To understand the transport and reaction kinetics of reactive carbon species in BPMs, experimental polarization curves were taken in a 4-probe experimental cell for a BPM immersed in three electrolytes relevant to EMCC and DOC applications: 1 M KHCO3, 0.5 M KHCO3, and simulated seawater (0.00211 M NaHCO3 + 0.5 M NaCl). Simulations of the BPM under polarization in these varying electrolytes were run and the simulated polarization curves were compared to the experimentally measured polarization curves (Figure , markers). Strong agreement between theory and experiments is observed in all three carbon-containing electrolytes for a single set of fitting parameters (Table ). Remarkably, the simulation can even capture the incredibly non-intuitive polarization behavior occurring at current densities < 20 mA cm -2 (Figure ). For these current densities, there is an initial onset in current density at ~0.4 V of applied membrane potential for both the 0.5 M KHCO3 and 1 M KHCO3 BPMs. The current density of these BPMs increases approximately linearly until ~0.7 V when the current density takes off exponentially. Conversely, for the seawater BPM, the current density does not have an initial takeoff at 0.4 V, so between 0.4 and 0.8 V the seawater BPM drives less current density than the KHCO3 BPMs. However, past the second onset at ~0.7 V, the current generated in the seawater BPM exceeds that of the KHCO3 BPMs. Notably, the initial linear takeoff of the KHCO3 BPMs at 0.4 V of membrane potential, along with the intriguing intersection and crossover between the seawater and (bi)carbonate polarization curves at ~0.75 V, represent heretofore unexplained phenomena that the model is capable of replicating with high accuracy. To uncover the origin behind these phenomena and deconvolute the individual contributions to the polarization curves of BPMs in reactive carbon solutions, the rates of the individual contributions to current density were calculated within the CL of the BPM. Within the CL, the current density must either be due to the crossover of unreactive co-ions (K + , Na + , or Cl -), or to the presence of electric-field-enhanced, net-charge-generating dissociation reactions. These contributions to the overall polarization curve are determined and shown in Figure and for BPMs operating in 1 M KHCO3 and simulated seawater, respectively. As expected, the current density for the simulated seawater case is primarily driven by salt crossover at low potentials and water dissociation at high potentials, as shown in previous literature. The 1 M KHCO3 case, however, is more intriguing. While previous studies have suggested that the low applied potential current onset for BPMs in weak buffer electrolytes is entirely driven by titration currents resulting from dissociation of the weak acid buffer (i.e., the HCO3 -anion in this case) in the CL, the model suggests that current density in the initial linear feature is still primarily dominated by field-enhanced water dissociation. Field-enhanced dissociation of the buffering anion accounts for up to 50% of the observed current density. Therefore, the model suggests that the use of 1 M KHCO3 buffer electrolytes forces an early onset of the electric-field-enhanced water-dissociation reaction.