28th February 2019

Scientists turn carbon dioxide back into coal

Australian researchers have demonstrated a liquid metal catalyst, able to turn carbon dioxide gas back into coal. This method could potentially offer a new way to store carbon in solid form.

Researchers have used liquid metals to turn carbon dioxide back into solid coal, in a world-first breakthrough that could transform our approach to carbon capture and storage (CCS). A team led by RMIT University in Melbourne, Australia, 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 offers an alternative pathway for safely and permanently removing this greenhouse gas from our atmosphere.

Current technologies for CCS focus on compressing CO2 into liquid form, transporting it to a suitable site and injecting it underground. But implementation has been hampered by engineering challenges, issues of economic viability and environmental concerns over leaks from storage sites. Converting CO2 into a solid could be a more sustainable approach, according to RMIT researcher Dr Torben Daeneke.

"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," said Daeneke. "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."

Lead author, Dr Dorna Esrafilzadeh, developed the electrochemical technique. To convert CO2, her team 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. 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.

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

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