Researchers at the University of Toronto Engineering have developed a new catalyst that efficiently converts captured carbon into valuable products such as ethylene and ethanol, even in the presence of sulfur oxide pollutants. This discovery provides a more economically viable method for carbon capture and improvement, potentially revolutionizing industries such as steel and cement production by allowing them to convert CO2 from waste streams more effectively.
An electrochemical catalyst for converting CO2 into valuable products can handle an impurity that poisons current versions.
A new catalyst boosts the conversion of captured carbon into commercial products, while maintaining high efficiency despite sulfur oxide impurities. This innovation could significantly reduce costs and energy requirements in carbon capture technologies, impacting heavy industries.
A new catalyst developed by University of Toronto Engineering researchers efficiently converts captured carbon into valuable products—even in the presence of a contaminant that degrades the performance of current versions.
The discovery is an important step toward more cost-effective carbon capture and storage techniques that can be added to existing industrial processes.
Advances in carbon conversion technologies
“Today, we have more and better options for low-carbon electricity generation than ever before,” says Professor David Sinton (MIE), senior author of a paper published in Energy of Nature on July 4 that describes the new catalyst.
“But there are other sectors of the economy that will be more difficult to decarbonise: for example, steel and cement production. To help these industries, we need to devise cost-effective ways to capture and improve the carbon in their waste streams.”
University of Toronto Engineering PhD students Rui Kai (Ray) Miao (left) and Panos Papangelakis (right) hold a new catalyst they designed to turn captured CO2 gas into valuable products. Their version works well even in the presence of sulfur dioxide, a pollutant that poisons other catalysts. Credit: Tyler Irving / University of Toronto Engineering
Use of electrolyzer in carbon transformation
Sinton and his team use devices known as electrolyzers to convert CO2 and electricity into products such as ethylene and ethanol. These carbon-based molecules can be sold as fuel or used as chemical feedstock to make everyday items like plastics.
Inside the electrolyzer, the conversion reaction occurs when three elements – CO2 gas, electrons and a water-based liquid electrolyte – come together on the surface of a solid catalyst.
The catalyst is often made of copper, but may also contain other metals or organic compounds that can further improve the system. Its function is to speed up the reaction and minimize the creation of unwanted byproducts, such as hydrogen gas, which reduce the efficiency of the overall process.
Addressing catalyst efficiency challenges
While many teams around the world have produced high-performance catalysts, almost all of them have been designed to operate on a pure CO2 supply. But if the carbon in question comes from smokestacks, the food is likely to be anything but clean.
“Catalyst designers generally don’t like to deal with impurities, and for good reason,” says Panos Papangelakis, a doctoral student in mechanical engineering and one of five co-lead authors on the new paper.
“Sulfur oxides, such as SO2, poison the catalyst by binding to the surface. This leaves fewer places for CO2 to react, and also causes the formation of chemicals you don’t want.
“This happens really quickly: while some catalysts can last hundreds of hours on clean feed, if you introduce these impurities, within minutes they can be down to 5% efficiency.”
Although there are well-established methods to remove impurities from CO2-rich exhaust gases before they are fed into the electrolyzer, they are time-consuming, energy-intensive, and increase the cost of carbon capture and upgrading. Moreover, in the case of SO2, even a little can be a big problem.
“Even if you reduce your exhaust gas to less than 10 parts per million, or 0.001% of the feed, the catalyst can be poisoned again in less than 2 hours,” says Papangelakis.
Innovations in catalyst design
In the paper, the team describes how they went about designing a more resilient catalyst that can handle SO2 by making two key changes to a typical copper-based catalyst.
On one side, they added a thin layer of polytetrafluoroethylene, also known as Teflon. This non-sticky material changes the chemistry on the catalyst surface, preventing reactions that enable SO2 poisoning.
In turn, they added a layer of Nafion, an electrically conductive polymer often used in fuel cells. This complex, porous material contains some areas that are hydrophilic, meaning they attract water, and other areas that are hydrophobic, meaning they repel water. This structure makes it difficult for SO2 to reach the catalyst surface.
Performance in adverse conditions
The team then fed this catalyst a mixture of CO2 and SO2, with the latter at a concentration of about 400 parts per million, typical of an industrial waste stream. Even under these difficult conditions, the new catalyst performed well.
“In the paper, we report a Faraday efficiency—a measure of how many of the electrons ended up in the desired products—of 50%, which we were able to maintain for 150 hours,” says Papangelakis.
“There are some catalysts that can start at a higher efficiency, maybe 75% or 80%. But again, if you expose them to SO2, within a few minutes or a few hours at the most, it comes down to almost nothing. We were able to withstand that.”
Future Directions and Implications
Papangelakis says that because his team’s approach does not affect the composition of the catalyst itself, it should be broadly applicable. In other words, teams that have already perfected high-performance catalysts should be able to use similar coatings to provide resistance to sulfur oxide poisoning.
Although sulfur oxides are the most challenging impurity in typical waste streams, they are not the only ones, and it is the full range of chemical contaminants that the team is addressing next.
“There are many other impurities to consider, such as nitrogen oxides, oxygen, etc.,” says Papangelakis.
“But the fact that this approach works so well for sulfur oxides is very promising. Prior to this work, it was simply taken for granted that you had to remove impurities before improving CO2. What we’ve shown is that there may be another way to deal with them, which opens up a lot of new possibilities.”
Reference: “Improving SO2 tolerance of CO2 reduction electrocatalysts using a polymer/catalyst/ionomer heterojunction design” by Panagiotis Papangelakis, Rui Kai Miao, Ruihu Lu, Hanqi Liu, Xi Wang, Adnan Ozden, Shijie Liu, Ning Sun, Colin P. O’Brien, Yongfeng Hu, Mohsen Shakouri, Qunfeng Xiao, Mengsha Li, Behrooz Khatir, Jianan Erick Huang, Yakun Wang, Yurou Celine Xiao, Feng Li, Ali Shayesteh Zeraati, Qiang Zhang, Pengyu Liu, Kevin Golovin, Jane Y. Howe. , Hongyan Liang, Ziyun Wang, Jun Li, Edward H. Sargent, and David Sinton, 4 Jul 2024, Energy of Nature.
DOI: 10.1038/s41560-024-01577-9