Voxel-based modelling of water distribution in PEFC porous media

Abstract

The macro-homogenous approach for modelling proton exchange membrane fuel cells (PEFCs) strives for optimisation of the fuel cell and its components. Water management in the gas diffusion layer (GDL) plays a fundamental role in the overall predictive power of a PEFC model. In our work the 3D-microstructures of the different cell components are investigated with modern and complementary imaging techniques such as X-ray tomography (GDL), FIB-tomography (MPL) and BIB-SEM (cross-sections of layer compounds). Transport relevant morphological parameters (i.e. phase volume fraction, tortuosity, constrictivity) are analysed for materials in the dry and in wet state. To circumvent the lack of a significant length scale separation between the pore-scale and the GDL thickness, we implemented a stochastic model that treats the water evolution in porous media on the corresponding voxel-data from tomography. The analysis, is based on the minimisation of the surface free energy and leads to a statistical physics characterisation of the water-medium interaction through advanced Monte Carlo simulation techniques. In such way the effective properties (permeability, conductivity) can be linked with the mentioned microstructure parameters and are used as input for modeling of the cell performance on a macro-homogeneous scale