EP0018970A1 - Elektroden für elektrolyseverfahren, insbesondere perchlorat-herstellung - Google Patents

Elektroden für elektrolyseverfahren, insbesondere perchlorat-herstellung

Info

Publication number
EP0018970A1
EP0018970A1 EP79900338A EP79900338A EP0018970A1 EP 0018970 A1 EP0018970 A1 EP 0018970A1 EP 79900338 A EP79900338 A EP 79900338A EP 79900338 A EP79900338 A EP 79900338A EP 0018970 A1 EP0018970 A1 EP 0018970A1
Authority
EP
European Patent Office
Prior art keywords
weight
platinum
coating
tin
electrode
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Withdrawn
Application number
EP79900338A
Other languages
English (en)
French (fr)
Inventor
Vittorio De Nora
Antonio Nidola
Placido Maria Spaziante
Guisseppe Bianchi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Diamond Shamrock Technologies SA
Original Assignee
Diamond Shamrock Technologies SA
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Diamond Shamrock Technologies SA filed Critical Diamond Shamrock Technologies SA
Publication of EP0018970A1 publication Critical patent/EP0018970A1/de
Withdrawn legal-status Critical Current

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Classifications

    • 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 invention relates to electrodes for use in electrolytic processes, of the type comprising an electrically-conductive and corrosion-resistant substrates having an electrocatalytically-active surface coating, and to electrolytic processes using such electrodes, especially (but not exclusively) as anodes for the production of chlorates, perchlorates and other persalts and percompounds including organic peroxyacids.
  • US Patent Specification 3,882,002 proposed an anode for chlorine production having a valve metal Substrate coated with an intermediate layer of tin dioxide which was covered with an outer layer of a platinum group metal or oxide thereof. Neither of these proposals was directed to improving electrolytic performance in the production of percompounds.
  • an object of the invention therefore is to provide an improved electrode suitable for use as an anode for the production of perchlorates and other persalts, but which may also be used in other applications, such as chlorate production.
  • an electrode comprises an electrically-conductive corrosion-resistant Substrate having an electrocatalytic coating and is characterized in that the coating contains a mixture of at least one platinum group metal and tin dioxide dispersed in one another throughout the coating in the ratio of 8: 5: 1 to 3: 2 by weight of the platinum group metals to the tin (as metal) of the tin dioxide.
  • the platinum group metal / tin dioxide coating may also contain a stabilizer / binder, for example a compound such as titanium dioxide, zirconium dioxide or Silicon dioxide. Additionally, the coating may include a filier, eg particles or fibers of an inert material, such as silica or alumina, particles of titanium, or zirconium silicate. Furthermore, the coating may also contain, eg, as a dopant the tin dioxide in a quantity up to about 30% by weight ⁇ as metal) of the tin dioxide, of at least one additional metal or oxide of zinc, cadmium, arsenic, antimony, bismuth., selenium and tellurium.
  • a stabilizer / binder for example a compound such as titanium dioxide, zirconium dioxide or Silicon dioxide.
  • the coating may include a filier, eg particles or fibers of an inert material, such as silica or alumina, particles of titanium, or zirconium silicate.
  • the coating may also
  • Such stabilizers or binders, fillers and dopants generally do not account for more than 70% of the total weight of the coating, usually far less.
  • the preferred amount corresponds to a ratio expressed as parts by weight of Sb / Bi: Sn (as metal) of at most about 1: 4 to about 1:10 or even as low as 1: 100.
  • the platinum group metals are ruthenium, rhodium, palladium, osmium, iridium and platinum. Platinum is the preferred platinum group metal in the coating, when a single metal is present, especially in anodes for perchlorate production. However, it is understood that alloys such as platinum-iridium and platinum-rhodium, also are useful for other applications. An alloy of platinum-palladium containing up to 20% palladium by weight of the alloy has given very satisfactory results for perchlorate production.
  • the platinum group metal (s) with one or more non-platinum group metals, for example an alloy or an intermetallic compound with one of the valve metals titanium, zirconium, hafnium y vanadium , niobium and tantalum, or with another transition metal, for example a metal such as tungsten, manganese or cobalt.
  • the substrates may consist of any of the aforementioned valve metals or alloys thereof, porous sintered titanium being preferred.
  • other electrically conductive and corrosion-resistant substrates may be used, such as expanded graphite.
  • platinum group metal '(s) and tin dioxide with possible additional dopants may be co-deposited chemically from Solutions of appropriate salts which are painted, sprayed or otherwise applied on the Substrate and then subjected to heat treatment, this process being repeated until a sufficiently thick layer has been built up.
  • thin layers of different components can be built up in such a way that the components are effectively mixed and dispersed in one another throughout the coating, possibly with diffusion between the layers, in contrast to the known prior art coatings such as that of US Patent Specification 3,882,002, in which the tin dioxide was applied as a separate intermediate layer covered by a platinum group metal.
  • alternate layers it is possible to deposit thin layers of platinum galvanically, which is advantageous, because gal vanically-deposited platinum has a lower ⁇ xygen evolution potential than chemi-deposited platinum.
  • the platinum-group metal or alloy / tin dioxide layer may be applied directly to the substrates, or to an intermediate layer, e.g. of co-deposited tin and antimony oxides or tin and bismuth oxides, or to intermediate, layers consistihg of one or more platinum group metals or their oxides, mixtures or mixed crystals of platinum group metals and valve metal oxides, intermetallics of platinum group metals and non-platinum group metals, and so forth.
  • the coating comprises 40 to 85 parts by weight of platinum, 0 to 20 parts by weight of palladium and 15 to 40 parts by weight (as Sn metal) of tin dioxide on a titanium, tantalum or titanium-tantalum alloy substrates.
  • This embodiment of an electrode of the invention when used as anode for perchlorate or persulphate production, has been found to have selective properties favoring the persalt production while hindering oxygen evolution.
  • the platinum metal acts as a catalyst for persalt production.
  • the tin dioxide acts as an oxygen evolution inhibitor by blocking peroxide decomposition, which can be regarded as the intermediate step of the unwanted oxygen evolution reaction.
  • the palladium acts as a diluent for the relatively more expensive platinum, without adversely affecting the oxygen inhibition effect of the tin dioxide.
  • Another aspect of the Invention is a process for the production of chlorates, perchlorates and other percompounds, e.g. persulphates, which is characterized by using as anode an electrode according to the invention, as defined above,
  • Fig. L shows a graph of the faraday efficiency of oxygen evolution as ordinate plotted against the tin content of the electrode coating as abscissa, the electrode being that described below in detail in Example I;
  • Fig. 2 shows a graph of the faraday efficiency of oxygen evolution as ordinate plotted against the palladium content of the electrode coating as abscissa, the electrode being that described below in detail in Example II.
  • Titanium coupons measuring 10 x 10 x 1 mm were sandblasted and etched in 20% hydrochloric acid and were thoroughly washed in water. The coupons were then coated with an aqueous solution of Chlorides of platinum and tin in different weight ratios. dried at 95 to 100 o C and then heated at 450 o C for 15 minutes in an oven with forced air ventilation. The procedure was repeated five times and the coupons were given a final heat treatment at 450 C for 60 minutes. The coatings, so produced contained Sn0 2 and platinum metal dispersed in one another.
  • coated coupons were tested as anodes for the production of sodium perchlorate by the electrolysis of a solution consisting of 100g / l NaC10 3 , 400g / l
  • Titanium coupons were coated as in Example but using various coating solutions containing platinum, palladium and tin chlorides, to produce mixed Pt-Pd-SnO 2 coatings having compositions as follows:

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Description

ELECTRODES FOR ELECTROLYTIC PROCESSES, ESPECIALLY PERCHLORATE PRODUCTION.
TECHNICAL FIELD
The invention relates to electrodes for use in electrolytic processes, of the type comprising an electrically-conductive and corrosion-resistant Substrate having an electrocatalytically-active surface coating, and to electrolytic processes using such electrodes, especially (but not exclusively) as anodes for the production of chlorates, perchlorates and other persalts and percompounds including organic peroxyacids.
BACKGROUND ART
For the production of perchlorate, various anode materials have been used commercially, including smooth massive platinum, platinized titanium or tantalum (despite a tendency to produce excess oxygen) and lead dioxide coated on titanium or graphite, although these lead dioxide anodes have a high overvoltage and wear rapidly.
Some proposals have already been made to combine platinum group metals and tin dioxide in electrode coating materials. For example, U.S. Patent Specification 3,701,724 mentioned an anode for chlorine production having a coating consisting essentially of a minor amount of a platinum group metal and/or platinum group metal oxides with a major amount of SnO2, Sb205, Sb203 or Ge02 and mixtures thereof. However, the Claims and examples of this patent are directed solely to such coatings containing platinum group metal oxides and there is no enabling disclosure of a coating containing a platinum group metal. Also, U.S. Patent Specification 3,882,002 proposed an anode for chlorine production having a valve metal Substrate coated with an intermediate layer of tin dioxide which was covered with an outer layer of a platinum group metal or oxide thereof. Neither of these proposals was directed to improving electrolytic Performance in the production of percompounds.
DISCLOSURE OF INVENTION
An object of the invention therefore is to provide an improved electrode suitable for use as an anode for the production of perchlorates and other persalts, but which may also be used in other applications, such as chlorate production. According to a main aspect of the invention, an electrode comprises an electrically-conductive corrosion-resistant Substrate having an electrocatalytic coating and is characterized in that the coating contains a mixture of at least one platinum group metal and tin dioxide dispersed in one another throughout the coating in the ratio of 8:5:1 to 3:2 by weight of the platinum group metals to the tin (as metal) of the tin dioxide.
The platinum group metal/tin dioxide coating may also contain a stabilizer/binder, for example a compound such as titanium dioxide, zirconium dioxide or Silicon dioxide. Additionally, the coating may include a filier, e.g. particles or fibres of an inert material, such as silica or alumina, particles of titanium, or zirconium silicate. Furthermore, the coating may also contain, e.g, as a dopant the tin dioxide in a quantity up to about 30% by weight {as metal) of the tin dioxide, of at least one additional metal or oxide of zinc, cadmium, arsenic, antimony, bismuth., selenium and tellurium.
Such stabilizers or binders, fillers and dopants generally do not account for more than 70% of the total weight of the coating, usually far less. In the case of antimony trioxide or bismuth trioxide as dopant, the preferred amount corresponds to a ratio expressed as parts by weight of Sb/Bi:Sn (as metal) of at most about 1:4 to about 1:10 or even as low as 1:100.
The platinum group metals are ruthenium, rhodium, palladium, osmium, iridium and platinum. Platinum is the preferred platinum group metal in the coating, when a Single metal is present, especially in anodes for perchlorate production. However, it is understood that alloys such as platinum-iridium and platinum-rhodium, also are useful for other applications. An alloy of platinum-palladium containing up to 20% palladium by weight of the alloy has given very satisfactory results for perchlorate production. Also, in sorae instances, it may be advantageous to alloy the platinum group metal(s) with one or more non-platinum group metals, for example an alloy or an intermetallic compound with one of the valve metals titanium, zirconium, hafniumy vanadium, niobium and tantalum, or with another transition metal, for example a metal such as tungsten, manganese or cobalt. The Substrate may consist of any of the aforementioned valve metals or alloys thereof, porous sintered titanium being preferred. However, other electrically conductive and corrosion-resistant Substrates may be used, such as expanded graphite. The platinum group metal'(s) and tin dioxide with possible additional dopants, such as antimony trioxide or bismuth trioxide, may be co-deposited chemically from Solutions of appropriate salts which are painted, sprayed or otherwise applied on the Substrate and then subjected to heat treatment, this process being repeated until a sufficiently thick layer has been built up.
Alternatively, thin layers of different components (e.g. alternate platinum or Pt/Pd alloy layers and layers of pure or doped tin dioxide) can be built up in such a way that the components are effectively mixed and dispersed in one another throughout the coating, possibly with diffusion between the layers, in contrast to the known prior art coatings such as that of U. S. Patent Specification 3,882,002, in which the tin dioxide was applied as a separate intermediate layer covered by a platinum group metal. Using this procedure of applying alternate layers, it is possible to deposit thin layers of platinum galvanically, which is advantageous, because gal vanically-deposited platinum has a lower σxygen evolution Potential than chemi-deposited platinum.
The platinum-group metal or alloy/tin dioxide layer may be applied directly to the Substrate, or to an intermediate layer, e.g. of co-deposited tin and antimony oxides or tin and bismuth oxides, or to intermediate, layers consistihg of one or more platinum group metals or their oxides, mixtures or mixed crystals of platinum group metals and valve metal oxides, intermetallics of platinum group metals and non-platinum group metals, and so forth.
In a preferred embodiment, the coating comprises 40 to 85 parts by weight of platinum, 0 to 20 parts by weight of palladium and 15 to 40 parts by weight (as Sn metal) of tin dioxide on a titanium, tantalum or titanium-tantalum alloy Substrate. This embodiment of an electrode of the invention, when used as anode for perchlorate or persulphate production, has been found to have selective properties favouring the persalt production while hindering oxygen evolution. The platinum metal acts as a catalyst for persalt production. The tin dioxide acts as an oxygen evolution inhibitor by blocking peroxide decomposition, which can be regarded as the intermediate step of the unwanted oxygen evolution reaction. Finally, tihe palladium acts as a diluent for the relatively more expensive platinum, without adversely affecting the oxygen inhibition effect of the tin dioxide.
Another aspect of the Invention is a process for the production of chlorates, perchlorates and other percompounds, e.g. persulphates, which is characterised by using as anode an electrode according to the invention, as defined above,
BRIEF DESCRIPTION OF DRAWINGS
In the accompanying drawings:
Fig. l shows a graph of the faraday efficiency of oxygen evolution as ordinate plotted against the tin content of the electrode coating as abscissa, the electrode being that described below in detail in Example I;
Fig. 2 shows a graph of the faraday efficiency of oxygen evolution as ordinate plotted against the palladium content of the electrode coating as abscissa, the electrode being that described below in detail in Example II.
BEST MODES FOR CARRYING OUT THE INVENTION
The following Examples are given to illusträte the invention.
EXAMPLE I
Titanium coupons measuring 10 x 10 x 1 mm were sandblasted and etched in 20% hydrochloric acid and were thoroughly washed in water. The coupons were then coated with an aqueous solution of Chlorides of platinum and tin in different weight ratios. dried at 95 to 100ºC and then heated at 450ºC for 15 minutes in an oven with forced air Ventilation. The procedure was repeated five times and the coupons were given a final heat treatment at 450 C for 60 minutes. The coatings, so produced contained Sn02 and platinum metal dispersed in one another.
The coated coupons were tested as anodes for the production of sodium perchlorate by the electrolysis of a solution consisting of 100g/l NaC103, 400g/l
NaClO4 and 5g/l Na2CrO4 at 30°C using a stainless steel cathode and a current density of 2KA/m2. Sodium chlorate was supplied and sodium perchlorate removed to maintain the concentrations in the electrolyte at a steady state. The faraday efficiency of the oxygen evolution reaction
(i.e. the unwanted side reaction in perchlorate production) was measured as a function of the percentage by weight of tin (as metal) in the mixed Pt-Sn02 coating. The results obtained are shown in Fig. 1, from which it can be seen that there is an Optimum oxygen-inhibition effect for a tin content in the ränge of about 25%-35% of the total weight of tin and platinum metals, and a very appreciable Inhibition of oxygen evolution for a tin content in the larger range from about 15% to about 40%.
EXAMPLE II
Titanium coupons were coated as in Example but using various coating Solutions containing platinum, palladium and tin Chlorides, to produce mixed Pt-Pd-SnO2coatings having compositions as follows:
These coupons were tested as anodes for perchlorate production under the same conditions as used in Example I. The faraday efficiency of the unwanted oxygen evolution reaction was measured as a function of the palladium metal content, and the results are shown in Fig. 2. This graph shows that, for a palladium content up to 20 % , the faraday efficiency remained low, i.e. the palladium did not adversely affect the Performance of the coating to inhibit oxygen evolution. However, above the critical Pd content of 20%, the faraday efficiency abruptly increased, the stability of the coating was lowered and some electrochemical corrosion took place. The coatings of Examples I and II were tested at different current densities, and it was found that the oxygen evolution faraday efficiency decreased with in 2 creasing current density up to about 2 KA/m , then remained stable above 2 KA/m2.

Claims

CLAIMS :
1. An electrode for use in electrolytic processes, comprising an electrically-conductive corrosion-resistant Substrate having an electrocatalytic coating, characterized in that the coating contains a mixture of at least one platinum group metal and tin dioxide dispersed in one another throughout the coating in the ratio of from 8.5:1 to 3:2 by weight of the platinum group metal (s) to the tin of the tin dioxide.
2. The electrode of claim 1 , characterized in that the platinum group metal is platinum.
3. The electrode of claim 1, characterised in that the coating comprises 40 to 85 parts by weight of platinum, 0 to 20 parts by weight of palladium and 15 to 40 parts by weight of tin.
4. The electrode of claim 1, 2 or 3, characterized in that the coating also contains at least one additional metal or oxide of zinc, cadmium, arsenic, antimony, bismuth, selenium and tellerium in a quantity up to 30% by weight of the tin.
5. The electrode of claim 4, characterized in that the coating contains one or more oxides of antimony and/or bismuth in an amount of at most 1 part by weight of Sb/Bi to 4 parts by weight of Sn.
6. A process for the production of chlorate perchlorates and other percompounds by electrolysis, characterized by using as anode an electrode as claimed in any preceding claim.
EP79900338A 1978-03-28 1979-11-05 Elektroden für elektrolyseverfahren, insbesondere perchlorat-herstellung Withdrawn EP0018970A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB1205278 1978-03-28
GB1205278 1978-03-28

Publications (1)

Publication Number Publication Date
EP0018970A1 true EP0018970A1 (de) 1980-11-26

Family

ID=9997561

Family Applications (2)

Application Number Title Priority Date Filing Date
EP79100917A Expired EP0004880B1 (de) 1978-03-28 1979-03-27 Elektroden für elektrolytische Verfahren, insbesondere zur Herstellung von Perchloraten
EP79900338A Withdrawn EP0018970A1 (de) 1978-03-28 1979-11-05 Elektroden für elektrolyseverfahren, insbesondere perchlorat-herstellung

Family Applications Before (1)

Application Number Title Priority Date Filing Date
EP79100917A Expired EP0004880B1 (de) 1978-03-28 1979-03-27 Elektroden für elektrolytische Verfahren, insbesondere zur Herstellung von Perchloraten

Country Status (5)

Country Link
EP (2) EP0004880B1 (de)
CA (1) CA1129809A (de)
DE (1) DE2965811D1 (de)
FI (1) FI66919C (de)
WO (1) WO1979000843A1 (de)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5544514A (en) * 1978-09-22 1980-03-28 Permelec Electrode Ltd Electrode for electrolysis and production thereof

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3616445A (en) * 1967-12-14 1971-10-26 Electronor Corp Titanium or tantalum base electrodes with applied titanium or tantalum oxide face activated with noble metals or noble metal oxides

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO7900843A1 *

Also Published As

Publication number Publication date
FI791004A (fi) 1979-09-29
WO1979000843A1 (en) 1979-11-01
CA1129809A (en) 1982-08-17
FI66919B (fi) 1984-08-31
EP0004880B1 (de) 1983-07-06
FI66919C (fi) 1984-12-10
EP0004880A1 (de) 1979-10-31
DE2965811D1 (en) 1983-08-11

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Inventor name: BIANCHI, GUISSEPPE