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.