Researchers from the University of Toronto's Faculty of Applied Science & Engineering have developed a novel device that employs electrochemistry to enhance the efficiency of direct air carbon capture. This innovative approach aims to accelerate the adoption of this emerging technology.
David Sinton, a professor in the department of mechanical and industrial engineering and a senior author on a paper published in Joule, explains, “Carbon capture technology has been evolving for years, and now it's gaining momentum as governments and industries invest in the necessary infrastructure for large-scale implementation.”
Sinton points out a significant challenge: existing processes consume a considerable amount of energy and release a notable quantity of carbon emissions. “By offering a more efficient solution, we can advocate for scaling up this technology to have a meaningful impact on climate change,” he says.
The team's focus is on improving a carbon capture technique called pH swing cycle. This method involves passing air through an alkaline liquid solution with a high pH. Carbon dioxide in the air reacts with the alkaline solution and is captured as carbonates. To regenerate the capture liquid, chemicals are added to turn the carbonates into solid salt. In the typical process, natural gas is burned to heat the salt and convert the carbonates back into CO2 gas for underground injection or conversion into other carbon-based products.
Yi (Sheldon) Xu, who contributed to the project as a Ph.D. candidate and postdoctoral fellow in Sinton's lab, notes, “When you analyze the entire process lifecycle, you find that for every ton of captured CO2, you generate roughly 300 to 500 kilograms of CO2 equivalent. While it's still a net gain, the energy-intensive steps, especially heating, negatively impact overall carbon efficiency.”
To address this issue, the team turned to electrochemistry—leveraging electrolyzers to drive chemical reactions with electricity and fuel cells to generate electricity from chemical reactions. Their breakthrough involved creating a single device capable of functioning as both a fuel cell and an electrolyzer. This innovative approach offers a new pathway to regenerate the alkaline solutions essential for carbon capture.
One of the team members, Jonathan Edwards, who holds a Ph.D. in mechanical engineering, explains the innovation: “Our device employs a single positive electrode for both the fuel cell and the electrolyzer. By alternating its mode every second, we enable two distinct reactions to occur on the same electrode surface.”
In the initial reaction, the electrolyzer employs electric current to extract alkali metal ions, thereby regenerating the strongly alkaline solution crucial for air capture. Simultaneously, hydrogen is generated and cycled back to the fuel cell side of the device, where it engages in a reaction producing electricity, which is subsequently fed back into the electrolyzer.
On the other hand, the fuel cell generates an acidic solution that reacts with carbonate salts from the air-capture unit, releasing CO2 gas. Once the CO2 is released, the resulting solution returns to the electrolyzer, thus completing the cycle.
This approach offers several benefits. Firstly, it eliminates the energy-intensive heating step altogether. Secondly, it relies on electricity instead of natural gas—this electricity could originate from low-carbon sources like solar, wind, or nuclear energy.
Additionally, the fact that two reactions take place at a single electrode reduces mass-transfer limitations, which are constraints on how quickly reactants can diffuse to the electrode surface. These limitations typically necessitate more energy to drive the reaction.
Shijie Liu, a Ph.D. candidate in mechanical and industrial engineering, shares their findings from a life-cycle analysis: “Our process produces only around 11 kg of CO2 equivalent per ton of captured CO2. This is roughly 40 times less than the current thermal process.”
The team's research has garnered global attention—they ranked among the top 60 in the XPRIZE Carbon Removal competition last year. With their work now published, they hope to attract more researchers to collaborate in optimizing this electrochemical pathway.
Yi (Sheldon) Xu outlines their current objectives: “We're currently focused on enhancing the capture fluid and further reducing process energy consumption. This involves utilizing sustainable and cost-effective materials and scaling up the technology for industrial use.”
Xu adds, “Moreover, there's potential for innovations in electrode design and other areas. Our vision is to establish this as a viable platform for carbon-capture plants that are more energy-efficient to construct and operate than the existing options. This could provide us with a potent tool to mitigate the effects of climate change.”
Source: University of Toronto