Turning CO2 into solid carbon for storage

RMIT University

A NEW carbon capture process has been developed that turns carbon dioxide gas into solid carbon that is easier to store.

In typical CO₂ capture processes, the CO₂ gas is pressurised to a liquid, which is then transported to a suitable site and stored underground. So far, these methods have proven to be extremely costly and have also raised some potential environmental concerns over the safe storage of CO₂ underground. A more efficient process has now been developed that converts the CO₂ gas to solid carbon.

The research was led by RMIT University, Melbourne, Australia, and involves using a liquid metal electrocatalyst to convert the CO₂ to solid carbon. Previously developed electrocatalysts were only able to convert CO₂ to solid carbon, such as carbon nanotubes, at temperatures above 600^oC, but this new method works at room temperature. The researchers used a gallium-based alloy containing cerium to produce flakes of solid carbon. Gallium-based alloys are ideal for liquid metal electrocatalysts because they remain liquid at room temperature.

"To date, CO2 has only been converted into a solid at extremely high temperatures, making it industrially unviable,” said Torben Daeneke, an Australian Research Council DECRA Fellow at RMIT. "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."

The liquid metal catalyst is resistant to coking, which is when the carbonaceous product adheres to the surface of the catalyst and thus reduces the activity of the catalyst. The researchers also tested a solid catalyst which had the same initial performance, but then the performance diminished rapidly due to coking, showing that the liquid state is crucial for continuous production.

The solid carbon is produced by the electrocatalyst when low potentials are used, but at higher potentials the dominant product is CO gas, which could be used to produce industrial chemicals and synthetic fuels. If the process is adopted at larger scales in the future, a portion of the produced carbonaceous material could also be used for electrode materials.

"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 Dorna Esrafilzadeh, a Vice-Chancellor's Research Fellow in RMIT's School of Engineering, and lead author of the work. "The process also produces synthetic fuel as a by-product, which could also have industrial applications."

Nature Communications http://doi.org/gfw8ps