Water control sheet, gas diffusion sheet, membrane-electrode assembly and polymer electrolyte fuel cell

#1. Field of the Invention

#The present invention relates to a water control sheet, a gas diffusion sheet, a membrane-electrode assembly and a polymer electrolyte fuel cell, and to an independent water control sheet which has a shape retention property to be handled by itself, and a gas diffusion sheet, membrane-electrode assembly and polymer electrolyte fuel cell utilizing the water control sheet.

#2. Related Background Art

#FIG. 1 is an electron micrograph of a gas diffusion sheet of example 1;

#FIG. 2 is an electron micrograph of a gas diffusion sheet of example 2;

#FIG. 3 is an electron micrograph of a water control sheet of example 3;

#The water control sheet according to the present invention is composed of a nonwoven fabric comprising conductive fibers containing conductive particles at least internally of a hydrophobic organic resin. The water control sheet according to the present invention is composed of the hydrophobic organic resin, so that it has superior water permeability even without impregnation with a hydrophobic resin such as fluororesins and also has a superior drainage property. The “hydrophobic organic resin” is an organic resin having 90° or more contact angle with water, the organic resin excluding diamonds, graphite and amorphous carbon. Such hydrophobic organic resin may include, for example, fluororesins such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesins (PFAs), tetrafluoroethylene-hexafluoropropylene copolymers (FEPs), ethylene-tetrafluoroethylene copolymers (ETFEs), ethylene-chlorotrifluoroethylene copolymers (ECTFEs), vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymers and copolymers composed of monomers constituting the above-mentioned resins; polyolefin resins such as polyethylene (PE), polypropylene (PP); polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN). These resins may be used alone or two or more resins may be mixed. Among these, fluororesins are suitable because of their improved heat resistance, chemical resistance and hydrophobicity.

#The conductive fibers according to the present invention contain the conductive particles at least internally of the hydrophobic organic resin so that they have superior electron transfer property in a fuel electrode or air electrode. When the conductive particles exist only on the outer surface of the hydrophobic organic resin, the conductivity may be reduced because the hydrophobic organic resin component serves as a resistance component. However, according to the present invention, the conductive particles exist internally of the hydrophobic organic resin, thereby realizing superior conductivity. In view of the conductivity, the conductive particles are preferably exposed from the hydrophobic organic resin. The expression “contain an conductive particle internally” means not only the situation in which the conductive particle is completely embedded in the hydrophobic organic resin, but also the situation in which a part of the conductive particle is exposed from the hydrophobic organic resin. The conductive fibers containing the conductive particles at least internally of the hydrophobic organic resin can be prepared by, for example, spinning a spinning solution containing the hydrophobic organic resin and the conductive particles.

#The conductive particle may be, but not limited to, carbon black, carbon nanotube, carbon nanofiber, metal particle, metal oxide particle or the like. Among these, carbon black is suitably used because of their chemical resistance, conductivity and dispersibility. The average primary particle diameter of such suitable carbon black may be, but not limited to, 5 nm to 200 nm, and more preferably 10 nm to 100 nm. The average primary particle diameter of the conductive particles is preferably smaller than the fiber diameter of conductive fiber to be described later, so that the particle may not be dropped and the shape of the fiber can be easily formed.