Determination of Material Properties of Gas Diffusion Layers: Experiments and Simulations Using Phase Contrast Tomographic Microscopy

Abstract

Understanding the transport properties of porous materials plays an important role in the development and optimization of polymer electrolyte fuel cells (PEFCs). In this study numerical simulations of different transport properties are compared and validated with data obtained using recently developed experimental techniques. The study is based on a Toray TGP-H-060 carbon paper, a common gas diffusion layer (GDL) material in PEFC. Diffusivity, permeability, and electric conductivity of the anisotropic, porous material are measured experimentally under various levels of compression. A sample of the GDL is imaged with synchrotron-based X-ray tomography under three different compression levels. Based on these three-dimensional images, diffusivity, permeability, and conductivity are calculated numerically. Experimental and numerical results agree in general. Deviations are observed for the through-plane conductivity. An explanation for the discrepancy is presented and affirmed by numerical simulations on a virtually created structure model. This proves that numerical simulation based on tomography data is a versatile tool for the investigation and development of porous structures used in PEFCs.

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

“…10. Table 8 This is conform to the simulations results from Becker et al [68]. They measured the permeability of Toray GDLs through-plane and in-plane.…”

Microstructure-property relationships in a gas diffusion layer (GDL) for Polymer Electrolyte Fuel Cells, Part I: effect of compression and anisotropy of dry GDL

“…There is an agreement that for many GDL materials the in-plane diffusivity in dry GDL is higher than the through-plane diffusivity (see e.g. [5,9,26]). However it is poorly understood which microstructure characteristics are responsible for this anisotropy.…”

“…In contrast to the gas diffusivity, the experimental evidence for the anisotropy of permeability is controversial. Some groups presented evidence for higher inplane permeability [26,27], whereas others argued for higher permeability in the through-plane direction [14], which they explained with smaller bottleneck dimensions in the in-plane direction. At this stage it is not clear why for example the narrow in-plane bottlenecks should only limit in-plane permeability and why they would not also limit the in-plane diffusivity?…”

“…In addition, we will also investigate microstructure effects controlling the electrical conductivity in the solid phases (fibers and binder), which is usually described to be higher for in-plane than for through-plane direction (e.g. [26,28]). …”

Computation of Thermal Conductivity of Gas Diffusion Layers of PEM Fuel Cells

“…A carbon cloth is shown as sample X-ray computed tomography (Ostadi et al, 2008;Pfrang et al, 2010) as well as synchrotron based tomography (Becker et al, 2008;Becker et al, 2009) have been used for imaging of gas diffusion layers at resolutions below 1 µm. Also membranes and membrane electrode assemblies (Garzon et al, 2007;Pfrang et al, 2011) have been imaged by X-ray computed tomography and even functioning fuel cells have been imaged by synchrotron-based methods and soft X-ray radiography e.g.…”