Analysis of uphill diffusion of CO2 driven by the chemical potential difference of H2O

While membrane-based CO 2 capture is a promising technology for separating CO 2 from low-concentration environments such as air, it is generally more energy-intensive than alternative separation methods like adsorption. The uphill diffusion of CO 2, driven by the dissipation of the chemical potential difference of water, can potentially reduce the energy demand of membrane-based CO 2 capture from dilute sources. In this analysis, we explore the coupling between CO 2 flux and H 2 O's chemical potential gradient, hypothesizing that dissipation of H 2 O chemical potential gradients and CO 2 -selective sorption enable CO 2 transport against its concentration gradient and even its chemical potential gradient. Through Onsager analysis and second-law thermodynamic evaluations, we demonstrate the feasibility of this mechanism under steady-state conditions from multiple perspectives, considering various thermodynamic and transport aspects. We also highlight how the level of CO 2 enrichment from the diluted feed to the more concentrated permeate depends on the fraction of water free energy utilized to drive uphill CO 2 diffusion. This analysis aims to provide a foundation and identify key targets for developing membrane materials and processes that are designed to exploit this coupling phenomenon.