Mass transport of different species plays a crucial role in electrochemical conversion of CO (Formula presented.) due to the solubility limit of CO (Formula presented.) in aqueous electrolytes. In this study, we investigate the transport of CO (Formula presented.) and other ionic species through the electrolyte and the membrane, and its impact on the scale-up process of HCOO (Formula presented.) /HCOOH formation. The mass transport of ions to the electrode and the membrane is modelled at constant current density. The mass transport limitations of CO (Formula presented.) on the formation of HCOO (Formula presented.) /HCOOH is investigated at different pressures ranges from 5–40 bar. The maximum achievable partial current density of formate/formic acid is increased with increasing CO (Formula presented.) pressure. We use an ion exchange membrane model to understand the ion transport behaviour for both the monopolar and bipolar membranes. The cation exchange (CEM) and anion exchange membrane (AEM) model show that ion transport is limited by the electrolyte salt concentrations. For 0.1 M KHCO (Formula presented.), the AEM reaches the limiting current density more quickly than the CEM. For the BPM model, ion transport across the diffusion layer on either side of the BPM is also included to understand the concentration polarization across the BPM. The model revealed that the polarization losses across the bipolar membrane depend on the pH of the electrolyte used for the CO (Formula presented.) reduction reaction (CO ₂RR). The polarization loss on the anolyte side decreases with an increasing pH, while, on the cathode side, it increases with increasing catholyte pH. With this combined model for the electrode reactions and the membrane transport, we are able to account for the various factors influencing the polarization losses in the CO (Formula presented.) electrolyzer. To complete the analysis, we simulated the full cell polarization curve and fitted with the experimental data.