By using a gas diffusion layer for a fuel cell comprising a fabric
comprising a warp thread and a weft thread which are made of carbon
fiber, wherein the distance X between adjacent intersections where the
warp and weft threads cross each other and the thickness Y of the fabric
satisfy the equation: 1.4.ltoreq.X/Y.ltoreq.3.5, the present invention
reduces the surface asperities of the substrate and prevents a micro
short-circuit resulting from the piercing of the polymer electrolyte
membrane of the fuel cell by the carbon fibers of the fabric so as to
improve the characteristics of the fuel cell.In order to further prevent
the piercing of the polymer electrolyte membrane by the carbon fibers of
the gas diffusion layer substrate, the rough surface of the carbon fabric
is smoothed by: (1) applying a clamping pressure of 1 to 20 kgf/cm.sup.2
to the contact area between each electrode and each conductive separator
plate of the fuel cell; or (2) heating the gas diffusion layer surface
before the gas diffusion layer is disposed onto the polymer electrolyte
membrane.