Catalyst paves the way for sustainable fuels from carbon dioxide

If the idea of ​​flying on battery powered commercial jets makes you nervous, you can relax a bit. Researchers have found a practical starting point for converting carbon dioxide into sustainable liquid fuels, especially for heavier modes of transport that could prove very difficult to electrify, such as airplanes, ships and trains. merchandise.

Carbon neutral re-use of CO₂ has emerged as an alternative to underground burial of greenhouse gases. In a new study published today in Nature Energy, researchers from Stanford University and the Technical University of Denmark (DTU) show how electricity and a catalyst rich in substances from the Earth can convert CO₂ carbon monoxide (CO) energy-rich better than conventional methods. The catalyst – the cerium oxide – is much more resistant to degradation. Remove oxygen from the CO₂ to produce CO gas is the first step to transform CO₂ in almost all liquid fuels and other products, such as synthetic gas and plastics. The addition of hydrogen to CO can produce fuels like synthetic diesel and the jet fuel equivalent. The team is considering using renewable energy to produce CO and for subsequent conversions, which would result in carbon-neutral products.

"We have shown that we can use electricity to reduce CO₂ in CO with a selectivity of 100% and without producing the undesirable byproduct of solid carbon, "said William Chueh, associate professor of science and materials engineering at Stanford, one of the three main authors of the study. ; article.

Chueh, aware of DTU's research in this area, invited Christopher Graves, associate professor at DTU's energy conversion and storage department, and Theis Skafte, a DTU PhD student of the time, to come to Stanford. and work together on technology.

"We were working on high temperature CO₂ Electrolysis for years, but collaboration with Stanford has been key to this breakthrough, "said Skafte, lead author of the study, who is now a postdoctoral researcher at DTU. "We realized something that we could not have separately – understanding both fundamental and practical demonstration of a more robust material."

Barriers to conversion

One of the advantages of sustainable liquid fuels compared to the electrification of transportation is that they can use existing gasoline and diesel infrastructure such as engines, pipelines and stations -service. In addition, barriers to the electrification of airplanes and ships – long haul travel and high battery weight – would not be a problem for energy-dense and carbon-neutral fuels.

Although plants reduce CO₂ to naturally occurring high carbon sugars, an artificial electrochemical pathway to CO has yet to be widely commercialized. Among the problems: appliances consume too much electricity, convert a small percentage of CO₂ molecules, or produce pure carbon that destroys the device. The researchers in the new study first looked at how different devices have been successful and failed in treating CO₂ electrolysis.

With the knowledge gained, researchers built two cells for CO₂ conversion tests: one with cerium oxide and the other with conventional nickel – based catalysts. The cerium oxide electrode remained stable, while carbon deposits damaged the nickel electrode, greatly shortening the life of the catalyst.

"This remarkable ceria capacity has major implications for the practical life of CO₂ electrolysers, "said Graves of DTU, lead author of the study and a visiting scholar at Stanford at the time. "Replacing the current nickel electrode with our new cerium oxide electrode in the next-generation electrolyzer would improve the life of the device."

Road to marketing

The elimination of early cell death could significantly reduce the cost of commercial CO production. The removal of carbon accumulation also allows the new type of device to convert more CO₂ CO, which is limited to well below 50% CO concentration in current cells. It could also reduce production costs.

"The mechanism of carbon removal on the cerium oxide is based on the sequestration of carbon in stable oxidized form. We could explain this behavior with computer models of CO₂ reduction at high temperature, which was then confirmed by X-ray photoelectron spectroscopy of the cell in operation ", said Michal Bajdich, lead author of the document and associate researcher at the Center SUNCAT Center for Interface Science and Catalysis, a partnership between the SLAC National Accelerator Laboratory and Stanford's School of Engineering.

The high cost of CO capture₂ prevents large-scale underground sequestration, and high costs may be an obstacle to the use of CO₂ make fuels and more sustainable chemicals. However, the market value of these products, combined with payments to avoid carbon emissions, could help technologies that use CO₂ overcome the cost hurdle faster.

Researchers hope their initial work on revealing CO mechanisms₂ Spectroscopy and modeling electrolysis devices will help others to adjust the surface properties of cerium oxide and other oxides to further improve CO₂ electrolysis.

Chueh is also a senior member of Stanford's Precourt Institute for Energy. Other co-authors of Stanford are former doctoral students Zixuan Guan, postdoc Michael Machala, former postdocs Matteo Monti and Chirranjeevi B. Gopal and SLAC postdoc Jose A. Garrido Torres. Lev Martinez, doctoral candidate and leader of the nanolab group, is also co-author of the DTU. Eugen Stamate and researcher Simone Sanna. The other co-authors are Ethan J. Crumlin, a researcher at the Lawrence Berkeley National Laboratory, and Max Garcia Melchor, assistant professor at Trinity College, Dublin.

This project was funded by Haldor Topsoe A / S, the Danish Innovation Fund, the Danish Agency for Science, Technology and Innovation and Energinet.dk., The US Department of Energy, the SUNCAT Center and a CAREER Award from the National Science Foundation.

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