Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) are pioneering a safer and more sustainable alternative. Using quinones - organic molecules dissolved in water - their new system offers an efficient and less hazardous approach to carbon capture. A study published in Nature Chemical Engineering delves into the underlying mechanisms of these electrochemical systems, providing insights that could refine and enhance their application.
The study, led by Kiana Amini, a former postdoctoral researcher at SEAS and now an assistant professor at the University of British Columbia, sheds light on the chemistry behind these systems. The research highlights the interplay of two distinct electrochemical processes that contribute to the system's performance, advancing the understanding of how aqueous quinone-based carbon capture works.
"If we are serious about developing this system to be the best it can be, we need to know the mechanisms that are contributing to the capture, and the amounts ... we had never measured the individual contributions of these mechanisms," Amini explained.
The system captures CO2 in two primary ways. The first, known as direct capture, involves charging the quinones to trigger a reduction reaction, which enables them to bind to CO2 molecules. This results in chemical compounds known as quinone-CO2 adducts. The second mechanism, indirect capture, involves increasing the solution's pH by charging the quinones and consuming protons. This alkaline environment facilitates CO2 conversion into bicarbonate or carbonate compounds.
To quantify these mechanisms, the researchers developed two experimental techniques. The first method utilized reference electrodes to measure voltage differences, providing insight into the behavior of quinones and their CO2-bound counterparts. The second method employed fluorescence microscopy to track chemical reactions in real-time, taking advantage of the unique fluorescence signatures of the compounds involved in the process.
"These methods allow us to measure contributions of each mechanism during operation," Amini said. "By doing so, we can design systems that are tailored to specific mechanisms and chemical species."
Michael J. Aziz, the Gene and Tracy Sykes Professor of Materials and Energy Technologies at SEAS, is the senior author of the study. Aziz's lab previously developed a redox flow battery technology that also uses quinone chemistry, further showcasing the versatility of these organic molecules in energy and environmental applications.
Quinones, found in crude oil and rhubarb, are abundant and capable of repeatedly capturing and releasing CO2. While challenges remain, such as the system's sensitivity to oxygen, the research provides tools for optimizing these systems for various industrial uses. The findings also pave the way for new lines of inquiry in carbon capture technology.
Research Report:In situ techniques for aqueous quinone-mediated electrochemical carbon capture and release
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