EP2162938A2 - Dispersion of composite materials, in particular for fuel cells - Google Patents

Abstract

The invention relates to the preparation of a catalytic composition that comprises a carbonated structuring material (MSC) associated with a catalyst (CAT). The invention comprises mixing a solution of a first solvent (SOL1) including the carbonated structuring material (MSC) and a solution of a second solvent (SOL2) including the catalyst (CAT), and agitating (AGM) the resulting mixture up to the precipitation if the catalyst on the carbonated structuring material. According to one aspect, the catalyst and the structuring material are not soluble in the mixture of the first and second solvents. The composition thus obtained can be used after filtration as a material for an electrode in a fuel cell.

Description

 Dispersion of composite materials, in particular for fuel cells

Technical area

The present invention relates to the field of fuel cells and more specifically to the active elements of these cells, as well as to their method of preparation. It relates in particular to a process for preparing a composite material comprising a carbonaceous structuring material associated with a catalyst, the materials that can be obtained by this process, as well as their applications in fuel cells.

State of the art

Two types of processes are generally used to prepare composite materials for fuel cells. The distinction between these methods is based on the dispersion mode of the carbon element.

When the carbon element is deposited on a support, various methods make it possible to introduce the catalytic element. The carrier, if conductive, may serve as an electrode and metal nanoparticles may be formed by electrochemically reducing a precursor of the catalyst.

The support provided with the carbon element can also be used for deposition of the catalyst under reduced pressure (known as CVD technique for "Chemical Vapor Deposition") or by vacuum evaporation, or by sputtering.

* Dispersion in liquid medium

When the carbon element is dispersed in a liquid medium, the catalytic element can be introduced in different ways. The more widespread way is to put the nanostructured carbon in dispersed form in a liquid medium in contact with a solution of a precursor of metal nanoparticles. We then performs a chemical treatment (by reduction) to form the catalytic element (technique described in particular in the publication by Carmo et al in J. Power Sources 142: 169-176 (2005)).

Another, more rare method consists in introducing the preformed catalytic element (in the form of nanoparticles) in the same solvent as that in which the carbon element is dispersed. An example of this approach is reported in L., W. Wu et al., Langmuir 20: 6019-6025 (2004). It is proposed to associate gold nanoparticles coated with thiol molecules bearing carboxylic functions with carbon nanotubes. The process involves a treatment of carbon nanotubes in nitric acid to form on their surface carboxylic functions that will allow interaction with the nanoparticles. In the experiments described, carbon nanotubes thus pretreated are dispersed in hexane and the nanoparticles are then dissolved in this same medium. A second example of the implementation of preformed catalytic nanoparticles is described in the publication by Mu et al. J. Phys. Chem. B 109: 22212-22216 (2005). Carbon nanotubes "used as received" are dispersed in toluene and platinum nanoparticles have on the surface triphenylphosphine molecules. The document emphasizes the importance of the solubility of the nanoparticles in the same solvent as that in which the nanotubes are dispersed (toluene). It is also indicated that the aromatic rings of the molecule that coats the nanoparticles play a unique role in the realization of the composite. The document further describes a test on the catalytic activity of composites with respect to the oxidation of methanol. These tests in cyclic voltammetry are preceded by a heat treatment which eliminates the organic coating of the nanoparticles present on the carbon nanotubes and leads to a partial aggregation of the nanoparticles and an increase in their average size. The mass proportions of the carbon nanotubes with respect to the platinum nanoparticles are at least 3.1%. Once the carbon / catalyst element composites have been made, they can be implemented in different ways in order to be tested for from the point of view of their catalytic activity, either by electrochemical tests by cyclic voltammetry, or by fuel cell tests. If the composites were made from ^of carbon elements dispersed in liquid medium, it is possible to typically achieve an ink from the dispersion after addition of an amphiphilic polymer, such as Nafion®, for example.

Some processes use filtration, especially those using carbon nanotubes as the carbon element. The document

WO 2006/099593 describes the production of "carbon nanotubes / catalyst" composites and then their filtration on a nylon filter to form a deposit of the composite in which the nanotubes are at least partially oriented. The deposit on the filter is then hot pressed with a second electrode and a Nafion® membrane. The nylon filter is then removed from the assembly. In these membrane / electrode assemblies, the minimum platinum loading is 0.1 mg platinum per cm ² .

Another example of this type of approach is described in document US-2004/0197638. The composite is produced by impregnation and reduction of a precursor of platinum-based catalysts on the carbon nanotubes, the precursor being dispersed in solution. The assembly is then filtered and assembled with a Nafion® membrane. The minimum platinum density of an electrode thus constituted is 3.4 μg / cm ² .

* Disadvantages of the state of the art

In these combinations, it is necessary to know the quantity of catalyst introduced and to make it as low as possible, with equal stack performance. The lowest platinum density mentioned in the prior art on an electrode seems to be 3.5 μg / cm ² according to US 2004/0197638. In this case, the method used uses a washing step where there is mention of unreacted platinum precursor, and a transfer step of the composite on the membrane of a fuel cell whose efficiency in Platinum can not be maximal. Since platinum is a precious metal whose cost accounts for a large part of the total cost of manufacturing a battery, it is necessary to use it in the smallest possible quantities while maintaining (or improving) the performances. of the pile. Furthermore, the platinum deposition efficiencies on the carbon supports must be as close as possible to 1. This is not the case in the prior art: the yields are not optimal, especially when: the synthesis of the composite , Firstly. and attaching the composite to the battery electrode, on the other hand.

The present invention improves the situation.

Presentation of the invention

The present invention firstly relates to a process for preparing a catalytic composition comprising a carbon structuring material associated with a catalyst.

The process according to the invention comprises the following steps: preparation of a mixture of a solution of a first solvent comprising a carbonaceous structuring material and a solution of a second solvent comprising the catalyst, and stirring of the mixture resulting ^until precipitation of the catalyst on the carbonated structuring material.

In particular, the catalyst and the structuring material are insoluble in the mixture of the first and the second solvent.

Thus, the process in the sense of the invention enables preparation of a composition cataljtique from ^a dispersion of a carbon material structured in a first solvent and adding a solution of a second solvent comprising the catalyst, catalyst being insoluble at least in the mixture final result. It is of course desirable that the structuring material is not soluble in the solvent mixture.

This is an original process to the knowledge of the inventors and effective for the combination of the catalytic element and a carbon element for the production of electrodes that can be used in a fuel cell and / or for other applications. conventional electrochemicals.

* Definitions

The term "catalytic composition" in the definition above should not be understood in a narrow sense. Indeed, each of the elements of the composition does not necessarily have a catalytic activity. This is a property of the composition as a whole. In general, the composition increases the rate of one or more chemical reactions without altering the overall Gibbs energy variation of the chemical reaction (s). Ideally, such a composition should retain its properties indefinitely. Nevertheless, it is recognized in the field that such an objective can not be envisaged in practice and that the activity of such compositions decreases with time, in particular because of external pollution. The specificity and activity of the compositions for and with respect to certain reactions is based on the nature of the catalyst that is employed.

Furthermore, for the purposes of the present invention, a "carbon structuring material" corresponds in particular to the materials typically used in fuel cells. Such a material is said structuring in the sense that the catalyst is deposited thereon. Such a material is generally in the form of a set of particles. It is advantageous that the smallest dimension of the particles is between 5 nm and 10 μm, and that their largest dimension is at most equal to 5 mm and generally greater than or equal to 1 μm.

Among the different morphologies carbonaceous structuring materials can be chosen especially from carbon nanotubes, carbon black, black ^acetylene, carbon blacks, or the carbon fibers obtained from son or fabric synthesized by carbonization of a polymer, or a mixture of at least two of these morphologies. For example, a mixture of fibers and nanotubes may have the advantage of having a double porosity. It ^s' will preferably carbon nanotubes, typically obtained by the pyrolysis and in particular by the method described in WO 2004/000727.

According to a particular embodiment 1 ^"invention, the material may be in the form of a set of multiple particles morphologies, including dual such as a mixture of nanotubes and fibers. Such material will generally include an amount between 1 for 1000 and 1 for 1 in nanotubes, and advantageously between 1 for 1000 and 1 for 10.

A "catalyst", in the sense of the present invention, typically corresponds to oxidation-reduction catalysts, and in particular those used in fuel cells and in the reduction of oxygen. They are generally solid compounds consisting of inorganic particles, such as particles of metal or metal oxides, or particles consisting of the combination of such particles with organic type compounds, in particular to form organometallic particles consisting of of an inorganic heart and an organic crown. Generally, the size of the catalyst particles chosen will be smaller than that of the particles of structuring material, and the particles of structuring material will advantageously be larger than the catalyst particles in at least one of their dimensions, for example the length. Typically it will be nanoscale catalyst particles. Preferably, the largest dimension of the catalyst particles does not exceed about 20% of the smaller dimension of the carbonaceous structuring material.

The metal is often chosen from noble metals and their alloys, and more particularly platinoids and platinoid alloys. Platinoids correspond to the platinum, iridium, palladium, ruthenium and osmium families. In a nonlimiting manner, platinum is nevertheless preferred in this family. The platinoid alloys comprise at least one platinoid. he can thus be ^of a natural alloy such as osmiridium (osmium and iridium) or artificial such as an alloy of platinum and iron, platinum and cobalt or platinum and nickel.

Organic type molecules in ^the combination forming the catalyst are advantageously chosen to be able to complex the surface of the inorganic particles. Complexation can be strong or weak. It is thus possible to employ organic molecules which bind weakly or strongly to inorganic particles by covalent or ionic bonds. Without limitation, the catalyst may thus consist of particles (and preferably nanoparticles) metal with organic coating. These may ^act such as particles described in WO 2005/021154.

It is of course possible to employ several catalysts in the composition.

For a more detailed discussion of the catalysts that may be employed in the context of the invention, it will be useful to refer to the examples presented in detail below.

A condition relating to the solvents is that the catalyst is insoluble in the final mixture of the two solvents.

In an embodiment described below, the catalyst is even insoluble already in the first solvent of the carbonaceous structuring material.

Thus, in what follows, the "first solvent" corresponds to a solvent in which the catalyst is insoluble. Solubility is defined as the analytical composition of a saturated solution as a function of the proportion of a given solute in a given solvent. It can in particular express itself in molarity. A solution containing a given concentration of compound is considered saturated if the concentration is equal to the solubility of the compound in this solvent. Thus, the solubility can be finite or minute and, in the latter case, the compound is soluble in any proportion in the solvent. Typically, a species is considered insoluble in a solvent if its solubility is less than or equal to 10 ^" mol / L.

In order to estimate the solubility of the catalyst in a given solvent, it is possible to measure the concentration of particle solutions by UV-visible spectrometry, or to observe their precipitation visibly.

Tests with isopropanol as "first solvent" gave satisfactory results. More generally, one can use the family of hydroxylated solvents, which belongs ^isopropanol, but methanol,

Ethanol, a glycol such as ethylene glycol, or use a mixture of these solvents.

The "second solvent" may be chosen to be the same or different from the first solvent. If it is different from the first, the mixture of solvents, in the proportions used, nevertheless leads to a mixture in which the catalyst is insoluble. However, in a preferred but nonlimiting embodiment, the first and the second solvent will be different.

Most solvents that can be used as "second solvent" are especially organic solvents such as dimethylsulfoxide, dichloromethane, chloroform and / or a mixture of these solvents.

It should be noted however that it is possible to use water as first and / or second solvents. More generally, couples of solvents ("first" and "second" solvents) will advantageously be defined for a catalyst nanoparticle bearing a given coating. For example. some nanoparticles are soluble in water in basic medium and precipitate when the medium becomes acidic. It is therefore possible within the meaning of ^the invention, to disperse the structuring material in water whose pH is adjusted to be acidic, while the nanoparticles are added in water in a basic medium. Of course, the pH of the solvents are chosen so that the mixture of the two media leads to a pH at which the nanoparticles are insoluble. Thus, it is possible to from ^a dispersion of structuring material in a basic medium, dissolving the catalyst in this dispersion and achieve an association controlled by progressively acidifying the pH of the mixture. * Examples of order of magnitude of proportions

The concentration of carbonated structuring material and catalyst can be a function of ^the intended application. Generally, the concentration of carbonaceous structuring material in the first solvent is typically between

1 mg / L and 10 g / L. It is preferably less than 100 mg / L, for example of the order of 20 mg / L.

The catalyst concentration in the second solvent is preferably between 10 ^-9 mol / l and ⁴ mol / l, ie between 1 mg / l and 10 g / l and preferably between 0.1 g / l and 2 g. / L.

The solution volume of the catalyst is preferably less than the volume of the dispersion of the carbonaceous structuring material, so as to promote the precipitation of the nanoparticles on the surface of the carbonaceous material (especially when the latter is in the form of nanotubes), the particles preferably remaining insoluble in the first solvent. Typically, the volume ratios are less than 1 to 5 and preferably of ^the order of 1 to 25.

* Preparation of solutions and mixing Solutions can be prepared in advance. It is advantageous that they are homogeneous.

The carbonaceous structuring material and / or the catalyst are preferably each distributed in its solvent in a substantially homogeneous manner so that the respective composition of the solutions is substantially identical throughout its volume. In order to obtain homogeneous dispersions, it is preferable to subject them to mechanical stirring before their recovery. Preferably, the mixture undergoes a mechanical stirrer, to make homogeneous the dispersion of carbonated structuring material in its solvent, accelerating ^the association of the catalyst and promote structuring material in fine homogeneous distribution of the catalyst on the structuring material. Thus, the solutions can be obtained by mechanical stirring, and optionally by ultrasonic treatment. In particular, the ultrasonic treatment of a solution comprising the structured material in the form of carbon nanotubes is advantageous because it makes it possible to separate the aggregates of aligned carbon nanotubes for which simple agitation would not have been sufficient. In addition, this treatment has the effect of breaking the nanotubes and reducing their original size. The average size of the nanotubes obtained is a function of the duration of the dispersive treatment.

The dispersions can subsequently be kept homogeneous by mechanical stirring.

It will therefore be noted that the carbonaceous structuring material is advantageously dispersed in its solvent. The resulting solution is called "dispersion" afterwards. In the same way, the solution resulting from the mixing of the structuring material dispersion and the catalyst solution also corresponds to a dispersion.

According to a first embodiment, the mixture is prepared by adding the dispersion comprising the structuring material to the solution comprising the catalyst. A second, preferred embodiment corresponds rather to the addition of the solution comprising the catalyst to the dispersion comprising the structuring material, as described in the embodiment examples below. The addition can be done directly or by a controlled drip at a typical rate of 1 mL / min for a concentration of, for example, from about 5 μg / L to 500 μg / L.

* Treatment of the mixture

Advantageously, the mixing of the solutions is also stirred, which can be carried out by any type of stirrer, such as a mechanical stirrer.

It is recommended to maintain stirring until precipitation of the catalyst on the structuring material is substantially complete. To check if the precipitation is substantially complete, it is possible to ^observe the supernatant after stopping ^the agitation. ^The optical absorption of the supernatant is usually intermediate between that of the initial mixture and that ^of a solution in the absence of catalyst and it may thus be compared to the respective absorptions. Thus, the precipitation is substantially complete if the absorbance of the supernatant is close to that of a catalyst-free solution, for example at a wavelength in the ultraviolet close to 300 nm.

In practice, the end of ^the mechanical agitation of the mixture may be applied if the absorbance of the supernatant in the mixture is less than, for example, 10% of the value of the absorbance of the mixture before stirring. A strong starting concentrations, a simple check with ^the naked eye ^the appearance of the supernatant as possible to assess the precipitation, especially by comparison with a catalyst-free solution.

Optional Additions According to a particular embodiment of the invention, it is possible to introduce one or more surfactants to at least one of the solutions or to the mixture. Surfactants are molecules comprising a lipophilic part (apolar) and a hydrophilic part (polar). Among the surfactants that can be used, mention may be made especially of: i) anionic surfactants whose hydrophilic part is negatively charged; ii) cationic surfactants whose hydrophilic part is positively charged; iii) zwitterionic surfactants which are neutral compounds with formal electrical charges. one unit and opposite sign iv) the amphoteric surfactants which are compounds behaving both as an acid or as a base depending on the medium in which they are placed (these compounds may have a zwitterionic nature), such as acids amines, v) neutral (nonionic) surfactants whose surfactant properties, especially hydrophilicity. are provided by unfilled functional groups such as an alcohol, an ether, an ester or an amide, containing heteroatoms such as nitrogen or oxygen; because of the low hydrophilic contribution of these functions, the nonionic surfactant compounds are most often polyfunctional.

In the case of a use of charged surfactants, these can of course carry several charges, such as for example a long carbon chain comprising from 5 to 22 carbon atoms and preferably 5 to 14. It may in particular be chains aliphatic.

In a preferred embodiment, at least Nafion® is used as surfactant (sulfated tetrafluoroethylene copolymer of molecular formula C ₇ HF ₃ O ₅ SC ₂ F ₄ ).

* Treatment of the mixture to isolate the composition According to one of the advantages provided by the invention and which will be described in detail below, the mixture thus obtained can retain its properties, in liquid form, for a few months. However, to subsequently isolate the composition comprising the catalyst associated with the carbon structure, the process in the sense of the invention may further comprise an additional step of removing the solvent from the composition.

The elimination can in particular be carried out by evaporation. It is recommended to perform this operation under reduced pressure. For this purpose, it is possible to use a rotary evaporator, for example. The operating conditions are typically a function of the nature of the solvent (s) used in the mixture.

^The insulation composite can also be achieved by filtration or spreading of the composition on a substrate of interest. It is preferable that the support of interest has a large surface area. This is generally a porous support and in particular a porous support electrical conductor diffusion layers of the fluids such as fabrics, papers, carbon felts or any other support of this type.

Electrodes are thus produced whose catalytic activity can be evaluated in a conventional electrochemical assembly in a three-electrode cell (FIG. 1) or in a fuel cell. With reference to FIG. 1, such an assembly conventionally comprises: a REF reference electrode, an ELE working electrode (comprising, for example, a sample of the composite obtained by the implementation of the invention, and a CELE counterelectrode). bathed in an acidic electrolyte BEL which may include dissolved oxygen.

^The catalytic activity of the electrode thus obtained can be improved by chemical or thermal treatment to remove an organic ring may be present on the catalyst particles. These treatments do not modify in any way the surface distribution of the catalyst on the structuring material.

* Other aspects of the invention

The invention also relates to compositions and composite materials obtainable by the method described above. It also relates to an electrode for electrochemical application, for example an electrode of a fuel cell, comprising a composite material obtained by the method according to the invention. Typically, an electrode within the meaning of the invention may comprise a platinum charge which may be low relative to the state of the art practice, for example greater than or of the order of 0.1 μg / cm ² .

It is possible to obtain surfaeiques densities of the catalyst on the same electrode, but, however, different volume densities, which result to be able to modulate at will the electrochemical behavior of ^the electrode. Indeed, on the electrode, the amount of platinum per unit area can be chosen by controlling two parameters: on ^the one hand, the total volume of slurry composition deposited on the carrier, on the other hand, the proportion by mass of ^the carbon member with respect to the catalytic element. When the catalyst used comprises particles according to ^the teaching of WO 2005/021154, the electrodes obtained by the implementation of the invention are active without ^it being necessary to carry out any post-treatment. Nevertheless, the performance in terms of current and oxygen reduction potential can be further improved by a conventional thermal or chemical treatment that does not alter the size or distribution of the nanoparticles precipitated on the carbonaceous structuring material.

* Improvements made by I Invention

^The combination of the catalyst with the carbonaceous material is a yield whose value is between 0.8 and 1. This result is achieved by using for the dispersion of carbonaceous materials wherein a solvent in the sense of the invention, the particles are not soluble.

The platinum / carbon mass ratio (denoted X for the ratio Pt / C) is controlled in a wide range and easily adjustable. The maximum value of this ratio X depends on the specific surface of the carbon element. The minimum value can be as low as 0.001, as will be seen in the embodiments below.

The compositions obtained are stable over time in a liquid medium and can keep their electrochemical activity for a period of several months (typically six months or more).

Electrodes with a platinum charge barely of the order of one-tenth of microgram per cm ² (for example 0.33 μg / cm ² ) can be achieved, and their electrochemical activity due to platinum is nevertheless ascertainable. The liquid dispersions of composite material are deposited simply by filtration or spreading on porous support (for example a support layer fuel cell diffusion apparatus such as tissue, paper, or carbon felt), with a typical filtration yield of 90 to 100%.

The electrodes exhibiting catalytic activity have very low carbon nanotube charges of the order of about ten micrograms per square centimeter.

Lists of figures

Other features and advantages of the invention will appear on examining the detailed description below and the appended drawings in which: Figure 1 shows a conventional electrochemical device called "3-electrode", ^the working electrode ELE being that containing the composition of the invention, Figure 2 schematically illustrates steps involved in the preparation of the composition in the sense of the invention, Figure 3 illustrates examples of platinum nanoparticles having an organic coating, Figure 4 is a TEM picture of a composite Pt-I nanopartieules platinum / carbon nanotubes, - Figure 5 is a TEM picture ^of a platinum nanopartieules composite Pt-2 / carbon nanotube mass fraction 4 / 5, to be filtered subsequently to form an electrode whose theoretical maximum charge in pure platinum is 56 μg / cm ² , Figure 6a is a SEM image of the composite of Figure 4, after wire FIG. 6b is an EDX diagram of the composition observed by SEM in FIG. 6a, FIG. 7 is a MET image of a composite of platinum nanoparticles Pt-I / carbon nanotubes, in mass proportion 2/3. , to be filtered subsequently to form an electrode whose theoretical maximum charge in pure platinum is 58 μg / cm ² , Figure 8 is a TEM picture ^of a composite of platinum nanoparticles Pt-1 / carbon nanotubes, in weight proportions of 1/1, to be then filtered to form an electrode having a maximum theoretical loading of pure platinum is 58 g / cm ^2, - Figure 9 is a TEM picture ^of a composite of platinum nanoparticles Pt 1 / nano carbon tubes, 3/2 mass ratio, to be then filtered to form an electrode whose theoretical maximum charge in pure platinum is 85 μg / cm ² , Figures 10a and 10b are MET images of a composite of platinum nanoparticles Pt-1 / carbon nanotubes in mass proportion

2/5. intended to be filtered in order to produce an electrode whose theoretical maximum charge in pure platinum is 29 μg / cm ² , FIG. 11 is a MET image of a composite of platinum nanoparticles Pt-1 / carbon nanotubes in mass proportion 1/1 on a larger scale by using an ultrasonic tank, which is then filtered to produce an electrode whose theoretical maximum charge in pure platinum is 67 μg / cm ² , FIG. 12 is a TEM image of a composite of platinum nanoparticles Pt-1 / carbon nanotubes in mass ratio 1/1 on a larger scale by use of an ultrasonic tank, then to be filtered on a larger apparatus to make a larger electrode diameter whose theoretical maximum charge in pure platinum is 73 μg / cm ² , FIG. 13 is a MET image of a composite of platinum nanoparticles Pt-1 / carbon nanotubes in a 1/10 mass ratio from a solution of n anoparticles at 50 μg / ml, which is then to be filtered in order to produce an electrode whose maximum charge in pure platinum is 6.7 μg / cm ² , FIGS. 14a and 14b are MET images of a composite of platinum nanoparticles Pt -1 / carbon nanotubes in mass proportions of 1/50 and 1/100, respectively, from a solution of nanoparticles at 10 and 5 μg / ml, respectively, the composite being intended for then be filtered to produce an electrode from the composite in 1/100 proportion whose theoretical maximum charge in pure platinum is then 0.66 μg / cm ² . Figure 15 is a TEM picture ^of a composite of platinum nanoparticles Pt-0 / carbon nanotube mass fraction 1/1 from a solution of nanoparticles 500 mcg / ml, the composite is intended to be filtered then to produce an electrode whose theoretical maximum charge in pure platinum is 66 μg / cm ² , Figure 16 is a MET image of a composite of platinum nanoparticles Pt-1 / carbon black in mass ratio 5/4 from a solution of nanoparticles at 500 μg / ml, the composite being intended to be filtered subsequently to produce an electrode whose theoretical maximum charge in pure platinum is 110 μg / cm ² , FIG. 17 compares the voltammogram of the electrochemical reduction of aqueous oxygen for the series of Example 7 (solid line) to the voltammogram of the response of the same sample in a solution containing no oxygen (dashed lines), FIG. 18 compares the voltammograms for the series of example 7

(Platinum ratio 1/1 - solid line), for the series of Example 9 (platinum ratio 1/10 - long / short broken lines) and for the series of Example 8

(Platinum ratio 1/100 - dashed lines), FIG. 19 compares the voltammograms for the series of Example 7 without chemical treatment with hydrogen peroxide (solid line), for the same series of Example 7 with treatment. 20 minutes with 30% hydrogen peroxide (long / short broken lines) and for the same series of Example 7 with chemical treatment of 30 minutes with 30% hydrogen peroxide (dotted lines), the figure Compares the voltammograms for the series of Example 7 without heat treatment and for the same series of Example 7 with heat treatment of 1 hour at 200 ^° C. under vacuum (dashed lines), FIG. 21 compares the voltammograms for two equivalent charges of approximately 0.65 μg / cm ² obtained from 100 μl of 20 mg / L dispersion in nanotubes (solid curve), and from 1 ml of dispersion to 2 mg / L (dashed line curves), - Figure 22 compares the voltammograms for small platinum loads, with in particular two samples from the same series of platinum density of 0.33 μg / cm ² (in dotted lines and long / short broken lines), and with twice as much platinum, a density of 0.65 μg / cm ² (solid line), - Figure 23 is a voltammogram measured with an electrode comprising a composite obtained from carbon black (Example 11 hereinafter described), FIG. 24 is a voltammogram measured with an electrode comprising a composite obtained from carbon fibers (Example 12 described hereinafter), FIG. image obtained by scanning electron microscopy of a co Mposite nanoparticles of Pt-O on a mixture of fibers and carbon nanotubes in a mass ratio of 1/60, the composite being intended to be subsequently filtered to produce an electrode whose theoretical pure platinum loading is of the order of 9 μg / cm ² ; FIG. 26 is a voltammogram illustrating the electrochemical activity of an electrode made according to another exemplary implementation (example 13a described below) with respect to the reduction of oxygen, FIG. is a voltammogram showing the electrochemical activity ^of an electrode formed according to another example implementation (example 13b described below) relative to the reduction of oxygen, FIG 28 is a voltammogram showing the electrochemical activity an electrode made according to another example of implementation (Example 13c described below) with regard to the reduction of oxygen, FIG. 29 is a voltammogram illustrating the elec Electrochemical analysis of an electrode made according to another example of implementation (example

14 described below) with respect to the reduction of oxygen, Figure 30 is a voltammogram showing ^the electrochemical activity ^of an electrode formed according to another example implementation (for example

15 described below) relative to the reduction of oxygen, FIG. 31 is a voltammogram illustrating the electrochemical activity of an electrode made according to another example of implementation (example

16 described below) with respect to the reduction of oxygen, FIG. 32 illustrates a formula of the particle of Pt-4, FIG. 33 is a voltammogram illustrating the electrochemical activity of an electrode made according to another example of implementation (Example 17 described below) relative to the reduction of oxygen, FIG. 34 is a voltammogram illustrating the electrochemical activity of an electrode produced according to another example of implementation (example

18 described below) with respect to the reduction of oxygen. FIG. 35 is a voltammogram illustrating the electrochemical activity of an electrode made according to another exemplary implementation (example

19 described below) relative to the reduction of oxygen, FIG. 36 is a voltammogram illustrating the electrochemical activity of an electrode made according to another example of implementation (example

Described below) relative to the reduction of oxygen, FIG. 37 is a voltammogram illustrating the electrochemical activity of an electrode made according to another example of implementation (example

21 described below) with respect to the reduction of oxygen, FIG. 38 is a voltammogram illustrating the electrochemical activity of an electrode made according to another exemplary embodiment (Example 22 described hereinafter) with respect to the reduction of oxygen, FIG. 39 is a voltammogram illustrating the electrochemical activity of an electrode made according to another example of implementation (example

23 described below) relative to the reduction of ^oxygen, FIG 40 is a voltammogram showing the electrochemical activity ^of an electrode formed according to another example implementation (for example

24 described below) with respect to the reduction of oxygen, Figure 41 is an image taken by optical mieroscopie ^of a sample carried out by deposition by spraying from a dispersion according to Example 13b containing carbon nanotubes and carbon fibers in which was added Nation, - the Figure 42 is a voltammogram showing the électroehimique activity of an electrode formed according to another example implementation (example 25 described below) relative to the reduction of ^oxygen.

Examples of achievement and results obtained

The catalytic materials used in the following embodiments are metallic nanoparticles, mainly so-called "functionalized" platinum nanoparticles, whose organic coating can be chemically modified and which already exhibit electrocatalytic activity vis-à-vis oxygen reduction, without the need for any chemical or physical pre-conditioning. Such platinum nanoparticles as catalyst are described in EP 1663487.

For example, one can have several types of particles and whose representations are given in Figure 2 and are called Pt-O, Pt-I, Pt-2, Pt-3.

These particles are crystalline and their size is between 2 and 3 μm. They are obtained in the form of powders from which concentration solutions chosen according to the intended applications (0.5 mg / ml, 0.05 mg / ml, or other) are prepared. According to the organic coating (Pt-O, Pt-I, Pt-2, Pt-3), the solvent used is polar aprotic such as dimethylsulfoxide or apolar (dichloromethane, chloroform, or other).

The solutions comprising the platinum nanoparticles are brown in color all the more intense as the concentration of the nanoparticles is high.

As indicated above, the carbonaceous materials are preferably multi-walled carbon nanotubes and synthesized in the laboratory by deposition in vapor phase (CVD) aerosol. This synthesis makes it possible to obtain nanotubes of controlled length. They are aligned so little entangled, and thus can be easily dispersed in a liquid medium, for example in isopropanol without additive, under the effect ^of a treatment with ultrasonic stable (by a power sensor or simply a ultrasonic laboratory tray). Before use, the nanotubes may also be heat-treated at ^2000.degree. C. for about two hours in order to remove a catalyst residue allowing their synthesis.

In some examples described here, the aim is the combination of nanotubes with nanoparticles. In other examples, however, it is shown that the process in the sense of the invention can be implemented with standard carbon blacks, and / or with carbon fibers whose diameter is of the order of ten micrometers. Mixtures of compositions based on different carbon-based supports can also be produced, in particular based on nanotubes on the one hand, and fibers on the other hand.

In most of the examples described below, the following steps will preferably be carried out.

A carbonaceous structuring material is dispersed in a liquid medium by weighing a given amount of carbonaceous material which is introduced into a container and in which a given volume of solvent is added. The solvent is chosen from the solvents in which the catalyst nanoparticles which will be added subsequently are not soluble. With reference to FIG. 2, it is generally possible to use a solution of isopropanol SOL1 comprising a concentration of carbon nanotubes MSC of the order of 20 mg / liter.

This preparation is subjected to an ultrasonic treatment (probe or ultrasonic tank) US so as to separate the aggregates of carbon nanotubes aligned. Simple mechanical agitation to break the nanotubes quickly and thus reduce their initial size may not be sufficient. The average size of the nanotubes obtained then depends on the duration of the dispersive treatment. We stop generally the treatment when the dispersion only visibly comprises small aggregates in the form of balls (and no longer aligned and interconnected nanotubes). A surfactant such as Nafion® can then be added as indicated above.

This dispersion is then mixed with a known volume of SO 2 solution of CAT catalyst nanoparticles (coated platinum, for example) of selected concentration. The volume of nanoparticle solution, preferably added dropwise, should preferably be small compared with the dispersion volume of the nanotubes so as to promote the precipitation of the nanoparticles on the surface of the nanotubes. Typically, volume ratios of the order of 1 to 25 have given good results.

Mechanical stirring is maintained AGM the mixture to a minimum the time required for the precipitation of nanoparticles on the nanotube ^is effected. A good way to know this time is to perform an optical LO reading of the supernatant. Alternatively, it is of course possible to measure this time for a first preparation and apply it systematically to subsequent preparations for the same nature of products in the same proportions. Indeed, if we change the nature of the dispersion solvent of the nanotubes SOL1, it is possible to cause the particles to precipitate more or less quickly. One may optionally add a surfactant thereafter, for example Nafion®.

The composite thus formed (catalyst element / carbon element) can be kept very long in the state (liquid). Nevertheless, it can be recovered in solid form, in particular by filtration, in which case the mixture is preferably stirred (AGM) again before recovering the composite. In particular, advantage is taken of the filtration on porous conductive supports.

It is important to emphasize, however, that filtration is not the only way. Other methods, such as simply spreading the composite dispersion on a support of the aforementioned type, are also possible as indicated above. To improve ^the catalytic activity of the composite material obtained, after preparation of electrodes, one can still provide a chemical treatment (an aqueous hydrogen peroxide solution 30% for 20 to 30 minutes), or preferably heat (at 200 ⁰ C under primary vacuum for 1 to 2 hours), so as to remove the organic corona present on the particles. These treatments do not modify the surface distribution of platinum on carbon.

* Properties and characterizations of the compositions obtained The fact that the nanoparticle / carbon support association is actually due to precipitation of the nanoparticles in a medium containing a large amount of solvent where these nanoparticles are not soluble can be demonstrated in two ways.

On the one hand, it is possible to observe that if the solid composite is recovered and it is returned to the presence of the solvent, the nanoparticles are dispersed again and thus separate from the nanotubes (visible coloration of the solvent after a few moments), which shows a real influence of (or) solvent (s).

On the other hand, by centrifugation of the dispersions, it is noted that the supernatant dispersions is virtually unstained compared to a control containing only nanoparticles in the same mixture of solvents and before precipitation of the particles.

Furthermore, the state of the carbon element / catalytic element association can be verified and controlled by Transmission Electron Microscopy (TEM) imaging from liquid suspensions or by microscopy.

Scanning Electronics (SEM) after deposition on porous conductive supports.

The catalytic activity of the composites filtered or spread on a porous conductive element (and optionally thermally or chemically treated thereafter) can be tested by cyclic voltammetry in a saturated medium. oxygen under 1 bar of pure oxygen, ^the éleetrolyte being perchloric acid at a concentration of 1 mol / L.

As noted above, electrode F, the amount of platinum per unit area can be adjusted by controlling two parameters: first, the total volume of composite slurry that will be deposited on the electrode, on ^the other hand , the mass proportion of the carbon element with respect to the catalytic element. In the case of a dispersion, the removal of these volumes is done with mechanical stirring so that it is reproducible and controlled. It is the control of the sampled volume which makes it possible to control the quantity of deposited composite and therefore the maximum amount of platinum that the electrode will comprise, hence the utility of the mechanical stirring in the process within the meaning of the invention. . This quantity can be checked a posteriori directly by weighing if the deposited mass is measurable (typically greater than 10 μg).

In the examples below, the weighings made it possible to show that the deposition efficiencies could reach almost 100%. They were nevertheless lower when the carbon element was a carbon black deposited by filtration.

Example 1

In a 10 ml flask, 2 mg of annealed carbon nanotubes (as carbonaceous structuring material) are weighed out and 5 ml of isopropanol (as the "first solvent") is added. The whole is treated for two minutes by ultrasound with a Bioblock Vibracell® 75043 probe at 20% of its maximum power. Then, 2 ml of solution of nanoparticles Pt-I as a catalyst (FIG. 3), concentration 418 μg / ml in dimethylsulfoxide, are added dropwise (approximately 1 ml / min) and with stirring. DMSO 3 (as "second solvent"). After addition, the resulting mixture is allowed to stir for four hours. After decantation, it is found that the supernatant is colorless, indicating that the particles are precipitated. This supernatant was removed and 3 mL of isopropanol was added along with 2 mL of 10% Nation® solution in water.

FIG. 4 shows a view of a drop of dispersion observed at TEM. Nanotubes are obtained almost completely covered with platinum nanoparticles (dark spots on the plate, about 2 to 3 nm in size, on the surface of the tubes).

EXAMPLE 2 1 mg of nanotubes with an initial average length of 150 μm are introduced into a 100 ml container. 50 ml of isopropanol are added. An ultrasound treatment of 4 minutes is carried out with a Bioblock Vibracell® 75043 probe at 30% of its maximum power. 2 ml of solution of nanoparticles of Pt-2 type (FIG. 3) at 415 μg / inL in dichloromethane are then added with stirring. After addition, stirring is continued for 24 hours.

FIG. 5 shows a view of a drop of dispersion observed at TEM. It is found that the nanotubes are almost entirely covered with nanoparticles.

Filtration of 10 ml of dispersion of the obtained composite (nanotubes / nanoparticles) on a 2.3 cm ² carbon felt disc gives a mass difference of 0.33 mg, which corresponds to a yield for the filtration of 91% of the platinum mass. The effective density of platinum nanoparticles (with organic coating) is 63 μg / cm ² , which corresponds to a pure platinum density (without coating) of about 51 μg / cm. In FIGS. 6a and 6b, a SEM / EDX observation of the deposition on the filter (scanning electron microscopy coupled with an X-ray energy dispersion analysis) shows that the distribution of the particles on the nanotubes during filtration and that the deposit on the nanotubes remains platinum with an organic ring around (presence of sulfur). The ratio of the introduced masses of nanoparticles and nanotubes is about 4/5.

Example 3 In a 100 ml container, 1.3 mg of nanotubes of initial average length 150 μm are introduced with 50 ml of isopropanol. An ultrasound treatment of 4 minutes is carried out with a Bioblock Vibracell® 75043 probe at 30% of its maximum power. 2 ml of solution of nanoparticles Pt-I at 432 μg / ml in DMSO are then added with stirring. Finally, it is left to agitate for 24 hours.

FIG. 7 shows a view of a drop of dispersion observed at TEM. It is found that nanoparticles are well present on carbon nanotubes.

Filtration of 10 mL of dispersion on a carbon felt disk gives a mass difference of 0.32 mg, which corresponds to 83% of the mass introduced. The ratio of introduced masses of nanoparticles and nanotubes is 2/3. The effective density of platinum nanoparticles (with organic coating) is 60 μg / cm ² , which corresponds to a pure platinum density (without coating) of about 48 μg / cm ² .

Example 4

In a 100 ml container, 1.0 mg of nanotubes of initial average length 150 μm are introduced with 50 ml of isopropanol (20 mg / l). An ultrasound treatment of 4 minutes is carried out with a Bioblock Vibracell® 75043 probe at 30% of its maximum power. 2 ml of solution of nanoparticles Pt-I at 432 μg / ml in DMSO are then added with stirring. Finally, it is left to agitate for 24 hours.

Figure 8 shows a view ^of a drop of dispersion deposited on a support for observation by TEM. The filtration of 10 ml of dispersion on a carbon felt disk gives on average a mass difference of 0.33 mg, which corresponds to 92% of the mass introduced. The ratio of the masses introduced of nanoparticles and nanotubes is 1. The effective density of platinum nanoparticles (with coating) is 66 μg / cm ² which corresponds to a pure platinum density (without coating) of approximately 53 μg / cm ² .

Example 5

In a 100 ml container, 1.0 mg of nanotubes of initial average length 150 μm are introduced with 50 ml of isopropanol. An ultrasound treatment of 4 minutes is carried out with a Biobloek Vibracell® 75043 probe at 30% of its maximum power. 3 ml of Pt-I nanoparticle solution at 432 μg / ml in DMSO are then added with stirring. Finally, it is left to agitate for 24 hours.

Figure 9 shows a view of a dispersion drop deposited on a support observed at TEM. The filtration of 10 ml of dispersion on a carbon felt disk gives on average a mass difference of 0.33 mg, which corresponds to 86% of the mass introduced. The ratio of introduced masses of nanoparticles and nanotubes is 3/2. The effective density of platinum nanoparticles (with coating) is 91 μg / cm 2 which corresponds to a pure platinum density (without coating) of about 73 μg / cm ² .

Example 6

In a 100-ml container, 1.0 mg of nanotubes with a mean initial length of 150 μm are introduced with 50 ml of isopropanol (20 mg / l). An ultrasound treatment of 4 minutes is carried out with a Biobloek Vibracell® 75043 probe at 30% of its maximum power. 1 ml of Pt-I nanoparticle solution at 432 μg / ml in DMSO is then added with stirring. Finally, let it shake for 1 day.

Figures 10a and 10b show a view of a drop of dispersion deposited on a support for observation with MET. The filtration of 10 ml of dispersion on a carbon felt disk gives on average a mass difference of 0.21 mg, which corresponds to 75% of the mass introduced. The ratio of the masses introduced nanoparticles and nano tubes is 2/5 and can be seen visually lower coverage of nanotubes than previously in Figures 10a and 10b.

The effective density of the nanoparticle is 28 μg / cm ² , which corresponds to a pure platinum density of approximately 22 μg / cm ²

Example 7

We check here that the change of scale is possible (with larger volumes). In a 2 L container, 20.1 mg of nanotubes of initial average length 150 μm are introduced with 1 L of isopropanol. This time, an ultrasonic treatment of 3 times 15 minutes is carried out in a Transsonic® TI-H 15 ultrasonic tank at 80% of its maximum power and a frequency of 25 kHz. 40 ml of Pt-I platinum nanoparticle solution at 500 μg / ml in DMSO are then added dropwise (approximately 1 ml / min) and with stirring. After addition, stirring is maintained for 3 days.

Figure 11 shows a view of a drop of the composite observed at TEM. There is still the deposition of nanoparticles on the carbon nanotubes. The ratio of introduced masses of nanoparticles and nanotubes is

1/1. The filtration of 10 ml of dispersion gives, on a disk of carbon felt, a mass difference of 0.35 mg, which corresponds to 92% of the mass theoretically introduced. The effective density of the nanoparticle is 83 μg / cm ² , which corresponds to a pure platinum density of approximately 66 μg / cm ² .

Example 7 -bis

In a 1L flask, 20.0 mg of nanotubes of initial average length 150 μm are introduced with 1 L of isopropanol. An ultrasonic treatment of 4 hours is carried out in a Transsonic® TI-H 15 ultrasonic bath at 90% of its maximum power and at 45 kHz. 40 ml of nanoparticle solution are then slowly added dropwise (approximately 1 ml / min) and with stirring. platinum Pt-I at 500 μg / mL in DMSO. After the addition, stirring is maintained for 3 days.

MET is observed on a drop of the composition obtained (Figure 12), the deposition of the particles on the nanotubes. The ratio of introduced masses of nanoparticles and nanotubes is

1/1. The filtration of 200 ml of dispersion gives a mass difference of 6.9 mg, on a carbon felt disk having an area of 44 cm ² , which corresponds to 91% of the mass theoretically introduced. The effective density of nanoparticles is 77 μg / cm ² , which corresponds to a pure platinum density of about 62 μg / cm ² .

Example 8

In a 500-ml container, 10.0 mg of nanotubes with an average length of 150 μm are introduced with 500 ml of isopropanol. An ultrasonic treatment of 4 times 15 minutes is carried out in a Transsonic® ultrasonic bath

TI-H 15, at 90% of its maximum power, at 25 kHz. A dispersion is obtained hereinafter referred to as "dispersion D".

100 ml of this dispersion are taken from the test tube and 4 ml of solution of platinum nanoparticles Pt-I at 50 μg / ml in DMSO are added with stirring. The mixture is finally stirred for a few days.

The presence of nanoparticles isolated and deposited on the surface of the nanotubes is observed with TEM on a drop taken from the mixture (FIG. 13).

Filtration of 10 mL of dispersion on a carbon felt disc

(2.3 cm ² ) gives a mass difference of 0.21 mg, which corresponds to 100% of the mass introduced. The ratio of the introduced masses of nanoparticles and nanotubes is 1/10. The effective density of nanoparticles is 8.4 μg / cm ² , which corresponds to a pure platinum density of about 6.7 μg / cm ² .

Example 9 were taken 100 ml of dispersion D nanotubes of ^Example 8 to réprouvette and added drop-by-drop (about 1 mL / min) and stirring 4 mL of Pt-I platinum nanoparticles solution at 10 μg / mL in DMSO. Then, stirring is continued for a few days.

A drop of the medium is observed at TEM (FIG. 14a) and the presence of nanoparticles on the nanotubes is observed. The ratio of masses introduced nanoparticles and nanotubes is 1/50.

Is removed a further 100 mL of the dispersion of nanotubes D of ^Example 8 and was added drop-by-drop (about 1 mL / min) with stirring 4 ml of solution of Pt-I platinum nanoparticles 5 mcg / mL in DMSO. The agitation is finally prolonged for a few days. A drop of the medium is observed at TEM (FIG. 14b) and the presence of nanoparticles on the carbon nanotubes is observed.

10 ml of the medium is removed and filtered on a carbon felt disc (2.3 cm ² surface). Weighing indicates a filtration efficiency of

95%. The ratio of the introduced masses of nanoparticles and nanotubes is 1/100. The effective nanoparticle density is 8.4 μg / cm ² , which corresponds to a pure platinum density of about 6.7 μg / cm ² .

Example 10

In a 500 mL container. 9.0 mg is introduced initial medium length nanotubes 150 .mu.m and 450 mL of ^isopropanol (20 mg / L). An ultrasonic treatment of 3 times 15 minutes is carried out in a Transsonic® container

TI-H 15 at 25 kHz and 90% of its maximum power. 18 ml of solution of Pt-O nanoparticles at 500 μg / ml in DMSO are then added with stirring and dropwise (approximately 1 ml / min). It is left to agitate for a few days.

Fig. 15 is a TEM image of a view of a drop of dispersion.

The filtration of 10 ml of dispersion on a carbon felt disk gives on average a mass difference of 0.35 mg, which corresponds to

90% of the total mass introduced. The ratio of the introduced masses of nanoparticles and nanotubes is 1/1. The effective density of nanoparticle is of 75 μg / cm ² , which corresponds to a pure platinum density of about 60 μg / cm ² here.

EXAMPLE 11 In a 250 ml container, 4.9 mg of carbon black is introduced

Vulcan® XC-72 with 250 mL isopropanol (20 mg / L). Ultrasonic treatment is carried out ^for about one minute in a Transsonic® TI-H container 15 to 25 kHz and 90% of its maximum power, so as to disperse the carbon black. 8 ml of solution of Pt-I nanoparticles at 500 μg / ml in DMSO are then added with stirring. It is left to agitate for a few days.

Fig. 16 is a TEM image of a view of a drop of dispersion.

Direct filtering of this dispersion alone gives a lower yield because the carbon black particles are too small to quickly fill the pores of the felt. It is therefore necessary to repeat the operation several times (that is to say filter the filtrate again as many times as necessary) on a prior deposition of nanotubes alone. Filtration of 20 mL of six-pass dispersion provides a yield of about 69%, which is significantly less than the yield obtained with nanotubes. A platinum density electrode estimated at 74 μg / cm ² is obtained. The weight ratio Platinum / Carbon in the dispersion is 4/5.

Example 12

Was cut from carbon cloth 15 mg of carbon fibers ^that are dispersed in a tube by vigorous stirring in 20 ml of isopropanol. The fibers are cut to have almost all millimeter size so that they disperse easily and that their removal is possible and reproducible with stirring. 0.25 ml of solution of Pt-I nanoparticles at 50 μg / ml in DMSO are added with stirring and the mixture is stirred for several days. 5 ml of dispersion are collected by pipette on a 2.3 cm ² carbon felt to form an electrode. The composite of platinum nanoparticles Pt-I / carbon fibers is obtained in approximate mass proportion of 1/1000. The composite then filtered to produce an electrode has a theoretical maximum charge in pure platinum of 1.1 μg / cm ² .

Example 13

The double porosity structure formation is shown by elaborating a dispersion containing a mixture of two types of structuring materials (carbon fibers and carbon nanotubes) and a volume of platinum nanoparticles of the Pt-O, Pt-I or Pt-type. 4 in solution in DMSO. Here, the platinum solution is added to a non-catalyzed fiber / nanotube mixture.

A few hundred milligrams of carbon fiber of millimeter length and a diameter of the order of 10 μm are cut from a carbon fabric. In a 1 liter container, 79 mg of carbon fibers, 15.5 mg of carbon nanotubes and 500 ml of isopropanol are introduced. Ultrasonic treatment is applied to the medium in a Transsonic® TI-H 15 ultrasonic bath at 100% peak power for 80 minutes and in 25 kHz scan mode. This medium is hereinafter called medium carbon fibers / carbon nanotubes.

a) Structure developed from carbon fiber / carbon nanotubes and Pt-O medium:

50 ml of the carbon fiber / carbon nanotube medium are removed and 0,150 ml of a 0.98 mg / ml solution of Pt-O nanoparticles in DMSO are added while stirring. Then, stir for 36 hours. Filtration of 10 ml of this dispersion on a 2.3 cm ² carbon felt disk gives on average a mass difference of 1.84 mg, which corresponds to 96% of the mass introduced. The ratio of introduced masses of nanoparticles and carbon element (carbon fibers plus carbon nanotubes) is of the order of 1/60. The effective density of platinum nanoparticles (with coating) is therefore of the order of 12 μg / cm ² . which corresponds to a pure platinum density (without coating) of the order of 9 μg / cm ² . Figure 25 shows an image recorded with a scanning electron microscope that illustrates the double porosity of the resulting layer. Figure 26 shows a voltammogram showing ^the electrochemical activity of the electrode relatively to the reduction of oxygen T. The reduction peak is observed at the potential of 0.50 V. the peak current is - 4.90 mA / cm ² .

b) Structure elaborated from the medium carbon fibers / carbon nanotubes and Pt-I:

50 ml of the carbon fiber / carbon nanotube medium are removed and 0.29 ml of Pt-I nanoparticle solution at 0.51 mg / ml in DMSO is added while stirring. Then, stir for 36 hours. Filtration of 10 ml of this dispersion on a 2.3 cm ² carbon felt disk averages a mass difference of 1.89 mg, which corresponds to 99% of the mass introduced. The ratio of the introduced masses of nanoparticles and carbon element (carbon fiber plus carbon nanotubes) is about 1/60. The effective density of platinum nanoparticles (with coating) is therefore of the order of 13 μg / cm ² which corresponds to a pure platinum density (without coating) of the order of 10 μg / cm ² . Figure 27 shows a voltammogram illustrating the electrochemical activity of the electrode with respect to the reduction of oxygen. The reduction peak is observed at the potential of 0.42 V, the peak current is -2.7 mA / cm ² .

c) Structure developed from carbon fiber / carbon nanotubes and Pt-4 medium:

50 ml of the carbon fiber / carbon nanotube medium are removed and 0.51 ml of 0.292 mg / ml Pt-4 nanoparticle solution in DMSO is added while stirring. Then, stir for 36 hours. Filtration of 10 ml of this dispersion on a 2.3 cm ² carbon felt disk gives on average a mass difference of 1.75 mg, which corresponds to 92% of the mass introduced. The ratio of the introduced masses of nanoparticles and carbon element (carbon fiber plus carbon nanotubes) is about 1/60. The effective density of platinum nanoparticles (with coating) is therefore of the order of 12 μg / cm ² which corresponds to a pure platinum density (without coating) of the order of 9 μg / cm ² . Fig. 28 shows a voltammogram illustrating the electrochemical activity of the electrode with respect to the reduction of oxygen. The peak reduction is observed at the potential of 0.40 V, the peak current is -2.95 mA / cm ² .

Example 14

Here, a volume of a 1/2 Pt / NT dispersion is added to a dispersion consisting of a mixture of uncatalyzed fibers and nanotubes.

80 μl of the medium carbon fibers / carbon nanotubes of Example 13 are taken out and 1 ml of a dispersion having a Pt ⁷ Nt ratio of Vz, made from Pt-I and at a nanotube concentration of 20 μg / mL. The filtration of 10 ml of this dispersion on a 2.3 cm ² carbon felt disk gives on average a mass difference of 1.86 mg, which corresponds to 99% of the mass introduced. The ratio of the introduced masses of nanoparticles and carbon element (carbon fibers plus carbon nanotubes) is of the order of 1/1500. The effective density of platinum nanoparticles (with coating) is of the order of 0.5 μg / cm ² which corresponds to a pure platinum density (without coating) of the order of 0.4 μg / cm ² . Figure 29 shows a voltammogram illustrating the electrochemical activity of the electrode relative to the reduction of oxygen. The peak reduction is observed at the potential of 0.09 V, the peak current is - 1, 25 mA / em ² .

Example 15

Here, we added another volume of a Pt / NT dispersion in proportion 1/2 to a dispersion consisting ^of a mixture of fibers and uncatalyzed nanotubes. 80 ml of the carbon fiber / carbon nanotube medium of Example 13 were taken out and 10 ml of a dispersion having a ratio of Pt / Nt of Vi, made from Pt-I and at a nanotube concentration of 20 μg / mL. Filtration of 10 ml of this dispersion on a 2.3 cm ² carbon felt disk gives on average a mass difference of 1.86 mg, which corresponds to 99% of the mass introduced. The ratio of the introduced masses of nanoparticles and carbon element (carbon fibers plus carbon nanotubes) is of the order of 1/1500. The effective density of platinum nanoparticles (with coating) is of the order of 5 μg / cm ² which corresponds to a pure platinum density (without coating) of the order of 4 μg / cm ² . Figure 30 shows a voltammogram illustrating the electrochemical activity of the electrode with respect to the reduction of oxygen. The reduction peak is observed at the potential of 0.50 V, the peak current is -2.50 niA / cm ² .

Example 16

Here was added a volume ^of a Pt / NT dispersion in proportion 1:10 to a dispersion consisting ^of a mixture of fibers and uncatalyzed nanotubes.

80 ml of the carbon fiber / carbon nanotube medium of Example 13 are taken out and 10 ml of dispersion having a Pt / Nt ratio of 1/10, made from Pt-I and at a nanotube concentration of 20 μg / mL. The filtration of 10 ml of this dispersion on a 2.3 cm ² carbon felt disk gives on average a mass difference of 1.86 mg, which corresponds to 99% of the mass introduced. The ratio of the introduced masses of nanoparticles and carbon element (carbon fibers plus carbon nanotubes) is of the order of 1/1500. The effective density of platinum nanoparticles (with coating) is of the order of 1 μg / cm ² which corresponds to a pure platinum density (without coating) of the order of 0.7 μg / cm ² . Figure 31 shows a voltammogram illustrating the electrochemical activity of the electrode performed with respect to the reduction of oxygen. The reduction peak is observed at the potential of 0.28 V, the peak current is - 1.55 m / cm ² . Example 17

An exemplary embodiment of dispersion in water is shown where the first solvent is an aqueous medium in acidic pH and the second solvent is an aqueous medium of basic pH. In a container of 500 mL was charged with 5 mg of carbon nanotubes and added 250 mL of ^water. The ultrasound treatment is carried out successively 5 times in the medium obtained in a Transsonic® Tl-H ultrasonic bath at 100% of its maximum power, for 10 minutes and in 25 kHz scanning mode. Then, vigorously mechanically stirred for 1 to 2 minutes. 80 ml of this medium is taken which is made slightly acid by addition of 2 drops of 3.7% hydrochloric acid. 1.63 ml of an aqueous solution at pH 12 of Pt-4 nanoparticles at 0.493 mg / ml are then added dropwise to the medium maintained under stirring. Finally, it is left to agitate for 24 hours. The filtration of 10 ml of this dispersion on a carbon felt disk gives on average a mass difference of 0.25 mg, which corresponds to 83% of the mass introduced. The ratio of the introduced masses of nanoparticles and nanotubes is ¹ A The effective density of platinum nanoparticles (with coating) is of the order of 35 μg / cm ² , which corresponds to a density of pure platinum (without coating) of 26 μg / cm ² . Figure 33 shows a voltammogram illustrating the electrochemical activity of the electrode performed relative to the reduction of oxygen. The peak reduction is observed at the potential of 0.54 V, the peak current is - 1.65 mA / cm ² .

Example 18 Another embodiment of dispersion in water is shown or the first solvent is an aqueous medium in acidic pH and the second solvent is an aqueous medium of basic pH.

In a 500 ml container, 5.2 mg of carbon nanotubes are introduced and 250 ml of water are added. 10 minutes of ultrasound treatment in the pulsed mode (that is to say alternately 1 second of ultrasound and 1 second of pause) are applied to the medium obtained, using a Vibracell Bioblock Vibracell probe. 40% of its maximum power. 80 ml of this medium is taken which is made slightly acid by addition of 2 drops of 3.7% hydrochloric acid. 1.68 ml of an aqueous solution at pH 12 of 0.494 μg / ml Pt-4 nanoparticles are then added dropwise to this medium, while stirring. Finally, it is left to agitate for 24 hours. The filtration of 10 ml of this dispersion on a 2.3 cm ² carbon felt disk gives on average a mass difference of 0.27 mg, which corresponds to 87% of the mass introduced. The ratio of the introduced masses of nanoparticles and nanotubes is Vi. The effective density of platinum nanoparticles (with coating) is of ^the order of 37 g / cm ^2, which corresponds to a density of pure platinum (without coating) of about 27 g / cm ^2. Figure 34 shows a voltammogram showing the electrochemical activity of ^the electrode relative to the reduction of oxygen. The reduction peak is observed at the potential of 0.61 V, the peak current is - 2.10 mA / cm ² .

Example 19

An example embodiment of a dispersion and its deposition by direct spreading on a carbon support is shown.

In a 100 ml container, 19.6 mg of carbon nanotubes are introduced and 60 ml of isopropanol are added. 10 minutes of ultrasound treatment in pulsed mode (that is to say alternately 1 second of ultrasound and 1 second of pause) is applied to the medium obtained using a Bioblock Vibracell probe at 40% of its power. Max. 12.4 ml of a solution of Pt-I nanoparticles in DMSO at 0.53 mg / ml are then added to the medium maintained under stirring and dropwise (1 ml / minute). After stirring for 36 hours, 2.5 ml of the dispersion are removed by means of a pipette and dispersed by spreading it over a total area of 27 cm ² of carbon felt, previously weighed and deposited on an absorbent paper. ^The electrode is then dried under primary vacuum and weighed. The weight gain following the deposition and after drying is 0.86 mg for a theoretical weight gain of 0.9 mg. The deposit efficiency is thus greater than 95%. The ratio of introduced masses of nanoparticles and nanotubes being 1/3, the effective density of platinum nanoparticles (with coating) is 8.0 μg / cm ² , ie on the order of 6.0 μg of pure platinum (without coating ) per square centimeter. From this 27 cm ² electrode, several circular electrodes of 3.14 cm ² are cut out. Several electrodes are tested for oxygen reduction and give electrochemical responses similar to that shown in Figure 35. The peak of reduction is observed at the potential of 0.45 V, the peak current is -1.80 mA ^; cm ² .

Example 20

Another example embodiment of a dispersion and its deposition by direct spreading on a carbon support is shown.

In a 100 ml container, 19.6 mg of carbon nanotubes are introduced and 60 ml of isopropanol are added. 10 minutes of ultrasound treatment in pulsed mode (alternating 1 second of ultrasound and 1 second of pause) is applied to the medium obtained using a Bioblock Vibracell probe at 40% of its maximum power. 12.4 ml of a solution of nanoparticles Pt-I in DMSO at 0.53 mg / ml are then added to the medium maintained under stirring and by drip at a rate of 1 ml / second. mL. After stirring for 36 hours, 2.5 ml of the dispersion are withdrawn by means of a pipette and distributed by dropwise spreading over an entire 30 cm ² carbon felt surface, weighed beforehand. and deposited on an absorbent paper. The electrode is then dried under a primary vacuum and weighed. Four additional sequences comprising an application of 2.5 ml of the solution followed by drying under a primary vacuum are carried out. The total mass accumulation of deposit is 4.30 mg for a theoretical mass of 4.5 mg. The deposit yield is therefore of the order of 95%. The ratio of the introduced masses of nanoparticles and nanotubes being 1/3, the effective density of platinum nanoparticles (with coating) is of the order of 37 g / cm ^2, approximately of ^the order of 27 micrograms of pure platinum by square centimeter. Figure 36 shows a typical response of electrochemical activity on a 3.14 cm ² cut on the electrode of 30 cm ² relative to the reduction of oxygen. The peak reduction is observed at the potential of 0.51 V, the peak current is - 2.00 mA / cm ² .

Example 21

An example of introducing Nation into the dispersion is shown. Here the deposition efficiencies of the dispersion are low.

In a 100 ml container, 18.3 mg of carbon nanotubes are introduced and 60 ml of isopropanol are added. The resulting medium was sonicated in a Transsonic® TI-H 15 ultrasonic bath at 100% peak power for 1 minute and in 25 kHz scan mode. 12.2 ml of a solution of Pt-I nanoparticles in DMSO at 0.496 mg / ml are then added to the medium maintained under stirring and dropwise at a rate of 1 ml / second. After stirring for 36 hours, 0.1 ml of Nation ® at 10% by weight in water is added and the medium is shaken vigorously using a VIBRAMAX 100 (Heidolph) stirrer at maximum speed for 90 minutes. minutes. 2.5 ml of the dispersion are then removed by means of a pipette and distributed by dropwise spreading over an entire 30 cm ² carbon felt surface, weighed beforehand and deposited on a surface. absorbent paper. The electrode is then dried under a primary vacuum at a temperature of 60 ^° C. and then weighed. The total mass gain of deposit is 1.37 mg for a theoretical weight gain of 2.14 mg. The deposit yield is therefore of the order of 64%, this because of the porosity of the felt and the fact that the dispersion is more finely divided because of the addition of Nation. The ratio of the introduced masses of nanoparticles and nanotubes being 1/3 in the formulation, the effective density of platinum nanoparticles (with coating) is of the order of 4.5 μg / cm ² , ie approximately 3.4 μg of pure platinum per square centimeter. Figure 37 shows a typical response of the electrochemical activity with respect to the reduction of oxygen on a 3.14 cm ² electrode cut on the 30 cm ² electrode. The reduction peak is observed at the potential of 0.40 V, the peak current is - 1.75 mA / cm ² . Example 22

It is shown another example of ^introduction of Nafion in the dispersion. In a 100 ml container, 18.3 mg of carbon nanotubes are introduced and 60 ml of isopropanol are added. Ultrasonic treatment was applied to the medium in a Transsonic® TI-H 15 ultrasonic bath at 100% peak power for 110 minutes and in 25 kHz scan mode. 12.2 ml of a solution of nanoparticles Pt-I in DMSO at 0.496 mg / ml are then added to this medium, which is kept stirring and dropwise at a rate of 1 ml / second. After stirring for 36 hours, 0.1 ml of Nafion® 10% by weight in water is added and the medium is shaken vigorously using a VIBRAMAX 100 (Heidolph) stirrer at maximum speed for 90 minutes. 2.5 ml of the dispersion are then pipetted off six times and dispersed slowly by spreading on a total of 30 cm ² of carbon felt surface, weighed beforehand. deposited on an absorbent paper. The electrode is then dried under a primary vacuum at a temperature of 60 ^° C. and then weighed. The total mass gain of deposit is of the order of 5.7 mg for a theoretical weight gain of the order of 12.88 mg. The yield of the deposit is therefore of the order of 43.5%, this because of the porosity of the felt and the fact that the dispersion is more finely divided because of the addition of Nafion. The ratio of the introduced masses of nanoparticles and nanotubes in the formulation being 1/3, the effective density of platinum nanoparticles (with coating) is of the order of 18 μg / cm ² , which is approximately of the order of 13 , 5 μg of pure platinum per square centimeter. Figure 38 shows a typical response of the electrochemical activity in respect of the reduction of oxygen on an electrode of 3.14 cm ^2, cut on ^the electrode of 30 cm ^2. The reduction peak is observed at the potential of 0.51 V. the peak current is - 4.00 mA / cm ² . Example 23

Here we show that the deposit ^of a layer of nanotubes by filtration retrieves high deposition yields when the dispersion contains Nafion. 39.3 mg of carbon nanotubes are introduced and placed in a 1.5 liter container in which 1 liter of isopropanol is added. Ultrasonic treatment was applied to the medium in a Transsonic® TI-H 15 ultrasonic bath at 100% peak power for 100 minutes in 25 kHz scan mode. On a previously weighed 38 cm ² felt surface, 200 ml of this dispersion are filtered. After drying, the deposited nanotube mass is 7.83 mg for a theoretical mass of 7.86 mg (ie with a yield of almost 100%). On the deposition of nanotubes present on the carbon felt, 5 ml of the dispersion described in Example 22 are homogeneously distributed by means of a pipette. The felt is deposited on a heated plate. at approximately 70 ^° C. The electrode is then dried under vacuum for 60 minutes and a mass increase of 5.51 mg is measured for a theoretical mass increase of 4.29 mg. The deposit yield is here more than 1 10%. An additional drying of 60 minutes at 80 ⁰ C does not cause additional loss of mass, so there are probably some solvents trapped in the structure. It is therefore shown that the deposition of a dispersion containing Nafion® (Example 22) on a support of suitable porosity makes it possible to carry out spreading with a high yield. Given the concentration of platinum nanoparticles in the dispersion of Example 22, a platinum density of approximately 11.1 μg / cm ² is calculated, which corresponds to approximately 8.3 μg / cm ² of pure platinum. . Figure 39 shows a typical response of the electrochemical activity with respect to the reduction of oxygen on a 3.14 cm ² electrode cut on the 38 cm ² electrode. The peak reduction is observed at the potential of 0.41 V, the peak current is - 5.1 1 mA / cm ² . Example 24

Here we show that the deposition ^of a nanotube layer by spreading on a carbon support allows users to find high deposition yields when the dispersion contains Nafion. This example is similar to ^Example 23 except that the deposition of nanotube prior to deposition of the dispersion of ^Example 22 is made by application and not by filtration of a dispersion of nanotubes without platinum.

35 mg of carbon nanotube are introduced and placed in a 100 ml container in which 80 ml of isopropanol are added. Ultrasound treatment is applied to the medium obtained in an ultrasound tank

Transsonic® TI-H 15 at 100% full power for 110 minutes in 25 kHz scan mode. 15 ml of this medium are homogeneously deposited with a pipette on a felt surface of approximately 25 cm ² , previously weighed and deposited on a heating plate at approximately 70 ^° C. The theoretical mass of deposited nanotubes is 6.56 mg. After drying, a mass increase of 6.21 mg is measured, ie a carbon nanotube deposition efficiency of 94.6%. On the same surface replaced on the heating plate, 2.5 ml of the dispersion of Example 22 is pipetted homogeneously. After drying under vacuum, a mass increase of 2.03 is measured. mg for a theoretical value of 2.14 mg. The yield is therefore of the order of 95%. Given the concentration of platinum nanoparticles in the dispersion of Example 22, a platinum density of about 8.0 μg / cm ² is calculated, which corresponds to about 6 μg / cm ² of pure platinum. Figure 40 shows a typical response of electrochemical activity with respect to the reduction of oxygen on a

3.14 cm ² cut on the 25 cm ² electrode. The peak reduction is observed at the potential of 0.33 V, the peak current is - 5.75 mA / cm ² .

Example 25 Here we show two things at once: it is possible to perform spreading by coating a dispersion with two structural elements containing carbonaceous Nation good yield of deposition on a suitable porous support, and - ^that one obtains a dual porosity structure in These conditions.

In this example it is shown that it is also possible to produce spreading deposits on suitable porosity supports from a dispersion such as that of Example 13b containing two structuring carbon elements such as carbon nanotubes and carbon fiber fibers. carbon, in which

Nafion.

As in Example 24, an electrode provided with a nanotube deposit produced by pipetting on a felt surface of about

25cm ² . An area of 7 cm ² is cut into this electrode which is weighed. In a volume of 40 ml of the dispersion used in Example 13b is added

0.230 mL of 10% Nafion solution in diluted water

10 times. The medium is left stirring for one hour. The 7 cm ² electrode is then placed on a heating plate heated to about 80 ^° C. and 25.6 ml of the dispersion are slowly pipetted homogeneously over a surface area of about 5 cm ² . The sample is then placed under a primary vacuum for 120 minutes and then in an oven heated at 80 ^° C. for 20 minutes.

After drying, an increase in mass of 7.92 mg is measured for a theoretical mass of 6.45 mg. The efficiency above 100% shows that there are trapped solvents in the structure, this is probably due to the presence of Nafion ®. Given the characteristics of the dispersion of Example 13b, a nanoparticle density of about 15.3 μg / cm ² is calculated, which corresponds to a pure platinum density of about 11.5 μg / cm ² . FIG. 41 shows an optical microscopy image of the sample which shows that a double-porosity structure similar to that of Example 13 is obtained. FIG. 42 shows a response of the electrochemical activity of an electrode of

3.14 cm ² cut into the 5 cm ² electrode relative to the reduction of ^the oxjgène. The reduction peak is observed at the potential of 0.39 V. The peak current is -17.21 mA / cm ² .

Λ tick electro-cataly Activity of the composites obtained The samples obtained by filtration ^of a nanoparticle assembly / nanotubes on carbon felt are tested in the following electrochemical conditions. A conventional three-electrode assembly is carried out with, preferably, a normal hydrogen electrode in a perchloric acid solution of 1 mol / L and saturated with oxygen under 1 bar of ^"pure oxygen. The scan rate is 100 mV / s.

FIG. 17 illustrates a voltammogram (current-voltage curve with, on the abscissa, the potential V in a sample ELE, relative to the selected reference REF, and, on the ordinate, the current i flowing in the sample ELE and the counter-electrode CELE, as shown in Figure 1). This voltammogram of FIG. 17 is characteristic of the electrochemical aqueous oxygen reduction response for the series of Example 7 (solid line curve) for which it is recalled that the samples are obtained by filtering 10 ml of dispersion on a single plate. carbon felt, to obtain a platinum charge of about 67 μg / cm ² . FIG. 17 compares this voltammogram with that (dotted line curve) of the same sample in a solution containing no oxygen (oxygen evacuated by bubbling argon in the solution). The reduction peak of 1 ^" oxygen occurs at the potential of 0.48 V and is -3.2 mA / cm ² .

This response is compared to that obtained for substantially lower platinum ratios (1/100 (dashed lines) and 1/10 (long / short dashed lines) according to Examples 9 and 8). It can be seen in FIG. 18 that an oxygen reduction current is obtained with Examples 8 and 9 which is not negligible compared to the reference (solid line) of Example 7 (ratio

1/1). These electrodes containing platinum charges very low (ratios 1/10 and 1/100) can therefore be used in advance fuel cell without losses of performance too high compared to usual loads of several hundred μg / cm ² .

As indicated above, these performances can still be improved by treating the electrodes chemically with oxygenated water. FIG. 19 illustrates the voltammograms of the electrodes initially loaded at 65 μg / cm ² in platinum (according to Example 7): without chemical treatment (curve in solid line). with 20 minutes treatment with 30% hydrogen peroxide (dotted line curve), and - with 30 minutes treatment with 30% hydrogen peroxide (long / short dashed curve).

Only the "go" scan (and not the full hysteresis) is shown for clarity in Figure 19.

It should be noted that treatment with hydrogen peroxide causes a loss of deposition, and therefore platinum, due to the release of gas during the treatment, especially since the treatment is long (long / short dashed curve). The electrodes are therefore less charged than initially.

Alternatively, heat treatment at 200 ^° C. under vacuum for 1 to 2 hours gives similar increases in performance. This heat treatment does not cause any significant loss of platinum material. Figure 20 illustrates this improvement.

Moreover, it has been verified by scanning electron microscopy that the two types of treatment (thermal and chemical) do not modify the morphology of the deposition of the nanoparticles on the surface of the nanotubes.

* Possibility of reducing the platinum charge

It is also possible to reduce the platinum loading by decreasing the filtered volume or by diluting the dispersions obtained. With reference to FIG. 20, the results are presented for two equivalent charges (approximately 0.65 μg / cm ² ), obtained: from 100 μL of dispersion to 20 mg / L in nanotubes (solid curve), and from 1 mL of 2 mg / L dispersion (dotted line curve), which corresponds to the previous solution diluted ten times. To improve their performance, the electrodes were heat-treated (1 to 2 hours at 200 ^° C. under vacuum). Given the uncertainties on the deposited mass and the oxygen concentration in solution, we can consider that the two samples respond in very similar ways.

The electrodes containing the lowest platinum loading tested (and whose electrocatalytic activity has nevertheless been demonstrated) were made with a composite dispersion of platinum nanoparticles / carbon nanotubes: at 1% platinum, 20 mg / L of nanotubes, and

5 mL of filtered dispersion on carbon felt.

The electrodes obtained were then heat-treated at 200 ^° C. before being tested in a three-electrode electrochemical cell.

Figure 22 shows the response of two of these electrodes (platinum density 0.33 μg / cm ² - dashed lines and long / short dashes) compared to an electrode with twice as much platinum (10 mL of the same filtered dispersion - 0.65 μg / cm ² of platinum - solid line). Given the uncertainties, the reproducibility of the results is good.

* Results obtained with particular achievements of the structuring material

Samples from embodiments similar to those of Example 11 also show a catalytic activity, with a reduction of aqueous oxygen, as shown in Figure 23. Here, 20 ml of dispersion containing carbon, filtered in a single pass on a deposit previous nanotubes. with an estimated filtration efficiency of 36% and a platinum loading estimated at 39 μg / cm ² . This sample n ^* has not been pretreated.

The samples from Example 12 also show catalytic activity, as shown in Figure 23. Here, 5 mL of dispersion was filtered. The theoretical maximum platinum loading is estimated at 1.1 μg / cm ² .

The shoulder observed is attributed to the reduction of aqueous oxygen at the platinum surface. This sample has not been pre-processed.

Claims

A process for preparing a catalyst composition comprising a carbonaceous structuring material associated with a catalyst. characterized in that it comprises the following steps: preparing a mixture ^of a solution of a first solvent comprising a carbonated structuring material and ^a solution of a second solvent comprising the catalyst, stirring the resulting mixture until precipitating the catalyst on the carbonaceous structuring material, and in that the catalyst and the structuring material are insoluble in the mixture of the first and the second solvent.

2. Method according to claim 1, characterized in that the catalyst is deposited on the structuring material, during said precipitation.

3. Method according to one of claims 1 and 2, characterized in that the carbonaceous structuring material comprises carbon nanotubes.

4. Method according ^to one of claims 1 to 3, characterized in that the carbonated structuring material comprises carbon black.

5. Method according to one of claims 1 to 4, characterized in that the carbonaceous structuring material comprises carbon fibers.

6. Method according to at least two of claims 3 to 5, characterized in that the carbonaceous structuring material comprises a mixture of carbon nanotubes and / or carbon black and / or carbon fibers.

7. Method according to one of the preceding claims, characterized in that the catalyst comprises metal particles.

8. Method according to claim 7, characterized in that said metal particles comprise at least one platinoid.

9. A method according to claim 8. characterized in that said particles have a size in ^the nanometer scale and comprise an organic coating of platinum metal (Pt-O, Pt-I; Pt-2, Pt-3).

10. Method according to one of the preceding claims, characterized in that the first solvent is a hydroxylated solvent among isopropanol, methanol, ethanol, a glycol such as ethylene glycol, and / or a mixture of these solvents .

11. Method according to one of the preceding claims, characterized in that the second solvent is of the dichloromethane type, dimethylsulfoxide, chloroform and / or a mixture of these solvents.

12. Method according to one of the preceding claims, characterized in that the catalyst is insoluble in the first solvent.

13. Method according to one of the preceding claims, characterized in that the solubility of the catalyst in the first solvent and / or in the mixture is less than 10 ^"9 mol / L.

14. Method according to one of the preceding claims, characterized in that the concentration of carbonaceous structuring material in the first solvent is between 1 mg / L and 10 g / L.

15. The method of claim 14, characterized in that the concentration of the carbonaceous material is a few tens of milligrams per liter.

16. Method according to one of the preceding claims, characterized in that the concentration of the catalyst in the second solvent is between Img / L and 10 g / L.

17. The method of claim 16. characterized in that the concentration of the catalyst in the second solvent is of the order of a few hundred micrograms per milliliter.

18. Method according to one of the preceding claims, characterized in that the mixture comprises more of the first solvent including the carbonaceous structuring material than the second solvent including the catalyst.

19. The method of claim 18, characterized in that the volume ratio of the second solvent comprising the catalyst relative to the first solvent comprising the carbonaceous structuring material is less than 1 to 5 and preferably of the order of 1 to 25.

20. Method according to one of the preceding claims, characterized in that the second solvent including the catalyst is added to the first solvent including the carbonaceous structuring material, in small successive amounts, to form said mixture.

21. Method according to one of the preceding claims, characterized in that the mixture is subjected to mechanical stirring (AGM) to distribute the catalyst substantially homogeneously on the carbonaceous structuring material.

22. The method of claim 21, characterized in that the mechanical stirring is activated at least ^until to obtain an optical appearance of the mixture near an optical appearance of a catalyst-free solution.

23. The method of claim 22, characterized in that ^the mechanical stirring is discontinued or activated in accordance with a reading optical (LO) of a supernatant in the mixture.

24. Method according to one of the preceding claims, characterized in that it further comprises a step of applying ^an ultrasonic treatment (US) at least carbonated structuring material in the first solvent.

25. The method of claim 24, taken in combination with claim 3, characterized in that the ultrasonic treatment separates nanotubes aggregates and / or breaks at least part of the nanotubes to reduce their size.

26. Process according to one of the preceding claims, characterized in that at least one surfactant is added to the first solvent comprising the carbonaceous structuring material and / or to the mixture.

27. The method of claim 26, characterized in that the surfactant is Nafion®.

28. Method according to one of the preceding claims, characterized in that it further comprises a step of separating and extracting the catalyst composition comprising the carbon structuring material associated with the catalyst, out of the mixture.

29. The method of claim 28, characterized in that the catalytic composition is extracted by filtering or spreading on a porous support.

30. Method according to one of Claims 28 and 29 taken in combination with Claim 9, characterized in ^that it further comprises a step of chemical or thermal treatment of said catalytic composition to remove said organic coating.

31. Method according ^to one of the preceding claims, wherein the catalyst composition has a modular electrochemical behavior function: firstly, the volume loading of the catalyst in the composition, and on the other hand, the surface density of the catalyst in the composition, characterized in that the method comprises a joint control ^of at least two parameters: first, a total volume of catalyst composition suspended in the mixture and on the other hand, a proportion by weight of the material carbonized with respect to the catalyst.

32. Catalytic composition obtained by the implementation of the method according to one of the preceding claims, characterized in that it comprises catalyst particles distributed on the carbonaceous structuring material.

33. Composition according to claim 32, characterized in that it comprises at least 80% of the catalyst initially introduced into the mixture.

34. Composition according to one of claims 32 and 33, characterized in that it comprises an areal density in the catalyst ^of at least 0.1 mg / cm ^2.

35. Composition according to one of claims 32 to 34, characterized in that it has an electrochemical activity.

36. An electrode, in particular a fuel cell, characterized in that ^it comprises a composition according to one of claims 32 to 35.