Imidazolium and picolinium-based electrolytes for electrochemical reduction of CO2 at high pressure

Abstract

Ionic liquids (ILs) have been considered among one of the most promising materials under investigation for integration of CO₂ capture and electrochemical reduction (ECR). In the design of an IL-based electrolyte that can be employed industrially, the understanding of the influence of IL structure on ECR was considered essential. In this context, electrolytes with trifluoromethanosulfonate (OTf) anion were investigated as aqueous electrolytes for electrochemical reduction of CO₂ at high pressure and near room temperature with zinc electrodes. The effect of replacing the 1-ethyl-3-methyl-imidazolium cation [EMIM] by 1-ethyl-3-picolinium [C₂(3)pic] and by 1-ethyl-4-picolinium [C₂(4)pic] cations was studied. The use of picolinium-based electrolytes in ECR is for the first time reported. A high-pressure single compartment test bed was used for electrolyte screening. Carbon monoxide productivities and selectivities were determined for the several electrolytes with different water contents. The electrolytes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Electrolyte conductivities and diffusion coefficients were estimated. The effect of the cations is complex as it affects conductivity, double layer structure, reaction reversibility and even the ionic liquid physical state. Notwithstanding, it is possible to tune these properties to achieve similar CO productions with reduced IL amounts, considering the nature of the cation and the water content, leading to the design of more cost effective electrolytes for efficient ECR process.