Eco-Friendly Electroreduction of Indium Tin Oxide Using SOM Anode in Molten Salts

Abstract

Indium Tin Oxide(ITO) has been widely used at transparent electrode of Light Emitting Diode(LED) or the material of Liquid Crystal Display(LCD). However, waste ITO is generated after process and wet recycling technology has been used. In the case of wet recycling technology, a large amount of acid required and process time is so long. Then, if waste ITO could be recycled by dry process, electroreduction process, it is expected to solve the economic and environmental problems. However, when graphite is used as anode, it generates greenhouse gases such as CO or CO2 gas and causes formation of dirty C dusts. In this study, electroreduction of Indium Tin Oxide using Solid Oxide Membrane anode was investigated in a molten salt of CaF2-NaF-CaO at 1150 °C under the inert atmosphere to replacing previous anode materials. The SOM process is a direct electrolytic reduction process using a solid-oxide oxygen ion conducting membrane, namely, yttria-stabilized zirconia (YSZ), with high-temperature molten salts as a reaction medium. To verify the possibility of replacing, waste ITO was used because of the large use in industry. Electrochemical behavior was investigated by CV(Cyclic Voltammetry) in molten salts using waste ITO and inert working electrodes. As a result, InSn metal was reduced by SOM process. After electroreduction process, the optimum ITO particle size is considered to be the range of 600 μm to 1000 μm due to considering the maximum reduction efficiency dependent on the sedimentation rate, specific melt droplet growth, and reduced InSn film formation. The reduced InSn alloy was analyzed by XRD and EDS and they were confirmed as InSn alloy, which is almost the same as the initial ITO composition.