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
• • 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
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
  • C25B11/093—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one noble metal or noble metal oxide and at least one non-noble metal oxide
• • 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

• ABSTRACT A method for manufacturing an electrode for use in electrochemical processes which comprises coating 21 support member made ofa film-forming metal or alloy thereof with a first layer of a mixture of a platinum group metal and a film-forming metal oxide and then coating said first layer with a second layer consisting of a film-forming metal oxide.
• the present invention relates to electrodes for electrochemical processes. More particularly it relates to electrodes comprising a support member of a filmforming metal carrying a coating which is active in transferring an electric current from the support member to ions of an electrolyte and is resistant to electrochemical attack.
• the present invention provides improved electrodes incorporating coatings comprising platinum group metal oxides.
• the electrodes of the invention are very useful as anodes in cells for the electrolysis of alkali metal chloride solutions. They are particularly useful in cells with flowing mercury cathodes, because the elec trodes have a high resistance to damage by short-circuit contact with the cathode, such as may occur accidentally even during the normal course of operation in these cells.
• the electrodes can also be used in other electrochemical processes, including other electrolytic processes, electrocatalysis, as for instance in fuel cells, electrosynthesis and cathodic protection.
• an electrode for use in electrochemical processes which comprises a support member made of a film-forming metal or alloy and a coating thereon consisting of a layer of a mixture of the oxide(s) of at least one platinum group metal in a proportion of -80 percent by weight and a film-forming metal oxide and superimposed on the said layer a layer of a film-forming metal oxide.
• the ratio of platinum group metal oxideszfilm-forming metal oxide in the layer of the said mixture is not less than 121 but is less than 2:1 by weight.
• a film-forming metal we mean one of the metals titanium, zirconium, niobium, tantalum and tungsten.
• a film-forming alloy we mean an alloy containing a major proportion of one of these metals and having anodic polarisation properties similar to the commercially pure metal.
• the support member of the electrode is preferably made of titanium or a titanium alloy having anodic polarisation properties similar to those of titanium.
• oxide(s) of at least one platinum group metal we mean the oxide(s) of at least one of the metals ruthenium, rhodium, palladium, osmium, iridium and platinum.
• the layer of the said mixture consists of ruthenium dioxide and titanium dioxide and the superimposed layer consists of titanium dioxide.
• the preferred method of forming the layer of mixed oxides on the support member is as follows.
• a coating of a paint composition comprising a thermally decomposable compound of at least one platinum group metal and a thermally decomposable organo-compound of a film-forming metal in an organic liquid vehicle and optionally also comprising a reducing agent, e.g., linalool, is applied to the support member, the coating is dried by evaporation of the liquid vehicle and the coated support is then heated in-an oxidising atmosphere, e.g., in air, at a temperature of at least 350C and preferably in the range 400-550C to convert the compounds of the platinum group metals and the film-forming metal to oxides of these metals.
• a reducing agent e.g., linalool
• Further coats of the paint composition may then be applied to the coated support, dried and heated in the same manner to increase the thickness of the mixed oxide layer to any desired extent.
• electrolysing alkali metal chloride solutions we prefer to build up a thickness of this layer in the range 10-l5g/m of the coated surface of the support member. This thickness is, however, in no way critical. Thinner or thicker coatings may be employed and the thickness will generally be chosen having regard to the wear to which the electrode will be submitted during use in the cell, which itself will be related inter alia to the current density at which the electrode will be required to operate.
• the preferred method of forming the superimposed layer of film-forming metal oxide is by applying over the mixed oxide layer a coating of a thermally decomposable organo-compound of the film-forming metal in an organic liquid vehicle, drying the coating by evaporation of the liquid vehicle and then heating the coating in an oxidising atmosphere, e.g., air, to convert the organo-compound of the film-forming metal to the oxide of the metal.
• the preferred thickness of this superimposed layer of film-forming metal oxide is in the range 2-10g/m of the coated surface.
• the desired thickness of this layer may be obtained by adjusting the viscosity of the coating composition by adding more or less of the organic liquid vehicle and/or by repeated application of thinner layers of coating composition, drying and heating each coating, to build up the desired thickness.
• thermally decomposable organo-compounds of the film-forming metals employed in forming the superimposed layer of film-forming metal oxide in accordance with the preceding paragraph are most suitably the alkyl titanates, the alkyl halotitanates wherein the halogen is chlorine, bromine or fluorine (alternatively known as titanium alkoxides and alkoxy-halides) and the corresponding alkyl compounds of other filmforming metals.
• Other suitable thermally decomposable organo-compounds are resinates of the film- .forming metals.
• the preferred compounds are the alkyl titanates and halotitanates, especially those in which the alkyl groups contain 2-4 carbon atoms each.
• Coatings of these preferred compounds applied in an organic liquid vehicle as aforesaid are suitably dried at a temperature of lOO-200C and then heated in an oxidising atmosphere at 250800C, preferably at 3505 50C, to convert the titanate compounds to titanium dioxide.
• thermally decomposable compounds of the film-forming metals listed in the preceding paragraph may also be employed in the paint compositions used for forming the under-layer of mixed oxides on the electrode support member.
• the alkyl titanates and the alkyl halotitanates wherein the halogen is chlorine, bromine or fluorine, especially those in which the alkyl groups contain 2-4 carbon atoms each are preferred.
• the thermally decomposable compounds of the platinum group metals used in these paint compositions may suitably be halides, e.g., ruthenium trichloride, halo-acid complexes, e.g., hexachloroplatinic acid, or resinates of these metals.
• the preferred platinum group metal compound is ruthenium trichloride.
• the invention is further illustrated by the following Example 5.
• EXAMPLE 1 A strip of titanium 35 cm long, cross section 6 mm X 1 mm was etched in oxalic acid solution, washed, dried and then painted with a mixture of 4.3g partly hydrated ruthenium trichloride, 12.0g n-pentanol and 6.4g tetrabutyl ortho titanate. The paint layer was dried at 180C and then fired by heating in air at 450C for 15 minutes. A total of six layers of this paint was applied, each layer being dried and heated in the same manner, to give a loading on the titanium surface of l4g/m of a coating consisting of 60 percent ruthenium dioxide and 40 percent titanium dioxide by weight.
• Samples cut from the coated strip were tested as anodes for chlorine production in sodium chloride brine containing 21.5% NaCl at pH 2-3 and a temperature of 65C.
• the samples operated with low overpotential (50 mV at a current density of 8 kA/m and they also showed excellent resistance to damage when contacted with the cathode amalgam in a mercury cell electrolysing sodium chloride brine.
• EXAMPLE 2 An anode whose working surface was in the form of a grid made up oftitanium strips and having a projected area of 0.1 m was in oxalic acid solution for 16 hours, washed and dried. The anode grid was then sprayed with a paint composition consisting of 60.5 g ruthenium trichloride and 90.0 g tetra-n-butyl ortho titanate in 300 g n-pentanol. The paint layer was dried in an oven at 180C and was then converted to a layer of composition 60% RuO /40% TiO by weight by heating in air in a furnace at 450C for 20 minutes.
• a further five layers of the same paint composition were then sprayed on to the anode, each layer being dried and then fired by heating in air as was the first layer.
• An outer layer consisting of titanium dioxide alone was then applied to the anode grid by spraying on to it three coats of a paint composition consisting of g tetra-n-butyl titanate in 75 g n-pentanol, each being dried at 180C and then fired in air at 450C for 20 minutes.
• the total loading of oxides deposited on the titanium grid was then 32 g/m projected area.
• the coated titanium anode was installed in a mercury-cathode cell electrolysing sodium brine, as a replacement for a graphite anode, and after operating satisfactorily for six months with an anode current of up to 900 amp. there was no apparent wear nor decline in performance.
• EXAMPLE 3 A titanium grid anode of 0.1 m projected area was coated as in Example 2 except that the paint composition used for the first six coats consisted of 55 g ruthenium trichloride and 101 g tetra-n-butyl ortho titanate in 300 g n-pentanol. This composition, after drying and firing, produced an underlayer on the titanium grid of composition 55% RuO /45% TiO by weight. The outer layer consisting of titanium dioxide alone was then deposited as in Example 2. This anode was also operated in a mercury-cathode cell electrolysing sodium chloride brine and also showed no signs of wear nor decline in performance after six months use with an anode current of up to 900 amp.
• the said support member is made of titanium or a titanium alloy having anodic polarisation properties similar to those of titanium.
• step (1) the thermally decomposable compound of at least one platinum group metal is ruthenium trichloride.
• step (1) the temperature at which each coating is heated in an oxidising atmosphere is in the range 400550C.
• step (1 the number of coatings of the said composition applied, dried and heated on the support member is sufficient to build up a layer of mixed oxides amounting to 10-15 g/m of the coated surface of this support memher.
• step (1) the thermally-decomposable organo-compound of a film-forming metal is an alkyl titanate or an alkyl halotitanate wherein the halogen is chlorine, bromine or fluorine.
• step (2) 8. A method according to claim 1, wherein the total amount of coating which is applied over the said layer of mixed oxides is sufficient to produce in step (2) a layer of film-forming metal oxide amounting to 2-10 g/m of the coated surface.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Secondary Cells (AREA)
• Chemically Coating (AREA)

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Cited By (21)

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Citations (8)

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• 1971
  • 1971-03-18 GB GB721171*[A patent/GB1352872A/en not_active Expired
• 1972
  • 1972-03-06 ZA ZA721481A patent/ZA721481B/xx unknown
  • 1972-03-06 NO NO707/72A patent/NO140235C/no unknown
  • 1972-03-10 AU AU39853/72A patent/AU463572B2/en not_active Expired
  • 1972-03-12 IL IL38958A patent/IL38958A/xx unknown
  • 1972-03-14 AR AR240928A patent/AR194834A1/es active
  • 1972-03-15 TR TR17134A patent/TR17134A/xx unknown
  • 1972-03-16 BE BE780756A patent/BE780756A/xx not_active IP Right Cessation
  • 1972-03-17 BR BR1555/72A patent/BR7201555D0/pt unknown
  • 1972-03-17 CH CH396672A patent/CH578625A5/xx not_active IP Right Cessation
  • 1972-03-17 JP JP2659972A patent/JPS559471B1/ja active Pending
  • 1972-03-17 IT IT7222049A patent/IT950343B/it active
  • 1972-03-17 CA CA137,422A patent/CA976505A/en not_active Expired
  • 1972-03-17 DD DD161624A patent/DD99934A5/xx unknown
  • 1972-03-17 NL NL7203580A patent/NL7203580A/xx active Search and Examination
  • 1972-03-17 FR FR7209511A patent/FR2130419B1/fr not_active Expired
  • 1972-03-17 DE DE19722213083 patent/DE2213083A1/de not_active Ceased
  • 1972-03-18 ES ES400915A patent/ES400915A1/es not_active Expired
  • 1972-03-20 AT AT235172A patent/AT312633B/de not_active IP Right Cessation
• 1973
  • 1973-09-04 US US394394A patent/US3869312A/en not_active Expired - Lifetime
• 1974
  • 1974-12-31 MY MY1974318A patent/MY7400318A/xx unknown

Patent Citations (9)

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