The simulations demonstrate that the accelerated current onset for KHCO3-exchanged BPMs is largely due to a reduction in the rate of interfacial recombination due to reaction of waterdissociation-generated OH -with HCO3 -to form CO3 via what is essentially an indirect HCO3 - dissociation pathway (water dissociation followed by bicarbonate to carbonate interconversion), and that the eventual increase of the seawater current density beyond the KHCO3 current densities is due to the seawater BPM possessing a larger electric field at a given membrane potential (see Section S6 for more detail regarding the reasoning for the observed curvature of the BPM polarization curves in these carbon containing electrolytes).