Virtual Material Design of PEM Fuel Cell Layers.

Jürgen Becker, Andreas Wiegmann
Fraunhofer ITWM, Kaiserslautern, Germany


Abstract  

The membrane electrode assembly (MEA) of a PEM fuel cell usually consists of 5 
layers: cathode gas diffusion layer (GDL), cathode catalyst layer, membrane, 
anode catalyst layer and anode GDL.  Additionally, a micro-porous layer (MPL) 
may be added between GDL and catalyst layer.
Improving the performance of the cell is possible by improving the cell as a 
whole, and also by optimizing each of the layers to its requirements.  On the 
one hand, one should choose the material with the best chemical properties.  
On the other hand, as material connectivity and pore morphology have a major 
impact on the properties of porous media, improving the microstructure of each 
layer is equally important.  Finding the best microstructure experimentally is 
often too costly or not possible, because any change would require changes in 
the production process.  Computer simulations help to determine the effective 
material properties of a layer without the need to produce it first.
Therefore, in this talk we will present methods to create micro-structural models 
of catalyst layer, MPL and GDL.  Using these models, one can predict effective 
properties of the layers, e.g. permeability, diffusivity, electric conductivity 
and thermal conductivity.  This is done by solving the appropriate partial differential 
equations on the micro-structural model.  E.g. the Stokes equation needs to be 
solved in order to obtain the effective permeability of the layer.  
This approach allows comparing various structural designs.
To validate the approach, we also compare experimentally measured GDL properties 
with numerically determined properties.  For this purpose, a tomography image of 
the GDL is used as model to ensure micro-structural similarity between 
experiment and simulation.