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This study investigates the H2O and CO2 sorption behavior of two chemically distinct polystyrene-divinylbenzene-based ion exchange sorbents: a primary amine and a permanently charged strong base quaternary ammonium (QA+) group with (bi)carbonate counter anions. We compare their distinct interactions with H2O and CO2 through simultaneous thermal gravimetric, calorimetric, gas analysis, and molecular modeling approaches to evaluate their performance for dilute CO2 separations like direct air capture. Thermal and hybrid (heat + low-temperature hydration) desorption experiments demonstrate that the QA+-based sorbent binds both water and CO2 more strongly than the amine counterparts but undergoes degradation at moderate temperatures, limiting its compatibility with thermal swing regeneration. However, a low-temperature moisture-driven regeneration pathway is uniquely effective for the QA+-based sorbent. To inform the energetics of a moisture-based CO2 separation (i.e., a moisture swing), we compare calorimetric water sorption enthalpies to Clausius–Clapeyron-derived total isosteric enthalpies. To our knowledge, this includes the first direct calorimetric measurement of water sorption enthalpy in a QA+-based sorbent. Both methods reveal monolayer-multilayer sorption behavior for both sorbents, with the QA+-based material having slightly higher water sorption enthalpies at the initially occupied strongest sorption sites. Molecular modeling supports this observation, showing higher water sorption energies and denser charge distributions in the QA+-based sorbent at λH2O = 1 mmol/mmolsite. Mixed gas experiments in the QA+-based sorbent show that not only does water influence CO2 binding, but CO2 influences water uptake through counterion-dependent hydration states, and that moisture swing responsiveness in this material causes hydration-induced CO2 release and drying-induced CO2 uptake, an important feature for low-energy CO2 separation under ambient conditions. Overall, the two classes of sorbents offer distinct pathways for the CO2 separation. 

Abstract Graphene-based electrodes have been extensively investigated for supercapacitor applications. However, their ion diffusion efficiency is often hindered by the graphene restacking phenomenon. Even though holey graphene is fabricated to address this issue by providing ion transport channels, those channels could still be blocked by densely stacked graphene nanosheets. To tackle this challenge, this research aims at improving the ion diffusion efficiency of microwave-synthesized holey graphene films by tuning the water interlayer spacer towards the improved supercapacitor performance. By controlling the vacuum filtration during graphene-based electrode fabrication, we obtain dry films with dense packing and wet films with sparse packing. The SEM images reveal that 20 times larger interlayer distance is constructed in the wet film compared to that in the dry counterpart. The holey graphene wet film delivers a specific capacitance of 239 F/g, ~82% enhancement over the dry film (131 F/g). By an integrated experimental and computational study, we quantitatively show that the interlayer spacing in combination with the nanoholes in the basal plane dominates the ion diffusion rate in holey graphene-based electrodes. Our study concludes that novel hierarchical structures should be further considered even in holey graphene thin films to fully exploit the superior advantages of graphene-based supercapacitors.