A new way to convert carbon dioxide (CO2) into sustainable liquid fuels has been developed by researchers from Stanford University and the Technical University of Denmark (DTU).
The researchers’ catalyst can covert CO2 into energy rich carbon monoxide (CO) more efficiently than conventional methods as the cerium oxide catalyst is more resistant to breaking down.
Stripping oxygen from CO2 to make CO gas is the first step to converting the gas into nearly any liquid fuel and other products, like synthetic gas and plastics. The addition of hydrogen to the CO can produce fuels much like synthetic diesel.
“We showed we can use electricity to reduce CO2 in CO with 100% selectivity and without producing the undesired by product of solid carbon,” said William Chueh, one of three authors of the study.
“We have been working on high-temperature CO2 electrolysis for years, but the collaboration with Stanford was the key to this breakthrough,” said Theis Skafte, Lead Author of the study.
Although plants reduce CO2 to carbon-rich sugars naturally, an artificial electrochemical route to CO has yet to be commercialised.
The researchers built two cells for CO2 conversion testing: one with cerium oxide and the other with conventional nickel-based catalysts. The ceria electrode remained stable, while carbon deposits damaged the nickel electrode, significantly shortening the catalyst’s lifetime.
“This remarkable capability of ceria has major implications for the practical lifetime of CO2 electrolyser devices,” said Christopher Graves, senior author of the study.
“Replacing the current nickel electrode with our new ceria electrode in the next generation electrolyser would improve device lifetime.”
Eliminating early cell death could significantly lower the cost of commercial CO production. The suppression of carbon build-up also allows the new type of device to convert more of the CO2 to CO, which is limited to well below 50% of CO product concentration in today’s cells.
“The carbon-suppression mechanism on ceria is based on trapping the carbon in stable oxidised form,” said Michal Bajdich, Senior Author of the paper.
“We are able to explain this behaviour with computational models of CO2 reduction at elevated temperature, which was then confirmed with X-ray photoelectron spectroscopy of the cell in operation.”
The researchers hope their work on the mechanisms in CO2 electrolysis devices by spectroscopy and modelling will help others in tuning the surface properties of ceria and other oxides to further improve CO2 electrolysis.
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