K₂CO₃ on porous supports for moisture-swing CO₂ capture from ambient air

Direct air capture (DAC) of CO₂ is an important technology to mitigate mobile carbon emissions, reduce atmospheric CO₂ concentration, and cope with climate change. Moisture-swing adsorption is regarded as one of the most promising technologies in DAC due to its low energy consumption and ease of operation. In this work, a cheap and easily available moisture-swing adsorbent of potassium carbonate loaded on porous supports (i.e., activated carbon, magnesium oxide, and zeolite) was prepared for CO₂ capture from ambient air. The composite adsorbent of potassium carbonate on activated carbon showed the best performance with a DAC capacity of 0.562 mmol/g at 25°C and 5% relative humidity. The effects of temperature, relative humidity, and CO₂ concentration on the adsorption performance were investigated systematically, as well as the cyclic DAC performance. In 50 adsorption–desorption cycles, the adsorption capacity of the composite adsorbent decreased by ~40% due to potassium carbonate leaching loss during water evaporation but can be fully recovered simply by re-impregnating with potassium carbonate again.