“By using electrochemistry to convert captured carbon into products with established markets, we provide new pathways to improving these economics, as well as a more sustainable source for the industrial chemicals that we still need.”Ted Sargent, Northwestern University

Researchers at Northwestern University have worked with an international team of collaborators to create acetic acid out of carbon monoxide derived from captured carbon. This innovation, which utilizes a novel catalyst created in the lab of Northwestern’s Ted Sargent, could spur new interest in carbon capture and storage.

“Carbon capture is feasible today from a technical point of view, but not yet from an economic point of view,” said Sargent, a professor of chemistry at the Weinberg College of Arts and Sciences and a professor of electrical and computer engineering at the McCormick School of Engineering. “By using electrochemistry to convert captured carbon into products with established markets, we provide new pathways to improving these economics, as well as a more sustainable source for the industrial chemicals that we still need.” Sargent and his colleagues report their work in a paper in Nature.

Sargent’s lab has a track record of using electrolyzers — devices in which electricity drives a desired chemical reaction forward — to convert captured carbon into key industrial chemicals such as ethylene and propanol. And now acetic acid as well.

Though acetic acid may be most familiar as the key component in household vinegar, this represents only a minor use.

“Acetic acid in vinegar needs to come from biological sources via fermentation because it’s consumed by humans,” said Josh Wicks, a recent University of Toronto PhD recipient and one of the paper’s four co-lead authors. “But about 90% of the acetic acid market is for feedstock in the manufacture of paints, coatings, adhesives and other products. Production at this scale is primarily derived from methanol, which comes from fossil fuels.”

Lifecycle assessment databases showed the team that for every kilogram of acetic acid produced from methanol, the process releases 1.6kg of carbon dioxide (CO2).

Their alternative method takes place via a two-step process: first, captured gaseous CO2 is passed through an electrolyzer, where it reacts with water and electrons to form carbon monoxide (CO). This gaseous CO is then passed through a second electrolyzer, where another catalyst transforms it into various molecules containing two or more carbon atoms.

“A major challenge that we face is selectivity,” Wicks said. “Most of the catalysts used for this second step facilitate multiple simultaneous reactions, which leads to a mix of different two-carbon products that can be hard to separate and purify. What we tried to do here was set up conditions that favor one product above all others.”

Vinayak Dravid, another senior author on the paper and a professor of materials science and engineering, is founding director of the Northwestern University Atomic and Nanoscale Characterization (NUANCE) Center. This allowed the team to access diverse capabilities for the atomic- and electronic-scale measurements of materials.

“Modern research problems are complex and multifaceted and require diverse yet integrated capabilities to analyze materials down to the atomic scale,” Dravid said. “Colleagues like Ted present us with challenging problems that stimulate our creativity to develop novel ideas and innovative characterization methods.”

The team’s analysis showed that using catalysts with a much lower proportion of copper (approximately 1%), compared with previous versions, would favor the production of just acetic acid. It also showed that elevating the pressure to 10 atmospheres should lead to record-breaking efficiency.

In the paper, the team reports achieving a faradic efficiency of 91%, meaning that 91 out of every 100 electrons pumped into the electrolyzers ended up in the desired product — in this case, acetic acid.

“That’s the highest faradic efficiency for any multi-carbon product at a scalable current density we’ve seen reported,” Wicks said. “For example, catalysts targeting ethylene typically max out around 70% to 80%, so we’re significantly higher than that.”

The new catalyst also appears to be relatively stable: while the faradic efficiency of some catalysts tends to degrade over time, the team showed that for their catalyst it remained at a high level of 85% even after 820 hours of operation.

Wicks hopes that the elements that led to the team’s success – including a novel target product, a slightly increased reaction pressure and a lower proportion of copper in the catalyst – inspire other teams to think outside the box.

“Some of these approaches go against the conventional wisdom in this field, but we showed that they can work really well,” he said. “At some point, we’re going to have to decarbonize all the elements of chemical industry, so the more different pathways we have to useful products, whether it’s ethanol, propylene or acetic acid, the better.”

This story is adapted from material from Northwestern University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.