An object of the present invention is to provide a gas diffusion electrode substrate that can facilitate both the supply of a reaction gas to a gas diffusion electrode and discharge of water as a reaction product. The present invention provides a gas diffusion electrode substrate including a carbon fiber nonwoven fabric having 30/cm.sup.2 to 5000/cm.sup.2 discontinuous protrusions dispersedly formed on at least one surface thereof, and a water repellent imparted to the carbon fiber nonwoven fabric.

Provided is a method for producing a gas diffusion electrode, with which it is possible to more effectively improve electrode performance, in cases in which a core-shell catalyst is used as an electrode catalyst. This method for producing gas diffusion electrode comprises: a first step in which a support layer having electron conductivity, water-repellency and gas diffusion properties is soaked in water; a second step in which the constituent materials of ink for forming a catalyst layer are put into a mixer and mixed by agitation to prepare an ink for forming a catalyst layer; and a third step in which the ink for forming a catalyst layer is used to form a catalyst layer on the surface of the support layer obtained in the first step. The ink for forming the catalyst layer contains a core-shell catalyst, a polyelectrolyte, water and alcohol. The alcohol is only a polyvalent alcohol.

Disclosed is a fuel cell with enhanced mass transfer characteristics in which a highly hydrophobic porous medium, which is prepared by forming a micro-nano dual structure in which nanometer-scale protrusions with a high aspect ratio are formed on the surface of a porous medium with a micrometer-scale roughness by plasma etching and then by depositing a hydrophobic thin film thereon, is used as a gas diffusion layer, thereby increasing hydrophobicity due to the micro-nano dual structure and the hydrophobic thin film. When this highly hydrophobic porous medium is used as a gas diffusion layer for a fuel cell, it is possible to reduce water flooding by efficiently discharging water produced by an electrochemical reaction of the fuel cell and to improve the performance of the fuel cell by facilitating the supply of reactant gases such as hydrogen and air (oxygen) to a membrane-electrode assembly (MEA).

The present invention provides a substrate film that has a catalyst coating liquid having good coating properties when producing a membrane electrode assembly, has a catalyst layer and support film having good release properties after the catalyst layer is transferred to an electrolyte membrane using a catalyst transfer sheet, and does not contaminate the catalyst layer. Provided is a substrate film for a catalyst transfer sheet, said substrate film being formed by introducing fluorine atoms to at least one surface of a base film formed from one or more types of polymers selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene napthalate, polyphenylene sulfide, polysulfones, polyether ketone, polyether ether ketone, polyimides, polyetherimide, polyamides, polyamide-imides, polybenzimidazoles, polycarbonates, polyarylates, and polyvinyl chloride, wherein the ratio, measured by X-ray photoelectron spectroscopy, of the number of fluorine atoms/the number of carbon atoms in the surface to which the fluorine atoms are introduced, i.e. the modified surface, is 0.02-1.9, inclusive.