Turning carbon dioxide back into coal could rewind 'emissions clock'

Researchers have used liquid metals to turn carbon dioxide back into solid coal, in a promising study that could transform the approach to carbon capture and storage.

The research team led by RMIT University say they have developed a new technique that can efficiently convert CO2 from a gas into solid particles of carbon.

Published in the journal Nature Communications, the research is said to offer an alternative pathway for safely and permanently removing the greenhouse gas from our atmosphere.

Researchers said current technologies for carbon capture and storage focused on compressing CO2 into a liquid form, transporting it to a suitable site and injecting it underground.

But implementation had been hampered by engineering challenges, issues around economic viability and environmental concerns about possible leaks from the storage sites.

Australian Research Council DECRA Fellow Dr Torben Daeneke and Vice-Chancellor's Research Fellow Dorna Esrafilzadeh. Photo / RMIT University

RMIT researcher Dr Torben Daeneke said converting CO2 into a solid could be a more sustainable approach.

"While we can't literally turn back time, turning carbon dioxide back into coal and burying it back in the ground is a bit like rewinding the emissions clock," Daeneke, an Australian Research Council DECRA Fellow, said.

"To date, CO2 has only been converted into a solid at extremely high temperatures, making it industrially unviable.

"By using liquid metals as a catalyst, we've shown it's possible to turn the gas back into carbon at room temperature, in a process that's efficient and scalable.

"While more research needs to be done, it's a crucial first step to delivering solid storage of carbon."

How the carbon conversion works

Lead author, Dr Dorna Esrafilzadeh, a Vice-Chancellor's Research Fellow in RMIT's School of Engineering, developed the electrochemical technique to capture and convert atmospheric CO2 to storable solid carbon.

To convert CO2, the researchers designed a liquid metal catalyst with specific surface properties that made it extremely efficient at conducting electricity while chemically activating the surface.

The carbon dioxide is dissolved in a beaker filled with an electrolyte liquid and a small amount of the liquid metal, which is then charged with an electrical current.

A schematic illustration showing how liquid metal is used as a catalyst for converting carbon dioxide into solid coal. Photo / RMIT University

The CO2 slowly converts into solid flakes of carbon, which are naturally detached from the liquid metal surface, allowing the continuous production of carbonaceous solid.

Esrafilzadeh said the carbon produced could also be used as an electrode.

"A side benefit of the process is that the carbon can hold electrical charge, becoming a supercapacitor, so it could potentially be used as a component in future vehicles."

"The process also produces synthetic fuel as a by-product, which could also have industrial applications."