Composite membrane and moisture adjustment module using same

1. A method of humidifying a fuel cell having a polymer electrolyte membrane, an anode, a cathode, a fuel electrode gas feed and an air electrode gas feed, said method comprising the step of providing in at least one of said fuel electrode gas feed and said air electrode gas feed a moisture adjustment module comprising a composite membrane wherein a moisture-permeable resin layer is interposed between porous membranes of expanded polytetrafluoroethylene having pores with mean pore diameter of 0.05 μm or greater and maximum pore diameter of 15 μm or less that constitute a pair and are structurally and materially identical, wherein pores of the porous membranes are not imbedded with said resin layer; and the mean thickness of the moisture-permeable resin layer is between 0.1 and 5 μm.

2. The method according to claim 1 , wherein said moisture-permeable resin comprises a water-resistant, moisture-permeable resin.

3. The method according to claim 2 , wherein the degree of swelling of said water-resistant, moisture-permeable resin, is 20 times or less.

4. The method according to claim 2 wherein said water-resistant, moisture-permeable resin comprises a crosslinked polyvinyl alcohol.

5. The method according to claim 2 , wherein said water-resistant, moisture-permeable resin comprises an ion-exchange fluororesin.

6. The method according to claim 5 , wherein said water-resistant, moisture-permeable resin comprises a perfluorosulfonic acid polymer.

7. The method according to claim 3 wherein said water-resistant, moisture-permeable resin comprises a crosslinked polyvinyl alcohol.

8. The method according to claim 1 wherein the void content of the said porous membranes is 40% or greater.

9. The method according to claim 1 wherein the mean thickness of said porous membranes is 1 to 200 μm.

10. The method according to claim 1 wherein a gas-permeable reinforcing element is layered on at least one of the porous membranes.

11. The method according to claim 1 further comprising superposing a plurality of said composite membranes with open spaces are left therebetween.

12. A fuel cell comprising a polymer electrolyte membrane, a fuel electrode, an air electrode, a fuel electrode gas feed, an air electrode gas feed, and disposed in at least one of said fuel electrode gas feed and said air electrode gas feed a moisture adjustment module comprising a composite membrane wherein a moisture-permeable resin layer is interposed between porous membranes of expanded polytetrafluoroethylene having pores with mean pore diameter of 0.05 μm or greater and maximum pore diameter of 15 μm or less that constitute a pair and are structurally and materially identical, wherein pores of the porous membranes are not imbedded with said resin layer; and the mean thickness of the moisture-permeable resin layer is between 0.1 and 5 μm.

13. A fuel cell according to claim 12 wherein at least one of said first and second micro-porous membranes is hydrophobic.

14. A fuel cell according to claim 12 wherein at least one of said first and second micro-porous membranes is hydrophilic.

15. A fuel cell according to claim 12 wherein said resin is a perfluorosulfonic acid polymer.

16. A fuel cell according to claim 12 wherein at least one of said pair of porous membranes has a reinforcing member attached to it.

17. A fuel cell according to claim 16 wherein said reinforcing member is a non-woven material.

18. A fuel cell according to claim 16 wherein said reinforcing member is a woven material.

19. A fuel cell according to claim 12 further comprising a plurality of said composite membranes in stacked relation with open spaces therebetween.