Exploring Phosphonium-Based Anion Exchange Polymers for Moisture Swing Direct Air Capture of Carbon Dioxide.

This study explores the performance and stability of ammonium and phosphonium-based polymeric ionic liquids (PILs) with methyl and butyl substituents in moisture-swing direct air capture of CO. The polymers are synthesized with chloride counterions, followed by ion exchange to the bicarbonate ion, and tests for CO capture capacity and stability under cyclic wet-dry conditions. The phosphonium polymer with methyl substituents [PVBT-MeP] demonstrates the highest CO capture capacity at ≈510 µmol g⁻¹, attributed to minimal steric hindrance and stronger ion pairing with bicarbonate.