AU2005325733A1 - High efficiency hypochlorite anode coating - Google Patents

Abstract

The present 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.

Description

WO 2006/080926 PCT/US2005/003046 1 TITLE: HIGH EFFICIENCY HYPOCHLORITE ANODE COATING BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is directed to an electrolytic electrode and a mixed metal oxide coating thereon for the generation of hypochlorite. 5 2. Description of the Related Art 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 10 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/I) and the desired hypochlorite concentrations exceed 8 g/l. Various solutions have been proposed to achieve high 15 concentration sodium hypochlorite solutions without deleteriously effecting current efficiency and electrode lifetime. For example, in U.S. Patent 4,495,048, there is 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 20 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. In U.S. Patent 4,517,068, an electrode, especially for chlorine and hypochlorite production, comprises an electrocatalyst consisting of 22-44 25 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. A method for manufacturing hypochlorite efficiently using an anode 30 having a coating of palladium oxide by 10 to 45 weight%, ruthenium oxide WO 2006/080926 PCT/US2005/003046 2 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 % is described in U.S. Patent 5,622, 613. 5 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/1) NaCI or KCI feed solutions and where desired hypochlorite concentrations 10 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 There has now been found an electrode coating which provides 15 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. In one embodiment, the invention is directed to an electrode for use 20 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 25 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 a) the molar ratio of the platinum group metal oxides to the valve metal oxide is from about 90:10 to about 40:60; 30 b) the molar ratio of the ruthenium to the iridium is from about 90:10 to about 50:50; and WO 2006/080926 PCT/US2005/003046 3 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 5 hypochlorite concentrations of at least 8 grams per liter. 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, 10 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, 15 palladium, and iridium, and a valve metal oxide of titanium, wherein (a) the molar ratio of the platinum group metal oxides to the valve metal oxide is from about 90:10 to about 40:60; (b) the molar ratio of the ruthenium to the iridium is from about 90:10 to about 50:50 and 20 (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 25 liter. DESCRIPTION OF THE INVENTION According to the present invention, an electrode having an electrocatalytic coating having a high current efficiency at high hypochlorite 30 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 WO 2006/080926 PCT/US2005/003046 4 from 16 to 0 grams per liter (g/1). 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 5 as limiting the invention. The electrode used in the present 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, 10 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 15 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 20 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. Of particular interest for its ruggedness, corrosion resistance and 25 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 30 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.

WO 2006/080926 PCT/US2005/003046 5 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 5 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. 10 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 15 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 4500C for a time of at least about 15 minutes, but most often a more elevated annealing temperature, e.g., 6000C to 8750C is 20 advantageous. 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, 25 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 30 film-forming metal oxide which, during application of the active coating, can be attacked by an agent in the coating solution (e.g. HCI) and reconstituted as a part of the integral surface film.

WO 2006/080926 PCT/US2005/003046 6 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, 5 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. 10 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. In plasma spraying for a suitably roughened metal surface, the material will be applied in particulate form such as droplets of molten metal. 15 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 20 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". The particulate material employed may be a valve metal or oxides 25 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. 30 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.

WO 2006/080926 PCT/US2005/003046 7 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 5 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. It will be understood from the foregoing that the surface may then 10 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 15 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. Patent 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 20 oxide based underlayers are disclosed in U.S. Patent 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. Following surface preparation, which might include providing a pretreatment layer such as described above, an electrochemically active 25 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 30 based, e.g., using alcohol solvent. However, it has been found that for the electrode of the present invention, the preferred coating composition solutions are typically those consisting of a mixed metal oxide coating of platinum group metal oxides and a valve metal oxide.

WO 2006/080926 PCT/US2005/003046 8 The platinum group metal oxides of the present invention preferably comprise, RuCI 3 , PdCI 2 , IrCI 3 , and hydrochloric acid, all in alcohol solution, in combination with a valve metal oxide. It will be understood that the RuCI 3 , PdCl 2 , IrCI 3 may be utilized in a form such as RuCI 3 xH 2 0, PdCI 2 5 xH 2 0 and IrCl3-xH 2 0. For convenience, such forms will generally be referred to herein simply as RuCI 3 , PdCI 2 and IrCI 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 10 substantially present as their oxides in the finished coating, and the reference to the metals is for convenience, particularly when referring to proportions. A valve metal component will be present in the coating composition in order to further stabilize the coating and/or alter the anode efficiency. 15 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 20 present 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, with titanium butoxide being preferred. The mixed metal oxide coating of the present invention will contain a 25 molar ratio of titanium 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+lr) of about 5:95 to about 40:60. A particularly preferred composition of the mixed metal oxide coating of the present invention will contain a molar ratio of titanium to precious metal 30 oxides of about 70:30 on a metals basis and a molar ratio of Pd:(Ru+lr) of about 20:80. The mixed metal oxide coating layers utilized herein will be applied by any of those means which are useful for applying a liquid coating WO 2006/080926 PCT/US2005/003046 9 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 5 above-mentioned coating compositions for providing an electrochemically active coating, a roller coating operation can be most serviceable. 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 10 amount of coating applied will be sufficient to provide in the range of from about 0.05 g/m 2 (gram per square meter) to about 6 g/m 2 , and preferably, from about 1 g/m 2 to about 4 g/m 2 based on ruthenium content, as metal, per side of the electrode base. Following application of the coating, the applied composition will be 15 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 20 about 450 0 C to about 550 0 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 0 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 25 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 30 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 WO 2006/080926 PCT/US2005/003046 10 temperatures of from about 4500C up to about 5500C. Baking times may vary from about 1 hour up to as long as about 6 hours. The following examples, unless otherwise noted as comparative examples, generally demonstrate the production of a high concentration 5 hypochlorite at increased efficiencies with an anode containing the coating of the present invention: EXAMPLE 1 A flat, titanium plate of unalloyed grade 1 titanium, measuring approximately 0.15 cm thick and approximately 10 x 15 cm was grit blasted 10 using alumina to achieve a roughened surface. The sample was then etched in a 90-950C solution of 18-20% hydrochloric acid for 25 minutes. Coating compositions as set forth in Table 1 were applied to separate samples measuring 10 cm x 15 cm x 0.15 cm of Grade 1 titanium which was prepared by grit blasting with 54 grit alumina. The coating 15 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 HCI. The compounds used were RuCI 3 , IrCI 3 , and PdCI 2 (all hydrated) and titanium orthobutyl titanate. After mixing to dissolve all of the salts, the solutions were applied to individual 20 samples of prepared titanium plates. The coatings were applied in layers by brushing, with each coat being applied separately and allowed to dry at 1100C for 3 minutes, followed by heating in air to 5000C for 6 minutes. A total of 5 coats was applied to each sample. Samples A-D are in accordance with the present invention., Sample E is considered a 25 comparative example.

WO 2006/080926 PCT/US2005/003046 11 Table I Sample Solution Concentration (gpl) 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) The hypochlorite efficiency of the samples was measured in a 5 beaker-cell by immersing an area of 26 cm 2 into a solution of 28 gpl NaCI with 1 gpl Na 2 Cr 2 0 7 and applying an anodic current of 4.86 amps (0.186A/cm 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 10 hypochlorite concentrations are plotted in Figure 1 and Table II. Table II Ru/Ir/Pd/Ti Ir/Pd/Ti Ru/Ir/Pd Ru/Pd/Ti Ru/Ir/Ti (Comp arative) NaOCl Efficiency NaOCI Efficiency NaOCI Efficiency NaOCI Efficiency NaOCl Efficiency (gPI) (%) (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 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 15 kA/m 2 in an electrochemical cell containing 150 g/l H 2

SO

4 at 650C. 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 Figure 2 and Table II, normalized for the amount of platinum group metal. Normalization was done by measuring 20 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 40kV (kilivolts) and current was 25 pA. The peaks measured WO 2006/080926 PCT/US2005/003046 12 were the Ru K-alpha, Pd K-alpha and Ir L-beta. The total counts of the Ru, Pd and/or Ir were used to normalize the lifetimes. It is, therefore, evident from the results of Table II that samples prepared according to the present invention have substantially increased 5 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. While in accordance with the patent statutes the best mode and preferred embodiment have been set forth, the scope of the invention is not 10 limited thereto, but rather by the scope of the attached claims.

Claims (15)

1. An electrode for use in the electrolysis of an aqueous solution for the production of hypochlorite, said electrode having an electrocatalytic 5 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 10 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 platinum group metal oxides to said valve metal oxide is from about 90:10 to about 40:60; 15 (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; 20 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 is a valve metal mesh, sheet, blade, tube, punched plate or 25 wire member.

3. An electrode according to claim 2, wherein said valve metal electrode base is one or more of titanium, tantalum, aluminum, hafnium, niobium, zirconium, molybdenum or tungsten, their alloys and intermetallic 30 mixtures thereof.

4. An electrode according to claim 3, wherein a surface of said valve metal electrode base is a roughened surface. WO 2006/080926 PCT/US2005/003046 14

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. 5

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 10 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. 15

9. An electrode according to claim 1, wherein said electrode is an anode utilized in the electrolysis of seawater.

10. An electrode according to claim 1, wherein said electrode 20 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 25 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 30 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; WO 2006/080926 PCT/US2005/003046 15 wherein a) the molar ratio of said platinum group metal oxides to said valve metal oxide is from about 90:10 to about 40:60; (b) the molar ratio of said ruthenium to said iridium is from about 5 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 10 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 is one or more of sodium chloride or potassium 15 chloride.

13. A process according to claim 11, wherein a surface of said anode is a roughened surface prepared by one or more steps of intergranular etching, grit blasting, or thermal spraying. 20

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. 25

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.