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

Abstract

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: w.lehnert@fz-juelich.de; Electrochemical society active member

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

“…This is also an extreme case -it is expected to be far away from real GDL structures of paper type [52,56]. In table 7 the deviation of the 50 % compressed binder type D simulations from the KozenyCarman trend is significantly lower than for the other cases.…”

“…The remaining solid material to be inserted for achieving the known porosity of 78 % is filled with binder. For this purpose randomly chosen pores built from fibers in a plane are filled with binder material according to Thiedmann's binder model [52,53] until the desired porosity is reached. The binder is dilated in z direction up to the thickness of the fiber layer.…”

“…The stochastic fiber model was developed further by Thiedmann et al [51,52,53]. An important feature of the planar approach is the assumption of isotropy in z direction and the validation of their model against 3D tomographic data.…”

“…Its geometry was generated by the 3D stochastic model from Thiedmann et al [51] with their extended binder model [52,53]. The chosen geometry model is favorable for virtual material design because of its planar oriented structure which is nevertheless validated against 3D data.…”

“…First, Hao and Cheng created their virtual geometry from the Schladitz model [49] whereas our approach is based on the model from Thiedmann [51] and its extension regarding the binder [52,53].…”