Increasing the hydrophilicity of carbon fiber paper by electropolymerization
View Patent ↗An electroconductive porous substrate such as carbon fiber paper with an electroconductive polymer deposited on the carbon fibers of the paper is used as a wicking material or diffusion medium in a fuel cell. The polymer may be deposited from a solution of monomers by electrochemical polymerization.
1. A method for making a hydrophilic wicking fuel cell diffusion medium comprising:
exposing a carbon fiber substrate to a solution comprising a monomer and an electrolyte, wherein the concentration of monomer is from about 0.5 M to about 1.5 M and the concentration of electrolyte is from about 0.01 M to about 1.5 M; and
electropolymerizing the monomer to form an electroconductive polymer on the carbon fiber substrate, wherein electropolymerizing includes:
providing the carbon fiber substrate as the anode of an electrochemical circuit including a counter-electrode;
applying a positive potential to the anode using a pulse voltage, the pulse voltage including a square wave function having a frequency from about 0.1 Hz to about 0.001 Hz, wherein the anode is at a voltage above the oxidation potential of the monomer;
thereby oxidizing the monomer to form the electroconductive polymer on the carbon fiber substrate surface.
2. A method according to claim 1 , wherein the carbon fiber substrate has a density from about 0.4 g/cm 3 to about 0.6 g/cm 3 .
3. A method according to claim 1 , wherein the carbon fiber substrate has a thickness from about 100 to about 1000 micrometers.
4. A method according to claim 1 , wherein the carbon fiber substrate has a porosity from about 70% to about 80%.
5. A method according to claim 1 , wherein the monomer is selected from the group consisting of pyrrole, thiophene, aniline, furan, azulene, carbazole, substituted derivatives thereof, and combinations thereof.
6. A method according to claim 1 , wherein the monomer is selected from the group consisting of β-alkyl thiophene, β-bromo thiophene, β-CH 2 CN thiophene, β, β-dibromothiophene, and combinations thereof.
7. A method according to claim 1 wherein the electrolyte is selected from the group consisting of camphor sulfonic acid, para-toluene sulfonic acid, dodecyl benzene sulfonic acid, sulfuric acid, alizarin red S-monohydrate, salts thereof, and combinations thereof.
8. A method according to claim 1 , wherein the hydrophilic wicking material produced has a surface free energy of more than 80 dyne/cm.
9. A method according to claim 1 , wherein the applying step includes a voltage from about 0.5 V to about 2.5 V.
10. A method according to claim 1 , wherein applying a positive potential to the anode using a pulse voltage further comprises a percent on/off time of 50/50.
11. A method according to claim 1 , wherein the electropolymerizing step results in the carbon fiber substrate coated with from about 5% to about 30% by weight of the electroconductive polymer.
12. A method according to claim 1 , wherein the electropolymerizing step results in the electroconductive polymer having a thickness from about 5% to about 10% of the diameter of the carbon fibers.
13. A method for making a hydrophilic wicking fuel cell diffusion medium, comprising
exposing a carbon fiber substrate to a solution comprising aniline and camphor sulfonic acid electrolyte; and
electropolymerizing the aniline to form polyaniline on the carbon fiber substrate, wherein electropolymerizing includes:
providing the carbon fiber substrate as the anode of an electrochemical circuit including a standard calomel reference electrode;
applying a positive potential to the anode comprising a square wave of applied voltage from 0.3 V to 0.8 V;
thereby oxidizing the aniline to form polyaniline on the carbon fiber substrate surface.