A fuel cell diffusion layer providing a preferential path by which liquid reactants
or byproducts may be supplied to or removed from a direct oxidation fuel cell is
described. The modified diffusion layer will be typically on the cathode side of
the fuel cell and its use is to eliminate or minimize flooding of the cathode diffusion
layer area, which is a performance limiting condition in direct methanol fuel cells.
In accordance with one embodiment of the invention, the diffusion layer includes
a substrate that is coated with a microporous layer. A pattern may be embossed
into the diffusion layer, to create preferential flow paths by which water will
travel and thereby be removed from the cathode catalyst area. This avoids cathode
flooding and avoids build up of potentially destructive pressure by possible cathodic
water accumulation. This also provides a means for collecting cathode water for
redirection In accordance with another aspect of the invention, the preferential
path is established by applying a thicker microporous layer to the carbon cloth
or carbon paper and drying it in such a fashion so that when it dries, the surface
of the microporous layer cracks to provide the pathways.
