Numerical investigation on the impact of anisotropic properties for porous transport layer in proton exchange membrane water electrolyzers

The anisotropic nature of the porous transport layer (PTL) significantly affects the performance of the proton exchange membrane water electrolyzer. This study develops a three-dimensional, two-phase, non-isothermal electrolyzer model that explicitly incorporates anisotropic effective properties (electrical conductivity, thermal conductivity, and permeability) of the PTL. Experimentally determined anisotropic coefficients for the anode PTL (APTL) are integrated into the model, and the accuracy of this model is validated by experimental data. A systematic comparison between anisotropic and isotropic models reveals significant discrepancies in polarization performance, thermal behavior, and mass transport characteristics under varied operating voltages, APTL thicknesses, porosities, and inlet flow velocities. The isotropic model underestimates current density by up to 3.69 % and oxygen mole fractions within the APTL by 6.45 % at 1.9 V. Compared to isotropic assumptions, the anisotropic model predicts elevated temperatures and sharper thermal gradients. Parametric analysis demonstrates that increased porosity and reduced thickness of APTL enhance reactant accessibility and product removal, lowering mass transport resistance and improving polarization performance. APTL thickness variations disproportionately affect discrepancies between isotropic and anisotropic predictions, while higher inlet flow velocities diminish the impact of PTL anisotropy on overall transport dynamics. These findings underscore the necessity of accounting for anisotropy in PTL design and modeling to optimize PEMWE efficiency and durability.