Pore Size-Dependent Origin of CO₂ Adsorption Thermodynamics within Porous Carbon under Broad-Ranging Operation...

Adsorption capture technology based on porous carbon is considered an important choice for the next generation of CO₂ capture crafts, where broad operation pressure variations in different industrial scenarios require the targeted design of porous structures. However, the complex pore structure of porous carbon makes the relationship between the pore structure and the pressure-driven CO₂ adsorption behavior still unclear. Herein, through experiments using model carbon adsorbents with precisely designed pore size distributions combined with molecular-level calculations of CO₂ adsorption thermodynamics, the pore size-dependent origin of CO₂ adsorption and multiscale condensation behavior was uncovered for the first time across a wide range of pressures (0.04 to 30 bar). Different from the traditional CO₂ monolayer or multilayer adsorption-filling process guided by micropore surface potential just at a single atomic scale, the actual CO₂ storage space and molecule aggregation behavior span both the atomic scale and the long-neglected mesoscopic scale (∼10 nm) under high adsorption pressure conditions. Interestingly, we demonstrate that the neglected large-sized mesopores can provide sufficient space for CO₂ molecule-confined flow and aggregation, thereby forming a new CO₂ molecule cluster phase in the pore center. This enables mesoporous carbon adsorbents to exhibit an anomalous enhancement of the CO₂ adsorption capacity under increased operation pressures. Guided by this novel insight, cost-effective activated carbon adsorbents with tunable pore size distributions are developed in which the mesopore-rich activated carbon demonstrates a state-of-the-art CO₂ adsorption performance with an excellent uptake of 23.2 mmol g^-1 at 20 bar. This work complements the existing CO₂ adsorption mechanism under broad-ranging pressures and offers guidance for the design of advanced carbon adsorbents for high-uptake CO₂ capture under selective pressures.