SO₂-Induced Selectivity Change in CO₂ Electroreduction

Electrochemical conversion of carbon dioxide (CO₂) to value-added chemicals has attracted much attention in recent years as a potential alternative to fossil resources. Although significant works have studied the influence of impurities in the electrolyte (e.g., metal ions), few studies have been performed to understand the influence of gaseous impurities in CO₂ electroreduction. Herein, we study the effects of sulfur dioxide (SO₂) on Ag-, Sn-, and Cu-catalyzed CO₂ electrolysis in a flow-cell electrolyzer in near-neutral electrolyte, representing a broad range of CO₂ reduction catalysts. We show that the presence of SO₂ impurity reduces the efficiency of converting CO₂ due to the preferential reduction of SO₂. In the cases of Ag and Sn, the effect of SO₂ impurity was reversible and the catalytic activities of both catalysts were recovered. On the contrary, a shift in selectivity toward formate accompanied by a suppression of multicarbon (C₂₊) products was observed on Cu catalyst, demonstrating that Cu is highly sensitive to SO₂ impurity. Our results suggest that CO₂ obtained from direct air capture technologies or biorefineries could be more suitable for Cu-catalyzed CO₂ electrolysis as these CO₂ sources would be relatively cleaner (SO₂-free) than fossil-derived sources such as power plants and can be directly coupled with distributed renewable energy sources such as wind and solar.