An international team of researchers has found a cheap and efficient substance that can remove carbon dioxide from the air.
It’s a type of metal-organic framework (MOF): a class of chemicals that are well known for their carbon capture properties, but are typically not very scalable or durable.
This MOF, however, is made from readily available aluminium hydroxide and formic acid, and works in all but the most humid conditions.
It’s called aluminium formate, or ALF.
“What makes this work exciting is that ALF performs really well relative to other high-performing CO2 adsorbents, but it rivals designer compounds in its simplicity, overall stability and ease of preparation,” says Dr Hayden Evans, a chemist at the US National Institute for Standards and Technology (NIST), and lead author on a paper published in Science Advances.
“It is made of two substances found easily and abundantly, so creating enough ALF to use widely should be possible at very low cost.”
Carbon capture is something of a problem child in decarbonisation: while there’s plenty of technology that does it well, much of it is too expensive for polluters to install on power stations. “Put it all together, you need some kind of wonder material,” says Evans.
“Here, we’ve managed to tick every box except stability in very humid conditions. However, using ALF would be inexpensive enough that a drying step becomes a viable option.”
According to Evans, ALF would cost less than one US dollar per kilogram.
The researchers tested ALF in simulated exhaust streams from coal-fire power stations, finding it selectively stuck to CO2, avoiding other gases.
Their analytical work showed that – like other MOFs – ALF looks like a cage filled with holes at a molecular level. CO2 molecules are just big enough to fit into the holes and get trapped.
The researchers are now interested in seeing whether the captured CO2 could then, possibly, be converted into formic acid to make more ALF, leading to a cyclic process.
“There is a great deal of research going on nowadays into the problem of what to do with all the captured CO2,” says Evans.
“It seems possible that we could eventually use solar energy to split hydrogen from water, and then combine that hydrogen with the CO2 to make more formic acid.
“Combined with ALF, that’s a solution that would help the planet.”
While the material is scalable, it’s not yet possible to use at scale.
Engineers need to figure out how to make large amounts, and coal-fired plants would need to have infrastructure in place to dehumidify the air first – but Evans says that the cost of this wouldn’t be prohibitive.
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