Investigation of bipolar plate and diffusion media interfacial structure in PEFCs: A fractal geometry approach

Abstract

The imperfect interfacial contact between the bipolar plate (BP) and the diffusion medium (DM) can have a significant impact on the multi-phase flow and current transport in an operating polymer electrolyte fuel cell (PEFC). The objective of this work is to describe the impact of the BP and DM surface morphologies and the resulting interfacial contact on PEFC performance. In this study, the surface morphology of several BP and DM samples was digitally characterized using optical profilometry (OP). The benchmark surface data were then utilized in a microscopic model developed to simulate the BP|DM interfacial contact under compression. The microscopic model is based on the fractal modeling approach, which provides an accurate representation of the BP|DM interfacial contact by suppressing the resolution dependence of the surface profiles in consideration. Results indicate that the uncompressed surface morphology of mating materials, elasticity of these components, and local compression pressure are the key parameters that influence the BP|DM contact. The model results show that the void space along the BP|DM interface can potentially store a significant amount of liquid water (from 0.85 to 3.5 mg/cm 2), which can result in reduced durability and performance of the PEFC. The model predicts that a 50% drop in the DM surface roughness results in nearly a 40% drop in the BP|DM contact resistance and a 15% drop in the BP|DM interfacial water storage capacity.