Dual-Cation Activation of N-Enriched Porous Carbons Improves Control of CO₂ and N₂ Adsorption Thermodynamics for Selective CO₂ Capture

Porous carbons have potential to facilitate energy-efficient separation of CO₂ from post-combustion flue gas. However, the complicated interplay between chemical and textural properties has prevented a comprehensive understanding of selective CO₂ adsorption. This study demonstrates how dual cation activation of carbons serves as a synthetic platform to help modulate porosity independent of nitrogen content. For samples derived from nitrogen-poor precursors, surface areas deviated significantly (2200–4500 m² g⁻¹) at a constant total nitrogen content (2.3 ± 0.3 at %). Surface area changed less for samples derived from nitrogen-rich precursors (400–675 m² g⁻¹ at 23.1 ± 0.1 at % N). Rigorous structure-function and thermodynamic analysis of these carbons not only helped to uncover the nature of the different adsorption sites, but also established a fundamental linear free energy exchange relationship. This coupled with material property correlations informed the properties that facilitated selective capture of CO₂. Critically, for these physisorptive carbons, selectivity is almost entirely a function of relative porosity and chemical adsorbent-adsorbate interactions play a negligible role.