Our model supports that SSA is at least partially driven by the accumulation or depletion of bicarbonate ions in the electrodes upon charging. When the gas-exposed electrode is the positive electrode (positive charging mode), then this leads to an overaccumulation of CO2 in that electrode, and CO2 release occurs. In contrast, when the gas-exposed electrode is the negative electrode (negative charging mode), depletion of bicarbonate and therefore CO2 sets up a driving force for CO2 capture. However, the model is not a full simulation of the experimental device, but rather a coarse representation that features considerable simplifications with respect to the actual device's features, and only incorporates continuum transport equations and the CO2-bicarbonate reaction.