Diffusion media with hydrophobic and hydrophilic properties
A diffusion medium for use in a PEM fuel cell contains hydrophobic and hydrophilic areas for improved water management. A hydrophobic polymer such as a fluororesin is deposited on the paper to define the hydrophobic areas, and an electroconductive polymer such as polyaniline or polypyrrole is deposited on the papers defining the hydrophilic areas. In various embodiments, a matrix of hydrophobic and hydrophilic areas on the carbon fiber based diffusion media is created by electropolymerization of a hydrophilic polymer onto a diffusion medium which has been previously coated with a hydrophobic polymer such as a fluorocarbon polymer. When an aqueous solution containing monomers for electropolymerization is contacted with a fluorocarbon coated diffusion medium, the hydrophilic polymer will be preferentially deposited on areas of the carbon fiber based diffusion medium that are not covered by the fluorocarbons.
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 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.
10. A diffusion medium according to claim 9 , wherein the hydrophobic polymer comprises a fluorocarbon polymer.
11. A diffusion medium according to claim 10 , wherein the hydrophobic polymer comprises polytetrafluoroethylene.
12. A diffusion medium according to claim 9 , wherein the electroconductive polymer comprises polyaniline or polypyrrole.
13. A diffusion medium according to claim 9 , wherein the hydrophobic areas are predominantly on one side of the substrate and the hydrophilic areas are predominantly on the other side.
14. A diffusion medium according to claim 9 , wherein the substrate comprises a carbon fiber paper.
15. A diffusion medium according to claim 14 , wherein the hydrophobic polymer comprises a fluorocarbon polymer.