Engineering researchers have made strides in developing carbon capture systems that utilize quinones, which are molecules dissolved in water, as effective capturing agents. Recent research sheds light on how these safer, water-based electrochemical systems work, allowing for improvements and advancements in their design.
Carbon capture is crucial for reducing atmospheric carbon dioxide during industrial processes, such as cement manufacturing or metal production. It is seen as a vital strategy in combating climate change. Current technologies, like amine scrubbing, face challenges due to their high energy demands and the use of hazardous chemicals.
In search of a better option, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have created carbon capture systems that harness quinones in water as their core components. A new publication in Nature Chemical Engineering delves into the fundamental mechanisms at play in these more benign, water-based electrochemical capture systems, setting the stage for further advancements.
The research, led by Kiana Amini, a former Harvard postdoctoral fellow and now an assistant professor at the University of British Columbia, examines the chemistry involved in an aqueous quinone-mediated carbon capture system, highlighting the interaction between two types of electrochemical reactions that enhance the system’s effectiveness.
Michael J. Aziz, the Gene and Tracy Sykes Professor of Materials and Energy Technologies at SEAS, is the senior author of this study. Aziz’s lab has previously developed a redox flow battery technology utilizing similar quinone chemistry for energy storage in commercial and grid applications.
Quinones are versatile, small organic compounds found in substances like crude oil and rhubarb, capable of capturing and releasing CO2 multiple times. Through laboratory studies, the Harvard team identified that quinones capture carbon through two different mechanisms. While these processes operate simultaneously, their individual contributions to carbon capture had previously been unclear, likened to an experimental device whose inner workings are unknown.
This research sheds light on these processes.
“If we’re intent on optimizing this system, understanding the mechanisms that contribute to carbon capture—and measuring their individual impacts—is essential. Until this point, we hadn’t quantified these specific contributions,” Amini stated.
One approach by which dissolved quinones capture carbon involves direct interaction, where quinones gain an electrical charge and undergo a reduction reaction that increases their attraction to CO2. This interaction allows quinones to bond with carbon dioxide molecules, forming chemical complexes referred to as quinone-CO2 adducts.
The second mechanism is an indirect mode of capture: charged quinones absorb protons, raising the solution’s pH. This transformation enables carbon dioxide to react with the now-alkaline solution, resulting in bicarbonate or carbonate compounds.
The researchers developed two experimental methods to assess the contributions of each mechanism in real-time. The first method involved using reference electrodes to observe voltage differences between the quinones and their resulting quinone-CO2 adducts.
The second employed fluorescence microscopy to differentiate between oxidized, reduced, and adducted chemicals, measuring their concentrations at high speed. This was achieved by discovering that the compounds involved in quinone-assisted carbon capture exhibit distinct fluorescence patterns.
“These techniques allow us to analyze the contributions of each mechanism during operational phases,” Amini explained. “This capability enables designed systems tailored to specific mechanisms and chemical components.”
This research enhances the understanding of aqueous quinone-based carbon capture technologies and provides useful tools for customizing designs for various industrial scenarios. While there are hurdles to overcome, such as oxygen sensitivity which could affect system efficiency, these discoveries present fresh opportunities for exploration.
The study was funded by the National Science Foundation and the U.S. Department of Energy.
