Organic-inorganic hybrid nanofibres having a mesoporous inorganic phase, preparation thereof by electrospinning, membrane, electrode, and fuel cell

Abstract

Organic-inorganic hybrid nanofibres comprising two phases: a first mineral phase comprising a structured mesoporous network with open porosity; and a second organic phase comprising an organic polymer, wherein said organic phase is basically not present inside the pores of the structured mesoporous network. A membrane and an electrode comprising said nanofibres. A fuel cell comprising said membrane and/or said electrode. A method of preparing said nanofibres by electrically assisted extrusion (electrospinning).

Claims

1. Organic-inorganic hybrid nanofibers comprising two phases: a first mineral phase comprising a structured mesoporous network with open porosity; and a second organic phase comprising an organic polymer, wherein said second organic phase is not present inside pores of the structured mesoporous network; wherein the first mineral phase has organic chemical functional groups, and wherein the second organic phase has organic chemical functional groups; wherein the organic chemical functional groups of the first mineral phase and the second organic phase are respectively chosen from among conductive and/or hydrophilic functional groups; and wherein said conductive functional groups are selected from the group consisting of cation exchange groups and anion exchange groups; wherein the cation exchange groups are selected from the group consisting of SO.sub.3M; PO.sub.3M.sub.2; and B(OM).sub.2, where M represents hydrogen and a monovalent metallic cation; and wherein the anion exchange groups are selected from the group consisting of pyridyl, imidazolyl, pyrazolyl, triazolyl, and radicals of formula .sup.+N(R.sup.6).sub.3X.sup. and .sup.+NR.sup.8X groups; wherein X represents an anion, and where each R.sup.6 is independently selected from the group consisting of H, an alkyl group, an aryl group, aromatic and non-aromatic basic radicals containing at least one radical selected from the group consisting of imidazole, vinylimidazole, pyrazole, oxazole, carbazole, indole, isoindole, dihydrooxazole, isooxazole, thiazole, benzothiazole, isothiazole, benzoimidazole, indazole, 4,5-dihydropyrazole, 1,2,3-oxadiazole, furazane, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,3-benzotriazole, 1,2,4-triazole, tetrazole, pyrrole, aniline, pyrrolidine, and pyrazole radicals; and the .sup.+NR.sup.8X groups, and R.sup.8 is a group, which forms with nitrogen .sup.+N a cycle of 4 to 10 ring atoms including carbon and nitrogen atoms; and wherein said organic chemical functional groups of the first mineral phase are located at a surface of the pores of the structured mesoporous network, and are bonded covalently to walls of the structured mesoporous network, wherein the organic-inorganic hybrid nanofibers further comprise nanoparticles of metal oxides, wherein the nanoparticles of the metal oxides spread and are bounded on at least one of external surfaces of the organic-inorganic hybrid nanofibers, and wherein a metal of the metal oxides is selected from the group consisting of gold, silver, platinum, palladium, nickel, copper, ruthenium, rhodium, cobalt, and an alloy thereof.

2. The organic-inorganic hybrid nanofibers according to claim 1, wherein the structured mesoporous network with open porosity is aligned in a determined, particular direction.

3. The organic-inorganic hybrid nanofibers according to claim 1, wherein the first mineral phase and the second organic phase are continuous and interwoven.

4. The organic-inorganic hybrid nanofibers according to claim 1, wherein the organic-inorganic hybrid nanofibers comprise a core consisting of the first mineral phase surrounded by a sheath consisting of the organic phase.

5. The organic-inorganic hybrid nanofibers according to claim 1, wherein the first mineral phase is discontinuous, and dispersed in the organic phase, which is continuous.

6. The organic-inorganic hybrid nanofibers according to claim 1, further comprising a third phase, inside the pores, consisting of at least one structuring, texturizing agent, optionally having organic chemical functional groups.

7. The organic-inorganic hybrid nanofibers according to claim 1, further comprising catalytic nanoparticles.

8. The organic-inorganic hybrid nanofibers according to claim 1, wherein the first mineral phase consists of at least one oxide selected from the group consisting of metal oxides, oxides of metalloids, and mixed oxides thereof.

9. The organic-inorganic hybrid nanofibers according to claim 1, wherein the structured mesoporous network has an organised structure with a repeating unit.

10. The organic-inorganic hybrid nanofibers according to claim 9, wherein the structured mesoporous network has a cubic, hexagonal, lamellar, vermicular, vesicular or bicontinuous structure.

11. The organic-inorganic hybrid nanofibers according to claim 1, wherein a size of the pores of the structured mesoporous network is 1 to 100 nm.

12. The organic-inorganic hybrid nanofibers according to claim 1, wherein the organic polymer is a thermostable polymer.

13. The organic-inorganic hybrid nanofibers according to claim 6, wherein the texturizing, structuring agent is selected from the group consisting of surfactants; acids; bases; phospholipids; amphiphilic multi-block copolymers including at least one hydrophobic block associated with at least one hydrophilic block.

14. A membrane comprising the organic-inorganic hybrid nanofibers according to claim 1, optionally deposited on a support.

15. An electrode comprising the organic-inorganic hybrid nanofibers claim 1.

16. A fuel cell comprising at least one membrane according to claim 14.

17. A method of preparing organic-inorganic hybrid nanofibers, according to claim 1, comprising: a) preparing at least one solution, in a solvent, of a mineral precursor A and/or of an organomineral precursor C to constitute the first mineral phase; b) adding at least one structuring, texturizing agent D of a mesoporous mineral phase to the solution prepared in step a), whereby a solution S1 is obtained; and, optionally, said solution S1 is hydrolysed and left to age; c) preparing a solution S2 of an organic polymer E in a solvent; d) carrying out simultaneous, separate electrically assisted extrusion of the solution S1 and of the solution S2 with a bicapillary electrically assisted extrusion device; or alternatively carrying out the electrically assisted extrusion of a mixture, optionally aged, of the solution S1 and the solution S2 with a monocapillary extrusion device; wherein said bicapillary electrically assisted extrusion device and said monocapillary extrusion device respectively comprise at least one syringe containing a solution(s) connected to a needle to which a voltage is applied, and a manifold or support, whereby a deposit of organic-inorganic hybrid nanofibers is obtained on the manifold or support; e1) carrying out heat treatment to consolidate the deposit of the organic-inorganic hybrid nanofibers; or, alternatively, e2) carrying out heat treatment to eliminate the organic polymer E, the structuring, texturizing agent D, and optionally the support, by calcination; f) totally or partially eliminating optionally, on conclusion of step e1, the structuring, the texturizing agent D and/or the organic polymer E; g) separating or eliminating optionally, on conclusion of step e1) step e2) or step f) the support; wherein the organic polymer E and/or the structuring, texturizing agent D carries (carry) organic chemical functional groups and/or precursor functional groups of these organic chemical functional groups, and/or the organomineral precursor C is a compound having (i) organic chemical functional groups or precursors thereof, that may be conductive and/or have hydrophilic functions, and (ii) functional groups which may become bonded to the surface of the pores of the structured mesoporous network.

18. The method according to claim 17, wherein the mineral precursor A is selected from the group consisting of metal salts, salts of metalloids, metal alkoxides, and alkoxides of metalloids.

19. The method according to claim 17, wherein a chelating agent B is also added to the solution S1.

20. The method according to claim 17, wherein the solution S1, the solution S2, or a mixture of the solutions S1 and S2, have a viscosity of 40 to 7,000 cps at 20 C.

21. The method according to claim 17, wherein a concentration in the solution S1 of the mineral precursor A and/or of the organomineral precursor C, and a concentration in the solution S2 of polymer E, expressed as a dry extract, are 15 to 60% by mass.

22. The method according to claim 17, wherein the solvents of the solutions S1 and S2 are low-volatility solvents, a vapour tension of which is lower than that of ethanol.

23. The method according to claim 17, wherein the solution S1 is left to age at a temperature of 0 C. to 300 C.; at a pressure of 100 Pa to 5.Math.10.sup.6 Pa; over a period of several minutes to several days.

24. The method according to claim 17, wherein, prior to the electrically assisted extrusion, the solution S1 and/or the solution S2 is (are) preheated to a temperature of 40 C. to 80 C.

25. The method according to claim 17, wherein the electrically assisted extrusion is controlled by acting on one or more of the following parameters: a deposition temperature; a relative humidity of an atmosphere in which the deposition is carried out; a voltage applied to the needle; a flow speed of the solutions or of the mixture in the syringe; a distance between the needle and the manifold or support; the atmosphere in which the deposition is carried out.

26. The method according to claim 25, wherein one or more of the parameters is (are) chosen in accordance with the following: deposition temperature: 20 C. to 200 C.; relative humidity of the atmosphere in which the deposition is carried out: 0 to 90%; voltage applied to the needle; 2 to 25 kV; flow speed of the solutions or of the mixture in the syringe: 0.1 to 20 mL/h; distance between the needle and the manifold or support: 2 to 25 cm; atmosphere wherein the deposition is carried out: Air, Nitrogen or Argon.

27. The method according to claim 17, wherein the solution S1 and/or the solution S2 comprise(s) catalytic nanoparticles.

28. The method according to claim 27, wherein a suspension of catalytic nanoparticles is spray-coated in a jet coming out of the needle of the electrically assisted extrusion device.

29. The method according to claim 17, wherein the method further comprises releasing or generating the organic chemical functional groups of the first mineral phase on the surface of the pores of the organic-inorganic hybrid nanofibers.

30. The organic-inorganic hybrid nanofibers according to claim 1, wherein the monovalent metallic cation is selected from the group consisting of Li.sup., Na.sup.+, K.sup.+, and N.sup.+(R.sup.4).sub.3; and wherein each R.sup.4 represents independently a hydrogen, an alkyl radical or an aryl radical.

31. The organic-inorganic hybrid nanofibers according to claim 1, wherein the X anion is selected from the group consisting of F, Cl, Br, I, NO.sub.3, SO.sub.4H and OR.sup.7, wherein R.sup.7 represents an alkyl group or an aryl group.

32. The organic-inorganic hybrid nanofibers according to claim 1, wherein .sup.+NR.sup.8X group is selected from the group consisting of imidazolinium, pyridinium, and pyrazolium cycle.

33. The organic-inorganic hybrid nanofibers according to claim 1, wherein the anion exchange group is an imidazolinium group.

34. The organic-inorganic hybrid nanofibers according to claim 1, wherein when R.sup.6 is an alkyl group or an aryl group, the alkyl group has from 1 to 10 C and the aryl group has from 6 to 10 C.

35. The organic-inorganic hybrid nanofibers according to claim 30, wherein when R.sup.4 is an alkyl radical or an aryl radical, the alkyl radical has from 1 to 10 C and the aryl radical has from 6 to 10 C.

36. The organic-inorganic hybrid nanofibers according to claim 31, wherein when R.sup.7 is an alkyl group or an aryl group, the alkyl group has from 1 to 10 C and the aryl group has from 6 to 10 C.

37. The organic-inorganic hybrid nanofibers according to claim 1, wherein the cation exchange groups are selected from the group consisting of SO.sub.3M; PO.sub.3M.sub.2; and B(OM).sub.2, where M represents hydrogen or a monovalent metallic cation.

38. The organic-inorganic hybrid nanofibers according to claim 1, wherein the cation exchange groups are selected from the group consisting of PO.sub.3M.sub.2 and B(OM).sub.2, where M represents hydrogen or a monovalent metallic cation.

39. The organic-inorganic hybrid nanofibers according to claim 1, wherein the nanoparticles of the metal oxides are distributed throughout the first mineral phase or the second organic phase or throughout both phases.

Description

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

(1) FIG. 1A is a schematic view of a monocapillary electrically assisted extrusion device, comprising a single reactor containing a mixture of a solution A and a solution B, which is extruded;

(2) FIG. 1B is a schematic sectional view of a fibre obtained with the device of FIG. 1A;

(3) FIG. 2A is a schematic view of a bicapillary electrically assisted extrusion device, comprising a first reactor, containing a solution A, which is embedded in a second reactor, containing a solution B, where solutions A and B are extruded simultaneously, separately and independently through concentric apertures, to form a single hybrid fibre according to the invention (FIG. 2B);

(4) FIG. 2B is a schematic sectional view of a hybrid fibre obtained with the device of FIG. 2A;

(5) FIG. 3A is a schematic view of a monocapillary electrically assisted extrusion device, comprising a single reactor containing a mixture of a solution A and of a solution B, which is extruded; wherein the monocapillary electrically assisted extrusion device is coupled to a device for spraying a solution C;

(6) FIG. 3B is a schematic sectional view of a fibre obtained with the device of FIG. 3A;

(7) FIG. 4A is a schematic view of a bicapillary electrically assisted extrusion device, comprising a first reactor, containing a solution A, which is embedded in a second reactor, containing a solution B, wherein solutions A and B are extruded simultaneously and independently through concentric apertures, to form a single hybrid fibre; wherein the bicapillary electrically assisted extrusion device is coupled with a device for spraying a solution C;

(8) FIG. 4B is a schematic sectional view of a fibre obtained with the device of FIG. 4A;

(9) FIGS. 5A to 5D are images obtained by scanning electron microscopy of the hybrid fibres obtained in example 1 by the method according to the invention, where these fibres have been subjected to one of the following ageing heat treatments: Heating at 70 C. for 12 hours (FIG. 5A); or alternatively Heating at 130 C. for 4 hours (FIG. 5B); or alternatively Heating at 70 C. and extraction of the surfactant by washing in ethanol (FIGS. 5C and 5D);

(10) The scales represented in FIGS. 5A to 5D are 2 m.

(11) FIGS. 6A to 6D are images obtained by scanning electron microscopy (SEM) of the PEOS/PVDF-HFP hybrid membranes obtained in example 2 by the method according to the invention, comprising one of the following ageing heat treatments: Ageing of the membrane at a temperature of 25 C. for one night (FIG. 6A); or alternatively Ageing of the membrane at a temperature of 70 C. for one night (FIG. 6B); or alternatively Ageing of the membrane at a temperature of 550 C. for one night (FIGS. 6C and 6D).

(12) The scales shown in FIGS. 6A and 6D represent 2 m, and the scales shown in FIGS. 6B and 6C represent 10 m.

(13) FIG. 7A is a photograph of an opaque membrane obtained in example 2 by the method according to the invention from solutions of PEOS/PVDF-HDP.

(14) The scale shown in FIG. 7A is a rule graduated in centimetres.

(15) FIG. 7B is a SEM image of the opaque membrane of FIG. 7A.

(16) The scale shown in FIG. 7B represents 20 m.

DETAILED DESCRIPTION OF THE INVENTION

(17) The following description is given principally in relation with the method for preparing nanofibres according to the invention.

(18) In what follows, therefore, a description is given of a method of preparation, according to the invention, of nanofibres of a conductive organic-inorganic hybrid material having a polymeric organic phase and a mesoporous mineral phase, and also optionally a third surfactant phase.

(19) It should be stipulated that nanofibres are generally understood to mean fibres which are 1 m to 50 mm in length, and preferably 1 m to 100 m in length, and the largest dimension of the section of which, which is the diameter in the case of a circular section, is generally 10 to 500 nm, and preferably 10 to 100 nm.

(20) This method firstly includes steps during which the various treatment solutions introduced into the reactor(s) of the electrically assisted extrusion system are prepared.

(21) 1.a Preparation of a Solution S1 of a Mineral, Inorganic Precursor A.

(22) Synthesis of the material according to the invention starts with the preparation of a solution S1 of at least one mineral, inorganic, precursor A and/or at least one organometallic precursor compound C which will constitute the architecture of the mineral mesoporous network.

(23) Precursor A may be chosen from among the metal salts, the salts of metalloids, the metal alkoxides, and the alkoxides of metalloids.

(24) In particular, precursor A may be chosen from among the salts and alkoxides of metalloids, the salts and alkoxides of transition metals, and the salts and alkoxides of lanthanides, such as the salts and alkoxides of silicon, titanium, zirconium, hafnium, aluminium, tantalum, tin, europium, cerium, zinc, magnesium, yttrium, lanthanum and gadolinium.

(25) This precursor A is diluted in a solvent or a mixture of solvents. The choice of this solvent or of this mixture of solvents is generally made according to the visco-elastic properties imposed by the electrically assisted extrusion method carried out according to the invention, and in accordance with the miscibility medium of the polymer which is subsequently used.

(26) The solvent or solvents is (are) generally chosen from among the low-volatility solvents. Low-volatility is understood to mean that this or these solvent(s) generally have a vapour tension lower than that of ethanol.

(27) The solvent or solvents is (are) typically chosen from among the alcohols, the amides, the ethers, the aldehydes and the ketones which are water-miscible or partially water-miscible and which have a low volatility. Preferred solvents are THF, DMF, NMP, MEK, and dioxane.

(28) Precursor organometallic compound C is generally a compound having hydroxyl functional groups or hydrolysable functional groups of the alkoxide type, and non-hydrolysable or grafted functional groups.

(29) It should be noted that an organometallic compound is understood to mean compounds comprising a metal but also compounds including a metalloid.

(30) Organometallic compound C may, for example, satisfy the formula R.sup.1.sub.xR.sup.2.sub.yMOR.sup.3.sub.(n(x+y)), or the formula ZR.sup.1.sub.xZR.sup.2.sub.yMOR.sup.3.sub.(n(x+y)), in which M and M represent a metalloid or a metal such as a transition metal or a lanthanide.

(31) M and M may, for example, be chosen from among silicon, titanium, zirconium, hafnium, aluminium, tantalum, tin, europium, cerium, zinc, magnesium, yttrium, lanthanum and gadolinium.

(32) n is the degree of valency of the metal, generally n may range from 1 to 10.

(33) X and Y may generally range from 0 to 1 and 10.

(34) Z is a complexing functional group of the monodentate type, such as an acetate, phosphonate or phosphate functional group, or a functional group of the bidentate type chosen, for example, among the -diketones and their derivatives, and the - or -hydroxyacids.

(35) In both these formulae, R.sup.1, R.sup.2, and R.sup.3 are organic substituents chosen, for example, from among H, the alkyl groups, notably having from 1 to 10 C, and the aryl groups, notably having from 6 to 10 C.

(36) One or more among substituents R.sup.1, R.sup.2, and R.sup.3 may include one or more cation exchange groups, such as groups SO.sub.3M, PO.sub.3M.sub.2, COOM, or B(OM).sub.2, in which M represents H, a monovalent metallic cation chosen, for example, from among lithium, sodium or potassium, or a N.sup.+R.sup.4.sub.3 group, where each R.sup.4 independently represents H, an alkyl group, notably having from 1 to 10 C, or an aryl group notably having from 6 to 10 C; or one or more precursor group(s) of cation exchange group(s) such as groups SO.sub.2X, COX, or PO.sub.3X.sub.2, where X represents F, Cl, Br, I or OR.sup.5, where R.sup.5 represents an alkyl group notably having from 1 to 10 C, or an aryl group notably having from 6 to 10 C; or one or more anion exchange group(s) such as groups .sup.+NR.sup.6.sub.3X.sup., where X represents an anion such as, for example, F, Cl, Br, I, NO.sub.3, SO.sub.4H or OR.sup.7, where R.sup.7 represents an alkyl group notably having from 1 to 10 C, or an aryl group notably having from 6 to 10 C, and where each R.sup.6 independently represents H, an alkyl group notably having from 1 to 10 C, or an aryl group notably having from 6 to 10 C, or .sup.+NR.sup.8X groups, where X is as defined above and R.sup.8 is a group which forms with nitrogen .sup.+N a cycle of 4 to 10 links including carbon and nitrogen atoms such as an imidazolinium, pyridinium or pyrazolium cycle.

(37) Preferred cation exchange groups are the SO.sub.3M groups and the PO.sub.3M.sub.2 groups and precursor groups of preferred cation exchange groups are the SO.sub.2X or PO.sub.3X groups.

(38) A preferred anion exchange group is the imidazolinium group.

(39) Solution S1 may include only one or several precursor(s) A, or alternatively solution S1 may include only one or several precursor(s) C, or alternatively solution S1 may include one or several precursor(s) A and one or several precursor(s) C.

(40) One may thus commence by preparing a solution of the (purely) metallic precursor(s) A, and add to this solution a molar fraction of precursor(s) C.

(41) Or, alternatively, precursor(s) C may be added to the solvent or solvents at the same time as the (purely) metallic precursor(s) A.

(42) When solution S1 contains both one or more metallic precursor(s) A and one or more organometallic precursor(s) C, the metal or metalloid of precursor A and the metal or metalloid of precursor C are chosen such that they are identical.

(43) The concentration of precursor A or the concentration of precursor C or the total concentration of precursor A and of precursor C in solution S1 is generally 1 to 40%, and preferably 1.5 to 30%, by mass. It should be noted that the concentrations are generally 15 to 320 times higher than the concentrations used in the conventional methods such as deposition by dip coating.

(44) Structuring, texturizing agent(s) D is (are) added to the solution containing precursor(s) A and precursor(s) C.

(45) The choice of the structuring, texturizing agent depends at once on the desired mesostructure, for example cubic, hexagonal, lamellar, vesicular or vermicular, on the size of the pores and of the walls of this mesostructure, and on its solubilisation in the solvent used for the other compounds of the present invention, namely the polymer, the precursor or precursors A, and/or precursor or precursors C.

(46) Surfactant texturizing agents of the ionic type will generally be used, such as the salts of alkyltrimethyl ammonium, for example cetyltrimethylammonium bromide or the salts of alkylphosphates and alkylsulfonates; or acids such as dibenzoyl tartric acid, maleic acid, and the long-chain fatty acids; or bases such as urea and the alkyl amines with a long chain, to build mesoporous structures the size of the pores of which is limited, for example, to one or several nanometres, for example 1.6 to 10 nm, and the size of the walls of which is also limited to one or several nanometres, for example 1 nm to 20 nm, notably approximately 1 nm.

(47) It is also possible to use lyotropic phases consisting of amphiphilic multi-block copolymers comprising at least one hydrophobic block associated with at least one hydrophilic block typically such as the Pluronics, for example Pluronic F 123 or Pluronic F 127, based on PEO (polyethylene oxide) and PPO (polypropylene oxide) of the (EO).sub.n(PO).sub.m-(EO).sub.n type, copolymers of the ((EO).sub.n(PO).sub.m).sub.xNCH.sub.2CH.sub.2N((EO).sub.n(PO).sub.m).sub.x (Tetronic) type, the compounds of formula C.sub.n(EO).sub.m(OH) (where C.sub.n is an alkyl and/or aryl chain, having for example from 1 to 20 C, and preferably from 6 to 20 C, where EO is ethylene oxide, and where m is an integer, for example from 10 to 200, for example the Brij, Triton, Tergitol or Igepal compounds, and the compounds of formula (EO).sub.m-sorbitan-C.sub.n (Tween) to prepare mesoporous phases of larger pore sizes, for example as high as 50 nm.

(48) These different blocks may also be of an acrylic nature: PMAc (poly(methacrylic acid) or PAAc (poly(acrylic acid), an aromatic nature: PS (Polystyrene), a vinylic nature: PQVP (polyvinylpyridine), PVP (polyvinylpyrrolidone), PVEE (polyvinylether), or another: PDMS (polysiloxane).

(49) These different blocks may be functionalised by one or more conductive group(s) of the cation exchange type; or one or more precursor group(s) of cation exchange group(s); or one or more anion exchange group(s); or one or more precursor group(s) of anion exchange group(s). These groups may notably be chosen from among the previously listed groups. PSS (poly(styrenesulfonic acid)) may be mentioned, for example.

(50) The chosen structuring agent(s) D may be added directly to the solution containing precursor(s) A and precursor(s) C, or alternatively agent(s) D may be previously dissolved or diluted in a hydro-alcoholic medium, or in a water-based solvent mixture compatible with the dilution medium of the polymer and of the metallic precursor.

(51) The concentration of the structuring agent(s) D in solution S1 is generally 1 to 20% by mass.

(52) Solution S1 may or may not be hydrolysed, for example in an acid or base catalytic medium, for a determined period which may be from one to several minutes up to one or more hours (2, 6, 12, 18, 24, 48 hours), for example 12 to 18 hours, depending on the choice of metallic precursor.

(53) Notably in the case of the highly reactive metallic precursors, such as zirconium-based or titanium-based precursors, a chelating agent B, such as acetylacetone, acetic acid or the phosphonates, may be introduced to control the hydrolysis-condensation of the inorganic network.

(54) 1.b Preparation of Solution S2 of at Least One Organic Polymer E.

(55) Organic polymer E is generally chosen for its mechanical properties, its chemical stability and/or its non-miscibility in the treating solution S1.

(56) This polymer is diluted or swollen with a solvent or mixture of solvents, preferably chosen from among the alcohols, ethers, amides, aldehydes and ketones which are water-miscible or partially water-miscible.

(57) The organic polymer(s) will generally be chosen from among the polyether ketones (PEK, PEEK, PEEKK); the polysulfones (PSU), for example Udel; the polyethersulfones, for example VITREX; the polyphenyl ether sulfones (PPSU), for example Radel; the styrene/ethylene (SES), styrene/butadiene (SBS) and styrene/isoprene (SIS), for example KRATON, copolymers; the polyphenylenes, such as the poly(phenylene sulfides) and the poly(phenylene oxides); the polyimidazoles, such as the polybenzimidazoles (PBI); the polyimides (PI); the polyamideimides (PAI); the polyanilines; the polypyrroles; the polysulfonamides; the polypyrazoles, such as the polybenzopyrazoles; the polyoxazoles, such as the polybenzoxazoles; the polyethers, such as the poly(tetramethylene oxides) and the poly(hexamethylene oxides); the poly((meth)acrylic acids); the polyacrylamides; the polyvinyls, such as the poly(vinyl esters), for example the polyvinyl acetates, the polyvinyl formates, the polyvinyl propionates, the polyvinyl laurates, the polyvinyl palmitates, the polyvinyl stearates, the polyvinyl trimethylacetates, the polyvinyl chloroacetates, the polyvinyl trichloroacetates, the polyvinyl trifluoroacetates, the polyvinyl benzoates, the polyvinyl pivalates, the polyvinyl alcohols; the acetal resins, such as the polyvinyl butyrals; the polyvinyl pyridines; the polyvinyl pyrrolidones; the polyolefines, such as the polyethylenes, the polypropylenes, the polyisobutylenes; the poly(styrene oxides); the fluorinated resins and the polyperfluorocarbons, such as the polytetrafluoroethylenes (PTFE), for example TEFLON; the poly(vinylidene fluorides) (PVDF); the polychlorotrifluoroethylenes (PCTFE); the polyhexafluoropropenes (HFP); the perfluoroalkoxides (PFA); the polyphosphazenes; the silicone elastomers; the block copolymers including at least one block consisting of a polymer chosen from among the above polymers.

(58) These different polymers may include one or more conductive group(s) of the cation exchange type; or one or more precursor group(s) of cation exchange group(s); or one or more anion exchange group(s); or one or more precursor group(s) of anion exchange group(s). These groups may notably be chosen from among the previously listed groups.

(59) The concentration of the organic polymer(s) in solution S2 is generally 1 to 50%, and preferably 1 to 30%.

(60) 1.d Preparation of the Surfacted Organic-Inorganic Hybrid Solution F

(61) Surfactant-based precursor solution D is added at ambient temperature to polymer solution E. After homogenisation of the medium the precursor solution made, based on an inorganic component, compound, A including a molar fraction X of C (for example 0x0.4) is added drop wise at ambient temperature to the reactive medium. Stirring at a controlled temperature between ambient temperature and reflux temperature is maintained for several hours. This ageing of the organic-inorganic hybrid solution may last for several days, depending on the choice of the polymer and of the inorganic network. The composition of the formulation is generally [A.sub.(1-X)-C.sub.X]-D.sub.Y-E.sub.Z-(H.sub.2O).sub.h where
Y=mol(D)/[mol[A.sub.(1-X)-C.sub.X])+mol(D) and 0Y0.2 and where Z=g(E)/[g(MO.sub.2)+g(E)] and 0Z0.9.
2. Preparation of Organic-Inorganic Hybrid Nanofibres

(62) In accordance with the invention, solution S1 and solution S2 are deposited on a support by carrying out the simultaneous and separate electrically assisted extrusion of solution S1 and of solution S2 with a bicapillary electrically assisted extrusion device; or alternatively by carrying out the electrically assisted extrusion of a mixture of solution S1 and of solution S2 with a monocapillary electrically assisted extrusion device.

(63) The monocapillary electrically assisted extrusion device comprises a reactor or syringe containing the solution to be extruded, connected to a metal needle. Such a device is well known to the man skilled in the art in this technical field, and is represented in FIG. 1A.

(64) It should be stipulated that in the figures references A, B and C designate, in respect of the devices (FIGS. 1A, 2A, 3A, 4A), respectively solutions S1, S2 and S3, and in respect of the fibres, respectively phases A, B, C, obtained from these solutions.

(65) The reactor or syringe (1) generally takes the form of a vertical cylindrical tank (2) of circular section, and with an open upper end which contains the solution to be extruded (3). The lower end of the tank has the shape of a truncated cone (4) converging towards a lower aperture of generally circular section (5) which is continued by a hollow tube or needle (6).

(66) A piston exerts a pressure on the upper surface (7) of the solution (3) contained in the syringe or reactor (1), by means of which the solution is expelled (8) through the aperture located at the end of the needle (6).

(67) The needle (6) is powered by a high voltage, and an electrical field is thus created between the needle (6) of the syringe and a substrate called the manifold (9), which acts as a counter electrode, and which is generally connected to earth (grounded) (10). The manifold (9) may be made of a conductive or semiconductive material. The manifold (9) may have a variety of shapes and sizes. The manifold (9) may thus be cylindrical, flat or circular. The manifold may be static, fixed, or may be dynamic, and be subjected to a rotary or lateral motion. The needle (6) may be positioned at an angle , generally 0 to 45, relative to the manifold (9).

(68) If the method according to the invention is accomplished with a monocapillary extrusion device such as the one represented in FIG. 1, the reactor, syringe of the device contains a mixture (3) of solutions S1 and S2 defined above, in which polymer E and precursors A and/or C are uniformly distributed at the molecular level before the extrusion, and it is therefore this mixture which is subjected to the electrically assisted extrusion.

(69) By this means, when a monocapillary extrusion device is used, composite fibres represented in FIG. 1B are obtained including a polymer matrix (11, phase B), in which the mesoporous, mineral, inorganic phase (phase A) is discretely distributed.

(70) The bicapillary electrically assisted extrusion reactor (21) represented in FIG. 2A, comprises two embedded reactors or syringes, for example a first reactor or syringe may consist of a first vertical cylinder of circular section as described above, and the second reactor may consist of the space (23) defined between the walls (22) of this first reactor and the walls (24) of a cylinder of larger diameter surrounding the first cylinder. The lower end of the first reactor has the shape of a truncated cone (25) converging towards a lower aperture of generally circular section (26) which is continued by a hollow tube (27). The lower end of the wall of the second reactor also has the shape of a converging truncated cone (28) surrounding the truncated cone (25) and terminating with a tubular wall surrounding the hollow tube (27).

(71) In the bicapillary electrically assisted extrusion reactor, the needle therefore comprises a central hollow tube (27) through which the solution (29) contained in the first reactor is expelled, and this central hollow tube of generally circular section (27) is surrounded by an annular tube (210) which is concentric to the first central hollow tube (27), through which the solution (211) contained in the second reactor is expelled, simultaneously and separately from the first solution.

(72) If the method according to the invention is accomplished with a bicapillary extrusion device such as the one represented in FIG. 1B, solution S1 (A) is generally contained in the first reactor, whereas solution S2 (B) is generally contained in the second reactor. The two solutions S1 and S2 are extruded independently, separately and simultaneously, respectively through the first central aperture of the needle, and through the second concentric, annular aperture of the needle.

(73) By this means, when a bicapillary electrically assisted extrusion device is used, hybrid fibres represented in FIG. 2B are obtained in which a core (212) made of a mesoporous mineral phase (phase A) is surrounded by a concentric casing, sheath, shell or sleeve (213) made of an organic polymer (phase B).

(74) Extrusion of the two solutions S1 and S2 is separate and independent, but simultaneous. Due to the fact that both these solutions are extruded through concentric apertures, this does not result in the formation firstly of a fibre from solution S1 and secondly of a fibre from solution S2, but instead in the formation of a single, hybrid, unitary fibre, having the structure described above and in FIG. 2B.

(75) The man skilled in the art concerning the structure of a bicapillary assisted extrusion device is aware that when such a device is used, two types of fibre are not obtained simultaneously, but instead a single type of fibre is obtained.

(76) The electrically assisted extrusion device used according to the invention, whether it is a monocapillary or bicapillary device, may possibly be coupled with a spray-coating device (31, 41) as is represented in FIGS. 3A) and (4A).

(77) This spray-coating device is generally positioned such that it sprays a solution S3, through a nozzle (32, 42), in the form of an aerosol or nebulisate in the jet (33, 43) coming out of the needle of the electrically assisted extrusion device, preferably in the vicinity of the aperture or apertures of the needle of the electrically assisted extrusion device.

(78) This solution, or rather suspension, S3 is generally a solution, or rather suspension, of nanoparticles (34, 44) of metals and/or metal oxides (phase C). These metals may be chosen from among gold, silver, platinum, palladium, nickel, copper, ruthenium, rhodium and cobalt.

(79) By this means nanofibres are obtained having a structure similar to that of the hybrid fibres prepared with an electrically assisted extrusion device which are represented in FIGS. 1B and 2B but which, in addition, are decorated by nanoparticles (34, 44) of metals and/or metal oxides. These nanofibres are represented in FIGS. 3B and 4B.

(80) It should be noted that if one or both solution(s) S1 or S2 also contains nanoparticles of metals and/or metal oxides, these nanoparticles may be found distributed throughout phase A or phase B, or throughout both phases. In this case, it is also possible, in addition, to spray a solution S3, as described above.

(81) In the method according to the invention, a multi-reagent synchronous control is accomplished, i.e. the sol-gel hydrolysis-condensation reactions, corresponding to a kinetic control, the mesoporous organisation of the networks, corresponding to a thermodynamic control, and the rheology of the mixture, allowing electrically assisted extrusion of the mixture, are controlled simultaneously.

(82) These different controls may be achieved by adjusting the parameters relating to the solution or solutions to be deposited defined above, and the parameters relating to the electrically assisted extrusion method itself.

(83) Thus, with regard to the parameters relating to the extrusion method, the electrically assisted extrusion temperature is generally regulated independently of the reactors and of the manifold, and is generally within the range from 20 C. to 200 C., preferably from 25 C. to 100 C., and even more preferably from 30 C. to 70 C.

(84) The relative humidity of the extrusion device is regulated within a range of 0 to 90%, preferably 5 to 90%, and even more preferably 5 to 60%.

(85) The voltage applied to the needle is generally within a range of 2 to 25 kV, preferably 5 to 20 kV, and even more preferably 8 to 15 kV.

(86) The flow speed of the solutions in the syringe is generally within a range of 0.1 to 20 mL/h, and preferably 0.1 to 10 mL/h.

(87) The distance between the needle (i.e. generally the tip or end of the needle) and the counter electrode (manifold or support) is generally 2 to 25 cm, and preferably 10 to 18 cm.

(88) Deposition may be accomplished in an atmosphere of air, nitrogen or argon.

(89) Adjustment of the applied voltage, of the ejection flow rate of the solution (equivalent to the flow speed in the syringe), and of the distance between the needle and the manifold, enables the diameter of the fibres and their texturizing to be controlled.

(90) Continuous controlled application of the voltage will be preferred to form fibres which are of uniform diameter, whereas isolated and controlled variations of the voltage will enable faults to be created in the texturizing of the fibres, and the growth of a three-dimensional fibrous network to be favoured.

(91) The fibres deposited on the substrate or support constituted by the manifold are then generally heat-treated at a temperature of between 50 C. and 300 C., and preferably between 40 C. and 200 C., depending on the nature of the polymer, generally to obtain consolidation. This treatment may be called an ageing treatment and, depending on the conditions that are used, enables a cohesive membrane to be obtained in which the fibres are generally bonded, glued, to one another.

(92) The duration of this consolidation treatment is generally 15 minutes to 24 hours, and preferably 1 to 15 hours.

(93) Or, alternatively, the heat treatment may be a calcination heat treatment during which the structuring agent D, organic polymer E, and optionally the support, are eliminated. This treatment is accomplished at a temperature higher than the ageing or consolidation treatment described above, for example at a temperature of over 300 C., and preferably 550 C. On completion of this treatment mineral fibres which now comprise only the mesoporous mineral phase are obtained. These nanofibres may optionally take the form of a membrane, or of a fabric of nanofibres of mineral phase, for example of silica.

(94) If the structuring agent has not been eliminated, and a consolidation, not a calcination, has been accomplished, then the texturizing, structuring agent such as a surfactant which was used for the mesostructuration of the inorganic network, and which is in the mesopores of the membrane, may possibly be eliminated completely or partially, preferably by a mild method such as, for example, washing, whether selective or not, in a solvent such as ethanol.

(95) The washing may be accomplished in an acidic hydro-alcoholic medium.

(96) A post-reaction to release or generate a conductive group bonded to the inorganic network may be accomplished. Typically, this type of post-reaction may be: oxidation of a mercaptan group (SH) by hydrogen peroxide into sulfonic acid SO.sub.3H or, hydrolysis of a dialkylphosphonate (RO).sub.2(O)P group by HCl directly, or through the formation of an intermediate compound (Me.sub.3SiO).sub.2(O)P, followed by hydrolysis by MeOH to form a phosphonic acid PO.sub.3H.sub.2.

(97) This post-reaction may also be a grafting of surface M-OH hydroxyls of the inorganic network of the membrane by a metal organo-alkoxide. In all these cases the membrane is placed in a liquid medium to allow it to swell, and to allow the reactive molecular entities to diffuse in the pores of the membrane.

(98) In order to prevent any parasitic reaction within the membrane during operation of the cell the membrane such as a proton conductive membrane may be purified by different washings, for example oxidising, acidic (or basic) and aqueous washings, which enable all the labile organic, organomineral or inorganic entities to be eliminated.

(99) The membrane may also be prepared in the form of a self-supporting film. This shaped film is then separated from its support by swelling in a solvent such as water.

(100) The invention will now be described with reference to the following illustrating and non-restricting examples.

EXAMPLES

Example 1

(101) In this example, hybrid fibres of zirconium oxide and of a PVDF-HFP copolymer are prepared.

(102) 0.52 g of the surfactant Pluronic F127, and 0.466 g of a PVDF-HFP copolymer (poly(vinylidene fluoride co-hexafluoropropene)), the mass percent of the hexafluoropropene chain is between 5 and 12%) is added to 0.65 g of acetic acid (a chelating agent), 4.0 g of a zirconium precursor, Zr(OiPr).sub.4 and 4.8 g of DMF.

(103) The solution is stirred over night in order to dissolve the ZrO.sub.2 precipitates which may be formed due to the presence of residual water.

(104) This solution (viscosity: 20 cPs, mass percent of the polymer: 4.4%, mass percent of the zirconium precursor: 38%) is used to prepare hybrid fibres of Pluronic F127/ZrO.sub.2/PVDF-HFP by monocapillary electrically assisted extrusion.

(105) The experimental conditions to obtain these fibres are as follows: a voltage of 15 kV between the needle and the counter electrode, a flow rate of 0.4 mL/h, 30% humidity, a temperature of 27 C. in the reactive medium (i.e. in the solution), a distance of 11 cm between the end of the needle and the counter electrode.

(106) The hybrid fibres obtained are subjected to one of the following ageing heat treatments: Heating at 70 C. for 12 hours (FIG. 5A); or alternatively Heating at 130 C. for 4 hours (FIG. 5B); or alternatively Heating at 70 C. and extraction of the surfactant by washing in ethanol (FIGS. 5C and 5D).

(107) FIGS. 5A, 5B, 5C, 5D are images obtained by scanning electron microscopy (SEM) of the fibres of Pluronic F127/ZrO.sub.2/PVDF-HFP obtained by electrically assisted extrusion from the solution prepared in the manner described above, where these fibres have also been subjected to one of the heat treatments described above.

(108) The diameter of the fibres obtained is approximately 260 nm50 nm. They are of uniform diameter. Depending on the applied heat treatment, they may have a particular geometry in the form of a vertebral column, backbone (FIG. 5D).

Example 2

(109) In this example, PEOS/PVDF-HFP hybrid fibres are prepared which may take the form of a membrane.

(110) The PEOS polysiloxanes are previously synthesised (water, TEOS and acid) by hydrolysis of the TEOS in an acidic medium in ethanol.

(111) The three constituents are mixed in the following proportions: H.sub.2O/Si=1.7 and pH=2.5, in a sealed flask, and they are then stirred for 3 days at 70 C.

(112) The solvent is evaporated from the previous solution using a rotavapour.

(113) The solution obtained in this manner is transparent, viscous (1,000 cPs) and is dried in a vacuum at ambient temperature to obtain a white powder.

(114) The solution subjected to the electrically assisted extrusion is then prepared as follows: the white powder prepared above is dissolved in a THF/DMF mixture (50/50 by mass). The copolymer (PVDF-HFP) (4.4% by mass) and the surfactant (Pluronic F127, 15.9%) are then added to this solution.

(115) This solution of high viscosity (100 cPs) is subjected to the electrically assisted extrusion.

(116) The solution subjected to the electrically assisted extrusion has the following composition: 450 mg of Pluronic F127; 125 mg of PVDF-HFP; 750 mg of PEOS prepared with a H.sub.2O/Si molar ratio of 1.7; 1.5 g of DMF; its viscosity is 100 cPs.

(117) The electrically assisted extrusion is accomplished at a voltage of 11 kV, with a flow rate of 0.5 mL/h, at ambient temperature, and with relative humidity (RH) of approximately 70% RH.

(118) The distance between the end of the needle and the counter electrode is 13 cm. The membrane is obtained after an extrusion time of 30 minutes.

(119) The membranes obtained are then subjected to one of the following ageing heat treatments: Ageing of the membrane at a temperature of 25 C. for one night; or alternatively Ageing of the membrane at a temperature of 70 C. for one night; or alternatively Ageing of the membrane at a temperature of 550 C. (for 2 hours to one night).

(120) FIGS. 6A, 6B, 6C and 6D have images obtained by scanning electron microscopy (SEM) of the PEOS/PVDF-HFP hybrid membranes obtained by electrically assisted extrusion from the solution prepared in the manner described above, wherein these membranes have also been subjected to one of the heat treatments described above.

(121) The morphology of the membrane depends on its ageing temperature after synthesis. Treatment at ambient temperature (25 C.) over night leads to the formation of individual fibres, although they may however be considered to form a membrane fabric, which is an element of interest for the electrode portion, with a diameter of approximately 1 m (FIG. 6A).

(122) Conversely, treatment of these fibres at 70 C. over night leads to the formation of a membrane with fibres bonded, glued, to one another (FIG. 6B).

(123) Finally, during the treatment of these fibres at 550 C. the polymer is eliminated, and a fabric of silica fibres is obtained (FIGS. 6C and 6D).

(124) The opaque membrane of FIGS. 7A and 7B was obtained under the conditions previously described above: ageing at ambient temperature, humidity: 70%, needle-counter electrode distance: 13 cm, extrusion time: 30 minutes, voltage: 11 kV

Example 3

(125) In this example, membranes based on CSPTMS (chlorosulfonylphenyltrinnethoxysilane)/PVDF-HFP/PEO are prepared.

(126) CSPTMS is a bifunctional compound of the organometallic type, as defined above.

(127) Polyoxyethylene (POE) is used as a structuring agent.

(128) Polyoxyethylenes of various molecular weights (10,000; 1,000,000; 16,000) are added to solutions containing the CSPTMS/PVDF-HFP mixture in order to obtain 50% by mass of PVDF-HFP (poly(vinylidene fluoride co-hexafluoropropene)), and the mass percent of the hexafluoropropene chain is between 5 and 12%).

(129) The different solutions are extruded at a voltage of 12.4 kV, with a distance between the end of the needle and the counter electrode of 10 to 11 cm, a variable humidity rate ranging from 0 to 20% RH, and with a flow rate of 0.15-0.3 ml/h, at ambient temperature, for one hour.

(130) The membranes obtained are flexible and opaque, and approximately 20 m thick. The thickness is principally regulated by the time during which the solution is spray-coated, whatever the PEO may be.

(131) 4-points conductivity measurements were made on these membranes.

(132) In the case of the membrane prepared from polyethylene glycol of molecular weight 10,000, the measured proton conductivities are 100 mS/cm at 80 C. under 100 kPa, whereas the conductivity is 43 mS/cm for a membrane prepared with a poly(ethylene oxide) of molecular weight 1,000,000.

(133) The fibres and membranes of the examples have a mineral phase with a structured mesoporous network with open porosity, which is as defined in the description given above, notably in respect of the size of the pores. The size of the pores was characterised by Transmission Electron Microscopy (TEM) and/or by X-ray diffraction (DRX at low angles) and/or by gas adsorption (BET).

(134) The mesostructure is characterised by X-rays diffraction (DRX) at low angles.

(135) The measurements made on the fibres and membranes of the examples give values for the size of the pores of the mineral phase in accordance with those given in the description.

(136) The diffractograms produced for the fibres and membranes of the examples show that mesostructuration of the mineral phase is present.

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