Expanding the Library of Ions for Moisture-Swing Carbon Capture

Abstract

Developing materials that can more efficiently and cheaply capture carbon dioxide from ambient atmospheric conditions is essential for improving negative emission technologies. This study builds on the promising moisture-swing modality for direct air capture of carbon dioxide by investigating the use of several new anions�orthosilicate, borate, pyrophosphate, tripolyphosphate, and dibasic phosphate�that when introduced into ionexchange resins allow for the cyclable capture of CO 2 under dry conditions and its release under wet conditions. These ions, as well as many others that failed to show moisture-swing performance, are tested and directly compared thermodynamically and kinetically to understand their differences. This includes the use of analytical approaches new to the carbon capture field, such as the correlation of adsorption isotherms to moisture-swing performance, the use of phase lag kinetics, the examination of the humidity-carbon capture hysteresis of the sorbents, and the precise quantification of ion loading using inductively coupled plasma−optical emission spectroscopy. Phosphate dibasic was found to have the largest mass-normalized CO 2 moisture-swing capacity, whereas phosphate tribasic had the best performance when factoring in kinetics, and pyrophosphate had the highest swing capacity when normalizing on a per-ion or per-unit-charge basis. This work not only sheds light on ways to improve DAC but also provides insights pertinent to the advancement of gas separation, negative emission technologies, and sorbent materials.

Polymer Sorbent Design for the Direct Air Capture of CO2

“…This work presents an alternative strategy for enhancing the CO 2 capture performance of moisture-swing absorbents. Similar hydrolysis behavior was also found in other anion types, such as S 2 – , SO 3 2– , and SO 4 2– , suggesting their potential for exploration in moisture swing DAC application . It was also found that the sorption kinetics of polymers are governed by physical properties such as particle size and microporous structures .…”

Confinement Effects on Moisture-Swing Direct Air Capture

“…to maintain charge neutrality. ,, Recent studies have shown that increasing the NR 4 + group density can result in a shorter half-time for CO 2 capture. , In addition, phosphate counterions demonstrate a greater capacity for CO 2 when compared with carbonate counterions . Reversible hydrolysis and neutralization reactions at the cation–anion active site within an ion-exchange resin are necessary for moisture-swing CO 2 capture. − Understanding how resin structure and anion type promote reversible hydolysis and neutralization within confined regions of sorbents remains an open question.…”

“…Here, we specifically aim to understand how the basicity of the counterion (e.g., anion) impacts moisture-swing direct air capture mechanisms. − Ion-exchange resins loaded with carbonate, phosphate, acetate, sulfide, and borate were synthesized and evaluated for the capture of CO 2 and moisture-swing CO 2 capture. This work reports two important discoveries that will help design better materials for moisture-swing CO 2 capture.…”