Multiphysics Modeling of Coupled Multiphase Transport and Electrocatalysis in Industrial Zero-Gap Alkaline Water Electrolyzers: Cell Size and Flow Field Effects

Large-scale alkaline water electrolysis (AWE) is essential for green hydrogen production, yet coupled multiphysics transport in industrial-scale cells remains insufficiently understood. A multiphysics model is developed for zero-gap AWE cells with different diameters. The anisotropic permeabilities of support meshes are determined via pore-scale simulations and incorporated into a REV-scale model coupling two-phase flow, species transport, electrochemistry, and heat transfer. The model is validated against a 5 MW commercial system with a mean relative error below 3%. The anode support mesh exhibits non-negligible permeability anisotropy. Under identical current density and flow coefficient, larger-diameter cells show higher electrochemical efficiency due to enhanced bubble removal. Increasing flow rate reduces gas blockage and improves two-phase uniformity, but with diminishing returns for large cells. For single-inlet/single-outlet configurations, varying flow rate alone cannot improve concentration and temperature uniformity. The multi-inlet design reduces top gas accumulation when the primary-to-secondary flow ratio is controlled; excessive secondary flow deteriorates uniformity. The multi-outlet design moderately improves gas removal but significantly enhances concentration and temperature uniformity, reducing dissolved hydrogen accumulation and improving safety. These flow-field optimizations are expected to help mitigate bubble-induced active-site loss and reduce local overpotential, thereby benefiting HER/OER catalyst performance. These findings support scale-up design and flow-field optimization of industrial AWE cells.