Carbon dioxide (CO2) capture is a promising method for facilitating the transition to a more sustainable society by reducing emissions of existing fossil-fuel-driven processes, offsetting hard-to-decarbonize sectors, and enabling net-negative applications. Current technologies typically utilize temperature- and/or pressure-driven approaches, which include absorption, adsorption, or membrane separations. While such methods have been demonstrated, even at commercial scales, broad adoption is hampered by drawbacks such as large energetic penalties, high upfront costs, complex process designs, limited scalability, low separation capacities, and suboptimal CO2 selectivity. Electrochemically-mediated carbon capture has recently gained interest as this approach can enable higher energetic efficiencies, direct integration of renewable energy, modular deployment, and operation at near ambient conditions. However, optimal material properties and system characteristics are not yet well understood, and it remains unclear under what set of conditions electrochemical technologies would offer an advantage over existing capture methods. In the early stages of technological development, as such, modeling analyses can help in estimating achievable performance bounds and developing system design guidelines. We specifically use mathematical modeling as a tool to (1) explore the interplay between material properties and design/operating factors and (2) identify key descriptors for high performance electrochemical CO2 separations. Here, I will present a thermodynamic modeling framework suitable for assessing the upper bounds on the thermodynamic (i.e. energetic) and faradaic (i.e. materials utilization) efficiencies of electrochemical carbon capture systems. Using the model, we identify effective molecular and electrolyte properties which maximize these efficiencies, while also considering the impact of other design factors (e.g., process configuration and state-of-charge swing). Finally, we compare the thermodynamic limits of electrochemically-mediated CO2 separations to traditional temperature-driven and pressure-driven processes, which can help establish target application spaces for each approach.

Thermodynamic considerations of electrochemical CO2 separation systems

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ACS Fall 2022

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