A parametric study of the effect of wetting and in proton exchange membrane (PFM) fuel cells morphological properties of the cathode porous transport layer (PTL), also known as the gas diffusion layer (GDL), on water transport in proton exchange membrane (PEM) fuel cells has been conducted using a two-dimensional network model that captures the two-phase capillary flow behavior. The effect of PTL wetting properties is explored by considering four contact angle values. The effect of the morphology is analyzed using six pore size distributions. These six pore size distributions are generated by varying the scale and shape parameters in Weibull probability distribution functions. Also, the effect of a microporous layer (MPL) on water transport in the PTL is considered. Inclusion of the MPL resulted in a significant increase in the percolation pressure and a reduction in the PTL water content due to the formation of a few localized fingers which serve as water conduits. When defects in the MPL were considered, the PTL water content remained low with percolation pressures reduced to values similar to a PTL without an MPL.

No abstract

Three novel iterative methodologies for coupling continuum and pore-network models (PNM) applied to polymer-electrolyte fuel cells (PEFCs) are presented. The modeling framework developed in this work merges the advantages of a continuum model, such as computational time, ease of implementation, and complicated physics, with those of relatively novel PNMs, such as discrete information on waterfront location and distribution. The outputs generated by the PNM are fed into the continuum model to compute electrochemical reaction rates and associated heat and mass fluxes. Out of three presented coupling methodologies, the most effective coupling is identified to be where locallyresolved effective diffusivity, thermal conductivity, and liquid permeability are computed with the PNM and fed into the continuum model and the fluxes from continuum model fed back into the PNM in an iterative scheme until solution convergence is reached. The described method is computationally efficient with stable convergence of less than five iterations. The proposed algorithms can be applied to multiple computational platforms and PEFC and related model architectures.

Water management remains a critical issue for polymer electrolyte fuel cell performance and durability, especially at lower temperatures and with ultrathin electrodes. To understand and explain experimental observations better, water transport in gas diffusion layers (GDLs) with macroscopically heterogeneous morphologies was simulated using a novel coupling of continuum and pore-network models. X-ray computed tomography was used to extract GDL material parameters for use in the pore-network model. The simulations were conducted to explain experimental observations associated with stacking of anode GDLs, where stacking of the anode GDLs increased the limiting current density. Through imaging, it is shown that the stacked anode GDL exhibited an interfacial region of high porosity. The coupled model shows that this morphology allowed more efficient water movement through the anode and higher temperatures at the cathode compared to the single GDL case. As a result, the cathode exhibited less flooding and hence better low temperature performance with the stacked anode GDL.

No abstract