Supercapacitive Swing Adsorption for Direct Air Capture

Supercapacitive Swing Adsorption has been investigated for Direct Air capture applications. Experiments have been carried out with three different activated carbon electrode pairs derived from garlic roots at -1V and with 1M MgCl2 as electrolyte using 400 ppm CO2 in N2 as the gas mixture. Sorption capacities between 30 and 37 mmol/kg have been measured which is about six times smaller compared to benchmark experiments with a 15%CO2/85%N2 gas mixture. The weak dependency of the sorption capacity from CO2 partial pressure can be explained by the ionic liquid-solid mechanism which is based on strong electrostatic forces between the electrodes and ions formed from CO2 hydrolysis. The adsorption rates are about an order of magnitude smaller for 400 ppm CO2 compared to 15% CO2 due to the higher impact of gas flow rates and greater CO2 dilution. The energy consumption varies between 492 and 697 kJ/mol which is an increase of a factor of 9-12 compared to the 15% CO2/85% N2 gas mixture. The higher energy consumption is mainly due to the lower sorption capacity and the longer potential holding times needed at 400 ppm CO2.