New Insights into the Mechanism of Electrochemical CO2 Capture by Supercapacitive Swing Adsorption

Carbon dioxide capture underpins an important range of technologies that can help to mitigate climate change. Improved carbon capture technologies that are driven by electrochemistry are under active development and it was recently found that supercapacitor energy storage devices can reversibly capture and release carbon dioxide. So-called supercapacitive swing adsorption (SSA) has several advantages over traditional carbon dioxide capture technologies such as lower energy consumption and the use of non-toxic materials. However, the mechanism for the capture of CO2 in these devices is poorly understood, making it challenging to design improved systems¬. In this work, the mechanism of SSA is investigated through COMSOL modelling and experimental measurements with a wide range of charging protocols. These investigations elucidate a mechanism whereby charging leads to bicarbonate depletion (or accumulation) in the electrodes, driving CO2 capture (or release) at the gas-exposed electrode. At very low charging currents we experimentally observe a decrease in the amount of carbon dioxide captured, suggesting the presence of competing processes at the two electrodes, and that SSA is an inherently kinetic phenomenon. This study highlights the importance of the operating conditions of these devices and may aid their development in the future.