Development of high capacity moisture-swing DAC sorbent for direct air capture of CO2

Direct air capture (DAC) of CO2 complements traditional carbon capture technologies to achieve zero-or negative-carbon emissions. One of the most promising DAC technologies is moisture-swing adsorption due to its low regeneration costs and easiness of operation, particularly when using amine-based anion-exchange resins (AER) as sorbents, but the limited CO2 sorption capacity and desorption efficiency of current AERs are still critical challenges hindering the large-scale implementation of DAC. For the first time, this work developed a novel diamine-based double quaternary ammonium anion-exchange resins (Diamine-DQ-AER) by modifying commercial resins with tertiary diamines. The significantly improved quaternary ammonium content in Diamine-DQ-AER (68-81 %) compared to diamine-based single quaternary ammonium anion-exchange resins (Diamine-SQ-AER) resulted in an unprecedented moisture-swing DAC capacity of 3.41 mmol/g under DAC conditions, nearly doubled that of Diamine-SQ-AER. Diamine-DQ-AER also showed a stable capacity in the 6-cycle test, outperforming most moisture-swing DAC sorbents reported in the literature. Moreover, a complete desorption kinetic curve was obtained using an optimized testing protocol. It found that the CO2 adsorption/desorption process involves two stages, and the material exhibited fast desorption kinetics in the 1st stage.