Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
  • C25D17/10—Electrodes, e.g. composition, counter electrode
• • 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
  • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
  • C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
• • 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

Definitions

• the present invention concerns an anode with high activity, dimensional stability and no dissolution in prolonged operation in electrochemical reactions such as electrolysis and electrodeposition.
• titanium and other metals are used as the anode for electrolysis of solution of electrolytic substances and electrodeposition. Since the anode is polarized at high potentials and exposed to highly oxidizing condition, use of such metals is to utilize the characteristics of the metals that they form corrosion-resistant insulating film under such highly oxidizing condition.
• the insulating surface film thus formed prevents the electron transfer through their surfaces which is the role of an electrode.
• titanium coated with oxides of an element or elements of the platinum group hereinafter referred to as "platinum group element(s)" resistant to highly oxidizing condition and having a high activity for the anode have been used.
• the electrode will consist of a continuum of titanium substrate and electrocatalyst consisting of double oxide of titanium ion and electrocatalyst metal ion.
• the currently used dimensionally stable anodes are composed of the titanium substrate coated with oxides of the platinum group elements such as RuO 2 , RhO 2 , PdO 2 , and IrO 2 .
• oxides have the same rutile structure as TiO 2 and their lattice constants are not largely different from those of TiO 2 , with a consequent continuity from the titanium substrate to the electrocatalyst.
• oxides IrO 2 is regarded to be the most suitable.
• the wide use of the precious metal electrodes will result in consumption of a large amount of precious metals, and will lead to the lack of the resources.
• the highly active electrode with the use of small amounts of precious metals is desirable.
• the coating substance on the titanium substrate prefferably has the same rutile structure as TiO 2 and to be stable even under highly oxidizing condition.
• Tin oxide, SnO 2 has the same rutile structure as TiO 2 and is stable even in highly oxidizing environments.
• the inventors found use of SnO 2 together with precious metal oxides. Electric conductivity of SnO 2 is not high, and this is a difficulty in using.
• the inventors found that addition of Sb to Sn enhances electric conductivity of SnO 2 .
• the object of the present invention is, utilizing the above-mentioned knowledge, to provide a dimensionally stable anode with high performance and durability for electrochemical reactions such as electrolysis and electrodeposition, and to_reduce consumption of the precious metals resulting in mitigation of the resource problems.
• the above object is accomplished by the electrode made by coating the titanium substrate with multiple oxide of the platinum group element(s) as well as Sn and Sb.
• the anode of the present invention for electrochemical reactions consists of the titanium substrate coated with multiple oxide of the platinum group element(s), and Sn and Sb, in which the cationic ratio of Sn to Sb is 1-40 and the sum of Sn and Sb is 90 cationic % or less.
• Corrosion resistant titanium is suitable for the conducting substrate of the electrode which is exposed to highly oxidizing environment.
• the substrate is subjected to treatments for removal of the air-formed oxide film and surface roughening to enhance adhesion of the electrocatalyst thereto.
• the titanium substrate is coated by repeated brushing of the solution such as butanol solution of adequate concentrations of salts of the platinum group element(s), and salts of Sn and Sb, and subsequent drying and calcinations at 550°C.
• the electrode with the electrocatalyst of multiple oxide consisting of oxides of Sn and Sb as well as one or more of the platinum group element(s) is prepared.
• the platinum group element(s) are the basic elements of the electrocatalysts of the present invention, and Ru, Rh, Pd, Os, Ir and Pt form MO 2 type oxide s . These oxides, except for PtO 2 , have the same rutile structure as TiO 2 and SnO 2 , and form solid solutions therewith.
• the lattice constants in "a"-axis and "b"-axis of PtO 2 are quite close to those of TiO 2 and SnO 2 , and hence, PtO 2 forms a single phase oxide with TiO 2 and SnO 2 .
• Sb is added for the purpose of enhancing the electric conductivity of the electrocatalyst that is insufficient in the multiple oxide consisting of only platinum group element(s) and Sb. If Sn is contained in such an amount that the cationic Sn/Sb ratio is 40 or higher, the oxides formed have sufficient electric conductivity, and hence the Sn/Sb ratio should be 40 or higher. However, excess addition of Sb rather decreases the electric conductivity of the multiple oxide, and hence, addition of Sb must be at such level that the cationic Sn/Sb ratio is unity or less.
• the electrodes of the present invention when used for electrochemical reactions as the anodes for electrolysis or electrodeposition, exhibit high activity and are capable of maintaining the dimension even in a prolonged operation without being dissolved.
• conventional oxide electrodes consisting of only platinum group element(s) or their_oxide or oxides, necessary amount of the precious metal is lower, and the costs for producing are cheaper with mitigation of problem of resources.
• a titanium mesh substrate made by punching a titanium_plate was immersed in 0.5 M HF solution for 5 min. to remove surface oxide film, and then subjected to etching in 11.5 M H 2 SO 4 solution at 80°C for the purpose of increasing the surface roughness until hydrogen evolution ceased. Titanium sulfate formed on the surface of the titanium mesh was washed away by flowing tap water for about 1 hr. Immediately before covering with the electrocatalysts the titanium mesh was ultrasonically rinsed with deionized water.
• the titanium mesh with the effective surface area of 20 cm 2 was coated by brushing mixed butanol solutions of 4.0 ml of 5 M K 2 IrCl 6 , 5.33 ml of 5 M SnCl 4 and 0.67 ml of 5 M SbCl 6 , dried at 90°C for 5 min. and calcined for conversion to oxide at 550°C for 10 min. This procedures were repeated until the weight of the oxide increased to about 45 g/m 2 .
• the electrode was obtained by final calcination at 550°C for 60 min.
• the cationic composition of the electrocatalyst thus formed was determined by EPMA.
• the cationic percentages of Ir, Sn and Sb were 65.6, 29.3 and 5.1, respectively.
• Example 2 The same surface treatments as Example 1, such as removal of the surface film, etching for surface roughening, rinsing with water and ultrasonic rinsing were applied to the punched titanium substrate meshes of the effective surface area of 20 cm 2 .
• the titanium meshes were coated by repetition of brushing of the butanol solutions, drying at 90°C for 5 min. and calcination for conversion to oxide at 550°C for 10 min. until the weight of the oxide increased to 45 g/m 2 .
• the electrodes were obtained by final calcination at 550°C for 60 min.
• the cationic compositions of the electrocatalysts thus formed were determined by EPMA as shown in Table 1. X-ray diffraction identified that the electrocatalysts of the electrodes were composed of the single phase triple oxide with the same rutile structure as IrO 2 .
• electrolysis was carried out in 3 M H 2 SO 4 at 40°C at current density of 10,000 A/m 2 , and the anode potential was measured.
• the period s of time during which the overpotential of the anode was kept at about 0.6 V are shown in Table 1, in which the period of time for the comparative IrO 2 anode in Example 1 is also shown. It was clarified that the anodes of the present invention have better durability as the oxygen evolution anodes in the electrolysis of strong acid in comparison with the conventional dimensionally stable anode.
• Example 2 The same surface treatments as Example 1, i.e., removal of the surface film, etching for surface roughening, rinsing with water and ultrasonic rinsing, were applied to the punched titanium substrate meshes of the effective surface area of 20 cm 2 .
• 5 M precious metal butanol solutions i.e., 5 M RuCl 3 , 5 M RhCl 3 , 5 M PdCl 3 , 5 M OsCl 3 , 5 M K 2 IrCl 6 and 5 M K 2 PtCl 6 butanol solutions.
• the solutions of the above 5 M precious metal butanol solutions, and the solutions of 5 M SnCl 4 and 5 M SbCl 6 also prepared as butanol solutions were mixed in_various ratios to prepare mixed solutions.
• the electrode were obtained by final calcination at 550°C for 60 min.
• the cationic compositions of the electrocatalysts thus formed were determined by EPMA and are shown in Table 2. X-ray diffraction identified that the electrocatalysts of the electrodes were composed of the single phase multiple oxide with the same rutile structure as IrO 2 .

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• Electrodes For Compound Or Non-Metal Manufacture (AREA)

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Citations (3)

• 2007
  • 2007-10-31 EP EP07119711A patent/EP2055806A1/fr not_active Ceased

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