Pore-scale study of water and mass transport characteristic in anion exchange membrane fuel cells with anisotropic gas diffusion layer

Abstract

The complicated microporous structure and spatial distribution characteristics of the gas diffusion layer have crucial impacts on the water management of an anion-exchange membrane fuel cell, in which water is produced at the anode and consumed at the cathode. Consequently, a three-dimensional pore network model is developed to numerically simulate hydrogen transport and liquid water removal in the anode gas diffusion layer. Anisotropy is an important property of the gas diffusion layer, and the quasi-static two-phase transport within the anisotropic GDL is investigated from various perspectives. Pore-scale simulations demonstrate that the variation of the relative diffusion coefficient with saturation can be described as g(S)= (1-S)2.3, and the relative permeability varies with saturation in the range of S1.5 and S3. What's more, high anisotropy has a positive effect on both hydrogen and liquid water transport, if the anisotropy parameter is increased from 1 to 1.55, the relative diffusion coefficient and water permeability at all thicknesses are increased by more than 11% and 16%, respectively. However, in practice, high anisotropy is detrimental to the liquid water removal under the rib. Moreover, wettability distribution has a negligible effect on two-phase transport within the highly anisotropic GDL, while the effect of thickness remains significant.