EP-2556187-B1 - ORGANIC-INORGANIC HYBRID NANOFIBRES HAVING A MESOPOROUS INORGANIC PHASE, PREPARATION THEREOF BY ELECTRICALLY ASSISTED EXTRUSION, MEMBRANE, ELECTRODE AND FUEL CELL

Inventors

• VALLE, KARINE
• BELLEVILLE, PHILIPPE
• PEREIRA, FRANCK
• LABERTY, CHRYSTEL
• Sanchez, Clément
• BASS, JOHN

Dates

Publication Date

20260506

Application Date

20110406

Claims (20)

1. 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, said organic phase being not present inside the pores of the structured mesoporous network; wherein the mineral phase has organic chemical conductive and hydrophilic functional groups, and wherein the organic phase has organic chemical conductive and/or hydrophilic functional groups, wherein the mineral phase is discontinuous, and dispersed in the organic phase, which is continuous.
2. Nanofibres according to claim 1, wherein said organic chemical functional groups of the mineral phase are located at the surface of the pores, and are bonded covalently to the walls of the mesoporous network.
3. Nanofibres 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 conductive and/or hydrophilic groups; preferably the structuring agent is chosen from among the surfactants, such as the salts of alkyltrimethyl ammonium, alkylphosphates and alkylsulfonates; acids such as dibenzoyl tartaric acid, maleic acid, the long-chain fatty acids; bases such as urea and the long-chain amines; phospholipids; doubly, twice, hydrophilic copolymers the amphiphilia of which is generated "in situ" by interaction with a substrate; amphiphilic multi-block copolymers including at least one hydrophobic block associated with at least one hydrophilic block.
4. Nanofibres according to any one of claims 1 to 3, wherein said conductive functional groups are chosen from among the cation exchange groups and/or the anion exchange groups.
5. Nanofibres according to any one of the preceding claims, further comprising, preferably on at least one of their surfaces, and even more preferably on at least one of their external surfaces, catalytic nanoparticles, preferably metallic nanoparticles and/or metal oxide(s) nanoparticles.
6. Nanofibres according to any of the preceding claims, wherein the mineral phase consists of at least one oxide chosen from among the metal oxides, the metalloid oxides, and the mixed oxides thereof, such as the oxides of silicon, titanium, zirconium, hafnium, aluminium, tantalum, tin, zinc, magnesium, rare earths or lanthanides such as europium, cerium, yttrium, lanthanum and gadolinium, and the mixed oxides thereof.
7. Nanofibres according to any one of the preceding claims, wherein the mesoporous network has an organised structure with a repeating unit ; preferably the mesoporous network has a cubic, hexagonal, lamellar, vermicular, vesicular or bicontinuous structure.
8. Nanofibres according to any one of the preceding claims, wherein the size of the pores of the mesoporous network is 1 to 100 nm, and preferably 2 to 50 nm.
9. Nanofibres according to any one of the preceding claims, wherein the organic polymer is a thermostable polymer preferably chosen from among the polyether ketones (PEK, PEEK, PEEKK); the polysulfones (PSU); the polyethersulfones; the polyphenyl ether sulfones (PPSU); the styrene/ethylene (SES), styrene/butadiene (SBS) and styrene/isoprene (SIS) 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); 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.
10. Membrane comprising the nanofibres according to any one of the preceding claims, optionally deposited on a support.
11. Electrode comprising the nanofibres according to any one of claims 1 to 9.
12. Fuel cell comprising at least one membrane according to claim 10 and/or one electrode according to claim 11.
13. Method of preparing organic-inorganic hybrid nanofibres, according to any one of claims 1 to 9, wherein the following steps are carried out: a) at least one solution is prepared, in a solvent, of a mineral precursor A and/or of an organometallic precursor C intended to constitute the mineral phase; preferably the precursor A is chosen from among the metal salts, the metalloid salts, the metal alkoxides, and the metalloid alkoxides; b) at least one structuring, texturizing agent D of the mesoporous mineral phase is added to the solution prepared in step a), whereby a solution S1 is obtained; and, optionally, said solution S1 is hydrolysed in basic catalytic medium and left to age; c) a solution S2 of an organic polymer E is prepared in a solvent; d) simultaneous, separate electrically assisted extrusion of solution S1 and of solution S2 is carried out with a bicapillary electrically assisted extrusion device; or alternatively the electrically assisted extrusion of a mixture, optionally aged, of solution S1 and solution S2 is carried out with a monocapillary extrusion device; wherein said devices comprise at least one syringe containing the solution(s) connected to a needle to which a voltage is applied, and a manifold or support, whereby a deposit of organic-inorganic hybrid nanofibres is obtained on the manifold or support; e1) heat treatment is carried out at a temperature between 50°C and 300°C to consolidate the deposited nanofibres; f) optionally, on conclusion of step e1, the structuring, the texturizing agent D is totally or partially eliminated; g) optionally, on conclusion of step e1) or step f) the support is separated or eliminated; method in which the polymer and/or structuring, texturizing agent D carries (carry) organic chemical conductive and/or hydrophilic functional groups and/or precursor functional groups of these organic chemical conductive and/or hydrophilic functional groups, and the organomineral precursor compound C is a compound carrying, on the one hand, organic chemical conductive and hydrophilic functional groups, or precursor functional groups of these organic chemical functional groups and, on the other hand, functional groups which may become bonded to the surface of the pores of the mesoporous network.
14. Method according to claim 13, wherein a chelating agent B such as acetylacetone or acetic acid is also added to solution S1.
15. Method according to claim 13 or 14, wherein solution S1, solution S2, or a mixture of solutions S1 and S2, have a viscosity of 40 to 7,000 cps at 20°C.
16. Method according to any one of claims 13 to 15, wherein the concentration in solution S1 of mineral precursor A and/or of organomineral precursor C, and the concentration in solution S2 of polymer E, expressed as a dry extract, are 15 to 60% by mass, and preferably 15 to 30% by mass.
17. Method according to any one of claims 13 to 16, wherein the solvents of solutions S1 and S2 are low-volatility solvents, the vapour tension of which is lower than that of ethanol.
18. Method according to any one of claims 13 to 17, wherein solution S1 is left to age at a temperature of 0°C to 300°C, and preferably 20°C to 200°C; at a pressure of 100 Pa to 5.10 6 Pa, and preferably 1,000 Pa to 2.10 5 Pa; over a period of several minutes to several days, preferably one hour to one week, and even more preferably 12 to 18 hours.
19. Method according to any one of claims 13 to 18, wherein, prior to the electrically assisted extrusion, solution S1 and/or solution S2 is(are) preheated to a temperature of 40°C to 80°C, and preferably 60°C to 70°C.
20. Method according to any one of claims 13 to 19, wherein the electrically assisted extrusion is controlled by acting on one or more, and preferably on all, of the following parameters: - the deposition temperature; - the relative humidity of the atmosphere in which the deposition is carried out; - the voltage applied to the needle; - the flow speed of the solutions or of the mixture in the syringe; - the distance between the needle and the manifold or support; - the atmosphere in which the deposition is carried out; preferably one or more, and preferably all, of the parameters is (are) chosen in accordance with the following: - Deposition temperature: 20°C to 200°C, preferably 25°C to 100°C, and even more preferably 30°C to 70°C; - Relative humidity of the atmosphere in which the deposition is carried out: 0 to 90%, preferably 5 to 90%, and even more preferably 5 to 60%; - Voltage applied to the needle; 2 to 25 kV, preferably 5 to 20 kV, and even more preferably 8 to 15 kV; - Flow speed of the solutions or of the mixture in the syringe: 0.1 to 20 mL/h, and preferably 0.1 to 10 mL/h; - Distance between the needle and the manifold or support: 2 to 25 cm, and preferably 10 to 18 cm; - Atmosphere wherein the deposition is carried out: Air, Nitrogen or Argon;

Description

DOMAINE TECHNIQUE La présente invention concerne des nanofibres hybrides organiques, inorganiques comprenant une phase inorganique, minérale, mésoporeuse, et une phase organique. L'invention concerne, en outre, un procédé de préparation de ces nanofibres par extrusion électro-assistée (aussi appelée « Electrospinning » en langue anglaise). L'invention concerne, en outre, une membrane et une électrode comprenant ces nanofibres. L'invention a trait également à une pile à combustible comprenant au moins une telle membrane et/ou au moins une telle électrode. Le domaine technique de l'invention peut être défini, de manière générale, comme celui des matériaux poreux plus particulièrement comme celui des matériaux dits mésoporeux et notamment comme celui des matériaux hybrides organiques-inorganiques mésoporeux. Plus précisément, l'invention se situe dans le domaine des matériaux mésoporeux destinés à des utilisations en électrochimie, en particulier dans les piles à combustibles, telles que les « PEMFC » (« Polymeric Electrolyte Membrane Fuel Cell », en anglais) appelées aussi piles à combustible à membranes échangeuses protoniques. ÉTAT DE LA TECHNIQUE ANTÉRIEURE On sait qu'un des éléments essentiels des piles à combustible, par exemple celles utilisées dans le secteur de l'automobile et de la téléphonie portable, est la membrane échangeuse protonique. Ces membranes électrolytes structurent le cœur de la pile à combustible, et doivent par conséquent présenter de bonnes performances en conduction protonique, ainsi qu'une faible perméabilité aux gaz réactants (H2/O2). Les propriétés des matériaux qui constituent les électrolytes solides polymériques formant ces membranes et qui doivent résister à des milliers d'heures de fonctionnement de la pile, sont essentiellement la stabilité chimique, et la résistance à l'hydrolyse et à l'oxydation, notamment la résistance hydrothermale, et une certaine flexibilité mécanique. Les membranes préparées à partir d'ionomères perfluorés, comme le Nafion®, remplissent ces exigences pour des températures de fonctionnement inférieures à 90°C. Cette température est cependant insuffisante pour permettre l'intégration des piles à combustible comprenant de telles membranes dans un véhicule. Cette intégration suppose en effet l'augmentation de la température de fonctionnement vers 100-150°C dans le but d'accroître le rendement de conversion courant/énergie et donc l'efficacité de la pile, de diminuer l'empoisonnement des catalyseurs par le monoxyde de carbone, mais également d'améliorer le contrôle de la gestion thermique en diminuant le volume du radiateur. Par ailleurs, l'efficacité de conduction des membranes protoniques est fortement liée à la présence d'eau dans le milieu. Or, à des températures supérieures à 100°C, l'eau est rapidement évacuée de la membrane, la conductivité chute et la perméabilité au combustible s'accroît. A ces températures, cette diminution des performances peut s'accompagner d'une dégradation de la membrane. Pour résoudre les problèmes de dessèchement des membranes dans les piles à combustibles à haute température, à savoir au moins égale à 100°C, le maintien d'une humidité relative maximale de 80-100% est nécessaire mais est difficilement réalisable par une source externe. Par contre, il est connu que l'insertion ou la croissance d'une charge hygroscopique « in situ » favorise la rétention d'eau à l'intérieur du polymère, retarde ce processus de déshydratation du milieu protonique, et assure ainsi la conduction des protons. Outre son caractère hydrophile, cette charge fonctionnelle peut posséder intrinsèquement des propriétés conductrices et ainsi accroître les performances de la membrane. Afin d'augmenter la rétention d'eau des membranes dans les piles à combustibles à haute température, de nombreuses membranes composites ont été développées, notamment par croissance de nanoparticules inorganiques hydrophiles. Ces nano-charges minérales peuvent être synthétisées par voie sol-gel dans des matrices organiques sulfonées perfluorées, mais aussi dans des matrices constituées de composés polyaromatiques, ou de polyéthers. Ces membranes sont nommées présentement membranes hybrides organiques-inorganiques. Les particules minérales peuvent être conductrices, ou bien non conductrices et simplement hydrophiles comme les oxydes de métaux et de métalloïdes. Outre l'amélioration de la gestion de l'eau à haute température, la diminution de la perméabilité de la membrane aux combustibles est démontrée dans ces membranes hybrides organiques-inorganiques par rapport aux membranes classiques de type Nafion® par exemple. La stabilité thermique et chimique reste toutefois limitée car inhérente à la matrice de polymère organique sulfoné utilisée. Parallèlement aux matériaux composites ou hybrides organiques-inorganiques, décrits plus haut, les matériaux mésoporeux initialement imaginés pour la catalyse, c'est-à-dire essentiellement la silice et les aluminosilicates, ont commencé à