Abstract
Owing to the spatial orientations of carbon fibers, the porous electrodes of proton exchange membrane (PEM) fuel cells exhibit strong structural anisotropy, which affects the transport of species, ions, electrons, liquid water, and heat along the in-plane and through-plane directions. To capture the anisotropies of species transport, charge migration, and heat transport for PEM fuel cells operated at various loads, a two-phase flow, non-isothermal, computational fluid dynamics (CFD) model was developed and experimentally validated. Various anisotropic parameters were separately studied, and their contributions to the overall cell performance at different loads were compared. The results indicated the significance of anisotropic transport processes inside the electrodes, as the isotropic electrode properties overpredicted the cell performance. Among all the studied parameters, the anisotropies of the ion conductivity and gas diffusivity deserve careful consideration due to their significant impact on the cell performance, especially at high current densities. The anisotropies of the electrode permeability for gas transport and thermal conductivity can be neglected because of their limited effects on the cell performance. The anisotropy of the electrode permeability for liquid-water transport under a capillary mechanism had a considerable influence on the cell performance owing to its impact on the water saturation within the electrode. (C) 2018 Elsevier Ltd. All rights reserved.