MXPA96003366A - Electroactivated material, its preparation and its employment in producing cat components - Google Patents

Abstract

Electroactivated material comprising fibers of which at least a portion is electrically conductive, a binder, characterized in that they further comprise an electrocatilitic agent consisting of ruthenium oxide, platinum, palladium, iridium or mixtures thereof, or of one or a plurality of amide oxides , distributed at least partly in an electroconductive support. The electroactivated material is particularly used as a cathode element of an electrolysis cell and in particular, a cell for the electrolysis of aqueous solutions of sodium chloride. The present invention also discloses a composite material comprising (a) a high porosity material, (b) the aforementioned electroactivated material. Finally, the invention relates to a composite material comprising from one phase to the other: (a) a metal surface of high porosity, (b) the aforementioned electroactivated material, (c) a separated

Description

ELECTROACTIVE MATERIAL. YOUR PREPARATION AND YOUR EMPLOYMENT IN PRODUCING CÁTODO COMPONENTS The present invention relates to an electroactivated material, which comprises fibers and a binder and additionally has an electrocatalytic agent in the form of particles including a precious metal oxide, or in the form of particles including a support and a coating based on such oxide.

The electroactivated material can be used especially as a component of the cathode of an electrolysis cell and, in particular, of a cell for the electrolysis of aqueous solutions of sodium chloride.

Also, it refers to a composite material comprising said material and to processes for the preparation of each of the two materials.

In recent years, the use of cathodes consisting of a metal surface, on which a fibrous sheet is deposited and then, optionally, a diaphragm, has been extended in the field of electrolysis of aqueous solutions of sodium chloride. These cathodes have a low overpotential with respect to the reaction for the production of hydrogen at the cathode and for this reason it has been possible to reduce the energy consumption.

It is also known to add electrocatalytic agents, such as nickel, for example, to the aforementioned sheet, in order to further increase its behavior. These agents can be used in the form of a powder dispersed in the fibrous sheet, mentioned above, or alternatively in the form of a deposit on the sheet, obtained, for example, by an electrochemical route.

However, cathodes of this type do not have a very high resistance to poisoning, due to the nature of the electrocatalytic agents and, therefore, they are deactivated relatively quickly.

The object of the present invention is to propose an electroactivated material and a composite material comprising the latter, which can be used as the cathode in a cell for the electrolysis of aqueous solutions of sodium chloride, in which the resistance to poisoning and , consequently, the time of life, they are increased. Therefore, the first object of the present invention is an electroactivated material comprising fibers, of which at least part are electrically conductive, and a binder and additionally comprises an electrocatalytic agent consisting of particles formed of ruthenium oxide , platinum, palladium or iridium, or their mixtures, or one or more of these oxides distributed, at least partially, on an electrically conductive support.

A second object of the invention consists of a composite material comprising: (a) a high porosity material and (b) the aforementioned electroactivated material.

A third object of the invention consists of a composite material comprising, from one face towards the other: (a) a metal surface of high porosity, (b) the aforementioned electroactivated material, and (c) a separator.

The invention also relates to a method for the preparation of an electroactivated material, which consists of carrying out the following steps: (a) preparing an aqueous suspension comprising the fibers, the binder, the electrocatalytic agent and, optionally, adjuvants; (b) deposit a sheet by filtering the suspension, with a programmed vacuum, through a material of high porosity; (c) remove the liquid and the sheet, thus formed, is optionally dried; (d) sinter, optionally, the sheet thus obtained.

The final object of the present invention is a method for the preparation of a composite material. This consists of carrying out the following stages: (a) preparing an aqueous suspension comprising the fibers, the binder, the electrocatalytic agent and, optionally, adjuvants; (b) deposit a sheet by filtering the suspension, with a programmed vacuum, through a material of high porosity; (c) remove the liquid and the sheet, thus formed, is dried, optionally; (d) the sheet, thus obtained, is optionally sintered; (e) a dispersion is deposited, in water or in an aqueous solution of sodium hydroxide, comprising the fibers, a binder and, optionally, adjuvants, on the sheet, filtering under a programmed vacuum; (f) remove the liquid and the diaphragm, thus formed, is optionally dried; (g) the whole unit sinters.

However, other advantages and features of the invention will become more readily apparent from the reading of the description and the examples that follow.

As indicated above, the electro-catalytic agent, which forms part of the composition of the electroactivated material, according to the invention, can be supplied in the form of particles based on ruthenium oxide, platinum, iridium or palladium, these oxides being alone or as a mixture. The agent can additionally be provided in the form of particles, which consist of an electrically conductive support, comprising, at least in part of the particles, a coating in the form of ruthenium oxide, platinum, iridium or palladium, these oxides being alone or as a mixture.

In the following, the aforementioned list will be denoted by the term precious metal (s). It will be understood that the precious metal term represents, sub-sequently, without distinction, one or more of the aforementioned metals.

The combination of these two variants can, of course, be considered.

The mixture will be understood means, first of all, the particles comprising several oxides or alternatively particles containing at least one oxide, in mixture with other particles, comprising at least one different oxide, or finally these two possibilities simultaneously. Such a definition is valid if the oxides are found throughout the thickness of the particle or simply in the form of a coating.

The electrocatalytic agent, according to the invention, is preferably provided in the form of a coating on a support.

The support consists of a material which is electrically conductive and stable under the conditions of a subsequent application of the material (pH and perature, especially).

More particularly, the latter is selected from iron, cobalt, nickel, Raney iron, Raney cobalt, Raney nickel, the elements of columns IV-A and V-A of the Periodic Table, carbon or graphite. Here and throughout the description, the commentaries related to the Periodic Table of the elements refer to those that appear in the supplement to the Bulletin de la Société Chimique de France (No. 1, January 1966).

The support is preferably supplied in the form of a powder. More particularly, the particle size of the support is between 1 and 100 μm. The specific surface of the support is not greater than 1000 m2 / g. More particularly, the specific surface varies between 5 and 500 m2 / g.

The proportion by weight, between the coating and the support, varies between 0.5 and 50. It should be noted that proportions outside, and more particularly higher than, those indicated above, can be considered. However, this does not introduce specific advantages in the behavior of the electroactivated material, while unnecessarily increasing its cost.

The electrocatalytic agent according to the invention can additionally comprise additives selected from iron, cobalt, nickel and / or their oxides.

The proportion of the additives, with respect to the precious metal oxide (by weight), varies from 0 to 50%.

The electrocatalytic agent that forms part of the composition of the electroactivated material, according to the invention, can be distributed or uniformly within said material or also assembled in a specific region of the latter, for example, in the periphery.

However, according to a preferred variant for carrying out the variant of the invention, the electrocatalytic agent is distributed uniformly throughout the body of the electroactivated material. The amount of the electrocatalytic agent in the material, according to the invention, represents 10 to 0% by weight, with respect to the combined fibers, binder and electrocatalytic agent.

In addition to this electrocatalytic agent, the material according to the invention comprises fibers, of which at least a part are electrically conductive.

These fibers are provided in the form of filaments, whose diameter is generally less than 1 mm and preferably between 10"" and 0.1 mm, and whose length is greater than 0.5 mm and preferably between 1 and 20 mm, said material having a resistivity equal to, or less than, 0.4 ohm-cm. Fibers consisting entirely of an electrically conductive material in intrinsic form. Mention may be made, as examples, of such materials of metal fibers and, in particular, iron fibers, fibers of ferrous alloys or nickel fibers, or carbon or graphite fibers.

It is also possible to use fibers that result from materials that are not electrically conductive, but that are made conductive by a treatment: mention may be made, as examples, of the asbestos fibers or zirconia fibers, made conductive by the chemical deposit or electrochemical of a metal, such as nickel. In the case of fibers made conductive by a treatment, this will be carried out under conditions that the resulting fiber has the aforementioned resistivity. According to a preferred embodiment of the invention, the electroactivated material comprises intrinsically conductive fibers and, more particularly, carbon or graphite fibers. Also, use is made of fibers having a monodisperse length, that is to say that the length of at least 80% and, more particularly, 90% of the fibers corresponds to the average length of the fibers ± 20% and advantageously around ± 10%.

The conductive fibers can additionally be combined with non-electrically conductive fibers, as long as the resistivity of the material is not greater than 0.4 ohm-cm. These fibers are generally provided in the form of filaments, whose geometric characteristics are analogous to those given for the conductive fibers, but the resistivity will be, by convention, greater than 0.4 ohm-cm. Mention may especially be made, as an illustration of non-conductive fibers, of inorganic fibers, such as asbestos fibers, glass fibers, quartz fibers, zirconia fibers or titanate fibers, or organic fibers, such as polypropylene fibers. or polyethylene, this polypropylene or polyethylene being optionally halogenated and especially fluorinated, poly-halovinylidene fibers and especially poly (vinylidene fluoride) fibers or alternatively fluorinated polymer fibers, which will appear later with respect to the binder of the sheets, according to the invention. According to a first variant, use is made of asbestos fibers, in particular in combination with carbon or graphite fibers.

According to a second variant, polytetrafluoroethylene fibers, also known hereinafter as PTFE fibers, are taken, in particular in combination with inorganic fibers, mentioned previously.

Preferably, the PTFE fibers have a diameter (D) generally between 10 and 500 μm, and their length (L) is such that the L / D ratio is between 5 and 500. Preferably, the PTFE fibers are used that the average dimensions are between 1 and 10 mm, for the length, and between 0 and 200 μm, for the diameter. Its preparation is described in U.S. Patent No. 4,444,640 and this type of PTFE fibers are known to those skilled in the art.

In a combination of conductive and non-conductive fibers, the proportion of the non-conductive fibers can represent up to 90% by weight and preferably between 20 and 70%. The electroactivated material according to the invention also comprises a binder selected from fluorinated polymers. The fluorinated polymer is a homopolymer or a copolymer derived, at least in part, from olefinic monomers, which are entirely substituted with fluorine atoms or entirely substituted with a combination of fluorine atoms and at least one of the chlorine atoms, bromine or iodine, per monomer. Examples of fluorinated homo- or copolymers may consist of polymers or copolymers derived from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene or bromotrifluoroethylene. These fluorinated polymers may also contain up to 75 mole percent units derived from other ethylenically unsaturated monomers, containing at least as many fluorine atoms as carbon atoms, such as, for example, vinylidene (di) fluoride or vinyl ethers and perfluoroalkyl, such as perfluoroalkoxyethylene. It is naturally possible to use in the invention several fluorinated homo- or copolymers, as defined above. Needless to say, it does not depart from the scope of the invention to combine with these fluorinated polymers a small amount, for example, up to 10 or 15% by weight, of polymers in which the molecule does not contain fluorine atoms, such as , for example, polypropylene. The binder can be provided in the form of a dry powder or a latex, that is to say an aqueous suspension, in which the solids content is between 30 and 70%. The amount of fibers in an electro-activated material, according to the present invention, represents 10 to 65% by weight, with respect to the combined fibers, the binder and the electrocatalytic agent.

The amount of the binder is between 5 and 20% by weight, with respect to the combined fibers, binder and electrocatalytic agent. However, in order to ensure a good consolidation in the electro-activated material, the binder preferably represents 20 to 50% by weight with respect to the fibers and the binder of the subsystem.

The materials, according to the present invention, may also contain adjuvants, such as, in particular, surfactants. In particular, ethoxylated alcohols or fluorocarbon compounds containing functionalized groups, alone or as a mixture, can be used as nonionic surfactants; these alcohols or these fluorocarbon compounds generally have carbon chains from Cg to C2o. Preferably use is made of ethoxylated alcohols which are ethoxylated alkylphenols, such as, in particular, octoxins.

The amount of the surfactant, which may be present in the sheets, according to the invention, can reach 10% by weight, with respect to the combined fibers, binder and electrocatalytic agent, and, more specifically, from 0.1 to 5. % by weight, with respect to the combined fibers, binder and electrocatalytic agent.

It is probably possible to use a thickener. The thickener is understood to mean, in accordance with the present invention, a compound which increases the viscosity of the solution and which has water retention properties, Natural or synthetic polysaccharides are generally used. of the biopolymers obtained by the fermentation of a carbohydrate under the effect of microorganisms.Xanthan gum is used commercially.This xanthan gum is synthesized using bacteria belonging to the genus of Xanthomonas and, more particularly, to the species described in Bergey's Manual of Determination Bacteriology (8 * Edition - 1974 - Williams N. Wilkins Co., Baltimore), such as Xanthomonas Jbegoniae, Xanthomonas campestris, Xanthomonas carotae, Xanthomonas hederae, Xanthomonas incanae, Xanthomonas malvacearum, Xanthomonas papavericola, Xanthomonas phaseoli , Xanthomonas pisi, Xanthomonas vasculorum Xanthomonas vesicatoria, Xanthomonas vitians or Xanthomonas pelargonil The Xanthomonas campestris specie is particularly highly suitable for the synthesis of xanthan gum.

Mention can be made, among other microorganisms capable of producing polysaccharides of similar properties, of bacteria belonging to the genus of Arthrojbacter, to the genus Erwinia, to the genus Azobacter or to the genus Agrobacter or to fungi belonging to the genus Sclerotium.

The xanthan gum can be obtained by any recourse known per se. The polysaccharide is conventionally isolated from the fermentation broth by evaporation, drying and grinding or by precipitation by means of a lower alcohol, separation of the liquid, drying and grinding, in order to obtain a powder. Commercially available powders have a particle size generally between 50 and 250 μm and a bulk density greater than about 0.7.

The amount of the thickener generally varies between 5 and 5% by weight, with respect to the combined fibers, binder and electrocatalytic agent.

The materials may also contain porogenic agents. It will be understood that when porogenic agents are used in the final material, the porosity, which is adjusted or modified under the effect of the decomposition or removal of these agents, in principle, no longer contains such agents. Mention may be made, as an illustration of the porogenic agents, of inorganic salts, which can then be removed by leaching, as well as salts that can be removed by chemical or thermal decomposition. These various products can, in particular, be selected from the alkali metal or alkaline earth metal salts, such as halides, sulfates, sulfonates, bisulfites, phosphates, carbonates or bicarbonates. Amphoteric alumina can also be mentioned. According to a specific embodiment of the invention, use is made of silica or its derivatives as the porogenic agent, which can be removed in sequence with n alkaline treatment.

All types of silica are suitable for this use and, more particularly, precipitated silicas or pyrogenic silicas.

The specific surface of this silica is, more particularly, between 100 and 300 m2 / g.

The amount and particle size of the porogenic agents are closely linked to the application for which the materials are intended. Simply by size order form, the particle size of the porogenic agents often varies between 1 and 50 μm and preferably between 1 and 15 μm. The quantity is selected according to the desired porosity, with the latter possibly reaching 90% or truly more (in accordance with the ASTM D 276-72 standard). A second object of the present invention consists of a composite material comprising a high porosity composite and having the electroactivated material described above.

The high porosity compound is generally chosen from metal surfaces or alternatively from fabrics, such as asbestos fabrics, wherein the mesh opening can be between 20 μm and 5 mm.

According to a preferred embodiment, the high porosity compound is a metal surface, known as the elemental cathode, which is made more particularly of iron, nickel or alternatively of stainless steel.

It is generally in the form of a mesh or a perforated metal component, which acts, more particularly, as a cathode in an electrolysis cell. This cathode may consist of a flat surface or of a set of flat surfaces or, in the case of electrolysis cells, of the type of a "glove finger" shall be provided in the form of cylinders, the guideline of which is one more surface. or less complex, generally of substantially rectangular shape, with rounded corners.

The composite material can be further combined with a separator, which can be a diaphragm or a membrane.

Generally, the diaphragms comprise fibers and a binder, selected from fluorinated polymers, as well as conventional adjuvants.

Anything previously exposed in relation to the fibers, binder and adjuvants used, remains valid and consequently will not be repeated again in this part.

In order not to go into excessive details, it is specified that the techniques for the manufacture of porous and microporous membranes and diaphragms are described in the following French patents: FR 2,229,739, FR 2,280,435 and FR 2,280,609 and French Patent Applications FR 81 688 and 85 4327, FR 89 10938 and FR 89 10937, the contents of which are incorporated herein by reference. Before describing the method for the preparation of the activated material and the composite material, according to the invention, a process for the preparation of the electrocatalytic agent will be presented.

The electrocatalytic agent used in the present invention can be obtained by any means known to those skilled in the art, which makes it possible, in particular in the case of supported particles, to have access to a particle structure comprising a support having a coating .

One of the suitable methods is to prepare a suspension or solution of a ruthenium, platinum, palladium or iridium compound, or mixtures thereof, optionally in the presence of the aforementioned additives and / or supports. The compounds of the precise metals, used for the preparation of the electrocatalytic agents, according to the invention, are selected from oxides or compounds capable of being converted into oxides by an appropriate treatment by heat (precursors).

Mention may be made, as the precursors, without intending to be limited to, the salts of organic or inorganic acids, ta > l as, for example, nitrates, halides, carbonates, sulfates, acetates, acetylacetonates, oxalates, tartrates, malonates or succinates.

Thus, ruthenium chloride, hexachloro-platinic acid, palladium nitrate, palladium chloride, iridium chloride or ruthenium nitrosotrinitrate.

These salts are, therefore, suspended or dissolved in a solvent. The solvent is generally selected from water or C ^ -Cg alcohols, such as methanol, ethanol or isopropanol. The content of the precious metal salt of the solution or suspension is generally between 0.1 and 5 M.

In the case where the additives form part of the composition of the electrocatalytic agents, they can be supplied in the form of oxide or in the form of oxide precursors or alternatively in a metal form. If the precursors are used, what has been said above with respect to precious metal precursors remains valid.

If a support is used and according to its nature, it may be preferable to use it after it has been subjected to a specific surface treatment. Thus, in the case where carbon is used as the support, first of all an oxidation is carried out, in order to increase the concentration of oxygen-containing groups on the surface. The treatment can be carried out in the presence of inorganic acids, such as nitric acid or sulfuric acid in particular, or by a thermal treatment under an oxidizing atmosphere.

The oxidation is preferably carried out in a liquid phase, by immersing the carbon in a solution of nitric acid at its boiling point, for about one hour. At the conclusion of this treatment, the product obtained is filtered and then rinsed with water.

If the support used is pyrophoric, as in particular the case of Raney nickel, a controlled oxidation is carried out, in the presence of hydrogen hydroperoxide, for example. According to a first variant of the preparation of an electrocatalytic agent, according to the invention, all constituent components of the agent are mixed in the form of a solution or suspension.

This variant is particularly appropriate in the case where the agent comprises a support and in the case where use is made of a precursor salt of the precious metal oxides, if appropriate comprising additives.

The mixing is generally carried out with stirring, at a temperature in the region of room temperature.

The components are contacted for a period of time from a few minutes to 24 hours.

According to a second variant, a solution or suspension of the constituent components of the electrocatalytic agent is prepared and a precipitation step is carried out. In such a case, the precious metal is used in the form of a solution of the precursors.

An agent which precipitates at least the metal is added to the solution or suspension. It should be noted that the precipitation of the additives, if they are present, is also possible.

All compounds are capable of being used, as long as they combine at least the precious metal in the form of an insoluble compound. Mention may be made, by way of example, of the hydroxides, carbonates or bicarbonates of an alkali metal or an alkaline earth metal, such as sodium, calcium or potassium.

Similarly, mention may be made of aqueous ammonia.

The precipitation agent is conventionally introduced into the support / precious metal mixture, but simultaneous introduction can be carried out.

This operation takes place with agitation and at a temperature in the region of room temperature. In such a case, it is possible to allow, after the introduction of the precipitation agent, a ripening period, optionally with stirring, from 1 to 10 hours. Following the filtration, the resulting solid is generally rinsed with a solvent, which may be identical or different from that used for the operation of contacting the components. Whichever variant is used, the next step is a drying step. According to a first embodiment, this operation can take place under vacuum or under air, at a temperature between the ambient temperature and the temperature at which the solvent is removed.

The duration of this operation is approximately a few minutes up to 12 hours. A second method consists in drying the solution by atomization. The latter can be carried out by means of any known sprayer, especially of the Buchi type.

However, according to a specific embodiment, the equipment is used as described in French Patent Applications FR 2,257,326, FR 2,419,754 and FR 2,431,321. In this case, the treatment gases are driven by a helical movement and flow in a vortex. The solution or suspension to be dried is injected along a trajectory, which joins the axis of symmetry of the helical trajectories of the gases, which makes it possible to completely transfer the amount of movement of the gases to the solution or suspension. The gases do provide a double function, spray the solution or suspension (conversion into fine droplets) and dry these droplets. Likewise, the residence time is less than 0.1 second, which decreases any risk of overheating as a result of excessively long contact with the gases.

"~" The treatment temperature is such that it makes it possible to evaporate the solvent and in the case where a salt of a precious metal has been used, to actually start the conversion of the salt to the oxide.

In general, and depending on the respective flow rates of the gases and the solution or suspension to be dried, the inlet temperature of the gases is between 600 and 900 ° C, preferably between 700 and 900 ° C. , and the exit temperature of the gases between 100 and 300 ° C, preferably between 150 and 250 ° C.

Before drying, a solid separation step can be carried out, if the variant used comprises passing through a suspension. The separation is generally carried out by filtration or centrifugation. The filtration is carried out by any means known to those skilled in the art, at atmospheric pressure or under vacuum. The dried product obtained is then subjected to a heat treatment in order to convert the salt of the precious metal into the oxide. This operation is carried out under a stream of air or oxygen, at a temperature between 200 and 800 ° C, depending on the nature of the precursor. The duration depends on the nature of the support, if present. Thus, the duration of the heat treatment may be longer if the support withstands high temperatures without deterioration or is converted to a compound which is not electrically conductive. In the form of an indication, the duration varies from a few seconds to 1 hour.

At the conclusion of the heat treatment, the particles can be deagglomerated by any means known to those skilled in the art, such as grinding. Finally, the additional rinsing steps, followed by filtration or centrifugation and by drying, can be carried out. Anything that has been described before with respect to these steps remains valid and will not be exposed here again.

The mechanical synthesis represents another method which is suitable for the preparation of the electro-catalytic agent.

This method is particularly appropriate when a support, a precious metal compound and, optionally, additives, are used in the solid form. In this case, a support is used which has a greater hardness than that of the two aforementioned compounds. In this way, after grinding the combined compounds, the formed particles of the support are obtained, whose periphery is enriched with the precious metal compound and, optionally, additives.

At the end of the grinding, a heat treatment may be necessary to convert the precious metal compound to the corresponding oxide.

This operation is then carried out under an oxidizing atmosphere at varying temperatures, depending on the nature of the compound to be converted, between 200 and 800 ° C.

If the compound is used in the oxide form, heat treatment is not necessary.

A method for the preparation of the electroactivated material will also now be described.

Thus, the material, according to the invention, is capable of being obtained by carrying out the following steps: (a) preparing an aqueous suspension comprising the fibers, the binder and the electrocatalytic agent and, optionally, adjuvants; (b) deposit a sheet by filtering the suspension, under a programmed vacuum, through a material of high porosity; (c) remove the liquid and the sheet, thus formed, is dried, optionally; and (d) the sheet, thus obtained, is sintered, optionally.

The amount of each of the various constituents of the aqueous suspension, prepared in Step (a), is such that it makes it possible to obtain a material having the characteristics of the composition, indicated particularly above. In a known manner and, mainly for reasons of ease of handling on an industrial scale, the solids content (i.e., fibers, binder, electrocatalytic agent and adjuvants) of the aforementioned dispersion is low. Generally of the order of 1 to 5% by weight of the total mixture.

Also, it may be advantageous to incorporate, in the suspension, a thickening agent, such as, for example, natural or synthetic polysaccharides. The dispersion can be obtained by mixing each of the constituents, in the required proportions, with water, optionally with adjuvants of the surfactant or the type of thickener added.

Then a sheet of the resulting dispersion is formed by filtration, under a programmed vacuum, through a high porosity material. This vacuum program consists of moving from atmospheric pressure to a final negative pressure (1.5 x 10 ~ 3 up to 4 x 10 ~ 4 Pa) and can be carried out continuously or in stages.

It is indicated here that the sheet is understood to be an average material whose thickness is generally between 0.1 and 5 mm and whose surface area can reach several square meters.

The sheet, from which the liquid has been removed and optionally dried, can be sintered.

The sintering is carried out conventionally under air, at a temperature higher than the softening point of the binder.

In the case where only the preparation of the electroactivated material is attempted, according to the invention, a subsequent treatment will be carried out in order to remove the porogenic agent, if present. Thus, in the case where the porogenic agent is silica, a treatment with sodium hydroxide is carried out.

If the object is to prepare a composite material, according to the invention, on a sheet obtained by carrying out the above steps, a dispersion is deposited by filtration under a programmed vacuum. This dispersion comprises the constituent components of a diaphragm and is obtained in a manner entirely analogous to the process used to prepare the first dispersion.

However, it should be noted that the constituent components of this dispersion can be dispersed in water or in an aqueous solution of sodium hydroxide.

In the second case, care will be taken in selecting the constituent components that are dispersible in such medium.

Analogously to the preparation of the first sheet, the liquid is removed and the diaphragm, thus formed, is optionally dried.

A sintering operation of the whole unit is carried out subsequently under conditions identical to those mentioned in Step (d).

It should be noted that various variants are possible with respect to sintering.

According to a first variant, each mentioned sintering step is carried out.

It should also be noted that this variant is particularly appropriate when the binder used in each of the dispersions is different.

Such a variant can be used similarly when the first dispersion comprises a porogenic agent, which can be removed by an alkaline treatment and when an aqueous solution of sodium hydroxide is the dispersion medium of the second. In that case, it is specified that a step of removal of the porogenic agent, if it forms part of the composition of the first dispersion, is not necessary after the sintering operation of Step (d), since the subsequent deposit of 1 diaphragm corresponds to treatment. According to a second variant and in the specific case where the two dispersions are in an aqueous medium and where the binder, which forms part of the composition of the two dispersions, mentioned above, is the same, advantageously only a simple stage of sintering is carried out, which corresponds to the Stage (f).

Concrete, but not limiting, examples of the invention will now be presented. E J E M P L O S EXAMPLES 1 TO 4 The object of Examples 1 to 4 is the study of the behavior of the electrocatalytic agent, in the form of pellets, obtained according to the following method: The electrocatalytic agent is mixed with a suspension of PTFE, which contains 60% solids, and the entire mixture is pressed against a nickel mesh with a pressure of 1000 kg / cm2.

A consolidation stage of the structure is then carried out, subjecting the pellets to a temperature of 350 ° -C. The compact pellets obtained were tested as the cathode of a cell for the electrolysis of an aqueous solution of sodium hydroxide.

Example 1, Comparative; The electrocatalytic agent is a nickel powder (spherical particles of 5 μm). Example 2; The electrocatalytic agent is ruthenium oxide.

Example 3; The electrocatalytic agent is a mixture obtained by mechanical synthesis, comprising the nickel powder of Example 1 and the ruthenium oxide powder, obtained in Example 2, in a ratio of 70/30 by weight.

This mixture was placed in a steel vessel under an inert nitrogen atmosphere and in the presence of small steel spheres (steel H-440). The whole mixture was stirred for 2 hours in a SPEX-8000 shaker. The milling process leads to a mixture of Ni and RuC > 2, in the form of particles, whose periphery is enriched with ruthenium oxide, with respect to the core. The average composition, by mass, is Ni n Ußn- Example 4: The electrocatalytic agent is based on graphite and ruthenium oxide. A graphite powder (Lonza), with a specific surface area of 300 m2 / g, was placed, for one hour, in a solution of nitric acid at its boiling point. The powder was then filtered, rinsed and dried. The powder was introduced into an aqueous solution of RUCI3 (10_1 M) and the mixture was stirred for 1 hour. The mixture was filtered and the resulting powder was rinsed 4 times with distilled water and dried for 12 hours at HOSC.

The final sintering was carried out at a temperature of 4502C powder, under an air stream, for 30 minutes. A stage of deagglomeration of the aggregates was performed by grinding.

The electrocatalytic agent, thus prepared, consists of the starting graphite covered with a layer of RUO3. The RUO3 percentage per mass is 9.95 ± 0.05%.

The electrocatalytic agents formed pellets, according to the procedure described above and the pellets obtained were tested in the evolution of hydrogen, under the following experimental conditions: - current density of 300 mA / cm2 - 6N NaOH solution - temperature of 202c.

The overpotentials represented in the table were determined from the potentials measured with respect to the reference electrode of Hg / HgO, connected to the electrode surface by means of a Luggin capillary.

The ohmic drop due to the electrical resistance of the electrolyte was corrected by impedometry.

A decrease in the overpotential and a stabilization of the latter, with respect to nickel, were observed using an electrocatalytic agent according to the invention. Examples 5 to 8 The object of these examples is the study of the behavior of electroactivated materials, that is to say composite materials consisting of an elemental cathode and a sheet comprising an electrocatalytic agent, as described in Examples 1 to 4. The preparation of the material high porosity + composed of the electroactivated material, which follows, is common for Examples 5 to 8: a) Preparation of the suspension 30 g of carbon fibers and 70 g of chrysotile asbestos fibers were placed in 7000 ml of softened water containing 3.3 g of surfactant (Triton® X 100, from the company Rohm and Haas).

After rotary stirring for 30 minutes, 35 g of PTFE was introduced in the form of a latex, with 60% solids content.

After homogenization, 100 g of Tixosil® 33J silica (Rhóne-Poulenc) was added and stirring was continued for 30 minutes. bl Introduction of electrocatalytic agent The electrocatalytic agent was incorporated into the suspension described in (a): Example 5, Comparative; 120 g of nickel, according to Example 1 Example 6; 115 g of ruthenium oxide, according to Example 2.

Example 7; 60 g of the electrocatalytic agent, according to example 3. Example 8; 170 g of the electrocatalytic agent, according to Example 4. c) Preparation of the composite material The suspension prepared in (b) was filtered through an elemental iron catheter, folded and rolled (diameter of the wires 2 mm, opening of 2 mm), applying a vacuum gradient from atmospheric pressure to a negative pressure of 300 mbar.

The combined elemental cathode and the electroactivated sheet unit were taken to an oven at 3502C for 30 minutes. d) Use in electrolysis The prepared materials were used as a component of the cathode in a cell for the electrolysis of an aqueous solution of 6N sodium hydroxide at a temperature of 802C, which is filtered through the cathode assembly.

The potential was measured with respect to the reference electrode of Hg / HgO, connected to the surface of the leaf by means of a Luggin capillary.

The ohmic drop due to the electrical resistance of the electrolyte was corrected by impedometry.

The density of the electrolyte current is 300 mA / cm2.

It can be seen from the analysis of this table that the incorporation of ruthenium oxide greatly reduces the overpotential of the cathode. This decrease becomes greater when the oxide is dispersed on a support.

EXAMPLES 9 TO 11 The purpose of these examples is the study of the behavior of electroactivated materials that consist of an elemental cathode, an electroactivated sheet and a diaphragm.

Example 9, comparative; The combined elemental cathode and the electroactivated sheet unit were obtained according to the method described for Examples 5 to 8, except for the fact that only the graphite powder was used. 1employee 10; the combined elemental cathode and the electroactivated sheet unit correspond to those obtained in Example 6.

Example 11; the combined elemental cathode and the electroactivated sheet unit correspond to those obtained in Example 8. In all three cases, a diaphragm was deposited on the combined electroactivated material / elementary unit of the cathode, according to the following procedure: A suspension was prepared, with stirring, which comprises: • 3.3 g of the surfactant; • 100 g of chrysotile asbestos fibers, with lengths less than 1 mm; • 20 g of PTFE in the form of latex, which contains approximately 60% by weight of solids; • 30 g of Tixosil® 33J (Rhóne-Poulenc), • deionized water, whose quantity is calculated in order to obtain approximately 4 liters of suspension and a solids content of approximately 4.5%.

The suspension was allowed to stand for at least 24 hours. This suspension was stirred for 30 minutes before use.

The required volume of the solution was removed, so as to contain the quantity of solids which is intended to be deposited in order to form the diaphragm (in the order of 1 to 2 kg / m2). The filtration was carried out under a programmed vacuum. A negative pressure was established and increased by 50 mbar per minute, in order to reach approximately 800 robbers. This negative pressure was maintained for 15 minutes at 800 mbar.

The combined unit was then sintered, after optional drying, at about 100 ° C, the combined diaphragm and cathode unit were brought to a temperature of 350 ° C, with a stationary stage at a temperature of about 3152 ° C, the whole process lasted approximately 1 hour and a half.

Then the silica was removed by an alkaline treatment with electrolytic sodium hydroxide, during the first moments of the electrolysis (in situ removal). The three composite materials of the elemental cathode / electroactivated material / diaphragm of a cell were tested in the electrolysis of an aqueous solution of sodium chloride. The chloride supply was kept constant at a concentration of 280 g / 1 and a temperature of 80ac.

? U |? O was calculated from the graph of cell potential (? U) as a function of the electrolysis current.

This table makes it possible to evaluate the activation of the cathode by the electrocatalytic agent. It seems clear that the use of ruthenium oxide substantially decreases the extrapolated potential and that this effect is increased when the ruthenium oxide is dispersed on a support (graphite, for example).

Claims (14)

1. An electroactivated material comprising fibers, of which at least a part are electrically conductive, and a binder, characterized in that it additionally comprises an electrocatalytic agent, which consists of particles formed of ruthenium oxide, platinum, palladium or iridium, or their mixtures , or at least one of the several oxides distributed, at least partially, on an electrically conductive support.

2. The material, according to the preceding claim, characterized in that the electrocatalytic agent is evenly distributed throughout the body of the material.

3. The material, according to the preceding claims, characterized in that the weight ratio of the coating, with respect to the support, varies from 0.5 to 50 for each particle.

4. The material, according to one of the preceding claims, characterized in that the support is selected from iron, cobalt, nickel, Raney iron, Raney cobalt, Raney nickel, the elements of columns IV-A and VA of the Periodic Table, and the carbon or graphite. to.

The material according to one of the preceding claims, characterized in that the particle size of the support is between 1 and 100 μm.

6. The material according to one of the preceding claims, characterized in that the electrocatalytic agent represents from 10 to 70% by weight, with respect to the fibers, binder and electrocatalytic agent combined.

The material, according to one of the preceding claims, characterized in that the electro-catalytic agent additionally comprises an additive, selected from iron, cobalt, nickel and / or its oxides.

8. The material, according to one of the preceding claims, characterized in that the fibers represent from 10 to 65% and the binder from 5 to 20%, with respect to the weight of the fibers, binder and electrocatalytic agent combined, the weight of the binder corresponds to 20 to 50% by weight, with respect to the fiber subsystem and binder.

9. A composite material, comprising: (a) a high porosity material and (b) the material according to one of claims 1 to 8.

The material, according to the preceding claims, characterized in that it comprises, from one face to the other: (a) a metal surface of high porosity, (b) electroactivated material and (c) a separator.

11. Process for the preparation of the material, according to one of claims 1 to 9, characterized in that the following steps are carried out: (a) preparing an aqueous suspension, comprising the fibers, the binder, the electrocatalytic agent and, optionally, , adjuvants; (b) deposit the sheet by filtration of said suspension, under a programmed vacuum, through a material of high porosity; (c) removing the liquid, and the sheet, thus formed, is dried, optionally; (d) sinter, optionally, the sheet, thus obtained.

12. Process for the preparation of a composite material, according to claim 11, characterized in that the following steps are carried out: (a) preparing an aqueous suspension, comprising the fibers, the binder, the electrocatalytic agent and, optionally, adjuvants; (b) deposit a sheet by filtering the suspension, under a programmed vacuum, through a material of high porosity; (c) removing the liquid, and the sheet, thus formed, is dried, optionally; (d) the sheet, thus obtained, is optionally sintered; (e) a dispersion is deposited, in water or in an aqueous solution of sodium hydroxide, comprising the fibers, a binder and, optionally, adjuvants, on the sheet, by filtration under a programmed vacuum; (f) removing the liquid, and the diaphragm, thus formed, is dried, optionally; (g) sinter the whole unit.

13. Process, according to the preceding claims, characterized in that, after Step (g), a treatment is carried out with an aqueous solution of an alkali metal hydroxide, if the dispersion of Step (e) is in water , and if she understands silica as a porogenic agent.

14. Process according to one of claims 11 and 12, characterized in that the step (d) of sintering is carried out if the binders of the dispersions of Steps (a) and (e) are different. ABSTRACT Electroactivated material comprising fibers of which at least one part is electrically conductive, a binder, characterized in that it further comprises an electrocatalytic agent consisting of articles of ruthenium oxide, platinum, palladium, iridium or mixtures thereof, or of one or both plurality of said oxides, distributed at least in part in an electroconductive support. The electroactivated material is particularly used as a cathode element of an electrolysis cell and in particular, a cell for the trolysis of aqueous solutions of sodium chloride. The present invention also discloses a composite material comprising (a) a high porosity material, (b) the aforementioned electroactivated material. Finally, the invention relates to a composite material comprising from one phase to the other: (a) a metal surface of high porosity, (b) the aforementioned electroactivated material, (c) a separator.