Carbon fiber paper and porous carbon electrode substrate for fuel cell therefrom

1. A porous carbon electrode substrate for a fuel cell comprising a carbon fiber paper having a surface area ratio of 1.05 or more, said porous carbon electrode substrate having a structure in which at least two carbon fiber papers, each containing a carbonized resin, are laminated, and at least one of the carbon fiber papers is the carbon fiber paper comprising carbon fibers having a surface area ratio of 1.05 or more, said porous carbon electrode substrate having a structure in which a plurality of carbon fiber papers, each containing a carbonized resin, are the same kind and are laminated in such a state that the same sides of the papers are each directed outward.

2. A porous carbon electrode substrate for a fuel cell according to claim 1 , wherein said electrode substrate has a thickness of at least 0.05 mm and at most 0.5 mm and a bulk density of at least 0.3 g/cm 3 and at most 0.8 g/cm 3 , and has a bending strength of 50 MPa or more and a deflection of 1.5 mm or more at the time of bending measured by a three-point bending test under the conditions of a strain speed of 10 mm/min, a distance between the supporting points of 2 cm and a test specimen width of 1 cm.

3. A porous carbon electrode substrate for a fuel cell according to claim 1 , which has a tensile strength of 25 MPa or more.

4. A porous carbon electrode substrate for a fuel cell according to claim 1 , which contains a carbonized resin in an amount of at least 10% by mass and at most 50% by mass.

5. A porous carbon electrode substrate for a fuel cell according to claim 1 , wherein a ratio of the MD surface resistance which is a surface resistance in the papermaking direction of the carbon fiber paper and the CMD surface resistance which is a surface resistance in the width direction which forms a 90 degree angle with the papermaking direction, is at least 1.0 and at most 2.5 in terms of MD surface resistance/CMD surface resistance.

6. A porous carbon electrode substrate for a fuel cell comprising a carbon fiber paper having a surface area ratio of 1.05 or more, said porous carbon electrode substrate having a structure in which at least two carbon fiber papers, each containing a carbonized resin, are laminated, and at least one of the carbon fiber papers is the carbon paper comprising carbon fibers having a surface area ratio of 1.05 or more, wherein the carbon fiber paper contains a carbonized resin, besides a first carbon fiber paper which is the carbon fiber paper comprising carbon fibers having a surface area ratio of 1.05 or more, at least one second carbon fiber paper which is a carbon fiber paper comprising carbon fibers having an average diameter of at least 6 μm and at most 20 μ and an average fiber length of at least 2 mm and at most 18 mm, said porous carbon electrode substrate being windable around a roll of 40 cm or less in outer diameter and has a length of 1 m or more.

7. A porous carbon electrode substrate for a fuel cell according to claim 6 , wherein said electrode substrate has a thickness of at least 0.05 mm and at most 0.5 mm and a bulk density of at least 0.3 g/cm 3 and at most 0.8 g/cm 3 , and has a bending strength of 50 MPa or more and a deflection of 1.5 mm or more at the time of bending measured by a three-point bending test under the conditions of a strain speed of 10 mm/min, a distance between the supporting points of 2 cm and a test specimen width of 1 cm.

8. A porous carbon electrode substrate for a fuel cell according to claim 6 , which has a tensile strength of 25 MPa or more.

9. A porous carbon electrode substrate for a fuel cell according to claim 6 , which contains a carbonized resin in an amount of at least 10% by mass and at most 50% by mass.

10. A porous carbon electrode substrate for a fuel cell according to claim 6 , wherein a ratio of the MD surface resistance which is a surface resistance in the papermaking direction of the carbon fiber paper and the CMD surface resistance which is a surface resistance in the width direction which forms a 90 degree angle with the papermaking direction, is at least 1.0 and at most 2.5 in terms of MD surface resistance/CMD surface resistance.

11. A porous carbon electrode substrate for a fuel cell according to claim 1 , which is windable around a roll of 40 cm or less in outer diameter and has a length of 1 m or more.

12. A porous carbon electrode substrate for a fuel cell according to claim 1 or 6 , wherein said porous carbon electrode substrate has a structure in which at least two carbon fiber papers, each containing a carbonized resin, are laminated, and the carbon fiber paper comprising carbon fibers having a surface area ratio of 1.05 or more is arranged as at least one outermost layer of the electrode substrate, and the outer side of said outermost layer carbon fiber paper has a surface roughness of 5 μm or less.

13. A porous carbon electrode substrate for a fuel cell according to claim 12 , wherein said electrode substrate has a thickness of at least 0.05 mm and at most 0.5 mm and a bulk density of at least 0.3 g/cm 3 and at most 0.8 g/cm 3 , and has a bending strength of 50 MPa or more and a deflection of 1.5 mm or more at the time of bending measured by a three-point bending test under the conditions of a strain speed of 10 mm/min, a distance between the supporting points of 2 cm and a test specimen width of 1 cm.

14. A porous carbon electrode substrate for a fuel cell according to claim 12 , which has a tensile strength of 25 MPa or more.

15. A porous carbon electrode substrate for a fuel cell according to claim 12 , which contains a carbonized resin in an amount of at least 10% by mass and at most 50% by mass.

16. A porous carbon electrode substrate for a fuel cell according to claim 12 , wherein a ratio of the MD surface resistance which is a surface resistance in the papermaking direction of the carbon fiber paper and the CMD surface resistance which is a surface resistance in the width direction which forms a 90 degree angle with the papermaking direction, is at least 1.0 and at most 2.5 in terms of MD surface resistance/CMD surface resistance.