CAREER: Combining Electrode Engineering with Electrochemical Modeling to Enable Atmospheric CO2 Capture

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The capture of carbon dioxide (CO2) directly from the atmosphere is emerging as a potential approach to climate change mitigation. However, the rapid separation and purification of CO2 from air can be very energy-intensive because of its low concentration (400 ppm). The development of highly energy-efficient CO2 capture technology will enhance the sustainability, affordability, and commercial appeal of capturing CO2 and converting it into useful chemicals and products. Most incumbent CO2 capture technologies run on heat, which typically requires burning fossil fuels. Heat-based CO2 capture methods also face a fundamental conversion efficiency limit in using heat for the work of separation. In contrast, CO2 capture using electrical rather than thermal energy is attractive because it does not face this efficiency limit. Moreover, it could be run using renewable energy conversion technology, which is increasingly available and inexpensive. This project will develop a new approach to energy-efficient CO2 separation that uses electro-active organic molecules attached to carbon electrodes. Polarizing these electrodes in an aqueous solution causes reversible changes in the pH of the solution, which enables CO2 separation. CO2 will be selectively absorbed in the form of carbonate ions under alkaline conditions and then released as a pure gas under acidic conditions. Experimental and modeling techniques will be used to understand how both the chemical composition of the electrode and its integration into an electrochemical flow cell influence the rate and energy efficiency of the overall separation process. Further, this project will engage Michigan residents in informal discussions and hands-on scientific demonstrations highlighting the need for and benefits of CO2 capture and utilization technology. With support from both the Interfacial Engineering and Electrochemical Systems programs, this project aims to advance a new way of using carbon electrodes, chemically functionalized with organic moieties, for energy-efficient electrochemical CO2 separation. Upon electric polarization, these electrodes can either absorb protons from or release them into solution, changing its pH, and thereby providing a mechanism for reactive CO2 capture and release. The extent and reversibility of pH changes that these electrodes can achieve are key factors controlling the energy efficiency of the separation process. These factors strongly depend on the strength of the electric field that the organic moiety experiences at the electrode/electrolyte interface. A combination of electroanalytical and in operando high-resolution x-ray spectroscopic techniques will be used to develop a mechanistic understanding of proton transfer as the chemistry of the moiety and manner of its installation on carbon vary. This knowledge will be exploited to engineer electrodes that will concentrate CO2 from the air when deployed in an aqueous electrochemical flow cell. Flow cell measurements will be used to validate a physics-based model for the separation process; the model will offer an understanding of how thermodynamic and kinetic losses dictate the overall energy input and efficiency for a given separation throughput. The education plan generates public exposure to the benefits of CO2 mitigation technology by offering face-to-face exchange between the community and researchers through discovery-based learning, informal discussion, targeted hands-on demonstrations, and a research exhibit.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.