U.S. patent application number 11/829561 was filed with the patent office on 2007-11-15 for high efficiency hypochlorite anode coating.
Invention is credited to Richard C. Carlson, Kenneth L. Hardee, Michael S. Moats.
Application Number | 20070261968 11/829561 |
Document ID | / |
Family ID | 38684092 |
Filed Date | 2007-11-15 |
United States Patent
Application |
20070261968 |
Kind Code |
A1 |
Carlson; Richard C. ; et
al. |
November 15, 2007 |
HIGH EFFICIENCY HYPOCHLORITE ANODE COATING
Abstract
The invention relates to an electrocatalytic coating and an
electrode having the coating thereon, wherein the coating is a
mixed metal oxide coating, preferably platinum group metal oxides,
with or without a valve metal oxide. The electrocatalytic coating
can be used especially as an anode component of an electrolysis
cell and in particular a cell for the electrolysis of aqueous
hypochlorite solutions.
Inventors: |
Carlson; Richard C.;
(Euclid, OH) ; Hardee; Kenneth L.; (Middlefield,
OH) ; Moats; Michael S.; (W. Valley City,
UT) |
Correspondence
Address: |
Michele M. Tyrpak;Eschweiler & Associates
National City Bank Building
629 Euclid Avenue, Suite 1000
Cleveland
OH
44114
US
|
Family ID: |
38684092 |
Appl. No.: |
11/829561 |
Filed: |
July 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/US05/03046 |
Jan 27, 2005 |
|
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11829561 |
Jul 27, 2007 |
|
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Current U.S.
Class: |
205/354 ;
204/292 |
Current CPC
Class: |
C25B 11/093 20210101;
C25B 1/26 20130101 |
Class at
Publication: |
205/354 ;
204/292 |
International
Class: |
C25B 1/00 20060101
C25B001/00 |
Claims
1. An electrode for use in the electrolysis of an aqueous solution
for the production of hypochlorite, said electrode having an
electrocatalytic coating thereon, with said electrode comprising: a
valve metal electrode base; a coating layer of an electrochemically
active coating on said valve metal electrode base, said coating
comprising a mixed metal oxide coating of platinum group metal
oxides and a valve metal oxide, said mixed metal oxide coating
consisting essentially of platinum group metal oxides of ruthenium,
palladium, and iridium, and a valve metal oxide of titanium;
wherein (a) the molar ratio of said valve metal oxide to said
platinum group metal oxides is from about 90:10 to about 40:60; (b)
the molar ratio of said ruthenium to said iridium is from about
90:10 to about 50:50 and (c) the molar ratio of said palladium
oxide to ruthenium plus iridium oxides is from about 5:95 to about
40:60, basis 100 mole percent of the metals present in the coating;
whereby said electrode operates at a high current efficiency to
produce hypochlorite concentrations of at least 8 grams per
liter.
2. An electrode according to claim 1, wherein said valve metal
electrode base comprises a valve metal mesh, sheet, blade, tube,
punched plate or wire member.
3. An electrode according to claim 2, wherein said valve metal
electrode base comprises one or more of titanium, tantalum,
aluminum, hafnium, niobium, zirconium, molybdenum or tungsten,
their alloys and intermetallic mixtures thereof.
4. An electrode according to claim 3, wherein a surface of said
valve metal electrode base comprises a roughened surface.
5. An electrode according to claim 4, wherein said surface is
prepared as by one or more of intergranlular etching, grit
blasting, or thermal spraying.
6. An electrode according to claim 4, wherein there is established
a ceramic oxide barrier layer as a pretreatment layer on said
roughened surface.
7. An electrode according to claim 4, wherein the molar ratio of
ruthenium oxide to iridium oxide is about 1:1.
8. An electrode according to claim 7, wherein the molar ratio of
said platinum group metal oxides and said valve metal oxide is
within the range of from about 4:1 to about 1:4.
9. An electrode according to claim 1, wherein said electrode
comprises an anode utilized in the electrolysis of seawater.
10. An electrode according to claim 1, wherein said electrode
operates at a current efficiency within the range of from about
from about 90% to about 100% over a hypochlorite concentration of
from 16 to 0 grams per liter.
11. A process for the electrolysis of an aqueous solution in an
electrolytic cell having at least one anode therein, said anode
having an electrocatalytic coating thereon, said process comprising
the steps of: providing an unseparated electrolytic cell;
establishing in said cell an electrolyte containing chloride;
providing said anode in said cell in contact with said electrolyte,
said anode having said electrocatalytic coating comprising a mixed
metal oxide coating of platinum group metal oxides and a valve
metal oxide, said mixed metal oxide coating consisting essentially
platinum group metal oxides of ruthenium, palladium, and iridium,
and a valve metal oxide of titanium; wherein a) the molar ratio of
said valve metal oxides to said platinum group metal oxides is from
about 90:10 to about 40:60; (b) the molar ratio of said ruthenium
to said iridium is from about 90:10 to about 50:50 and (c) the
molar ratio of said palladium oxide to ruthenium plus iridium
oxides is from about 5:95 to about 40:60, basis 100 mole percent of
the metals present in the coating; impressing an electric current
on said anode; and oxidizing chloride at said anode to produce
hypochlorite at concentrations of at least 8 grams per liter.
12. A process according to claim 11, wherein said chloride
electrolyte in said cell comprises one or more of sodium chloride
or potassium chloride.
13. A process according to claim 11, wherein a surface of said
anode comprises a roughened surface prepared by one or more steps
of intergranular etching, grit blasting, or thermal spraying.
14. The process of claim 13 wherein said anode surface comprises
titanium and said electrocatalytic coating is provided on said
titanium member by a procedure including electrostatic spray
application, brush application, roller coating, dip application and
combinations thereof.
15. A process according to claim 12, wherein said ruthenium oxide
and iridium oxide are present in a molar proportion of from about
1:3 to about 4:1.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of PCT/US2005/03046,
filed Jan. 27, 2005, the contents of which are herein incorporated
by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention is directed to an electrolytic electrode and a
mixed metal oxide coating thereon for the generation of
hypochlorite.
[0004] 2. Description of the Related Art
[0005] The use of mixed metal oxide coatings for the generation of
hypochlorite by electrolyzing brine solutions is widely known in
the art. Conventionally, when hypochlorite is manufactured through
the electrolysis of brine, however, the available chlorine
concentration of the hypochlorite product can be as low as 1 weight
percent (wt %) or less. Additionally, current efficiency and
electrode lifetimes diminish where brine feed solutions are less
concentrated (i.e., 10-30 g/l) and the desired hypochlorite
concentrations exceed 8 g/l.
[0006] Various solutions have been proposed to achieve high
concentration sodium hypochlorite solutions without deleteriously
effecting current efficiency and electrode lifetime. For example,
there has been taught a filter press type electrolytic cell where
in sodium hypochlorite is produced at a reduced cell voltage and
improved current efficiency. The anode in the electrolytic cell
consists of a titanium substrate having a coating of a ternary
mixture of 3 to 42% by weight platinum oxide, 3 to 34% by weight
palladium oxide, 42% by weight ruthenium dioxide and 20-40% by
weight titanium oxide.
[0007] There has also been taught an electrode, especially for
chlorine and hypochlorite production, comprises an electrocatalyst
consisting of 22-44 mol % ruthenium oxide, 0.2-22 mol % palladium
oxide and 44-77.8 mol % titanium oxide. The electrocatalyst may
form a coating on a valve metal substrate and may be topcoated with
a porous layer of titanium or tantalum oxide.
[0008] A method for manufacturing hypochlorite efficiently using an
anode having a coating of palladium oxide by 10 to 45 weight %,
ruthenium oxide by 15 to 45 weight %, titanium dioxide by 10 to 40
weight % and platinum by 10 to 20 weight %, as well as an oxide of
at least one metal selected from cobalt, lanthanum, cerium or
yttrium by 2 to 10 weight has previously been described.
[0009] It would be desirable to provide an electrode having an
electrocatalytic coating thereon which is capable of providing
improved electrode lifetimes and operating efficiencies in
electrolyte environments used for the generation of hypochlorite
from 15-30 grams per liter (g/l) NaCl or KCl feed solutions and
where desired hypochlorite concentrations exceed 8 g/l. It would be
further desirable to provide such an electrode at reduced costs as
compared to platinum based formulations.
SUMMARY OF THE INVENTION
[0010] There has now been found an electrode coating which provides
improved lifetimes while maintaining high efficiencies in
electrolytic solutions for the generation of hypochlorite. The
coating is a mixed metal oxide coating consisting of combinations
of the oxides of palladium, iridium, ruthenium and titanium.
[0011] In one embodiment, the invention is directed to an electrode
for use in the electrolysis of an aqueous solution for the
production of hypochlorite, the electrode having an
electrocatalytic coating thereon, with the electrode comprising a
valve metal electrode base; a coating layer of an electrochemically
active coating on the valve metal electrode base, the coating
comprising a mixed metal oxide coating of platinum group metal
oxides and a valve metal oxide, the mixed metal oxide coating
consisting essentially of platinum group metal oxides of ruthenium,
palladium, and iridium, and a valve metal oxide of titanium;
wherein [0012] a) the molar ratio of the valve metal oxides to
platinum group metal oxides is from about 90:10 to about 40:60;
[0013] b) the molar ratio of the ruthenium to the iridium is from
about 90:10 to about 50:50; and [0014] c) the molar ratio of the
palladium oxide to ruthenium plus iridium oxides is from about 5:95
to about 40:60, basis 100 mole percent of the metals present in the
coating; whereby the electrode operates at a high current
efficiency to produce hypochlorite concentrations of at least 8
grams per liter.
[0015] In another embodiment, the invention is directed to a
process for the electrolysis of an aqueous solution in an
electrolytic cell having at least one anode therein, the anode
having an electrocatalytic coating thereon, the process comprising
the steps of providing an unseparated electrolytic cell,
establishing in the cell an electrolyte containing chloride,
providing the anode in the cell in contact with the electrolyte,
the anode having the electrocatalytic coating comprising a mixed
metal oxide coating of platinum group metal oxides and a valve
metal oxide, the mixed metal oxide coating consisting essentially
of platinum group metal oxides of ruthenium, palladium, and
iridium, and a valve metal oxide of titanium, wherein [0016] (a)
the molar ratio of the valve metal oxides to the platinum group
metal oxides is from about 90:10 to about 40:60; [0017] (b) the
molar ratio of the ruthenium to the iridium is from about 90:10 to
about 50:50 and [0018] (c) the molar ratio of the palladium oxide
to ruthenium plus iridium oxides is from about 5:95 to about 40:60,
basis 100 mole percent of the metals present in the coating;
impressing an electric current on the anode; and oxidizing chloride
at the anode to produce hypochlorite at concentrations of at least
8 grams per liter.
DESCRIPTION OF THE DRAWING FIGURES
[0019] FIG. 1 is a graph of the current efficiencies for the
production of hypochlorite of the coatings according to the
invention and a comparative coating as a function of hypochlorite
concentrations.
[0020] FIG. 2 is a graph of the lifetime in hours of the coatings
according to the invention and a comparative coating.
DESCRIPTION OF THE INVENTION
[0021] According to the invention, an electrode having an
electrocatalytic coating having a high current efficiency at high
hypochlorite concentrations, e.g., >8 gpl (grams per liter) and
having a low electrode potential and improved lifetimes is
provided. In one embodiment, depending upon the hypochlorite
concentration, the current efficiency will be from about 90% to
about 100% over a hypochlorite concentration of from 16 to 0 grams
per liter (g/l). The electrode having the electrocatalytic coating
described herein will virtually always find service as an anode.
Thus, the word "anode" is often used herein when referring to the
electrode, but this is simply for convenience and should not be
construed as limiting the invention.
[0022] The electrode used in the invention comprises an
electrocatalytically active film on a conductive base. The
conductive base may be a metal such as nickel or manganese or a
sheet of any film-forming metal such as titanium, tantalum,
zirconium, niobium, tungsten and silicon, and alloys containing one
or more of these metals, with titanium being preferred for cost
reasons. By "film-forming metal" it is meant a metal or alloy which
has the property that when connected as an anode in the electrolyte
in which the coated anode is subsequently to operate, there rapidly
forms a passivating oxide film which protects the underlying metal
from corrosion by electrolyte, i.e., those metals and alloys which
are frequently referred to as "valve metals", as well as alloys
containing valve metal (e.g., Ti--Ni, Ti--Co, Ti--Fe and Ti--Cu),
but which in the same conditions form a non-passivating anodic
surface oxide film. Plates, rods, tubes, wires or knitted wires and
expanded meshes of titanium or other film-forming metals can be
used as the electrode base. Titanium or other film-forming metal
clad on a conducting core can also be used. It is also possible to
surface treat porous sintered titanium with dilute paint solutions
in the same manner.
[0023] Of particular interest for its ruggedness, corrosion
resistance and availability is titanium. As well as the normally
available elemental metals themselves, the suitable metals of the
substrate include metal alloys and intermetallic mixtures, as well
as ceramics and cermets such as contain one or more valve metals.
For example, titanium may be alloyed with nickel, cobalt, iron,
manganese or copper. More specifically, grade 5 titanium may
include up to 6.75 weight percent aluminum and 4.5 weight percent
vanadium, grade 6 up to 6 percent aluminum and 3 percent tin, grade
7 up to 0.25 weight percent palladium, grade 10, from 10 to 13
weight percent plus 4.5 to 7.5 weight percent zirconium and so
on.
[0024] By use of elemental metals, it is most particularly meant
the metals in their normally available condition, i.e., having
minor amounts of impurities. Thus, for the metal of particular
interest, i.e., titanium, various grades of the metal are available
including those in which other constituents may be alloys or alloys
plus impurities. Grades of titanium have been more specifically set
forth in the standard specifications for titanium detailed in ASTM
B 265-79. Because it is a metal of particular interest, titanium
will often be referred to herein for convenience when referring to
metal for the electrode base.
[0025] Regardless of the metal selected and the form of the
electrode base, before applying a coating composition thereto, the
electrode base is advantageously a cleaned surface. This may be
obtained by any of the treatments used to achieve a clean metal
surface, including mechanical cleaning. The usual cleaning
procedures of degreasing, either chemical or electrolytic, or other
chemical cleaning operation may also be used to advantage. Where
the base preparation includes annealing, and the metal is grade 1
titanium, the titanium can be annealed at a temperature of at least
about 450.degree. C. for a time of at least about 15 minutes, but
most often a more elevated annealing temperature, e.g., 600.degree.
C. to 875.degree. C. is advantageous.
[0026] For most applications, it is advantageous to obtain a base
with a surface roughness. This will be achieved by means which can
include intergranular etching of the metal, plasma spray
application, which spray application can be of particulate valve
metal or of ceramic oxide particles, or both, etching and sharp
grit blasting of the metal surface, optionally followed by surface
treatment to remove embedded grit and/or clean the surface, or
combinations thereof. In some instances the base can simply be
cleaned, and this gives a very smooth substrate surface.
Alternatively, the film-forming conductive base can have a
pre-applied surface film of film-forming metal oxide which, during
application of the active coating, can be attacked by an agent in
the coating solution (e.g. HCl) and reconstituted as a part of the
integral surface film.
[0027] Etching will be with a sufficiently active etch solution to
develop a surface roughness and/or surface morphology, including
possible aggressive grain boundary attack. Typical etch solutions
are acid solutions. These can be provided by hydrochloric,
sulfuric, perchloric, nitric, oxalic, tartaric, and phosphoric
acids as well as mixtures thereof, e.g., aqua regia. Other etchants
that may be utilized include caustic etchants such as a solution of
potassium hydroxide/hydrogen peroxide, or a melt of potassium
hydroxide with potassium nitrate. Following etching, the etched
metal surface can then be subjected to rinsing and drying steps.
The suitable preparation of the surface by etching has been more
fully discussed in U.S. Pat. No. 5,167,788, which patent is
incorporated herein by reference.
[0028] In plasma spraying for a suitably roughened metal surface,
the material will be applied in particulate form such as droplets
of molten metal. In this plasma spraying, such as it would apply to
spraying of a metal, the metal is melted and sprayed in a plasma
stream generated by heating with an electric arc to high
temperatures in inert gas, such as argon or nitrogen, optionally
containing a minor amount of hydrogen. It is to be understood by
the use herein of the term "plasma spraying" that although plasma
spraying is preferred the term is meant to include generally
thermal spraying such as magnetohydrodynamic spraying, flame
spraying and arc spraying, so that the spraying may simply be
referred to as "melt spraying" or "thermal spraying".
[0029] The particulate material employed may be a valve metal or
oxides thereof, e.g., titanium oxide, tantalum oxide and niobium
oxide. It is also contemplated to melt spray titanates, spinels,
magnetite, tin oxide, lead oxide, manganese oxide and perovskites.
It is also contemplated that the oxide being sprayed can be doped
with various additives including dopants in ion form such as of
niobium or tin or indium.
[0030] It is also contemplated that such plasma spray application
may be used in combination with etching of the substrate metal
surface. Or the electrode base may be first prepared by grit
blasting, as discussed hereinabove, which may or may not be
followed by etching.
[0031] It has also been found that a suitably roughened metal
surface can be obtained by special grit blasting with sharp grit,
optionally followed by removal of surface embedded grit. The grit,
which will usually contain angular particles, will cut the metal
surface as opposed to peening the surface. Serviceable grit for
such purpose can include sand, aluminum oxide, steel and silicon
carbide. Etching, or other treatment such as water blasting,
following grit blasting can be used to remove embedded grit and/or
clean the surface.
[0032] It will be understood from the foregoing that the surface
may then proceed through various operations, providing a
pretreatment before coating, e.g., the above-described plasma
spraying of a valve metal oxide coating. Other pretreatments may
also be useful. For example, it is contemplated that the surface be
subjected to a hydriding or nitriding treatment. Prior to coating
with an electrochemically active material, it has been proposed to
provide an oxide layer by heating the substrate in air or by anodic
oxidation of the substrate as described in U.S. Pat. No. 3,234,110.
Various proposals have also been made in which an outer layer of
electrochemically active material is deposited on a sublayer, which
primarily serves as a protective and conductive intermediate.
Various tin oxide based underlayers are disclosed in U.S. Pat. Nos.
4,272,354, 3,882,002 and 3,950,240. It is also contemplated that
the surface may be prepared as with an antipassivation layer.
[0033] Following surface preparation, which might include providing
a pretreatment layer such as described above, an electrochemically
active coating layer is applied to the substrate member. As is
typically representative of the electrochemically active coatings
that are often applied, are those provided from active oxide
coatings such as platinum group metal oxides, magnetite, ferrite,
cobalt spinel or mixed metal oxide coatings. They may be water
based, such as aqueous solutions, or solvent based, e.g., using
alcohol solvent. However, it has been found that for the electrode
of the invention, the coating composition solutions are typically
those consisting of a mixed metal oxide coating of platinum group
metal oxides and a valve metal oxide.
[0034] The platinum group metal oxides of the invention preferably
comprise, RuCl.sub.3, PdCl.sub.2, IrCl.sub.3, and hydrochloric
acid, all in alcohol solution, in combination with a valve metal
oxide. It will be understood that the RuCl.sub.3, PdCl.sub.2,
IrCl.sub.3 may be utilized in a form such as RuCl.sub.3 xH.sub.2O,
PdCl.sub.2 xH.sub.2O and IrCl.sub.3.xH.sub.20. For convenience,
such forms will generally be referred to herein simply as
RuCl.sub.3, PdCl.sub.2 and IrCl.sub.3. Generally, the metal salts
will be dissolved in an alcohol such as either isopropanol or
butanol, all combined with or with out small additions of
hydrochloric acid, with n-butanol being preferred. It will be
understood that the constituents are substantially present as their
oxides in the finished coating, and the reference to the metals is
for convenience, particularly when referring to proportions.
[0035] A valve metal component will be present in the coating
composition in order to further stabilize the coating and/or alter
the anode efficiency. Various valve metals can be utilized
including titanium, tantalum, niobium, zirconium, hafnium,
vanadium, molybdenum, and tungsten, with titanium being preferred.
The valve metal component can be formed from a valve metal
alchoxide in an alcohol solvent, with or without the presence of an
acid. Such valve metal alchoxides which are contemplated for use in
the invention include methoxides, ethoxides, isopropoxides and
butoxides. For example, titanium ethoxide, titanium propoxide,
titanium butoxide, tantalum ethoxide, tantalum isopropoxide or
tantalum butoxide may be useful. In one embodiment, the valve metal
alchoxide comprises titanium butoxide.
[0036] The mixed metal oxide coating of the invention will contain
a molar ratio of valve metal oxide to platinum group metal oxides
of from about 90:10 to about 40:60, a molar ratio of ruthenium to
iridium of about 90:10 to about 50:50 and a molar ratio of
Pd:(Ru+Ir) of about 5:95 to about 40:60. A particularly preferred
composition of the mixed metal oxide coating of the invention will
contain a molar ratio of titanium to precious metal oxides of about
70:30 on a metals basis and a molar ratio of Pd:(Ru+Ir) of about
20:80.
[0037] The mixed metal oxide coating layers utilized herein will be
applied by any of those means which are useful for applying a
liquid coating composition to a metal substrate. Such methods
include dip spin and dip drain techniques, brush application,
roller coating and spray application such as electrostatic spray.
Moreover, spray application and combination techniques, e.g., dip
drain with spray application can be utilized. With the
above-mentioned coating compositions for providing an
electrochemically active coating, a roller coating operation can be
most serviceable.
[0038] Regardless of the method of application of the coating,
conventionally, a coating procedure is repeated to provide a
uniform, more elevated coating weight than achieved by just one
coating. However, the amount of coating applied will be sufficient
to provide in the range of from about 0.05 g/m.sup.2 (gram per
square meter) to about 6 g/m.sup.2, and preferably, from about 1
g/m.sup.2 to about 4 g/m.sup.2 based on ruthenium content, as
metal, per side of the electrode base.
[0039] Following application of the coating, the applied
composition will be heated to prepare the resulting mixed oxide
coating by thermal decomposition of the precursors present in the
coating composition. This prepares the mixed oxide coating
containing the mixed oxides in the molar proportions, basis the
metals of the oxides, as above discussed. Such heating for the
thermal decomposition will be conducted at a temperature of about
450.degree. C. to about 550.degree. C. for a time of from about 3
minutes to about 15 minutes per coat. More typically, the applied
coating will be heated at a more elevated temperature of up to
about 490-525.degree. C. for a time of not more than about 20
minutes per coat. Suitable conditions can include heating in air or
oxygen. In general, the heating technique employed can be any of
those that may be used for curing a coating on a metal substrate.
Thus, oven coating, including conveyor ovens may be utilized.
Moreover, infrared cure techniques can be useful. Following such
heating, and before additional coating as where an additional
application of the coating composition will be applied, the heated
and coated substrate will usually be permitted to cool to at least
substantially ambient temperature. Particularly after all
applications of the coating composition are completed, postbaking
can be employed. Typical postbake conditions for coatings can
include temperatures of from about 450.degree. C. up to about
550.degree. C. Baking times may vary from about 1 hour up to as
long as about 6 hours.
[0040] The following examples are included to demonstrate
particular embodiments of the invention. It should be appreciated
by those of skill in the art that the techniques disclosed in the
examples which follow represent techniques discovered by the
inventors to function well in the practice of the invention.
However, those of skill in the art should, in light of the
disclosure, appreciate that many changes can be made in the
specific embodiments which are disclosed and still obtain a like or
similar result without departing from the spirit and scope of the
invention.
EXAMPLE 1
[0041] A flat, titanium plate of unalloyed grade 1 titanium,
measuring approximately 0.15 cm thick and approximately 10.times.15
cm was grit blasted using alumina to achieve a roughened surface.
The sample was then etched in a 90-95.degree. C. solution of 18-20%
hydrochloric acid for 25 minutes.
[0042] Coating compositions as set forth in Table 1 were applied to
separate samples measuring 10 cm.times.15 cm.times.0.15 cm of Grade
1 titanium which was prepared by grit blasting with 54 grit
alumina. The coating solutions A-D were prepared by dissolving
sufficient amount of metals, as chloride salts, to achieve the
concentrations listed in the table to a solution of n-butanol and
4.2 vol % concentrated HCl. The compounds used were RuCl.sub.3,
IrCl.sub.3, and PdCl.sub.2 (all hydrated) and titanium orthobutyl
titanate. After mixing to dissolve all of the salts, the solutions
were applied to individual samples of prepared titanium plates. The
coatings were applied in layers by brushing, with each coat being
applied separately and allowed to dry at 110.degree. C. for 3
minutes, followed by heating in air to 500.degree. C. for 6
minutes. A total of 5 coats was applied to each sample. Samples A-D
are in accordance with the invention. Sample E is considered a
comparative example. TABLE-US-00001 TABLE I Solution Concentration
(gpl) Sample Coating Ru Ir Pd Ti A Ru/Ir/Pd/Ti 20.9 20.9 10.5 43.9
B Ru/Pd/Ti 20.9 10.5 43.9 C Ru/Ir/Pd 20.9 20.9 10.5 D Ir/Pd/Ti 20.9
10.5 43.9 E Ru/Ir/Ti 20.9 20.9 43.9 (Comparative) * Salts are
chlorides, except Ti, which is Titanium orthobutyl titanate)
[0043] The hypochlorite efficiency of the samples was measured in a
beaker-cell by immersing an area of 26 cm.sup.2 into a solution of
28 gpl NaCl with 1 gpl Na.sub.2Cr.sub.2O.sub.7 and applying an
anodic current of 4.86 amps (0.186 A/cm.sup.2). A titanium cathode
was used, spaced 3 mm from the anode. A sample was pulled every 8
minutes and titrated for hypochlorite. The current efficiencies for
the production of hypochlorite as a function of hypochlorite
concentrations are plotted in FIG. 1 and Table II. TABLE-US-00002
TABLE II Ru/Ir/Ti Ru/Ir/Pd/Ti Ir/Pd/Ti Ru/Ir/Pd Ru/Pd/Ti
(Comparative) NaOCl Efficiency NaOCl Efficiency NaOCl Efficiency
NaOCl Efficiency NaOCl Efficiency (gpl) (%) (gpl) (%) (gpl) (%)
(gpl) (%) (gpl) (%) 2.36 88.5 2.71 103.6 2.49 95.7 2.51 96.6 2.26
86.5 4.78 88.6 5.12 97.1 4.92 93.9 5.11 97.4 4.43 83.9 7.09 86.9
7.74 96.8 7.39 93.0 7.69 96.8 6.43 80.5 9.30 84.8 10.27 95.6 9.71
90.9 10.21 95.6 8.31 77.3 11.49 83.0 12.54 92.4 11.49 85.3 12.61
93.6 9.80 72.3
[0044] The set of samples, A-E, were then operated as anodes in an
accelerated test as an oxygen-evolving anode at a current density
of 10 kA/m.sup.2 in an electrochemical cell containing 150 g/l
H.sub.2SO.sub.4 at 65.degree. C. Cell voltage versus time data was
collected every 30 minutes and the lifetime taken as the inflexion
point at which the voltage began to increase rapidly. The results
are summarized in FIG. 2 and Table II, normalized for the amount of
platinum group metal. Normalization was done by measuring the x-ray
fluorescence count for the metal peaks using a Jordan Valley EX-300
spectrometer with a Rh tube and a 0.15 mm Sn filter. The applied
voltage was 40 kV (kilivolts) and current was 25 .mu.A. The peaks
measured were the RuK-alpha, Pd K-alpha and Ir L-beta. The total
counts of the Ru, Pd and/or Ir were used to normalize the
lifetimes.
[0045] It is, therefore, evident from the results of Table II that
samples prepared according to the invention have substantially
increased current efficiencies versus the comparison example while
improving or meeting the lifetime as evidenced by the extended time
before a significant rise in voltage (>1 volt) occurs.
[0046] Although the disclosure has been shown and described with
respect to one or more embodiments and/or implementations,
equivalent alterations and/or modifications will occur to others
skilled in the art based upon a reading and understanding of this
specification. The disclosure is intended to include all such
modifications and alterations and is limited only by the scope of
the following claims. In addition, while a particular feature may
have been disclosed with respect to only one of several embodiments
and/or implementations, such feature may be combined with one or
more other features of the other embodiments and/or implementations
as may be desired and/or advantageous for any given or particular
application. Furthermore, to the extent that the terms "includes",
"having", "has", "with", or variants thereof are used in either the
detailed description or the claims, such terms are intended to be
inclusive in a manner similar to the term "comprising."
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