Choline Chloride-Carboxylic Acid Based Deep Eutectic Solvents as Advantageous Electrolytes for Direct Electrochemical Conversion of Tin Oxide to Tin

Abstract

Tin oxide (SnO2) pastes prepared by mixing SnO2 powder and various choline chloride (ChCl)-based deep eutectic solvents (DESs) were coated onto screen-printed carbon electrode (SPCE) and directly converted to tin (Sn) metal via potentiostatic electrolysis in the corresponding DESs. It is found that a successful conversion could be achieved in the carboxylic acid-containing DESs rather than in the acid-free DESs, which indicates that the organic acid is the key for the direct electrochemical conversion from a metal oxide to metal. This process may be expanded to the extraction of metals from used metal oxides that are insoluble in water as well as the recent DESs without inconvenient and/or harsh processes.