Thermodynamics of Multistage Electrochemically Mediated Carbon Capture Systems

Electrochemically mediated sorbent-based carbon capture systems have recently gained attention as an alternative to traditional thermally driven separations. Realizations of such systems typically require a choice between thermodynamically favorable but practically challenging two-stage systems, which combine activation with capture and deactivation with release, or pragmatic but less energy-efficient stepwise four-stage processes decoupling these steps. In this work, we present a thermodynamic assessment of novel multistage systems that are shown to combine the practicality of sequential unit operations with the thermodynamic favorability of concerted operations. A generalized thermodynamic assessment shows that these systems approach the thermodynamic minimum energy of separation in the limit of many stages for an arbitrary sorbent chemistry. Staged desorption is further shown to dramatically decrease the amount of gas in the cell during deactivation, potentially reducing bubble-driven inefficiencies.