초록 ▼

A porous diffusion media according to the present invention is positioned against a catalyst layer of the membrane electrode assembly, the porous matrix comprises carbon paper, and the water transfer particles comprise carbon fibers or powders. Relatively high and relatively low water transfer parti

A porous diffusion media according to the present invention is positioned against a catalyst layer of the membrane electrode assembly, the porous matrix comprises carbon paper, and the water transfer particles comprise carbon fibers or powders. Relatively high and relatively low water transfer particle density regions alternate across the porous diffusion media. A first major face of the media may be collectively more hydrophilic than the second major face and the second major face may be collectively more hydrophobic than the first major face. The diffusion media is positioned against the catalyst layer along the first major face of the diffusion media and against a flow field of the fuel cell along the second major face of the diffusion media. The porous diffusion media comprises hydrophobic material disposed along the second major face of the diffusion media.

대표청구항 ▼

What is claimed is: 1. A porous diffusion media comprising a porous matrix carrying a distribution of water transfer particles, wherein: said diffusion media defines a major planar dimension and first and second major faces substantially parallel to said major planar dimension of said diffusion med

What is claimed is: 1. A porous diffusion media comprising a porous matrix carrying a distribution of water transfer particles, wherein: said diffusion media defines a major planar dimension and first and second major faces substantially parallel to said major planar dimension of said diffusion media; said distribution of water transfer particles defines a plurality of high particle density regions characterized by a relatively high density of said water transfer particles and a plurality of low particle density regions characterized by a relatively low density of said water transfer particles; said relatively high and relatively low particle density regions alternate across said major planar dimension of said porous diffusion media; respective properties of said relatively high and relatively low particle density regions vary across a cross section of said porous diffusion media between said first and second major faces of said diffusion media such that said first major face is collectively more hydrophilic than said second major face and said second major face is collectively more hydrophobic than said first major face, wherein the first major face and the second major face each comprise hydrophilic and hydrophobic portions; and said porous diffusion media further comprises a layer of hydrophobic material disposed along one of said first or second major faces of said diffusion media. 2. A porous diffusion media as claimed in claim 1 wherein said water transfer particles are selected from carbon, graphite, non-perfluorinated polymers, metal oxides, and combinations thereof. 3. A porous diffusion media as claimed in claim 2 wherein said non-perfluorinated polymers comprise polyvinylidine fluoride (PVDF) and said metal oxides comprise silicon dioxide. 4. A porous diffusion media as claimed in claim 1 wherein said water transfer particles comprise a carbon/polymer composite. 5. A porous diffusion media as claimed in claim 1 wherein said water transfer particles are selected from carbon fibers or powders, graphite fibers or powders, and combinations thereof. 6. A porous diffusion media as claimed in claim 1 wherein said water transfer particles comprise a material forming said porous matrix. 7. A porous diffusion media as claimed in claim 6 wherein said porous matrix comprises carbon paper and said water transfer particles comprise carbon fibers or powders. 8. A porous diffusion media as claimed in claim 6 wherein said porous matrix comprises carbon paper and a layer of hydrophobic material and said water transfer particles comprise carbon fibers or powders. 9. A porous diffusion media as claimed in claim 1 wherein said water transfer particles are distributed across a cross section of said porous diffusion media between said first and second major faces of said diffusion media. 10. A porous diffusion media as claimed in claim 1 wherein said relatively high and relatively low particle density regions alternate across at least one of said first and second major faces of said diffusion media. 11. A porous diffusion media as claimed in claim 10 wherein said alternating density regions are characterized by a periodicity of less than about 1 cm. 12. A porous diffusion media as claimed in claim 1 wherein said relatively high and relatively low particle density regions alternate across said first and second major faces of said diffusion media. 13. A porous diffusion media as claimed in claim 1 wherein respective cross-sectional dimensions of said relatively high and relatively low particle density regions vary inversely across a cross section of said porous diffusion media between said first and second major faces of said diffusion media. 14. A porous diffusion media as claimed in claim 13 wherein said respective cross-sectional dimensions of said relatively high and relatively low particle density regions vary such that one of said major faces is dominated by said relatively high particle density regions while the other of said major faces is dominated by said relatively low particle density regions. 15. A porous diffusion media as claimed in claim 1 wherein a density value of said relatively high particle density regions remains substantially uniform from one high particle density region to the next across one of said first and second major faces of said diffusion media. 16. A porous diffusion media as claimed in claim 1 wherein a density value of said relatively high particle density regions varies from one high particle density region to another high particle density region across one of said first and second major faces of said diffusion media. 17. A porous diffusion media as claimed in claim 16 wherein said variation in said density value defines a profile that increases from a flow field inlet region of said diffusion media to a flow field outlet region of said flow field. 18. A porous diffusion media as claimed in claim 1 wherein said porous matrix defines a substantially uniform porosity profile across said major planar dimension. 19. A porous diffusion media as claimed in claim 1 wherein said porous matrix comprises an electrically conductive material selected from carbon paper, graphite paper, cloth, felt, foam, carbon or graphite wovens, carbon or graphite non-wovens, metallic screens or foams, and combinations thereof. 20. A porous diffusion media as claimed in claim 1 wherein said porous matrix defines a thickness of between about 20 μm and about 1000 μm. 21. A porous diffusion media as claimed in claim 1 wherein said porous matrix defines a thickness of about 200 μm. 22. A porous diffusion media as claimed in claim 1 wherein said porous matrix defines a porosity characterized by a permeometer number of about 50 ft3/min./ft2 at about 0.5 inches of water. 23. A porous diffusion media as claimed in claim 1 wherein said porous matrix defines a porosity characterized by a Gurley permeometer number of between about 20 ft3/min./ft2 and about 100 ft3/min./ft2 at about 0.5 inches of water. 24. A porous diffusion media as claimed in claim 1 wherein said porous diffusion media further comprises a binder configured to at least partially secure said water transfer particles to said porous matrix. 25. A porous diffusion media as claimed in claim 24 wherein said binder comprises a fluoropolymer. 26. A porous diffusion media as claimed in claim 1 wherein said hydrophobic layer has a thickness of up to about 125 μm. 27. A porous diffusion media as claimed in claim 1 wherein said layer of hydrophobic material disposed along one of said first and second major faces is characterized by a loading of up to about 5 mg per cm2 of diffusion media surface area. 28. A porous diffusion media as claimed in claim 1 wherein said layer of hydrophobic material is configured such that it is more repellent to water droplets than said relatively high and relatively low particle density regions of said porous diffusion media. 29. A porous diffusion media as claimed in claim 1 wherein said layer of hydrophobic material comprises one of carbon, graphite, a fluoropolymer, a polymer, and combinations thereof. 30. A porous diffusion media as claimed in claim 29 wherein said hydrophobic material comprises a fluoropolymer produced from one of polytetrafluoroethylene (PTFE), tetrafluoroethylene (TFE), ethylenetetrafluoroethylene (ETFE), fluorinated ethylenepropylene (FEP), a perfluoroalkoxy compound, and combinations thereof. 31. A porous diffusion media as claimed in claim 29 wherein said hydrophobic material comprises a polymer selected from polyphenylene, polyvinylidine fluoride (PVDF), and combinations thereof. 32. A porous diffusion media as claimed in claim 1 wherein said water transfer particles are characterized by dimensions sufficiently small enough to permit migration of said water transfer particles through a thickness dimension of said porous matrix defined between said first and second major faces of said diffusion media. 33. A device comprising a porous diffusion media positioned against a catalyst layer, wherein: said diffusion media defines a major planar dimension and first and second major faces substantially parallel to said major planar dimension of said diffusion media; said porous diffusion media comprises a porous matrix carrying a distribution of water transfer particles; said distribution of water transfer particles defines a plurality of high particle density regions characterized by a relatively high density of said water transfer particles and a plurality of low particle density regions characterized by a relatively low density of said water transfer particles; said relatively high and relatively low particle density regions alternate across said major planar dimension of said porous diffusion media; respective properties of said relatively high and relatively low particle density regions vary across a cross section of said porous diffusion media between said first and second major faces of said diffusion media such that said first major face is collectively more hydrophilic than said second major face and said second major face is collectively more hydrophobic than said first major face, wherein the first major face and the second major face each comprise hydrophilic and hydrophobic portions; and said diffusion media is positioned against said catalyst layer along said first major face of said diffusion media. 34. A device as claimed in claim 33 wherein respective cross-sectional dimensions of said relatively high and relatively low particle density regions vary inversely across a cross section of said porous diffusion media between said first and second major faces of said diffusion media such that said first major face is characterized by high particle density regions of relatively large cross sectional dimensions and said second major face is characterized by high particle density regions of relatively small cross sectional dimensions. 35. A device as claimed in claim 34 wherein said diffusion media is positioned against said catalyst layer along said first major face of said diffusion media. 36. A device as claimed in claim 33 wherein said porous diffusion media comprises hydrophobic material disposed along said second major face of said diffusion media. 37. A device as claimed in claim 33 wherein said device further comprises additional structure defining, in combination with said catalyst layer and said porous diffusion media, a membrane electrode assembly interposed between an anode flow field and a cathode flow field. 38. A device as claimed in claim 37 wherein said device further comprises additional structure defining, in combination with said membrane electrode assembly, said anode flow field, and said cathode flow field, a fuel cell. 39. A device as claimed in claim 38 wherein said water transfer particles are characterized by migrational freedom sufficient to permit transfer of said water transfer particles to a surface of said catalyst layer during operation of said fuel cell. 40. A device as claimed in claim 39 wherein said fuel cell defines a motive power source of said vehicle. 41. A device as claimed in claim 38 wherein said device further comprises additional structure defining, in combination with said fuel cell, a vehicle. 42. A device comprising a membrane electrode assembly interposed between an anode flow field and a cathode flow field of a fuel cell, wherein: a porous diffusion media is positioned against a catalyst layer of said membrane electrode assembly; said porous diffusion media comprises a porous matrix carrying a distribution of water transfer particles; said porous matrix comprises carbon paper and said water transfer particles comprise carbon fibers or powders; said distribution of water transfer particles defines a plurality of high particle density regions characterized by a relatively high density of said water transfer particles and a plurality of low particle density regions characterized by a relatively low density of said water transfer particles; said relatively high and relatively low particle density regions alternate across a major planar dimension of said porous diffusion media parallel to first and second major faces of said diffusion media; respective properties of said relatively high and relatively low particle density regions vary across a cross section of said porous diffusion media between said first and second major faces of said diffusion media such that said first major face is collectively more hydrophilic than said second major face and said second major face is collectively more hydrophobic than said first major face, wherein the first major face and the second major face each comprise hydrophilic and hydrophobic portions; said diffusion media is positioned against said catalyst layer along said first major face of said diffusion media; said diffusion media is positioned against a flow field of said fuel cell along said second major face of said diffusion media; said porous diffusion media comprises hydrophobic material disposed along said second major face of said diffusion media; and said hydrophobic material comprises polytetrafluoroethylene (PTFE).