Climate change is one of the greatest challenges the world faces in the 21st century. The Intergovernmental Panel on Climate Change (IPCC) estimates that to limit global temperature increase to 1.5 °C above preindustrial levels, the world needs to achieve net carbon neutrality by 2050. Although expanding renewable energy will be vital to reach this goal, 2 certain industries such as cement manufacturing are intrinsically linked to CO 2 emissions, while in the short term, fossil fuels will continue to be vital to the world economy. Carbon dioxide capture at point sources is currently one of the cheapest ways to reduce industrial greenhouse gas emissions, and can help to close this gap. The IPCC asserts that all pathways to limit global warming to 1.5 °C will require "carbon dioxide removal (CDR) on the order of 100-1000 GtCO 2 over the 21st century", where CDR refers to removal of carbon dioxide from the atmosphere rather than point emissions. Other estimates require annual CO 2 capture of 75-175 MtCO 2 in the UK alone to meet net-zero targets. The best-developed carbon capture technique is solvent scrubbing, where aqueous amine solvents are used to selectively absorb CO 2 . Heating the solvent, known as a temperature swing, drives CO 2 out for storage and returns the system to its original state. However, raising the temperature of a large volume of solvent requires substantial energy input, limiting efficiency. Amine solvents can also corrode equipment, be poisoned by impurities in the flue gas, or escape as vapor to cause environmental damage. These issues mean that electrochemical swing adsorption, an emerging CO 2 capture technology driven by electrochemistry, may have potential advantages. Supercapacitive swing adsorption (SSA) is a form of electrochemical swing CO 2 capture based on charging supercapacitors. One electrode of the supercapacitor is exposed to a CO 2 -containing gas and the other is completely soaked in electrolyte. When the supercapacitor is charged, CO 2 is selectively adsorbed from the gas (and released with discharging). The effect has primarily been studied with activated carbon electrodes and aqueous sodium chloride electrolyte, an affordable and environmentally-friendly model system. SSA systems, however, have limited CO 2 capacities compared to amine scrubbing, typically ~60 mmol of CO 2 per kg of adsorbent, 14 while amine scrubbing can reach ~800 mmol of CO 2 per kg of solvent. Performance has been improved by adding ion exchange membranes above the electrodes to increase the selectivity for the CO 2 -derived ions H + , HCO 3 -in the electric double layer. Little energy is wasted adsorbing electrolyte ions, so the membrane capacitive deionization approach is significantly more energy efficient. However, the added cost and complexity from the ion-exchange membranes is a drawback compared to the simple SSA approach. Besides low capacities, an additional challenge is the lack of fundamental understanding of electrochemical CO 2 capture by supercapacitors. To address these challenges, here we explore new charging proto-cols and experimental set-ups to obtain new insights into the mechanisms of supercapacitive swing adsorption. To monitor the electrochemical adsorption of CO 2 by supercapacitors we adopted an electrochemical cell equipped with a gas pressure sensor for monitoring gas uptake and release (Figure , also see Supplementary Information). Briefly, symmetric activated carbon-based supercapacitors (YP50-F carbon, Kuraray) with 1 M NaCl (aq.) electrolyte are housed in a gas-tight Swagelok cell assembly. The top electrode is directly in contact with a gas reservoir filled with pure CO 2 . As in previous work on SSA, we chose activated carbon electrodes as they have large capacitances, excellent electronic conductivities, and low cost. Our choice of YP50-F activated carbon, rather than the previously studied BPL activated carbon, was motivated by the higher capacitance of YP50-F in 1 M NaCl (aq.) electrolyte (see Figure ). Gas adsorption measurements showed that YP50-F is a microporous carbon with a BET surface area of 1690 m 2 g -1 (see Figure ). To date, the bulk of the SSA literature has focused on charging the supercapacitor with the negative electrode exposed to the gas, which we will term negative charging. We are only aware of one published experiment in which the positive electrode is exposed to the gas (positive charging). Therefore, we examined the effect of both negative and positive charging (representative data shown in Figure and the overall experiment in Figure ). Initial experiments with negative charging revealed reversible electrochemical adsorption (Figure ). As in the literature, we observed CO 2 adsorption when carrying out negative charging i.e. when the cell voltage is varied between 0 and -1 V, CO 2 is adsorbed by the supercapacitor. When discharging back to 0 V, the adsorbed CO 2 is released. In contrast to previous work , here we employed YP50-F activated carbon, demonstrating that electrochemical CO 2 adsorption by supercapacitors is not limited to the previously studied BPL activated carbon.