Investigating Liquid Water Transport in Different Pore Structure of Gas Diffusion Layers for PEMFC Using Lattice Boltzmann Method

Abstract

Proton exchange membrane fuel cells (PEMFC) require a gas diffusion layer (GDL) and micro porous layer (MPL) to aid in the transport of liquid fuel to the catalyst layer. The GDL needs to remain saturated to assist in the chemical reaction at the catalyst layer. The mass transport through the gas diffusion media is essential to the operation of the PEMFC system. Previously, to observe the liquid flow through gas diffusion media, X-ray CT scans were used. X-ray CT scans have limitations in the resolution capability. When applying a microporous layer to a GDL sample, X-ray CT’s have difficulties capturing the saturation at the micro scale level. In this work, direct modeling using the Lattice Boltzmann Method (LBM) [1-3] was applied to micro X-ray CT scans of commercial carbon paper gas diffusion media geometries. The LBM, combined with computational fluid dynamic modeling techniques, can accurately predict liquid saturation at the macro and micro scale, which provides more insight into the mass transport phenomena through the GDL. Three injection cases, seen in Figure 1, were investigated using different samples. The rib and channel wall boundary were created to represent the effect of the flow-field area inside the PEMFC. Liquid water flow through samples with and without MPL’s were studied. The primary focus of this work is to understand the transport of liquid water through the gas diffusion media, determine which injection case results in the most liquid saturation, and if the addition of an MPL increases or decreases saturation levels inside the GDL. Figure 2 shows an example of the predictions of water evolution inside sample EP40-T, without the addition of a MPL. The sample was ran at all three injection cases. When comparing each case, a dual injection point with a land and channel orientation, case 3, resulted in the most liquid present inside the sample. This work will be extended to include the effect of non-uniform wettability of GDL on water transport and saturation.