Oxygen-assisted supercapacitive swing adsorption of carbon dioxide

We report on the supercapacitive swing adsorption (SSA) of carbon dioxide at different voltage windows in the presence of oxygen using activated carbon electrodes, and deliquescent, aqueous electrolytes. The presence of O₂ in the CO₂/N₂ gas mixture results in an up to 11 times higher CO₂ adsorption capacity with 3 M MgBr₂ (at 0.6 V) and up to 4–5 times higher adsorption capacity with 3 M MgCl₂ (at 1 V). A tradeoff between high CO₂ adsorption capacities and lower coulombic efficiencies was observed at voltages above 0.6 V. The energetic and adsorptive performance of the electrodes in the presence of oxygen below 0.5 V was similar to the performance with a CO₂/N₂ mixture without oxygen at 1 V. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the electrodes demonstrate that the specific capacitance increases while the diffusion resistance decreases in the presence of oxygen. Oxygen concentrations ranging between 5–20 % give similar energetic and adsorptive performance. The electrodes exhibit stable performance for up to 100 cycles of operation.