Supercapacitive Swing Adsorption of Carbon Dioxide

Abstract Carbon capture is essential for reduction of carbon dioxide (CO2) pollution from flue gas which is emitted during fossil fuel combustion. The flue gas is mainly composed of 15% CO2 and 85% N2 and it requires high selectivity for gas purification. Some methods have been developed for carbon capture such as Pressure Swing Adsorption (PSA) and Temperature Swing Adsorption (TSA). Unfortunately, these techniques use a lot of energy during the desorption step that reduces power generation efficiency. An ideally effective carbon capture technique needs to promote CO2 adsorption and desorption at the proper times during the separation cycles, without incurring a large parasitic energy load. A new gas adsorption technique is presented, Supercapacitive Swing Adsorption (SSA), in which CO2 is either actively adsorbed or desorbed by repeated capacitive charge and discharge of supercapacitor carbon electrodes and energy used in adsorption can principally be recovered upon desorption. It is shown that reversible adsorption/desorption of CO2 from a 15% CO2 and 85% N2 gas mixture can be achieved when an electrically conducting high surface area porous carbon material is brought into contact with carbon dioxide gas and an aqueous sodium chloride electrolyte. When the supercapacitor carbon electrodes are charged, the electrolyte ions are spontaneously organized into an electric double layer at the surface of each porous carbon electrode. The presence of this double layer leads to reversible, selective adsorption and desorption of the CO2 as the supercapacitor is charged and discharged. Moreover, it is also shown that SSA has the ability to separate CO2 from N2, with a high selectivity for CO2 and only a weak dependence on the CO2 partial pressure in a CO2/N2 gas mixture. The amount of adsorbed CO2 scales with applied voltage and with the mass of the porous carbon sorbent, which is inexpensive, robust and environmentally friendly. The effect barely depends on temperature.