The effects of SO2 impurities on CO2 electroreduction on bare silver and SiO2 coated silver in different cell geometries†

Abstract

Electrochemical CO₂ reduction presents an opportunity to transform waste flue gas with water and renewable electricity into chemicals or fuels. However, the energy-intensive nature of purification of flue gas underscores the appeal of directly utilizing the flue gas streams containing impurities. In this study, we investigate the impact of SO₂ impurities on CO₂ electroreduction in two electrochemical cell geometries: an H-cell and a membrane electrode assembly (MEA) cell. We observe distinctly different behavior of the Ag on carbon black (Ag/CB) catalyst under SO₂ impurities in the H-cell compared to the MEA cell, where SO₂ impurities exhibit a more pronounced effect on Ag/CB catalysts in the H-cell than in the MEA cell. This difference is attributed to the higher solubility of SO₂ in the electrolyte compared to CO₂, resulting in an accumulation effect and causing differences in the SO₂ concentration near the electrode between the H-cell and the MEA system. By depositing a very thin SiO₂ coating on the outermost surface of the Ag/CB catalyst using atomic layer deposition (ALD), the impact of SO₂ on the catalyst's selectivity is diminished. This is attributed to the permeability difference between CO₂ and SO₂ through the SiO₂ coatings and results in a local SO₂ concentration difference between samples with and without SiO₂ coatings.