University of Toronto Engineering researchers 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 contaminants. The breakthrough offers a more economically viable method of carbon capture and upgrading that could revolutionize industries such as steel and cement by enabling them to more efficiently convert CO2 from waste streams.
An electrochemical catalyst for converting CO2 into valuable products can withstand the impurity that poisons current versions.
The new catalyst improves the conversion of captured carbon into commercial products and maintains high efficiency despite sulfur oxide impurities. This innovation could significantly reduce costs and energy requirements in carbon capture technologies, impacting heavy industry.
A newly designed catalyst created by University of Toronto Engineering researchers efficiently converts captured carbon into valuable products – even in the presence of a contaminant that reduces the performance of current versions.
The discovery is an important step toward more cost-effective carbon capture and storage techniques that could 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), lead author of the paper published in Energy of nature July 4, which describes a new catalyst.
“But there are other sectors of the economy that will be more difficult to decarbonize: steel and cement production, for example. To help these industries, we need to find cost-effective ways to capture and upgrade 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 convert captured CO2 gas into valuable products. Their version works well even in the presence of sulfur dioxide, a contaminant that poisons other catalytic converters. Credit: Tyler Irving / University of Toronto Engineering
Use of electrolyser 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 fuels or used as chemical raw materials to make everyday items such as plastics.
Inside the electrolyzer, a conversion reaction occurs when three elements — CO2 gas, electrons and a water-based liquid electrolyte — combine 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 formation of unwanted by-products, such as hydrogen gas, which reduce the efficiency of the entire process.
Solving Catalyst Efficiency Problems
While many teams around the world are building high-performance catalysts, almost all of them are designed to work with a clean CO2 feed. But if the carbon in question comes from chimneys, the feed 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-authors of the new paper.
“Sulfur oxides such as SO2 poison the catalyst by binding to the surface. This leaves less room for the CO2 to react and also creates chemicals you don’t want.
“It happens really quickly: while some catalysts can last for hundreds of hours on a clean feed, if you put these impurities in, they can be down to 5% efficiency in minutes.”
Although there are well-established methods for removing impurities from CO2-rich exhaust gases prior to feeding them to the electrolyser, they require time, energy and increase the cost of carbon capture and upgrading. In addition, in the case of SO2, it can be a bit of a big problem.
“Even if you get the exhaust down to less than 10 parts per million, or 0.001% injection, the catalytic converter can still be poisoned in less than 2 hours,” says Papangelakis.
Innovations in catalyst design
In this paper, the team describes how they designed a more durable catalyst that could withstand 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-stick material changes the chemistry on the catalyst surface and prevents reactions that allow SO2 poisoning.
On the other hand, 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 surface of the catalyst.
Performance under adverse conditions
The team then filled this catalyst with a mixture of CO2 and SO2, with an SO2 concentration of about 400 ppm, which is typical of an industrial waste stream. Even under these demanding conditions, the new catalyst performed well.
“In the paper, we report a Faraday efficiency – a measure of how many 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 off with higher efficiency, maybe 75% or 80%. But again, if you expose them to SO2 for a few minutes or a few hours at most, it drops to next to nothing. We’ve been 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 widely applicable. In other words, teams that have already perfected high-performance catalysts should be able to use similar coatings to gain resistance to sulfur oxide poisoning.
Although sulfur oxides are the most challenging contaminant in typical waste streams, they are not the only one, and it is a whole set 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 would need to remove impurities before upgrading CO2. We’ve shown that there can be another way to deal with them, which opens up a lot of new possibilities.”
Reference: “Improving SO2 Tolerance of CO2 Reduction Electrocatalysts Using 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