(Industrial Electrochemistry and Electrochemical Engineering Division Student Achievement Award) Quantifying Energy Losses in Electrochemical Carbon Capture Systems
Authors: Clarke Lauren E. , Brushett Fikile R. 
Published: September 2023

Society-wide decarbonization is a grand challenge of the 21st century that will require wide-scale deployment of various carbon-neutral and carbon-negative technologies. Carbon dioxide (CO2) capture is one promising method as it provides a means to offset emissions from existing fossil-fuel-driven processes and hard-to-decarbonize sectors.[1], [2] State-of-the-art approaches for carbon capture typically utilize temperature-driven processes where CO2 is captured and released at lower and higher temperatures, respectively.[3], [4] While such methods have been demonstrated, even at commercial scales, broad adoption is hampered by drawbacks including large energetic penalties, high capital costs, and limited scalability. Electrochemical carbon capture methods have recently gained interest as these approaches have the potential to enable higher energetic efficiencies, modular deployment, and operation at ambient conditions. These technologies can also be readily coupled with renewable energy sources, avoiding emissions associated with electricity generation from fossil fuels.

While there are several proposed approaches for electrochemical CO2 separation, I will specifically discuss systems that employ soluble, redox active capture molecules with CO2 binding strengths that vary with changes in oxidation state. To date, the majority of research activities have focused on the discovery of stable capture molecules and electrolyte formulations that enable high separation capacities and energetically-efficient operation. At this early stage of development, modeling analyses hold considerable value in defining achievable performance bounds and describing key relationships between molecular properties, system design, and cell performance. In this talk, I will discuss how cell-level models can be used to understand performance features of electrochemical CO2 separation systems.[5], [6] First, I will describe the modeling framework and key parameters that characterize molecular / electrolyte properties as well as relative rates of mass transport, kinetics, and ionic conduction. Second, I will quantify potential magnitudes of energy losses arising from thermodynamic cycle irreversiblities, mass transport / kinetics within the porous electrodes, and ohmic resistance of the membrane or separator. I will also illustrate system tradeoffs between energy requirements and other important metrics (e.g., faradaic efficiency and operating current density). Third and finally, I will describe how results from this work can inform ongoing molecular and device engineering campaigns. Specifically, I will highlight performance-defining parameters and target property values, providing the research community with a means of evaluating capture molecule / electrolyte effectiveness and expected reactor performance.

Acknowledgements:

This research was supported by the Alfred P. Sloan Foundation. LEC acknowledges additional funding from the MIT School of Engineering Charles M. Vest Fellowship.

References:

International Energy Agency, Net Zero by 2050, Paris, (2021) https://www.iea.org/reports/net-zero-by-2050.

M. Allen et al., IPCC, 2018: Summary for Policymakers, p. 1–24, (2018).

C. Chao, Y. Deng, R. Dewil, J. Baeyens, and X. Fan, Renew. Sustain. Energy Rev., 138, 110490 (2021).

M. Fasihi, O. Efimova, and C. Breyer, J. Clean. Prod., 224, 957–980 (2019).

L. E. Clarke, M. E. Leonard, T. A. Hatton, and F. R. Brushett, Ind. Eng. Chem. Res., 61, 10531–10546 (2022).

L. E. Clarke and F. R. Brushett, In Preparation. (2023).