Local Structural Characteristics of Pore Space in GDLs of PEM Fuel Cells Based on Geometric 3D Graphs

Physical properties affecting transport processes inside the gas diffusion layer (GDL) in fuel cells mainly depend on the microscopic structure of its pore space. The presented characterization of the pore space is based on geometric 3D graphs, representing the complex microscopic structure. This description of the open volume contains the essential information on the geometrical structure of the pore space such as its connectivity. Additionally, the geometric structure of the graph, i.e., its vertices and edges, can be marked to display transport related properties such as pore diameters and pore necks. This 3D graph representation allows for an investigation of the local structural characteristics of the GDL by considering local tortuosity characteristics, pore sizes, and connectivity characteristics, respectively. The notion of a local shortest path length through the pore space of the GDL is introduced and the probability distribution of this random variable is computed. Its mean value is related to the (physical) tortuosity which is given by the ∗Corresponding author: [email protected]; Electrochemical society active member Institute of Stochastics, Ulm University, 89069 Ulm, Germany Zentrum für Sonnenenergie– und Wasserstoff–Forschung Baden–Württemberg, 89081 Ulm, Germany present address: BASF Fuel Cell GmbH, 65926 Frankfurt/Main, Germany Helmholtz-Zentrum Berlin für Energie und Materialien, 14109 Berlin, Germany Forschungszentrum Jülich GmbH, 52425 Jülich, Germany