EP1145343A2 - Electrode a diffusion gazeuse et application aux processus electrochimiques catalyses - Google Patents
Electrode a diffusion gazeuse et application aux processus electrochimiques catalysesInfo
- Publication number
- EP1145343A2 EP1145343A2 EP99964740A EP99964740A EP1145343A2 EP 1145343 A2 EP1145343 A2 EP 1145343A2 EP 99964740 A EP99964740 A EP 99964740A EP 99964740 A EP99964740 A EP 99964740A EP 1145343 A2 EP1145343 A2 EP 1145343A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- texture
- face
- activated carbon
- hydrophobic material
- fabric
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/96—Carbon-based electrodes
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
- C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
- C25B11/031—Porous electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/8605—Porous electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/10—Fuel cells with solid electrolytes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Definitions
- the invention relates to gas diffusion electrodes used in catalyzed electrochemical processes. Fields of application are fuel cells of the proton exchange membrane type and electrochemical reactors, for example for the manufacture of chlorine / soda. The invention also relates to a method for producing such electrodes.
- An electrode of the type used in fuel cells with a proton exchange membrane comprises a diffusion zone and an active zone.
- the diffusion zone can comprise a substrate such as a carbon or graphite fabric which performs a diffusion function, in order to distribute towards the active zone a received gas, a function of current collector, due to its properties of electrical conduction, and a structural function, to impart mechanical strength to the electrode.
- the active area includes a catalyst, such as platinum, in contact with an electrolyte.
- the diffusion zone is defined by a layer formed by a carbon fabric embedded in a hydrophobic material, PTFE (polytetrafluoroethylene) loaded with carbon black.
- the active area is formed by carbon grains, possibly activated, supporting platinum particles in contact with a solid electrolyte, such as the "Nation" from the company DuPont de Nemours.
- Known electrodes of this type suffer from limitation phenomena.
- the activated carbon grains have a tortuosity which makes it difficult for the combustible gas (H 2 ) to access the catalyst particles.
- the constitution of the active zone formed by an accumulation of carbon grains of a few hundreds of nm to a few ⁇ m in diameter, induces a damaging ohmic fall.
- the method for manufacturing these known electrodes comprises a heat treatment for sintering PTFE, carried out after formation of the active zone, therefore capable of altering the catalyst.
- the diffusion zone of the electrode is formed of a mixture of acetylene black and PTFE while the active zone is formed of a mixture of activated carbon fibers carrying the metal catalyst, acetylene black and PTFE .
- the whole is shaped and subjected to a heat treatment.
- the object of the invention is to propose gas diffusion electrodes making it possible to improve the operation and the yield of the electrochemical devices in which they are used.
- Another object of the invention is to propose a method for manufacturing gas diffusion electrodes which does not cause any deterioration of the catalyst and which, moreover, allows optimal use thereof.
- the substrate is a coherent texture at least partially coated with hydrophobic material.
- activated carbon fibers is meant herein continuous or discontinuous activated carbon filaments, preferably continuous filaments to promote electronic conduction.
- coherent texture of activated carbon fibers is meant here a texture intrinsically having sufficient mechanical properties not only to be able to be manipulated during the electrode manufacturing process, but also to give the latter the mechanical strength required for its Implementation.
- the activated carbon fiber texture is a fabric.
- Other coherent textures could be used, such as sheets of unidirectional fibers, possibly superimposed in different directions, and linked together, for example by needling.
- the term “fabric” will be used to denote the coherent texture.
- the invention is remarkable in that the activated carbon fiber fabric fulfills both the functions of diffusion of the gas admitted through the fabric, of electronic conduction, of structural element giving the mechanical strength to the electrode and of catalyst support.
- the fabric offers the admitted gases a network of micro-channels leading to the catalyst particles, which allows the gases to react on each active part supported by the fabric.
- the activated carbon fiber fabric being organized in the form of a network of small diameter filaments, this results in a reduction in tortuosity and ohmic drop in comparison with the carbon grains used in the prior art mentioned more high.
- the fabric of activated carbon fibers which is preferably made of fibers with a cellulose precursor and more particularly with a radiation precursor, advantageously has a porosity characterized by pores of very small average size, typically between 0.3 nm and 10 nm. , which allows maximum dispersion of the catalyst particles and obtaining an optimal size for them, with a view to better exploitation of the electrode.
- the activated carbon fiber fabric it has a first face coated in the hydrophobic material, such as PTFE, and a second face on which the catalyst particles are fixed.
- a method for producing a gas diffusion electrode comprising providing an activated carbon fiber substrate, bringing the substrate into contact with an electrochemical reaction catalyst precursor and treating precursor for obtaining catalyst particles fixed on the fibers of the substrate, is characterized in that an activated carbon fiber substrate is used in the form of a coherent texture such as a fabric, having a first and a second face, a part of the texture adjacent to the first face is coated with a hydrophobic material, and the catalyst is deposited on fibers of the remaining part of the texture adjacent to the second face.
- a controlled oxidation treatment of the fabric in activated carbon fibers is carried out before deposition of the catalyst, so as to increase the rate of functional groups making up the surface chemistry of the activated carbon fabric.
- the deposition of the catalyst can be carried out by cation exchange or by liquid impregnation with a precursor salt of the catalyst.
- Such catalyst deposition processes on activated carbon fibers are described in patent application WO 99/26721 A of the applicant.
- a deposit of catalyst on carbon fibers activated by cation exchange to obtain substrates having high catalytic and electrocatalytic properties is also envisaged in the document by PP Andonoglou et al. "Preparation and electrocatalytic activity of rhodium modified pitch-based carbon fiber electrodes" Electrochimica Acta 44 (1998) p. 1455-1465.
- the precursor is a salt of the catalyst
- the treatment of the precursor comprises a step of reduction of the salt by a gas admitted through the first face of the fabric.
- the electrode thus obtained thus offers a network of micro-channels allowing the gases to reach each active part supported by the activated tissue.
- Activated carbon fiber fabric can be obtained in different ways.
- a first possibility consists in making a fabric of carbon precursor fibers, in particular a cellulose, and more particularly a rayon and in carrying out a heat treatment phase of carbonization of the carbon precursor.
- the carbon fiber fabric obtained is activated by heat treatment under an oxidizing atmosphere.
- a second possibility consists in starting with a fabric of carbon precursor fibers and in impregnating the latter with a composition making it possible, after carbonization, to obtain directly a fabric in activated carbon fibers.
- the carbon precursor is preferably a cellulose, more particularly a rayon.
- the impregnation is carried out with a composition containing a mineral constituent having a function of promoter of the dehydration of the cellulose, for example of phosphoric acid.
- Partial coating of the carbon fiber fabric activated by a hydrophobic material can be carried out in different ways: coating the first face of the fabric, co-laminating the fabric with a sheet of hydrophobic material placed on the first face of the fabric, against - bonding of a sheet of hydrophobic material on the first face of the fabric or else projection of a composition containing the hydrophobic material on the first face of the fabric, while the second face is advantageously heated, for example between 120 ° C. and 160 ° C, to prevent this composition from becoming fixed there.
- the hydrophobic material is sintered by a heat treatment carried out before deposition of the catalyst, therefore it is incapable of affecting the latter.
- the method is implemented on a strip of fabric made of activated carbon fibers in movement in which the electrodes are finally cut.
- FIG. 1 is a very schematic view of a first embodiment of an electrode to gas diffusion according to the invention
- FIG. 2 shows the successive steps of a method of producing the electrode of Figure 1;
- FIG. 3 is a very schematic view of a second embodiment of a gas diffusion electrode according to the invention.
- FIG. 4A to 4C illustrate an embodiment of the method according to the invention on a strip of activated carbon fiber fabric running
- FIG. 5 is a picture with a transmission electron microscope showing catalyst particles on the surface of an activated carbon fiber in an electrode produced according to the invention.
- FIG. 6 illustrates the size distribution of catalyst particles attached to the activated carbon fibers of an electrode produced according to the invention.
- FIG. 1 shows a gas diffusion electrode 10 according to the invention, in a fuel cell electrochemical cell with a proton exchange membrane.
- a gas diffusion electrode 10 in a fuel cell electrochemical cell with a proton exchange membrane.
- two electrodes receiving respectively hydrogen gas (H 2 ) and oxygen gas (0 2 ) support a catalyst, usually platinum (Pt) in the form of particles.
- the electrodes are separated by a membrane into a solid electrolyte, usually of "Nation” from the DuPont de Nemours Company, which has ionic groups SO 3 " proton exchangers.
- the flow of electrons (2e) between the anode and the cathode generates an electric current used in a charge external to the fuel cell.
- the electrode 10 for example the anode, comprises a fabric 12 made of activated carbon fibers.
- a fabric 12 made of activated carbon fibers.
- other types of coherent textures capable of ensuring the structural and electronic conduction functions could be used, such as sheets of unidirectional fibers, possibly superimposed in different directions and linked together, for example by needling.
- the face 12a of the fabric 12, exposed to the incident gas (H 2 ) and ensuring a diffusion function is coated in a matrix 14 of a hydrophobic and gas-permeable material which occupies substantially half the thickness of the fabric.
- the material 14 is for example microporous PTFE.
- catalyst in this case platinum (Pt).
- This same part of the fabric carrying the catalyst is coated in a matrix 18 containing a solid electrolyte, such as "Nation” and which may also contain a hydrophobic material, such as PTFE, in respective proportions by mass typically of 90% and 10 %.
- the cathode has a structure similar to that of the anode, the quantity of catalyst deposited and the relative proportions of "Nation" and of PTFE can however be different.
- PTFE by its hydrophobic nature, prevents fabrics made of activated carbon fibers acting as current collectors, from being drowned by the water produced by the reaction.
- Hydrophobic microporous materials other than PTFE may be suitable as constituting matrices 14 and 18.
- fluorinated polymers such as PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), these being possibly used alone or in combination with each other and / or with PTFE.
- the activated carbon fiber fabric is preferably formed of fibers with a cellulosic precursor, in particular with a rayon precursor.
- the fabric in particular when it is formed from fibers originating from rayon precursors, has a specific surface, a microporosity and a rate of functional surface groups (active sites) which make it suitable for the effective fixing of metallic catalyst, not only platinum, but also ruthenium, rhenium, palladium, iridium, nickel, or other metals or combinations of metals known as catalysts.
- the specific surface is at least equal to 200 m 2 / g, preferably at least equal to 600 m 2 / g and can reach and even exceed 1500 m 2 / g.
- the porosity is characterized by pores having average dimensions of between 0.3 nm and 10 nm.
- the carbon fibers with a ray precursor have a level of oxygenated surface groups such that it promotes the presence of active sites.
- the fabric is however subjected to a gentle oxidation treatment, for example with sodium hypochlorite, in order to boost the surface chemistry of the activated carbon fibers and ensure good dispersion of the catalyst.
- the invention is not however limited to cellulosic precursors, in particular rayon, although they are preferred.
- the fibers of the activated carbon fabric can be obtained from other carbon precursors such as preoxidized polyacrylonitrile (PAN), phenolic precursors and isotropic pitches with, preferably, oxidation treatment for example with nitric acid before deposition of the catalyst.
- FIG. 2 shows the successive stages of an embodiment of the electrode 10.
- the first step 20 is to provide an activated carbon fiber fabric. As indicated above, there are two different ways to do this.
- a first possibility consists in starting from a carbon fiber fabric and in subjecting it to an activation treatment.
- the carbon fiber fabric is obtained directly from carbon threads originating from a carbon precursor by heat treatment or from carbon precursor threads, the heat treatment for transformation of the precursor then being carried out after production of the fabric.
- the carbon precursor used is cellulose, more particularly rayon.
- the heat treatment for transforming rayon into carbon comprises a precarbonization phase at a temperature between 350 ° C and 420 ° C, preferably at around 400 ° C, followed by a final carbonization phase at a temperature between 1000 ° C and 1300 ° C, preferably at 1200 ° C, under a nitrogen atmosphere and for a period of between 0.7 min and 1.3 min.
- the final carbonization can be carried out under reduced pressure, for example between 5 Pa and 60 Pa, which promotes the elimination of impurities entrained with the gaseous effluents and the migration of alkaline impurities on the surface of the fibers from which they can be removed by simple rinsing with demineralized water, without the need for acid washing, carbon fibers of high purity are then obtained, the carbon content being greater than 99%, the ash content less than 0.3% and the level of alkaline impurities less than 1500 ppm.
- the fibers obtained are also remarkable in that they consist structurally of a large number of very small crystallites having an average height L c of approximately 1 nm and an average lateral size L a of approximately 3 nm.
- Activation is carried out by heat treatment of the carbon fiber fabric under an oxidizing atmosphere, such as water vapor or, preferably, carbon dioxide or a mixture of carbon dioxide and water vapor.
- the heat treatment temperature is preferably between 850 ° C and 950 ° C and its duration is preferably between 50 min and 300 min depending on the specific surface desired.
- Continuous activation can be achieved by scrolling the carbon fiber fabric through a heat treatment area of an oven in which an oxidizing gas flow is maintained. Such a method is described for example in the document FR 2 741 363 A.
- the fabric Activation gives the fabric the specific surface area and porosity desired.
- the specific surface is greater than 600 m 2 / g, and even at
- the porosity is characterized by pores with an average diameter between 0.3 nm and 10 nm and an overall porosity rate between 30% and 50%. This is measured by the known technique of X-ray scattering at small angles (or DPAX technique). It consists in exposing the fibers to an X-ray beam under conditions such that there is an electronic density contrast between the voids (pores) and the material (carbon), therefore a diffusional intensity linked to the total porosity rate of the fibers. of carbon.
- a second possibility consists in starting with a fabric of carbon precursor fibers and in impregnating the latter with a composition making it possible, after carbonization, to obtain directly a fabric in activated carbon fibers.
- the carbon precursor is preferably a cellulose, more particularly a rayon.
- the impregnation is carried out with a composition containing a mineral constituent having a function of promoter of the dehydration of the cellulose, for example chosen from phosphoric acid, zinc chloride, potassium sulphate, potassium hydroxide, diamonic phosphate and ammonium chloride.
- the impregnation is carried out by a composition containing phosphoric acid so that the mass of acid fixed on the tissue is between 10% and 22% of the mass of dry tissue.
- the heat treatment includes a rise in temperature at a speed of between 1 and 15 ° C / min followed by a plateau at a temperature between 350 ° C and 500 ° C under an inert atmosphere or under an atmosphere containing a reaction activator such as carbon dioxide or water vapor.
- a reaction activator such as carbon dioxide or water vapor.
- Such a method is described in international patent application WO 98/41678 A in the name of the applicant. It is thus possible to obtain an activated carbon fiber fabric having a specific surface greater than 600 m 2 / g, for example around 1000 m 2 / g, or even more.
- post-treatment can be carried out at a temperature of approximately 1000 ° C. under a non-oxidizing atmosphere, for example under nitrogen, for approximately 3 min.
- the electrical conductivity of the activated carbon fibers obtained can be improved by using a rayon precursor containing carbon black, the latter having been incorporated in the viscose bath, before spinning.
- a second step 22 is preferably carried out which consists in subjecting the activated carbon fabric to gentle oxidation in order to improve the surface chemistry and subsequently to promote the dispersion of the catalyst particles.
- This controlled oxidation can be carried out by immersing the tissue in a bath of an oxidizing composition, then optional washing, rinsing with water and drying.
- the oxidizing composition is for example a solution of sodium hypochlorite NaOCI, the washing being carried out by then passing through a hydrochloric acid bath.
- Other oxidizing compositions can be used, for example nitric acid HN0 3 .
- the "mild" character of the oxidation is due to a limited exposure to the oxidizing composition, for example between 1 and 3 hours in a NaOCI solution containing 2.5% of active chlorine, at ambient temperature.
- the next step 24 consists in coating part of the activated carbon fabric, comprising the face 12a thereof, with the matrix 14 of microporous hydrophobic material, the other face 12b remaining free.
- the coating is carried out with a liquid composition having a surface tension greater than that of the fabric 12, to prevent the latter from being completely wet and to limit the formation of the matrix on the single face 12a.
- An emulsion based on one or more fluorinated polymers, such as PTFE, PVDF, PVF, to which one or more surfactants are added, is used for example.
- Another possibility is to spray the hydrophobic material by means of nozzles on the face 12a of the fabric, while the other face 12b is heated by a stream of hot air. The heating is carried out at a temperature between 120 ° C and 160 ° C, for example about 150 ° C.
- a thin sheet for example a web of 12 to 50 g / m 2 of polyester, polyamide or polyurethane, can be interposed between the sheet 14 ′ and the fabric 12.
- the material of the matrix 14, for example PTFE, is advantageously charged with carbon black. It is then sintered at a temperature between about 350 ° C and 390 ° C.
- the next step 26 consists in depositing the catalyst on the remaining free part of the fabric 12, adjacent to the face 12b.
- impregnation can be carried out with an aqueous solution containing a catalyst precursor, preferably a precursor capable of giving the desired precursor by a reduction reaction.
- a catalyst precursor preferably a precursor capable of giving the desired precursor by a reduction reaction.
- the precursor is for example H 2 PtCl6.
- the hydrophobic nature of the matrix material 14 limits the impregnation to the part that remains free of the fabric 12, which is the aim sought.
- the reduction of platinum is carried out under a stream of hydrogen gas.
- hydrogen gas is admitted through the face 12a coated by the microporous matrix 14.
- the platinum thus reduced will necessarily be accessible again by hydrogen gas or another gas.
- the preferential route created in this way allows to reduce the phenomenon of limitation by diffusion of the gas towards the catalyst, during the use of the electrode.
- the deposition of the catalyst can be carried out by cation exchange.
- the fabric 12 of activated carbon fibers is admitted into a bath containing ammonia and a dissolved mass of precursor salt of catalyst, with nitrogen bubbling.
- the precursor salt can be Pt (NH 3 ) 6 , Cl 2 and the molar ratio between ammonia and the precursor salt being for example from 1 to 0.01. The balance is allowed to take place for approximately 1 hour.
- protons are removed from the -OH type anchoring sites on the surface of the carbon fibers, which promotes the formation of an ionic bond with the metal salt Pt (NH 3 ) 6 2+ 2 CI " .
- the texture is washed and dried.
- the reduction of the platinum is then carried out, for example by a stream of hydrogen gas, that this is advantageously admitted through the face 12a of the fabric 12.
- a cellulosic precursor in particular a rayon precursor for the activated carbon fiber fabric
- a rayon precursor for the activated carbon fiber fabric
- the fabric has the advantage of giving the fabric a microporosity and a rate of functional surface groups (active sites) which make it suitable for fixing of metal catalyst in the form of very small particles.
- the carbon fibers with a radiated precursor have a residual oxygen content such that it promotes the presence of active sites.
- the rate of functional surface groups obtained is thus high and can be further increased by the controlled oxidation step.
- the porosity and surface chemistry characteristics allow dispersion of the catalyst in the form of fine particles, with an average size of between approximately 1 nm and 3 nm, with an exceptionally high dispersion rate, of between 0.3 and 0.7, the dispersion being favored by the gentle oxidation treatment.
- the dispersion rate represents the ratio between the number of metallic atoms surface area and the total number of metallic atoms. It is measured by hydrogen chemisorption.
- the mass percentage of platinum deposited relative to the mass of activated carbon fiber fabric alone can easily exceed 3% and reach 7% or more.
- the method of fixing the catalyst by liquid impregnation or cation exchange and reduction has, in particular, the advantage of distributing the catalyst evenly over the activated carbon fabric.
- a last step 28 consists in coating the part of the fabric 12 carrying the catalyst with the matrix 18 of "Nation” and hydrophobic material, for example PTFE.
- a liquid composition containing "Nation” and PTFE is sprayed on the side of the face 12b of the texture 12 in the desired proportions.
- Example An activated carbon fabric is produced from a rayon satin fabric made up of a multifilament viscose, the fabric being produced from 15x15 woven threads (15 threads per cm in warp and weft).
- the fabric After desizing, the fabric is charred by being brought to a temperature of approximately 400 ° C. for approximately 12 h and then to a final temperature of approximately 1200 ° C. for approximately 1 min under nitrogen at a pressure of 30 Pa.
- Activation fabric obtained is made by scrolling the fabric in a heat treatment zone of an oven under an atmosphere consisting of 100% carbon dioxide. This area is materialized by a tunnel-shaped muffle along which the fabric is continuously advanced. The activation treatment is carried out at a temperature of approximately 920 ° C. and the residence time at this temperature is approximately 1 h.
- - fiber size on average a diameter of 9 ⁇ m (with a multi-lobed fiber type morphological facies)
- surface chemistry acid functional groups up to 0.3 to 0.8 meq / g (millimole / g) of which 0 0.02 to 0.06 meq / g of carboxylic functions at the surface of the fibers.
- the activated carbon fabric 12, unwound from a coil 30, is immersed in a bath 32 of sodium hypochlorite NaOCI containing 2.5% active chlorine where it remains for 2 h at room temperature. Then, the tissue is washed in a bath 34 of 1N hydrochloric acid HCl where it remains for 10 min at room temperature. Rinsing in a bath 36 of mineralized water is then carried out for a residence time of 30 min.
- the activated carbon fabric thus oxidized is admitted into an oven 38 to be dried for 1 hour at 160 ° C. before being taken up on a reel 40.
- the surface chemistry of the oxidized fabric results in an average content of 2.8 meq / g of carboxylic acid functions.
- the fabric is then coated on its face 12a with PTFE, more preferably, according to a continuous process (FIG. 4B).
- the fabric 12 is unwound from the spool 40 and passes through a spraying station 42, between one or more rows of nozzles 44 directed towards the face 12a of the fabric and means 46 for blowing hot air.
- the nozzles are supplied with PTFE added with carbon black, under a pressure of 2.10 5 Pa.
- the air, coming from a blowing device (not shown), is directed towards the face 12b of the fabric by passing through a electric heater so that the temperature of the air entering the fabric surface is around 150 ° C.
- the PTFE sprayed on the face 12a of the fabric is sintered at a temperature of 380 ° C. by passing through an oven 48, then the fabric is taken up on a spool 50 at the outlet of the oven.
- a first layer of PTFE representing 10% by mass of the mass of tissue alone is also formed.
- a second layer of sintered PTFE is then formed in the same way by taking up the fabric wound on the spool 50, the quantity of sprayed PTFE being chosen to form an additional layer representing 30% by mass of the mass of tissue alone.
- a layer of PTFE with a total thickness of approximately 110 ⁇ m is obtained, perfectly homogeneous.
- the face 12b is free of any PTFE, the current of hot air at 150 ° C. preventing the migration of PTFE grains towards this face.
- the fabric 12 partially coated with PTFE is provided with catalyst particles deposited on its face 12b, again preferably according to a process in which the fabric runs continuously (FIG. 4C).
- the fabric unwound from a reel 60 passes through a bath 62 containing ammonia and a dissolved mass of Pt (NH 3 ) ⁇ Cl 2 salt in a molar ratio of 1 to 0.01, with bubbling nitrogen.
- the residence time is approximately 1 hour.
- the fabric is then washed by passage through a bath 64 of demineralized water with a residence time of approximately 30 min.
- the fabric On leaving the bath 64, the fabric is dried by passing through a tunnel 66 at a temperature of approximately 120 ° C. under nitrogen and then is admitted into a hydrogenation oven 68 where the platinum salt is reduced, at a temperature of about 300 ° C. Hydrogen is admitted through the face 12a of the tissue.
- the fabric passes into a passivation compartment 70 under a mixture of nitrogen and oxygen (with a volume rate of 1% of oxygen) before being collected on a storage reel 80.
- the process used for depositing the catalyst ensures a homogeneous distribution of the catalyst particles on the surface of the fibers accessible to the gases passing through the face 12a of the fabric.
- the use of the reduced catalyst is therefore optimal.
- the amount of platinum attached to the tissue is approximately 3% by mass relative to the mass of the tissue alone.
- FIG. 5 shows the particles, or grains, of platinum 80 on the surface of a fiber 82 on the fabric obtained after reduction of the platinum salt.
- the platinum particles are present essentially on the periphery of the fibers over a thickness of 0.1 ⁇ m.
- the size distribution of these particles is shown in Figure 6. It is substantially homogeneous and centered on 2.5 nm.
- the passivation treatment in compartment 80 gives the strip of tissue carrying the catalyst particles sufficient stability to be kept as it is, before cutting electrodes to the desired dimensions before coating the face 12b carrying the catalyst with an electrolyte. solid or bringing this face into contact with a liquid electrolyte, depending on the application envisaged.
- the coating of the face 12b with a solid electrolyte of the "Nation" type and PTFE, to form the matrix 18 of FIG. 1, can be carried out by spraying on the face 12b of a composition containing the "Nation "and PTFE in the desired proportions.
- This coating can be carried out on the cut electrodes or on the strip of fabric unwound continuously from the reel 80, the cutting then being carried out.
- An electrode as obtained by a process as described above can also be advantageously used in an electrochemical cell of chlorine / sodium hydroxide manufacture with liquid electrolyte.
- an electrochemical reactor containing an aqueous NaCl solution is used as the electrolyte.
- a membrane is placed in the reactor between the anode and the cathode, the pH of the electrolyte being equal to approximately 3 on the anode side and 14 on the cathode side.
- the reaction produces chlorine gas:
- thermodynamic potential between the anode and the cathode which is theoretically equal to 2.18 V, in practice reaches around 3 V due to the overvoltages linked to the different reaction kinetics and the ohmic drops in the electrolyte and the membrane. .
- a gas diffusion electrode as an air diffusion electrode (or oxygen) as a cathode or as a hydrogen diffusion electrode as an anode brings particular advantages.
- oxygen gas supplied to a gas diffusion electrode used as a cathode, the reactions on the anode side and on the cathode side become respectively:
- thermodynamic potential decreases appreciably, which results in an energy gain of 25 to 30%, from where a considerable advantage for an electrochemical process traditionally very large consumer of electrical energy. .
- thermodynamic potential decreases.
- the impregnation process can be used with metals M which can be in the form of anionic complex MCI X in an acid medium, while the cation exchange process can be used with metals M which can be in the form of a cationic salt of the type [M (NH3) x ] y + , yCf, for example.
- the metal catalysts can be chosen from other noble metals than platinum, such as palladium, iridium, rhodium, or from transition elements, in particular cobalt, iron, nickel, copper and manganese. It is also possible to fix bimetallic catalysts to the fabric of activated carbon fibers, by combining two noble metals or a noble metal and a transition element, for example palladium-copper or palladium-nickel catalysts.
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Metallurgy (AREA)
- Materials Engineering (AREA)
- Engineering & Computer Science (AREA)
- Inert Electrodes (AREA)
- Catalysts (AREA)
- Fuel Cell (AREA)
- Electrodes For Compound Or Non-Metal Manufacture (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
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FR9816630 | 1998-12-30 | ||
FR9816630A FR2788168A1 (fr) | 1998-12-30 | 1998-12-30 | Electrode a diffusion gazeuse supportant un catalyseur de reaction electrochimique |
PCT/FR1999/003316 WO2000041251A2 (fr) | 1998-12-30 | 1999-12-30 | Electrode a diffusion gazeuse et application aux processus electrochimiques catalyses |
Publications (1)
Publication Number | Publication Date |
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EP1145343A2 true EP1145343A2 (fr) | 2001-10-17 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP99964740A Withdrawn EP1145343A2 (fr) | 1998-12-30 | 1999-12-30 | Electrode a diffusion gazeuse et application aux processus electrochimiques catalyses |
Country Status (6)
Country | Link |
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US (1) | US6444347B1 (fr) |
EP (1) | EP1145343A2 (fr) |
JP (1) | JP2002534773A (fr) |
CA (1) | CA2321517A1 (fr) |
FR (1) | FR2788168A1 (fr) |
WO (1) | WO2000041251A2 (fr) |
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Publication number | Priority date | Publication date | Assignee | Title |
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CA1084477A (fr) * | 1975-07-22 | 1980-08-26 | Brian D. Mcnicol | Catalyseurs a support de graphite polycristallin |
JPS6025528B2 (ja) * | 1975-12-04 | 1985-06-19 | 東洋紡績株式会社 | 活性炭素繊維 |
JPS62154461A (ja) * | 1985-12-26 | 1987-07-09 | Toho Rayon Co Ltd | 電極材用活性炭素繊維 |
JPS6414873A (en) * | 1987-07-07 | 1989-01-19 | Mitsubishi Electric Corp | Electrode for fuel cell |
US5395705A (en) * | 1990-08-31 | 1995-03-07 | The Dow Chemical Company | Electrochemical cell having an electrode containing a carbon fiber paper coated with catalytic metal particles |
FR2760759B1 (fr) * | 1997-03-14 | 1999-06-11 | Carbone Ind | Procede de realisation de textures activees en fibres de carbone |
FR2771309B1 (fr) * | 1997-11-24 | 2000-02-11 | Messier Bugatti | Elaboration de support de catalyseur en fibres de carbone active |
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1998
- 1998-12-30 FR FR9816630A patent/FR2788168A1/fr not_active Withdrawn
-
1999
- 1999-12-30 WO PCT/FR1999/003316 patent/WO2000041251A2/fr not_active Application Discontinuation
- 1999-12-30 EP EP99964740A patent/EP1145343A2/fr not_active Withdrawn
- 1999-12-30 US US09/623,206 patent/US6444347B1/en not_active Expired - Fee Related
- 1999-12-30 CA CA002321517A patent/CA2321517A1/fr not_active Abandoned
- 1999-12-30 JP JP2000592889A patent/JP2002534773A/ja active Pending
Non-Patent Citations (1)
Title |
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Also Published As
Publication number | Publication date |
---|---|
CA2321517A1 (fr) | 2000-07-13 |
US6444347B1 (en) | 2002-09-03 |
JP2002534773A (ja) | 2002-10-15 |
WO2000041251A2 (fr) | 2000-07-13 |
FR2788168A1 (fr) | 2000-07-07 |
WO2000041251A3 (fr) | 2001-10-04 |
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