Hybrid organic-inorganic nanofibers with mesoporous inorganic phase, their preparation by electro-assisted extrusion, membrane, electrode and fuel cell

Abstract

The invention relates to: hybrid organic-inorganic nanofibers comprising two phases, namely, a first mineral phase comprising a structured open-pore mesoporous network and a second organic phase comprising an organic polymer, said organic phase being essentially absent from the interior of the pores of the structured mesoporous network; membrane and electrode comprising said nanofibers; fuel cell comprising said membrane and / or said electrode; and method for preparing said nanofibers by electrically assisted extrusion.

Description

TECHNICAL FIELD

[0001] The present invention relates to organic-inorganic hybrid nanofibers comprising an inorganic, mineral, mesoporous phase, and an organic phase.

[0002] The invention also relates to a method for preparing these nanofibers by electro-assisted extrusion (also called "Electrospinning" in English).

[0003] The invention further relates to a membrane and an electrode comprising these nanofibers.

[0004] The invention also relates to a fuel cell comprising at least one such membrane and / or at least one such electrode.

[0005] The technical field of the invention can be defined, in general, as that of porous materials, more particularly as that of so-called mesoporous materials, and especially as that of mesoporous organic-inorganic hybrid materials.

[0006] More specifically, the invention lies in the field of mesoporous materials intended for uses in electrochemistry, in particular in fuel cells, such as "PEMFCs" ("Polymeric Electrolyte Membrane Fuel Cell" in English) also called proton exchange membrane fuel cells. PREVIOUS STATE OF THE ART

[0007] We know that one of the essential elements of fuel cells, for example those used in the automotive and mobile phone sectors, is the proton exchange membrane.

[0008] These electrolyte membranes form the core of the fuel cell and must therefore exhibit good proton conduction performance, as well as low permeability to reactant gases (H₂ / O₂). The properties of the materials that constitute the solid polymeric electrolytes forming these membranes, and which must withstand thousands of hours of fuel cell operation, are essentially chemical stability, resistance to hydrolysis and oxidation, including hydrothermal resistance, and a certain degree of mechanical flexibility.

[0009] Membranes prepared from perfluorinated ionomers, such as Nafion®, meet these requirements for operating temperatures below 90°C.

[0010] This temperature, however, is insufficient to allow the integration of fuel cells with such membranes into a vehicle. This integration requires increasing the operating temperature to around 100-150°C in order to improve the current-to-energy conversion efficiency and therefore the fuel cell's overall effectiveness, reduce carbon monoxide poisoning of the catalysts, and also improve thermal management by reducing the radiator's volume.

[0011] Furthermore, the conductivity of proton membranes is strongly linked to the presence of water in the medium. However, at temperatures above 100°C, water is rapidly removed from the membrane, conductivity drops, and fuel permeability increases. At these temperatures, this decrease in performance can be accompanied by membrane degradation. To address membrane drying problems in high-temperature fuel cells, i.e., at least 100°C, maintaining a maximum relative humidity of 80-100% is necessary but is difficult to achieve through an external source.

[0012] However, it is known that the insertion or growth of a hygroscopic filler "in situ" promotes water retention within the polymer, delays the dehydration process of the proton medium, and thus ensures proton conduction. In addition to its hydrophilic nature, this functional filler can intrinsically possess conductive properties and thereby enhance membrane performance.

[0013] To increase the water retention of membranes in high-temperature fuel cells, numerous composite membranes have been developed, notably through the growth of hydrophilic inorganic nanoparticles. These mineral nanofillers can be synthesized via the sol-gel process in perfluorinated sulfonated organic matrices, as well as in matrices composed of polyaromatic compounds or polyethers. These membranes are currently referred to as organic-inorganic hybrid membranes.

[0014] Mineral particles can be conductive, or non-conductive and simply hydrophilic like oxides of metals and metalloids.

[0015] In addition to improved water management at high temperatures, these organic-inorganic hybrid membranes demonstrate reduced membrane permeability to fuels compared to conventional membranes such as Nafion®<. However, thermal and chemical stability remains limited due to the inherent nature of the sulfonated organic polymer matrix used.

[0016] Alongside the composite or organic-inorganic hybrid materials described above, the mesoporous materials initially conceived for catalysis, that is to say essentially silica and aluminosilicates, have begun to attract the attention of some electrochemists.

[0017] Let us recall that, specifically, in the context of this, so-called mesoporous materials are solids which have within their structure pores with a size typically between 1 and 100 nm, preferably between 2 and 50 nm (the latter range corresponding to the IUPAC definition of mesoporosity), which is intermediate between that of micropores (zeolite-type compounds) and that of macropores.

[0018] Typically, mesoporous materials are amorphous or crystalline metal oxides in which the pores are usually randomly distributed with a very wide distribution of pore size.

[0019] Structured mesoporous materials, also called "mesostructured" materials, are structured porous networks with an organized spatial arrangement of mesopores. This spatial periodicity of the pores is characterized by the appearance of at least one low-angle diffraction peak in an X-ray diffraction pattern; this peak is associated with a repetition distance that is generally between 2 and 50 nm. The mesostructure is verified by transmission electron microscopy. The mesoporosity can be free or functionalized by chemical groups or nanoparticles.

[0020] In this context, the sol-gel process offers innovative strategies in the construction of these organized mesoporous structures, notably by inorganic polymerization within organized molecular systems (OMS) of surfactants or within organized polymeric systems (OPS) of block copolymers.

[0021] In the presence of SMO-type texturizing agents, soft sol-gel chemistry allows the synthesis, from inorganic and organometallic precursors, of such mesostructured organomineral networks, known as organic-inorganic hybrid materials. The properties of these mesoporous organic-inorganic hybrid materials depend not only on the chemical nature of the organic and inorganic components, but also on the synergy that can arise between these two chemistries.

[0022] This is why these materials are often referred to as "multifunctional" materials.

[0023] The degree of organization is governed by the nature of these two organic and inorganic entities, but also by the multi-scale arrangement of this structure. Thus, the integration of chemical functionalities capable of inducing specific properties into an ordered mesoporous structure, both in the "walls" and in the pores, is of great interest in various applications, for example in catalysis, filtration, and electrochemistry.

[0024] Furthermore, the texturing of mesostructured networks in nanofibers leads to the formation of tissues, membranes, and films.

[0025] Furthermore, the use of such mesoporous hybrid fibers in fuel cells offers many possibilities promoting transport properties and continuity of conduction pathways.

[0026] In fuel cells, membranes serve as a support for catalytic materials responsible for the oxidation of hydrogen at the anode and the reduction of oxygen at the cathode. They are therefore generally composed of three main components: an electrical conductor such as carbon, an electrolyte, and a catalytic material such as platinum particles that catalyze the redox reactions. These reactions occur primarily at the interface of these three components (the triple point), which must therefore be accessible to the reactant gases. One of the main objectives in a fuel cell is to reduce and optimize the amount of catalyst, such as platinum.

[0027] These membrane materials are shaped today by liquid processes such as coating or by melt processes such as extrusion.

[0028] Although the possible use in electrochemical devices of mesoporous inorganic materials, such as mesostructured mesoporous silicas constructed by SMO and SPO, has already been mentioned, it turns out that such materials cannot give rise to a direct application in fuel cells because it is impossible to put them in the form of fibers constituting a membrane by implementing the processes mentioned above.

[0029] There is therefore a need for a mesoporous material that can be put into the form of fibers constituting a membrane, in particular a homogeneous and flexible membrane.

[0030] We also know the electro-assisted extrusion process (“electrospinning” in English).

[0031] Electro-assisted extrusion is a shaping process that leads to the production of fibers by applying a significant potential difference between the tip of a metal needle connected to a syringe containing the chemical solution, and a conductive electrode support positioned at a given distance from said syringe to collect the fibers thus formed.

[0032] Previous work on electro-assisted extrusion processes has focused primarily on the fabrication of polymer nanofibers. This choice is driven by the method itself, which requires the use of viscoelastic solutions. Recent work shows that sol-gel solutions, due to their physicochemical characteristics, are well-suited to this type of deposition and represent a promising synthetic route, particularly for the development of composite or ceramic nanofibers.

[0033] The use of inorganic soils has made it possible to synthesize silica nanofibers [1], oxide / oxide composite nanofibers (TiO2 / SiO2) [2], monometallic ceramic nanofibers (Al2O3) [2] or heterometallic (PbZrxTi1-xO3(PZT)) [3].

[0034] The morphology of nanofibers depends on many parameters related to the equipment such as the applied voltage, the distance between the needle and the electrode, the size of the needle, etc., but also on the physico-chemical characteristics of the solution such as rheology, surface tension, concentration, etc.

[0035] In these reviews, the literature shows that the sol-gel transition can occur in the initial solution or during fiber preparation [5]. According to this literature data, the timing of this step does not appear to influence fiber morphology.

[0036] The incorporation of an organic polymer, such as PVP, into the sol-gel precursor solution, such as transition metal alkoxides, can be used to increase and control the viscosity of the electrospinner solution, thus imparting its viscoelastic characteristics. Under these conditions, a continuous three-dimensional inorganic network forms within the polymer matrix. Fibers composed of an organic / inorganic composite network are then directly obtained. Removal of the organic phase by heat treatment allows the synthesis of ceramic fibers.

[0037] This method has been used for the synthesis of various oxides such as: TiO₂, SiO₂, SnO₂, ITO, GeO₂, NiFe₂O₄, LiCoO₂, and BaTiO₃. Besides PVP, various host polymers are cited in the literature, such as poly(vinyl) alcohol (PVA), poly(vinyl acetate), and PEO [6]. The combinations between the "host" polymer and the "guest" inorganic network are therefore numerous. Consequently, a wide variety of oxide nanofibers are mentioned: Al₂O₃, CuO, NiO, TiO₂-SiO₂, V₂O₅, ZnO, Co₃O₄, Nb₂O₅, MoO₃, and MgTiO₃ [6].

[0038] Furthermore, ceramic nanofibers other than oxides are also prepared by this process. For example, document [2] describes the synthesis of SiC fibers by electrospinning from a solution of Novolaque resin and tetraethyl orthosilicate, followed by high-temperature pyrolysis.

[0039] Zhao et al., 2007 (Materials Letters, vol. 62, pages 143-146) describe the fabrication of mesoporous silica nanofibers by electro-assisted co-extrusion of a precursor sol and a polymer. In this paper, the hydrolysis of the mineral phase employs acid catalysis, resulting in nanofibers comprising a mineral core and a sheath containing the organic phase.

[0040] Electro-assisted extrusion also allows the synthesis of hollow nanotubes or nanofibers [13, 14]. In this case, a different experimental setup is used [15, 16]. Two immiscible viscous solutions are placed in coaxial capillaries. For example, these could be a mineral oil and a PVP / Ti(O / Pr)₄ solution. Using this technique, it is possible to obtain nanofibers with a mineral oil core and a TiO₂ / PVP composite surface. Selective dissolution of the mineral oil allows the production of fibers with TiO₂ / PVP composite walls. Polycrystalline ceramic fibers can also be synthesized by simultaneously removing the PVP and mineral oil through a judicious heat treatment.

[0041] The introduction of nanoparticles directly into the aforementioned fibers is also described in the literature. In this case, it is necessary to disperse the nanoparticles in mineral oil beforehand.

[0042] The surface area of ​​nanofibers can also be increased by creating porosity. Increasing the specific surface area of ​​nanofibers is of interest for numerous applications such as catalysis, fuel cells, batteries, and solar cells. Two approaches to creating porosity in these nanofibers are described in the literature.

[0043] The first approach involves inducing porosity during the sol-gel synthesis of metal oxide nanofibers and imparting a specific structure to this porosity through the use of texturizing agents such as surfactants. Mesostructured nanofibers are synthesized, and the porosity is released during the heat treatment of the fibers by removing the structuring agent. Various compositions have thus been studied with SiO₂, TiO₂, Ta₂O₅, TaNbO₅, as well as Nb₂O₅ and V₂O₅ [4].

[0044] The second approach involves using an experimental setup with two coaxial capillaries for solution flow, similar to that used for hollow fiber synthesis. In document [16b], this setup is used to prepare porous ceramic nanofibers. Two immiscible polymers are used, one of which is mixed with organometallic precursors from the inorganic phase. The polymers are diluted in two miscible solvents, and the solutions are placed in each of the reactors. During the process, the two media mix, resulting in phase separation between the two organic polymers in the "jet." After calcination, the organic polymers decompose, leaving porosity. The resulting fibers are therefore highly porous.

[0045] In both the first and second approaches, porosity is generated during a heat treatment, in particular a calcination treatment, and no chemical functionality remains.

[0046] The development of membrane materials by electro-assisted extrusion for application in fuel cells is just beginning to attract interest

[21] ,

[22] . The first document concerns the assisted extrusion of Nafion® or electrolyte polymers such as polysulfones.

[0047] In particular, document

[21] describes the preparation of membranes in four steps including the formation of proton-conducting nanofibers, the creation of a network of interconnected fibers, and the filling of the porosity between the fibers with an inert polymer.

[0048] It follows from the above that there is a need for nanofibers in an organic-inorganic hybrid material comprising a first mineral phase including a structured mesoporous network with open porosity, and a second organic phase including an organic polymer.

[0049] In particular, there is a need for nanofibers in a mesostructured organic-inorganic hybrid material which include organic functions preferably covalently linked to the mesoporous network, for example in metal or metalloid oxide.

[0050] The aim of the present invention is to meet, among other things, these needs, and to provide such nanofibers in an organic-inorganic hybrid material comprising a structured inorganic mesoporous network.

[0051] The aim of the present invention is, moreover, to provide a method for preparing these nanofibers which is simple, reliable, and which makes it possible in particular to obtain organic-inorganic hybrid nanofibers comprising organic chemical functions linked to the structured inorganic mesoporous network.

[0052] The object of the present invention is further to provide such nanofibers and a method for preparing such nanofibers which do not have the drawbacks, defects, limitations and disadvantages of the prior art organic-inorganic hybrid nanofibers and methods for preparing organic-inorganic hybrid nanofibers and which overcome the problems of the prior art hybrid nanofibers and methods for preparing hybrid nanofibers. DESCRIPTION OF THE INVENTION

[0053] This goal and others are achieved, in accordance with the invention, by organic-inorganic hybrid nanofibers as defined in claims 1 to 9, 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 not being present inside the pores of the structured mesoporous network.

[0054] The second organic phase may be essentially constituted or made up of said organic polymer and may be called the polymeric organic phase.

[0055] Hybrid organic-inorganic nanofibers having the specific structure according to the invention, with a mineral, inorganic, mesoporous phase and an organic phase, have never been described in the prior art where there is no mention of nanofibers in which the growth of mesoporous mineral networks, in particular conductive and hydrophilic, has been achieved in a matrix comprising a mechanically structuring organic polymer.

[0056] Advantageously, the nanofibers according to the invention comprise a structured mesoporous network with open porosity oriented in a determined, preferred, particular direction, which is preferably the direction of the length of the nanofibers, which promotes and guarantees the continuity of the conduction paths provided however that it has open porosity.

[0057] Open porosity is defined as porosity formed with open pores and therefore remaining accessible to conductive species.

[0058] This property of nanofibers according to the invention is particularly advantageous in proton-conducting membranes.

[0059] According to a first embodiment not part of the invention, the mineral phase and the organic phase are continuous and intermingled.

[0060] In other words, the inorganic, mineral phase and the organic phase, according to this first realization, form co-continuous networks with a controlled interface between the two networks.

[0061] In particular, nanofibers can comprise a core consisting of the mineral phase surrounded by a sheath consisting of the organic phase.

[0062] According to a second embodiment of the invention, the mineral phase is discontinuous and dispersed in the organic phase, which is continuous.

[0063] The mineral phase may contain non-hydrolyzable organic chemical functions.

[0064] These organic chemical functions are generally covalently linked to the mesoporous network, for example to the oxide network.

[0065] These organic chemical functions are conductive and hydrophilic.

[0066] These organic chemical functions can be located anywhere within the mesoporous network. Thus, organic chemical functions can be found on the surface of the pores, covalently bound to the walls of the mesoporous network.

[0067] The presence of these organic functions in the mineral phase, the mesoporous network, is very interesting for many applications, particularly in the fields of catalysis, detection, and energy production devices.

[0068] Hybrid nanofibers exhibiting organic chemical functions linked in particular by covalence to a mesoporous network for example in oxide are not known in the prior art, represented in particular by the documents cited above.

[0069] Similarly, the organic phase may exhibit non-hydrolyzable organic chemical functions.

[0070] These organic chemical functions of the organic phase are conductive and / or hydrophilic functions.

[0071] The material may optionally include, in addition, a third phase within the pores consisting of at least one structuring, texturizing agent such as a surfactant.

[0072] This structuring, texturizing agent may optionally have organic chemical functions, preferably non-hydrolyzable, preferably chosen from conductive and / or hydrophilic functions, but only in the case where at least one of the other phases has conductive and / or hydrophilic functions.

[0073] Conducting functions generally refer to functions that exhibit ionic conductivity, preferably proton conductivity.

[0074] In the case where the material has three phases (organic, mineral, surfactant), the mineral phase has conductive functions and at least one of the phases chosen from the surfactant phase and the organic phase may have conductive functions; it is also possible that all three phases have conductive functions.

[0075] In general, the nanofibers according to the invention exhibit open porosity, serving in particular as a continuous proton conduction network. Preferably, the mesoporous backbone is hygroscopic and possesses conductive functionality within its pores (for example, a functionalized metal oxide), thus ensuring proton transport and hydration. The organic polymer phase serves as a support and primarily provides the structure of the conduction medium.

[0076] A true synergy occurs between the two phases which imparts to the nanofibers according to the invention a unique combination of chemical, physical, electrical, mechanical properties never before achieved in the prior art.

[0077] It can be said that the nanofibers according to the invention exhibit a hierarchy of their properties, both chemical and mechanical, at different levels of organization, which opens up interesting perspectives for electrochemical applications involving complex systems and diverse properties.

[0078] In other words, the nanofibers according to the invention exhibit a hierarchy of their properties and are made up of a "multifunctional" material, with multiple properties, whose different functions and properties are distributed at each dimensional scale of the material, namely the millimeter scale, the micrometer scale, the nanometer scale and the Angstrom scale.

[0079] Thus, the nanofibers according to the invention can exhibit functionality, chemical properties, on the surface of pores of the inorganic mesoporous network, i.e. at a nanometric scale, while the mechanical properties can rather be communicated to the fibers by the polymer, at a millimetric scale.

[0080] Advantageously, the conducting functions can be chosen from cation exchange groups and / or anion exchange groups.

[0081] The cation exchange groups can be chosen, for example, from the following groups: -SO3 M'; -PO3 M'2; -COOM' and -B(OM')2, where M' represents hydrogen, a monovalent metal cation chosen for example from Li+, Na+, K+, or -N+, R4<3 where each R4< independently represents a hydrogen, an alkyl radical for example from 1 to 10 C or an aryl radical for example from 6 to 10 C.

[0082] Anion exchange groups can be chosen, for example, from the following groups: pyridyl; imidazolyl; pyrazolyl; triazolyl; radicals of the formula -N+< R6<3 X'-<, where X' represents an anion such as F, Cl, Br, I, NO3, SO4H, or OR7<, R7< being an alkyl radical, for example, from 1 to 10C or an aryl radical, for example, from 6 to 10C, and where each R6< independently represents a hydrogen, an alkyl radical, for example, from 1 to 10C, or an aryl radical, for example, from 6 to 10C; and aromatic or non-aromatic basic radicals containing at least one radical selected from the following radicals: 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.

[0083] Advantageously, the nanofibers according to the invention can further comprise, preferably on at least one of their surfaces, and even more preferably on at least one of their outer surfaces, catalytic nanoparticles.

[0084] Preferably, these catalytic nanoparticles can be chosen from metallic and / or metallic oxide nanoparticles.

[0085] These nanoparticles can be made up entirely or partly of platinum, ruthenium, rhodium, gold, nickel, cobalt, or a mixture and / or alloy of these.

[0086] The inorganic mineral phase is generally made up of at least one oxide chosen from among metal oxides, metalloid oxides and mixed oxides of these.

[0087] The said oxide is generally chosen from oxides of silicon, titanium, zirconium, hafnium, aluminium, tantalum, tin, zinc, magnesium, rare earths or lanthanides such as europium, cerium, yttrium, lanthanum and gadolinium, and mixed oxides of these.

[0088] The mineral phase of the material according to the invention is a mesostructured phase, this means, more precisely, that the mesoporous network has an organized structure with a repeating pattern.

[0089] For example, the mesoporous network can exhibit a cubic, hexagonal, lamellar, vermicular, vesicular or bicontinuous structure.

[0090] The pore size of the mesoporous network is generally from 1 to 100 nm, preferably from 2 to 50 nm.

[0091] The organic polymer of the organic phase must generally meet a number of conditions.

[0092] First and foremost, the polymer in question must generally be thermostable; by thermostable, we mean that it retains its properties under the action of heat.

[0093] The polymer must also generally not be susceptible to hydrolysis and oxidation at particularly high temperatures, especially at the operating temperatures of fuel cells, and this for several thousand hours.

[0094] In addition, the polymer chosen should generally be: soluble in hydro-alcoholic, alcoholic or other water-miscible solvents since the organization of the possible surfactant in liquid medium, texturizing agent of the mesoporous phase, takes place in highly polar media such as water, alcohols, ethers, ketones, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone; plastic, to provide sufficient flexibility to the inorganic mesoporous phase and form a self-supporting film, that is to say that the polymer can be described as a (mechanically) structuring polymer; this polymer must not essentially play the role of texturizing agent capable of generating mesoporosity.

[0095] The organic polymer will generally be chosen from among polyetherketones (PEK, PEEK, PEEKK); polysulfones (PSU), for example Udel®; polyethersulfones, for example VITREX®; polyphenylethersulfones (PPSU), for example Radel®; styrene / ethylene (SES), styrene / butadiene (SBS), and styrene / isoprene (SIS) copolymers, for example KRATON®; polyphenylenes, such as poly(phenylene sulfide) and poly(phenylene oxide); polyimidazoles, such as polybenzimidazoles (PBI); polyimides (PI); polyamideimides (PAI); polyanilines; polypyrroles; polysulfonamides; polypyrazoles, such as polybenzopyrazoles; and polyoxazoles, such as polybenzoxazoles. polyethers, such as poly(tetramethylene oxide) and poly(hexamethylene oxide); poly(methacrylic acid); polyacrylamides;polyvinyls, such as poly(vinyl esters), for example polyvinyl acetates, polyvinyl formates, polyvinylpropionates, polyvinyllaurates, polyvinyl palmitates, polyvinyl stearates, polyvinyltrimethyl acetates, polyvinylchloroacetates, polyvinyltrichloroacetates, polyvinyltrifluoroacetates, polyvinylbenzoates, polyvinylpivalates, polyvinyl alcohols; acetal resins, such as polyvinyl butyrals; polyvinylpyridines; polyvinylpyrrolidones; polyolefins, such as polyethylenes, polypropylenes, polyisobutylenes; poly(styrene oxide); fluorinated resins and polyperfluorocarbons, such as polytetrafluoroethylenes (PTFE), for example TEFLON®; polyvinylidene fluoride (PVDF); polychlorotrifluoroethylenes (PCTFE); polyhexafluoropropenes (HFP); perfluoroalkoxides (PFA); polyphosphazenes; silicone elastomers;sequenced copolymers comprising at least one sequence consisting of a polymer selected from the above polymers;

[0096] When the material includes a third phase within the pores, this third phase can consist of a texturizing or structuring agent. This texturizing or structuring agent can be chosen from among surfactants, which can be selected from: alkyltrimethylammonium salts, alkylphosphates, and alkylsulfonates; acids such as dibenzoyl tartaric acid, maleic acid, or long-chain fatty acids; bases such as urea or long-chain amines; phospholipids; doubly hydrophilic copolymers whose amphiphilicity is generated "in situ" by interaction with a substrate; and amphiphilic multiblock copolymers comprising at least one hydrophobic block associated with at least one hydrophilic block.Among these polymers, we can cite, for example, the Pluronic ®< based on PEO (poly(ethylene oxide)) and PPO (poly(propylene oxide)) of the type (EO) n -(PO) m -(EO) n , the copolymers of the type ((EO) n -(PO) m ) x -NCH 2 CH 2 N-((EO) n -(PO) m ) x (Tetronic ®< ), the C n (EO) m (OH) family (C n =alkyl and / or aryl chain, EO=ethylene oxide chain), for example Brij ®< , Triton ®< or Igepal ®< , and the (EO) m -sorbitan-C n family (Tween ®< ).

[0097] It is important to note that the organic polymer of the organic phase should not be confused with a potential surfactant polymer. Although both are referred to as "polymers," these compounds differ in both their structure and their effects. The organic phase polymer plays a role in the mechanical structuring of the entire hybrid material, while the potential surfactant polymer is described as a "texturizing" or "structuring" agent, referring to its role in structuring and texturing the mesoporous network.

[0098] The invention further relates to a membrane comprising the nanofibers as described above, optionally deposited on a support.

[0099] By membrane, we generally mean that the material is in the form of a film or sheet with a thickness, for example, from 50 nm to a few millimeters, preferably from 10 to 500 nm, and that in this membrane, the fibers are generally linked and / or glued and / or welded.

[0100] The invention also relates to an electrode comprising nanofibers, as described above.

[0101] The excellent properties of the nanofibers according to the invention, in the form of a membrane and / or electrode, make them particularly suitable for use in an electrochemical device, for example a fuel cell.

[0102] The invention therefore also relates to a fuel cell comprising at least one membrane and / or electrode as described above.

[0103] The invention also relates to a process for preparing organic-inorganic hybrid nanofibers, as described above, in which the following successive steps are carried out: a) at least one solution is prepared in a solvent of a mineral precursor A and / or an organometallic precursor C intended to constitute the mineral phase; b) at least one structuring agent D, texturizing the mesoporous mineral phase, is added to the solution prepared in step a), thereby obtaining a solution S1; and this solution S1 is hydrolyzed in a basic catalytic medium and allowed to mature; c) a solution S2 of an organic polymer E is prepared in a solvent; d) simultaneous, separate electro-assisted extrusion of solution S1 and solution S2 is carried out with a bicapillary electro-assisted extrusion device; or alternatively, electro-assisted extrusion of a mixture, possibly matured, of solution S1 and solution S2 is carried out with a monocapillary extrusion device;said devices comprising at least one syringe containing the solution(s) connected to a needle to which a tension is applied, and a collector or support, by means of which organic-inorganic hybrid nanofibers are deposited on the collector or support; f) e1) a heat treatment is carried out at a temperature between 50°C and 300°C to consolidate the deposited nanofibers; optionally at the end of step e1), the structuring, texturizing agent D is totally or partially removed; g) optionally at the end of step e1) or step f), the support is separated or possibly removed.

[0104] It is obvious that possible steps f) and g) may not be carried out if agent D or the support has already been previously eliminated.

[0105] Polymer E and structuring, texturizing agent D can be chosen from among the polymers and texturizing, structuring agents mentioned above in the description of the nanofibers according to the invention.

[0106] It should be noted that the structuring agent D or a solution thereof in a solvent (preferably analogous to the solvent of solution S1 and / or solution S2) may optionally be added to solution S2 instead of being added to the solution prepared in step a), or the structuring agent D or a solution thereof in a solvent (preferably analogous to the solvent of step a) and / or solution S2) may be added both to the solution prepared in step a) (thus performing step b)) and to solution S2.

[0107] Advantageously, precursor A can be selected from metal salts, metalloid salts, metal alkoxides, and metalloid alkoxides. The metals and metalloids can be selected from those mentioned above in the description of the nanofibers according to the invention.

[0108] Advantageously, the polymer and / or the structuring agent, texturizer D such as a surfactant D, carry conductive and / or hydrophilic organic chemical functions and / or precursor functions of these organic chemical functions such as conductive and / or hydrophilic functions.

[0109] Advantageously, a chelating agent B, such as acetylacetone or acetic acid, can also be added to solution S1.

[0110] Advantageously, the organo-mineral precursor compound C is a compound carrying, on the one hand, conductive and hydrophilic organic chemical functions or precursor functions of these organic chemical functions, and, on the other hand, functions capable of binding to the surface of the pores of the mesoporous network.

[0111] Advantageously, solution S1, solution S2, or the mixture of solutions S1 and S2, have a viscosity of 40 to 7000 cps at 20°C.

[0112] Advantageously, the concentration of solution S1 in mineral precursor A and / or organo-mineral precursor C and the concentration of solution S2 in polymer E, expressed as dry extract, can be from 15 to 60% by mass, preferably from 15 to 30% by mass.

[0113] Advantageously, the solvents of solutions S1 and S2 are low-volatility solvents whose vapor pressure is lower than that of ethanol.

[0114] Advantageously, the solution S1 can be allowed to mature at a temperature of 0°C to 300°C, preferably from 20°C to 200°C; at a pressure of 100 Pa to 5.10 6< Pa, preferably from 1000 Pa to 2.10 5< Pa; for a period of a few minutes to a few days, preferably from one hour to one week, preferably still from 12 to 18 hours.

[0115] Advantageously, prior to electro-assisted extrusion, solution S1 and / or solution S2 can be preheated to a temperature of 40°C to 80°C, preferably 60°C to 70°C.

[0116] Advantageously, electro-assisted extrusion can be controlled by acting on one or more, and preferably all, of the following parameters: the deposition temperature; the relative humidity of the atmosphere in which the deposition is carried out; the tension applied to the needle; the flow rate of the solutions or mixture in the syringe; the distance between the needle and the collector or support; the atmosphere in which the deposition is carried out.

[0117] Advantageously, one or more, and preferably all, of these parameters may be chosen in accordance with the following: Deposition temperature: 20°C to 200°C, preferably 25°C to 100°C, and 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 preferably 5 to 60%; Voltage applied to the needle: 2 to 25 kV, preferably 5 to 20 kV, and preferably 8 to 15 kV; Flow rate of the solutions or mixture in the syringe: 0.1 to 20 mL / h, preferably 0.1 to 10 mL / h; Distance between the needle and the collector or support: 2 to 25 cm, preferably 10 to 18 cm; Atmosphere in which the deposition is carried out: Air, Nitrogen or Argon.

[0118] Advantageously, solution S1 and / or solution S2 comprises(s) catalytic nanoparticles, preferably metallic nanoparticles and / or metallic oxides.

[0119] Advantageously, a suspension of catalytic nanoparticles, preferably metal and / or metal oxide nanoparticles, can be sprayed into the jet(s) exiting the needle of the electro-assisted extrusion device.

[0120] Advantageously, the process further includes a final treatment step to release or generate organic chemical functions such as conductive and / or hydrophilic functions on the surface of the nanofiber pores.

[0121] As mentioned above, the process according to the invention can be described as a process for preparing a membrane with controllable porosity made up of nanofibers which contain at least one mesostructured inorganic structure with organic chemical functions covalently linked to the inorganic network and providing specific conductive and proton properties; these fibers being integrated into an organic polymer which gives the membrane other properties, such as mechanical, hydrophobic / hydrophilic properties.

[0122] The preparation of such a multifunctional membrane (i.e., exhibiting several types of properties) with hierarchical properties implies a number of obstacles to overcome in order to obtain two co-continuous networks with a controlled interface between the two networks.

[0123] According to the invention, these obstacles are overcome by: The control of the rheology of solutions formulated for electrospinning, meaning they generally exhibit viscoelastic properties, is crucial. Viscosity influences the morphology of the resulting fibers, and the viscosities used in the process according to the invention are generally very high, significantly higher than the viscosity of solutions in wet processes such as dip-coating. These viscosities are generally greater than or equal to 40 cP, preferably from 40 to 7000 cP, and even more preferably from 100 to 500 cP.

[0124] The polycondensation state of the sol-gel solution and the choice of solvent are therefore very important and this is why, according to the invention, weakly volatile solvents will be preferred, i.e. solvents whose vapor pressure is less than or equal to that of ethanol, for solutions S1 and S2; The control of the mesostructuring of the network, for example, of the oxide network in the presence of the structuring and texturizing agent, under suitable sol-gel growth conditions of the functionalized mesoporous inorganic phase during the electro-assisted extrusion process; the control of the interface between the two phases, inorganic and organic polymer, with an inorganic solution that must have viscoelastic characteristics comparable to those observed in polymers. These requirements can be met by controlling the kinetics of the hydrolysis and condensation reactions, by adjusting the pH and / or by optimizing soil aging, for example, by modulating its heating.control of ambient humidity, airflow (preferably laminar), and system temperature with independent management of reactor and electrode temperatures at the electro-assisted extrusion device level to manage interfiber porosity to form in a single step dense electrolyte membranes for fuel cells or porous membrane structures for PEMFC catalytic supports.

[0125] According to the invention, one or more, and preferably all, of the parameters relating to the materials and the process involved in the preparation of such nanofibers are controlled simultaneously. The process according to the invention, in its most advantageous embodiments, achieves simultaneous reaction control of inorganic and organometallic precursors in the presence of catalysts and organic polymers.

[0126] In other words, according to the invention, what could be called a multi-reactive synchronous control associated with the regulation of process parameters is achieved.

[0127] The invention will be better understood upon reading the following description, given by way of illustration and not limitation, with reference to the accompanying drawings in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0128] There Figure 1A is a schematic view of a single-capillary, electro-assisted extrusion device, comprising a single reactor containing a mixture of solution A and solution B, which is extruded; The Figure 1B is a schematic cross-sectional view of a fiber obtained with the device of the Figure 1A ; There Figure 2Ais a schematic view of a bicapillary electro-assisted extrusion device, comprising a first reactor containing a solution A nested within a second reactor containing a solution B, solutions A and B being extruded simultaneously, separately and independently through concentric orifices to form a single hybrid fiber according to the invention ( Figure 2B ) ; There Figure 2B is a schematic cross-sectional view of a hybrid fiber obtained with the device of the Figure 2A , such a fiber not being part of the invention; The Figure 3A is a schematic view of a single-capillary, electro-assisted extrusion device, comprising a single reactor containing a mixture of solution A and solution B, which is extruded; the single-capillary, electro-assisted extrusion device being coupled to a spraying device for solution C; The Figure 3B is a schematic cross-sectional view of a fiber obtained with the device of the Figure 3A; There Figure 4A is a schematic view of a bicapillary electro-assisted extrusion device, comprising a first reactor containing solution A nested within a second reactor containing solution B, solutions A and B being extruded simultaneously and independently through concentric orifices to form a single hybrid fiber; the bicapillary electro-assisted extrusion device being coupled to a device for spraying solution C; The Figure 4B is a schematic cross-sectional view of a fiber obtained with the device of the Figure 4A , such a fiber not being part of the invention; The Figures 5A to 5D are images obtained by scanning electron microscopy of the hybrid fibers obtained in Example 1, which are not part of the invention, these fibers having been subjected to one of the following thermal aging treatments: Heating at 70°C for 12 hours ( Figure 5A ); or Heating at 130°C for 4 hours ( Figure 5B ); or Heating to 70°C and extraction of the surfactant by washing in ethanol ( Figures 5C and 5D ) ;

[0129] The scales shown on the Figures 5A to 5D are 2 µm.

[0130] - THE Figures 6A to 6D are scanning electron microscopy (SEM) images of PEOS / PVDF-HFP hybrid membranes obtained in Example 2, which is not part of the invention, comprising one of the following aging heat treatments: Aging of the membrane at a temperature of 25°C overnight ( Figure 6A ); or aging of the membrane at a temperature of 70°C overnight ( Figure 6B ); or aging of the membrane at a temperature of 550°C overnight ( Figures 6C and 6D ) .

[0131] The scales carried on the Figures 6A and 6D represent 2 µm, and the scales marked on the Figures 6B and 6C represent 10 µm. There Figure 7Ais a photograph of an opaque membrane obtained in Example 2 not forming part of the invention from PEOS / PVDF-HDP solutions.

[0132] The scale carried on the Figure 7A is a ruler graduated in centimeters. There Figure 7B is a SEM image of the opaque membrane of the Figure 7A .

[0133] The scale carried on the Figure 7B represents 20 µm. DETAILED DESCRIPTION OF THE INVENTION.

[0134] The following description is made in relation to the process of preparing nanofibers according to the invention.

[0135] We therefore describe in what follows a process for preparing according to the invention nanofibers of a conductive organic-inorganic hybrid material having a polymeric organic phase and a mesoporous mineral phase, as well as possibly a third surfactant phase.

[0136] Let us specify that by nanofibers, we generally mean fibers with a length of 1 µm to 50 mm, preferably from 1 µm to 100 µm and whose largest dimension of the cross-section, which is the diameter in the case of a circular cross-section, is generally from 10 to 500 nm, preferably from 10 to 100 nm.

[0137] This process includes, firstly, steps in which the various treatment solutions introduced into the reactor(s) of the electro-assisted extrusion system are prepared. 1.a Preparation of a solution S1 of a mineral, inorganic precursor A.

[0138] The synthesis of the material according to the invention begins with the preparation of a solution S1 of at least one mineral precursor, inorganic A and / or at least one organometallic precursor compound C which will constitute the architecture of the mineral mesoporous network.

[0139] The precursor A can be chosen from metal salts, metalloid salts, metal alkoxides, metalloid alkoxides.

[0140] In particular, precursor A can be chosen from metalloid salts and alkoxides, transition metal salts and alkoxides, and lanthanide salts and alkoxides, such as silicon, titanium, zirconium, hafnium, aluminum, tantalum, tin, europium, cerium, zinc, magnesium, yttrium, lanthanum, and gadolinium salts and alkoxides.

[0141] This precursor A is diluted in a solvent or mixture of solvents. The choice of this solvent or mixture of solvents is generally made according to the viscoelastic properties imposed by the electro-assisted extrusion process implemented according to the invention, and the miscibility medium of the polymer used subsequently.

[0142] Generally, the solvent(s) is / are chosen from among low-volatility solvents. By low volatility, we mean that this / these solvent(s) generally has a vapor pressure lower than that of ethanol.

[0143] Typically, the solvent(s) is / are chosen from alcohols, amides, ethers, aldehydes, and ketones that are miscible or partially miscible with water and have low volatility. Preferred solvents include THF, DMF, NMP, MEK, and dioxane.

[0144] The precursor organometallic compound C is generally a compound that includes hydroxyl or hydrolyzable alkoxide-type functions, and non-hydrolyzable or grafted functions.

[0145] It should be noted that by organometallic compound we mean compounds including a metal but also compounds including a metalloid.

[0146] The organometallic compound C can respond, for example, to the formula R 1< x R 2< y MOR 3< (n-(x+y)) , or to the formula ZR 1< x ZR 2< y M'OR 3< (n-(x+y)) , in which M and M' represent a metalloid or a metal such as a transition metal or a lanthanide.

[0147] M and M' could, for example, be chosen from silicon, titanium, zirconium, hafnium, aluminum, tantalum, tin, europium, cerium, zinc, magnesium, yttrium, lanthanum and gadolinium.

[0148] n is the degree of valence of the metal, generally n can range from 1 to 10.

[0149] X and Y can generally range from 0 or 1 to 10.

[0150] Z is a monodentate-type complexing function, such as an acetate, phosphonate, phosphate function, or a bidentate-type function chosen for example from β-diketones and their derivatives, and α or β-hydroxy acids.

[0151] In these two formulas, R1<, R2<, and R3< are organic substituents chosen for example from H, alkyl groups especially from 1 to 10 C, and aryl groups especially from 6 to 10 C.

[0152] One or more of the substituents R1<, R2<, and R3< may include one or more cation exchange group(s) such as -SO3M", -PO3M"2, -COOM'', or -B(OM")2 groups, in which M" represents H, a monovalent metal cation chosen for example from lithium, sodium, potassium, or a -N+< R4<3 group, where each R4< independently represents H, an alkyl group in particular from 1 to 10 C, or an aryl group in particular from 6 to 10 C; or one or more precursor group(s) of cation exchange group(s) such as SO2X, COX, or PO3X2 groups, where X represents F, Cl, Br, I or OR5<, where R5< represents an alkyl group, in particular from 1 to 10 C, or an aryl group, in particular from 6 to 10 C;or one or more anion exchange group(s) such as - +< NR 6< 3 X' -< groups, where X' represents an anion such as, for example, F, Cl, Br, I, NO 3 , SO 4 H or OR 7< , where R 7< represents an alkyl group, in particular from 1 to 10 C, or an aryl group, in particular from 6 to 10 C, and where each R 6< independently represents H, an alkyl group, in particular from 1 to 10 C, or an aryl group, in particular from 6 to 10 C, or - +< NR 7 X' groups, where X' is as defined above and R 7< is a group which forms with nitrogen +< N a ring of 4 to 10 links comprising carbon and nitrogen atoms such as an imidazolinium, pyridinium or pyrazolium ring.;

[0153] Preferred cation exchange groups are the -SO3M' and -PO3M"2 groups and precursor groups of preferred cation exchange groups are the -SO2X or -PO3X groups.

[0154] A preferred anion exchange group is the imidazolinium group.

[0155] Solution S1 may include only one or more precursor(s) A, or solution S1 may include only one or more precursor(s) C, or solution S1 may include one or more precursor(s) A and one or more precursor(s) C.

[0156] Thus, we can start by preparing a solution of the (purely) metallic precursor(s) A and add to this solution a mole fraction of the precursor(s) C.

[0157] Or, precursor(s) C can be added to the solvent(s) at the same time as the (purely) metallic precursor(s) A.

[0158] When the 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 so as to be identical.

[0159] The concentration of precursor A, or the concentration of precursor C, or the total concentration of precursor A and precursor C in solution S1 is generally 1 to 40%, preferably 1.5 to 30% by mass. It should be noted that these concentrations are generally 15 to 320 times higher than the concentrations used in conventional processes such as dip coating.

[0160] To the solution which contains precursor(s) A and precursor(s) C, we add the structuring agent(s), texturizing agent(s) D.

[0161] The choice of the structuring, texturizing agent depends both on the desired mesostructure, for example cubic, hexagonal, lamellar, vesicular or vermicular, on the size of the pores and walls of this mesostructure, and on its solubilization in the solvent used for the other compounds of the present invention, namely the polymer, precursor or precursors A, and / or precursor or precursors C.

[0162] We will generally use ionic type surfactant texturizing agents, such as alkyltrimethylammonium salts, for example cetyltrimethylammonium bromide or alkylphosphate and alkylsulfonate salts; or acids such as dibenzoyltartaric acid, maleic acid, and long-chain fatty acids; or bases such as urea and long-chain alkyl amines, to construct mesoporous structures whose pore size is limited, for example, to one or a few nanometers, for example 1.6 to 10 nm, and the wall size also to one or a few nanometers, for example 1 nm to 20 nm, especially about 1 nm.

[0163] Lyotropic phases can also be used, consisting of amphiphilic multiblock copolymers comprising at least one hydrophobic block associated with at least one hydrophilic block, typically such as Pluronic®<, for example Pluronic®< F 123 or Pluronic®< F 127, based on PEO (polyethylene oxide) and PPO (polypropylene oxide) of the type (EO)n-(PO)m-(EO)n, copolymers of the type ((EO)n-(PO)m)x-NCH2CH2N-((EO)n-(PO)m)x (Tetronic®<), compounds of the formula Cn(EO)m(OH) (where Cn is an alkyl and / or aryl chain, for example from 1 to 20 C, 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 compounds Brij ®< , Triton ®< , Tergitol ®< or Igepal ®< , and the compounds of formula (EO) m -sorbitan-C n (Tween ®< ) to prepare mesoporous phases of larger pore size, for example up to 50 nm.

[0164] These different blocks may also be of acrylic nature PMAc (poly(methacrylic acid) or PAAc (poly(acrylic acid)), aromatic PS (Polystyrene), vinyl PQVP (polyvinylpyridine), PVP (polyvinylpyrrolidone), PVEE (polyvinyl ether), or other PDMS (polysiloxane).

[0165] These different blocks can be functionalized by one or more cation exchanger conductive groups; or one or more precursor groups for cation exchanger groups; or one or more anion exchanger groups; or one or more precursor groups for anion exchanger groups. These groups can be chosen from among those already listed above. For example, PSS (polystyrenesulfonic acid) is an example.

[0166] The chosen structuring agent(s) D can(s) be added directly to the solution containing precursor(s) A and precursor(s) C, or agent(s) D can(s) be previously dissolved or diluted in a hydro-alcoholic medium or in an aqueous-based solvent mixture compatible with the dilution medium of the polymer and the metallic precursor.

[0167] The concentration of the structuring agent(s) D in the solution S1 is generally from 1 to 20% by mass.

[0168] The S1 solution is hydrolyzed in a basic catalytic medium for a determined period which can range from one to a few minutes up to one or more hours (2, 6, 12, 18, 24, 48 hours), for example from 12 to 18 hours depending on the choice of the metallic precursor.

[0169] Particularly in the case of highly reactive metallic precursors, such as zirconium or titanium-based precursors, a chelating agent B, such as acetylacetone, acetic acid or phosphonates, may be introduced to control the hydrolysis-condensation of the inorganic network. 1.b Preparation of solution S2 of at least one organic polymer E.

[0170] Organic polymer E is generally chosen for its mechanical properties, for its chemical stability and / or for its non-miscibility in the treatment solution S1.

[0171] This polymer is diluted or swollen with a solvent or mixture of solvents chosen preferably from alcohols, ethers, amides, aldehydes and ketones miscible or partially miscible with water.

[0172] The organic polymer(s) will generally be chosen from among polyetherketones (PEK, PEEK, PEEKK); polysulfones (PSU), for example Udel®; polyethersulfones, for example VITREX®; polyphenylethersulfones (PPSU), for example Radel®; styrene / ethylene (SES), styrene / butadiene (SBS), and styrene / isoprene (SIS) copolymers, for example KRATON®; polyphenylenes, such as poly(phenylene sulfide) and poly(phenylene oxide); polyimidazoles, such as polybenzimidazoles (PBI); polyimides (PI); polyamideimides (PAI); polyanilines; polypyrroles; and polysulfonamides. polypyrazoles, such as polybenzopyrazoles; polyoxazoles, such as polybenzoxazoles; polyethers, such as poly(tetramethylene oxide) and poly(hexamethylene oxide); poly(meth)acrylic acid; polyacrylamides;polyvinyls, such as poly(vinyl esters), for example polyvinyl acetates, polyvinyl formates, polyvinylpropionates, polyvinyllaurates, polyvinyl palmitates, polyvinyl stearates, polyvinyltrimethyl acetates, polyvinylchloroacetates, polyvinyltrichloroacetates, polyvinyltrifluoroacetates, polyvinylbenzoates, polyvinylpivalates, polyvinyl alcohols; acetal resins, such as polyvinyl butyrals; polyvinylpyridines; polyvinylpyrrolidones; polyolefins, such as polyethylenes, polypropylenes, polyisobutylenes; poly(styrene oxide); fluorinated resins and polyperfluorocarbons, such as polytetrafluoroethylenes (PTFE), for example TEFLON®; polyvinylidene fluoride (PVDF); polychlorotrifluoroethylenes (PCTFE); polyhexafluoropropenes (HFP); perfluoroalkoxides (PFA); polyphosphazenes; silicone elastomers;sequenced copolymers comprising at least one sequence consisting of a polymer selected from the above polymers;

[0173] These different polymers may include one or more cation exchanger conductive groups; or one or more precursor groups for cation exchanger groups; or one or more anion exchanger groups; or one or more precursor groups for anion exchanger groups. These groups may be chosen from among those already listed above.

[0174] The concentration of the organic polymer(s) in the S2 solution is generally from 1 to 50%, preferably from 1 to 30%. 1.d Preparation of the surfaced organic-inorganic hybrid solution F

[0175] The precursor solution based on surfactant D is added at room temperature to the polymer solution E. After homogenization of the medium, the precursor solution based on inorganic component A, containing a mole fraction X of C (e.g., 0 ≤ X ≤ 0.4), is added dropwise at room temperature to the reaction medium. Stirring is maintained at controlled temperatures from room temperature to reflux for several hours. This maturation of the organic-inorganic hybrid solution can be extended to several days depending on the choice of polymer and inorganic network. The formulation composition is generally [A(1-X)-CX]-DY-EZ-(H₂O)h, where Y = mol(D) / [mol[A(1-X)-CX]) + mol(D)] and 0 ≤ Y ≤ 0.2, and where Z = g(E) / [g(MO₂) + g(E)] and 0 ≤ Z ≤ 0.9. 2. Preparation of organic-inorganic hybrid nanofibers

[0176] According to the invention, the solution S1 and the solution S2 are deposited on a support by carrying out the simultaneous electro-assisted extrusion, separate of the solution S1 and the solution S2 with a bicapillary electro-assisted extrusion device; or by carrying out the electro-assisted extrusion of a mixture of the solution S1 and the solution S2 with a monocapillary electro-assisted extrusion device.

[0177] The single-capillary, electro-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 those skilled in this field of technology and is illustrated in the Figure 1A .

[0178] Note that in the figures, references A, B and C designate, with regard to the devices ( Figures 1A, 2A , 3A, 4A) respectively the solutions S1, S2 and S3 and with regard to the fibers, respectively the phases A, B, C, obtained from these solutions.

[0179] The reactor or syringe (1) is generally in the form of a vertical cylindrical reservoir (2) with a circular cross-section and an open upper end which contains the solution to be extruded (3). The lower end of the reservoir is in the form of a truncated cone (4) converging towards a lower orifice, generally circular in cross-section (5), which continues as a hollow tube or needle (6).

[0180] A piston exerts pressure on the upper surface (7) of the solution (3) contained in the syringe or reactor (1), thereby expelling the solution (8) through the orifice at the end of the needle (6).

[0181] The needle (6) is powered by a high voltage, creating an electric field between the syringe needle (6) and a substrate called a collector (9), which acts as a counter-electrode and is generally connected to ground (10). The collector (9) can be made of a conductive or semiconducting material. The collector (9) can vary in shape and size; for example, it can be cylindrical, flat, or circular. The collector can be static (fixed) or dynamic (rotating or translating). The needle (6) can be positioned at an angle Θ, typically from 0° to 45°, relative to the collector (9).

[0182] In the case where the process according to the invention is carried out with a single-capillary extrusion device such as that shown in the Figure 1, the reactor, syringe of the device contains a mixture (3) of the solutions S1 and S2 defined above in which the polymer E and the precursors A and / or C are uniformly distributed at the molecular level before extrusion, and it is therefore this mixture which is subjected to electro-assisted extrusion.

[0183] Thus, when a single-capillary extrusion device is implemented, composite fibers are obtained, as shown in the diagram. figure 1B comprising a polymer matrix (11, phase B) in which the inorganic, mesoporous mineral phase (phase A) is distributed in a discrete manner.

[0184] The two-capillary electro-assisted extrusion reactor (21) shown on the figure 2AThe device comprises two nested reactors or syringes. For example, a first reactor or syringe may consist of a first vertical cylinder with a circular cross-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 larger-diameter cylinder surrounding the first cylinder. The lower end of the first reactor is shaped like a truncated cone (25) converging towards a lower orifice, generally circular in cross-section (26), which continues as a hollow tube (27). The lower end of the wall of the second reactor is also shaped like a converging truncated cone (28) surrounding the truncated cone (25) and terminating in a tubular wall surrounding the hollow tube (27).

[0185] In the bicapillary electro-assisted extrusion reactor, the needle therefore includes 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 cross-section (27) is surrounded by an annular tube (210) 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.

[0186] In the case where the process according to the invention is carried out with a bicapillary extrusion device such as that shown in the Figure 1BSolution S1 (A) is generally contained in the first reactor, while 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 orifice of the needle and through the second concentric annular orifice of the needle.

[0187] When a bicapillary electro-assisted extrusion device is implemented, hybrid fibers are obtained, as shown in the image. figure 2B in which a core (212) in mesoporous mineral phase (phase A) is surrounded by a concentric sheath (213) in organic polymer (phase B). Such fibers are not part of the invention.

[0188] The extrusion of the two solutions S1 and S2 is separate, independent, but simultaneous. Because these two solutions are extruded through concentric orifices, a fiber is not formed from solution S1 and a fiber from solution S2, but rather a single, hybrid fiber with the structure described above and on the figure 2B .

[0189] The person skilled in the art regarding the structure of a bicapillary assisted extrusion device knows that when such a device is implemented, one does not obtain simultaneously two types of fiber but rather only one type of fiber.

[0190] The electro-assisted extrusion device implemented according to the invention, whether a single-capillary or double-capillary device, can optionally be coupled to a spray-coating device (31, 41) as shown in the figures (3A) and (4A) )

[0191] This spraying device is generally arranged to spray through a nozzle (32, 42) a solution S3 in the form of an aerosol, nebulized in the jet (33, 43) exiting the needle of the electro-assisted extrusion device preferably in the vicinity of the orifice or orifices of the needle of the electro-assisted extrusion device.

[0192] 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 can be chosen from gold, silver, platinum, palladium, nickel, copper, ruthenium, rhodium, and cobalt.

[0193] This yields nanofibers with a structure analogous to that of the hybrid fibers prepared with an electro-assisted extrusion device shown in the diagrams. Figures 1B and 2Bbut which, moreover, are "decorated" by nanoparticles (34, 44) of metals and / or metal oxides. These nanofibers are shown on the Figures 3B and 4B Nanofibers, as represented in the figure 4B are not part of the invention.

[0194] It should be noted that if one or both solutions S1 or S2 also contain metal and / or metal oxide nanoparticles, these nanoparticles may be distributed throughout phase A or phase B, or throughout both phases. In this case, a solution S3 can also be sprayed as described above.

[0195] In the process according to the invention, synchronous multi-reactive control is carried out, that is to say that the sol-gel hydrolysis-condensation reactions are controlled simultaneously, which corresponds to kinetic control, the mesoporous organization of the networks which corresponds to thermodynamic control, and the rheology of the mixture which allows electro-assisted extrusion of the mixture.

[0196] These different controls can be ensured by acting on the parameters relating to the solution or solutions to be deposited which have already been defined above and on the parameters relating to the electro-assisted extrusion process itself.

[0197] Thus, regarding the parameters relating to the extrusion process, the electro-assisted extrusion temperature is generally regulated independently of the reactor(s) and the collector and is generally in the range of 20°C to 200°C, preferably from 25°C to 100°C, and preferably still from 30°C to 70°C.

[0198] The relative humidity of the extrusion device is regulated in a range of 0 to 90%, preferably 5 to 90%, and preferably still 5 to 60%.

[0199] The voltage applied to the point is generally in a range of 2 to 25 kV, preferably 5 to 20 kV, and preferably even more 8 to 15 kV.

[0200] The flow rate of the solution(s) in the syringe is generally in the range of 0.1 to 20 mL / h, preferably 0.1 to 10 mL / h.

[0201] The distance between the needle (i.e. usually the tip, end of the needle) and the counter electrode (collector or support) is usually 2 to 25 cm, preferably 10 to 18 cm.

[0202] The deposition can take place under an atmosphere of air, nitrogen or argon.

[0203] Adjusting the applied voltage, the solution ejection rate (equivalent to the flow rate in the syringe) and the distance between the needle and the collector allows control of the fiber diameter and their texture.

[0204] A continuously controlled application of tension will be preferred to form fibers homogeneous in diameter, while point-by-point and controlled variations in tension will create defects in the texture of the fibers and promote the growth of a three-dimensional fibrous network.

[0205] The fibers deposited on the substrate, which is the collector, are then heat-treated at a temperature between 50°C and 300°C, preferably between 40°C and 200°C, depending on the polymer, generally to achieve consolidation. This treatment can be called aging treatment and, depending on the conditions implemented, allows for the creation of a coherent membrane in which the fibers are generally bonded to each other.

[0206] The duration of this consolidation treatment is generally from 15 minutes to 24 hours, preferably from 1 to 15 hours.

[0207] If consolidation has been carried out, then the texturizing, structuring agent such as a surfactant which has been used for the mesostructuring of the inorganic network and which is found in the mesopores of the membrane, can possibly be removed totally or partially, preferably by a gentle method, such as selective or non-selective washing in a solvent such as ethanol.

[0208] Washing can be carried out in an acidic hydroalcoholic environment.

[0209] A post-reaction can be performed to release or generate a conductive function linked to the inorganic network. Typically, this type of post-reaction might be: an oxidation of a mercaptan group (-SH) by hydrogen peroxide to sulfonic acid SO3H or, the hydrolysis of a dialkylphosphonate (RO)2(O)P- function by HCl directly or via the formation of an intermediate (Me3SiO)2(O)P- then hydrolysis by MeOH to form a phosphonic acid -PO3H2.

[0210] This after-reaction can also involve the grafting of surface hydroxyl groups (M-OH) of the membrane's inorganic network by a metal organoalkoxide. In all these cases, the membrane is placed in a liquid medium to allow it to swell and the reactive molecular entities to diffuse into the membrane pores.

[0211] In order to avoid any parasitic reaction within the membrane during the operation of the cell, the membrane such as a proton conducting membrane can be purified by different washings for example oxidizing, acidic (or basic) and aqueous which make it possible to eliminate all labile organic, organomineral or inorganic entities.

[0212] The membrane can also be prepared as a self-supporting film. This film is then detached from its backing by swelling in a solvent such as water. EXAMPLES Example 1 not forming part of the invention :

[0213] In this example, hybrid fibers of zirconium oxide and a PVDF-HFP copolymer are prepared.

[0214] 0.52 g of the surfactant Pluronic ®< F127, and 0.466 g of a PVDF-HFP copolymer (poly(vinylidene fluoride co-hexafluoropropene)), the mass content of the hexafluoropropene chain is between 5 and 12%) are added to 0.65 g of acetic acid (chelating agent), 4.0 g of a zirconium precursor, Zr(OiPr) 4 and 4.8 g of DMF.

[0215] The solution is stirred overnight to dissolve any ZrO2 precipitates that may form due to the presence of residual water.

[0216] This solution (viscosity: 20 cPs, mass content of polymer: 4.4%, mass content of zirconium precursor: 38%) is used to prepare hybrid fibers of Pluronic ®< F127 / ZrO 2 / PVDF-HFP by single-capillary electro-assisted extrusion.

[0217] The experimental conditions for obtaining these fibers 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 reaction medium (i.e. in the solution), a distance of 11 cm between the tip of the needle and the counter electrode.

[0218] The resulting hybrid fibers are subjected to one of the following heat aging treatments: Heating at 70°C for 12 hours ( Figure 5A ) ; or Heating at 130°C for 4 hours ( Figure 5B ); or Heating to 70°C and extraction of the surfactant by washing in ethanol ( Figures 5C and 5D ).

[0219] THE Figures 5A, 5B, 5C, 5Dare scanning electron microscopy (SEM) images of Pluronic®< F127 / ZrO2 / PVDF-HFP fibers obtained by electro-assisted extrusion from the solution prepared in the manner described above, these fibers having also undergone one of the heat treatments described above.

[0220] The diameter of the fibers obtained is approximately 260 nm ± 50 nm. They are homogeneous in diameter. Depending on the heat treatment applied, they can exhibit a particular spine-like geometry ( Figure 5D ). Example 2 not forming part of the invention :

[0221] In this example, PEOS / PVDF-HFP hybrid fibers are prepared which can be in the form of a membrane.

[0222] PEOS polysiloxanes are first synthesized (water, TEOS, and acid) by hydrolysis of TEOS in acidic medium in ethanol.

[0223] The three components are mixed in the following proportions: H2O / Si = 1.7 and pH = 2.5, in a closed bottle, then they are shaken for 3 days at 70°C.

[0224] The solvent is evaporated from the previous solution using a "rotary steamer".

[0225] The resulting solution is transparent, viscous (1000 cPs) and is dried under vacuum at room temperature to obtain a white powder.

[0226] The solution subjected to electro-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 added to this solution.

[0227] This high viscosity solution (100 cPs) is subjected to electro-assisted extrusion.

[0228] The solution subjected to electro-assisted extrusion has the following composition: 450 mg of Pluronic ®< F127; 125 mg of PVDF-HFP; 750 mg of PEOS prepared with a molar ratio H 2 0 / Si of 1.7; 1.5 g of DMF; its viscosity is 100 cPs.

[0229] Electro-assisted extrusion is carried out under a voltage of 11 kV, with a flow rate of 0.5 mL / h, at ambient temperature, and under a relative humidity (“RH”) of approximately 70% RH.

[0230] The distance between the tip of the needle and the counter electrode is 13 cm. The membrane is obtained after an extrusion time of 30 minutes.

[0231] The resulting membranes are then subjected to one of the following thermal aging treatments: Aging the membrane at a temperature of 25°C overnight; or Aging the membrane at a temperature of 70°C overnight; or Aging the membrane at a temperature of 550°C (for 2 hours to overnight).

[0232] THE Figures 6A, 6B, 6C and 6D present scanning electron microscopy (SEM) images of PEOS / PVDF-HFP hybrid membranes obtained by electro-assisted extrusion from the solution prepared in the manner described above, these membranes having also undergone one of the aging heat treatments described above.

[0233] The morphology of the membrane depends on its aging temperature after synthesis. Treatment at room temperature (25°C) overnight results in the formation of individual fibers which can nevertheless be considered to form a membrane tissue, which is an interesting element for the electrode part, with a diameter of approximately 1 µm ( Figure 6A ).

[0234] On the contrary, treating these fibers at 70°C overnight results in the formation of a membrane with fibers stuck together ( Figure 6B ).

[0235] Finally, when these fibers are treated at 550°C, the polymer is eliminated and a silica fiber fabric is obtained ( Figures 6C and 6D ).

[0236] The opaque membrane of Figures 7A and 7B was obtained under the conditions already described above: aging at room temperature, humidity: 70%, needle-to-electrode distance: 13 cm, extrusion time: 30 minutes, voltage: 11 kV. Example 3 not forming part of the invention :

[0237] In this example, membranes are prepared based on CSPTMS (chlorosulfonylphenyltrimethoxysilane) / PVDF-HFP / PEO.

[0238] CSPTMS is a bifunctional organometallic compound, as defined above.

[0239] Polyoxyethylene (POE) is used as a structuring agent.

[0240] Polyoxyethylenes of varying molecular weight (10,000; 1,000,000; 16,000) are added to solutions containing the CSPTMS / PVDF-HFP mixture to obtain 50% by mass of PVDF-HFP (poly(vinylidene fluoride co-hexafluoropropene)), the mass content of the hexafluoropropene chain is between 5 and 12%).

[0241] The extrusion of the different solutions takes place under a voltage of 12.4 kV, with a distance between the tip of the needle and the counter electrode of 10 to 11 cm, a variable humidity level ranging from 0 to 20% RH, and with a flow rate of 0.15-0.3 ml / h, at room temperature, for one hour.

[0242] The resulting membranes are flexible, opaque, and approximately 20 µm thick. The thickness is primarily determined by the time during which the solution is sprayed, regardless of the PEO.

[0243] Four-point conductivity measurements were performed on these membranes.

[0244] For the membrane prepared from polyethylene glycol with a molecular weight of 10,000, the measured proton conductivities are 100 mS / cm at 80°C under 100 kPa, while the conductivity is 43 mS / cm for a membrane prepared with poly(ethylene oxide) with a molecular weight of 1,000,000.

[0245] The fibers and membranes in the examples exhibit a mineral phase with a structured, open-porosity mesoporous network, as defined above, particularly with regard to pore size. Pore size was characterized by Transmission Electron Microscopy (TEM) and / or low-angle X-ray diffraction (LAXD) and / or gas adsorption (BET).

[0246] The mesostructure is characterized by low-angle X-ray diffraction (XRD).

[0247] Measurements taken on the fibers and membranes of the examples show pore size values ​​of the mineral phase in agreement with those given in the description.

[0248] The diffractograms produced on the fibers and membranes of the examples show the presence of a mesostructuration of the mineral phase. REFERENCES

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Claims

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 5.106 Pa, and preferably 1,000 Pa to 2.105 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;21. Method according to any one of claims 13 to 20, wherein solution S1 and / or solution S2 comprise(s) catalytic nanoparticles, preferably metallic nanoparticles and / or nanoparticles of metal oxides.

22. Method according to any one of claims 13 to 21, wherein a suspension of catalytic nanoparticles, preferably nanoparticles of metals and / or of metal oxides, is spraycoated in the jet(s) coming out of the needle of the electrically assisted extrusion device.

23. Method according to any one of claims 13 to 22, wherein the method also includes a final treatment step to release or generate organic chemical functional groups such as conductive and / or hydrophilic functional groups on the surface of the pores of the nanofibres.

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