Thin-film TiO2 electrode surface characterization upon CO2 reduction processes

The effect of electrochemical reduction of CO₂ on the structure and morphology of titanium(IV) oxide thin films was examined after a fixed-potential bulk electrolysis process. Films deposited on ITO (Indium-Tin Oxide) substrates were used as the working electrodes and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm]BF₄]) as solvent and as supporting electrolyte. Grazing incidence X-ray diffraction analysis performed before and after the electrolysis process indicated no microstructural changes of the anatase films. X-ray photoelectron spectroscopy revealed peaks associated with adsorbed carbonate ions at 288 eV and CO₂ species at 293 eV, whereas Ti2p peaks displacements for CO₂-saturated TiO₂/ITO surfaces in BMIm]BF₄] revealed chemical bonding effects. Auger electron spectroscopy revealed a high carbon content on CO₂-exposed films, and suggested a strong chemisorption of CO₂ and CO₃²⁻ species on the TiO₂/ITO surface in BMIm]BF₄] solvent system. A significant decrease in carbon content after bulk electrolysis indicated that the CO₂ electroreduction process is not controlled by either diffusion or by adsorption of CO₂ on the TiO₂/ITO electrode surface.