1. A fuel cell comprising:
an anode;
a cathode;
a proton exchange membrane disposed between the anode and the cathode;
a fluid distribution chamber associated with the cathode having a gas entrance and a gas exit side;
a fluid distribution chamber associated with the anode having a gas entrance and a gas exit side;
a diffusion medium disposed within the fluid distribution chamber associated with the cathode, the fluid distribution chamber associated with the anode, or both, wherein the diffusion medium spans the fluid distribution chamber from the entrance side to the exit side, and wherein at least one of the diffusion media comprises:
an electrically conductive porous material;
a hydrophobic polymer deposited on the porous material defining hydrophobic areas; and
a hydrophilic polymer deposited on the porous material defining hydrophilic areas.
2. A fuel cell according to claim 1, wherein the hydrophobic polymer comprises a fluorocarbon polymer.
3. A fuel cell according to claim 2, wherein the hydrophobic polymer comprises polytetrafluoroethylene.
4. A fuel cell according to claim 1, wherein the hydrophilic polymer comprises polyaniline.
5. A fuel cell according to claim 1, wherein the hydrophilic polymer comprises polypyrrole.
6. A fuel cell according to claim 1, wherein at least one of the diffusion media comprising hydrophobic polymer and hydrophilic polymer has a different content of hydrophobic polymer in an area of the diffusion medium adjacent the entrance side than in an area of the diffusion medium adjacent the exit side.
7. A fuel cell according to claim 6, wherein a diffusion medium disposed adjacent the cathode has a higher content of hydrophobic polymer in an area of the diffusion medium adjacent the exit side than in an area adjacent the entrance side.
8. A fuel cell according to claim 1, wherein the porous material comprises carbon fiber paper.
9. A method of preparing a diffusion medium having hydrophobic areas and hydrophilic areas, comprising;
a) depositing a hydrophobic polymer onto a porous substrate in a pattern such that a portion of the substrate is left uncovered with polymer; and thereafter
b) depositing an electroconductive polymer onto the uncovered portion of the substrate.
10. A method according to claim 9, wherein the hydrophobic polymer comprises a fluorocarbon polymer.
11. A method according to claim 9, wherein the fluorocarbon polymer comprises polytetrafluoroethylene.
12. A method according to claim 9, wherein the electroconductive polymer comprises polyaniline or polypyrrole.
13. A method according to claim 9, comprising depositing the hydrophobic polymer predominantly on one side of the substrate and the electroconductive polymer predominantly on the other side.
14. A method according to claim 9, wherein step a) comprises:
wetting the substrate which is a sheet of carbon fiber paper with solvent in an aqueous emulsion comprising the hydrophobic polymer;
contacting the wet sheet with a pattern member comprising one or more openings oriented to correspond to a predetermined pattern; and
evaporating the solvent from the sheet while the sheet is in contact with the pattern member, whereby the hydrophobic polymer is concentrated on the sheet at the openings.
15. A method according to claim 14, wherein the contacting step comprises holding the sheets between two mold surfaces, wherein at least one mold surface comprises openings through which the solvent can evaporate.
16. A method according to claim 15, wherein one mold surface comprises openings and the other mold surface is solid.
17. A method according to claim 14, wherein both mold surfaces comprise openings, and wherein a pattern of hydrophobic polymer is deposited on both sides of the sheets.
18. A method according to claim 14, wherein the pattern member comprises a screen.
19. A method according to claim 14, wherein evaporating is accomplished by heating the sheet to remove solvent.
20. A method according to claim 14, wherein at least one side of the sheet is coated over 10 to 90% of its area with fluorocarbon polymer.
21. A method according to claim 14, wherein at least one side of the sheet is coated over 10 to 60% of its area with fluorocarbon polymer.
22. A method according to claim 9, wherein step b) comprises depositing the electroconductive polymer from an aqueous solution of monomers by electrochemical polymerization.
23. A method according to claim 22, wherein the solution comprises an electrolyte and a monomer selected from the group consisting of pyrrole, thiophene, aniline, furan, azulene, carbazole, and derivatives thereof.
24. A method according to claim 23, wherein the monomer comprises aniline.
25. A method according to claim 23, wherein the monomer comprises pyrrole.
26. A diffusion medium for use in a PEM fuel cell containing hydrophobic and hydrophilic areas for improved water management comprising:
a porous conductive substrate having two sides
a hydrophobic polymer deposited on the substrate defining the hydrophobic areas; and
an electroconductive polymer deposited on the substrate defining the hydrophilic areas.
27. A diffusion medium according to claim 26, wherein the hydrophobic polymer comprises a fluorocarbon polymer.
28. A diffusion medium according to claim 27, wherein the hydrophobic polymer comprises polytetrafluoroethylene.
29. A diffusion medium according to claim 26, wherein the eletroconductive polymer comprises polyaniline or polypyrrole.
30. A diffusion medium according to claim 26, wherein the hydrophobic areas are predominantly on one side of the substrate and the hydrophilic areas are predominantly on the other side.
31. A diffusion medium according to claim 26, wherein the substrate comprises a carbon fiber paper.
32. A diffusion medium according to claim 31, wherein the hydrophobic polymer comprises a fluorocarbon polymer.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A device for imitating diamonds and their common substitutes used in jewelry, in the sense that it exhibits thermal conductivity and electrical resistance of diamonds and their.
2. Device as in claim 1, which comprises a set of separate members, one imitating diamonds with their high thermal conductivity and very high electrical resistance, another imitating silicon carbide with its high thermal conductivity and small but measurable electrical conductivity, yet another imitating silicon carbide with greater electrical conductivity, yet another for those diamond imitations which possess low thermal conductivity, and, finally, an electrically conductive member for verifying ability of the gem tester to detect when gem setting, like a ring, is touched by the probe accidentally instead of the gem.
3. Device as in claim 1, with members, which have desirable combination of thermal and electrical properties, made in a sandwich form with:
top layer made of metal or alloy, which is touched by thermal-electrical sensor of a gem tester and has required thermal conductivity and a very small electrical resistance;
middle layer made of material with required electrical resistance; and
bottom layer made of a good conductor through which the test voltage is applied.
4. Device as in claim 1, where the members, which imitate gems with high thermal conductivity, like diamond and silicon carbides, has a top layer made of any material, most likely metal or alloy, with high thermal conductivity and very low electrical resistance.
5. Device as in claim 1, where the member, which imitates diamond fakes with low thermal conductivity has the top layer made of any material, most likely metal or alloy, with sufficiently low thermal conductivity and very low electrical resistance, e.g. stainless steel, which can be made to have specified thermal conductivity.
6. Device as in claim 1, where the member which imitates diamonds has the middle layer made of a good insulator, e.g. insulating plastic or air.
7. Device as in claim 1, where the members, which imitate gems with measurable electrical conductivity, have their middle layer made of anti-static plastics, like Durathane, or other high resistivity material, which can be made to have required electrical resistance; two different grades are used for the members imitating high and low resistance silicon carbide crystals.
8. Device as in claim 1, where the member, which imitates diamond fakes with low thermal conductivity that do not require electrical testing has the middle layer made of a good insulator, e.g. insulating plastic or air.
9. Device as in claim 1, which is equipped with a member made of metal for applying test voltage via a finger of the person using it, or any other means for connecting to a test voltage source.
10. Device as in claim 1, where all members are mounted on an electrically conductive base, typically made of metal, through which test voltage can be delivered to those members of the device whose electrical resistance must be evaluated in the course of a test, namely the conductive pad imitating metal and the middle layers of the members imitating diamond substitutes with measurable electrical conductivity.
11. Device as in claim 1, where all members are assembled in a compact block in a piece of electrically insulating material with very low thermal conductivity.
12. Device as in claim 1, where the block of members as in claim 11 is placed in a protective casing, to prevent accumulation of moisture or other foreign substance on its surface, which could cause electrical leakage across the surface.
13. A method for simulating thermal conductivity and electrical resistance of materials by using three substitute materials, each exhibiting one of the required properties, assembled in a layered structure as in claim 3.
14. A method for verifying performance of gem and diamond testers, which employ measurement of thermal and electrical conductivities, using the apparatus as in claim 1.