DMSO Assists in Achieving Efficient CO₂ Electroreduction

Dimethyl sulfoxide (DMSO) is a sulfur-containing organic compound with the molecular formula C₂H₆OS. It is a colorless and odorless transparent liquid at room temperature. It has high polarity, high boiling point and good thermal stability. DMSO is commonly used as a solvent for acetylene, aromatic hydrocarbons, sulfur dioxide and other gases, as well as acrylic fiber spinning solvent. It is an extremely important aprotic polar solvent that is soluble in both water and organic solvents. It has strong permeability to the skin and helps drugs penetrate into the human body. It can also be used as a pesticide additive. It is also a very important chemical reagent.

Aqueous CO₂ electroreduction (CO₂RR) is an important means of CO₂ resource utilization, but it is limited by the competitive hydrogen evolution reaction (HER). Recently, researchers have proposed a new strategy to partially replace water molecules in the alkali metal cation solvation layer with aprotic small organic molecules to reduce the proton source content in the electrical double-layer structure, thereby inhibiting HER and improving the selectivity of CO₂RR.

The researchers designed a molecular-level control strategy for the solvation layer, using small aprotic organic molecules with high Gutmann donor numbers to replace the water molecules in the alkali metal cation solvation layer to reduce the content of interface water molecules and the relative content of proton sources, effectively inhibiting the progress of competitive HER in the CO₂RR process. Organic molecules can interact with adsorbed water molecules, promote the dissociation process of water molecules and participate in the protonation process of CO₂, improving the activity of CO₂RR. At the same time, this molecular-level control strategy has good universality and has been successfully applied to Ag, Zn and Sn electrodes in K-ion electrolyte systems containing DMSO and DMF.

By conducting electrochemical tests on electrolytes containing different concentrations of DMSO, it was found that the FE_H2 of the Ag foil electrode gradually decreased as the DMSO content increased; and when the DMSO content reached 7M and 8M, the hydrogen evolution selectivity increased. Correspondingly, the activity of CO₂RR showed a trend of increasing first and then decreasing. Taking 5M DMSO as the optimal model, the FE_CO at different potentials is higher than that of the electrolyte without DMSO, with the highest value reaching 99.2%, and good CO selectivity can be achieved in a wide voltage range. On the contrary, the CO₂RR activity of the electrolyte added with CH₃CN is close to that of the original electrolyte.

Reference

1. Molecular Engineering of Cation Solvation Structure for Highly Selective Carbon Dioxide Electroreduction
   Angew. Chem. Int. Ed., 2023