ANIONIC POLYELECTROLYTE

Abstract

The present invention relates to a composite material comprising a porous solid matrix having interconnected channels, said matrix comprising sulfonate groups on at least a part of the surface of said channels, wherein a sulfonate group is in ionic interaction with a quaternary ammonium of a polymerizable molecule. The present invention also relates to a method for preparing such a composite material and applications thereof.

Claims

1. A composite material comprising a porous solid matrix having interconnected channels, said matrix comprising sulfonate groups on at least a part of the surface of said channels, wherein a sulfonate group is in ionic interaction with a quaternary ammonium of a polymerizable molecule.

2. The composite material according to claim 1, wherein said porous solid matrix is a sulfonated tetrafluoroethylene membrane.

3. The composite material according to claim 1, wherein said polymerizable molecule is polymerized thereby forming an oligomer.

4. The composite material according to claim 1, wherein said polymerizable molecule is a polymerizable molecule of formula (I): ##STR00002## wherein n is 1, 2 or 3, “alkyl” is a linear or branched saturated alkyl group optionally substituted, R1, R2 and R3 are substituents of the nitrogen atom, either identical or different, Xn are substituents of the Silicon atom, either identical or different, and at least one Xn represents a polymerizable group.

5. The composite material according to claim 1, wherein Xn, identical or different, are independently selected among alkoxy groups, optionally substituted.

6. The composite material according to claim 1, wherein R1, R2 and R3 are a linear saturated alkyl, either identical or different.

7. The composite material according to claim 1, wherein said polymerizable molecule is a N-dialkoxysilylalkyl-N,N,N-tri-alkylammonium or N-trialkoxysilylalkyl-N,N,N-tri-alkylammonium.

8. The composite material according to claim 1, wherein said porous solid matrix is conducting ions.

9. A method for preparing a composite material as defined according to claim 1, wherein said method comprises: a providing a porous solid matrix having interconnected channels, said matrix comprising sulfonate groups on at least a part of the surface of said interconnected channels; contacting said porous solid matrix with a polymerizable molecule comprising a quaternary ammonium thereby forming ionic interactions between a sulfonate group and quaternary ammonium.

10. The method according to claim 9, wherein said method comprises: polymerizing, said polymerizable molecule after having contacted said porous solid matrix with said polymerizable molecule.

11. The method according to claim 9 or 10, wherein said method comprises: exchanging a counter-ion of said quaternary ammonium.

12. The method according to claim 9, wherein said polymerizable molecule is deposited by chemical vapor deposition on at least a part of the surface of said interconnected channels of said porous solid matrix.

13. The method according to claim 9, wherein said polymerizable molecule is deposited by dipping said porous solid matrix into a solution comprising said polymerizable molecule.

14. The method according to claim 9, wherein said polymerizable molecule is deposited by chemical vapor deposition on at least a part of the surface of said interconnected channels of said porous solid matrix and then by dipping said porous solid matrix into a solution comprising said polymerizable molecule.

15. The method according to claim 9, wherein the contact of said porous solid matrix with a polymerizable molecule comprising a quaternary ammonium is performed at a temperature of more than 30° C.

16. A fuel cell comprising a composite material as defined according to claim 1 or obtainable according to a method comprising a providing a porous solid matrix having interconnected channels, said matrix comprising sulfonate groups on at least a part of the surface of interconnected channels; contacting said porous solid matrix with a polymerizable molecule comprising a quaternary ammonium thereby forming ionic interactions between a sulfonate group and quaternary ammonium.

17. (canceled)

18. The composite material according to claim 1 which is a membrane in a fuel cell or in a captor.

19. The composite material according to claim 1, wherein said porous solid matrix is a Nafion® membrane.

20. The composite material according to claim 4, wherein Xn are methoxy groups.

21. The method according to claim 11, wherein the exchanging a counter-ion of said quaternary ammonium is performed by providing OH.sup.− ion to said quaternary ammonium.

Description

[0118] In the figures:

[0119] FIG. 1 illustrates the stability of the ionic grafting, highlighted by long time water washing of NRE212-TMSPA grafted.

[0120] FIG. 2 illustrates the full polymerization, highlighted by exchange with ionic H.sup.+ resin of NRE212-TMSPA grafted.

[0121] FIG. 3 illustrates the ionic nature of the interaction between sulfonate and quaternary ammonium, highlighted by water washing of NRE212-TMAC grafted.

[0122] FIG. 4 illustrates the reversibility of the ionic interaction, highlighted by exchange with ionic H.sup.+ resin of NRE212-TMAC grafted.

[0123] FIG. 5 illustrates the characterization of an anionic fuel cell realized according to the invention.

EXAMPLES

Example 1—Preparation of a Composite Material According to the Invention by CPV

[0124] This process is used to convert a cationic catalyst ink to an anionic one after spraying or commercial cationic electrodes made with Vulcan Xc-72 with platinum and Nafion before assembling.

[0125] The sample, a 9 mm diameter disk of vulcan XC-72 with 20% platinum is placed in a sealed glass vial above a drop of 30 μl of TMSPA (in solution in methanol 50%). Adsorption is allowed at 10° C. during one day. Then, the sample is placed at 60° C. in a new vial with a drop of water during one day to allow the hydrolysis and the polymerization of the adsorbed molecules of silane.

Example 2—Preparation of a Composite Material According to the Invention by Dip Impregnation

[0126] A 5×7 cm plate of Nafion® NRE 212 is immerged and agitated in a closed glass box containing 25 ml of TMSPA (in solution in methanol 50%) avoiding contact with the walls. Adsorption is allowed at 10° C. during one day. The pH of the solution decreases to 3, indicating the expulsion of the hydronium ions from the nafion when they are replaced by quaternary ammonium silane ions. Then, the plate is placed in another clean closed glass box with 25 ml of TMSPA during another day at 10° C. After that, the plate is placed in a new closed glass box with a drop of water at 60° C. during one day to hydrolyze and polymerize the silane.

Example 3—Technical Results on the Composite Material

[0127] The characterization by Infrared spectroscopy of a composite material according to example 2 is then realized. The stability of the result was insured by washing with water during 3 weeks (FIG. 1). The total polymerization was proved (no residual monomers) by washing with water in the presence of ion exchange resin H.sup.+ (FIG. 2).

[0128] As a comparison, FIGS. 3 and 4 represent the characterization by Infrared spectroscopy of a composite material wherein the grafting is realized in the same conditions but with Tetramethylammonium chloride (TMAC: CAS 75.57.0), a non polymerizable molecule. The exchange with H.sup.+ resin proves the ionic nature of the sulfonate-quaternary ammonium bond.

Example 4—Preparation of a Fuel Cell According to the Invention

[0129] The anionic membrane, a 11 mm diametrer disk of Nafion-C, is realized according to example 2 of the invention with Nafion® NRE212 and a TMSPA solution at 50% in methanol. Two 9 mm diameter commercial electrodes made of Vulcan Xc-72 with 20% platinum are modified in gazeous phase according to example 1 of the invention and then pressed at 60° C. at the center on each side of the Nafion-CI membrane. The assembly is mounted in a homemade cell of active area equal to 0.07 cm.sup.2 and connected with hydrogen source produced by electrolysis. Oxygen is from humidified ambiant air.

Example 5—Technical Results on the Fuel Cell

[0130] The characteristic curve of Voltage (mV) as a function of Intensity (μA) for a device according to example 5 is shown on FIG. 5. The OCV and the short circuit current are equal respectively to 700 mV and 3 μA.

[0131] As the electrode membrane assembly is not optimized, because the contact area between the membrane and the catalyst is very small (observed after disassembly of the fuel cell after the test), the inventor considers these first results as very promising for an industrial device.