Carbon dioxide is a major greenhouse gas causing climate change and global warming. About 80% of the anthropogenic CO2 emissions stem from the burning of fossil fuels (coal, petroleum, and natural gas). Currently, ca. 40 Gtons of CO2 are emitted into the atmosphere annually. Therefore, there is a significant interest in developing carbon-capture technologies to separate CO2 from flue gases, and from air. To make a significant impact on climate change, carbon capture will likely need to be applied at the gigaton scale, placing extreme demands on the scalability of a carbon capture technology. The most mature CO2 capture technologies use aqueous amine solutions. Amines are suitable to react with CO2 in low concentrations and have a high selectivity for CO2. However, the reverse process of CO2 release is energy-intensive due to the strong chemical bonds (C-N bonds) formed during the capture process. In addition, aqueous amine solutions are corrosive, volatile, toxic, and sensitive toward oxidation and SOx/NOx contaminants in flue gas. Pressure swing adsorption (PSA) and thermal swing adsorption (TSA) are intensively investigated as alternatives to liquid amine solutions. They use the changes in either pressure or temperature to adsorb and release CO2 from a solid sorbent. Among solid sorbents for TSA and PSA, physisorbents are not very selective, and prone to preferred water adsorption. Chemisorbing, grafted amines have similar selectivity as liquid amines, but tend to degrade relatively easily, and the desorption step is energy-intensive. Electrochemical techniques have recently emerged as alternatives to pressure and temperature-swing processes. However, many of them use quite complicated cell architectures that are difficult to scale. Frequently, expensive materials such as bipolar membranes, ion-exchange membranes, carbon nanotubes, ionic liquid electrolytes, and specialty polymers are used raising concerns about capital cost. Some electrochemical techniques, e.g. EMAR, also employ amines which have the above-mentioned limitations. Most electrochemical capture techniques involve redox-processes which tend to have limited cycle life, and slow kinetics. Some, for example sea water electrolysis, produce toxic and corrosive by-products, such as chlorine gas, and currently require expensive noble metal catalysts to overcome overpotentials. While scaling concepts for electrochemical devices such as batteries and fuel cells are well explored, scaling concepts for electrochemical carbon capture techniques have been very little investigated thus far. Only very recently, Hemmatifar et al. demonstrated a scalable direct air capture module with stackable redox-cells using quinone-and ferrocenecontaining polymers on carbon nanotube/carbon paper supports as electrodes, ionic liquids as electrolyte, and nickel foam as gas conduit. Supercapacitive swing adsorption (SSA) is an electrostatic carbon capture technique that our research group is currently developing. In SSA, selective and reversible adsorption and desorption of carbon dioxide is achieved by supercapacitive charge and discharge of activated carbon electrodes. In comparison to other electrochemical carbon capture techniques, it is very simple, and requires only inexpensive, little toxic, and robust materials. SSA can be performed in modules with two activated carbon electrodes separated by a cellulose-based separator containing an aqueous electrolyte, for example NaCl, NaHCO3, or MgBr2 (Figure ). In the modules, the negative electrode is interfaced with a carbon cloth that acts as a gas conduit. During the capacitive charging of the electrodes to a potential of typically 1V, the CO2-containing gas mixture is streamed through the carbon cloth, and diffuses into the electrodes, where CO2 is selectively adsorbed. The adsorption is easily reversed by discharging the electrodes, releasing the CO2 back into the gas phase. Because capacitive charge and discharge is known to be achievable at a high energy round-trip efficiency, SSA has the potential to separate CO2 at a low energy consumption. Supercapacitors are known to have cycle times greater than 100,000 cycles suggesting that SSA may have a similar cycle life leading to low annualized capital and maintenance cost. In our earlier work, we used BPL 4x6 activated carbon and 1M aqueous NaCl as electrolyte in single cell SSA modules with one electrode pair leading to a sorption capacity of ~60 mmol/kg at an energy penalty of ~200 kJ/mol at a cell voltage of 1V using 15%CO2/85%N2 as a flue gas simulant. The adsorption is extremely selective for CO2 over N2 (N2 is even slightly repelled from the electrodes upon charging), which is explained by the ionic liquid-solid adsorption mechanism described further below. The performance was later improved by the use of garlic root-derived activated carbon which enhanced the adsorption capacity to ~300 mmol/kg and improved the energy consumption to ~70 kJ/mol at 1V. Cell voltage increase to 1.4 V further improved the sorption capacity to ~500 mmol/kg at an energy consumption of ~150 kJ/mol. The cycles were highly repeatable and reversible in tests lasting up to 130 h. The adsorption in SSA is believed to occur through three possible mechanisms, the ionic liquidsolid mechanism, the molecular liquid-solid mechanism, and the molecular gas-solid mechanism. In the ionic liquid-solid mechanism, the CO2 hydrolyzes in the aqueous electrolyte inside the activated carbon pores and adsorbs to the pore surfaces of the positive and negative electrode electrostatically in form of bicarbonate/carbonate anions, and protons, respectively. This mechanism is highly selective for CO2 over N2 O2, and Ar because these gases do not hydrolyze to form ions in aqueous solution. In the molecular liquid-solid mechanism, molecular CO2 inserts into the double layer formed at the electrodes due to a different solubility of CO2 in the double layer compared to the free solution. In the molecular gas-solid mechanism, molecular CO2 adsorbs to pores that are not infiltrated by the electrolyte. These pores exist because not all carbon pores are hydrophilic enough to allow for electrolyte infiltration. We have recently shown by contrastmatched neutron scattering that only about 20% of the pore volume in activated carbon BPL Carbon 4x6 is actually infiltrated by a 1M NaCl aqueous electrolyte. A quantitative analysis of these mechanisms will be subject of future research.