The validated model was employed to resolve local concentrations and microenvironments within BPMs exchanged with the aqueous reactive carbon solutions. The simulated concentration profiles of HCO3 -, CO3 2-, CO2, and H + within a BPM exchanged with 1 M KHCO3 at applied potentials of 0 V, 0.2 V, 0.5 V, and 1.0 V, are shown in Figure . Concentration profiles for OH -as well as local pH can be found in Figure -15. At equilibrium (0 V), both electrolyte boundary layers are fixed at their equilibrium concentrations for all species. Furthermore, within the BPM, there are no concentration gradients, and the concentrations are consistent with those determined by Donnan equilibrium with the interstitial pore volume. Because of Donnan equilibrium with the catholyte, the CEL is fully exchanged with K + cations (Figure -17), and the AEL is fully exchanged with (bi)carbonates. Therefore, the pH in the CEL at equilibrium is near neutral, and that in the AEL is alkaline (~pH 9) (Figure ).