Rational design of ionic compounds for electrocatalytic reduction of carbon dioxide

Electrochemical reduction of carbon dioxide is one of the plausible approaches towards renewable energy carriers. When coupled with electricity, which can be provided by sustainable technologies, it becomes a method of high importance with potential value for future energy challenges. However, the electrochemical version of the CO2 reduction reaction (CO2RR) proceeds through highly energetic intermediates, therefore efficient catalytic and co-catalytic systems are needed. Recently, considerable attention was dedicated to application of ionic liquids (ILs) as promising promoters for the CO2RR. While most efforts in this domain have been concentrated on spectroscopic and electrochemical investigation of existing IL-based systems and on the development of more active electrodes, there are only a limited number of studies discussing the structure/activity relationships of ILs in the CO2RR. Our aim was to fill this gap and to find new classes of ILs that are able to promote CO2RR. Another aim of our project was to delineate the basic trends in the structures of the active co-catalysts and provide descriptors for the promoting activity. In this work three new classes of ILs are evaluated for the CO2RR. Within each IL series the structures of the cationic core were varied, the dependencies of the stabilities and activities of the ILs on the structure are discussed. Additionally, a fundamentally new type of ionic systems based on deep eutectic solvents was applied to the CO2RR and found to be a highly active, cheap and non-toxic alternative for the conventional ILs. Based on the obtained results, the charge and its accessibility are suggested to be the main descriptors for the activity of the ionic catalysts in non-aqueous environments.