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New Energy World magazine logo
New Energy World magazine logo
ISSN 2753-7757 (Online)

Electrified charcoal ‘sponge’ can soak up CO2 directly from the air


Sample of activated charcoal Photo: University of Cambridge/Alex Forse
Sample of activated charcoal used for CO2 capture

Photo: University of Cambridge/Alex Forse

Researchers at the University of Cambridge have developed a low-cost, energy-efficient method for making materials that can capture CO2 directly from the air.

The method uses a process similar to charging a battery to charge activated charcoal, which is often used in household water filters. By charging the charcoal sponge with ions that bond with CO2, the researchers found the charged material could successfully capture CO2 directly from the air. They also found that the charged charcoal sponge is potentially more energy-efficient than current carbon capture approaches, since it requires much lower temperatures to remove the captured CO2 for storage. The results are reported in the journal Nature.


‘Capturing carbon emissions from the atmosphere is a last resort, but given the scale of the climate emergency, it’s something we need to investigate,’ says Dr Alexander Forse from the Yusuf Hamied Department of Chemistry, who led the research. Direct air capture (DAC), which uses sponge-like materials to remove CO2 from the atmosphere, is one potential approach for carbon capture, but current approaches are expensive, require high temperatures and the use of natural gas, and lack stability, say the researchers. ‘We wanted to see if activated charcoal might be an option, since it’s cheap, stable and made at scale,’ explains Forse.


Activated charcoal is used in many purification applications, such as water filters, but normally it can’t capture and hold CO2 from the air. Inside a battery, charged ions are inserted into one of the battery’s electrodes. Forse and his colleagues hypothesised that the same thing could be achieved in an activated charcoal cloth functioning as an electrode. They imagined that ‘charging’ the inexpensive cloth with hydroxides, which have an electrical charge, would make it suitable for carbon capture, since the hydroxide ions forming in the tiny pores of the charcoal form reversible bonds with CO2.


And so it proved. Tests of the charged charcoal sponge showed that it could successfully capture CO2 directly from the air, thanks to the bonding mechanism of the hydroxides.


According to Forse, the rates of CO2 capture are already comparable to existing materials. However, ‘what’s even more promising is this method could be far less energy-intensive, since we don’t require high temperatures to collect the CO2 and regenerate the charcoal sponge’, he adds.


To collect the CO2 from the charcoal, the material is heated to reverse the hydroxide-CO2 bonds. Most materials currently used for direct air capture of CO2 need to be heated to temperatures as high as 900°C, often using natural gas. However, the charged charcoal sponges developed by the Cambridge team only require heating to 90–100°C, temperatures that can be achieved using renewable electricity. In fact, they are warmed by resistive heating, which essentially heats them from the inside out, making the process faster and less energy-intensive.


The materials do, however, have limitations. ‘We are working now to increase the quantity of CO2 that can be captured, and in particular under humid conditions, where performance decreases,’ notes Forse.