to compare the associated energy penalty to the overall cell voltage as the number of BPMs in the stack is increased. to form H + and OH -. The H + react with HCO3 -in the catholyte to form CO2. Once the in situ generated CO2 has exceeded its solubility limit in the catholyte, it exits the aqueous phase in the form of bubbles. OH -from water dissociation reacts with HCO3 -absorbed in the AEL to form CO3 2-that transports back into the anolyte. Spectator co-ions from the anolyte or catholyte can cross through the membrane to reduce the developed pH gradient.