CA2583827A1 - Undivided electrolytic chlorate cells with coated cathodes - Google Patents

Abstract

The present invention provides novel undivided electrolytic chlorate cells with one or more cathodes in fluid communication with a catalytic metal cathode electrodepositing solution. The invention further includes undivided electrolytic chlorate cells including one or more dimensionally stable anodes and one or more cathodes coated with a catalytic metal cathode coating. Also provided are methods of coating a cathode, where the cathode forms part of an undivided electrolytic chlorate cell.

Description

UNDIVIDED ELECTROLYTIC CHLORATE CELLS WITH COATED
CATHODES
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Patent Application No.
60/617,762, filed October 12, 2004, which is incorporated herein by reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

[0002] Sodium chlorate is commonly used as a bleaching chemical in the pulp and paper industry. Sodium chlorate is produced by electrolyzing sodium chloride in an electrolytic cell using a direct current. The electrolytic cell typically includes dimensionally stable anodes ("DSAs"), and cathodes constructed from uncoated steel or uncoated titanium. This process is energy intensive, requiring approximately 5000 KWhr of electricity to produce 1 metric ton of sodium chlorate. During the production of sodium chlorate, sodium chloride is oxidized to form chlorine on the positive electrode (called the anode). The chlorine then chemically transforms to sodium chlorate under controlled chemical conditions.
On the negative electrode (called the cathode), water is reduced to form hydrogen gas as a by-product of the electrochemical reaction. However, a certain amount of electrical energy is wasted in producing hydrogen gas on the cathode. The wasted electrical energy is commonly referred to as hydrogen overvoltage. The present invention solves these and other problems in the art of chlorate production.

BRIEF SUMMARY OF THE INVENTION

[0003] The present invention provides novel undivided electrolytic chlorate cells and methods of making the cells thereof. It has been discovered that undivided electrolytic chlorate cells including a dimensionally stable anode and a cathode coated with a catalytic metal cathode coating may be used to produce chlorate in an efficient and cost effective manner. It has also been discovered that cathodes forming part of an undivided electrolytic chlorate cell may be coated, in the presence of the anode, by electrodeposition of a catalytic metal from a catalytic metal cathode electrodepositing solution without the use of a physical barrier separating the anode and cathode.

[0001] In one aspect, an undivided electrolytic chlorate cell is provided. The undivided electrolytic cell includes an anode and a cathode. The cathode is in fluid communication with a catalytic metal cathode electrodepositing solution.

[0002] In another aspect, a method of coating a cathode is provided. The cathode forms part of an undivided electrolytic chlorate cell. The method includes the step of contacting the cathode with a catalytic metal cathode electrodepositing solution. The method also includes the step of electrodepositing a catalytic metal from the catalytic metal cathode electrodepositing solution onto the cathode thereby forming a catalytic metal cathode coating on the cathode.

[0003] In another aspect, the present invention provides an undivided electrolytic chlorate cell. The cell includes a dimensionally stable anode and a cathode. The cathode is coated with a catalytic metal cathode coating.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIG. 1 illustrates an exemplary monopolar SEC. A is the electrical connection of the negative terminal of the DC power supply; B is the electrical connection to the positive terminal of the DC Power Supply; C is the anode; and D is the cathode.

[0005] FIG. 2 illustrates an exemplary bipolar SEC. A is the electrical connection of the negative terminal of the DC power supply; B is the electrical connection to the positive terminal of the DC Power Supply; C is the anode; D is the cathode; and E is the bipolar late where the (+) side is anodic and the (-) side is cathodic.

[0006] FIG. 3 illustrates an exemplary monopolar MEC. A is the electrical connection between each single electrolytic cell (SEC); B is the respective SEC.

[0007] FIG. 4 illustrates an exemplary bipolar MEC. A is the electrical connection between each SEC; B is the bipolar SEC.

[0008] FIG. 5 are graphs corresponding to Table 3, consisting of sodium chloride (NaC1) concentration versus days of operation, sodium chlorate (NaC103) concentration versus days of operation, cell voltage (Voltage) versus days of operation, k factor versus days of operation, molybdenum (Mo) and calcium (Ca) concentrations versus days of operation.

DETAILED DESCRIPTION OF THE INVENTION
Definitions [0009] As used herein, a "single electrolytic cell" ("SEC") means an apparatus having 1 or more anode plates in combination with corresponding cathode plates (e.g. 1 anode plate with lor 2 cathode plates or n_2 anode plates in combination with n-1, n or n+1 cathode plates). _ [0010] A "multiple electrolytic cell" ("MEC") is an apparatus having more than assembled as part of an electrical circuit in which the electrolytic cell configuration is 2a monopolar or bipolar. Figures 1, 2, 3 and 4 illustrate monopolar SEC, bipolar SEC, monopolar MEC and bipolar MEC examples respectively.

[0014] The term "in-situ," refers to a process (e.g. coating, electrodepositing) which is performed in an intact (e.g. a pre-assembled) electrolytic cell, such as an electrolytic chlorate cell. Thus, in-situ processes do not require mechanical disassembly of an electrolytic cell (e.g. a SEC or MEC) to separate one or more anode plates from cathode plates, for example between electrodeposition and chlorate production, or between chlorate production and electrodeposition.

DESCRIPTION
[0015] The present invention provides novel undivided electrolytic chlorate cells having catalytic metal coated cathodes. The electrolytic cells are cost-efficient, energy-efficient, and allow for convenient in-situ coating of cathodes in the undivided electrolytic chlorate cells thereby avoiding time consuming and costly disassembly of the cells.

Undivided Electrolytic Chlorate Cells [0016] An "electrolytic chlorate cell" is an apparatus containing an anode and a cathode in which chemical reactions are caused by applying an external potential difference, typically greater than, and opposite to, the galvanic electromotive force of the cell.
Electrolytic chlorate cells generally convert electrical energy into chemical energy. The chemical reactions usually do not occur spontaneously at the electrodes when they are connected through an external circuit. The reaction is typically forced by applying an external electrical current. Thus, an electrolytic chlorate cell is an assembled electrolytic cell apparatus. A wide variety of electrolytic chlorate cell configurations are useful in the art of chlorate production. For a detailed discussion of electrolytic chlorate cell configurations and the chemistry of chlorate production, see Colman, "Electrolytic Production of Sodium Chlorate," no. 204, vol. 77, the American Institute of Chemical Engineers (1981), which is herein incorporated by reference in -its entirety for all purposes. See also, "Sodium Chlorate," in the Encyclopedia of Chemical Processing and Design, Ed. McKetta, J., vol.
51, pp. 126-18 8 (New York), Marcel Dekker, Inc.

[0017] An "undivided electrolytic chlorate cell" is an electrolytic chlorate cell that has no physical barrier (e.g. a membrane or diaphragm) between the anode and the cathode that functions to separate the cell liquor. Thus, the cathode and anode are present in a single chamber. In some embodiments, the electrolytic chlorate cell forms part of a multiple electrolytic cell. Thus, undivided electrolytic chlorate cells may be in the form of a single cell or form part of a multiple electrolytic cell, such as a multiple electrolytic chlorate cell.
[0018] In undivided electrolytic chlorate cells, an external potential difference is applied sufficient for electrolysis of an aqueous solution comprising sodium chloride (also referred to herein as "brine" or "chlorate liquor"). This electrolysis produces chlorine gas at the anode and hydrogen gas at the cathode. Since the hydrogen is produced by breaking up water molecules, the solution becomes basic near the cathode and a solution of sodium hydroxide (also called "caustic" or "alkali") is produced. The production of chlorate in an undivided electrolytic chlorate cell may be summarized by the follows reactions:
20- Clz + 2e-2H20 + 2e o- H2 + 20H"
C12 + H20 HOC1 + H} + Cl"
HOCI H+ + C1O-2HC1O + C10- C103- + 20- +2H+

[0019] The anode and cathode may be any appropriate shape and composed of any suitable material. For example, the cathode may be composed of any appropriate conductive material suitable for conditions of chlorate electrolysis. Useful metals include those comprising iron, titanium, and/or steel. The cathode may be in any appropriate shape, such as a solid sheet, bar, or other solid metal configuration, or a metal mesh or screen of high surface area.

[0020] Anodes useful in the present invention include those comprising an electrically conductive anode substrate, such as titanium, tantalum, niobium and zirconium.
Typically, the anode includes one or more anode coating(s) on the surface of an anode substrate.
Useful anode coatings include those comprising ruthenium, titanium, tantalum, niobium, zirconium, platinum, palladium, iridium, tin, rhodium, antimony, and appropriate alloys, combinations, and/or oxides thereof. In some embodiments, the anode substrate is a titanium anode substrate. In some embodiments, the anode coating is a ruthenium-antimony oxide anode coating (i.e. a coating comprising ruthenium and antimony, e.g. a ruthenium-antimony mixed oxide) or derivative thereof. In other embodiments, the anode coating is a ruthenium-titanium oxide anode coating or derivative thereof. In other embodiments, the anode coating is a ruthenium-titanium-antimony anode oxide coating or derivative thereof.

[0021] In some embodiments, the anode is a dimensionally stable anode (DSA).
Dimensionally stable anodes are well known in the art of electrolytic cells.
See, for example, WO 4101852, WO 4094698, US 6071570, US 5672394, US 4233340, US
5679225, US 5593556, US 5989396, US 5419824, US 4528084, and US 6572758, each of which are herein incorporated by reference in their entirety for all purposes.
DSAs are highly corrosion resistant electrodes that have electrochemically active surface coatings.
DSAs were developed to overcome the limitations of carbon and graphite electrodes, which are gradually eroded or decomposed during electrolytic cell operation.
Dimensionally stable anodes are typically comprised of a titanium or similar valve metal substrate coated with a platinum metal or ruthenium oxide alone or in combination with other oxides and/or compounds.

[0022] Thus, in one aspect, the present invention provides an undivided electrolytic chlorate cell with a dimensionally stable anode and a cathode. The cathode is coated with a catalytic metal cathode coating.

Catalytic Metal Cathode Electrodepositing solution and CoatinLys [0023] A "catalytic metal cathode electrodepositing solution" is a solution from which a catalytic metal or metals are electroplated onto a cathode to form a catalytic metal cathode coating. The catalytic metal cathode coating includes a catalytic metal that catalyzes the chlorate cell hydrolysis reaction that forms hydrogen and hydroxide at the cathode, thereby reducing hydrogen overvoltage. Where the anode includes a coating, the catalytic metal cathode electrodepositing solution typically does not degrade the anode coating (e.g. a titanium-ruthenium containing anode coating) before, during, and/or after electrodeposition.
In some embodiments, the catalytic metal cathode coating is a metal alloy (i.e. a catalytic metal alloy cathode coating). The term "coating," when used in reference to a cathode coating, refers to at least a partial covering of the cathode. Therefore, a cathode coating may cover a portion or all of the cathode in order to decrease hydrogen overvoltage.
[0024] A catalytic metal includes metal alloys, such as iron-molybdenum alloys and derivatives thereof. Other catalytic metals include platinum, iron-oxide, iron-tungsten alloys, combinations, and derivatives thereof.

[0025] In some embodiments, the catalytic metal cathode electrodepositing solution is an iron-molybdenum cathode electrodepositing solution. Iron-molybdenum cathode electrodepositing solutions include a molybdenum component (molybdenum in a form capable of being electroplated onto a cathode, e.g. Na2MoO4) and an iron component (iron in a form capable of being electroplated onto a cathode, e.g. FeC13 or FeSO4).
Thus, iron-molybdenum cathode electrodepositing solutions include iron-molybdate cathode electrodepositing solutions. The electrodepositing solution may further comprise an iron chelating agent (e.g. Na4P2O7 or C6H5Na3O7). The electrodepositing solution may further comprise a buffering agent, such as bicarbonate (e.g. NaHCO3).

[0026] Useful iron-molybdenum cathode coatings include those having from 5-95%
molybdenum by weight. In some embodiments, the iron-molybdenum cathode coating contains from 5-50% molybdenum by weight. In other embodiments, the iron-molybdenum cathode coating contains from 10-50% molybdenum by weight. In other embodiments, the iron-molybdenum cathode coating contains from 15-55% molybdenum by weight. In another embodiment, the iron-molybdenum cathode coating contains from 8-56%
molybdenum by weight. In another embodiment, the iron-molybdenum cathode coating contains from 8-49% molybdenum by weight. In another einbodiment, the iron-molybdenum cathode coating contains from 10-40% molybdenum by weight. In another embodiment, the iron-molybdenum cathode coating contains from 25-35%
molybdenum by weight. In another embodiment, the iron-molybdenum catllode coating contains from 25-30% molybdenum by weight. In some embodiments, the iron-molybdenum cathode coating comprises 10-20% molybdenum by weight. In some embodiments, the iron-molybdenum cathode coating coinprises 15-18% molybdenum by weight.

[0027] Useful iron-molybdenum cathode electrodepositing solutions include those having from 5-95% molybdenum by weight. In some embodiments, the iron-molybdenum cathode electrodepositing solution includes molybdenum in a concentration from 0.2 g/L
to 25 g/L.
In other embodiments, the iron-molybdenum cathode electrodepositing solution includes molybdenum in a concentration from 0.3 g/L to 20 g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes molybdenum in a concentration from 0.4 g/L to 16g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes molybdenum in a concentration from 0.476 g/L to 15.86 g/L.

[0028] In some embodiments, the iron-molybdenum cathode electrodepositing solution includes iron in a concentration from 0.5 g/L to 50 g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes iron in a concentration from 0.7 g/L to 40 g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes iron in a concentration from 0.5 g/L to 5 g/L when used with a pyrophosphate chelating agent. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes iron in a concentration from 0.9 g/L to 3.5 g/L when used witll a pyrophosphate chelating agent. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes iron in a concentration from 0.93 g/L to 3.1 g/L
when used with a pyrophosphate chelating agent. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes iron in a concentration fiom 35 g/L to 45 g/L when used with a citrate chelating agent. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes iron in a concentration of from 39g/L to 40 g/L when used with a citrate chelating agent. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes iron in a concentration of about 39 g/L when used with a citrate chelating agent.

[0029] In some embodiments, the iron-molybdenum cathode electrodepositing solution includes a sodium molybdate dehydrate molybdenum component in a concentration from 0.5 g/L to 60 g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a sodium molybdate dehydrate molybdenum component in a concentration from 1.0 g/L to 45 g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a sodium molybdate dehydrate molybdenum component in a concentration from 1.2 g/L to 40 g/L.

[0030] In some embodiments, the iron-molybdenum cathode electrodepositing solution includes a ferric chloride hexahydrate iron component in a concentration from 3.5 g/L to 35g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a ferric chloride hexahydrate iron component in a concentration from 4.0 g/L to 30g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a ferric chloride hexahydrate iron component in a concentration from 4.5 g/L to 27g/L. In some related embodiments, the ferric chloride hexahydrate iron component is used with a pyrophosphate chelating agent.

[0031] In some embodiments, the iron-molybdenum cathode electrodepositing solution includes a ferrous sulphate heptahydrate iron component in a concentration from 180 g/L to 220g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a ferrous sulphate heptahydrate iron component in a concentration from 190 gIL to 200g/L. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a ferrous sulphate heptahydrate iron component in a concentration of about 195 g/L. In some related embodiments, the ferrous sulphate heptahydrate iron component is used with a citrate chelating agent.

[0032] The catalytic metal cathode coating preferably does not interfere with the chlorate producing chemistry. Essential intermediates, such as hypochlorite, are preferably not degraded by the catalytic metal cathode coating or the products of catalytic metal cathode coating degradation (e.g. nickel, copper, and/or cobalt metal ions) during normal operation of the cell. Thus, in some embodiments, power failures (depolarizations, including random power failures) during use of the electrolytic cell will not cause contamination of the chlorate liquor with ions known to catalyze hypochlorite degradation, such as nickel, cobalt, and/or copper. In some embodiments, the catalytic metal cathode coating is capable of resisting single or multiple power failures.

[0033] In some embodiments, the coating and/or electrodepositing solution does not contain significant amounts of nickel, cobalt, and/or copper. In other embodiments, the coating and/or electrodepositing solution does not contain nickel, cobalt, and/or copper. A
significant amount of nickel, cobalt, and/or copper is an amount of nickel, cobalt, and/or copper that, when incorporated into the catalytic metal cathode coating of the present invention, releases into the chlorate liquor during operation of the cell in amounts that degrade hypochlorite to an extent that renders the cell economically inefficient and/or inoperational for large scale commercial purposes in undivided cells.

[0034] Where the catalytic metal cathode electrodepositing solution is an iron-molybdenum cathode electrodepositing solution, the solution may include an iron chelating agent. A number of appropriate iron chelating agents are useful in the electrodepositing solution of the present invention, including pyrophosphate and citrate (e.g.
Na4P2O7 or C6H5Na3O7 and hydrates thereof).

[0035] The catalytic metal cathode electrodepositing solution may also include a buffering agent, such as bicarbonate (e.g. NaHCO3). Buffering agents useful in the present invention include those that are capable of maintaining the pH below 10. In some embodiments, the electrodepositing solution is maintained at a pH below 9. In some embodiments, the electrodepositing solution is maintained at a pH below 8. In some embodiments, the electrodepositing solution is maintained at a pH below 7. In some embodiments, the electrodepositing solution is maintained at a pH below 6.5.
In some embodiments, the electrodepositing solution is maintained at a pH from 5-10.
In some embodiments, the electrodepositing solution is maintained at a pH from 6-10.
In some embodiments, the electrodepositing solution is maintained at a pH from 6-9. In some embodiments, the electrodepositing solution is maintained at a pH from 6-8.

[0036] In otller embodiments, the electrodepositing solution is a non-tartrate ion solution.
[0037] In some embodiments, the undivided electrolytic chlorate cells having cathodes coated with catalytic metal cathode coating provides substantial energy savings during operation of the cell relative to cells having uncoated cathodes (e.g. under the conditions of Example 5 below). In some embodiments, the voltage saving is greater than or equal to 350 millivolts. In another embodiment, the voltage saving is greater than or equal to 200 millivolts. In another embodiment, the voltage saving is greater than or equal to 100 millivolts. In another einbodiment, the voltage saving is from 350 millivolts to 400 millivolts. In another embodiment, the voltage saving is from 300 millivolts to 400 millivolts. In another embodiment, the voltage saving is from 200 millivolts to 400 millivolts. In another embodiment, the voltage saving is from 100 millivolts to 400 millivolts.

[0038] In some embodiments, the iron-molybdenum cathode electrodepositing solution includes a molar ratio of iron chelator to iron of from about 1:1 to about 8:1. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a molar ratio of iron chelator to iron of from about 2.5:1 to about 3.5:1. In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a molar ratio of iron chelator to iron of about 3:1. In some embodiments, the iron chelator is sodium pyrophosphate (including hydrates thereof). In some embodiments, the iron is present as ferric chloride (including hydrates thereof). In other embodiments, the iron-molybdenum cathode electrodepositing solution includes a molar ratio of iron chelator to iron of about 1:1. In some embodiments, the iron chelator is sodium citrate (including hydrates thereof). In some embodiments, the iron is present as ferrous sulphate (including hydrates thereof). In some embodiments the iron chelator as pyrophosphate is present in a mole ratio to iron of 3:1. In some embodiments the iron chelator as citrate is present in a mole ratio to iron of 1:1.

Methods of Coating Cathodes In-Situ [0039] In another aspect, the present invention provides a method of coating a cathode.
The cathode forms a portion of an undivided electrolytic chlorate cell. The method includes contacting the cathode with a catalytic metal cathode electrodepositing solution, and electrodepositing a catalytic metal (e.g. iron-molybdenuin) from the catalytic metal cathode electrodepositing solution onto the cathode thereby forming a catalytic metal cathode coating on the cathode. Thus, the electrodeposition is performed in-situ in the presence of the anode (i.e. the anode is in fluid communication with the electrodepositing solution).
[0040] Where a catalytic metal is electrodeposited from the catalytic metal cathode electrodepositing solution, one skilled in the art will immediately understand that not all of the components of the catalytic metal cathode electrodepositing solution is necessarily electrodeposited (e.g. the buffering agent and/or the chelating agent). The process of electrodepositing catalytic metals onto a substrate from an electrodepositing solution is well known in the art. Using the teachings disclosed herein, it within the abilities of one of skill in the art to determine the appropriate electrodepositing conditions.

[0041] Thus, in one aspect, the present invention provides an undivided electrolytic chlorate cell with an anode and a cathode. The cathode is in fluid communication with a catalytic metal cathode electrodepositing solution. Typically, the anode is also in fluid communication with the catalytic metal cathode electrodepositing solution.

[0042] The metllod may further include, prior to the step of contacting the cathode with a catalytic metal cathode electrodepositing solution, the step of washing the cathode with an acidic solution. The washing may further include washing the anode with the acidic solution. In some einbodiments, after step washing the cathode with an acidic solution and before contacting the cathode with a catalytic metal catliode electrodepositing solution, the method includes the step of washing the cathode with water. In some embodiments, the method includes the step of washing the cathode and anode with water.

[0043] The properties of catalytic metal cathode electrodepositing solutions and catalytic metal cathode coatings are discussed in detail above and are equally applicable to the methods of the present invention. Thus, in some embodiments, the catalytic metal cathode electrodepositing solution is an iron-molybdenum cathode electrodepositing solution, as described above. Therefore, the catalytic metal cathode coating may an iron-molybdenum cathode coating and the catalytic metal may be iron-molybdenum. In some embodiments, the catalytic metal cathode coating is capable of resisting single or multiple power failures.
In some embodiments, the catalytic metal cathode coating provides a voltage saving of at least 200 millivolts as describes above.

[0044] The properties of suitable anodes and cathodes are also described above and are equally applicable to the methods of the present invention. For exainple, in some embodiments, the anode is a dimensionally stable anode (e.g. comprising a ruthenium dioxide coating). In some einbodiments, the cathode comprises steel or titanium.

[0045] In some embodiments, the electrolytic chlorate cell forms part of a multiple electrolytic cell.

[0046] Contacting the cathode with a catalytic metal cathode electrodepositing solution may be accomplished by any appropriate means. Typically, the catalytic metal cathode electrodepositing solution is allowed to flow into the undivided electrolytic chlorate cell at an appropriate flow rate thereby contacting the cathode. The appropriate flow rate is selected to allow electrodeposition of one or inore catalytic metals from the solution to the cathode while replenishing reagents consumed in the electrodepositing process.

[0047] Electrodeposition may be performed at any appropriate temperature of the catalytic metal cathode electrodepositing solution. Where it is desired to decrease electrodeposition time and/or increase current efficiencies, the temperature of the catalytic metal cathode electrodepositing solution may be increased above ambient temperature (i.e.
room temperature). In some embodiments, the temperature of the catalytic metal cathode electrodepositing solution is from 40 C to 100 C during electrodeposition. In other embodiments, the temperature of the catalytic metal cathode electrodepositing solution is from 50 C to 80 C. In other embodiments, the teinperature of the catalytic metal cathode electrodepositing solution is from 50 C to 70 C. In other embodiments, the temperature of the catalytic metal cathode electrodepositing solution is about 70 C. In some embodiments, the electrodepositing solution is electrodeposited from 40 to 100 minutes. In other embodiments, the electrodepositing solution is electrodeposited from 50 to 90 minutes. In other embodiments, the electrodepositing solution is electrodeposited for about 75 minutes.
In other embodiments, the electrodeposition current efficiency (i.e. the portion of current used to electrodeposit the electrodepositing solution relative to the total amount of current applied) is from about 40% to about 80%. In other embodiments, the electrodeposition current efficiency is from about 55% to about 65%.

[0048] The tenns and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed. Moreover, any one or more features of any embodiment of the invention may be combined with any one or more other features of any other embodiment of the invention, without departing from the scope of the invention. For example, any feature of the methods of coating cathodes described above can be incorporated into any of the asseinblies, apparatuses or systems without departing from the scope of the invention.
EXAMPLES
[0049] The following examples are provided for the purpose of describing and illustrating a few exemplary embodiments of the invention only. Other einbodiments of the invention are possible, but are not described in detail here. Thus, these examples are not intended to limit the scope of the invention in any way.

Example 1 [0050] Iron-molybdenum was electrodeposited in-situ to chlorate cell cathodes (20 cmZ) using a 333 ml plating solution at a flow rate of 1.7 L/min, and 0.43 m/s bulk electrolyte flow and bulk electrolyte velocity, respectively.

[0051] The plating conditions are shown below in Table 1. Although not shown in Table 1, NaHCO3 was included in the plating solution at a concentration of 75 g/L.

Table 1 Na2MoO4 Na4P2O7 2H20 FeCI3 6H20 10H20 P207:Fe Temp. CD Plating l*t pH pH
Mole Ratio Time Final /L (M) (g/L) M /L (M) M/M C A/dma min C=A*s 0.00 1.2 5 4.5 0.017 22.5 0.05 3.0 25 3.5 86 3600 7.6 8.4 Abbreviations: M = molar, A =amperes, C = coulombs, dm2 = decimeter squared, min. _ minutes, C = degrees Celsius, EDX = energy dispersed X-ray analysis, wt. =
weight, C.C.E. = cathodic current efficiency, dep. = deposition, XRF = X-ray fluorescence, ID =
identification, I = current in amperes, t=time in seconds, s= seconds, L=litres, g =grams, S2mz = micro-ohms meters squared, mg = milligrams, ml = millilitres.

[0052] Characterization data for the plated cathodes are shown in Table 2 below.
Table 2 % EDX
Blade Dep. XRF Mo C.C.E. Analysis Cross Section EDX wt.
Weight Mo/mg % wt. % %
ID (mg) dep. Mo Fe Mo Fe 49 139 0.24 23.3 20.8 22.6 77.4 27.5 72.5 [0053] Chlorate cells containing iron-molybdenum plated cathodes as described above were tested for their ability to produce chlorate. The results are shown in Table 3 below and in graph form in FIG. 5. K factor is determined by the linear slope of cell voltage (Voltage) versus current density between the current densities of 2000 to 4000 Amperes/meter2.
EC 120 refers to an anode model of particular supplier of anodes. Stahrmet Steel refers to a cathode model of particular supplier of cathodes. The cathode was coated in-situ at day 16.
Notice the voltage difference between day 15 and days 17 to 101 of >_ 277 millivolts.

Table 3 Days NaCI NaCIO3 Voltage % O2 k factor Mo Ca /L /L (V) SZmZ m /L m /L
1 111 490 3.364 2.3 188 2 97 3.358 2.25 187 3 97 501 3.339 2.115 186 6 99 3.327 1.95 185 7 101 3.318 1.91 187 8 103 3.308 1.905 186 9 108 3.31 1.91 185 10 109 467 3.305 1.89 185 13 111 462 3.307 1.91 182 14 112 3.303 1.9 182 15 111 469 3.313 1.835 183 17 105 2.87 1.865 187 0.69 0.11 116 449 2.919 1.865 195 0.23 0.1 22 105 2.93 1.795 193 23 108 2.931 1.875 196 24 108 465 2.93 1.88 197 Days NaCI NaC103 Voltage % O2 k factor Mo Ca /L /L (V) nma m /L m /L
28 98 467 2.941 1.87 198 0.09 0.15 29 110 2.935 1.925 198 30 111 458 2.935 1.895 197 31 114 2.925 1.83 195 34 107 463 2.937 1.895 199 35 106 2.936 1.87 200 36 105 472 2.93 1.905 198 37 104 2.94 1.87 200 38 115 460 2.927 1.88 198 0.19 0.23 41 101 2.948 1.865 203 42 113 2.931 1.855 199 43 116 447 2.933 1.84 198 44 104 2.946 1.835 199 45 102 467 2.947 1.875 202 48 98 472 2.956 1.81 200 49 106 2.949 1.85 202 50 111 456 2.953 1.83 204 0.67 0.48 51 107 2.95 1.85 203 52 110 2.936 1.815 198 55 112 449 2.967 1.835 56 109 2.973 1.87 206 57 106 472 2.973 1.82 58 102 2.985 1.865 2.27 0.49 59 101 2.985 62 102 485 3.014 1.82 2.5 63 102 3.026 1.88 69 104 465 3.038 1.87 70 101 3.034 1.89 208 0.9 71 105 3.038 76 99 3.032 1.88 77 107 3.032 78 111 3.034 1.89 205 79 112 3.029 1.91 80 110 3.035 1.92 202 0.38 83 103 479 3.038 84 106 3.034 1.94 205 85 104 472 3.034 1.87 86 104 3.032 1.94 202 87 109 3.022 1.95 0.25 90 110 469 3.026 1.95 91 110 3.029 1.95 199 92 111 3.029 1.93 93 113 3.034 1.94 200 94 106 458 3.033 1.91 97 96 465 3.038 1.94 98 105 3.034 1.92 200 99 105 3.042 1.97 100 102 3.039 1.96 201 101 106 3.036 1.96 Example 2 [0054] Cathode "AW26-IS 1" (Example 2A) was plated using a new steel substrate and cathode "AW26-IS3" (Example 2B) was plated using a previously used steel substrate.
AW2 6-IS 1 and AW26-IS3 were in-situ plated using identical plating solutions without opening the cells. The in-situ coatings were analyzed via the plating solution before and after plating by ICP analysis for the estimation of the deposited Fe-Mo amount and current efficiency for electrodeposition. The plating solution (1.43 litres) contained 1.8 g/L
Na2MoO4.2H20 (sodium molybdate dihydrate), 9 g/L FeC13.6HZ0 (ferric chloride hexahydrate), 45 g/L Na4P2O7 10H20 (sodium pyrophosphate decahydrate), 75 g/L
NaHCO3 (sodium bicarbonate).

Example 2A
[0055] Cathode AW26-IS 1 was prepared as follows: A new steel cathode substrate was immersed in 8 weight % hydrochloric acid that had been heated to 40 C and allowed to naturally cool for 1 hour to remove mill scale and rust. Residual acid on the cathode substrate was then removed by rinsing the cathode under flowing tap water for 20 seconds followed by deionised water rinsing from a wash bottle. The cathode was then dried with compressed air. A test cell was assembled with the acid cleaned new cathode and a new EC120 anode. The test cell was used for chlorate electrolysis for 1 week using the following conditions: Electrode gap 2.5 mm; Temperature 80 C; Electrolyte bulk pH 6.0-6.1; NaCI concentration 100 grams/litre; Sodium dichromate concentration 4 grams/litre;
Sodium sulphate concentration 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L
magnesium ions added to the NaCI input; Anode and cathode areas were 100 cm2 (height 32.5 cm);
Electrolyte flow rate through the test cell: 0.51itres/ampere-hour; Electrode current density 3000 amperes/metre2. After 1 week of chlorate electrolysis the test cell was drained while maintaining a polarization potential on the cell until the cell was completely drained to prevent cathode corrosion.

[0056] The cell was rinsed by pumping through approximately 1 litre of deionised water.
The cell was acid cleaned by filling the cell with 8 weight% hydrochloric acid preheated to C and allowing the acid to soak for 1 hour without disassembly of the cell.
The spent acid was drained and the acid cleaned cell was rinsed by pumping through approximately 1 litre of deionised water without disassembly of the cell. The plating solution described above was pumped through the cell via recycle, from a 1.43 litre tank solution, at a bulk electrolyte velocity of 0.1 metres/second. Electrodeposition was carried out at 70 C for 75 minutes (9000 coulombs) at a current density of 2.0 amperes/decimetre2. ICP
analysis indicated that 1.08 g of coating was deposited at 61.5% current efficiency with 18 weight %
molybdenum and 82% iron in the coating.

[0057] The electroplated cell was rinsed of spent plating solution by pumping through 1 litre of deionised water. The electroplated test cell was used for chlorate electrolysis using the following conditions: Electrode gap 2.5 mm; Temperature: 80 C; Electrolyte bulk pH:
6.0-6.1; NaCI concentration 100 grams/litre; Sodium dichromate concentration 4 grams/litre; Sodium sulphate concentration 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L
magnesium ions added to the NaCI input; Electrolyte flow rate through the test cell 0.5 litres/ampere-hour; Electrode current density 3000 amperes/metre2.

[0058] Cell voltage and oxygen evolution (an indirect method of measuring chlorate production efficiency) was recorded after allowing one day for stabilization.
Starting on the 3rd day with coated cathode, 6 minute long cell depolarizations (power-interruptions) were carried out daily to determine the robustness of cathode deposits under unforeseen power failures during chlorate electrolysis. On day 27 a 2.5 hour rather than 6 minute power stoppage occurred.

[0059] The following Table 4 indicates that in-situ plating of Fe-Mo alloy on the test cell cathode substrate resulted in a cell voltage saving of 330 millivolts even after 13 cumulative power outages including a very long power outage with no sacrifice in chlorate production efficiency as measured by % oxygen in the electrolysis cell exhaust.

Table 4 % Oxygen in Electrolysis Cell Days Cumulative Number Voltage Exhaust Notes of Power Outages 1 3.205 1.72 2 3.232 1.685 3 3.267 1.73 6 3.288 1.77 7 3.281 1.76 8 2.845 1.575 Plated 9 2.894 1.59 10 1 2.914 1.62 1 st power off 13 2 2.907 1.645 % Oxygen in Electrolysis Cell Days Cumulative Number Voltage Exhaust Notes of Power Outages 14 3 2.917 1.67 15 4 2.92 1.66 17 5 2.943 1.7 20 6 2.944 1.775 21 7 2.952 1.72 22 8 2.94 1.73 23 9 2.941 1.73 24 10 2.951 1.715 27 11 2.967 1.81 2 1/2 hour power off 28 12 2.963 1.74 29 13 2.958 1.72 Example 2B
[0060] Cathode AW26-IS3 was prepared as follows. A used steel cathode that was substantially used for prior chlorate production was immersed in 8 weight %
hydrochloric acid that had been heated to 40 C and allowed to naturally cool for 1 hour.
Residual acid on the cathode substrate was then removed by rinsing the cathode under flowing tap water for 20 seconds followed by deionised water rinsing from a wash bottle. The cathode was then dried with compressed air. A test cell was asseinbled with the acid cleaned new cathode and a new ruthenium dioxide containing DSA. The test cell was used for chlorate electrolysis for 1 week using the following conditions: Electrode gap 2.5 inm;
Temperature 80 C; Electrolyte bulk pH 6.0-6.1; NaCI concentration 100 grams/litre; Sodium dichromate concentration 4 grams/litre; Sodium sulphate concentration 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L magnesium ions added to the NaCI input; Anode and cathode areas were 100 cm2 (height 32.5 cm); Electrolyte flow rate through the test cell:
0.51itres/ainpere-hour; Electrode current density 3000 amperes/metre2.

[0061] After 1 week of chlorate electrolysis the test cell was drained while maintaining a polarization potential on the cell until the cell was completely drained to prevent cathode corrosion. The cell was rinsed by pumping through approximately 1 litre of deionised water. The cell was acid cleaned by filling the cell with 8 weight%
hydrochloric acid preheated to 40 C and allowing the acid to soak for 1 hour without disassembly of the cell.
The spent acid was drained and the acid cleaned cell was rinsed by pumping through approximately 1 litre of deionised water without disassembly of the cell. The plating solution described previously was pumped through the cell via recycle, from a 1.43 litre tank solution, at a bulk electrolyte velocity of 0.1 metres/second.
Electrodeposition was carried out at 70 C for 75 minutes (9000 coulombs) at a current density of 2.0 amperes/decimetre2. ICP analysis indicated that 0.99 g of coating was deposited at 59.1%
current efficiency with 21 weight % molybdenum and 79% iron in the coating.
The electroplated cell was rinsed of spent plating solution by pumping through 1 litre of deionised water.

[0062] The electroplated test cell was used for chlorate electrolysis using the following conditions: Electrode gap 2.5 mm; Temperature 80 C; Electrolyte bulk pH 6.0-6.1; NaC1 concentration 100 grams/litre; Sodium dichromate concentration 4 grams/litre;
Sodium sulphate concentration 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L
magnesium ions added to the NaC1 input; Electrolyte flow rate through the test ce110.5 litres/ampere-hour;
Electrode current density 3000 amperes/metreZ. The first cell voltage was recorded after allowing one day for stabilization.

[0063] Starting the 4th day with the coated cathode, 6 minute long cell depolarizations (power-interruptions) were carried out daily to determine the robustness of cathode deposits under unforeseen power failures during chlorate electrolysis.

[0064] The following Table 5 indicates that in-situ plating of Fe-Mo alloy on the test cell cathode substrate resulted in a cell voltage saving of 362 millivolts even after 18 cumulative power outages with no sacrifice in chlorate production efficiency as measured by % oxygen in the electrolysis cell exhaust.

Table 5 % Oxygen in Electrolysis Cell Days Cumulative Number Voltage Exhaust Notes of Power Outages 1 3.381 2.29 2 3.375 2.06 5 3.35 1.975 6 3.347 2 7 3.357 1.99 8 3.345 1.97 Plated 9 2.955 1.66 12 1 2.955 1.815 1 st power off 13 2 2.988 1.88 14 3 2.978 1.85 15 4 2.979 1.84 16 5 2.974 1.83 19 6 2.972 1.78 % Oxygen in Electrolysis Cell Days Cumulative Number Voltage Exhaust Notes of Power Outages 20 7 2.973 1.80 21 8 2.972 1.78 22 9 2.976 1.83 23 10 2.974 1.87 26 11 2.973 1.84 27 12 2.976 1.82 28 13 2.985 1.83 29 14 2.975 1.82 30 15 2.981 1.83 35 16 2.995 1.84 36 17 2.995 1.85 37 18 2.995 1.88 Example 3 [0065] In order to show that electroplating on a Fe-Mo previously coated substrate is possible, Cathode "AW26-IS5" was prepared by in-situ acid stripping of Cathode "AW26-IS2", followed by in-situ plating (i.e. acid stripping and plating conducted without disassembling the cell). Cathode "AW26-IS2" was previously plated in an identical manner to Cathode "AW26-IS 1" (Example 2A) and had been used continuously for 164 days in sodium chlorate production while being exposed to 114 controlled power outages lasting 6 minutes each (with no more than one power outage conducted per day).

[0066] The plating solution (1.43 litres) used to prepare Cathode "AW26-IS5"
contained 1.8 g/L NaZMoO4.2H20 (sodium molybdate dihydrate), 9 g/L FeC13.6H20 (ferric chloride hexahydrate), 45 g/L Na4P2O7.10H20 (sodium pyrophosphate decahydrate), 75 g/L
NaHCO3 (sodium bicarbonate). The in-situ coating was analyzed via the plating solution before and after plating by ICP analysis for the estimation of the deposited Fe-Mo amount and current efficiency for electrodeposition.

[0067] Cathode "AW26-IS5" was prepared as follows. A test cell was assembled with Cathode "AW26-IS2" previously used for 164 days in sodium chlorate production and a new ruthenium dioxide containing DSA. The test cell was used for chlorate electrolysis for 3 days using the following conditions: Electrode gap 2.5 mm; Temperature 80 C;
Electrolyte bulk pH 6.0-6.1; NaCl concentration 100 grams/litre; Sodium dichromate concentration 4 grams/litre; Sodium sulphate concentration 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L magnesium ions added to the NaCl input; Anode and cathode areas were 100 cm2 (height 32.5 cm); Electrolyte flow rate through the test cell 0.5 litres/ampere-hour; Electrode current density 3000 amperes/metre2.

[0068] After 3 days of chlorate electrolysis the test cell was drained without disassembly of the cell. The cell was rinsed by pumping through approximately 0.5 litre of deionised water without disassembly of the cell. The cell was acid cleaned to strip the previous coating by filling the cell with 8 weight percent hydrochloric acid preheated to 40 C and allowing the acid to soak for 1 hour without disassembly of the cell. The spent acid was drained and the cell was re-filled with as second batch of fresh 8 weight percent hydrochloric acid pre-heated to 40 C and soaked for 2 hours without disassembly of the cell.

[0069] The spent acid was drained and the cell was re-filled with a third batch of fresh 8 weight percent hydrochloric acid pre-heated to 40 C and soaked for 2 hours without disassembly of the cell. The test cell was drained of spent acid and rinsed by pumping through 0.5 litre of deionised water without disasseinbly of the cell. The plating solution described above was pumped through the cell via recycle, from a 1.43 litre tank solution, at a bulk electrolyte velocity of 0.1 metres/second. Electrodeposition was carried out at 70 C
for 75 minutes (9000 couloinbs) at a current density of 2.0 amperes/decimetre2 without disassembly of the cell. ICP analysis indicated that 1.06 g of coating was deposited at 62.7 % current efficiency with 17.4 weight % molybdenum and 82.6 % iron in the coating.

[0070] The electroplated cell was rinsed of spent plating solution by pumping through 0.5 litre of deionised water without disassembly of the cell. The electroplated test cell was used for chlorate electrolysis using the following conditions: Electrode gap 2.5 mm; Temperature 80 C; Electrolyte bulk pH 6.0-6.1; NaCI concentration 100 grams/litre; Sodium dichromate concentration 4 grams/litre; Sodium sulphate concentration 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L magnesium ions added to the NaCI input; Electrolyte flow rate through the test cell 0.5 litres/ampere-hour; Electrode current density 3000 amperes/metre2.
[0071] Cell voltage and oxygen evolution (an indirect method of measuring chlorate production efficiency) was recorded after allowing one day for stabilization.
Starting on the 3rd day with coated cathode, 6 minute long cell depolarizations (power-interruptions) were carried out daily to determine the robustness of cathode deposits under unforeseen power failures during chlorate electrolysis.

[00721 The following Table 6 indicates that in-situ recoated Fe-Mo alloy, plated after acid stripping the previous Fe-Mo coated cathode used in chlorate production, resulted in a cell voltage saving of 319 millivolts after 6 cumulative power outages with no sacrifice in chlorate production efficiency as measured by % oxygen in the electrolysis cell exhaust.

Table 6 Oxygen in Cumulative Number Electrolysis Cell Days of Power Outages Voltage Exhaust Notes (%) 0 3.308 1.815 Operation with Uncoated Cathode 1 2.899 1.475 1st day with AW26-IS2 4 1 2.951 1.73 J, 1 1 Continuous operation 164 114 2.992 1.735 Shut Down 1 3.024 1.71 Restarted with Used AW26-2 3.038 1.74 3 3.032 Acid Stripped and Plated as 4 2.938 1.72 5 2.982 1.63 6 1 2.980 1.635 1st power outage 9 2 2.982 1.635 3 2.982 1.64 11 4 2.980 1.67 12 5 2.985 1.635 13 6 2.989 1.66 17 7 2.989 1.68 Example 4 [0073] Another example of plating on a previously Fe-Mo coated substrate was conducted using a plating formulation that produced a higher molybdenum containing coating.
10 Cathode "AW24-IS2" was prepared by in-situ acid stripping Cathode "Pilot #3", followed by in-situ plating (i.e. acid stripping and plating conducted without opening the cell).
Cathode "Pilot #3" was previously plated in a pilot scale operation consisting of a 15 metre2 commercial cell with a plating solution consisting of 65.082 Kg of NaZPzO7 (sodium pyrophosphate anhydrous), 12.96 Kg FeC13 (ferric chloride anhydrous), 4.32 Kg NaMoO4.2HZ0 (sodium molybdate dihydrate), 179.7 Kg NaHCO3 (sodium bicarbonate) in 2470L of deionised water. Plating of "Pilot #3" was conducted at 3300 amperes, solution flow rate of 216 gallon per minute, approximately 70 to 75 C for 90 minutes.
Hydrogen gas produced during the plating process was diluted with air to ensure safe operation of the process. ICP analysis indicated that a coating of 1605 g of coating was deposited at 47.9%
current efficiency with 17 weight % molybdenum and 83 weight % iron in the coating.
[0074] Catllode "Pilot #3" was obtained by opening the 15 m'' cell and cutting a 100 cm' (height 32.5 cm) cathode sample for operation in a sodium chlorate producing test cell.
"Pilot #3" was placed into a sodium chlorate producing test cell that was previously operated with an uncoated mild steel cathode. "Pilot #3" was operated continuously in sodium chlorate production for 115 days and exposed 41 power outages of 6 minute duration (with no more than one power outage per day). At the conclusion of chlorate operation with "Pilot #3", the coating was in-situ acid stripped and then in-situ plated as "AW24-IS2" (acid stripping and plating without disassembly of the cell). "AW24-IS2" was plated using 1.43 litres of plating solution having 40 g/L NaZMoO~.2H20 (sodium molybdate dihydrate), 9 g/L FeC13.6H20 (ferric chloride hexahydrate), 45 g/L
Na4P2O7.10H20 (sodium pyrophosphate decahydrate), 75 g/L NaHCO3 (sodium bicarbonate). Estimation of the deposited Fe-Mo amount and current efficiency were conducted by preparing a duplicate cathode in a separate plating cell, determining molybdenum and iron content by x-ray fluorescence (XRF) and current efficiency by weight gain.

[0075] Cathode "AW24-IS2" was prepared as follows. A sodiuin chlorate producing test cell was assembled with an uncoated mild steel cathode and new ruthenium dioxide containing DSA and operated for 4 days to obtain baseline cell voltage data.
The uncoated mild steel cathode was replaced by Cathode "Pilot #3" prepared by conditions described above and operated in sodium chlorate production for 115 days and exposed 41 power outages of 6 minute duration (with no more than one power outage per day) using the following conditions: Electrode gap 2.7 mm; Temperature 80 C; Electrolyte bulk pH 6.0-6.1; NaCI concentration 100 grams/litre; Sodium dichromate concentration 4 grams/litre;
Sodium sulphate concentration 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L
magnesium ions added to the NaCl input; Anode and cathode areas were 100 cm2 (height 32.5 cm);
Electrolyte flow rate through the test cell 0.51itres/ampere-hour; Electrode current density:
3000 amperes/metre'.

[0076] At the conclusion of sodium chlorate operating with "Pilot #3", the test cell was drained without disassembly of the cell. The cell was rinsed by pumping through approximately 0.5 litre of deionised water without disassembly of the cell.
The cell was acid cleaned to strip the previous coating by filling the cell with 8 weight percent hydrochloric acid preheated to 40 C and soaking the cell for 1 hour without disassembly of the cell. The spent acid was then drained and the cell was re-filled with as second batch of fresh 8 weight percent hydrochloric acid preheated to 40 C and soaked for 2 hours without disassembly of the cell.

[0077] The spent acid was drained and the cell was re-filled with a third batch of fresh 8 weight percent hydrochloric acid pre-heated to 40 C and soaked for 2 hours without disassembly of the cell. The test cell was drained of spent acid and rinsed by pumping through 0.5 litre of deionised water without disassembly of the cell. The plating solution described above for "AW24-IS2" was pumped through the cell via recycle, from a 1.43 litre tank solution, at a bulk electrolyte velocity of 0.1 metres/second.
Electrodeposition was carried out at 70 C for 50 minutes at a current density of 3.5 amperes/decimetre2 without disassembly of the cell. XRF analysis and weight gain of a separate duplicate cathode indicated that approximately 0.92 g of coating was deposited at 49.4 % current efficiency with 49 weight % molybdenum and 51 weight % iron in the coating. The electroplated cell was rinsed of spent plating solution by pumping througli 0.5 litre of deionised water without disassembly of the cell.

[0078] The electroplated test cell was used for chlorate electrolysis using the following conditions: Electrode gap: 2.7 mm; Temperature 80 C; Electrolyte bulk pH 6.0-6.1; NaCI
concentration: 100 grains/litre; Sodium dichromate concentration 4 grams/litre; Sodium sulphate concentration: 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L
magnesium ions added to the NaCI input; Electrolyte flow rate through the test cell 0.5 litres/ampere-hour;
Electrode current density 3000 amperes/metre2.

[0079] Cell voltage and oxygen evolution (an indirect method of measuring chlorate production efficiency) was recorded after allowing one day for stabilization.
Starting on the 4th day with recoated cathode, 6 minute long cell depolarizations (power-interruptions) were carried out daily to determine the robustness of cathode deposits under unforeseen power failures during chlorate electrolysis.

[0080] The following Table 7 indicates that in-situ recoated of Fe-Mo alloy after stripping off of Fe-Mo coating used in the chlorate resulted in a cell voltage savings of 304 millivolts even after 9 cumulative power outages with no sacrifice in chlorate production efficiency as measured by % oxygen in the electrolysis cell exhaust.

Table 7 Oxygen in Cumulative Number Electrolysis Cell Days of Power Outages Voltage Exhaust Notes (%) 4 3.245 1.80 Mild steel cathode 2.811 1.69 Fe-Mo coated Cathode "Pilot #3"
l. 1 1 11 2.906 1 l J. Continuous operation 118 41 2.988 1.760 119 In-situ acid stripped and recoated as AW24-122 2.936 1.695 123 1 2.938 1.705 1st Power Outage 124 2 2.942 1.67 125 3 2.944 1.645 126 4 2.937 1.61 129 5 2.934 1.645 130 6 2.936 1.645 131 7 2.943 1.62 132 8 2.943 1.615 133 9 2.941 1.635 137 10 2.959 1.670 5 Example 5 [0081] Another example of plating on a previously coated substrate was conducted using a plating fonnulation prepared from a citrate based plating bath instead of a pyrophosphate based plating bath to illustrate plating bath flexibility.

[0082] Cathode "Citrate #1" was prepared by in-situ acid stripping Cathode "AW26-IS4", followed by in-situ plating (i.e. acid stripping and plating conducted without disassembly of the cell). Cathode "AW26-IS4" was prepared in an identical manner to Cathode "AW26-IS1" described in Example 1 but was instead operated continuously for 119 days in sodium chlorate production at 4.0 kA/m2 and 85 C and exposed to 83 power outages of 6 minutes (with no more that one power outage conducted per day).

[0083] The plating solution (1.43 litres) used to prepare Cathode "Citrate #1"
contained 2.4 g/L Na2MoO4=2H20 (sodium molybdate dihydrate), 195 g/L FeSO4=7H2O (ferrous sulphate heptahydrate), 206 g/L C6H5Na3O7=2H20 (sodium citrate dihydrate).

(ammonium hydroxide) solution was added to the plating solution until pH 6.1 was reached.

Estimation of the deposited Fe-Mo amount and current efficiency were conducted by preparing a duplicate cathode in a separate plating cell, determining molybdenum and iron content by x-ray fluorescence (XRF) and current efficiency by weight gain.

[0084] Cathode "Citrate #1" was prepared as follows. A test cell was assembled with cathode coated with "AW26-IS4" coating previously used for 119 days in sodium chlorate production and a new Eltech ruthenium dioxide containing DSA. The cell was acid cleaned to strip the previous coating by filling the cell with 8 weight percent hydrochloric acid preheated to 40 C and soaking the cell for 1 hour without disassembly of the cell. The spent acid was then drained and the cell was re-filled with as second batch of fresh 8 weight percent hydrochloric acid preheated to 40oC and soaked for 2 hours without disassembly of the cell. The spent acid was drained and the cell was re-filled with a third batch of fresh 8 weight percent hydrochloric acid pre-heated to 40 C and soaked for 2 hours without disassembly of the cell.

[0085] The test cell was drained of spent acid and rinsed by pumping through 0.5 liter of deionised water without disassembly of the cell. The plating solution described above for Catllode "Citrate #1" was pumped through the cell via recycle, from a 1.43 litre tank solution, at a bulk electrolyte velocity of 0.1 metres/second.
Electrodeposition was carried out at ambient temperature for 60 minutes at a current density of 3.5 amperes/decimetre2 without disassembly of the cell. XRF analysis and weight gain of a separate duplicate cathode indicated that approximately 1.02 g of coating was deposited at 32.1 %
current efficiency with 19.9 weight % molybdenum and 80.1 weight % iron in the coating. The electroplated cell was rinsed of spent plating solution by pumping through 0.5 litre of deionised water without disassembly of the cell.

[0086] The electroplated test cell was used for chlorate electrolysis using the following conditions: Electrode gap 2.7 mm; Temperature 80 C; Electrolyte bulk pH 6.0-6.1; NaCI
concentration 100 grams/litre; Sodium dichromate concentration 4 grams/litre;
Sodium sulphate concentration 14 grams/litre; 2 mg/litre calcium and 0.4 mg/L
magnesium ions added to the NaCI input; Electrolyte flow rate through the test cell 0.5 litres/ampere-hour;
Electrode current density 3000 amperes/metre2.

[0087] Cell voltage and oxygen evolution (an indirect method of measuring chlorate production efficiency) was recorded after allowing one day for stabilization.
Starting on the 3rd day with coated cathode, 6 minute long cell depolarizations (power-interruptions) were carried out daily to determine the robustness of cathode deposits under unforeseen power failures during chlorate electrolysis.

[0088] The following Table 8 indicates that in-situ recoated Fe-Mo alloy, plated with a citrate based plating solution after acid stripping the previous Fe-Mo coated cathode used in chlorate production, resulted in a cell voltage saving of 317 millivolts as compared to a typical cell voltage realized with an uncoated mild steel cathode, which is 3.254 V (average of measured cell voltage with an uncoated mild steel cathode in Table 4).

Table 8 Oxygen in Cumulative Number Electrolysis Cell Days of Power Outages Voltage Exhaust Notes 1 In-situ acid stripped and plated as "Citrate #1"
2 2.892 1.94 3 2.917 1.845 4 1 2.928 1.86 1s' power outage 8 2 2.965 1.87 Example 6 [0089] An example comparing methods of estimating the deposited Fe-Mo amount and current efficiency by ICP analysis of the plating solution before and after plating versus XRF and weight gain measurements of the cathode subsequent to plating was conducted.

[0090] In Example 2A, ICP (inductively coupled plasma) analysis of the plating solution before and after plating indicated that Cathode "AW26-IS 1" contained 1.08 g of coating, deposited at 61.5% current efficiency with 18.4 weight % molybdenum and 81.6 weight %
iron in the coating.

[0091] Cathode "AW26-A2" was prepared in an identical manner to "AW26-IS1".
XRF
(X-ray fluorescence) analysis and weight gain measurement of "AW26-A2"
immediately after plating indicated that "AW26-A2" contained 1.08 g of coating, deposited at 63.9%
current efficiency with 17.8 weight % molybdenum and 82.2 weight % iron in the coating.

Claims (19)

WHAT IS CLAIMED IS:

1. A combination of a catalytic metal cathode electrodepositing solution and an undivided electrolytic chlorate cell for use in methods of coating cathodes in-situ, said undivided electrolytic chlorate cell comprising an anode and a cathode, wherein said cathode is in fluid communication with said catalytic metal cathode electrodepositing solution.

2. The undivided electrolytic chlorate cell of claim 1, wherein said catalytic metal cathode electrodepositing solution is an iron-molybdenum cathode electrodepositing solution.

3. The undivided electrolytic chlorate cell of claim 1, wherein said anode is a dimensionally stable anode.

4. The undivided electrolytic chlorate cell of claim 1, wherein said cathode comprises steel, iron or titanium.

5. The undivided electrolytic chlorate cell of claim 2, wherein said iron-molybdenum cathode electrodepositing solution comprises molybdenum in a concentration from 0.2 g/L to 25g/L.

6. The undivided electrolytic chlorate cell of claim 1, wherein said electrolytic chlorate cell forms part of a multiple electrolytic cell.

7. A method of coating a cathode in-situ, said cathode forming part of an undivided electrolytic chlorate cell, said method comprising:
(a) contacting said cathode with a catalytic metal cathode electrodepositing solution, and (b) electrodepositing a catalytic metal from said catalytic metal cathode electrodepositing solution onto said cathode thereby forming a catalytic metal cathode coating on said cathode.

8. The method of claim 7, wherein said catalytic metal cathode electrodepositing solution is an iron-molybdenum cathode electrodepositing solution, said catalytic metal cathode coating is an iron-molybdenum coating, and said catalytic metal is iron-molybdenum.

9. The method of claim 7, wherein said electrolytic chlorate cell forms part of a multiple electrolytic cell.

10. The method of claim 7, wherein said catalytic metal cathode coating is capable of resisting single or multiple power failures.

11. The method of claim 7, wherein said anode is a dimensionally stable anode comprising ruthenium dioxide.

12. The method of claim 7, wherein said cathode comprises steel, iron or titanium.

13. The method of claim 7, further comprising, prior to step (a):
(al) washing said cathode with an acidic solution.

14. The method of claim 13, wherein said washing further comprises washing said anode with said acidic solution.

15. The method of claim 13, further comprising after step (a1) and before step (a):
(a2) washing said cathode with water.

16. The method of claim 15, wherein said washing said cathode with water further comprises washing said anode with water.

17. An undivided electrolytic chlorate cell comprising a dimensionally stable anode and a cathode, wherein said cathode is coated with a catalytic metal cathode coating.

18. The undivided electrolytic chlorate cell of claim 17, wherein said catalytic metal cathode coating is an iron-molybdenum cathode coating.

19. The undivided electrolytic chlorate cell of claim 17, wherein said dimensionally stable anode comprises ruthenium dioxide.