Polymeric ionic liquids (PILs) are promising CO₂ sorbents, as their behaviors are tunable by assembling ion pairs. This work aims to design CO₂ sorbents with unique moisture-swing adsorption performance by assembling different anions on quaternary-ammonium-based PILs. Two aspects of the sorbent design were studied: the suitability of the CO₂ affinity for different applications (e.g., direct air capture or flue gas capture) and capability for moisture-swing adsorption. Carbonate, fluoride, and acetate were chosen as counteranions, as they are representative anions with different basicity, valence, and water affinity. CO₂ affinity was found to positively correlate with the pKa value of the counteranion, except for fluoride, which has an intrinsic character of attracting protons. The moisture swing capacity is determined by the difference between the hydration energies of the reactant and product after CO₂ adsorption and followed the order carbonate > fluoride > acetate. Further investigations revealed that the repulsion between the two quaternary ammonium cations could promote the dissociation of hydrated water, which results in the lowest activation energy for CO₂ adsorption for the PIL with carbonate. Therefore, the PIL with carbonate is potentially a desirable candidate for air capture and moisture-swing regeneration, while the PIL with acetate is suitable for CO₂ capture under high partial pressure and regeneration through conventional approaches. This study provides a quantitative microscopic insight into the role of the anion in CO₂ adsorption and paves the way toward the optimal PIL structure for CO₂ capture under specific circumstances.

中文翻译：

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通过聚合物离子液体的阴离子筛选设计水变CO ₂吸附剂

聚合离子液体（PIL）是有前途的CO ₂吸附剂，因为它们的行为可通过组装离子对来调节。这项工作旨在通过在季铵基PIL上组装不同的阴离子来设计具有独特的水分波动吸附性能的CO ₂吸附剂。研究了吸附剂设计的两个方面：CO ₂亲和力在不同应用中的适用性（例如，直接空气捕获或烟道气捕获）和湿气波动吸附能力。选择碳酸盐，氟化物和乙酸盐作为抗衡阴离子，因为它们是具有不同碱性，化合价和水亲和力的代表性阴离子。发现CO ₂亲和力与p K正相关抗衡阴离子的值（氟化物除外）具有吸引质子的固有特征。水分摆动能力由CO ₂吸附后反应物和产物的水合能之差确定，并依次为碳酸盐>氟化物>乙酸盐。进一步的研究表明，两个季铵阳离子之间的排斥作用可促进水合水的离解，从而使碳酸根对PIL的CO ₂吸附活化能最低。因此，含碳酸盐的PIL可能是空气捕获和潮气再生的理想候选物，而含乙酸盐的PIL适用于CO ₂在高分压下捕集并通过常规方法再生。这项研究为阴离子在CO ₂吸附中的作用提供了定量的微观见解，并为在特定情况下捕获CO ₂的最佳PIL结构铺平了道路。