METHOD FOR GROWING CARBON NANOTUBE ON THE SURFACE AND IN THE BODY OF A POROUS CARBON-CONTAINING SUBSTRATE AND USE FOR THE PRODUCE OF AN ELECTRODE

Description

TECHNICAL FIELD

[0001] The present invention belongs to the field of electrical energy storage and release devices and, in particular, to the field of electrodes especially useful for supercapacitors.

[0002] More particularly, the present invention proposes an electrode having (i) a support made of a porous carbon material, (ii) vertically aligned carbon nanotubes (VACNT for "Vertically Aligned Carbon Nanotubes") on said support and in the volume of said support and (iii) an electrically conductive organic polymer.

[0003] To this end, the present invention relates, firstly, to a process for synthesizing vertically aligned carbon nanotubes (VACNTs) by chemical vapor deposition (CVD) on the surface and within the volume of a porous carbon substrate. The present invention also relates to the composite material thus obtained and its uses, in particular for the preparation of an electrode as previously described. PREVIOUS STATE OF THE ART

[0004] To enable the growth of renewable energies and the reduction of gas emissions, electricity storage is one of the greatest challenges to overcome. Among the many autonomous energy sources, supercapacitors, based on rapid charge / discharge cycles of ions on carbon surfaces, fall between capacitors and batteries. Their high storage efficiency (>95%), safety, reliability, and lifespan make them good candidates to complement or replace existing solutions such as, for example, electrochemical batteries, flywheel batteries, or magnetic storage.

[0005] Supercapacitors, whose market is booming, have two electrodes, i.e. an anode and a cathode, which are electrically isolated by a separator, with an electrolyte placed between each electrode and the separator.

[0006] One of the important parameters for a supercapacitor is the system's capacitance, which, as a reminder, is defined as the property of an electrical conductor to hold a certain level of electrical charge at a given electrical potential. This capacitance depends primarily on the relationship between the materials chosen for the electrodes, the design of these electrodes, and the electrolyte.

[0007] Among all the materials studied, in particular, any porous carbonaceous material with electrical conductivity suitable for use as a supercapacitor electrode can be considered both as the active material and as the current collector. For example, fabrics made of carbon fibers are materials that meet these requirements.

[0008] The use of carbon fiber fabrics as supercapacitor electrodes is widely studied and involves combining the carbon fiber fabric with a pseudocapacitive material, including electrically conductive polymers (ECPs), primarily polyaniline and polypyrrole (PPY). Notable examples include the work of Ma et al which electrochemically deposit PPY on the surface of carbon fiber fabrics, giving the electrode a high capacitance: 3300 mF / cm2 < 10m V / s in sulfuric acid (H2SO4) (between 0 and 1.6 V) [1]. Other deposition techniques are also implemented, such as the vapor-phase polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) on carbon fiber fabrics, giving the electrode interesting energy and power densities. [2].Beyond the association between carbon fiber fabrics and conductive polymers, metal oxides such as, for example, manganese oxide (MnO2), have also been associated with carbon fiber fabric by anodic electrodeposition, giving the electrode an interesting cyclability in sodium sulfate (Na2SO4). [3].

[0009] The integration of carbon nanostructures, particularly carbon nanotubes (CNTs), onto the surface of carbon fiber fabric has also been the subject of much research, both for applications in structural materials or multi-functional materials, and for energy storage applications. In the latter case, this integration makes it possible to give the electrode controlled nanometric porosity, a higher specific surface area, and electrical conductivity, which have beneficial impacts on electrode performance. [4].The integration of carbon nanotubes onto the surface of carbon fiber fabric can be achieved in different ways: either by depositing a suspension of nanotubes onto the surface of the carbon fiber fabric, or by direct growth of the nanotubes onto the carbon fiber fabric using chemical vapor deposition (CVD). [5,6].

[0010] The direct growth route of carbon fiber nanotubes (CFTs) via chemical vapor deposition (CVD) is of interest due to its ease of preparation and the close cohesion it provides for the association between the carbon fiber fabric and the nanotubes. Notable examples include the work of Lv et al which are focused on the growth of vertically aligned nanotubes on carbon fiber fabrics for applications in energy storage in supercapacitors [7].This work highlights the control of carbon nanoparticle (CNP) loading by the synthesis time, which influences CNP length, given that CNPs are primarily distributed on the surface of the tissue. This material exhibits interesting properties in terms of cyclability in aqueous media and is competitive with commercial carbon-based systems. The authors explain that these properties are linked to a specific hierarchical 3D architecture featuring large mesopore sizes and aligned channels within the CNP network, facilitating the diffusion of electrolyte ions.

[0011] Faraji et al (2018, Nanotechnology, vol. 29, 295602) describe the preparation of secondary carbon nanotubes (CNTs) on a primary CNT foam. Although the secondary CNTs obtained in this document are present not only on the surface of the CNT foam but also throughout its volume, they do not appear as vertically aligned carbon nanotubes.

[0012] An et al. (2011, Applied Surface Science, vol. 258, pages 1069-1076) propose a process for synthesizing VACNTs on a carbon fiber fabric. An alumina layer is deposited on this fabric, which is then impregnated with an iron-based catalyst solution before VACNT synthesis by CCVD (Combustion Chemical Vapor Deposition) using acetylene as the carbon source. Furthermore, based on Figures 4(c) and (d), it is explained that the alumina layer appears to have prevented the diffusion of the iron-based catalyst particles into the porous substrate, thus allowing for dense VACNTs to be obtained on the surface of this substrate (page 1072, right column, first row). The resulting porous carbon material therefore contains no VACNTs by volume.

[0013] International application WO 2009 / 103925 proposes a method for growing VACNT on carbon substrates such as carbon fibers or on metallic substrates in a single growth reactor. [8]. This process comprises a first phase of depositing a ceramic sublayer followed by a second phase of depositing carbon nanotubes onto said sublayer. The organization of the various elements of the device used for this process is clearly shown in Figure 15. [8] The injection of the sprayed precursors is carried out parallel to the plane of the substrate. This is referred to as "horizontal" injection. Furthermore, although it is envisaged that the second step of the process could be carried out at a pressure lower than atmospheric pressure, a pressure between 900 mbar (9 x 10⁴ Pa) and 1000 mbar (10⁵ Pa) is used for this step. [8].

[0014] International application WO 2015 / 071408 relates to a process for the continuous fabrication of aligned nanostructures such as VACNTs on a support by catalytic chemical vapor deposition [9]. This application also considers that the process used includes the two steps as described in [8], The ceramic underlayer is deposited in a pre-treatment chamber. (See international application WO 2015 / 071408) [9], The pulverized precursors used during nanostructure deposition are injected in a direction that is essentially perpendicular, and preferably perpendicular, to the conveying means. In other words, the injection direction is essentially perpendicular to the plane of the substrate. Just as for [8], it is envisaged, in [9],that the pressure during VACNT growth can be lower than atmospheric pressure. However, this step is carried out at a pressure between 900 mbar (9 x 10⁴ Pa) and 1000 mbar (10⁵ Pa). Furthermore, a porous carbon support is not described as usable in [9] (see from page 24, line 27 to page 25, line 4), all the examples carried out using a quartz support.

[0015] The architectures described above, featuring a carbon fiber fabric covered with randomly distributed or vertically aligned nanotubes, can serve as supports for the deposition of pseudocapacitive materials as previously mentioned. Two methods for preparing these materials are reported in the literature: either the nanotubes are initially deposited on the surface of the fibers followed by the pseudocapacitive material deposition, or the pseudocapacitive material is initially deposited on the surface of the fibers followed by the nanotube deposition. Most studies employing this approach utilize randomly distributed nanotubes on the surface of the carbon fiber fabrics, and sometimes even graphene.We can cite in particular the work of Li and Chen who report studies on the addition of NTC on tissue previously covered with polyaniline thus highlighting a flexible electrode exhibiting a high capacitance of 5611 mF / cm 2< at 1 mV / s and 3381 mF / cm 2< at 20 mV / s in aqueous electrolytic medium (H 2 SO 4 ).

[10] . Yesi et al conducted studies on the growth of randomly distributed nanotubes on carbon fiber fabrics followed by the deposition of polypyrrole at 1430 mF / cm² < 20 mV / s in H₂SO₄

[11] . Note that the use in

[10] And

[11] The use of an acidic aqueous electrolyte has the disadvantage of presenting a narrow potential range.

[0016] Beyond this work, patent application CN 102354612 reports a different concept in which nanotubes, vertically aligned with the surface of carbon fiber fabrics and obtained by direct growth by CVD, are electrochemically coated with MnO2 nanoparticles, a pseudo-capacitive material.

[12] . This material consists of a conductive and porous network with a large specific surface area, excellent mechanical strength, and chemical stability, making it ideal as a high-performance supercapacitor electrode. However, this material has limited operating voltages and cycling is only possible in aqueous or protonic media.

[0017] Due to the growing interest in porous carbon material supercapacitors, the inventors set themselves the goal of proposing an electrode comprising such a material, achievable via an easily industrializable process and exhibiting interesting properties, particularly in terms of capacitance and especially in terms of surface capacitance. DESCRIPTION OF THE INVENTION

[0018] The present invention makes it possible to achieve the goal set by the inventors since, thanks to their work, they were able to show that it was possible to further improve, from the synthesis of VACNTs, the performance, particularly in terms of capacitance, of electrodes with a support in porous carbon material having VACNTs and an organic polymer matrix that conducts electricity.

[0019] Indeed, through a judicious choice of the operating conditions used during the synthesis of VACNTs based on the process described in [8],The inventors were able to obtain a porous carbon support material that contains VACNTs not only on its surface but also throughout its volume. The operating conditions selected by the inventors—namely, the pressure at which VACNT growth is carried out and the injection orientation of the precursors necessary for this growth—allowed the integration of VACNTs both on the surface and throughout the volume of the porous carbon support material. The presence of these VACNTs within the material's volume generates a larger carbon surface area available for subsequent PCE deposition, increases the specific surface area, and maintains or even increases the material's electrical conductivity, resulting in beneficial impacts on the performance of the electrode containing such a material.

[0020] Thus, the present invention relates to a method for equipping a support made of a porous carbon material with vertically aligned carbon nanotubes as defined in claim 1 of the attached set of claims, said method comprising a first step of depositing a ceramic underlayer on said support followed by a second step of synthesis, by catalytic chemical vapor deposition, of said vertically aligned carbon nanotubes on the support obtained following the first step, the carbon source necessary for the synthesis during this second step being injected in a direction substantially perpendicular to the plane of the support and at a pressure between 3.10 4< Pa (300 mbar) and 6.10 4< Pa (600 mbar).

[0021] The term "support made of a porous carbonaceous material" refers to a support made of a material consisting essentially of a carbon skeleton and exhibiting pores. Advantageously, for applications in electrode preparation, this material is electrically conductive.

[0022] The support, made of a porous carbon material, implemented within the framework of the present invention is in the form of carbon fibers. In the case of carbon fibers, these fibers are either in non-woven form, such as bundles or unidirectional (UD) fibers, or in woven form, thus forming a fabric (or a sheet). In the case of carbon fibers or a carbon fiber fabric, the pores of the porous material correspond to the empty spaces between the carbon fibers.

[0023] The support used in the invention has a shape adapted to its subsequent use, particularly for preparing an electrode. By way of illustration, this support may be flat or ribbon-like. Typically, the support used in the invention has a thickness between 1 µm and 1 mm, and in particular between 2 µm and 500 µm.

[0024] The terms "embossing a porous carbonaceous material support with vertically aligned carbon nanotubes" or "embossing a porous carbonaceous material support with vertically aligned carbon nanotubes" refer to synthesizing carbon nanotubes on the surface and within the volume of the support. These nanotubes extend substantially perpendicularly to the surface of the support; that is, the axis of the carbon nanotubes is substantially perpendicular to the axis of the carbon fibers present on the surface and within the volume of the support, or the axis of the carbon nanotubes is substantially perpendicular to the surface of the cell walls on the surface and within the volume of the carbon foam. These carbon nanotubes form mats whose base corresponds either to carbon fibers or to the cell walls of a carbon foam.

[0025] The first and second steps of the process according to the invention are steps well known to a person skilled in the art, notably described in international application WO 2009 / 103925 [8] and the international application WO 2015 / 071408 [9]. These steps can be performed in batches (batch-to-batch technique) or in a continuous process (roll-to-roll technique), and are therefore easily industrialized. It should be noted that, as previously explained, the process according to the present invention differs from prior art processes, firstly, in the direction of injection of the precursors necessary for the growth of the carbon nanotubes and, secondly, in the pressure at which this growth is carried out.

[0026] Thus, the first step consists of forming a ceramic underlayer on the porous carbonaceous substrate. By "ceramic," we mean either an oxide ceramic chosen from the group consisting of a silicon oxide (SiO₂) with 0 <x≤2), de l'oxyde d'aluminium (Al 2 O 3 ), de l'oxyde de zirconium (ZrO 2 ) ou de l'oxyde de titane (TiO 2 ) qu'une céramique non oxyde choisie dans le groupe constitué par du carbure de silicium (SiC), du carbonitrure de silicium (SiCN), du nitrure d'aluminium (AIN), du nitrure de titane (TiN), de l'oxynitrure de silicium (SiON) ou de l'oxycarbonitrure de silicium (SiOCN). Avantageusement, la céramique mise en œuvre dans le procédé selon l'invention est une céramique oxyde et notamment de l'oxyde de silicium (SiO x avec 0<x≤2). Cette première étape est réalisée en décomposant chimiquement, par pyrolyse, des précurseurs de céramique du type précurseurs organométalliques tels que les alcoxysilanes comme le tetraéthoxysilane (TEOS).Other usable precursors are provided in . [8]. Prior to their decomposition, the precursors are dissolved or suspended in a liquid organic solvent at ambient temperature and pressure, such as, by way of illustrative but not exhaustive examples, benzene, toluene, xylene, cyclohexane, hexane, or heptane. Typically, this first step is carried out at the temperature and pressure defined in claim 1. It has been demonstrated that the thickness of the resulting ceramic sublayer influences the subsequent growth of the VACNTs. Thus, a person skilled in the art can, through routine practice, determine the most suitable thickness. This layer acts as a diffusion barrier between the substrate and the precursors necessary for VACNT growth.

[0027] Indeed, the synthesis in the second step takes place in the presence of precursors, namely a catalytic source and a carbon source. The catalytic source can be pre-deposited onto the support or, conversely, co-injected with the carbon source. When the catalytic source is pre-deposited, this pre-deposition is achieved using a physical technique. By way of illustration, this pre-deposition is carried out by injecting the catalytic source under the same conditions, in terms of injection direction and pressure, as those defined for the injection of the carbon source according to the process of the invention.

[0028] The catalytic source is chosen from among transition metal metallocenes such as ferrocene, nickelocene, cobaltocene, or any mixture thereof. The carbon source, possibly containing other atoms such as nitrogen, which can be liquid, solid, or gaseous, is chosen from among hydrocarbons, alcohols, carbon monoxide, carbon halides, toluene, cyclohexane, vegetable oils, benzylamine, acetonitrile, ethylenediamine, dicyanopentane, ethylene, acetylene, xylene, methane, and any mixture thereof. In the case of a solid carbon source such as camphor, it must undergo a sublimation step during the synthesis.In a particular embodiment of this synthesis involving the co-injection of the catalytic source and the carbon source, ferrocene is transported into the reactor using a toluene solution in aerosol form.

[0029] In the second step of the process according to the invention, this synthesis is carried out at a temperature between 500°C and 1100°C. In some embodiments, this temperature is between 800°C and 1000°C. In other embodiments, it can be between 500°C and 750°C.

[0030] First, the process according to the present invention is characterized by the injection direction of the carbon source and the catalytic source (in the case of co-injection). Indeed, the carbon source and the catalytic source (in the case of co-injection) required for the synthesis in the second step is / are injected in a direction substantially perpendicular to the plane of the support. This configuration is defined herein as the "vertical configuration," as opposed to the "horizontal configuration" used in [8]. By "substantially perpendicular", we mean that the direction of injection and the plane of the support form an angle between 60° and 120° and in particular of the order of 90° (i.e. 90° ± 20° or even 90° ± 10°).

[0031] Furthermore, the injection of the carbon source and the catalytic source (in the case of co-injection) is carried out at a pressure between 3.10 4< Pa (300 mbar) and 6.10 4< Pa (600 mbar).

[0032] Thus, the growth rate of carbon nanotubes is relatively high, specifically ranging from 1 µm / min to 30 µm / min, depending on the operating conditions (temperature and pressure) used. It is possible to control the length of the carbon nanotubes by varying the synthesis time of the carbon nanotubes, i.e., the duration of the second step of the process according to the invention.

[0033] The first and second stages of the process according to the invention are carried out in an enclosure, closed and resistant to high temperature and reduced pressure.

[0034] In a first form of implementation of the process according to the invention, the first step and the second step of the process according to the invention are carried out in the same reaction chamber, the latter being present in the enclosure as previously defined.

[0035] In a second embodiment of the process according to the invention, the first and second steps are carried out respectively in a first chamber, referred to as the "pretreatment chamber," and in a second chamber, referred to as the "reaction chamber." These two separate chambers are located within the enclosure as previously defined. The pressure at which the first step is carried out is identical to that used in the second step.

[0036] In this first and second form of implementation, the flow of ceramic precursors is injected in a direction substantially perpendicular to the plane of the support and the first step is carried out at the same pressure as that implemented during the second and at the same temperature as that implemented during the second step.

[0037] The present invention also relates to the support containing vertically aligned carbon nanotubes obtained by the process according to the invention. These carbon nanotubes exhibit good anchoring and adhesion to the support, i.e., to the carbon fibers or the cell walls of the carbon foam, which promotes good electrical charge and heat transfer between the nanotubes and the carbon fibers or carbon foam.

[0038] The latter is clearly distinct from the material obtained following the process that is the subject of international application WO 2009 / 103925 [8].Indeed, by injecting the carbon nanotube precursors parallel to the surface of the support (i.e., horizontally), carbon nanotubes primarily grow on the surface fibers of the support. However, short, misaligned carbon nanotubes can also grow on some of the carbon fibers in a subsurface area whose volume does not exceed 10% of the total volume of the support. Conversely, within the framework of the present invention, and as illustrated in the Figure 2C below, carbon nanotubes are present in a subsurface area whose volume represents more than 20%, in particular more than 40%, in particular more than 60% and, more particularly, more than 80% of the total volume of the support in a carbon material.

[0039] Advantageously, for the support obtained by the process according to the invention, the density of the vertically aligned carbon nanotubes can be variable. The density of the carbon nanotubes on the surface of the support is advantageously between 10⁶ and 10¹³ nanotubes.cm⁻². It is thus possible to obtain a material exhibiting dense mats of vertically aligned carbon nanotubes, with densities on the order of 10⁸ to 10¹² nanotubes.cm⁻², and in particular on the order of 10¹⁰ to 10¹² nanotubes.cm⁻². Furthermore, the support also exhibits vertically aligned carbon nanotubes throughout its volume.

[0040] For the support obtained by the process according to the invention, the carbon nanotubes advantageously have an average length greater than 10 µm. In certain embodiments, this average length can be greater than 20 µm, particularly greater than 30 µm, especially greater than 50 µm, and more particularly greater than 100 µm. The highest value mentioned is advantageously obtained for the vertically aligned carbon nanotubes present on the surface of the support, the length of the vertically aligned carbon nanotubes present within the volume of the support being shorter due to diffusion and precursor availability issues. Furthermore, some of the vertically aligned carbon nanotubes present on the surface of the porous carbon support material can have a length on the order of 150 µm (150 µm ± 30 µm).

[0041] The properties of the support containing vertically aligned carbon nanotubes obtained by the process according to the invention make it a good candidate for preparing an electrode and also as a catalyst support. The present invention therefore relates to the use of this support as a catalyst support. This use has applications, in particular, for the subsequent synthesis of carbon nanotubes or silica nanotubes, or for the production of hydrogen. In this case, the supported catalysts can be based on molybdenum, nickel, cobalt, iron, or molecular complexes such as cobalt dioxime derivatives.

[0042] The support according to the present invention is particularly useful for preparing an electrode. Thus, the present invention also relates to a method for preparing an electrode comprising a support made of a porous carbonaceous material, vertically aligned carbon nanotubes, and an electrically conductive polymer matrix, said method comprising the following successive steps: a) equipping a support made of a porous carbon material with vertically aligned mats of carbon nanotubes according to the process previously described; b) electrochemically depositing said polymer matrix onto said carbon nanotubes from an electrolytic solution comprising at least one precursor monomer of said matrix.

[0043] Following the synthesis of vertically aligned carbon nanotubes (i.e., after step (a) and prior to step (b), the vertically aligned carbon nanotubes can be subjected to an oxidative treatment (or pretreatment) aimed at oxidizing the surface of the nanotubes and / or preparing the surface for future oxidation by radical formation. Oxidation modifies the surface of the nanotubes, notably by attaching and / or introducing oxygen-rich groups such as carboxylic (-COOH, i.e., -C(=O)OH), hydroxyl (-OH), alkoxyl (-OX, where X represents an alkyl, acyl, or aroyl group), carbonyl (-C(=O)-), percarbonic (-C(=O)-O-OH), and sometimes amide (-CONH) groups to the ends or defects of the nanotubes.

[0044] Such an oxidative treatment relies on two main types of surface modifications based on: physical treatments such as plasma treatment, particularly oxygen treatment, UV treatment, X-ray or γ treatment, electron and heavy ion irradiation treatment or chemical treatments such as alcoholic potash treatment, treatment with a strong acid (HCl, H2SO4, HNO3, HClO4), treatment with soda, treatment with a strong oxidant (KMnO4, K2Cr2O7, KClO3 or CrO3 in hydrochloric acid, sulfuric acid or nitric acid), ozone treatment and thermal treatment under an oxygenated atmosphere (O2, H2O,...).

[0045] Such nanotubes, once this oxidative treatment has been implemented, can take the form of surface-modified nanotubes such as, for example, negatively charged nanotubes.

[0046] Step (b) of the process according to the present invention consists of applying, electrochemically, to the mats of carbon nanotubes synthesized in step (a) on the surface and in the volume of the support in a porous carbon material, an electrically conductive polymer matrix.

[0047] In the context of the present invention, the term "electrically conductive polymer matrix" refers to a structure in the form of a porous or non-porous film on the surface of the carbon nanotubes used in the process of the invention, and essentially composed of one or more electrically conductive (co)polymer(s). In the carbon nanotube mat obtained following step (a) of the process, the matrix is ​​associated with the carbon nanotubes by being deposited along the entire length of the VACNTs, that is, on and at the level of the lateral surface of the carbon nanotubes, advantageously forming a sheath around the nanotubes, as well as in the space between the nanotubes. Advantageously, the thickness of this sheath is homogeneous for a carbon nanotube and, more advantageously, it is homogeneous for all the carbon nanotubes on the surface and throughout the volume of the support made of a porous carbon material.

[0048] For the purposes of this invention, "electrically conductive (co)polymer" means a (co)polymer whose main polymer chain and optionally its side chains have at least one double bond or at least one aromatic ring. Typically, an electrically conductive (co)polymer is obtained by polymerizing one (or more) monomer(s) bearing a double bond and / or an aromatic ring and optionally a heteroatom such as an oxygen atom, a nitrogen atom, a sulfur atom, or a fluorine atom.

[0049] The polymer matrix implemented within the framework of the present invention advantageously consists of one (or more) (co)polymer(s) selected from polyfluorenes, polypyrenes, polyazulenes, polynaphthalenes, polypyrroles, polycarbazoles, polyindoles, polyazepines, polyanilines, polythiophenes, polyphenylene sulfide, or ABA-type polymers composed of an aromatic B unit such as benzene, thiophene, pyrrole, carbazole, fluorene, optionally functionalized by conjugated alkyl, alkoxy, oligoether, thioether, or alkene or alkyne chains, and electropolymerizable A units of the type thiophene, alkylthiophene, 3,4-alkylenedioxythiophene and their derivatives, or pyrrole, alkylpyrrole, N-alkylpyrrole, 3,4-alkylenedioxypyrrole and their derivatives.

[0050] Advantageously, the polymer matrix implemented within the framework of the present invention consists of one (or more) (co)polymer(s) selected from polypyrroles, polycarbazoles, polyanilines and polythiophenes.

[0051] A person skilled in the art knows various precursor monomers that can be used to obtain, by polymerization, the polymers listed above.

[0052] As examples, polypyrroles can be obtained by polymerization of one (or more) monomer(s) chosen from pyrrole and pyrrole derivatives. A pyrrole derivative is advantageously a pyrrole substituted by at least one substituent chosen from a linear, branched, or cyclic (hetero)alkyl group in C1 to C10, and in particular in C1 to C5, possibly substituted; a halogen atom; an -OH group; a -COOH group; an alkoxyalkyl group in C2 to C20, and in particular in C2 to C10, possibly substituted; an alkoxyl polyether; an alkylene polyether; a (hetero)aryl group in C3 to C20, and in particular in C4 to C16, possibly substituted; or a (hetero)aralkyl group in C3 to C20, and in particular in C4 to C16, possibly substituted. Such a pyrrole derivative is notably an alkylpyrrole, an N-alkylpyrrole or a 3,4-alkylenedioxypyrrole.A pyrrole derivative can also be a pyrrole substituted by at least two substituents forming a bridging group at C1 to C10 and particularly at C1 to C5, possibly including a heteroatom. Examples of usable pyrrole derivatives include 3-methylpyrrole, 3-ethylpyrrole, 3-butylpyrrole, 3-bromopyrrole, 3-methoxypyrrole, 3,4-dichloropyrrole, and 3,4-dipropoxypyrrole.

[0053] By "possibly substituted", in the context of the present invention, means a group that can be substituted by -OH, -COOH, a halogen atom or an alkyl in C1 to C4.

[0054] As examples, polycarbazoles can be obtained by polymerization of one (or more) monomer(s) chosen from carbazole and carbazole derivatives. A carbazole derivative is advantageously a carbazole substituted by at least one substituent chosen from a linear, branched, or cyclic (hetero)alkyl group in C1 to C10, and in particular in C1 to C5, possibly substituted; a halogen atom; an -OH group; a -COOH group; an alkoxyalkyl group in C2 to C20, and in particular in C2 to C10, possibly substituted; an alkoxyl polyether; an alkylene polyether; a (hetero)aryl group in C3 to C20, and in particular in C4 to C16, possibly substituted; or a (hetero)aralkyl group in C3 to C20, and in particular in C4 to C16, possibly substituted. A derivative of a carbazole can also be a carbazole substituted by at least two substituents forming a bridging group at C1 to C10 and in particular at C1 to C5 possibly including a heteroatom.

[0055] As examples, polyanilines can be obtained by polymerization of one (or more) monomer(s) chosen from aniline and aniline derivatives. An aniline derivative is advantageously an aniline substituted by at least one substituent chosen from a linear, branched or cyclic (hetero)alkyl group in C1 to C10 and especially in C1 to C5, possibly substituted; a halogen atom; an -OH group; a -COOH group; an alkoxyalkyl group in C2 to C20 and especially in C2 to C10, possibly substituted; an alkoxyl polyether; an alkylene polyether; a (hetero)aryl group in C3 to C20 and especially in C4 to C16, possibly substituted; or a (hetero)aralkyl group in C3 to C20 and especially in C4 to C16, possibly substituted. An aniline derivative can also be an aniline substituted by at least two substituents forming a bridging group at C1 to C10 and especially at C1 to C5 possibly including a heteroatom.

[0056] As examples, polythiophenes can be obtained by polymerization of one (or more) monomer(s) chosen from thiophene and thiophene derivatives. A thiophene derivative is advantageously a thiophene substituted by at least one substituent chosen from a linear, branched or cyclic (hetero)alkyl group in C1 to C10 and especially in C1 to C5, possibly substituted; a halogen atom; an -OH group; a -COOH group; an alkoxyalkyl group in C2 to C20 and especially in C2 to C10, possibly substituted; an alkoxyl polyether; an alkylene polyether; a (hetero)aryl group in C3 to C20 and especially in C4 to C16, possibly substituted; or a (hetero)aralkyl group in C3 to C20 and especially in C4 to C16, possibly substituted. Among the thiophenes substituted by at least one (hetero)aryl at C3 to C20, we can mention the thiophenes substituted by at least one perfluorinated aryl at C3 to C20.A thiophene derivative can also be a thiophene substituted by at least two substituents forming a bridging group at C1 to C10 and particularly at C1 to C5, possibly including a heteroatom. Examples of usable thiophene derivatives include 3-acetic acid thiophene, 3,4-ethylenedioxythiophene, 3-methylthiophene (3MT), 3,4-dimethylthiophene, 3-ethylthiophene, 3-butylthiophene, 3-bromothiophene, 3-methoxythiophene, 3,4-dimethoxythiophene, 3,4-dichlorothiophene, 3,4-dipropoxythiophene, and 3-perfluorophenylthiophene.

[0057] Advantageously, step (b) of the process according to the invention comprises the following substeps: b 1 ) bring the support made of porous carbon material having vertically aligned carbon nanotubes into contact with an electrolytic solution containing the precursor monomer(s) of said conductive polymer matrix; b 2 ) polarize said carbon nanotubes by which said conductive polymer matrix is ​​electrochemically deposited on said carbon nanotubes.

[0058] The electrolytic solution used in the process according to the invention comprises one or more different monomers, precursor(s) of the electrically conductive polymer matrix in a solvent. The latter may be a protic solvent, an aprotic solvent, an ionic liquid, or a mixture thereof.

[0059] By "mixture" we mean a mixture of at least two different protic solvents, a mixture of at least two different aprotic solvents, a mixture of at least two different ionic liquids, a mixture of at least one protic solvent and at least one aprotic solvent, a mixture of at least one protic solvent and at least one ionic liquid, or a mixture of at least one aprotic solvent and at least one ionic liquid.

[0060] For the purposes of this invention, "protic solvent" means a solvent which comprises at least one hydrogen atom capable of being released as a proton and advantageously selected from the group consisting of water, deionized water, distilled water, acidified or basic water, acetic acid, hydroxylated solvents such as methanol and ethanol, low molecular weight liquid glycols such as ethylene glycol, and mixtures thereof.

[0061] For the purposes of this invention, "aprotatory solvent" means a solvent which is not capable of releasing or accepting a proton under non-extreme conditions and advantageously selected from halogenated alkanes such as dichloromethane; dimethylformamide (DMF); ketones such as acetone or 2-butanone; acetonitrile; propylene carbonate, gamma-butyrolactone (GBL), tetrahydrofuran (THF); N-methylpyrrolidone (NMP); dimethyl sulfoxide (DMSO) and mixtures thereof.

[0062] When the solvent used is a protic solvent, an aprotic solvent, or a mixture thereof, the electrolytic solution usable within the scope of the present invention comprises, in addition to this solvent, an electrolyte in the form of a salt dissolved in the solvent. The anion of this salt may be selected from inorganic anions such as Br⁻, Cl⁻, HCO₃⁻, H₂PO₄⁻, Cr₂O₄³⁻, BF₄²⁻, or PF₆²⁻; organic anions; polymeric anions; and biological anions. The cation of this salt is a metallic cation such as Li⁺, Na⁺, Mg²⁺, Cu²⁺, Zn²⁺, and Al³⁺.

[0063] Other examples of solvents and electrolytes usable within the scope of the present invention are given in paragraphs

[0040] to

[0048] of US patent application 2003 / 077515

[13] .

[0064] In the context of the present invention, an "ionic liquid" is an organic salt in a liquid state at a temperature below 100°C and in particular in a liquid state at room temperature (i.e. 22°C ± 5°C).

[0065] Among these ionic liquids, we can mention ionic liquids having at least one protic or aprotic cation, substituted or unsubstituted, chosen from the pyridinium family: pyridazinium, pyrimidinium, pyrazinium, imidazolium, pyrazolium, thiazolium, oxazolium, triazolium, ammonium, pyrrolidinium, pyrrolinium, pyrrolium, piperidinium, and at least one anion, organic or unsubstituted or unsubstituted, chosen from: F-<; Cl-<; Br-<; I-<; NO3-<; N(CN)2-<; BF4-<; ClO4-<; PF6-<; RSO4-<; RSO3-<; RCOO-< where R is an alkyl or phenyl group; (CF3)2PF4-<; (CF3)3PF3-<; (CF 3 ) 4 PF 3 -< ; (CF 3) 5 PF -< ; (CF 3) 6 P -<; (CF 2 SO 3 -<) 2; (CF 2 CF 2 SO 3 -< ) 2; (CF 3 SO 2 ) 2 N -< ; CF 3 CF 2 (CF 3 ) 2 CO -< ; (CF 3 SO 2 ) 2 CH -< ; (SF 5) 3 C -<; (CF 3 SO 2 ) 3 C; [O(CF 3 ) 2 C 2 (CF 3 ) 2 O] 2 PO -< ; CF 3 (CF 2 ) 7 SO 3 -< ; CNSe -< ; CNS -< ; bis(oxalato)borate and an anion derived from imidazole.

[0066] Other examples of cations that can be used for the ionic liquid implemented in the present invention are described in international application WO 2012 / 004317

[14] (page 24, lines 1 to 22). Similarly, other ionic liquids usable within the scope of the present invention are described in international application WO 2008 / 016990

[15] (page 18, lines 5 to 23).

[0067] Advantageously, the ionic liquid used in the context of the present invention is selected from the group consisting of a dialkylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([DAPyr][TFSI]), a dialkylpyrrolidinium bis(fluoromethylsulfonyl)imide ([DAPyr][FSI]), a dialkylpyrrolidinium tetrafluoroborate ([DAPyr][BF4]), a dialkylpyrrolidinium hexafluorophosphate ([DAPyr][PF6]), a dialkylpyrrolidinium selenocyanate ([DAPyr][SeCN]), a dialkylpyrrolidinium thiocyanate ([DAPyr][SCN]), a dialkylpyrrolidinium bromide ([DAPyr][Br]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide ([EMI][FSI]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI][BF4]), 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMI][PF6]), 1-ethyl-3-methylimidazolium selenocyanate ([EMI][SeCN]), 1-ethyl-3-methylimidazolium thiocyanate ([EMI][SCN]),1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMI][TFSI]), 1-Butyl-3-methylimidazolium tetrafluoroborate ([BMI][BF4]), 1-Butyl-3-methylimidazolium hexafluorophosphate ([BMI][PF6]), 1-Methyl-3-n-hexylimidazolium iodide ([MHIm][I]) and butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([BtMA][TFSI]).

[0068] In a particular embodiment, the solvent of the electrolytic solution implemented in the process according to the invention is a mixture of at least one ionic liquid as previously defined and at least one protic solvent as previously defined.

[0069] In another particular embodiment, the solvent of the electrolytic solution used in the process according to the invention is a mixture of at least one ionic liquid as previously defined and at least one aprotic solvent as previously defined. In particular, in this embodiment, the aprotic solvent is acetonitrile, and the ionic liquid may be any one of the ionic liquids previously considered.

[0070] The proportions of ionic liquid and protic or aprotic solvent in the electrolytic solution implemented in the present invention vary according to the viscosity of the ionic liquid in order to maintain a low overall viscosity for this solution, ensuring good diffusion of the species within the liquid medium filling the inter-tube spaces. These proportions can range from 15 to 85% by volume for the protic or aprotic solvent and the remainder to 100% for the ionic liquid. Thus, the mixture can comprise between 60 and 85% by volume of protic or aprotic solvent and between 15 and 40% by volume of ionic liquid, and in particular approximately 75% (i.e., 75% ± 5%) by volume of protic or aprotic solvent and approximately 25% (i.e., 25% ± 5%) by volume of ionic liquid. A particular example of such a mixture is a mixture of about 75% by volume of acetonitrile and about 25% of [EMI][TFSI] or [EMI][BF4].Alternatively, the mixture may contain between 40 and 60% by volume of protic or aprotic solvent and between 40 and 60% by volume of ionic liquid, and in particular about 50% (i.e., 50% ± 5%) by volume of protic or aprotic solvent and about 50% (i.e., 50% ± 5%) by volume of ionic liquid. A specific example of such a mixture is a mixture of about 50% by volume of acetonitrile and about 50% of [EMI][TFSI] or [EMI][BF4].

[0071] The precursor monomer(s) of the conductive polymer matrix is / are present in the electrolytic solution in a maximum quantity determined by its solubility in the solvent used. Typically, the precursor monomer(s) of the conductive polymer matrix is / are present in an amount between 2% and 20% by volume relative to the total volume of said electrolytic solution.

[0072] Furthermore, the electrolytic solution must have a suitable viscosity to allow homogeneous penetration between the carbon nanotubes (inter-tube spacing ranging from a few nanometers to hundreds of nanometers), ideally throughout the entire thickness of the mats present on the surface and within the volume of the porous carbon substrate. In the case of an electrolytic solution whose solvent contains at least one ionic liquid, its viscosity depends strongly on the nature and proportion of the ionic liquid it contains. Typically, this viscosity ranges from 0.37 mPa·s to 200 mPa·s, and advantageously from 1.0 mPa·s to 36 mPa·s under standard temperature and pressure conditions.

[0073] The electrochemical deposition of the electrically conductive polymer matrix onto the carbon nanotubes during step (b) or substep (b2) of the process according to the invention can involve either a cyclic method or a static method, pulsed or non-pulsed, with either voltage or current being applied. In a particular embodiment, it is possible to perform this electrochemical deposition by combining these different methods. In other words, the electrochemical deposition process can be carried out by a cyclic method and / or a pulsed or continuous galvanostatic method and / or a pulsed or continuous potentiostatic method. The deposition process consists of oxidizing a precursor monomer present in the electrolyte to polymerize it and ensure its deposition as an electrically conductive polymer around and on the carbon nanotubes.

[0074] The electrochemical deposition in step (b) or substep (b2) of the process according to the invention is typically carried out in an electrochemical cell equipped with two electrodes (working electrode and counter electrode) or three electrodes (working electrode, counter electrode, and reference electrode). The working electrode (or anode) is the porous carbon support containing the carbon nanotubes, while the counter electrode (or cathode) is, for example, a platinum grid or a platinized titanium plate or a paste of carbon black and activated carbon encapsulated in a stainless steel grid or a paste of carbon black, activated carbon, and Teflon encapsulated in a stainless steel grid for electrical contact. The counter electrode has a surface area and capacitance adapted to the surface area and capacitance of the working electrode.When present, the reference electrode which allows the potential value of the working electrode to be known at any time is typically a pseudo-reference type electrode made of metal such as, for example, a silver wire or a platinum wire.

[0075] The electrochemical device implemented in the invention comprises an electrochemical cell as previously defined associated with a current or voltage generator.

[0076] The cyclic electrochemical deposition method, or cyclic voltammetry, consists of varying the potential of the working electrode at a given scan rate. The applied voltage range is chosen according to the desired potential range for the working electrode. Advantageously, during step (b) or substep (b2) of the process according to the invention, the voltage can vary from -3 to +3 V and, in particular, from -2 to +2 V, depending on the monomer and electrolyte chosen. The current varies according to the sample size and the scan rate such that the current density is on the order of 10 mA.cm⁻². The scan rate is notably between 2 and 500 mV / s, in particular, between 3 and 100 mV / s, and more particularly, between 5 and 30 mV / s. The number of cycles is notably between 15 and 200 and, in particular, between 20 and 150.As an illustrative example of conditions used during cyclic voltammetry for the monomer 3-methylthiophene (3MT) at a concentration of 0.4 M in an equivolume mixture of acetonitrile and [EMI][TFSI], we can cite: . an imposed voltage between -0.5 and 1.6 V at a sweep rate of 20 mV / s for 24 cycles; an imposed voltage between -0.5 and 1.35 V at a sweep rate of 20 mV / s for 10 cycles then an imposed voltage between -0.5 and 1.25 V at a sweep rate of 20 mV / s for 26 cycles.

[0077] The pulsed potentiostatic or pulsed galvanostatic method consists of alternating periods of deposition of the electroconductive polymer (t ON) and periods of rest (t OFF) by applying a voltage or a current, respectively, between the cathode and the anode. In the process according to the invention, the deposition time corresponds to the oxidation of the precursor monomer. This oxidation is achieved by applying either a current for a given time (t ON) (chronopotentiometry) or a voltage for a given time (t ON) (chronoamperometry). During t OFF, the monomer is not oxidized, allowing it time to diffuse within the carbon nanotube mat. This rest period t OFF can be achieved by opening the electrical circuit or by applying a current or voltage lower than that applied during the deposition time t ON, thus preventing oxidation of the monomer.During this rest time t OFF, agitation of the electrolytic solution can be implemented to facilitate the diffusion of the monomer within the mat of vertically aligned carbon nanotubes.

[0078] Determining the most suitable t ON and t OFF times depending on the electroconductive polymer to be deposited is a routine task for a person skilled in the art.

[0079] In pulsed or non-pulsed chronopotentiometry, the current applied during the deposition time tON corresponds to a specific value that is adjusted to obtain a voltage sufficient to oxidize the precursor monomer. This specific value depends on the type of precursor monomer(s) used and the viscosity of the electrolytic solution. For example, in the case of the 3MT monomer, for a support surface made of porous carbonaceous material containing carbon nanotubes on the order of 1 cm2, and for an electrolytic solution whose solvent is composed of acetonitrile (75% or 50% by volume) and EMITFSI (25% or 50% by volume), the specific current value is approximately 4 mA.

[0080] In pulsed or non-pulsed chronoamperometry, the voltage applied during the deposition time tON corresponds to a specific value that is adjusted to obtain a current sufficient to oxidize the precursor monomer. This specific value depends on the type of precursor monomer(s) used and the viscosity of the electrolytic solution. For example, in the case of the 3MT monomer, for a support surface made of porous carbonaceous material containing carbon nanotubes on the order of 1 cm2 and for an electrolytic solution whose solvent is composed of acetonitrile (75% or 50% by volume) and EMITFSI (25% or 50% by volume), the specific voltage value is approximately 1.5 V (i.e., 1.5 V ± 0.2 V).

[0081] When the technique used in step (b) or substep (b2) of the process according to the invention is a pulsed technique, the number of pulses is defined by the mass quantity of polymer to be deposited. Typically, the number of pulses varies from 5 to 1000.

[0082] The duration of step (b) or substep (b2) of the process according to the invention, implementing either a cyclic voltammetry method or a pulsed or non-pulsed potentiostatic or galvanostatic method, varies from a few minutes to several hours. Typically, this duration is between 5 minutes and 8 hours, advantageously between 10 minutes and 4 hours, and, in particular, between 15 minutes and 2 hours. It depends on the amount of polymer to be deposited to obtain a homogeneous deposit around the vertically aligned carbon nanotubes. Those skilled in the art will be able to adapt this duration, without inventive effort, according to the density and length of the vertically aligned carbon nanotubes and the amount of polymer matrix to be deposited.

[0083] Finally, it is possible to combine pulsed potentiostatic or pulsed galvanostatic methods. For example, it is possible to first set the voltage (chronoamperometry) to oxidize the electroconductive polymer already deposited during previous cycles, then set the current (chronopotentiometry) to oxidize the monomer, and then leave the electrical circuit open to allow the monomer to diffuse within the vertically aligned carbon nanotubes.

[0084] Step (b), and in particular substep (b2), of the process according to the invention are carried out at a temperature between 15°C and 100°C, and advantageously at ambient temperature (i.e., 22°C ± 5°C). The temperature may be adjusted according to the desired viscosity of the electrolytic solution.

[0085] Furthermore, step (b), and in particular substep (b2), of the process according to the invention can be carried out under an uncontrolled atmosphere, i.e., in ambient air. Alternatively, they can be carried out in an atmosphere with the least possible oxygen and water content. To this end, this step and substep can be carried out in an inert atmosphere. For this purpose, an inert gas such as argon or nitrogen can be used to generate this inert atmosphere. The use of an inert atmosphere combined with bubbling an inert gas in the electrolytic solution makes it possible to remove any oxygen that may be present in the latter.

[0086] It should be noted that the electrochemical deposition during step (b) and in particular substep (b 2) of the process according to the invention can be industrialized, for example by a batch to batch or continuous process technique (the so-called "roll to roll" technique) with the support being a porous carbonaceous material bathed in an electrolytic solution as previously defined.

[0087] The duration of step (b), and in particular substep (b2) of the process according to the invention, allows the mass percentage of the electrically conductive polymer matrix relative to the total mass of the composite consisting of vertically aligned carbon nanotubes coated with this electrically conductive polymer matrix to be adjusted in order to maximize the capacitance of the composite once manufactured, thereby providing a supercapacitor using such a composite as an electrode, which exhibits the highest possible capacitance. The electrically conductive polymer matrix represents a mass percentage relative to the total mass of said composite of up to 99%, in particular between 5 and 95%, and especially between 10 and 80%.The mass of the electrically conductive polymer matrix and that of the composite can be obtained by TGA for "Thermo Gravimetric Analysis" and / or by weighing and / or by integrating the current that has passed through the electrical circuit during the polymerization step.

[0088] Following step (b) and in particular following substep (b 2), the process according to the invention may include a rinsing step and optionally a drying step.

[0089] The main purpose of the rinsing step is to clean and remove any residues / impurities, such as monomers or oligomers, that may remain on parts of the support, carbon nanotubes, or polymer matrix and that have not been deposited. Such residues / impurities could cause problems during the encapsulation step and lead to malfunctions of the supercapacitor. Advantageously, the rinsing step is carried out by soaking the support, which consists of a porous carbon material containing carbon nanotubes and an electrically conductive polymer matrix, in an organic solvent such as acetonitrile, acetone, ethanol, or isopropanol. Those skilled in the art will be able to determine the most suitable organic solvent for the rinsing step, ensuring that it does not detach the polymer matrix.The rinsing process involves soaking the support, made of a porous carbon material with carbon nanotubes and an electrically conductive polymer matrix, in the solvent for a variable time of 2 to 30 minutes, and repeating the operation if necessary up to five times, for example.

[0090] Furthermore, the optional step of drying the support made of a porous carbon material, containing carbon nanotubes and an electrically conductive polymer matrix, can be carried out by leaving it, after rinsing, exposed to air to allow the rinsing solvent to evaporate. Alternatively, this drying can be performed under inert gas flow or by heating the support made of a porous carbon material, containing carbon nanotubes and an electrically conductive polymer matrix, under vacuum, inert gas, or with an infrared lamp. This alternative can be implemented in a continuous process.

[0091] The present invention also relates to an electrode that can be prepared by the process according to the invention as previously defined. This electrode has a support made of a porous carbonaceous material, containing vertically aligned carbon nanotubes on its surface and throughout its volume, and an electrically conductive polymer matrix. It is therefore a monolayer electrode.

[0092] Everything previously stated about the support made of a porous carbon material and about the vertically aligned carbon nanotubes also applies to the electrode according to the present invention i.e. comprising this support and these carbon nanotubes.

[0093] The mass percentage of the electrically conductive polymer matrix expressed in relation to the total mass of the composite including the carbon nanotubes and this matrix is ​​between 10% and 90%, in particular between 10% and 80%, in particular, between 40% and 70%.

[0094] Finally, the electrode according to the invention advantageously has a capacitance of at least 200 mF / cm2< and in particular of at least 230 mF / cm2<.

[0095] The present invention also relates to the use of such an electrode, or one that can be prepared by the process of the invention, as a positive / negative electrode in an electricity storage and release device such as a supercapacitor or a battery, as an electrode for a photovoltaic device, in materials for CO2 storage, or as an electrode for electrochemical sensors. Thus, the present invention relates to a device comprising an electrode according to the present invention or one that can be prepared by the process of the invention, said device being selected from the group consisting of an electricity storage and release device such as a supercapacitor or a battery; a photovoltaic device; a material for CO2 storage; and an electrochemical sensor.

[0096] In one particular embodiment, an electricity storage and release device according to the invention comprises at least two single-layer electrodes (positive and negative) or at least three electrodes, including two single-layer (positive) electrodes and one double-layer (negative) electrode. As a reminder, a single-layer electrode has only one active surface, while a double-layer electrode has two active surfaces, one on each of its two opposite faces.

[0097] Other features and advantages of the present invention will become apparent to those skilled in the art upon reading the following examples given by way of illustration and not limitation, with reference to the attached figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] THE Figures 1A and 1Bshow scanning electron microscopy (SEM) images taken at different magnifications of a VACNT growth on carbon fiber fabric obtained by the CVD synthesis process in a horizontal configuration (comparative example). Figure 2 presents SEM micrographs showing: the growth of VACNT preferentially on surface fibers of the tissue ( Figures 2A and 2B ) and the growth of VACNTs on surface fibers but also on those located within the tissue thickness ( Figure 2C ). There Figure 3 presents the cyclic voltammetry curves obtained for the unannealed carbon fiber fabric during the polymerization of P3MT. Figure 4 presents the cyclic voltammetry curves obtained during the polymerization of P3MT for the carbon fiber fabric essentially surface-coated with VACNT. Figure 5presents the cyclic voltammetry curves obtained during the polymerization of P3MT for the carbon fiber fabric coated on the surface and throughout its volume with VACNT. Figure 6 presents the cyclic voltammetry curves for a raw, unannealed fiber fabric (1), a carbon fiber fabric essentially surface-bound with VACNT (2), and a carbon fiber fabric with VACNT both surface-bound and bulk-bound (3). Figure 7 presents the cyclic voltammetry curves for a raw unannealed fiber fabric, coated with P3MT (1'), a carbon fiber fabric essentially surface-covered with VACNT, coated with P3MT (2') and a carbon fiber fabric surface- and volume-covered with VACNT, coated with P3MT (3'). DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION I. Summary of VACNTs. I.1. On the surface of a carbon fiber fabric (comparative example). Preliminary note

[0099] In order to synthesize VACNTs only on the surface of a carbon fiber fabric, the technique used is the so-called "horizontal configuration" technique described in international application WO 2009 / 050247 [8] and implementing the device shown schematically in Figure 15 of this same application. Protocol

[0100] In both horizontal and vertical configurations (see section 1.2 below), the synthesis of VACNTs on a carbon fiber fabric involves 2 steps taking place in the same reactor: Deposition of a SiOx sublayer acting as a diffusion barrier for the metallic catalyst necessary for VACNT growth. The Si-based organometallic precursor used is tetraethyl orthosilicate (TEOS). This deposition takes place at relatively low pressure and moderate temperature; VACNT growth from a precursor mixture comprising a catalytic source and a carbon source, which in this example are the organometallic precursor ferrocene and the liquid hydrocarbon toluene. This growth is carried out at atmospheric pressure.

[0101] The synthesis conditions are summarized in Table 1 below. Table 1: VACNT synthesis parameters on carbon fiber fabrics (horizontal injection configuration) Anhydrous Toluene Injection / TEOS Toluene / Ferrocene Injection Synthesis temperature (°C) 500 850 Argon flow rate (L / min) 5 3 Pressure (mbar) 100 1000 Average mass of injected liquid (g / min) 0,1 1,06 Concentration in the precursor mixture 1 mol / L of TEOS 2.5 wt% of Ferrocene Injection duration(s) 360 450 Result

[0102] There Figure 1AThis image presents a photograph of the carbon fiber fabric obtained following the synthesis process described above and shows mats of carbon nanotubes (CNTs) aligned across the entire surface of the fabric. Figure 1B offers a higher magnification image of the edge of a carpet of NTC deposited on fiber showing the presence of aligned NTCs. I.2. On the surface and within the volume of a carbon fiber fabric. System implemented

[0103] In order to synthesize VACNTs on the surface and in the volume of a carbon fiber fabric, the technique used is the so-called "vertical configuration" technique.

[0104] This summary may use the devices illustrated in Figures 1 to 3 of the international application WO 2015 / 071408 [9]. It can also be achieved by implementing a device modified from the device shown schematically in Figure 15 of international application WO 2009 / 050247 [8].

[0105] The modified device adapted for synthesis in a vertical configuration is composed, like the device shown schematically in Figure 15 of international application WO 2009 / 050247 [8] (the references below correspond to the references used in this Figure), in three parts: 1) An injection system comprising at least one fluidly connected reservoir to at least one injector, and typically two reservoirs R1 and R2 fluidly connected to two injectors IN1 and IN2, for injecting liquid precursor solutions into the evaporator EV as fine droplets, the latter vaporizing the previously formed fine droplets; 2) A reactor (or reaction chamber) CR containing a support made of porous carbonaceous material, typically arranged and held on a substrate holder such as a stainless steel substrate holder, and in which the carrier gas stream carries the reactive precursor vapor. This reactor is placed in a tubular or square-section FO furnace; and 3) A cooling and SO trapping system for treating the furnace outlet gases before extraction.

[0106] However, the modified device adapted for synthesis in a vertical configuration differs from the device shown schematically in Figure 15 of international application WO 2009 / 050247 [8] by the following two elements: The EV evaporator is fluidly connected at the level of the upper part of the CR reactor and no longer at the level of the upstream part (i.e. the inlet) of the reactor, whereby the injection of the fine droplets is done in an essentially perpendicular direction (i.e. 90° ± 30°), advantageously perpendicular to the plane of the support; the pressure in the reactor at which the second step of the process, i.e. the deposition of the VACNTs, is carried out is less than 800 mbar and no longer at atmospheric pressure. Protocol

[0107] As previously explained, the vertical synthesis of VACNTs involves the same two steps taking place in the same reactor as those defined for horizontal synthesis. The conditions for this synthesis are summarized in Table 2 below. Table 2: VACNT synthesis parameters on carbon fiber fabrics (vertical injection configuration) Anhydrous Toluene Injection / TEOS Toluene / Ferrocene injection (5%) Synthesis temperature (°C) 850 850 Argon flow rate (L / min) 5 3 Pressure (mbar) 400 400 Mass of liquid injected (g / h) 40 70 Concentration in the precursor mixture 1 mol / L of TEOS 5 wt% of Ferrocene Injection duration(s) 1200 1500 Result

[0108] THE Figures 2A, 2B and 2C present SEM images of carbon fiber tissues coated with nanotubes and obtained in a vertical configuration ( Figure 2C ), a comparison with samples obtained in horizontal configuration ( Figures 2A and 2BThis is also present in these images. Thus, it clearly appears that growth in the horizontal configuration leads to the formation of VACNTs preferentially on fibers present on the surface of the tissue, whereas in the vertical configuration, and in conjunction with a reduction of the working pressure in the reactor, the aligned nanotubes form both on the surface fibers of the tissue and on the fibers within the tissue thickness. Therefore, the process in its vertical configuration, and by applying a working pressure lower than atmospheric pressure, allows for the growth of VACNTs within the volume of the fibrous preform. II. Electrodeposition of P3MT and evaluation of the capacitance of the electrodes produced.

[0109] The following four examples aim to demonstrate the advantages of having nanotube mats on the surface and within the bulk of carbon fiber fabrics. In other words, they highlight the benefits of nanostructuring on the surface and within the bulk of carbon fiber fabrics for the deposition of the conductive polymer and the capacitance developed by the resulting electrodes.

[0110] For this reason, all tests were carried out at a constant charge quantity, namely 2 C, in order to be able to compare the different configurations in terms of capacitance values ​​obtained. II.1. Electrodeposition of P3MT on raw carbon fiber fabric and evaluation of capacitance (comparative example).

[0111] The aim here is to estimate the possibility of depositing conductive polymer on the surface of synthetic raw fiber fabrics, i.e. fibers covered with an organic sizing layer, necessary for the handling of carbon fiber fabrics and well known in the aeronautical field.

[0112] The sample of raw carbon fibers underwent cyclic voltammetry electrodeposition (-0.5 V to 1.6 V at 20 mV·s⁻¹) in an equivolume mixture of EMITFSI / CH₃CN containing 0.4 M of 3-methylthiophene monomer. To achieve a charge quantity (Qp) of 2 C, 100 polymerization cycles were applied, but it proved difficult to reach the intended charge of 2 C, with the charge quantity plateauing at 1.75 C. Figure 3 This is explained by a pronounced resistive effect of the fabric and by a surface area developed by the fabric which remains limited. II.2. Electrodeposition of P3MT on annealed and SiOx-coated carbon fiber fabric and evaluation of capacitance (comparative example).

[0113] For this test, the carbon fibers were annealed under argon flow at 3 L.min -1 and at 850°C and then coated with SiOx in accordance with the first step of the process according to the invention (see Table 2).

[0114] In this case, it turned out that the deposition of P3MT was impossible due to overly resistive behavior explained by the presence of an insulating SiOx film on the surface of the fibers. II.3. Electrodeposition of P3MT on VACNT distributing essentially on the fibers arranged on the surface of the carbon fiber fabric and evaluation of the capacitance (comparative example).

[0115] In this sample, the VACNTs are primarily distributed on the fiber surface through a horizontal synthesis process. Thus, the fibers within the bulk of the fabric do not contain VACNTs, and their surface is essentially composed of a SiOx layer. Nanostructuring the surface of the carbon fiber fabric therefore allows for a slight increase in the active surface area available for P3MT deposition, but the fibers within the bulk are inactive due to their SiOx-coated surface.

[0116] This sample of VACNT supported on carbon fiber fabric underwent cyclic voltammetry electrodeposition (-0.5 V to 1.6 V at 20 mV.s-1, in an equivolume mixture of EMI-TFSI / CH3CN containing 0.4 M of 3-methylthiophene monomer) of 38 deposition cycles to obtain a charge Qp = 2.14 C ( Figure 4 ). The deposition of P3MT is then possible, but only on the carbon nanotubes present on the surface fibers of the fabric, the SiOx-coated fibers in the volume of the fabric being too resistive to allow the deposition of PCE. II.4. Electrodeposition of P3MT on VACNT distributing both on the surface fibers and in the volume of the carbon fiber fabric and evaluation of the capacitance.

[0117] On this sample, the VACNTs are distributed on the fibers located both on the surface and within the volume of the carbon fiber fabric by implementing the process of the invention. The active surface area developed by the VACNTs is therefore greater than that of the bare or SiOx-coated fibers, and most of the fibers constituting the fabric are coated with VACNTs. This sample of VACNTs supported on carbon fiber fabric underwent cyclic voltammetry electrodeposition (-0.5 V to 1.6 V at 20 mV.s⁻¹, in an equivolume mixture of EMI-TFSI / CH₃CN containing 0.4 M of 3-methylthiophene monomer) of 24 deposition cycles to obtain a charge Qp = 2.05 C ( Figure 5 ). The deposition of P3MT is then possible, and in view of the electrochemical signal, all the carbon nanotubes present on the surface and in the volume of the fibrous tissue appear to have been coated by the P3MT. III. Comparison based on the different configurations of nanotubes supported on carbon fiber fabrics and electrochemical conditions.

[0118] The set of results presented for different configurations of nanotubes supported on carbon fiber fabrics and electrochemical conditions allows us to establish points of comparison in terms of performance and in particular concerning surface capacitance. III.1. Comparison 1: electrodes with only the nanotube mat supported on carbon fiber fabrics (without PCE).

[0119] Since the capacitance of an electrode without P3MT is indirectly proportional to the active surface area of ​​the electrode, comparing the capacitances of electrodes under the same electrochemical conditions is a good comparative indicator of the active surfaces of each type of electrode.

[0120] Thus, for the same geometric surface of the electrode, the electrochemical characterization was carried out by cyclic voltammetry (-0.5 V to 1.6 V at 20 mV.s -1< , in an equivolume mixture of EMI-TFSI / CH 3 CN).

[0121] Table 3 below shows the surface discharge capacitances for each electrode under the same electrochemical conditions, and the Figure 6 reports the voltamograms carried out under the analysis conditions. Table 3 Csd / mF.cm-2 Raw fiber fabric with sizing (uncooked) 22 Fiber fabric / VACNT (surface) 14 Fiber fabric / VACNT (surface and volume) 79

[0122] These results highlight the significant effect of the presence of nanotubes within the bulk of the fibrous preform, which is explained by an increase in the available active surface area. It is also important to note that the capacitance of the fabric containing VACNTs localized only on the surface fibers is lower than that of the raw fabric. This is because the fibers within the bulk are partially coated with a resistive SiOx sublayer, which blocks the electrochemical response of the oxide-coated fiber. III.2. Comparison 2: electrodes composed of VACNT supported on carbon fiber fabrics and covered with P3MT.

[0123] P3MT deposition is carried out for the same amount of polymerization charge (Qp ~ 2 C) and the storage properties of the electrodes are compared to equivalent geometric surface area.

[0124] Table 4 below shows the surface discharge capacitances for each electrode under the same electrochemical conditions and is based on the examples in points II.1, II.3 and II.4 as previously described. Figure 7 reports the voltamograms carried out under the analysis conditions. Table 4 Electrodeposition of P3MT Cyclic Voltammetry -0.5 V to 1.6 V Surface capacitance Qp / C Number of cycles Csd / mF.cm-2 Fabric made from raw, unrefined fibers 1,75 100 145 Fiber fabric / VACNT (surface) 2,14 38 172 Fiber fabric / VACNT (surface and volume) 2,05 24 241

[0125] For a nearly identical amount of polymerization charge (Qp ~ 2C), the electrode developing the largest active area (fibers / VACNTs on the surface and in the volume) shows the highest specific capacitance, and only 24 cycles are required to obtain the amount of charge of 2C. These results clearly highlight the important role of nanotubes located on the surface and in the volume: the nanostructuring of P3MT via the VACNTs present on the fibers both on the surface and in the volume of the tissue makes it possible to significantly improve the performance of the carbon fiber-based electrode.

[0126] Thus, a 40% increase in capacitance is observed in the fabric containing VACNT-coated fibers on the surface and throughout the volume of the fibrous preform, compared to the preform containing only VACNT-coated surface fibers. The increase is even greater (66%) when compared to the raw fabric without nanotubes. REFERENCES BIBLIOGRAPHIQUES

[0127] [1] Ma et al, 2016, « Asymmetric hybrid capacitors based on novel bearded carbon fiber cloth-pinhole polyaniline electrodes with excellent energy density », RSC Adv., vol. 6, pages 82995-83002. [2] Zhao et al, 2016 « Vapor-phase polymerization of poly(3,4-ethylenedioxythiophene) nanofibers on carbon cloth as electrodes for flexible supercapacitors », Nanotechnology, vol. 27. [3] Ye et al, 2017, « Morphology controlled MnO2 electrodeposited on carbon fiber paper for high-performance supercapacitors », J. Power Sources, vol. 351, pages 51-57. [4] Hsu et al, 2017, « High-cell-voltage supercapacitor of carbon nanotube / carbon cloth operating in neutral aqueous solution », J. Materials Science, vol. 22, pages 3383-3387. [5] Hiremath et al, 2017, « Recent developments in carbon fibers and carbon nanotube-based fibers: a review », Polymer Reviews, vol. 57, pages 339-368.[6] Pozegic et al, 2016, « Multi-functionnal carbon fibre composites using carbon nanotubes as an alternative to polymer sizing », Scientific Reports, vol. 6, Article number 37334. [7] Lv et al, 2012, « Vertically aligned carbon nanotubes grown on carbon fabric with high rate capability for super-capacitors », Synthetic Metals, vol. 162, pages 1090-1096. [8] Demande internationale WO 2009 / 103925 au nom du CEA publiée le 27 août 2009. [9] Demande internationale WO 2015 / 07148 au nom du CEA publiée le 21 mai 2015.

[10] Li et Chen, 2017, « Polyaniline / carbon nanotubes-decorated activated carbon fiber felt as high-performance, free-standing and flexible supercapacitor electrodes », J. Mater. Sci., vol. 52, pages 12348-12357.

[11] Yesi et al, 2016, « Directly-grown hierarchical carbon nanotube polypyrrole core-shell hybrid for high-performance flexible supercapacitors », Chem Sus Chem, vol. 6, pages 370-378.

[12] Patent application CN 102354612 in the name of University of Tianjin published on February 15, 2012.

[13] US patent application 2003 / 077515 in the name of Chen et al published on April 24, 2003.

[14] International application WO 2012 / 004317 on behalf of CEA, Université François Rabelais & Université de Cergy Pontoise published on January 12, 2012.

[15] International application WO 2008 / 016990 on behalf of Ada Technologies published on February 7, 2008.

Claims

1. Method for providing a substrate made of a porous carbon material with vertically aligned carbon nanotubes, said method comprising a first step of depositing a ceramic sublayer on said substrate, said ceramic sublayer being either made of an oxide ceramic chosen from the group consisting of silicon oxide (SiOx with 0<x ≤2), aluminum oxide (Al2O3), zirconium oxide (ZrO2) and titanium oxide (TiO2) or made of a non-oxide ceramic chosen from the group consisting of silicon carbide (SiC), silicon carbonitride (SiCN), aluminum nitride (AIN), titanium nitride (TiN), silicon oxynitride (SiON) and silicon oxycarbonitride (SiOCN), followed by a second step of synthesis, by catalytic chemical vapor deposition, of said vertically aligned carbon nanotubes on the support obtained after the first step, said synthesis being carried out in the presence of precursors consisting of a catalytic source chosen from transition metal metallocenes and a carbon source chosen from hydrocarbons, alcohols, carbon monoxide, carbon halides, toluene, cyclohexane, vegetable oils, benzylamine, acetonitrile, ethylenediamine, dicyanopentane, ethylene, acetylene, xylene, methane and any mixtures thereof, characterized in that the precursors of the ceramic sublayer are injected in a direction substantially perpendicular to the plane of the substrate, in that the carbon source required for the synthesis during said second step is injected in a direction substantially perpendicular to the plane of the substrate and at a pressure between 3.104 Pa (300 mbar) and 6.104 Pa (600 mbar), in that said substrate made of a porous carbon material is in the form of a carbon fibre fabric, in that said injection direction and said plane of the substrate form an angle of between 60° and 120° and in that said first step and said second step are carried out at the same pressure and at the same temperature, said temperature being between 500°C and 1100°C.

2. Method according to claim 1, characterized in that said ceramic is an oxide ceramic and in particular SiOx silicon oxide with 0<x≤2.

3. Method according to claim 1 or 2, characterized in that said carbon source is co-injected with the catalytic source necessary for the synthesis during said second step.

4. Method according to claim 3, characterized in that the catalytic source in the form of ferrocene is co-injected with the carbon source in the form of a toluene solution in aerosol form.

5. Method according to any one of claims 1 to 4, characterized in that said first step and said second step are carried out in the same reaction chamber.

6. Method according to any one of claims 1 to 4, characterized in that said first step and said second step are carried out respectively in a first chamber referred to "pretreatment chamber" and in a second chamber referred to "reaction chamber".

7. Support provided with vertically aligned carbon nanotubes obtained by a method as defined in any one of claims 1 to 6.

8. Method for preparing an electrode comprising a substrate made of a porous carbon material, vertically aligned carbon nanotubes and an electrically conductive polymer matrix, said method comprising the following successive steps: a) providing a substrate made of a porous carbon material with mats of vertically aligned carbon nanotubes according to a method as defined in any one of claims 1 to 6; b) electrochemically depositing said polymer matrix on said carbon nanotubes from an electrolytic solution comprising at least one monomer precursor of said matrix.

9. Method according to claim 8, characterized in that, after said step (a) and prior to said step (b), the vertically aligned carbon nanotubes are subjected to an oxidizing treatment or pre-treatment.

10. Method according to claim 8 or 9, characterized in that said electrochemical deposition method is carried out by a cyclic method and / or a pulsed or continuous galvanostatic method and / or a pulsed or continuous potentiostatic method.

11. Method according to any one of claims 8 to 10, characterized in that, after said step (b), the method has a rinsing step and optionally a drying step.

12. Electrode prepared by a method as defined in any one of claims 8 to 11.

13. Use of an electrode according to claim 12 as a positive / negative electrode of a device for storing and returning electricity such as a supercapacitor or a battery, as an electrode for a photovoltaic device, in materials for storing CO2 or as an electrode for electrochemical sensors.