Investigating the influence of ionic liquids on the visible-light induced photoelectrochemical reduction of CO2

Abstract

Valorization of carbon dioxide is a promising approach that could simultaneously address multiple global issues. Reduced emission to the atmosphere signifies minimized impact on global warming, while the abundant, non-toxic, and renewable nature of CO2 is aligned with the vision for sustainable processes. Nevertheless, the viability of this option requires an efficient catalytic system since the reduction of this greenhouse gas to value-added chemicals is hindered by a high thermodynamic and kinetic barrier. Research on visible light photocatalyzed carbon dioxide reduction revealed that photocatalytic systems consisting of a ruthenium-based photosensitizer and a rhenium-based photocatalyst exhibit high selectivity for carbon monoxide formation. Additionally, electrochemical reduction provides the possibility to control the process by varying the applied potential in a compact set-up. Photoelectrochemical reduction of carbon dioxide combines photo- and electrocatalysis towards mutually beneficial interactions. The applied potential can improve the separation of charges, while light irradiation reduces the required overpotential of the electrocatalytic process. Hence, the photocathodes act as both, catalyst and light harvester. Furthermore, past research demonstrated the advantages of ionic liquids as cooperative media, due to their ability to solubilize large concentrations of carbon dioxide and, in specific instances, minimize the required applied potential for the reduction. Consequently, we aim to combine the advantages of these methods into a photoelectrochemical set-up and investigate the influence of ionic liquids on the reduction efficiency of carbon dioxide to carbon monoxide. Preliminary UV-Vis spectroscopy data, as shown in figure 1, have already confirmed that the synthesized materials combining rhenium, ruthenium and an ionic liquid in a polymer framework show high correlation with reported absorbance values for the corresponding monomers (i.e., [Ru(bpy)3][PF6], Re(bpy)(CO)3Cl, and EMIM Br), enabling photocatalytic reduction in the visible-light region above 445 nm. By fabricating a conductive polymer film of these components on a cathode, the reduction can be further enhanced through the applied potential in a photoelectrochemical set-up to determine the optimal reaction conditions.