Copper–silver combo efficiently converts CO2

Capturing carbon dioxide and converting it into valuable resources such as chemicals or fuel is a challenge being tackled by a growing number of researchers worldwide.

Investigating fast and cost-effective ways to convert carbon dioxide into fuel, an international team of researchers has used a series of catalytic reactions to reduce CO₂ to methane. The team’s approach eliminates an intermediate step usually needed in the reduction process.

“We want to supply renewable electricity and take carbon dioxide from the atmosphere and convert it to something else in one step,” said Bingjun Xu, assistant professor of chemical and biomolecular engineering at the University of Delaware. “This is a key contribution to this vision.”

The conversion of carbon dioxide into valuable fuels involves starting with a surface made of copper, which can be used to reduce CO₂ into carbon monoxide. From here, carbon monoxide can be further transformed into substances such as methane. This process is relatively simple, but requires two reactors and costly separation and purification steps.

Published in the journal Nature Communications, the team’s research used computations and experiments to design a ‘one-pot’ catalysis system. Add carbon dioxide, and a series of chemical reactions will happen without the need to stop and add more chemicals.

To do this, the team added nanostructured silver surfaces — developed by co-author Qi Lu of Tsinghua University in China (formerly a postdoctoral associate in the Department of Chemical and Biomolecular Engineering at the University of Delaware) — to the copper surfaces. The silver portion attracts carbon monoxide molecules, which then migrate to the copper portion and reduce to methane. The system yields a higher concentration of methane than copper-only systems.

“In this work, the primary novelty is to combine these two [copper and silver] in a configuration so that several steps of reaction could occur in one system,” said Xu. “We systematically modified the composition; the silver-to-copper ratio in the structure. Those are key to the selectivity and ability to combine the reactions.”

Previous attempts to combine copper with precious metal in this way have failed, but the group developed a special type of electrode structure that enabled the system to work successfully. The research was the result of a collaborative effort, with research groups contributing spectroscopy, computation and studies of the reactivity of materials.

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