Electrochemical CO2 reduction to formate on indium catalysts prepared by electrodeposition in deep eutectic solvents

[Display omitted] •Indium was deposited from deep eutectic solvents on copper and carbonaceous substrates.•Indium coatings were used as catalysts for the electrochemical CO2 reduction.•The indium coatings were stable after two-hour CO2 electrolysis.•The main product of the electrochemical CO2 reduction was formate.•The use of gas diffusion electrodes improved the formation rate of formate. The electrochemical conversion of CO2 to high-value molecules is an elegant alternative for combining CO2 utilization with renewable energy conversion and storage. Herein we report the preparation and characterization of indium catalysts for the electrochemical CO2 reduction to formate. Indium coatings were prepared by electrodeposition from a deep eutectic solvent (DES) comprising 1:2 M choline chloride and ethylene glycol (12CE). The electrochemical behavior of indium chloride in this DES was investigated by cyclic voltammetry (CV) on copper, glassy carbon (GC) and platinum electrodes. The effect of InCl3 concentration, electrolyte temperature and deposition method on the phase and morphology of the coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Indium deposits on copper and carbon were deployed as catalysts for the CO2 electrolysis in aqueous media. Chemical analysis by HPLC, GC, and NMR revealed an optimum efficiency toward formate at −1.9 V vs. Ag/AgCl. Indium coatings prepared by potentiostatic deposition showed faradaic efficiencies (FE) up to 72.5%. Gas diffusion electrodes (GDE) coated with indium led to formate concentrations up to 76 mM and formation rates of 0.183 mmol cm−2 h−1, which was considerably superior to indium coatings on planar electrodes.