The renewed popularity of research in fuel cells relies on several interesting and fundamental points that remains to be clarified, with each design providing different challenges in model development. For polymer electrolyte fuel cells (PEFC), some of the most currently studied aspects concerns the liquid water dynamics and electrocatalytic activity for the oxygen reduction reaction. For such aspects, an impressive amount of data and models have been published. For less popular aspects, on the other hand, a lack of proper investigation and difficulty to obtain reliable data has led to assumptions regarding the physical effects and mathematical formulation used in present computational models. One example is reactant transport in PEFC porous layers, which was largely assumed to be diffusion-controlled, and is currently broadly modeled using Darcy's law, despite a lack of proper evidence of its validity. Using recent experimental data on reactant transport in commonly used PEFC porous layers for validation, a finite elements model is used to show that Darcy's law is inappropriate to reproduce the convective transport of reactants in these porous media, showing qualitative and quantitative discrepancies, as evidenced in the Figure. On the other hand, the broader Darcy-Brinkman formulation, where Darcy's law represents the low porosity limit, is shown to accurately reproduce the experimental data. The results points to the need for improved models to correctly treat the convective reactant transport in the gas-diffusion layer, and, more importantly, evidences the role of convection in reactant distribution in the porous media.

Comparison between Darcy's law and Darcy-Brinkman formulation for reactant transport in PEFC porous media

251st National Meeting (2016)

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