CA1244375A - Production of cathode for use in electrolytic cell - Google Patents
Production of cathode for use in electrolytic cellInfo
- Publication number
- CA1244375A CA1244375A CA000461595A CA461595A CA1244375A CA 1244375 A CA1244375 A CA 1244375A CA 000461595 A CA000461595 A CA 000461595A CA 461595 A CA461595 A CA 461595A CA 1244375 A CA1244375 A CA 1244375A
- Authority
- CA
- Canada
- Prior art keywords
- platinum group
- group metal
- cathode
- electrolytic cell
- additive
- 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.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/56—Electroplating: Baths therefor from solutions of alloys
- C25D3/62—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of gold
-
- 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
- C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
- C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal
Abstract
ABSTRACT
PRODUCTION OF CATHODE FOR USE IN ELECTROLYTIC CELL
A method of producing a cathode which operates at low hydrogen over-voltage in the electrolysis of water or aqueous solutions by electrodepositing on a nickel or nickel alloy substrate a coating comprising at least an outer layer of at least one platinum group metal, the outer layer of the platinum group metal being deposited from a plating bath which contains a solution of at least one platinum group metal compound and at least one additive of the type which suppresses maxima in polarographic waves associated with reactions carried out at a dropping mercury electrode, said additive being further selected from those which do not react with the platinum group metal in the plating bath, such as gelatin, bromophenol blue and iso-octyl phenoxy-polyethoxy ethanol.
PRODUCTION OF CATHODE FOR USE IN ELECTROLYTIC CELL
A method of producing a cathode which operates at low hydrogen over-voltage in the electrolysis of water or aqueous solutions by electrodepositing on a nickel or nickel alloy substrate a coating comprising at least an outer layer of at least one platinum group metal, the outer layer of the platinum group metal being deposited from a plating bath which contains a solution of at least one platinum group metal compound and at least one additive of the type which suppresses maxima in polarographic waves associated with reactions carried out at a dropping mercury electrode, said additive being further selected from those which do not react with the platinum group metal in the plating bath, such as gelatin, bromophenol blue and iso-octyl phenoxy-polyethoxy ethanol.
Description
3~5 . . , .~
,, PRODUCTIO~ OF CATHODE FOR USE IN ELECTROLYTIC CELL
~his invention relates to production of a cathode for use in an electrolytic cell~ and in particular to production of a cathode which has a low hydrogen over-voltage when used in the electrolysis of water or aqueous solutions, e.g. aqueous alkali metal halide solutions.
The voltage at which an aqueous solution may be electrolysed is made up of the sum of a number of elements, namely the theoretical electrolysing voltage, the over voltages at the anode and cathode, the resistance of the solution which is electrolysed, the resistance of the diaphragm or membrane, if any, positioned between the anode and cathode, and the resistance of the metallic conductors and their contact resistances.
In view of the high cost of electrical power it is desirable to reduce the voltage at which a solution is electrolysed to as low a value as possible. In the electrolysis of water or aqueous solutions there is considerable scope for achieving such a reduction in electrolysing vol~age by reducing ~he hydrogen over-voltage at the cathode.
There have been many prior proposals of means of achieving such a reduction in hydrogen over-voltage.
For example, it is known that the hydrogen over-voltage at a cathode may be reduced by increasing the surface area of the cathode, for example by etching the surface of the cathode, e.g. in an acid, or ~y grit-blasting the surface of the cathode, or by coating the surface of the cathode with a mixture of metals and selectively leaching one of the metals from the coating.
~24~375
,, PRODUCTIO~ OF CATHODE FOR USE IN ELECTROLYTIC CELL
~his invention relates to production of a cathode for use in an electrolytic cell~ and in particular to production of a cathode which has a low hydrogen over-voltage when used in the electrolysis of water or aqueous solutions, e.g. aqueous alkali metal halide solutions.
The voltage at which an aqueous solution may be electrolysed is made up of the sum of a number of elements, namely the theoretical electrolysing voltage, the over voltages at the anode and cathode, the resistance of the solution which is electrolysed, the resistance of the diaphragm or membrane, if any, positioned between the anode and cathode, and the resistance of the metallic conductors and their contact resistances.
In view of the high cost of electrical power it is desirable to reduce the voltage at which a solution is electrolysed to as low a value as possible. In the electrolysis of water or aqueous solutions there is considerable scope for achieving such a reduction in electrolysing vol~age by reducing ~he hydrogen over-voltage at the cathode.
There have been many prior proposals of means of achieving such a reduction in hydrogen over-voltage.
For example, it is known that the hydrogen over-voltage at a cathode may be reduced by increasing the surface area of the cathode, for example by etching the surface of the cathode, e.g. in an acid, or ~y grit-blasting the surface of the cathode, or by coating the surface of the cathode with a mixture of metals and selectively leaching one of the metals from the coating.
~24~375
- 2 - QM.32854 Other methods of producing a low hydrogen over-voltage cathode which have been described involve coating the surface of a cathode with an electrocatalytically-active material. Examples of prior disclosures of coated cathodes include the following.
US Patent 4,100,049 discloses a cathode comprising a substrate of iron, nickel, cobalt or alloys thereof and a coating of a mixture of a precious metal oxide, particularly palladium oxide, and a valve metal oxide particularly zirconium oxide.
British Patent 1,511,719 discloses a cathode comprising a metal substrate, which may be ferrous metal, copper or nickel, a coating of cobalt, and a further coating consisting of ruthenium.
Japanese Kokai 54 090080 - published 17 July 1979 -Tokuyama Soda Co. Ltd. discloses pre-treating an iron cathode with perchloric acid followed by sinter coating the cathode with cathode active substances, which may be ruthenium, iridium, iron or nickel in the form of the metal or a compound of the metal.
Japanese Kokai 54 110983 - published 30 July 1979 -Chlorine Engineers discloses a cathode, which may be of mild steel, nickel or nickel alloy and a coating of a dispersion of nickel or nickel alloy particles and a cathode activator which comprises one or more of platinum, ruthenium, iridium, rhodium, palladium or osmium metal or oxide.
Japanese Kokai 51 117180 - published - 15 October 1976 -Tokayoshi Honma discloses a cathode having a base of a valve metal and a coating of an alloy of at least one platinum group metal and a valve metal, and optionally a top coating of at least one platinum group metal.
A low hydrogen over-voltage cathode may be produced by applying such a coating to the surface of a cathode which has also been treated in order to increase the surface area of the cathode.
` ~Z~3 75 -Many of the aforementioned cathodes, ; particularly those coated with a coating of an electro-- catalytically-active material, suffer from the : disadvantage that, althouyh the initial hydrogen over-. 5 voltage at the cathode may be low, the hydrogen over-voltage tends to increase with time of use and the low hydrogen over-voltage performance may be short-lived, The present invention relates to a method of production of a cathode the surface of which comprises an electrodeposited layer of a platinum group metal which cathode operates at low hydrogen over-voltage for a prolonged period of time when used in the electrolysis of water or aqueous solutions, and which is strongly adherent to the cathode substrate.
According to the present invention there is provided a method of producing a cathode by electro-depositing on a nickel or nickel alloy substrate a coating comprisin~ at least an outer layer of at least on~ platinum group metal, characterised in that the said outer layer of the platinum group metal is electrodeposited from a plating bath which contains a solution of at least one platinum group metal compound and at least one additive of the type which supresses maxima in polarographic waves associated with reactions carried out at a dropping mercury electrode, herein-after referred ~o as the additive, said additive being further selected from those which do not rPact with the platinum group metal compound in the plating bath.
The substrate of the cathode may be made of 30 nickél or a nickel alloy or it may comprise a substrate of another material having an outer face of nickel or nickel alloy. For example, the cathode may comprise a core of ano~her metal, e.g. steel, and an outer face of nickel or nickel alloy.
~4~3~75 -ICI Q~ 32854 The substrate of the cathode may have any desired structure. For e~ample, it may be in the form of a plate, which may be foraminate, e.g. the cathode may be a perforated plate, or it may be in the form o~
an expanded m0tal, or it may be a woven or unwoven mesh. The cathode i~ not necessarily in plate form.
Thus, it m~y be in the form of a plurality of ~o-called cathode ~ingers between which the anodes o~ th~
electrolytic cell may be placed.
As it a55ists in the production of a cathode - which operat~s with a low hydrogen over-voltage it is desirable that ~he surface of the nickel or nic~el alloy substrate has a high urface area. Such a high surface area may be achieved by roughening the ~urface of the nicXel or nickel allcy substrate, ~or e~ample by grit-blasing the surface, or by chemically etching the surface, or by anodically polari~ing the cathode in an acidic medium in order to etch the surfaces.
By "platinum group metal'', or '`p}atinum group metal compound", we mean a metal, or a compound thereof, selected ~rom the group platinum, rut~enium, rhodium, palladium, iridium and osmium.
Plating baths containing a pLatinum group metal compound, and method~ of application of a platinum - 25 group metal coating from such plating baths, are well known in the art.
Suitable compounas of a platinum group metal include, or example, inorganic acid salt~ of platinum group metals, e.g. chlorides, nitrates, or sulphates. A
particularly suitable platinum group metal compound is chloroplatinic acid.
The platinum group metal compound may be an organic acid salt o~ a platinum group metal, for example, an acetate, formate or a propionate.
r.~ J
~2~L375 The ~olution of ~he platinum group metal compound in the plating bath will generally be an aqueou~ solution, e.g. an aqueous ~olution o an acid.
In general, the concentration of the platinum group metal compound in the plating bath will be in the range 0.1 g/l to 20 g/l based on the platinum in the compound, although lt is to be under~tood that this concentration range is not limiting and that platinum group metal compound concentrations outside this range may be used if desired. An upper limit of the platinum metal compound concentration may be set by the ~olubility of the compound, and it may be preerred not to use a very low concentration as the current eficiency o~ the plating process may be undesirably low.
In effecting the electrodeposition the nickel or nickel alloy sub~trate iq placed in the plating bath and electrically connected as a cathode and elsctrolysi~ is effected with an anode of a platinum yroup metal or of another metal which has a ~urface of a platinum group metal, e.g. a platlnum group metal coated titanium anode. A suitable cathode current density at which to e~fect the electrodeposition i~ in the rangs 10 to 1000 Amps per ~quare metre ~A/m2) of cathode surface, although current den~ities ou~side thi~ range may be used if desired. The lower the current density used the longer will be the time re~uired to produce a coating o~ a given thicknes~. At very high current densit~es the current efficien~y of the plati~g proces3 may be reduced and the adhesion of the coating may not be as great a~ may be desired.
The temperature of the plating bath may suitably be in a range from ambient tempeIa~ure up ~o lOO~C.
.~. ~ .
t It is desirable that the plating bath be agitated during the electroplating process.
The plating bath may contain more than one platinum group metal compound so that the electro-deposited coating on the nickel or nickel alloy substrate comprises more than one platinum group metal.
Additives which suppress ma~ima in polargraphic waves are described, for example, in "The Principles and Applications o Polarography" by G W C Millar, Longmans, 1957. Certain of these compounds, for instance methyl red and methylene blue reduce the platinum metal compounds in the plating baths and precipitate platinum group metal powder. Such compounds are excluded from the scope of the present invention as - the additive for use in the method must be one which does not react with the platinum group metal compound in the plating bath.
Whether or not a particular additive of the type which suppresses maxima in polarographic waves reacts with a particular platinum group metal compound may be determined by means of simple experiment, e.g. by observing the effect of the additive on the platinum group metal compound in the plating bath.
Cathodes which comprise a nickel or nickel alloy substrate and an electrodeposited coating thereon of a platinum group metal, even if they possess a low initial hydrogen over-voltage when used in ~he electrolysis of water or aqueous solutions, show an increase in hydrogen over-voltage after only a short period of time. However, and by way of contrast, where the platinum group metal coating is applied from a plating bath which also comprises an additive as hereinbefore described, the cathode may be operated for `- ~2~375 : a longer period of tLme, and generally for a prolonged period of ~ime, at a low hydrogen overvoltage.
In carrying out ~he method of the invention the amount of the additive in the plating bath may vary over a wide range, and th~ operative range is not the same for all additives. Additives of low ~olubility in the solvent of the plating ba~h may be u~ed up to the ma~imum solubility, wherea~ additive~ of high solubility may be ~ound to prevent electrodeposition of the platinum group metal if used at ~igh concentration.
The latter usually exert their best effect at about half the minimum concentration which prevents ~lectro-deposition of the platinum group metal. In ~eneral for there to be obtained a u-~eful effect on the hydrogen lS over-voltage performance of the cathode a concentration o at least 1 part per million weight/volume o~
additive in the plating bath is required, although much higher concentrations may be used. The efect of change of the concentration of additive used in the plating bath on the rate of depo~ition of the ~oating may readily be determined by mean~ of ~imple experiment, and will vary with the nature of the addltive.
A Ruitable additive i9 gelatine. Other suitable additives are for instance ethoxylated alkyl phenol3, agar-agar, gum arabic, high molecular w~ight polye~hylene glycol, gum aca~ia, cellulose .
derivative , e.g. methyl cellulo~e, bromo phenol blue, poly vinyl alcohol, the ~odium ~alt~ of long ~hain alkyl benzena sulphonate~, peptone, glycerol, the sodium ~al~s of alkyl aryl polye~her ~ulphonate~, perfluoroalXyl sulphonates, e.g. alXal~ m~tal ~alt~ o~
. perfluoroalkyl sulphonate3. Suitable amounts of the~e ,~,~j ~2~375 additives will be apparent from the examples shown hereinafter.
The plating bath may con~ain more than one additive.
The adhesion of the coating on the substrate and the current efficiency of the electrodeposition is greater where the coating is deposited from a plating bath containing a solution of low pH. For this reason a pH of less than 5.0 is preferred, more preferably less than 2.
The whole of the platinum group metal coating of the cathode may be deposited on the nickel or nickel alloy substrate from a plating bath containing an additive as defined hereinbefore. However, it is within the scope of the invention to apply to the nickel or nickel alloy substrate an initial coating of a platinum ; group metal by electrodeposition from a conventional plating bath which does not contain an additive as hereinbefore described or, by other means, and only an outer surface layer of platinum group m~tal need then be deposited by electrodeposition from a plating bath containing the a~oresaid additive to produce a surace in accordance with the method of the invention.
It is also within the scope of the invention to ` 25 deposit the platinum group metal coating according to - the method of the invention onto a coating of a material other than a platinum group metal on the surface of the nickel or nickel alloy substrate.
- It is possible that the coating of platinum - 30 group metal deposited by electrodeposition in the method of the invention may contain some platinum group metal deposited by other means, for example by exchange with, or displacement of, nickel in the substrate of the cathode.
~2~375 A suitable thickness of platinum group metal coating applied by the method of the invention is at least 0.1 micron based on the projected area of the cathode. The cathode will of course have a longer lasting low hydrogen overvoltage performance the greater the thickness of the coating. The coating thickness may be 10 microns or greater.
The cathode produced in the method of the invention is particularly suitable for use in the electrolysis of water or aqueous solutions, for example, aqueous alkali metal chloride solutions, e.g.
aqueous sodium chloride solutions, as it operates in such electrolysis at low hydrogen over-voltage for a prolonged period of time.
The cathode is suitable for use in an electrolytic cell comprising an anode, or a plurality of anodes, a cathode, or a plurality of cathodes, and optionally a separator positioned between each adjacent anode and cathode. The separator may be a porous electrolyte permeable diaphragm or it may be a hydraulically impermeable cation permselective membrane. The separator is preferably a membrane.
The anode in the electrolytic cell may be metallic, and the nature of the metal will depend on the nature of the electrolyte to be electrolysed in the electrolytic cell. A preferred metal is a film-forming metal, particularly where an aqueous solution of an alXali metal chloride is to be electrolysed in the cell.
The film-forming metal may be one of the metals titanium, zirconium, niobium, tantalum or tungsten or an alloy consisting principally of one or more of these metals and having anodic polarisation properties which are comparable with those of the pure metal. It is . .
preferred to use titanium alone, or an alloy based on titanium and having polarisation properties comparable with those of titanium.
The anode may have a coating of an electro-conducting electro-catalytically active material.
Particularly in the case where an aqueous solution of an alkali metal chloride is to be electrolysed this coating may for example consist of one or more platinum group metals, that is platinum, rhodium, iridium, 10 ruthenium, osmium and palladium, or alloys of the said metal~, and/or an oxide or oxides thereof. The coating may consist of one or more of the platinum group metals and/or oxides thereof in admixture with one or more non-noble metal oxides, particularly a film-forming 15 metal oxide. Especially suitable electro-catalytically active coatings include platinum itself and those based on ruthenium dioxide/titanium dioxide, ruthenium dioxide/tin dioxide, and ruthenium dioxide/tin dioxide/
titanium dioxide.
Such coatings, and methods of application thereof, are well known in the art.
Cation permselective membranes are known in the art. The membrane is preferably a fluorine-containing polymeric material containing anionic groups. The 25 polymeric material is preferably a fluoro-carbon containing the repeating groups CmF2m ]M and [ CF2 - CF ]N
X
where m has a value of 2 to 10, and is preferably 2, the ratio of M to ~ is preferably such as to give an equivalent weight or the groups X in the range 500 to 2000, and X is chosen from ~2~alL3~75 A or [ OCF2 - CF ] A
P
z where p has the value of for example 1 to 3, Z is fluorine or a perfluoroalkyl group having from 1 to 10 carbon atoms, and A is a group chosen from the groups:
1 0 -cF2so3H
-XlS03H
-COOH and _XloH
or derivatives of the said groups, where Xl is an aryl group. Preferably A represents the group S03H or -COOH.
S03~ group-containing ion exchange membranes are sold under the trademark 'Nafion' by E I DuPont de Nemours and Co Inc and -COOH group-containing ion exchange membranes under the trademark 'Flemion' by the Asahi Glass Co Ltd.
The invention is illustrated by the following Example.
Example 1 A 10.5 cm2 flat disc of nickel of 1 mm thickness (BS NAll Vickers Hardness 100) was treated with trichloroethylene vapour to remove traces of oil and grease from the surface of the disc. The surface of the disc was then roughened by gri~-blasting with 60-80 mesh fused alumina and the disc was then washed in aqua regia and finally in water. After drying the disc in a current of warm air the disc was immersed in a plating
US Patent 4,100,049 discloses a cathode comprising a substrate of iron, nickel, cobalt or alloys thereof and a coating of a mixture of a precious metal oxide, particularly palladium oxide, and a valve metal oxide particularly zirconium oxide.
British Patent 1,511,719 discloses a cathode comprising a metal substrate, which may be ferrous metal, copper or nickel, a coating of cobalt, and a further coating consisting of ruthenium.
Japanese Kokai 54 090080 - published 17 July 1979 -Tokuyama Soda Co. Ltd. discloses pre-treating an iron cathode with perchloric acid followed by sinter coating the cathode with cathode active substances, which may be ruthenium, iridium, iron or nickel in the form of the metal or a compound of the metal.
Japanese Kokai 54 110983 - published 30 July 1979 -Chlorine Engineers discloses a cathode, which may be of mild steel, nickel or nickel alloy and a coating of a dispersion of nickel or nickel alloy particles and a cathode activator which comprises one or more of platinum, ruthenium, iridium, rhodium, palladium or osmium metal or oxide.
Japanese Kokai 51 117180 - published - 15 October 1976 -Tokayoshi Honma discloses a cathode having a base of a valve metal and a coating of an alloy of at least one platinum group metal and a valve metal, and optionally a top coating of at least one platinum group metal.
A low hydrogen over-voltage cathode may be produced by applying such a coating to the surface of a cathode which has also been treated in order to increase the surface area of the cathode.
` ~Z~3 75 -Many of the aforementioned cathodes, ; particularly those coated with a coating of an electro-- catalytically-active material, suffer from the : disadvantage that, althouyh the initial hydrogen over-. 5 voltage at the cathode may be low, the hydrogen over-voltage tends to increase with time of use and the low hydrogen over-voltage performance may be short-lived, The present invention relates to a method of production of a cathode the surface of which comprises an electrodeposited layer of a platinum group metal which cathode operates at low hydrogen over-voltage for a prolonged period of time when used in the electrolysis of water or aqueous solutions, and which is strongly adherent to the cathode substrate.
According to the present invention there is provided a method of producing a cathode by electro-depositing on a nickel or nickel alloy substrate a coating comprisin~ at least an outer layer of at least on~ platinum group metal, characterised in that the said outer layer of the platinum group metal is electrodeposited from a plating bath which contains a solution of at least one platinum group metal compound and at least one additive of the type which supresses maxima in polarographic waves associated with reactions carried out at a dropping mercury electrode, herein-after referred ~o as the additive, said additive being further selected from those which do not rPact with the platinum group metal compound in the plating bath.
The substrate of the cathode may be made of 30 nickél or a nickel alloy or it may comprise a substrate of another material having an outer face of nickel or nickel alloy. For example, the cathode may comprise a core of ano~her metal, e.g. steel, and an outer face of nickel or nickel alloy.
~4~3~75 -ICI Q~ 32854 The substrate of the cathode may have any desired structure. For e~ample, it may be in the form of a plate, which may be foraminate, e.g. the cathode may be a perforated plate, or it may be in the form o~
an expanded m0tal, or it may be a woven or unwoven mesh. The cathode i~ not necessarily in plate form.
Thus, it m~y be in the form of a plurality of ~o-called cathode ~ingers between which the anodes o~ th~
electrolytic cell may be placed.
As it a55ists in the production of a cathode - which operat~s with a low hydrogen over-voltage it is desirable that ~he surface of the nickel or nic~el alloy substrate has a high urface area. Such a high surface area may be achieved by roughening the ~urface of the nicXel or nickel allcy substrate, ~or e~ample by grit-blasing the surface, or by chemically etching the surface, or by anodically polari~ing the cathode in an acidic medium in order to etch the surfaces.
By "platinum group metal'', or '`p}atinum group metal compound", we mean a metal, or a compound thereof, selected ~rom the group platinum, rut~enium, rhodium, palladium, iridium and osmium.
Plating baths containing a pLatinum group metal compound, and method~ of application of a platinum - 25 group metal coating from such plating baths, are well known in the art.
Suitable compounas of a platinum group metal include, or example, inorganic acid salt~ of platinum group metals, e.g. chlorides, nitrates, or sulphates. A
particularly suitable platinum group metal compound is chloroplatinic acid.
The platinum group metal compound may be an organic acid salt o~ a platinum group metal, for example, an acetate, formate or a propionate.
r.~ J
~2~L375 The ~olution of ~he platinum group metal compound in the plating bath will generally be an aqueou~ solution, e.g. an aqueous ~olution o an acid.
In general, the concentration of the platinum group metal compound in the plating bath will be in the range 0.1 g/l to 20 g/l based on the platinum in the compound, although lt is to be under~tood that this concentration range is not limiting and that platinum group metal compound concentrations outside this range may be used if desired. An upper limit of the platinum metal compound concentration may be set by the ~olubility of the compound, and it may be preerred not to use a very low concentration as the current eficiency o~ the plating process may be undesirably low.
In effecting the electrodeposition the nickel or nickel alloy sub~trate iq placed in the plating bath and electrically connected as a cathode and elsctrolysi~ is effected with an anode of a platinum yroup metal or of another metal which has a ~urface of a platinum group metal, e.g. a platlnum group metal coated titanium anode. A suitable cathode current density at which to e~fect the electrodeposition i~ in the rangs 10 to 1000 Amps per ~quare metre ~A/m2) of cathode surface, although current den~ities ou~side thi~ range may be used if desired. The lower the current density used the longer will be the time re~uired to produce a coating o~ a given thicknes~. At very high current densit~es the current efficien~y of the plati~g proces3 may be reduced and the adhesion of the coating may not be as great a~ may be desired.
The temperature of the plating bath may suitably be in a range from ambient tempeIa~ure up ~o lOO~C.
.~. ~ .
t It is desirable that the plating bath be agitated during the electroplating process.
The plating bath may contain more than one platinum group metal compound so that the electro-deposited coating on the nickel or nickel alloy substrate comprises more than one platinum group metal.
Additives which suppress ma~ima in polargraphic waves are described, for example, in "The Principles and Applications o Polarography" by G W C Millar, Longmans, 1957. Certain of these compounds, for instance methyl red and methylene blue reduce the platinum metal compounds in the plating baths and precipitate platinum group metal powder. Such compounds are excluded from the scope of the present invention as - the additive for use in the method must be one which does not react with the platinum group metal compound in the plating bath.
Whether or not a particular additive of the type which suppresses maxima in polarographic waves reacts with a particular platinum group metal compound may be determined by means of simple experiment, e.g. by observing the effect of the additive on the platinum group metal compound in the plating bath.
Cathodes which comprise a nickel or nickel alloy substrate and an electrodeposited coating thereon of a platinum group metal, even if they possess a low initial hydrogen over-voltage when used in ~he electrolysis of water or aqueous solutions, show an increase in hydrogen over-voltage after only a short period of time. However, and by way of contrast, where the platinum group metal coating is applied from a plating bath which also comprises an additive as hereinbefore described, the cathode may be operated for `- ~2~375 : a longer period of tLme, and generally for a prolonged period of ~ime, at a low hydrogen overvoltage.
In carrying out ~he method of the invention the amount of the additive in the plating bath may vary over a wide range, and th~ operative range is not the same for all additives. Additives of low ~olubility in the solvent of the plating ba~h may be u~ed up to the ma~imum solubility, wherea~ additive~ of high solubility may be ~ound to prevent electrodeposition of the platinum group metal if used at ~igh concentration.
The latter usually exert their best effect at about half the minimum concentration which prevents ~lectro-deposition of the platinum group metal. In ~eneral for there to be obtained a u-~eful effect on the hydrogen lS over-voltage performance of the cathode a concentration o at least 1 part per million weight/volume o~
additive in the plating bath is required, although much higher concentrations may be used. The efect of change of the concentration of additive used in the plating bath on the rate of depo~ition of the ~oating may readily be determined by mean~ of ~imple experiment, and will vary with the nature of the addltive.
A Ruitable additive i9 gelatine. Other suitable additives are for instance ethoxylated alkyl phenol3, agar-agar, gum arabic, high molecular w~ight polye~hylene glycol, gum aca~ia, cellulose .
derivative , e.g. methyl cellulo~e, bromo phenol blue, poly vinyl alcohol, the ~odium ~alt~ of long ~hain alkyl benzena sulphonate~, peptone, glycerol, the sodium ~al~s of alkyl aryl polye~her ~ulphonate~, perfluoroalXyl sulphonates, e.g. alXal~ m~tal ~alt~ o~
. perfluoroalkyl sulphonate3. Suitable amounts of the~e ,~,~j ~2~375 additives will be apparent from the examples shown hereinafter.
The plating bath may con~ain more than one additive.
The adhesion of the coating on the substrate and the current efficiency of the electrodeposition is greater where the coating is deposited from a plating bath containing a solution of low pH. For this reason a pH of less than 5.0 is preferred, more preferably less than 2.
The whole of the platinum group metal coating of the cathode may be deposited on the nickel or nickel alloy substrate from a plating bath containing an additive as defined hereinbefore. However, it is within the scope of the invention to apply to the nickel or nickel alloy substrate an initial coating of a platinum ; group metal by electrodeposition from a conventional plating bath which does not contain an additive as hereinbefore described or, by other means, and only an outer surface layer of platinum group m~tal need then be deposited by electrodeposition from a plating bath containing the a~oresaid additive to produce a surace in accordance with the method of the invention.
It is also within the scope of the invention to ` 25 deposit the platinum group metal coating according to - the method of the invention onto a coating of a material other than a platinum group metal on the surface of the nickel or nickel alloy substrate.
- It is possible that the coating of platinum - 30 group metal deposited by electrodeposition in the method of the invention may contain some platinum group metal deposited by other means, for example by exchange with, or displacement of, nickel in the substrate of the cathode.
~2~375 A suitable thickness of platinum group metal coating applied by the method of the invention is at least 0.1 micron based on the projected area of the cathode. The cathode will of course have a longer lasting low hydrogen overvoltage performance the greater the thickness of the coating. The coating thickness may be 10 microns or greater.
The cathode produced in the method of the invention is particularly suitable for use in the electrolysis of water or aqueous solutions, for example, aqueous alkali metal chloride solutions, e.g.
aqueous sodium chloride solutions, as it operates in such electrolysis at low hydrogen over-voltage for a prolonged period of time.
The cathode is suitable for use in an electrolytic cell comprising an anode, or a plurality of anodes, a cathode, or a plurality of cathodes, and optionally a separator positioned between each adjacent anode and cathode. The separator may be a porous electrolyte permeable diaphragm or it may be a hydraulically impermeable cation permselective membrane. The separator is preferably a membrane.
The anode in the electrolytic cell may be metallic, and the nature of the metal will depend on the nature of the electrolyte to be electrolysed in the electrolytic cell. A preferred metal is a film-forming metal, particularly where an aqueous solution of an alXali metal chloride is to be electrolysed in the cell.
The film-forming metal may be one of the metals titanium, zirconium, niobium, tantalum or tungsten or an alloy consisting principally of one or more of these metals and having anodic polarisation properties which are comparable with those of the pure metal. It is . .
preferred to use titanium alone, or an alloy based on titanium and having polarisation properties comparable with those of titanium.
The anode may have a coating of an electro-conducting electro-catalytically active material.
Particularly in the case where an aqueous solution of an alkali metal chloride is to be electrolysed this coating may for example consist of one or more platinum group metals, that is platinum, rhodium, iridium, 10 ruthenium, osmium and palladium, or alloys of the said metal~, and/or an oxide or oxides thereof. The coating may consist of one or more of the platinum group metals and/or oxides thereof in admixture with one or more non-noble metal oxides, particularly a film-forming 15 metal oxide. Especially suitable electro-catalytically active coatings include platinum itself and those based on ruthenium dioxide/titanium dioxide, ruthenium dioxide/tin dioxide, and ruthenium dioxide/tin dioxide/
titanium dioxide.
Such coatings, and methods of application thereof, are well known in the art.
Cation permselective membranes are known in the art. The membrane is preferably a fluorine-containing polymeric material containing anionic groups. The 25 polymeric material is preferably a fluoro-carbon containing the repeating groups CmF2m ]M and [ CF2 - CF ]N
X
where m has a value of 2 to 10, and is preferably 2, the ratio of M to ~ is preferably such as to give an equivalent weight or the groups X in the range 500 to 2000, and X is chosen from ~2~alL3~75 A or [ OCF2 - CF ] A
P
z where p has the value of for example 1 to 3, Z is fluorine or a perfluoroalkyl group having from 1 to 10 carbon atoms, and A is a group chosen from the groups:
1 0 -cF2so3H
-XlS03H
-COOH and _XloH
or derivatives of the said groups, where Xl is an aryl group. Preferably A represents the group S03H or -COOH.
S03~ group-containing ion exchange membranes are sold under the trademark 'Nafion' by E I DuPont de Nemours and Co Inc and -COOH group-containing ion exchange membranes under the trademark 'Flemion' by the Asahi Glass Co Ltd.
The invention is illustrated by the following Example.
Example 1 A 10.5 cm2 flat disc of nickel of 1 mm thickness (BS NAll Vickers Hardness 100) was treated with trichloroethylene vapour to remove traces of oil and grease from the surface of the disc. The surface of the disc was then roughened by gri~-blasting with 60-80 mesh fused alumina and the disc was then washed in aqua regia and finally in water. After drying the disc in a current of warm air the disc was immersed in a plating
3~5 ba~h comprising water, chloroplatinic acid at a concentration of 1 g/l based on the platinum metal, and 2 x 10-3 g/l of Triton X-lOO*(iso-octyl phenoxy polyethoxy ethanol) as additive. The plating bath had a pH of 2.8 and the temperature of the bath was maintained at 60C.
The nickel disc was connected as a cathode in the plating bath and a platinum foil was used as the anode, and electrolysis was effected at a cathode current density of 240 A/m2 for 4~ minutes. ~he resultant platinum plated nickel disc was removed from the bath and washed with water and was found to have a coating of 1.02 micron thickness of platinum based on the projected surface area of the nickel.
The thus coated nickel disc was installed as a cathode in an electrolytic cell equipped with a titanium grid anode having a coating of 35~ by weight ~U2 and 65~ by weight Tio2, the anode and cathode being separated by a cation-exchange membrane comprising a perfluoropolymer having carboxylic acid ion-exchange groups and an ion-exchange capacity of 1.5 milli equivalents per gram of dry membrane.
A saturated aqueous solution of sodium chloride was charged continuously to the anode compartment of the electrolytic cell, the cathode compartment was filled with 25% by weight aqueous sodium hydroxide solution, and electrolysis was commenced at a current density of 3 kA/m2 of cathode surface. Water was charged continuously to the cathode compartment at a rate sufficient to maintain a concentration of 35~ by weight of sodium hydroxide in the cathode compartment.
The hydrogen over-voltage at the cathode as a function of time was measured, with the following results.
* 1'rademark ,~t`~, ~1 ~2~9L3'75 - Time (days) ~ydrogen over-voltage (m volts) By way of comparison the above procedure was repeated except that the Triton X-100 was omitted from the plating bath.
~he hydrogen over-voltage at the cathode as a function of time was measured, with the following results 25Time (days) Hydrogen over-voltage (m volts) ~0 357 ~L2~3~S
Examples 2 to 7 In eight separate examples the electroplating procedure of Example l was repeated on nickel cathodes under the following conditions.
' Platin~ bath - chloroplatinic acid (l g/l ; 5 based on Pt) in water.
pH - 1.45 Temperature - 62C
Current density - 190 A/m2 Electroplating time - 3 minutes Triton X-100 additve - various concentrations.
- Thereafter, the thus coated cathodes were installed in electrolytic cells and an aqueous sodium chloride solution was electrolysed therein, following the procedure as described in Example 1. The effect of the concentration of the Triton X-100 additive on the hydrogen overvoltage of the cathodes 1 day after electrolysis is shown in the following Table 3.
_ABL~ 3 Example 2 3 4 5 6 7 comparison Concentration of ~`, Triton X-100 ppm20 100 250 600 1000 4000 0 Hydrogen over-voltage m volts94 53 63125101 359 194 Examples 8 to 17 . . ~
In ten separate examples the electroplating procedure of Example 1 was repeated on nickel cathodes under the following conditions.
.
Plating bath - chloroplatinic acid in water (1 g/l based on Pt) - 1.45 Temperature - 60C
- 5 Current density - 217 A/m2 Electroplating time - 1 minute Additive - 1000 ppm (various) Thereafter, the thus coated cathodes were installed in electrolytic cells and an aqueous sodium chloride solution was electrolysed therein, following the procedure as described in E~ample 1. The effect of the different additives on the hydrogen over-voltage of the cathodes is shown in the following Table 4.
~Z~3~
t o~ ~9 ~ o `g ~g ~ ~ o o C~ o ~ ~ o u~ D ~ O 00 O
~ ~ o ~ o CO ~9 ~ ~ t` ~ CO ~
C O ,~
~ ~ CO ~ I` o U~
O , ~
~ O ~D 1` 0 ~ r~ r~ o u~ _1 E~
o co a~ ~ o -^ a o ~ x ~
o ~ ~ o o rc ~ ~ o ~n o ~ o ~ ~ ~ c ~
u~ I C ~ --I O ~ ,C ~ a) ~ ~ ~ O ~ ~l O >1 X rl ~ OQ, ~ Q, ~1 C ~ n~ l h ~-1 ~ ,C C)n~ X O O O O O ~
u~ o c~ o -1 u ~) u ~1 ~ ~ h X ~ O ~ 1 U1 ,C ~ Q, n~
~ u ~ o ~. ~ e ~,1 Ql O ~
3 ~J ~ O ~ ,C ~1 ~ O ~ 1 0 ~
0 ~ h `- O E~ O ~
.a _ Q
o O
.-1 ~0 ~ o ~ ~ ~ ~ u~
~ ~ --~ ~ ~ ~ ~ ~ ~ ~
~ o ~ c)
The nickel disc was connected as a cathode in the plating bath and a platinum foil was used as the anode, and electrolysis was effected at a cathode current density of 240 A/m2 for 4~ minutes. ~he resultant platinum plated nickel disc was removed from the bath and washed with water and was found to have a coating of 1.02 micron thickness of platinum based on the projected surface area of the nickel.
The thus coated nickel disc was installed as a cathode in an electrolytic cell equipped with a titanium grid anode having a coating of 35~ by weight ~U2 and 65~ by weight Tio2, the anode and cathode being separated by a cation-exchange membrane comprising a perfluoropolymer having carboxylic acid ion-exchange groups and an ion-exchange capacity of 1.5 milli equivalents per gram of dry membrane.
A saturated aqueous solution of sodium chloride was charged continuously to the anode compartment of the electrolytic cell, the cathode compartment was filled with 25% by weight aqueous sodium hydroxide solution, and electrolysis was commenced at a current density of 3 kA/m2 of cathode surface. Water was charged continuously to the cathode compartment at a rate sufficient to maintain a concentration of 35~ by weight of sodium hydroxide in the cathode compartment.
The hydrogen over-voltage at the cathode as a function of time was measured, with the following results.
* 1'rademark ,~t`~, ~1 ~2~9L3'75 - Time (days) ~ydrogen over-voltage (m volts) By way of comparison the above procedure was repeated except that the Triton X-100 was omitted from the plating bath.
~he hydrogen over-voltage at the cathode as a function of time was measured, with the following results 25Time (days) Hydrogen over-voltage (m volts) ~0 357 ~L2~3~S
Examples 2 to 7 In eight separate examples the electroplating procedure of Example l was repeated on nickel cathodes under the following conditions.
' Platin~ bath - chloroplatinic acid (l g/l ; 5 based on Pt) in water.
pH - 1.45 Temperature - 62C
Current density - 190 A/m2 Electroplating time - 3 minutes Triton X-100 additve - various concentrations.
- Thereafter, the thus coated cathodes were installed in electrolytic cells and an aqueous sodium chloride solution was electrolysed therein, following the procedure as described in Example 1. The effect of the concentration of the Triton X-100 additive on the hydrogen overvoltage of the cathodes 1 day after electrolysis is shown in the following Table 3.
_ABL~ 3 Example 2 3 4 5 6 7 comparison Concentration of ~`, Triton X-100 ppm20 100 250 600 1000 4000 0 Hydrogen over-voltage m volts94 53 63125101 359 194 Examples 8 to 17 . . ~
In ten separate examples the electroplating procedure of Example 1 was repeated on nickel cathodes under the following conditions.
.
Plating bath - chloroplatinic acid in water (1 g/l based on Pt) - 1.45 Temperature - 60C
- 5 Current density - 217 A/m2 Electroplating time - 1 minute Additive - 1000 ppm (various) Thereafter, the thus coated cathodes were installed in electrolytic cells and an aqueous sodium chloride solution was electrolysed therein, following the procedure as described in E~ample 1. The effect of the different additives on the hydrogen over-voltage of the cathodes is shown in the following Table 4.
~Z~3~
t o~ ~9 ~ o `g ~g ~ ~ o o C~ o ~ ~ o u~ D ~ O 00 O
~ ~ o ~ o CO ~9 ~ ~ t` ~ CO ~
C O ,~
~ ~ CO ~ I` o U~
O , ~
~ O ~D 1` 0 ~ r~ r~ o u~ _1 E~
o co a~ ~ o -^ a o ~ x ~
o ~ ~ o o rc ~ ~ o ~n o ~ o ~ ~ ~ c ~
u~ I C ~ --I O ~ ,C ~ a) ~ ~ ~ O ~ ~l O >1 X rl ~ OQ, ~ Q, ~1 C ~ n~ l h ~-1 ~ ,C C)n~ X O O O O O ~
u~ o c~ o -1 u ~) u ~1 ~ ~ h X ~ O ~ 1 U1 ,C ~ Q, n~
~ u ~ o ~. ~ e ~,1 Ql O ~
3 ~J ~ O ~ ,C ~1 ~ O ~ 1 0 ~
0 ~ h `- O E~ O ~
.a _ Q
o O
.-1 ~0 ~ o ~ ~ ~ ~ u~
~ ~ --~ ~ ~ ~ ~ ~ ~ ~
~ o ~ c)
Claims (10)
1. An elecrolytic cell comprising an anode or a plurality of anodes, a cathode or a plurality of cathodes, and a separator positioned between each adjacent anode and cathode, in which the cathode or cathodes have been produced by electro-depositing on a nickel or nickel alloy substrate a coating comprising at least an outer layer of at least one platinum group metal, in which the said outer layer of the platinum group metal has been deposited from a plating bath which contains a solution of at least one platinum group metal compound and at least one additive of the type which suppresses maxima in polarographic waves associated with reactions carried out at a dropping mercury electrode, said additive being further selected from those which do not react with the platinum group metal in the plating bath.
2. An electrolytic cell as claimed in Claim 1 in which the platinum group metal compound comprises a compound of platinum.
3. An electrolytic cell as claimed in Claim 2 in which the platinum group metal compound comprises chloroplatinic acid.
4. An electrolytic cell as claimed in Claim 1 in which the solution of the platinum group metal compound is an aqueous solution.
5. An electrolytic cell as claimed in Claim 1 in which the concentration of platinum group metal compound in the plating bath is in the range 0.1 g/1 to 10 g/l.
6. An electrolytic cell as claimed in Claim 1 in which the electrodeposition is effected at a cathode current density in the range 10 to 1000amps per square metre of cathode surface.
7. An electrolytic cell as claimed in Claim 1 in which concentration of the additive in the solution is at least 1 part per million weight/volume.
8. An electrolytic cell as claimed in Claim 1 in which the additive is selected from gelatin, bromophenol blue, and iso-octyl phenoxy-polyethoxy ethanol.
9. An electrolytic cell as claimed in Claim 1 in which the pH of the solution is less than 2Ø
10. An electrolytic cell as claimed in Claim 1 in which the platinum group metal coating deposited in the method of the invention has a thickness of a least 0.1 micron.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB838323390A GB8323390D0 (en) | 1983-08-31 | 1983-08-31 | Production of cathode |
| GB8323390 | 1983-08-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1244375A true CA1244375A (en) | 1988-11-08 |
Family
ID=10548134
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000461595A Expired CA1244375A (en) | 1983-08-31 | 1984-08-22 | Production of cathode for use in electrolytic cell |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4586998A (en) |
| EP (1) | EP0139382B1 (en) |
| JP (1) | JPS6089591A (en) |
| CA (1) | CA1244375A (en) |
| DE (1) | DE3469570D1 (en) |
| GB (2) | GB8323390D0 (en) |
| ZA (1) | ZA846551B (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4721551A (en) * | 1986-11-06 | 1988-01-26 | The Regents Of The University Of California | Iridium treatment of neuro-stimulating electrodes |
| AU2144392A (en) * | 1991-06-11 | 1993-01-12 | Electric Power Research Institute, Inc. | Methods for cleaning cathodes |
| US5580838A (en) * | 1995-06-05 | 1996-12-03 | Patterson; James A. | Uniformly plated microsphere catalyst |
| US6634363B1 (en) * | 1997-04-07 | 2003-10-21 | Broncus Technologies, Inc. | Methods of treating lungs having reversible obstructive pulmonary disease |
| GB2348209B (en) * | 1999-03-24 | 2001-05-09 | Ionex Ltd | Water purification process |
| GB2351089B (en) * | 1999-06-15 | 2001-04-18 | Hong Kong Productivity Council | Platinum electroforming/electroplating bath and method |
| US20020000380A1 (en) * | 1999-10-28 | 2002-01-03 | Lyndon W. Graham | Method, chemistry, and apparatus for noble metal electroplating on a microelectronic workpiece |
| TW200304503A (en) * | 2002-03-20 | 2003-10-01 | Asahi Chemical Ind | Electrode for generation of hydrogen |
| GB0408805D0 (en) * | 2004-04-08 | 2004-05-26 | Accentus Plc | Precious metal recovery |
| US20050230262A1 (en) * | 2004-04-20 | 2005-10-20 | Semitool, Inc. | Electrochemical methods for the formation of protective features on metallized features |
| JP7144251B2 (en) * | 2018-09-10 | 2022-09-29 | 田中貴金属工業株式会社 | Electrode for hydrogen generation and method for producing the same |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT247093B (en) * | 1962-10-08 | 1966-05-25 | Engelhard Ind Inc | Method and bath for the production of adhesive precipitates from platinum with improved overvoltage properties |
| GB1237077A (en) * | 1967-11-10 | 1971-06-30 | Ici Ltd | Electrodeposition of a platinum metal on titanium or titanium alloy to make an electrode |
| US3974058A (en) * | 1974-09-16 | 1976-08-10 | Basf Wyandotte Corporation | Ruthenium coated cathodes |
| CH576529A5 (en) * | 1974-10-09 | 1976-06-15 | Bbc Brown Boveri & Cie | |
| JPS51117181A (en) * | 1975-04-08 | 1976-10-15 | Takatomi Honma | Cathod for electrolysis |
| US4100049A (en) * | 1977-07-11 | 1978-07-11 | Diamond Shamrock Corporation | Coated cathode for electrolysis cells |
| JPS5490080A (en) * | 1977-12-28 | 1979-07-17 | Tokuyama Soda Co Ltd | Method of producing cathode |
| JPS5948872B2 (en) * | 1978-02-20 | 1984-11-29 | クロリンエンジニアズ株式会社 | Electrolytic cathode and its manufacturing method |
| US4273624A (en) * | 1979-03-28 | 1981-06-16 | Board Of Regents, State Of Florida, For The Use And Benefit Of The University Of Florida | Thin platinum films on tin oxide substrates |
| US4416742A (en) * | 1980-09-25 | 1983-11-22 | Nippon Mining Co., Ltd. | Process and electrolytic bath for making a rhodium-plated article having a black or blue color |
-
1983
- 1983-08-31 GB GB838323390A patent/GB8323390D0/en active Pending
-
1984
- 1984-08-16 DE DE8484305567T patent/DE3469570D1/en not_active Expired
- 1984-08-16 GB GB848420874A patent/GB8420874D0/en active Pending
- 1984-08-16 EP EP84305567A patent/EP0139382B1/en not_active Expired
- 1984-08-20 US US06/642,166 patent/US4586998A/en not_active Expired - Fee Related
- 1984-08-22 ZA ZA846551A patent/ZA846551B/en unknown
- 1984-08-22 CA CA000461595A patent/CA1244375A/en not_active Expired
- 1984-08-31 JP JP59180829A patent/JPS6089591A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0139382B1 (en) | 1988-03-02 |
| JPS6089591A (en) | 1985-05-20 |
| EP0139382A1 (en) | 1985-05-02 |
| GB8420874D0 (en) | 1984-09-19 |
| DE3469570D1 (en) | 1988-04-07 |
| GB8323390D0 (en) | 1983-10-05 |
| US4586998A (en) | 1986-05-06 |
| ZA846551B (en) | 1985-06-26 |
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