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WO2003018469A1 - Electrode de reaction electrochimique, procede de fabrication et dispositif d'application - Google Patents

Electrode de reaction electrochimique, procede de fabrication et dispositif d'application Download PDF

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Publication number
WO2003018469A1
WO2003018469A1 PCT/US2002/026653 US0226653W WO03018469A1 WO 2003018469 A1 WO2003018469 A1 WO 2003018469A1 US 0226653 W US0226653 W US 0226653W WO 03018469 A1 WO03018469 A1 WO 03018469A1
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WO
WIPO (PCT)
Prior art keywords
platinum
catalyst
layer
ion
substrate
Prior art date
Application number
PCT/US2002/026653
Other languages
English (en)
Inventor
Alexander M. Timonov
Sergey Anatolievich Logvinov
Nikolay Shkolnik
Sam Kogan
Original Assignee
Engen Group, Inc.
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Publication date
Application filed by Engen Group, Inc. filed Critical Engen Group, Inc.
Priority to JP2003523141A priority Critical patent/JP2005501177A/ja
Priority to EP02761457A priority patent/EP1434734A1/fr
Publication of WO2003018469A1 publication Critical patent/WO2003018469A1/fr

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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
    • H01M4/88—Processes of manufacture
    • H01M4/8803—Supports for the deposition of the catalytic active composition
    • H01M4/881—Electrolytic membranes
    • 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
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/13—Ozone
    • 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
    • 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
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
    • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded
    • 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
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
    • H01M4/8882—Heat treatment, e.g. drying, baking
    • 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
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
    • H01M4/926—Metals of platinum group supported on carriers, e.g. powder carriers on carbon or graphite
    • 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
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • 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
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/921—Alloys or mixtures with metallic elements
    • 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 present invention refers to methods for the manufacture of gas-diffusion electrodes having porous conducting substrate on which a layer of ion-exchange polymer is applied - in particular, to methods for introducing catalyst particles into the electrode structure.
  • the invention may be used for manufacturing electrodes used for fuel cells, water electrolysis, ozone production, as well as electrodes for other electrochemical devices.
  • the present invention is also related to the construction and method of production of electrodes for electrochemical reactions, for electrolysis primarily, as well as to the construction of an electrolyzer including such electrodes.
  • the invention may be used for ozone production through decomposition of water by the electrochemical method, and for manufacturing of fuel cells
  • Said proton-conducting material contains a multitude of acidic functional groups, each of which has a cation capable of substitution. Then said substrate is placed into an electrochemical cell with a counter-electrode and electrolyte.
  • the electrolyte is an aqueous solution that contains complex a ino-platinic cations .
  • a voltage sufficient for the deposition of platinum particles in the areas where the proton-conducting material contacts electron-conducting material is then supplied to electrodes.
  • Electrodes in which a layer of ion-exchange polymer (having channel-cluster structure) is applied on said porous conductive substrate are produced by methods described above. Nano-sized particles of metal catalyst are reduced in the channels of said ion-exchange polymer (directly on the substrate) in these electrodes.
  • the known methods are characterized by the fact that ions of metal catalyst are contained in the liquid phase of electrolyte in the course of electrochemical deposition of metal catalyst particles. Under the action of electric field and as a result of diffusion processes, these ions of metal catalyst are continuously supplied to the channels of ion-exchange polymer.
  • Electrodes are known, as well as methods of their production and electrolyzers, e.g. for ozone generation.
  • the electrodes include of a porous conducting substrate, for instance, of graphite, and a layer of metallic catalyst applied to one of the sides of the substrate.
  • the thin layer of catalyst is applied, as a rule, by spray coating, compression molding, or application of a catalyst-containing colloidal solution with subsequent evaporation of the solution.
  • the formation of the catalyst layer on the porous conducting substrate is done by applying a catalyst-containing liquid and its subsequent evaporation.
  • the electrode substrate is made of porous titanium.
  • a viscous platinum-containing solution is applied onto the surface of the substrate. Then the layer is dried, a new layer is applied and dried again. After that the lead catalyst is applied over the layer of platinum.
  • the principal disadvantage of the known devices and technologies for ozone production is the low yield of the final product. This is explained, first, by the inefficient utilization of the catalyst, whose activity obviously cannot be 100% due to imperfections of the method of applying the catalyst to the electrode and the resulting non-uniform size of the catalyst particles, and partial catalyst poisoning on contact of the electrode with air. A thicker catalyst layer will only make the process costlier, therefore, optimization of the amount of catalyst with its activity retained becomes a topical technological issue. Second, the yield of ozone is negatively affected by the products of anode and cathode reactions being mixed together. To prevent this from happening, a separating membrane is inserted into the electrolytic cell, made of porous polymer material, which is mechanically strong, resistant to aggressive media, highly conductive and possessing a capacity for selective ion exchange .
  • a solid polymer electrochemical generator of hydrogen and oxygen is known, where electrodes of porous titanium are used, with a "Nafion" membrane - a solid polymer electrolyte
  • the principle of operation of the known electrolyzer as a hydrogen and oxygen generator is as follows. Distilled water is supplied into the anodic space of the electrolyzer and via the pores of the anode to the electrode/"Nafion" boundary area. Within this boundary area electric oxidation of water takes place, with oxygen release. Oxygen is removed from the reaction zone through the pores of the electrode, and the gas permeability of the "Nafion" prevents oxygen from entering the cathode space and producing an explosive fulminating mixture. Hydrated protons move through the membrane towards the cathode, where they are reduced with the release of gaseous hydrogen.
  • the present invention includes a new and improved method for the manufacture of catalytically active gas- diffusion electrode that is free from disadvantages mentioned above .
  • One exemplary embodiment of the present invention consists in the following.
  • a blank of an electrode (in the form of conducting porous substrate having a layer of ion-exchange polymer having channel-cluster structure applied onto said substrate) is subjected to the following processing.
  • a portion of the protons in the ion- exchange polymer located on the channel walls of the channel-cluster structure of said polymer are substituted by cations containing a metal catalyst. Said substitution is carried out by ionic exchange.
  • conducting substrate (with a layer of ion-exchange polymer having channel-cluster structure applied onto it) is kept in a solution (in which cations containing metal catalyst are present) for a certain period of time.
  • cations Due to diffusion, cations penetrate into the channels of the channel-cluster structure of the layer of the ion-exchange polymer, where they replace a portion of protons of the ion-exchange polymer.
  • cations that now replace protons in the channel-cluster structure of the layer of ion-exchange polymer are reduced electrochemically in a solution of electrolyte that doesn't contain ions of the catalytically active metal.
  • Particles of metal catalyst are deposited on the conducting substrate of the electrode during this reduction. Catalyst is deposited on the substrate only in those locations where the channels of the channel-cluster structure of the layer of the ion-exchange polymer contact the substrate.
  • Catalytic metal is deposited on the substrate only in those locations where the channels of the channel-cluster structure of the layer of the ion-exchange polymer contact the substrate.
  • the amount of introduced metal can be easily controlled via the concentration of solution containing cations of catalytic metal and the duration of time the layer of ion-exchange polymer is kept in said solution.
  • an electrode with high ionic conductivity and high electrochemical activity is produced using the minimum amount of catalyst required for the manufacture of said electrode.
  • a porous conducting substrate with a layer of ion- exchange polymer from 10 to 30 ⁇ in thickness can be used in a specific embodiment of the implementation of this method.
  • the layer of ion-exchange polymer on the porous conducting substrate can be thin and can even have gaps. Particles of catalyst will be reduced on the substrate only in those locations where the channels of the channel-cluster structure of the ion-exchange polymer contact the substrate. They won't be reduced on those areas of the substrate that are not covered with a layer of the ion-exchange polymer.
  • Aqueous solutions of complex compounds of metal catalysts can be used as solutions containing ions of metal catalysts.
  • Cation halogen-amine complexes containing platinum group metals can be used as complex compounds of catalytic metals.
  • the cation complex containing platinum tPtEn 2 Cl 2 l + , cation complex containing ruthenium [RuEn 2 Cl 2 ] + , cation complex containing iridium [IrEn 2 Cl2] + in which En - ethylenediamine H2N-CH2- CH2-NH2)
  • the cation complex containing platinum [Pt (NH 3 ) 4 C1 2 ] 2+ can be used.
  • cations that are formed as a result of dissociation of salts of catalyst metals in aqueous solutions when the concentration of said salts is from 10 " to 5*10 " mol/1, can be used as said cations containing catalyst metal.
  • the electrode can be washed with water prior to electrochemical reduction with the aim to remove the remnants of aqueous solution containing cations including those cations that have not formed bonds with the ion-exchange polymer.
  • Electrochemical reduction can be carried out in an electrolysis bath, using an electrolyte that need not contain cations of catalytic metals - for example, in a bath containing sulfuric acid with concentration 0-05-2 mol/1.
  • this process should be carried out at a potential that is less negative than that at which hydrogen is released (reduced) under given conditions. It is necessary to prevent hydrogen release because free hydrogen has the ability to reduce cations anywhere within the cluster structure, not just on the surface of the substrate.
  • a potential difference is applied between a counter-electrode that is placed into the bath for the electrochemical reduction and the electrode upon which catalyst is being deposited. If the difference in potentials is too high, then hydrogen will be released which, in turn, will reduce cations of catalytic metal in any area of the channel-cluster structure of the ion- exchange polymer (i.e. not only on the substrate surface areas where said substrate is in contact with the channels of the channel-cluster structure of the ion-exchange polymer) .
  • first particles of metal catalyst such as platinum
  • the decrease of the overvoltage of hydrogen may take place. This may lead to the release of hydrogen and speeding up of the reduction of metal due to chemical reduction in addition to electrochemical reduction. If this speedup is not desirable, for example, when we need to conserve the amount of precious metal, the decrease of voltage will stop the hydrogen formation.
  • electrochemical reduction is carried out preferably using direct or pulse current with an effective value of cathodic current density ranging from 15 to 200 mA/cm and at a temperature ranging from 20 to 95°C for a period of 1 to 2 hours.
  • said electrochemical reduction is preferably carried out using direct or pulse current with the effective value of cathodic current density ranging from 0.5 to 2 A/cm and at a temperature ranging from 20 to 95°C for a period of 1 to 2 hours.
  • Cations that are formed as a result of dissociation in an aqueous solution of lead (II) nitrate or solution of lead (II) acetate are used as lead cations, and electrochemical reduction of lead is carried out at a cathodic density ranging from 10 to 300 mA/cm and at a temperature ranging from 20 to 95°C for a period of 1 to 2 hours.
  • An electrode for electrochemical reactions includes a porous conducting substrate, a layer of a polymer ion-exchange membrane having a channel-clustered structure, formed on the surface of the above-mentioned substrate, and particles of a metallic catalyst fixed to the above-mentioned substrate in locations where the latter conjugates with the channels of the channel-clustered structure of the said layer of the ion-exchange membrane.
  • Carbon or titanium may be used as a material for the porous conducting substrate of the electrode.
  • a layer of the ion-exchange membrane can be made, for example, out of a solid polymer electrolyte, in particular, of "Nafion" carbon tetrafluoride polymer.
  • the thickness of the ion-exchange membrane layer can be from 10 to 30 ⁇ .
  • the catalyst particles can include metals of the platinum series, e.g. platinum or iridium, or ruthenium.
  • the composition of the metallic catalyst can include different metals at the same time, e.g. platinum and iridium, platinum and lead, in proportions by weight varying from 1:5 to 1:15. With that, the particles of different metals may be either randomly located in the catalyst layer, or in successive layers, e.g. lead layer over platinum layer.
  • One exemplary method of electrode manufacturing includes the following stages:
  • a layer of the polymer ion-exchange membrane having a channel-clustered structure is formed on a porous conducting substrate.
  • the layer of the polymer ion-exchange membrane having a channel-clustered structure may be formed in two ways.
  • the first way is to apply a layer of the colloidal solution of the oligomer in an organic solvent, for example, isopropanol, onto the porous conducting substrate with subsequent heating until the polymer layer of the ion- exchange membrane is formed.
  • an organic solvent for example, isopropanol
  • the isopropanol solution of the oligomer in concentration of 8 to ' 12 % by weight is applied to the substrate, and heating of the substrate with the colloidal solution of the oligomer applied to it is done at a temperature of 70 to 100°C for 1 to 1.5 hours.
  • the second way is to apply a layer of the colloidal solution of the polymer in an organic solvent to the porous conducting substrate with subsequent drying by heating until the polymer layer of the ion-exchange membrane with channel- clustered structure is formed.
  • the drying of the colloidal solution of the polymer by heating is done at a temperature in the range of 30 to 100°C for 0.8 to 1.5 hours. 2. Embedding and fixing the catalyst in the reaction zone of the electrode are performed, i.e. the formation of the catalyst layer.
  • cations of one or different metals are introduced into the channels of the channel-clustered structure by means of ion exchange, which are then reduced electrochemically to produce metallic catalyst particles on the porous surface of the substrate in locations where the channels of the channel-clustered structure of the ion-exchange membrane layer conjugate with the substrate.
  • the above-mentioned process of the catalyst layer formation is repeated in succession.
  • Ion exchange saturation of the membrane with the cations of a metal to be used as catalyst
  • concentration of the complex compound or the salt of the metal in the solution, the time of exposure are determined by the desired surface concentration of the metallic catalyst in the electrode.
  • [PtEn 2 Cl2] may be used as a cationic complex compound, where En is ethylenediamine, H2N-CH2-CH2- NH 2 .
  • Electrochemical reduction of platinum is performed at a current density within the range of 0.5 to 1 A/cm and at a temperature of 70 to 90°C for 1 to 2 hours.
  • Conditions for introducing ruthenium, or iridium, or a mixture of the platinum series metals, or platinum and lead (in proportion of 1:5 to 1:15 by weight) as catalysts are analogous (at that the particles of different metals will be randomly located within the catalyst layer) .
  • platinum and lead for example, and it is required that on the electrode the particles of the latter catalyst (i.e. lead) were located over the particles of the former (i.e. platinum), the catalysts are successively introduced in the electrode, i.e. the above-mentioned process of forming the catalyst layer is repeated in succession.
  • platinum cations are first introduced into the channels of the channel-clustered layer of the ion-exchange membrane by means of ion exchange, and reduced electrochemically to obtain metallic particles of the catalyst on the porous surface of the substrate in locations where the channels of the channel-clustered structure of the ion-exchange membrane layer conjugate with the substrate. Further on lead cations are introduced into the channels of the channel-clustered layer of the ion-exchange membrane by means of ion exchange, and reduced electrochemically to obtain metallic particles of lead on the surface of the particles of the first catalyst - platinum.
  • [PtEn2Cl 2 ] 2+ is used as a cationic complex compound for obtaining the first metallic catalyst. Electrochemical reduction of platinum is performed at a current density within the range of 0.5 to 1 A/cm and at a temperature of 70 to 90°C for 1 to 2 hours.
  • Electrochemical reduction of lead is performed at a current density within the range of 0.1 to 0.3 A/ /cm 2 for 1 to 2 hours .
  • the course of action is as follows. For instance, if platinum is used as the first catalyst metal, and iridium is used as the second catalyst metal, then in order to obtain the above- mentioned first catalyst during the introduction of platinum
  • the complex compound of platinum [PtEn 2 Cl2] 2+ is used in ion exchange, where En is ethylenediamine, H2N-CH2-CH2-NH2, at that the electrochemical reduction of platinum is performed at a current density within the range of 0.5 to 1 A/cm 2 and at a temperature of 70 to 90°C for 1 to 2 hours,
  • the complex compound of iridium [IrEn2Cl 2 ] 2+ is used in ion exchange, where En is ethylenediamine, H2N-CH2-CH2-NH2, at that the electrochemical reduction of platinum is performed at a 0 current density within the range of 0.5 to 1 A/cm 2 and at a temperature of 70 to 90°C for 1 to 2 hours.
  • En is ethylenediamine, H2N-CH2-CH2-NH2
  • the electrochemical reduction of platinum is performed at a 0 current density within the range of 0.5 to 1 A/cm 2 and at a temperature of 70 to 90°C for 1 to 2 hours.
  • Conditions for obtaining multi-layer catalysts with any other combination of metals of platinum series or their combination with ruthenium are similar. 5
  • the electrolyzer according to the present invention includes an anode and a cathode, either of those made in the form of the electrode according to any of the above-listed embodiments, i.e. having a porous conducting substrate, a 0 layer of the polymer ion-exchange membrane of channel- clustered structure formed on the surface of the above- mentioned substrate, and metallic catalyst particles fixed to the above-mentioned substrate in locations where the latter conjugates with the channels of the channel-clustered structure of the above-mentioned layer of the ion-exchange membrane, also the electrolyzer includes a separating membrane installed between the anode and the cathode, the above-mentioned separating membrane made out of a polymer ion-exchange material having a channel-clustered structure. The layer of the ion-exchange membrane of the anode and the cathode conjugates with the separating membrane.
  • the exemplary electrolyzer construction includes that both anode and cathode having principally identical catalyst layers .
  • the thickness of the layer of the separating membrane should not exceed 100 ⁇ m.
  • the layer of the electrode ion- exchange membrane and the separating membrane may be made of the same material, for instance, of a solid polymer electrolyte, specifically, of "Nafion" carbon tetrafluoride polymer.
  • the size of the particles and their stability are determined by the fact that the electrochemical process of the reduction of the complex is localized in the channels of the membrane layer; - a reliable contact between the catalyst particles and the electrode substrate, which is achieved by using the electrochemical method of catalyst formation;
  • Distinctive features of the present electrode include its surface layer of the polymer ion-exchange membrane having a unique channel-clustered structure, the composition of the catalyst and the location of the catalyst in the zone of electrochemical reaction - i.e. in the area where the substrate and the surface layer (membrane) are conjugated.
  • Distinctive features of the present method include process steps and conditions for producing the surface layer (membrane) of the electrode, introducing and localizing the catalyst, catalyst composition and the nature of the membrane .
  • Distinctive features of the device - electrolyzer - include the unique anode and cathode, the electrolyte, conjugation of the modified electrode with the electrolyte.
  • Fig. 1 shows the structure of an electrode, where: 1 - porous conducting substrate, 2 - layer of ion-exchange polymer.
  • Fig. 2 schematically shows the segment of an electrode with catalyst consisting of particles of one substance, where: 3 - channels of the channel-cluster structure of layer 2 of ion-exchange polymer, 4 - nano-sized particles of catalyst.
  • Fig. 3 schematically shows the segment of an electrode with a catalyst consisting of particles of two substances, which are applied layer-by-layer one after another, where: 5 - nano-sized particles of one catalyst, 6 - nano-sized particles of another catalyst.
  • Fig. 4 shows the characteristics of catalytic activity of electrodes made by a method disclosed herein.
  • Fig. 5 shows a group of volt-ampere characteristics of an exemplary embodiment of an electrolyzer that includes electrodes made by a method disclosed herein.
  • Fig. 6 presents structural layout of an ozone-producing electrolyzer that includes the principles of the present invention.
  • Gas-diffusion electrodes comprising porous conducting substrate 1 with a layer 2 of ion-exchange polymer with a channel-cluster structure and layer 2 applied onto said substrate such electrodes are used in various applications - e.g. for fuel cells, electrolysis of water, and ozone production.
  • Porous carbon or porous titanium can be used as the material for the porous conducting substrate.
  • the porous conducting substrate may be required to have hydrophobic properties. This can be achieved for example by introducing water repellant into the substrate material.
  • Fluorocarbon polymer sold under the trademark "Nafion", owned by E.I. DuPont de Nemours and Company Corporation, can be used as an ion-exchange polymer.
  • nano-sized particles of metal catalyst should be present in the areas where porous conducting substrate is in contact with channels of the layer of ion-exchange polymer.
  • a method according to the present invention is embodied in the following manner.
  • a blank which consists of a porous conducting substrate with a layer of ion-exchange polymer from about 10 to 30 ⁇ m in thickness, is first submerged in a solution that contains cations of catalytic metal.
  • Cations of catalytic metal are produced by dissolving complex compounds of catalytic metals or salts of catalytic metals.
  • the cations diffuse in the electrolyte, penetrate into the channels of the ion-exchange polymer and replace protons in the ion-exchange polymer (in said channels) by ion exchange. Then cations in the channels of the ion-exchange polymer that have replaced the protons are reduced electrochemically.
  • the reduction process is carried out in a solution that does not contain cations of the catalytic metal. For example, the reduction can be carried out in a bath containing an acid solution.
  • the layer Of polymer and the substrate can be washed in water prior to the reduction step.
  • nano-sized particles of catalytic metal are deposited on those substrate areas, which make contact with the channels of the channel-cluster structure of the ion-exchange polymer (see Fig. 2) .
  • Platinum group metals in particular, platinum, ruthenium, iridium and lead may be used as catalytic metals.
  • this process should be carried out at a potential that is less negative than that at which hydrogen is released (reduced) under given conditions. It is necessary to prevent hydrogen release because free hydrogen has the ability to reduce cations anywhere within the cluster structure, not just on the surface of the substrate.
  • cation complexes are suitable for reducing the catalyst under said conditions that prevent hydrogen release: complex compound of platinum [PtEn 2 Cl2] Cl 2 , complex compound of ruthenium [RuEn2Cl 2 ]Cl, complex compound of iridium [IrEn 2 Cl2] CI, where En - is ethylenediamine H2N-
  • Example 1 Manufacture of a gas-diffusion electrode with a porous conducting substrate having hydrophobic properties .
  • a blank (consisting of a substrate with hydrophobic properties and a layer of ion-exchange polymer) is placed in an aqueous solution of one of the following complex compounds: complex compound of platinum [PtEn 2 Cl2] CI2, complex compound of ruthenium [RuEn2Cl2. CI, complex compound of iridium, or complex compound of platinum [Pt (NH 3 ) Cl2] CI2 with the concentration being within the range from 10 "4 to 5-10 "2 mol/1. After said blank has been kept in said solution for a time period ranging from several minutes to 10 hours, depending upon the particle size desired, it should be washed in distilled water.
  • Electrochemical reduction of the catalyst particles can be performed in a cell with solid electrolyte or liquid electrolyte.
  • liquid electrolyte e.g. a solution of sulfuric acid of concentration from 0.05 to 2 mol per liter
  • electrolysis cell with electrolyte into which both said electrode blank and counter-electrode are submerged
  • solutions of salts e.g. sodium sulfate of the same molar concentration, can be used as electrolyte.
  • an electrolysis cell When reduction is carried out in a cell with solid polymer electrolyte, an electrolysis cell is used, in which said electrode blank and counter-electrode are separated by a membrane made of proton-exchange polymer (e.g. Nafion 117) .
  • a membrane made of proton-exchange polymer e.g. Nafion 117
  • Electrochemical reduction is carried out using direct or pulse current with the effective value of current density ranging from 15 to 200 mA/cm and at a temperature ranging from 20 to 95°C for a period of about 1 to 12 hours.
  • Fig. 4 gives the characteristics of specific activity of catalyst in a hydrogen-oxygen fuel cell made by the proposed technology having the following catalyst loadings: anode - Pt in the amount of 0.01 mg/cm , cathode - Pt in the amount 0.03 mg/cm' 2
  • the substrate was carbon fabric (0.5 mm thick), onto which a gas-diffusion layer consisting of carbon and water repellant was applied under pressure.
  • the amount of water repellant used was 10 % for the cathode and 15 % for the anode.
  • a 5 % Nafion solution was spray-coated onto electrode blank surface. Then this solution was dried for a period of 1 hour at a temperature of 70°C.
  • the thickness of the Nafion layer was equal to 15 ⁇ m (for cathode) and 30 ⁇ m (for anode) .
  • Electrode blanks were placed in a 0.001 M solution of complex [PtEn 2 Cl2_ Cl 2 for a period of 20 minutes for the anode, and 60 minutes for the cathode. Reduction was carried out in two stages. During the first stage a 200 mA/cm 2 current was applied for 2 hours for anode and 4 hours for cathode. During the second stage the current was decreased to 50 mA/cm 2 and applied for a period of 4 hours for anode and 6 hours for cathode.
  • Example 1 includes in the following.
  • a colloid solution of oligomer in an organic solvent with a concentration in the range from 8 to 12 % by weight is applied onto a porous electrically conductive substrate made out of porous carbon or titanium.
  • a porous electrically conductive substrate made out of porous carbon or titanium.
  • 0.2 ml of oligomer solution in isopropanol with a concentration of 8.6 % by weight is applied onto 1 cm 2 surface of porous carbon or titanium.
  • the substrate with the applied colloid solution is heated up until a polymer layer of an ion-exchange membrane with a channel-clustered structure is formed on the porous surface of the substrate. Said heating is conducted at a temperature in the range from 70 to 100°C during a period from 1 to 1.5 hours.
  • the thickness of membrane produced following the thermal treatment of the electrode lies within 10-30 ⁇ m. Produced membrane is characterized by high adhesion to substrate.
  • Polymer layer of an ion-exchange membrane may be produced as a result of the application of a colloid solution of polymer and subsequent drying of this solution. Drying of a colloid solution of polymer is conducted at a temperature from 30 to 100°C during a period from 0.8 to 1.5 hours. Produced membrane is characterized by high adhesion to substrate.
  • the next step in the electrode manufacturing process includes in the introduction of a cation complex compound into the channels of a channel-clustered structure of a layer of an ion-exchange membrane.
  • a cation complex compound for example, compounds based on platinum and iridium.
  • [PtEn2Cl 2 ] 2+ is used as a cation complex for the purpose of deposition of platinum catalyst on a substrate.
  • Cation complex compound is introduced into a membrane in an aqueous solution of the source complex [PtEn2Cl2] 2+ with a concentration of 10 mole/1.
  • the final concentration of platinum catalyst is determined by the period during which an electrode with a membrane stays in platinum complex (this period varies from 20 minutes to 3 hours) . For instance, to attain surface concentration of a platinum catalyst equal to 10 ⁇ 5 g/cm 2 , one would have to hold a substrate with a membrane layer in said solution for a period of one hour.
  • Electrochemical reduction of platinum is carried out with current density being in the range from 0.5 to 1 A/cm and at a temperature from 70 to 90°C during a period from 1 to 2 hours.
  • the steps of the introduction of a cation complex compound and electrochemical reduction of a metal catalyst may be repeated several times.
  • Example 2 Manufacture of a gas-diffusion electrode with a porous conducting substrate that does not have hydrophobic properties.
  • a blank (consisting of a substrate and.a layer of ion- exchange polymer) is placed in an aqueous solution of one of the complex compounds listed in Example 1. Replacement of a portion of the protons on the walls of the channel-cluster structure of the ion-exchange polymer with cations of the complex compound is performed in the same manner as in Example 1.
  • Electrochemical reduction of catalyst particles is carried out in liquid electrolyte using direct or pulse current.
  • the effective value of current density ranges from 0.5 to 2 A/cm at a temperature ranging from 20 to 95°C for a period of 1 to 2 hours.
  • Fig. 5 shows the volt-ampere characteristics of an electrolyzer, in which electrodes manufactured by the described technology were employed.
  • Curve 1 was obtained with a surface concentration of platinum catalyst equal to 10 ⁇ g/cm 2 for the cathode and 20 ⁇ g/cm 2 for the anode.
  • Curve 2 was obtained with a surface concentration of platinum catalyst equal to 20 ⁇ g/cm for the cathode and 40 ⁇ g/cm for the anode.
  • Curve 3 was obtained with a surface concentration of platinum catalyst equal to 40 ⁇ g/cm for the cathode and 80 ⁇ g/cm 2 for the anode.
  • the thickness of the ion-exchange polymer layer was 100 ⁇ m. It can be seen from the graphs that acceptable densities of electrolysis current at low values of voltage are attained using electrodes having low loadings of a catalyst.
  • Electrodes of porous titanium were used as electrodes.
  • a layer of ion-exchange polymer was applied by spray-coating 5% Nafion solution onto the electrode blank surface. Then this solution was dried for a period of 1 hour at a temperature of 70°C.
  • electrode blanks were placed in a 0.001 M solution of complex [PtEn2Cl2] Cl 2 for a period of 15 minutes (at a concentration of 10 ⁇ g/cm 2 ) , 30 minutes (at a concentration of 20 ⁇ g/cm 2 ) , 60 minutes (at a concentration of 40 ⁇ g/cm 2 ) , and 120 minutes (at a concentration of 80 ⁇ g/cm 2 ) .
  • Reduction was carried out using 1 A/cm current for a period of 1 hour at a temperature of 35°C.
  • Example 3 Manufacture of a gas-diffusion electrode having a layer-by-layer arrangement of platinum and lead catalyst layers.
  • Catalyst particles may include of two and more metals .
  • Fig. 3 shows a catalyst including of platinum particles 5 and lead particles 6. In this case the proportion of platinum and lead by weight will be in the range from 1:5 to 1:15.
  • Particles 5 and 6 of the catalyst also make electrical contact with conducting substrate 1 at the junctures of conducting substrate 1 with channels 3 of the channel-clustered structure of layer 2 of the ion-exchange membrane .
  • Electrochemical reduction of nano-sized crystalline particles of lead was performed using a current density ranging from 10 to 300 mA/cm 2 at a temperature ranging from 20 to 95°C for a period of 1 to 2 hours.
  • Electrodes for an electrochemical ozonizer were manufactured by the method claimed herein.
  • the loading of platinum catalyst on the cathode was equal to 0.01 mg/cm 2 .
  • the anode was made using two layers of catalyst. The layer immediately adjacent to the substrate was platinum at a loading of 0.01 mg/cm 2 . The next layer, formed above the platinum layer, was lead at a loading of 0.05 mg/cm 2 .
  • Preparation of the electrode and application of the layers was the same as those described in Example 2. Then anode blanks were placed in a 0.2 M aqueous solution Pb(N0 3 ) 2 for a period of 1 hour.
  • Electrochemical reduction of lead to achieve a surface concentration of 50 ⁇ g/cm was performed using a current density with an effective value equal to 100 mA/cm 2 for a period of 2 hours.
  • oxidation of lead to lead (IV) oxide was performed.
  • a catalytic layer of D-modification of lead dioxide (oxidation mode was as follows: current density - 150 mA/cm 2 , duration - 1 hour) was formed on the electrode surface during this process.
  • a membrane made of Nafion 117 was installed in the ozonizer between the electrodes.
  • An assembly (consisting of electrodes and membrane) with an active area equal to 7 cm 2 , with the value of current equal to 2 A and voltage equal to 4 V produced a concentration of ozone in water that was no less than 0.5 mg/1 with the flow rate of water equal to 2 liters per minute.
  • Example 3 following the reduction of metal platinum, the following steps are to be performed.
  • lead cations Pb 2+ was introduced into a channel-clustered structure of a polymer using the ion exchange method for this purpose (for example, implantation of cations was carried out from 0.2 ml of an aqueous solution of Pb(N0 3 ) 2 during a period from 20 minutes to 2 hours) , after which step the electrochemical reduction of catalyst cations ' on electrode surface is performed (said reduction is accompanied by the production of metal lead deposits of nano size with a surface concentration from 10 ⁇ 5 to 10 ⁇ 4 g/cm 2 ) .
  • the reduction was carried out in an electrolytic cell with current density being of the order of 0.1 A/cm during a period of approximately 2 hours.
  • a construction of an electrolyzer is shown in Fig. 6.
  • a device for ozone production includes of two plates 7 having grating-type elements 8 intended for supplying water and removing gas. Plates 7 squeeze together cathode 9 and anode 10, between which separating membrane 11 is placed (this separating membrane is a solid polymer electrolyte - for example, of "Nafion" type) .
  • This layer of polymer ion-exchange membrane 2 serves as a carrier for particles of metallic catalyst.
  • a specific feature of the construction of described electrolyzer intended for ozone production includes in the fact that a gap between cathode 9 and anode 10 doesn't exceed 100 ⁇ m, which fact makes it possible to create electric field of high strength in the inter-electrode space. Such field strength is comparable with the conditions for ozone production in a corona discharge. It facilitates the weakening of bonds in an oxygen molecule which fact results in the increase in ozone production efficiency.
  • the suggested construction of the device enables one to attain greater yield of ozone as compared to other known constructions of ozone producing devices.
  • the use of electrodes according to the present invention allows one to attain 1% output of ozone (current output) at a room temperature, and the use of the combined catalyst allows one a to attain 4-5% output of ozone (current output) at a room tempe'rature .
  • Practical implementation of the inventions disclosed herein goes beyond specific examples given above. It will be apparent that none of the figures are necessarily drawn to scale. Other and further modification, enhancements, and changes can be made to the herein disclosed embodiments ' without departing from the spirit and scope of the present invention. The selection of materials can be standard and are well known in the art.

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  • Manufacturing & Machinery (AREA)
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  • Thermal Sciences (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
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  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
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Abstract

L'invention concerne des procédés de fabrication d'une électrode à diffusion gazeuse utilisée dans l'électrolyse de l'eau et dans la production d'ozone, ainsi que d'autres dispositifs électrochimiques. Une partie des protons d'un polymère échangeur d'ions (2) est substituée dans les canaux (3) d'une structure de canaux regroupée d'un polymère échangeur d'ions (2) par des cations de catalyseur métallique (4). Cette substitution est réalisée au moyen d'un procédé échangeur d'ions. Ensuite, ces cations sont électrochimiquement réduits sous forme de particules métalliques d'un catalyseur (4) sur les zones des substrats (1) où ce dernier est en contact avec les canaux (3) de la structure de canaux regroupée de la couche polymère échangeuse d'ions (2).
PCT/US2002/026653 2001-08-22 2002-08-21 Electrode de reaction electrochimique, procede de fabrication et dispositif d'application WO2003018469A1 (fr)

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JP2003523141A JP2005501177A (ja) 2001-08-22 2002-08-21 電気化学的反応電極、製造方法、及びその適用機器。
EP02761457A EP1434734A1 (fr) 2001-08-22 2002-08-21 Electrode de reaction electrochimique, procede de fabrication et dispositif d'application

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JP2006040703A (ja) * 2004-07-27 2006-02-09 Aisin Seiki Co Ltd 固体高分子型燃料電池の触媒担持方法、膜電極接合体
KR100647700B1 (ko) * 2005-09-14 2006-11-23 삼성에스디아이 주식회사 담지 촉매 및 이를 이용한 연료전지
US8846161B2 (en) * 2006-10-03 2014-09-30 Brigham Young University Hydrophobic coating and method
CA2664536A1 (fr) * 2006-10-03 2008-04-10 Sonic Innovations, Inc. Revetement hydrophobe et oleophobe et procede pour preparer celui-ci
US7709413B2 (en) 2007-11-26 2010-05-04 Kabuhsiki Kaisha Toshiba Solid catalysts and fuel cell employing the solid catalysts
US10658678B2 (en) * 2014-06-17 2020-05-19 Georgetown University Electrocatalysts, and fuel cells containing them
US9777382B2 (en) * 2015-06-03 2017-10-03 Kabushiki Kaisha Toshiba Electrochemical cell, oxygen reduction device using the cell and refrigerator using the oxygen reduction device
KR102054981B1 (ko) * 2017-08-16 2019-12-12 한국과학기술원 산화 이리듐 나노 촉매 및 그 제조방법
GB201719463D0 (en) 2017-11-23 2018-01-10 Johnson Matthey Fuel Cells Ltd Catalyst
CN110600808B (zh) * 2019-09-20 2022-04-12 哈尔滨工业大学 一种氟化碳改善固态电解质界面锂枝晶的方法
EP4421212A1 (fr) * 2021-10-20 2024-08-28 Toray Industries, Inc. Assemblage membrane-électrodes et dispositif d'électrolyse de l'eau
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