A Numerical Study of Structural Change and Anisotropic Permeability in Compressed Carbon Cloth Polymer Electrolyte Fuel Cell Gas Diffusion Layers

Abstract

The effect of compression on the actual structure and transport properties of the carbon cloth gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC) are studied here. Structural features of GDL samples compressed in the 0.0–100.0 MPa range are encapsulated using polydimethylsiloxane (PDMS) and by employing X‐ray micro‐tomography to reconstruct direct digital 3D models. Pore size distribution (PSD) and porosity data are acquired directly from these models while permeability, degree of anisotropy and tortuosity are determined through lattice Boltzmann (LB) numerical modelling. The structural models reveal that structural change proceeds through a three‐step process, while PSD data suggests a characteristic peak in the pore diameter of 10–14 μm and a decrease in the mean pore diameter from 33 to 12 μm over the range of tested pressures. A mathematical relationship between compression pressure and permeability is determined based on the Kozeny–Carman equation, revealing a one order of magnitude reduction in through‐plane permeability for a two order of magnitude increase in pressure. The results also reveal that the degree of anisotropy peaks in the range of 0.3–10.0 MPa, suggesting that in‐plane permeability can be maximised relative to through‐plane permeability within a material‐specific range of compression pressures.

3D analysis, modeling and simulation of transport processes in compressed fibrous microstructures, using the Lattice Boltzmann method

“…Ostadi, Rama et al investigated in LB simulations on GDL structures which were obtained from nano-computed tomography. They characterized the structure according to geometric characteristics, anisotropy and effects of compression [41,42,21,43,44,45,46]. As in the macrohomogeneous approaches mentioned before also the simulations on the reconstructed microstructure show the evidence of the non-isotropic transport properties on the behavior of the mass transport on higher spatial scales.…”

Effect of compression on the water management of polymer electrolyte fuel cells: An in-operando neutron radiography study

“…Their investigations show that doubling the anode GDL thickness with the increase in interior porosity (similar to the lower compression ratio) allows more liquid water transport through the membrane and out of the anode. Xray micro-tomography has been combined with Lattice Boltzmann numerical modelling [16] to analyse the pore-scale water transport behaviour under different compression levels. They suggested that the internal pressure exerted on the carbon cloth GDL should be within 0.3-10.0 MPa to achieve the optimum transport properties of a PEFC.…”

Effects of Compression on the Removal of Water Droplet from GDLs of PEM Fuel Cells

“…Therefore, porous electrodes of PEMFC, especially their gas diffusion layers (GDLs), are practically under compression and deformation. . GDL, which is made from porous materials like carbon paper, plays a key role in a PEMFC performance via providing mass transfer and conductivity for the CL .…”