Water-soluble pyridinium redox mediators for pH-swing CO ₂ capture

Electrochemical pH-swing processes offer a promising route for energy-efficient CO₂ capture but require robust redox mediators. This paper reports three water-soluble 4-substituted pyridinium redox mediators (BzM, BzSP, AcSP) for electrochemical pH-swing carbon capture and systematically evaluates their performance through H-cell and flow cell configurations. Highly water-soluble mediators bearing a propylsulfonate group can be readily synthesized in one step on a 20 g scale. We find that the inclusion of a benzoyl group at the 4-position is critical for attaining high current densities. The zwitterionic BzSP exhibits around 90% CO₂ capture efficiency and optimal CO₂ capture capacity (102 kJ mol_CO₂ ^-1) in a flow cell. These findings establish molecular design principles for pyridinium-based mediators in energy-efficient carbon management.