used to investigate the structural morphology of the deposited materials.Gallium electrodeposition was studied from a bath composed of gallium(III) chloride, an inert background salt and DME. The electroreduction process occurred in two steps: (1) from gallium(III) to gallium(I), and (2) from gallium(I) to gallium(0). Metallic gallium was deposited as spheres with diameters of several hundreds of nanometers that were stacked on top of each other. X-ray photoelectron spectroscopy revealed that each gallium sphere was covered by a thin gallium oxide shell. These shells prevent individual gallium spheres from agglomerating to larger entities. Electrochemical experiments indicated that these oxide layers were electrically conductive. It was demonstrated that electrodeposition proceeded via a droplet-on-droplet electrodeposition mechanism. A growth mechanism for an individual growing gallium sphere was also postulated.Indium electrodeposition was studied from a bath composed of indium(III) methanesulfonate, a background salt and DMSO. indium(III) methanesulfonate was synthesized from methanesulfonic acid and indium(III) oxide. The latter is an intermediate formed during the purification of indium from primary and secondary resources. Conversion of indium(III) oxide into metallic indium could therefore lower the energetic cost of its production. Analogously to gallium, Indium(III) is reduced to indium(I), and then to indium(0). It was demonstrated that indium(I) disproportionates to indium(III) and indium(0), leading to the formation of micron-sized metallic indium particles in the electrolyte. At 26 °C, indium deposited as smooth, flat films whereas at 160 °C, it deposited as liquid indium droplets. Electrodeposition of indium above its melting point enables the process to be performed in a continuous manner; indium droplets accumulate and grow, and will ultimately glide off the electrode, and drop to the bottom of the cell, forming a liquid pool from which the metal can be tapped off.In the attached figure, SEM images of (1) gallium deposited at 26 °C and (2) indium, deposited at 26 °C and 160 °C are shown. Figure 1