A separator includes a gas flow path forming body, which includes a substrate made of stainless steel, a resin layer arranged on the substrate, and a conductive layer arranged on the surface of the resin layer. The resin layer contains a filler, which has conductivity and greater hardness than an oxide film of the substrate. The conductive layer contains graphite. The filler extends through the oxide film of the substrate and contacts the base material.

A separator includes a gas flow path forming body, which includes a substrate made of stainless steel, a resin layer arranged on the substrate, and a conductive layer arranged on the surface of the resin layer. The resin layer contains a filler, which has conductivity and greater hardness than an oxide film of the substrate. The conductive layer contains graphite. The filler extends through the oxide film of the substrate and contacts the base material.

A multi-acid polymer disclosed herein has the formula

##STR00001##

wherein R is one or more units of a non-SOF.sub.2 or non-SO.sub.2Cl portion of a polymer precursor in sulfonyl fluoride or sulfonyl chloride form, X is a non-sulfonyl halide group of a multi-sulfonyl halide compound having a minimum of two acid giving groups, and Y is remaining sulfonyl halide groups of the multi-sulfonyl halide compound.

A multi-acid polymer disclosed herein has the formula

##STR00001##

wherein R is one or more units of a non-SOF.sub.2 or non-SO.sub.2Cl portion of a polymer precursor in sulfonyl fluoride or sulfonyl chloride form, X is a non-sulfonyl halide group of a multi-sulfonyl halide compound having a minimum of two acid giving groups, and Y is remaining sulfonyl halide groups of the multi-sulfonyl halide compound.

A method of manufacturing gas diffusion layers (GDL) with a defined pattern of hydrophobic and hydrophilic regions is used to produce electrically conductive porous materials with distributed wettability. The method includes a) Coating the external and internal surfaces of a porous base material made of carbon fiber or Titanium with Fluoroethylene-Propylene (FEP) and/or perfluoroalkoxy (PFA) and/or Ethylene-Tetrafluoroethylene (ETFE) or any other hydrophobic polymer; b) Exposing the coated material to irradiation through a blocking mask such that only parts of the coated porous material are exposed; and c) Immersing the previously exposed material in a monomer solution and heating to a temperature higher than 45° C., resulting in the graft co-polymerization of monomers on the FEP layer.

A method of manufacturing gas diffusion layers (GDL) with a defined pattern of hydrophobic and hydrophilic regions is used to produce electrically conductive porous materials with distributed wettability. The method includes a) Coating the external and internal surfaces of a porous base material made of carbon fiber or Titanium with Fluoroethylene-Propylene (FEP) and/or perfluoroalkoxy (PFA) and/or Ethylene-Tetrafluoroethylene (ETFE) or any other hydrophobic polymer; b) Exposing the coated material to irradiation through a blocking mask such that only parts of the coated porous material are exposed; and c) Immersing the previously exposed material in a monomer solution and heating to a temperature higher than 45° C., resulting in the graft co-polymerization of monomers on the FEP layer.

A gas diffusion electrode is provided that enables the achievement of a fuel cell which has high drainage performance and maintains good power generation performance, while exhibiting high power generation performance particularly at a low temperature (40° C.), if used in the fuel cell. The gas diffusion electrode includes a microporous layer on at least one surface of a conductive porous substrate, wherein the microporous layer has a fluorine compound region having a length of 3-10 μm and a void having a length of 3-10 μm.

A method of treating a carbon substrate, includes the successive steps of impregnating the carbon substrate with an aqueous solution containing an amorphous fluorinated copolymer of tetrafluoroethylene and of perfluoromethoxy dioxole, drying the carbon substrate at a pressure lower than the atmospheric pressure, and obtaining a carbon substrate impregnated with a fluorinated copolymer. Such a carbon substrate may be used as a gas diffusion layer in a fuel cell.

A porous carbon sheet includes a carbon fiber and a binding material, wherein when in a measured surface depth distribution, a ratio of an area of a portion having a depth of 20 μm or less in a measured area of one surface is a surface layer area ratio X, and a ratio of an area of a portion having a depth of 20 μm or less in a measured area of another surface is a surface layer area ratio Y, the surface layer area ratio X is larger than the surface layer area ratio Y, and a difference between the surface layer area ratios is 3% or more and 12% or less.

A fuel cell module includes an electrode membrane assembly and a pair of separators. The electrode membrane assembly includes an electrode portion and a pair of gas diffusion layers. The electrode portion includes a polymer electrolyte membrane, an anode electrode formed on a first surface of the polymer electrolyte membrane, and a cathode electrode formed on a second surface of the polymer electrolyte membrane. One of the pair of gas diffusion layers is in contact with an anode surface of the electrode portion at which the anode electrode is disposed, and the other is in contact with a cathode surface of the electrode portion at which the cathode electrode is disposed. The separators sandwich the electrode membrane assembly from respective the anode surface and the cathode surface. The electrode membrane assembly and each separator are adhered to each other by a plurality of resin portions made of a resin which at least partially contains fibers. At least a part of each gas diffusion layer is impregnated with the resin.