Understanding the Role of Organic Cations on the Electrochemical Reduction of CO2 in Aprotic Electrolytes

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Electrochemical reduction of CO2 (CO2R) offers an appealing way to store intermittent energy produced by renewable electricity sources and sustainably produce chemicals that are currently derived from petroleum. It is well known that CO2R performance is affected by not only the structure and composition of (electro)catalysts but also by the microenvironment surrounding catalytic active sites. The impact of supporting electrolytes on the kinetics of CO2R in aqueous electrolytes has been the subject of many studies. However far less work has been done to understand the influence of the electrochemical environment in non-aqueous solvents for CO2 reduction, despite their favorable physiochemical properties. Here, we describe a physical model that rationalizes the observed influence of choice of organic cation on catalytic performance in non-aqueous electrolytes. Using results from a combination of kinetic, spectroscopic, and computational techniques, we argue that the interfacial electric field present at the catalyst surface is sensitive to the molecular identity of the quaternary organic cation in the electrolyte. In contrast to aqueous electrochemical systems, our results attribute the changes in the reaction energetics for CO generation to differences in the metal-cation distance rather than the change of interfacial cation concentration for solvated alkali metal cations. These findings provide critical insights into the role of electric fields in influencing surface reactivity for critical electrochemical processes. They also provide new tools for the design of selective and efficient electrocatalysts needed for decarbonization of the fuels and chemicals industries beyond the active sites.