Immobilized CmpA: decreasing the cost and increasing the efficiency of ion exchange for direct air capture

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About This Project

While electrochemical direct air capture (eDAC) systems are some of the most theoretically efficient of all direct air capture systems, they are limited by the efficiency of their ion exchange mechanisms, and OpEx associated with replacing them. The cyanobacterial bicarbonate transport protein, CmpA, selectively binds bicarbonate over other forms of dissolved inorganic carbon. Here, we outline a proposal to study an immobilized protein model for facilitating anion exchange within an eDAC system.

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What is the context of this research?

Carbon dioxide removal (CDR) will be necessary to save the planet from 1.5C of warming. One group of CDR technologies, known as direct air capture (DAC), have reached deployment scale in recent years. Electrochemical DAC (eDAC) is one of the most theoretically efficient DAC pathways, and often relies on pH differentials to adsorb and desorb CO2 selectively.(1) eDAC systems use ion exchange membranes (IEMs) to facilitate the movement of specific ions, often bicarbonate, between solutions of different pH.(2)

What is the significance of this project?

Since the efficiency of an eDAC IEM is defined as the amount of dissolved inorganic carbon (DIC) transported across the membrane over the charge transported, bicarbonate selectivity is paramount to efficiency, as divalent carbonate is half as efficient.(2) Finally, as a % of total system costs, protein production (1-10%) is well below IEM replacement (~32%) for a theoretical DAC system.(2)

These findings suggest that a protein-based ion exchange mechanism with high selectivity for bicarbonate could potentially both decrease cost, and increase efficiency.

CmpA, a cyanobacterial membrane protein, binds bicarbonate with a high selectivity over other forms of DIC.(3) Additionally, CmpA has good production characteristics as it is stable and expresses well in E. Coli. (3)

What are the goals of the project?

This project seeks to examine immobilized CmpA as a novel ion exchange mechanism within a hypothetical pH shift eDAC system. This hypothetical system will contain an absorption solution of pH 8, and desorption solution of pH 5, with bead-bound CmpA used to selectively shuttle bicarbonate between the two.

While the intricacies of a full eDAC system are outside the scope of this project, I am proposing two experimental goals: the immobilization of CmpA onto a solid support, and quantification of DIC flux through a single cycle of capture and release by immobilized CmpA.


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I will need these funds to purchase materials and reagents. A budget breakdown is included in the solution section.

Project Timeline

Following is a timeline for our experimental goals, assuming work can begin by November 15th.

Dec 06, 2023

Express and Purify the Relevant Proteins

Dec 20, 2023

Immobilize CmpA 

Feb 14, 2024

Characterize Protein Activity and Carbon Flux 

Meet the Team

August Kane
August Kane

Team Bio

Ethan Jones and Pamela Silver of the Silver Lab at Harvard Medical School.

August Kane

My name is August Kane, and I am a senior studying Biomedical Engineering and Chemistry at Harvard. I am pursuing this project because I am passionate about the environment and hope to work in the field of climate biotech after graduation.

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