Effect of Support Surface Properties on CO₂Capture from Air by Carbon-Supported Potassium Carbonate

Direct CO2 capture from air is of prime importance to mitigate the negative effects of global warming. Potassium carbonate (K2CO3) is a promising sorbent for the capture of CO2 from air. K2CO3 chemisorbs CO2 from air in the presence of water (the so-called carbonation reaction), even in very low concentrations (410 ppm). To make efficient use of K2CO3, it is dispersed on a support. Carbon-based supports are promising because of their high hydrothermal stability. Carbons have different structural and chemical properties; however, these can be tuned during preparation. Little is known about the relation between carbon properties and their performance, after K2CO3 deposition. We investigated the role of support surface composition on the performance of carbon-supported K2CO3. By using carbons with different numbers of surface oxygen groups, that is, different polarities, we show that K2CO3 supported on an apolar carbon results in a higher capacity CO2 capture. We propose that a polar support attracts polar H2O molecules on the K2CO3 sorbent, resulting in a low carbonation. In contrast, an apolar support lowers the local H2O concentration on the sorbent and favorably attracts apolar CO2 molecules, hence promoting carbonation.