The route to carbon-neutral fuels

Researchers have discovered what they call “a practical starting point” for converting carbon dioxide (CO2) into sustainable liquid fuels.

In a paper in the journal Nature Energy, a team from Stanford University, US, and the Technical University of Denmark (DTU) describes how electricity and an “Earth-abundant catalyst” can convert CO2 into energy-rich carbon monoxide (CO) more effectively than conventional methods. 

The key, they say, is that the catalyst – cerium oxide – is much more resistant to breaking down. 

And the potential is to produce a carbon-neutral product that is a viable alternative to electrification of transport systems – not to mention other products such as synthetic gas and plastics.

“We showed we can use electricity to reduce CO2 into CO with 100% selectivity and without producing the undesired by-product of solid carbon,” says Stanford’s William Chueh, one of three senior authors of the paper. 

The researchers say a way to convert CO2 into CO has yet to be widely commercialised because of various performance problems with previous attempts. Thus, their first step was to analyse how and why different devices had succeeded and failed in CO2 electrolysis.

They then 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,” says DTU’s Christopher Graves. 

“Replacing the current nickel electrode with our new ceria electrode in the next generation electrolyser would improve device lifetime.” 

The researchers say the suppression of carbon build-up allows their new device to convert more of the CO2 to CO and thus improve on the less than 50% CO product concentration common in today’s cells. This, they add, could reduce production costs.

“The carbon-suppression mechanism on ceria is based on trapping the carbon in stable oxidised form,” says senior author Michal Bajdich. 

“We were 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.”