Activated Carbon Fiber Felt Composites for the Direct Air Capture of Carbon Dioxide

Negative emissions technologies to mitigate climate change require innovative solutions for the direct air capture (DAC) of CO₂ from the atmosphere. K₂CO₃ readily reacts with CO₂ to form KHCO₃; however, bulk K₂CO₃ suffers from very slow sorption kinetics. By incorporating K₂CO₃ into activated carbon (AC) fiber felts, the sorption kinetics were significantly improved by increasing the surface area of K₂CO₃ in contact with air. The AC-K₂CO₃ fiber composite felts are flexible, cheap, easy to manufacture, chemically stable, and show excellent DAC capacity and (de)sorption rates, with stable performance up to ten cycles. Cyclic testing was demonstrated with 4 h sorption and 0.5 h desorption intervals. The best composite felts collected an average of 478 μmol of CO₂ per gram of composite during 4 h of exposure to ambient air (19 % relative humidity) that had a CO₂ concentration of 400-450 ppm after regeneration at 125 °C in an air furnace. An increase in the dew point temperature from 0 to 12 °C decreased sorption performance of the composite felts by 40 %.