WO2008012423A2

WO2008012423A2 - Method of manufacturing a solid membrane of fluorinated polymer by ink jet printing.

Info

Publication number: WO2008012423A2
Application number: PCT/FR2007/001261
Authority: WO
Inventors: Frédéric PRUVOST
Original assignee: Altatech Semiconductor
Priority date: 2006-07-28
Filing date: 2007-07-23
Publication date: 2008-01-31
Also published as: TW200818584A; FR2904477B1; WO2008012423A3; FR2904477A1

Abstract

Method of manufacturing a solid membrane of protonic conductor fluorinated polymer for fuel cell is accomplished by depositing on a substrate drops of a mixture, preferably in the form of micro-drops, by means of at least one ink jet print head, for example controlled by a piezoelectric element. The mixture comprises a polyhydric alcohol and a solution based on protonic conductor fluorinated polymer.

Description

Process for producing a solid fluoropolymer membrane by ink jet printing

Technical field of the invention

The invention relates to a method for producing a solid proton conductive fluoropolymer membrane for a fuel cell and more particularly for a fuel micropile.

State of the art

The manufacture of fuel cells, and more particularly PEMFC (Proton Exchange Membrane Fuel CeII) fuel cells involves a solid proton conductive polymer membrane. An example will be given later.

Among the proton conductive polymers, the fluorinated polymers such as the sulfonated tetrafluoroethylene copolymer are, by their performances, the most widespread in PEMFC cells.

On the other hand, the technique for manufacturing fluoropolymer membranes such as the sulfonated tetrafluoroethylene copolymer is not satisfactory. Indeed, the polymer is generally dissolved in solution before being manually deposited on a support using a syringe. A drying step then makes it possible to form a solid electrolyte membrane. Such a technique is not very precise and is not industrializable for the purpose of high volume production.

In particular, the printing techniques are known as described in documents US2002 / 134501 A1 and US2005100776A1. For the sulfonated tetrafluoroethylene copolymer, the latter is, in general, dissolved in water, propanol, ethanol and certain ethers in a small amount. Solutions comprising the sulfonated tetrafluoroethylene copolymer are, for example, marketed by Du Pont de Nemours, under the name of Nafion® range. More particularly, the proportions of sulfonated tetrafluoroethylene copolymer, water and propanol, in the solution, are, in general, respectively between 5% and 50%, between 30% and 90% and between 0 and 48% while the proportions ethanol and various ethers remain less than 4% and less than 1%, respectively. By way of example, there are solutions of Nafion® that can contain 10% by weight of polymer in water and solutions containing 20% by weight of polymer in 34% by weight of water, 44% by weight of propanol and 2% by weight of ethanol.

The documents US2003 / 060356A1, US2004 / 209153A1, US2004 / 151970A1 and US6074692A1 disclose other chemical additives that may be used for dissolution.

Object of the invention

The invention aims to overcome the disadvantages of the prior art. More particularly, the object of the invention is to propose a manufacturing method making it possible, in an industrializable manner, to obtain a uniform solid membrane made of proton conductive fluorinated polymer for a fuel cell.

For this purpose, the invention introduces a method for manufacturing a fuel cell element, of the type comprising the following steps: a) preparing a first electrode, able to form a support, b) depositing on the first electrode a membrane solid electrolyte in proton conductive fluorinated polymer, and c) depositing a second electrode, opposite the first, on the solid electrolyte membrane, characterized in that step b) comprises the following substeps: b1) preparing a proton-conducting fluorinated polymer-based mixture, of at least one solvent, and at least one polyol, b2) by means of an ink-jet printing head, depositing drops of the mixture obtained in b1) on the first electrode, as electrolyte, and b3) solidify said deposited drops, before proceeding to step c).

According to one embodiment, the manufacturing method uses an inkjet printing head which is controlled by a piezoelectric element.

According to another embodiment, said print head comprises one or more injection nozzles, each nozzle preferably being controlled individually by a piezoelectric element.

The piezoelectric element can be controlled by an electrical signal of frequency between 1 Hz and 2OkHz.

The drops mentioned above have a diameter that varies according to the electrical signal emitted by the piezoelectric element, the pressure of the mixture in the tank of the print head, and the output diameter of the print head. This diameter may be about 60 .mu.m, for example between 20 .mu.m and 100 .mu.m.

Therefore, the drops also have a diameter of about 60 .mu.m, for example between 20 .mu.m and 100 .mu.m. The drops may have a volume of between 1 μL and approximately 10 μL. According to one embodiment, during the execution of manufacturing method described above, step b2) and step b3) are repeated 1 to 10 times before step c).

The deposition of the drops in step b2) can be carried out in a chosen pattern. This pattern may be for example a mesh whose centers of the different cells are spaced from each other by a predetermined distance, which may for example be between 10 .mu.m and 100 .mu.m.

The mixture obtained during step b1) of the manufacturing process can comprise between 5% and 50%, preferably between 5% and 35%, and even more preferably between 10% and 35% by volume of polyol.

The fluoropolymer used in the process according to the invention may for example be a sulfonated tetrafluoroethylene copolymer or a perfluoroalkoxy.

The solvent in the mixture obtained in step b1) of the process according to the invention may comprise water. This solvent may further comprise propanol and / or ethanol and / or ethers.

The support of the process can be maintained at a temperature between 0 ⁰ C and 100 ⁰ C. This support can be secured to a moving part and moves at a predetermined speed relative to the print head.

In step b3) of the manufacturing process the solidification of the drops is done by evaporation of the polyol and the solvent.

According to one embodiment, the polyol may be ethylene glycol.

The invention also relates to a fuel micropile comprising at least one element manufactured according to the method described above. Other features and advantages of the present invention will become apparent upon consideration of the detailed description hereinafter.

Example of a method for manufacturing a known micropile

The PEMFC (Proton Exchange Membrane Fuel CeII) fuel cells can be manufactured from a silicon substrate in the following sequence: 1. anisotropic etching of the silicon substrate for the formation of the hydrogen passage channels;

- 2. Sputter deposition of the gold anode collector;

- 3. deposition of an insulating resin, photopolymerization of the resin through a mask, removal of the resin in the unexposed areas; - 4. Oxygen plasma cleaning resin residues that may be present in the channels;

- 5. manual micropipette deposition of a layer of graphite serving as a diffusion layer of hydrogen;

- 6. Electrochemical deposition of a conductive polyaniline polymer on the hydrogen diffusion layer. This layer serves as a support for the catalyst deposited on its surface;

- 7. Electrolytic deposition of anodic catalyst in platinum carbon or platinum;

- 8. Manual coating of the electrolyte membrane proton exchange;

9. Deposition by coating of the cathode catalyst in platinum;

- 10. Spray deposition through a mechanical mask of the gold cathode collector.

Variants of such a process can be used to manufacture fuel cells in general. As has been seen, the electrolyte used in step 8 may be in the form of a solid proton conductive polymer membrane.

Description of particular embodiments

A solid proton conductive fluoropolymer membrane, for a fuel cell and more particularly for a PEMFC fuel micropile, is obtained by depositing, on a support, drops of a mixture comprising a polyol and a fluoropolymer-based solution. proton conductor. The support is, for example, a thin layer forming the electrode of a fuel cell, a second electrode can then be deposited directly on said membrane.

The proton conducting fluorinated polymer is preferably selected from a sulfonated tetrafluoroethylene copolymer and a perfluoroalkoxy and is dissolved. Thus, the proton conducting fluorinated polymer solution preferably comprises a solvent comprising water with optionally propanol, ethanol and various ethers. The proportion of solvent in the solution is preferably between 15% and 50%, the remainder being preferably the pure fluorinated polymer. The solution is, for example, a solution of the type marketed under the name of Nafion® by the company Du Pont de Nemours or of the type marketed under the name of Hyflon® by Solvay Solexis. In addition, an additional amount of water may be added to said commercial solution.

Mixing said solution with a polyol, for example with ethylene glycol, also called glycol, makes it possible to manufacture the solid membrane by inkjet printing and, preferably, by piezoelectric type inkjet printing. The ink jet printing makes it possible to form, by ejection, drops and more particularly micro-drops of mixture depositing on the support, before drying and forming the membrane. The volume proportion of polyol in the mixture is more particularly between 5% and 50%, preferably between 5% and 35% and more preferably between 10% and 35%.

Indeed, a solid membrane constituted by the proton conductive fluorinated polymer and for example tetrafluoroethylene copolymer, is formed from drops of said mixture deposited on the support, via at least one jet printing head. ink, and more particularly of the piezoelectric type. More particularly, several drops are deposited successively, in various places on the surface of the support. The successive deposition of the drops is, for example, carried out using one or more print heads. The one or more printheads may comprise one or more injection nozzles, each nozzle being preferably controlled individually by a piezoelectric element. The volume of each drop depends, more particularly, on the diameter of the orifice of the injection nozzle, the parameters that control the pressure of the mixture in the reservoir of the print head, and the parameters of the electrical signal controlling the piezoelectric element. , when it controls the inkjet print head. Thus, a drop generated by an inkjet printing head may have a volume ranging from about 1 picolitre to about ten nanoliters. The frequency of the electrical signal controlling the piezoelectric element is between 1 Hz and 20 kHz and more particularly between 1 and 10 kHz.

The carrier, secured to a moving part of the printing equipment, preferably moves in two X and Y directions relative to said print head, with a predetermined movement speed, so that the different drops are spaced from each other by a predetermined distance. In other words, the drops are therefore uniformly deposited in a mesh. The drops spread, then, on the support. The solution drying by evaporation of the solvent and the polyol, thus forming a solid, uniform and smooth membrane of pure fluorinated polymer,

The spreading of the drops can be controlled by heating to a predetermined temperature of the support and / or by a modification of the wettability of the surface of the support vis-à-vis the deposited solution and / or by the predetermined distance, center center, between two adjacent drops (also called no). This corresponds substantially to the distance between the centers of two adjacent cells of the mesh defined above, at which the drops are deposited. The pitch depends in particular on the speed of movement and the frequency of ejection of the drops. For example, the pitch between two adjacent drops may be between 10 .mu.m and 100 .mu.m and the temperature of the support may be between 0 ⁰ C and 100 ° C. The thermalization of the support must be done beforehand during the deposition of the drops.

Such a technique makes it possible to quickly and efficiently make electrolytic membranes for fuel cells, directly on a fuel cell electrode. Thus, several steps of manufacturing the fuel cell can be carried out using the inkjet technique, for example: deposition of the lower electrode material, deposition of the electrolyte membrane, deposition of the electrode material higher. This makes it possible to consider the integration of these steps in a single equipment, which would make the manufacturing process of fuel cells much more robust. In addition, the use of the technique of the present invention results in uniform membrane thicknesses that promote the reproducibility of the performance of the fuel cells so manufactured.

The addition of solvent and polyol to the proton conductive fluoropolymer makes it possible, in fact, to reduce the viscosity of the polymer to a value allowing the formation of drops from an inkjet printing head. In addition, the polyol makes it possible to increase the drying time of the solution based on fluoropolymer. Indeed, without polyol, the solution may dry before being deposited on the support and in particular in the print head.

In a first example, tests were carried out using a mixture comprising 1 third by volume of a solution of Nafion® comprising 20% by weight of fluoropolymer, 34% by weight of water and 46% by weight of water. alcohol, 1 third by volume of ethylene glycol and 1 third by volume of water. The mixture is deposited on a support in the form of drops, using a piezoelectric type inkjet printing head. The output diameter of said print head is 60 μm and the electrical parameters used to control the piezoelectric element of the print head are as follows:

This makes it possible to form drops having a diameter of the order of 60 μm and a volume of about 110 picoliters.

The drops are deposited on a square section of 10mm x 10mm of a support such as a wafer type plate having a diameter of 100 mm.

(ie 4 inches). As shown in the table below, seven trials have were made, by varying the temperature of the support, I not between the drops and the number of deposited layers.

It has been found that the use of an ink jet printhead controlled by a piezoelectric element makes it possible to easily and industrially obtain a smooth and uniform tetrafluoroethylene copolymer solid membrane. By way of example, the π ° 7 test, with the deposition of 10 layers, a support temperature of 35 ° C. and a pitch of 42 μm, makes it possible to obtain a smooth and uniform membrane with a thickness of 7 μm. These tests make it possible to determine the optimal conditions (pitch and temperature T of the support) to obtain membranes having a substantially constant thickness while depositing as much material as possible each time. Thus, the pair pitch = 42μm and T = 35 ⁰ C shows the best results.

In a second example, tests were carried out from a solution comprising 50% by volume of the Nafion® solution used for the first example, 25% by volume of ethylene glycol and 25% by volume of water with the same print head as in the first example. The signal used to control the piezoelectric element of the print head is a unipolar signal having the following parameters:

These parameters make it possible to reduce the length of the comet of the drop and allow ejection stops of drops lasting more than 30 seconds without requiring maintenance or purging of the print head. In this case, a stop ejection drops, for a significant time, does not cause clogging of the print head while usually for stops greater than 30s, purges and automatic cleaning of the head must be made to avoid blocking it. In addition, for a mixture containing no polyol, a stop of a second mouth the print head by drying the solution. Finally, increasing the drying time of the mixture makes it possible to obtain membranes of uniform thickness. The drops have, indeed, the time to coalesce together rather than to dry as soon as the impact with the support.

The drops are deposited on a square section of 10mm x 10mm of a support such as a "wafer" type plate having a diameter of 100mm (4 inches). As shown in the table below, 5 tests were carried out, with a support temperature of 35 ° C and varying the pitch between the drops and the number of layers deposited.

In the second example, the tests were performed with a higher proportion of Nation® solution compared to the tests of the first example. However, the fact of being able to increase the proportion of the Nation® solution in the mixture can be interesting, since a greater quantity of polymer is deposited on the support, once the solvents have been evaporated and the deposition time also called cycling time can to be diminished,

Two different step values (42 and 20μm) were also tested. The passage of a step of 42 .mu.m and 20 .mu.m also makes it possible to increase the quantity of polymer deposited, even if the drying time is also increased. However, the tests show that by decreasing the proportion of ethylene glycol and water and therefore increasing the proportion of

Nation®, the drops remain easily ejected from the print head, while limiting the cycle times, with the same uniformity characteristics as in the first example.

Claims

claims

A method of manufacturing a fuel cell element, of the type comprising the following steps: a) preparing a first electrode, capable of forming a support, b) depositing on the first electrode a solid electrolyte membrane made of proton conductive fluoropolymer, and c) depositing a second electrode, opposite the first, on the solid electrolyte membrane, characterized in that step b) comprises the following substeps: b1) preparing a proton conducting fluorinated polymer-based mixture , at least one solvent, and at least one polyol, b2) by means of an ink-jet printing head, depositing drops of the mixture obtained in b1) on the first electrode, as electrolyte, and b3) solidify said deposited drops, before proceeding to step c).

2. The manufacturing method according to claim 1, characterized in that the ink jet printhead is controlled by a piezoelectric element.

3. The manufacturing method according to claim 1, characterized in that the print head comprises one or more injection nozzles, each nozzle preferably being controlled individually by a piezoelectric element.

4. Manufacturing process according to claims 2 or 3, characterized in that the piezoelectric element is controlled by an electrical signal frequency between 1 Hz and 2OkHz.

5. Manufacturing process according to claims 2 to 4, characterized in that the drops have a diameter depending on the electrical signal emitted by the piezoelectric element, the pressure of the mixture in the tank of the print head, and the output diameter of the print head.

6. Manufacturing method according to one of the preceding claims, characterized in that the output diameter of the print head is about 60 .mu.m.

7. Manufacturing process according to one of the preceding claims, characterized in that the drops have a diameter of about 60 .mu.m.

8. Manufacturing process according to one of the preceding claims, characterized in that the drops have a volume of between 1 pL and about 10OnL

9. The manufacturing method according to one of the preceding claims, characterized in that one repeats 1 to 10 times step b2) and step b3) before step c).

10. The manufacturing method according to one of the preceding claims, characterized in that the deposition of the drops in step b2) is performed in a chosen pattern.

11. The manufacturing method according to claim 10, characterized in that the chosen pattern is a mesh whose centers of the different cells are spaced from each other by a predetermined distance.

12. The manufacturing method according to claim 11, characterized in that the predetermined distance is between 10 .mu.m and 100 .mu.m.

13. The manufacturing method according to one of the preceding claims, characterized in that said mixture obtained in step b1) comprises between 5% and 50% by volume of polyol.

14. The manufacturing method according to one of the preceding claims, characterized in that said mixture obtained in step b1) comprises between 5% and 35% by volume of polyol.

15. The manufacturing method according to one of the preceding claims, characterized in that said mixture obtained in step b1) comprises between 10% and 35% by volume of polyol.

16. The manufacturing method according to one of the preceding claims, characterized in that the fluoropolymer is a sulfonated tetrafluoroethylene copolymer.

17. The manufacturing method according to one of the preceding claims, characterized in that the fluorinated polymer is a perfluoroalkoxy.

18. The manufacturing method according to one of the preceding claims, characterized in that the solvent in the mixture obtained in step b1) comprises water.

19. The manufacturing method according to claim 18, characterized in that said solvent further comprises propanol and / or ethanol and / or ethers.

20. Manufacturing process according to one of the preceding claims, characterized in that the support is maintained at a temperature between 0 ⁰ C and 100 ⁰ C.

21. The manufacturing method according to one of the preceding claims, characterized in that in step b3) solidification of the drops is by evaporation of the polyol and the solvent.

22. Manufacturing method according to one of the preceding claims, characterized in that the support is secured to a moving part and moves at a predetermined speed relative to the print head.

23. Manufacturing process according to one of the preceding claims, characterized in that the polyol is ethylene glycol.

24. Micropile fuel, characterized in that it comprises at least one element manufactured according to the method of one of the preceding claims.