Novel catalyst could improve economic case for carbon capture and storage

The catalyst was developed in the lab of professor Ted Sargent, Northwestern University’s Lynn Hopton Davis and Greg Davis 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.

“Carbon capture is feasible today from a technical point of view, but not yet from an economic point of view,” Sargent said in a statement. “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.”

The international team’s work is detailed in Nature.

“About 90 per cent of the acetic acid market is for feedstock in the manufacture of paints, coatings, adhesives and other products,” said Josh Wicks, one of the paper’s four co-lead authors. “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 CO2.

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

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“A major challenge that we face is selectivity,” said Wicks. “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 favour one product above all others.”

The team’s analysis showed that using a much lower proportion of copper (approximately one per cent) compared with previous catalysts would favour the production of just acetic acid. It also showed that elevating the pressure to 10 atmospheres would enable the team to achieve record-breaking efficiency. In the paper, the team also reports a faradic efficiency of 91 per cent.

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

According to Northwestern, the new catalyst also appears to be relatively stable: while the faradic efficiency of some catalysts tend to degrade over time, the team showed that it remained at a high level of 85 per cent even after 820 hours of operation.