(343f) Moisture Driven Pump to Concentrate CO2 from Air

Strong base anion exchange membranes (sb-AEM) can bind CO₂ isothermally and reversibly from air (40 Pa) and release at pressures up to 4 kPa using a change in water activity . This work presents the results of an unsteady finite-difference numerical diffusion-migration-reaction model that predicts the flux of carbon through these materials with an applied moisture gradient. CO2 reacts with hydroxide counter ions in the AEM materials forming bicarbonate species. The application of moisture shifts the equilibrium of the HCO3/CO3 distribution - the moisture-swing - creating a net current of dissolved inorganic carbon against the CO2 partial pressure gradient. The flux of CO2 is enhanced by the ionic species transport and is limited by the extent of the moisture swing response and magnitude of partially hydrated ion diffusivities. The model uses experimentally determined water transport and isotherm properties of commercial hydroxide exchanged quaternary amine AEM. In the limit of fast reaction, CO2 flux is expected to approach 20 x 10^-6 mol m^-2 s^-1 under room temperature conditions. A pumping flux may be sustained up to counter pressures of 4 kPa if a sufficient moisture gradient is sustained. This presentation will report on the optimal application of a water gradient and discuss relevant material properties to best exploit the moisture driven response. This work reveals a new approach for carbon dioxide concentration that has potential to be coupled with other regeneration mechanisms for energy efficient direct air capture.