Tuning the Polarity of Dinitrile-Based Electrolyte Solutions for CO2 Electroreduction on Copper Catalysts

The development of carbon dioxide electrochemical reduction (CO2ER) has mainly focused on aqueous electrolytes. However, the low solubility of apolar CO2 in polar water negatively impacts the electrochemical process, especially mass transport. Organic-based electrolytes, such as methanol, acetonitrile, and dimethylformamide, have been explored as an alternative due to increased CO2 solubility. Yet, insights into other organic electrolytes are scarce. Dinitrile solvents have decreased polarity in comparison to the mononitrile solvent acetonitrile and thus can potentially further increase CO2 solubility and advance the reaction’s performance. Herein, the novelty of dinitrile-based electrolytes for the application of CO2ER is explored. Acetonitrile, adiponitrile, and sebaconitrile were used to study the effects of a secondary nitrile group addition and the length of the aliphatic, nonpolar chain on salt solubility, electrolyte conductivity, and CO2 solubility. Electrochemical effects were evaluated through cyclic voltammetry (CV) and chronoamperometry (CA) measurements with copper (Cu) and copper oxide (CuO) commercial nanoparticle catalysts. DFT calculations were employed to further explore the CO2 interactions with the selected solvents. Finally, it was found that tuning the polarity of the nitrile solvent results in a profound effect on the physiochemical properties of the electrolyte solutions, markedly CO2 solubility and the CO2ER.