Carbon-dioxide (CO2) emissions account for 76% of total greenhouse-gas emissions and are currently 50% higher than pre-industrial levels. As a result, temperatures are expected to rise at least 2°C unless CO2 is captured and removed from the atmosphere. Traditional direct-aircapture technologies (DAC), use alkaline aqueous sorbents (e.g., KOH(aq)) to capture ambient CO2 as mixtures of (bi)carbonates, which are thermally-decomposed into a pure CO2 gas stream for permanent removal (Figure ). Unfortunately, this technology is energy intensive and expensive, largely because of the significant thermal energy penalty (>150 kJ mol -1 ) required to regenerate the sorbent after it has captured CO2 (Figure ). This thermal energy is often provided by burning natural gas, which results in CO2 emissions that reduce the net amount of CO2 removed from the atmosphere by DAC. Electrochemically-mediated carbon capture (EMCC) can address the challenges associated with thermal sorbent regeneration by using low-cost renewable electricity to trigger the capture and release of CO2 from the sorbent. The low-temperature nature of EMCC also circumvents the thermal efficiency limits associated with desorbing CO2 at high-temperature in fired reboilers and calciners. Many chemistries have been explored for EMCC, such as nucleophilic sorbents that can absorb or desorb CO2 when oxidized or reduced at an electrode surface and amine-based sorbents that capture CO2 homogeneously and release that CO2 upon the reaction with cupric (Cu 2+ ) ions generated via electrochemical redox. However, these specific EMCC technologies have not been demonstrated at current densities beyond 5 mA cm -2 , necessitating large, costly reactors or long residence times. Bipolar-membrane electrodialysis (BPM-ED) is a promising EMCC technology that uses water dissociation to mediate CO2 capture and sorbent regeneration at relevant current densities (i.e., >100 mA cm -2 ; Figure ). At the heart of this technology is a BPM, which consists of anion-and cation-exchange layers (AEL and CEL) that are laminated together often with a catalyst layer (CL) at the interface. Under a reverse bias, the strong electric field formed at the interface of the oppositely-charged AEL and CEL layers drives water dissociation into acid (H + ) and base (OH -) (Eq. ( )). The acid produced in the CEL is used to shift the bicarbonate and carbonate equilibrium (Eq. ( )-( )) towards CO2, and the base produced in the AEL is used to regenerate the alkalinity of the carbonate sorbent. A key advantage of BPM-ED is the use of water as the reactant, which enables higher current densities than other EMCC technologies because of the high concentration of water (55 M) in aqueous CO2 capture solutions. Notwithstanding, the energy intensity of BPM-ED typically exceeds 300 kJ mol -1 because of the water dissociation overpotential and ohmic resistances in the BPM. Further optimization is therefore required for BPM-ED to become more efficient than thermal CO2 sorbent regeneration. BPM-ED is also capable of removing CO2 from seawater at current densities exceeding 50 mA cm -2 (Figure ), i.e., direct ocean capture (DOC). By using seawater as the sorbent, instead of a concentrated bicarbonate solution, the natural process of CO2 absorption and conversion into bicarbonates is leverged and obviates the need for a Capex-intensive air contactor. In the DOC configuration, the OH -transported from the AEL can be reacted with dissolved bicarbonates in the seawater to form a mineralized carbonate stream that can be precipitated and sequestered, or fed back into the ocean to help reverse the effects of ocean acidification. CO2 that is formed by BPM-ED can be collected outside the device for conversion or storage elsewhere, or directly transported to a CO2 reduction catalyst within the same device for direct conversion. The challenge with BPM-ED is that the energy intensities reported in the literature (300 to 1000 kJ mol -1 CO2) are significantly higher than the minimum thermodynamic energy required to separate CO2 from air (20 kJ mol -1 ). Unfortunately, while the mechanism of in-situ CO2 capture and sorbent regeneration via BPM-ED has been well established experimentally, very few theoretical studies have simulated BPMs immersed in carbon-containing solutions to resolve the dominant energy losses. Sabatino et al. developed process-level simulations to show the critical role BPM performance has on the energy intensity and overall technoeconomic feasibility of BPM-ED EMCC. However, the simulations treated the BPM as a black-box, with no information provided regarding ionic transport, water dissociation kinetics, or the material properties of the BPM that would be required to achieve the necessary performance enhancements. Lees et al. and Kas et al. have helped to resolve the mechanism of in-situ CO2 generation in BPM-based electrolyzers that convert (bi)carbonate capture solutions to carbon monoxide, or methane. However, these models only considered the CEL of the BPM, ignoring the AEL and the water dissociation CL where protons and hydroxide are generated. This simplification renders the models incapable of predicting the primary factors influencing the energy intensity of BPM-ED: carbon crossover, water dissociation overpotential, and ohmic loss. There is also little precedent for modeling the transport of dilute carbon species in seawater feedstocks used for DOC. Models that relate the chemistry and material properties of BPMs to the energy intensity of BPM-ED are therefore warranted. In this work, we demonstrate a comprehensive model of BPM-ED based on our prior work modeling multi-component transport in BPMs, now with the homogeneous reaction kinetics of reactive carbon species (Eq. ( )-( )). The model is validated by comparison with experimental data for various carbon-containing solutions, and is used to elucidate the nature of in-situ CO2 generation and sorbent regeneration in BPMs employed for EMCC. Additionally, concentration profiles and fluxes of all carbon species, protons, and hydroxide anions are resolved such that performance tradeoffs between CO2 generation and carbon crossover can be explored. Lastly, sensitivity analysis provides improved understanding of ideal BPM and system properties to enhance CO2 capture efficiency, setting the stage for BPMs optimized for carbon capture processes.