Gas Diffusion Layer for Fuel Cell, Method of Manufacturing the Same, and Unit Cell for Fuel Cell Including the Same

Abstract

A gas diffusion layer for a fuel cell constituting a unit cell of the fuel cell includes a base layer including short carbon fibers and having a reinforcing portion formed in a predetermined area thereof in a thickness direction with continuous carbon fibers oriented in the reinforcing portion. One method of manufacturing the gas diffusion layer includes preparing a mixed dispersion in which short carbon fibers are mixed, orienting continuous carbon fibers on a conveyor belt, forming a paper having a reinforcing portion in which the continuous carbon fibers are oriented by supplying the prepared mixed dispersion to the conveyor belt on which the continuous carbon fibers are oriented, and forming a base layer by impregnating the paper with a hydrophobic agent.

What is claimed is: 
     
         1 . A gas diffusion layer for a fuel cell constituting a unit cell of the fuel cell, the gas diffusion layer comprising:
 a base layer including short carbon fibers and having a reinforcing portion formed in a predetermined area thereof in a thickness direction with continuous carbon fibers oriented in the reinforcing portion.   
     
     
         2 . The gas diffusion layer of  claim 1 , wherein the continuous carbon fibers of the reinforcing portion formed in the base layer are oriented in one direction along a plane perpendicular to the thickness direction, while being spaced apart from each other. 
     
     
         3 . The gas diffusion layer of  claim 1 , wherein each of the continuous carbon fibers of the reinforcing portion has a diameter of 6 to 12 μm. 
     
     
         4 . The gas diffusion layer of  claim 3 , wherein:
 the continuous carbon fibers of the reinforcing portion are formed in bundles, each of the bundles including a plurality of the continuous carbon fibers; and   each of the bundles of the continuous carbon fibers has a thickness of 50% or less of a total thickness of the base layer.   
     
     
         5 . The gas diffusion layer of  claim 4 , wherein each of the bundles of the continuous carbon fibers in the reinforcing portion is spaced apart from an adjacent bundle of the continuous carbon fibers at a distance of 2 to 20 mm. 
     
     
         6 . The gas diffusion layer of  claim 1 , wherein the reinforcing portion is formed adjacent to a first surface of the base layer. 
     
     
         7 . The gas diffusion layer of  claim 6 , further comprising a micro porous layer formed on a second surface of the base layer, wherein the first surface of the base layer is opposite the second surface of the base layer. 
     
     
         8 . The gas diffusion layer of  claim 6 , further comprising a micro porous layer formed on the first surface of the base layer. 
     
     
         9 . A method of manufacturing a gas diffusion layer for a fuel cell constituting a unit cell of the fuel cell, the method comprising:
 preparing a mixed dispersion in which short carbon fibers are mixed;   orienting continuous carbon fibers on a conveyor belt;   forming a paper having a reinforcing portion in which the continuous carbon fibers are oriented by supplying the prepared mixed dispersion to the conveyor belt on which the continuous carbon fibers are oriented; and   forming a base layer by impregnating the paper with a hydrophobic agent.   
     
     
         10 . The method of  claim 9 , wherein in the orienting of the continuous carbon fibers, the continuous carbon fibers are oriented in one direction, while being spaced apart from each other. 
     
     
         11 . The method of  claim 9 , wherein:
 in the orienting of the continuous carbon fibers, the continuous carbon fibers are prepared in bundles, each of the bundles including a plurality of the continuous carbon fibers, and the bundles of the continuous carbon fibers are oriented in close contact with or adjacent to a surface of the conveyor belt; and   in the forming of the paper, the mixed dispersion is supplied to the surface of the conveyor belt at a thickness greater than that of each of the bundles of the continuous carbon fibers.   
     
     
         12 . The method of  claim 11 , wherein in the forming of the paper, the mixed dispersion is supplied at a thickness at least two times greater than that of each of the bundles of the continuous carbon fibers. 
     
     
         13 . The method of  claim 11 , wherein:
 in the orienting of the continuous carbon fibers, each of the continuous carbon fibers forming the bundles has a diameter of 6 to 12 μm; and   each of the bundles of the continuous carbon fibers is spaced apart from an adjacent bundle of the continuous carbon fibers at a distance of 2 to 20 mm.   
     
     
         14 . The method of  claim 11 , further comprising, after the forming of the base layer, forming a micro porous layer by applying a slurry in which a hydrophobic agent is mixed with carbon-based powder onto a first surface of the base layer, wherein the first surface is opposite a second surface of the base layer on which the reinforcing portion is formed. 
     
     
         15 . The method of  claim 11 , further comprising, after the forming of the base layer, forming a micro porous layer by applying a slurry in which a hydrophobic agent is mixed with carbon-based powder onto a surface of the base layer on which the reinforcing portion is formed. 
     
     
         16 . A unit cell for a fuel cell, the unit cell comprising:
 a membrane-electrode assembly;   a pair of gas diffusion layers disposed on outer surfaces of the membrane-electrode assembly, respectively, wherein each of the gas diffusion layers includes a base layer including short carbon fibers and having a reinforcing portion formed in a predetermined area thereof in a thickness direction with continuous carbon fibers oriented in the reinforcing portion; and   a pair of flow field type separators disposed on outer sides of the gas diffusion layers, respectively, and bent so that lands and channels are alternately formed.   
     
     
         17 . The unit cell of  claim 16 , wherein the continuous carbon fibers of the reinforcing portion formed in the base layers of the gas diffusion layers are oriented in one direction, while being spaced apart from each other. 
     
     
         18 . The unit cell of  claim 17 , wherein:
 the lands and the channels formed in the separators are formed to be aligned in one direction; and   a direction in which the continuous carbon fibers of the reinforcing portion are oriented is kept at an angle of 45 to 90° with respect to the direction in which the lands and the channels of the separators are formed.   
     
     
         19 . The unit cell of  claim 16 , wherein:
 the base layers of the gas diffusion layers are disposed to face the separators;   the gas diffusion layers further include a micro porous layer formed on a first surface of the base layers facing the membrane-electrode assembly; and   the reinforcing portions of the gas diffusion layers are formed adjacent to a second surface of the base layers facing the separators.   
     
     
         20 . The unit cell of  claim 16 , wherein:
 the base layers of the gas diffusion layers are disposed to face the separators;   the gas diffusion layers further include a micro porous layer formed on a first surface of the base layers facing the membrane-electrode assembly; and   the reinforcing portions of the gas diffusion layers are formed adjacent to the first surface of the base layer facing the micro porous layer.