Fluorinated proton-conducting inorganic particles and use of said particles in proton-conducting membranes

Abstract

Silica particles bonded to polymer chains consisting of at least one polymer comprising at least one fluorinated styrene repeating unit comprising at least one proton-conducting group, optionally in the form of a salt, the bonding between the particles and each of the chains being carried out by an organic spacer group.

Claims

1. Particles of silica bonded to polymer chains constituted of at least one polymer comprising at least one fluorinated styrenic repetitive unit carrying at least one proton-conducting group, optionally in the form of a salt, with the bond between said particles and each one of these chains being carried out via at least one organic spacer group.

2. Particles of silica according to claim 1, wherein the fluorinated styrenic repetitive unit or units have the following formula (I): ##STR00033## Z.sup.1 corresponds to a fluorinated phenylene group; and E.sup.1 corresponds to a single bond or an organic spacer group; E.sup.2 corresponds to a proton-conducting group, optionally in the form of a salt.

3. Particles of silica according to claim 2, wherein E.sup.1 is a single bond.

4. Particles of silica according to claim 2, wherein E.sup.1, when it is an organic spacer group, is an alkylene group, a —S-alkylene- group or an —O-alkylene group.

5. Particles of silica according to claim 1, wherein the fluorinated styrenic unit is a unit having the following formula (IV): ##STR00034## E.sup.1 corresponds to a single bond or an organic spacer group; and E.sup.2 corresponds to a proton-conducting group, optionally in the form of a salt.

6. Particles of silica according to claim 1, wherein the fluorinated styrenic unit has one of the following formulas (V), (VI) or (VII): ##STR00035## wherein R is a hydrogen atom or a cation.

7. Particles of silica according to claim 1, wherein the polymer comprising at least one fluorinated styrenic repetitive unit carrying at least one proton-conducting group, optionally in the form of a salt, also comprises at least one non-fluorinated styrenic repetitive unit carrying at least one proton-conducting group, optionally in the form of a salt.

8. Particles of silica according to claim 7, wherein the non-fluorinated styrenic repetitive unit or units have the following formula (VIII): ##STR00036## wherein: Z.sup.2 corresponds to a non-fluorinated phenylene group; and E.sup.3 corresponds to a proton-conducting group, optionally in the form of a salt.

9. Particles of silica according to claim 7, wherein the non-fluorinated styrenic repetitive unit is a repetitive unit coming from the polymerisation of a monomer of the family of the styrenesulphonic acids, said acids can be in the form of a salt.

10. Particles of silica according to claim 7, wherein said non-fluorinated styrenic repetitive unit is a unit having the following formula (IX): ##STR00037## wherein R is a hydrogen atom or a cation.

11. Particles of silica according to claim 1, wherein the organic spacer group or groups have the following formula (X):
—X.sup.1—R.sup.1—X.sup.2  (X) wherein: X.sup.1 is the group covalently bonded to the particles; R.sup.1 is an organic group forming a bridge between X.sup.1 and X.sup.2; and X.sup.2 is the group covalently bonded to a polymer chain.

12. Particles of silica according to claim 11, wherein the group X.sup.1 is a group having the following formula (XI): ##STR00038## X.sup.3 being an alkylene group; the brackets present on the oxygen atoms indicating the locations of bonds with the particle and the bracket has on X.sup.3 indicating the location by which is carried out the bond with R.sup.1.

13. Particles of silica according to claim 11, wherein the group X.sup.2 is an alkylene group.

14. Particles of silica according to claim 11, wherein the group R.sup.1 is an aromatic group.

15. Particles of silica according to claim 11, wherein the organic spacer group or groups have the following formula (XII): ##STR00039## the brackets present on the oxygen atoms indicating the locations of bonds with the particle and the bracket present on the group —(CH.sub.2).sub.n4— indicating the location by which is carried out the bond with the polymer chain, while n.sub.3 and n.sub.4 correspond to the number of repetitions of units taken in brackets, with these numbers being whole numbers ranging from 1 to 15.

16. Particles of silica according to claim 1, which are: particles of silica bonded to polymer chains formed by polymers resulting from the chaining of a repetitive unit having formula (V) or (VI): ##STR00040## with each one of said polymer chains being bonded to said particles via at least one organic spacer group having formula (XII): ##STR00041## the brackets present on the oxygen atoms indicating the locations of bonds with the particle and the bracket present on the group —(CH.sub.2).sub.n4— indicating the location by which is carried out the bond with the polymer chain, while n.sub.3 and n.sub.4 correspond to the number of repetitions of units taken in brackets, with these numbers being whole numbers ranging from 1 to 15; particles of silica bonded to polymer chains formed by copolymers resulting from the chaining of a repetitive unit having formula (V) as defined above and of a repetitive unit having formula (IX): ##STR00042## with each one of said polymer chains being bonded to said particles via at least one organic spacer group having formula (XII) as defined above; or particles of silica bonded to polymer chains formed by copolymers resulting from the chaining of a repetitive unit having formula (VI) as defined above and of a repetitive unit having formula (IX) as defined above, with each one of said polymer chains being bonded to said particles via at least one organic spacer group having formula (XII) as defined above.

17. Proton-conducting composite material comprising a polymeric matrix within which particles are dispersed as defined according to claim 1.

18. Conducting composite material according to claim 17, wherein the polymeric matrix is a non-proton-conducting polymer.

19. Composite material according to claim 18, wherein the non-proton-conducting polymer is a fluorinated polymer.

20. Fuel cell membrane comprising a conducting composite material as defined according to claim 17.

21. Fuel cell device comprising at least one electrode-membrane-electrode assembly, wherein the membrane is as defined according to claim 20.

22. Method for preparing particles as defined in claim 1, said method comprising the following steps: a) a step of putting into contact particles of silica with an initiating compound of a polymerisation of the ATRP type, said compound comprises at least one group able to be grafted to said particles, whereby particles grafted by the remainder of said initiating compound are obtained; b) a step of putting into contact said particles obtained in a) with: at least one fluorinated styrenic monomer optionally carrying at least one proton-conducting group, optionally in the form of a salt; and optionally, at least one non-fluorinated styrenic monomer carrying at least one proton-conducting group, optionally in the form of a salt; whereby there is a polymerisation of the ARTP type of said monomer or monomers from the aforementioned remainders; c) when the repetitive unit coming from the polymerisation of the fluorinated styrenic monomer is not carrying at least one proton-conducting group, optionally in the form of a salt, a step of introducing on this repetitive unit of at least one proton-conducting group, optionally in the form of a salt, with the unit thus corresponding to a fluorinated styrenic repetitive unit carrying at least one proton-conducting group, optionally in the form of a salt.

Description

DETAILED EXPOSURE OF PARTICULAR EMBODIMENTS

Example 1

(1) This example shows the preparation of the particles of silica covalently bonded to a polymerisation initiator of the ATRP type according to the following reaction scheme:

(2) ##STR00024##

(3) Silica (6 g, is about 0.02 mol of silanol on the surface) and toluene (500 mL) are introduced in a bicol under an argon flow. The resulting mixture is passed through ultrasound, in order to disperse the silica well in the toluene. Then the mixture is brought to reflux. Chloromethylphenylethyltrimethoxysilane (10 g, 0.036 mol) is introduced drop by drop into the mixture. The reflux is left for 4 hours.

(4) The functionalised particles of silica are then isolated via centrifugation then purified by two successive dispersion/centrifugation cycles in ethanol and acetone.

(5) The recovered particles of silica are then dried in the oven at 80° C. for one night.

Example 2

(6) This example shows the ATRP polymerisation of 2,3,4,5,6-pentafluorostyrene from functionalised particles of silica obtained in the example 1.

(7) The reaction scheme is as follows:

(8) ##STR00025##

(9) BPy corresponding to the bipyridine and DMSO to the dimethylsulfoxide and n.sup.1 corresponding to the repetition number of the repetitive unit between brackets.

(10) The 2,3,4,5,6-pentafluorostyrene is distilled beforehand and the polymerisation reactor is heated in a vacuum (3 heating/cooling cycles) before use.

(11) Dimethylsulfoxide (DMSO) (200 mL) is degassed in a vacuum by bubbling the argon for 15 minutes in a bicol. The distilled 2,3,4,5,6-pentafluorostyrene (10 g) and the silica obtained at the end of the example 1 (2 g) are then introduced under argon flow into the bicol. Two vacuum/argon cycles are carried out then argon is set to bubble in the mixture.

(12) When the silica is perfectly dispersed in the mixture, bipyridine (0.05 M) and copper chloride (0.08 M) are introduced under an argon flow. Three vacuum/argon cycles are finally carried out.

(13) Then the bicol is set in place under stirring in an oil bath preheated to 80° C. After about 30 minutes of polymerisation, the mixture becomes very viscous and the stirring becomes difficult. The reaction is then stopped by the venting of the system. The mixture changes from a brown colour to a green colour.

(14) The mixture is diluted with tetrahydrofurane (THF) for about 2 hours, so as to obtain a liquid solution.

(15) The particles are precipitated in isopropanol, solubilised in THF, then reprecipitated twice in water with strong stirring.

(16) The particles are then dried in the oven at 60° C. for one night and have the form of a white solid.

Example 3

(17) This example shows the preparation of a sulphur polymer obtained by sulphuration of the polymer grafted on the silica obtained in the example 2.

(18) The reaction scheme is as follows:

(19) ##STR00026##

(20) DMSO corresponding to the dimethylsulfoxide, RT corresponding to the ambient temperature and n.sup.1 corresponding to the repetition number of the repetitive unit between brackets.

(21) The grafted particles obtained in the example 2 are dispersed in DMSO (200 mL) in a flask at ambient temperature for 1 hour, the particles thus dispersed undergo a phenomenon of swelling. Then hydrogen sulphate monohydrate (1.2 eq. in relation to the number of moles of monomer units) is introduced little by little into the flask still at ambient temperature.

(22) A first colorimetric transition is observed from pale yellow to blue then a disappearance of the blue coloration.

(23) The reaction mixture then changes after 30 minutes to a green colour and, at the end of the reaction, the mixture has a blue homogenous colour.

(24) The reaction mixture has, at the end of the reaction, a very high viscosity. It is diluted in water than is precipitated twice with isopropanol.

(25) The product coming from the reprecipitation is dried via lyophilisation and has the form of a yellow solid.

Example 4

(26) This example shows the preparation of a sulphur polymer obtained by sulphonation of the grafted polymer obtained in the example 3.

(27) The reaction scheme is as follows:

(28) ##STR00027##

(29) RT corresponding to the ambient temperature and n corresponding to the repetition number of the repetitive unit between brackets.

(30) In a 100 mL flask, the product obtained in the example 3 (2 g) is put into suspension in formic acid for 30 minutes. The flask is then placed in an ice bath. After 15 minutes, hydrogen peroxide (2 eq. in relation to the number of monomer units) is introduced drop by drop. The mixture is then placed at ambient temperature for 18 hours then at reflux for 5 hours.

(31) The product is precipitated in isopropanol then is added into an aqueous solution of sodium hydroxide (1 M). The mixture is then stirred for 24 hours. The product is filtered and rinsed with isopropanol. The final product is placed in the oven at 60° C. for one night.

Example 5

(32) This example shows the preparation of a sulphonated polymer comprising a sulphur organic spacer group obtained by sulphonation of the grafted polymer of the example 3 according to the following reaction scheme:

(33) ##STR00028##

(34) In a flask, the product obtained in the example 3 (1 g) is put into suspension in soda at 1M (25 mL) at ambient temperature for 1 hour. 1,3-propanesultone (1.2 eq. in relation to the number of moles of monomer units) is diluted in dioxane (5 mL) then introduced drop by drop at ambient temperature. The mixture is then set to reflux for 24 hours.

(35) The mixture is filtered and wash with water. A colourless gel is obtained.

(36) The product is dried in the oven at 60° C. for one night.

Example 6

(37) This example shows the ATRP polymerisation of 2,3,4,5,6-pentafluorostyrene and of tetra-n-butylammonium styrenesulphonate from functionalised particles of silica obtained in the example 1.

(38) The reaction scheme is as follows:

(39) ##STR00029##

(40) BPy corresponding to the bipyridine, DMSO to the dimethylsulfoxide, TBA corresponding to tetra-n-butylammonium and n.sup.1 and n.sup.2 corresponding to the repetition numbers of the repetitive units between brackets.

(41) The 2,3,4,5,6-pentafluorostyrene is distilled beforehand and the polymerisation reactor is heated in a vacuum (3 heating/cooling cycles) before use.

(42) The tetra-n-butylammonium styrenesulphonate is prepared by cation exchange between the hydrogen of the tetra-n-butylammonium and the sodium ion of the sodium styrenesulphonate.

(43) Dimethylsulfoxide (DMSO) (200 mL) is degassed in a vacuum by bubbling the argon for 15 minutes in a bicol. The distilled 2,3,4,5,6-pentafluorostyrene (5 g), the tetra-n-butylammonium styrenesulphonate (5 g) and the silica obtained at the end of the example 1 (2 g) are then introduced under argon flow into the bicol. Two vacuum/argon cycles are carried out then argon is set to bubble in the mixture.

(44) When the silica is perfectly dispersed in the mixture, bipyridine (0.05 M) and copper chloride (0.08 M) are introduced under an argon flow. Three vacuum/argon cycles are finally carried out.

(45) Then the bicol is placed under stirring in an oil bath preheated to 80° C. After about 4 hours of polymerisation, the mixture becomes very viscous and the stirring becomes difficult. The reaction is then stopped by the venting of the system. The mixture changes from a brown colour to a green colour.

(46) The mixture is diluted with tetrahydrofurane (THF) for about 2 hours, so as to obtain a liquid solution.

(47) The particles are precipitated in isopropanol, solubilised in THF, then reprecipitated twice in water with strong stirring.

(48) The particles are then dried in the oven at 60° C. for one night and have the form of a white solid.

Example 7

(49) This example shows the preparation of a sulphur polymer obtained by sulphuration of the polymer grafted on the silica obtained in the example 6.

(50) The reaction scheme is as follows:

(51) ##STR00030##

(52) The conditions for carrying out this preparation are identical to those of the example 3.

Example 8

(53) This example shows the preparation of a sulphur polymer obtained by sulphonation of the grafted polymer obtained in the example 7.

(54) The reaction scheme is as follows:

(55) ##STR00031##

(56) The conditions for carrying out this preparation are identical to those of the example 4.

Example 9

(57) This example shows the preparation of a sulphonated polymer comprising a sulphur organic spacer group obtained by sulphonation of the grafted polymer of the example 7 according to the following reaction scheme:

(58) ##STR00032##

(59) The conditions for carrying out this preparation are identical to those of the example 5.

Example 10

(60) In this example is shown the preparation of membranes from particles of the examples 4, 5, 8 and 9.

(61) To do this, in a 50 mL Erlenmeyer flask, a copolymer of vinylidene fluoride and of hexafluoropropene (known as the abbreviation poly(VDF-co-HFP) (1 g) is introduced. Then the particles concerned (1.631 g) and dimethylsulfoxide (26 g) are introduced into the Erlenmeyer flask.

(62) The resulting mixture is heated under moderate stirring at 60° C., in order to accelerate the solubilisation of the poly(VDF-co-HFP) and of the particles. The mixture is then passed through ultrasound for 45 minutes, in order to dissociate the particle aggregates. A yellow solution results.

(63) The solution, after having been degassed, is poured onto a glass plate cleaned beforehand with acetone then with methanol and finally with acetone, with the pouring being carried out using a manual applicator of the “Hand coater” type provided with an air-gap of 500 μm. The glass plate, on which the solution was poured, is placed on a plate heated to 110° C., still under a laminar flow hood, for a few hours in order to evaporate the solvent. Use of the laminar flow hood for the pouring and the evaporation is justified in order to prevent the introduction of dusts into the membranes.

(64) After having been detached from the glass plate, the membrane is dried then is put into contact, under moderate stirring, with a concentrated solution of sulphuric acid at 98% at ambient temperature for 4 days.

(65) The membrane is then rinsed three times with distilled water and dried at ambient temperature between several absorbent papers.

(66) As mentioned hereinabove, this protocol was carried out respectively with the particles obtained in the examples 4, 5, 8 and 9.

(67) The membranes obtained with these particles were subjected to a thermohydric ageing test by immersing them in water at 80° C. for 5 days. The gravimetric reading of the membranes at the end of this immersion shows no loss of weight of the membrane. The IR analyses carried out with the membranes reveal, moreover, the presence of organic functions associated with the polymer present on the particles.

(68) These results attest that the fluoration of the conducting polymer makes it possible to prevent the elution of the particles within the membranes.

(69) For the purposes of information, the membranes that do not contain fluorinated polymer lose up to 30% of their weight at the end of the thermohydric ageing test.