i.e. the system is mass transport limited (SI Figure ). With a charging time of ~5-20 min there is little CO2 flux going from the gas chamber into the gas-exposed electrode once the cell voltage is at its minimal value of -0.4V (SI Figure ), showing that the adsorption is near its maximum as we indeed see in Figure . For the long charging time of 130 minutes there is now instead CO2 flux going into the gas chamber from the gas-exposed electrode, originating from the electrode that is not exposed to the gas (SI Figure ). This reversibility is a delayed response to the increase in CO2 concentrations in the bottom electrode, thereby counteracting the initial adsorption, as we indeed hypothesised for the thermodynamic regime. However, quantitatively there are some differences between the model and experiments (Figure ). This can possibly be explained by the coarse minimalistic features of the model, which do not emulate the full detail of the device and only incorporates continuum transport of ionic and chemical species with one possible chemical reaction, thereby foregoing any other possible physical mechanism that might also be at play here.