Every year, power plants and factories release billions of tons of carbon dioxide (CO₂) into the atmosphere. Methods exist to capture that CO₂ using chemical solutions and, separately, to convert pure CO₂ into useful fuels and chemicals. But doing both steps at once, in a cost-efficient and scalable way, has been difficult.
Now, researchers at the University of Chicago Pritzker School of Molecular Engineering (UChicago PME) and the U.S. Department of Energy’s Argonne National Laboratory have developed a system that can simultaneously capture and convert CO₂. The approach, they reported in Nature Energy, offers a more efficient and potentially lower-cost approach than carrying out each step separately.
By swapping the water usually used in carbon capture and conversion systems for a different solvent, the team was able to capture CO₂ more efficiently and convert it into carbon monoxide, an industrially relevant building block for the chemical industry used to make a wide range of fuels and chemicals today. They also turned to zinc, rather than the usual silver, to catalyze the conversion reaction, bringing costs for the process down further.
“The concept of being able to integrate capture and conversion into a single step is a relatively new one, and we’ve made significant headway in not only showing that this is possible but that it can be done under conditions that are relevant for industrial deployment,” said Chibueze Amanchukwu , Neubauer Family Assistant Professor of Molecular Engineering at UChicago PME and senior author of the new study.
One process instead of two
In conventional carbon capture, amines — nitrogen-based compounds that bind readily to CO₂ — are dissolved in water. Releasing the captured CO₂ for later use requires heating the solution to temperatures as high as 150°C and compressing the CO₂. Meanwhile, if that captured CO2 was converted in water, water carries out unwanted side reactions, ultimately leading to hydrogen gas.
Amanchukwu, whose lab focuses on electrochemistry in non-aqueous solvents, was brought together with scientists at Argonne National Laboratory through the University of Chicago Joint Task Force Initiative, a program designed to foster collaboration between the two institutions. About four years ago, the group formed a team and asked themselves what big problem was worth tackling together. They landed on reactive capture — the idea that CO₂ could be converted directly into a useful product while still bound to the amine.
“The challenge with current capture methods comes when you need to recover that CO₂. You need to boil the solution, which requires significant energy,” said first author of the study Reginaldo Gomes, who completed his PhD at UChicago PME and is now a postdoctoral researcher at Argonne. “We asked whether, instead of going though those costly steps, we could use electricity to convert the captured CO₂ directly into something valuable.”