Computational modeling of inhomogeneities in the scale-up of industrial CO2 electrolyzers for formate production

CO₂ electroreduction (CO₂ER) offers a sustainable pathway for producing value-added chemicals from CO₂ using renewable electricity. Among its products, formate (HCOO⁻) is particularly attractive for energy storage and industrial applications. However, scaling CO₂ER systems from laboratory to industrial dimensions presents challenges including inhomogeneous reactant distribution, mass transport limitations, and local pH gradients. These effects are exacerbated at high current densities, leading to intensified CO₂ depletion and increased hydrogen evolution (HER). In this study, a validated 2D transient-state model is developed to investigate the impact of cell height, operating pressure, and electrolyte flow rate on formate production performance. Results show that shorter cells (4 cm) better maintain Faradaic efficiency by reducing HER and reactant depletion, whereas longer cells (40 cm) exhibit pronounced concentration gradients and non-uniform current densities. Operating at elevated pressures (5.5 atm) improves CO₂ solubility, limiting efficiency loss to 11 %, compared to 16 % at 1.5 atm under current densities of 150–400 mA cm⁻². These insights provide design and operation guidelines for optimizing industrial-scale CO₂ electrolyzers for efficient formate production.