Organic electrolyte cations promote non-aqueous CO2 reduction by mediating interfacial electric fields

Abstract

The electrochemical reduction of CO2 is sensitive to the microenvironment surrounding catalytic active sites. Although the impact of changing electrolyte composition on rates has been studied intensively in aqueous electrolytes, less is known about the influence of the electrochemical environment in non-aqueous solvents. Here we demonstrate that organic alkylammonium cations influence catalytic performance in non-aqueous media and describe a physical model that rationalizes these observations. Using results from kinetic, spectroscopic and computational techniques, we argue that the strength of the electric field at the catalyst surface is sensitive to the molecular identity of the organic cation in the electrolyte. This is true irrespective of solvent, electrolyte ionic strength or electrolyte anion. Our results suggest that changes in the interfacial electric field strength can be attributed to differences in the cation–electrode distance. Changes in the electric field strength affect CO formation rates as they modify the energetics of the kinetically relevant CO2 activation step. Electrolyte cations have been shown to have a strong impact on reactivity in electrocatalytic CO2 reduction. However, most studies have been performed in an aqueous environment. Here the effect of various alkylammonium cations on CO2 reduction in aprotic solvents is investigated, with the interfacial electric field induced by the cations shown to be a dominant factor.