Scientists use liquid metals to turn carbon dioxide gas back into coal
If we're going to curb the worst case scenario of climate change, it's not enough to just cut back on future carbon dioxide emissions – we need to remove some of what's already in the air. Capturing carbon from the air and sequestering it is emerging as a viable strategy, and now scientists have developed a new method to turn CO2 gas back into solid coal, that can then be buried, or even used for electronic components.
Many projects are currently experimenting with new ways to capture carbon from the point of emission. The gas is run through and absorbed by metal-organic frameworks, porous powders, bubble-like membranes, or materials made of clay or coffee grounds.
But that's only half the story – what do you do with that captured carbon? After it's extracted from those capture materials, the gas can then be reused to make concrete, fizzy drinks or fuels, or in larger amounts it can be stashed away underground. To store CO2, it's usually compressed into a liquid form or bonded with water, and then injected deep underground. There, it interacts with basalt rock and solidifies into a carbonate mineral, reportedly in as little as two years.
But other studies have found that this process may not be as effective as it seems. An MIT investigation found that only a thin top layer was turning solid – underneath was still a large pocket of gas. That keeps it out of the atmosphere for now, but has the potential to leak in the future and release it all back into the air, undoing all our hard work.
So the new study set out to develop a way to solidify carbon before it's stashed underground, so there's no chance of escape. The team was made up of researchers from Australia, Germany, China and the US.
Solidifying carbon at room temperature
Key to the new method is a liquid metal catalyst, made up of a gallium alloy and cerium, which was developed by the team. Carbon dioxide is first dissolved into a beaker containing an electrolyte liquid, then a small amount of the liquid metal catalyst is added. When an electrical current is applied, the catalyst chemically activates the surface of the mixture, which slowly converts the CO2 into solid flakes of carbon.
The catalyst was designed to be an excellent conductor of electricity, and efficient at performing the reaction. And because it's a liquid the carbon flakes don't stick to it, which they tend to do if it's a solid catalyst. That keeps it running for longer without fouling up.
The researchers say this process can be done at room temperature, unlike other carbon conversion processes that require high temperatures and, as a result, consume a lot of energy. This method meanwhile can be done in a lab with relatively inexpensive and commonplace equipment, and a small source of electricity.
"To date, CO2 has only been converted into a solid at extremely high temperatures, making it industrially unviable," says Torben Daeneke, an author of the study. "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."
Once that carbon has been solidified, it can then be safely stored underground indefinitely, without fear of it leaking back into the atmosphere. But interestingly, that isn't the only potential outcome.
"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," says Dorna Esrafilzadeh, lead author of the study. "The process also produces synthetic fuel as a by-product, which could also have industrial applications."
The technique has plenty of potential for helping to remove greenhouse gases from the atmosphere, but as with any of these kinds of studies, more research will need to be done to see how effective it could be at an industrial scale, both logistically and economically.
The research was published in the journal Nature Communications. The team describes the work in the video below.