Electrode for hypochlorite evolution

Abstract

The present invention relates to electrodes for hypochlorite evolution, comprising an electrically conductive substrate and a catalytic coating applied on the substrate, and a multilayer process for manufacturing the same.

Description

Technical Field

[0001] This invention relates to an electrode for hypochlorite precipitation and a method for manufacturing the same. Background Technology

[0002] Electrodes for hypochlorite precipitation, used alone or in combination with other processes (UV, ozone), can be advantageously used in batteries and systems for water treatment applications. In particular, these electrodes can be successfully used in the field of domestic water disinfection, including pools and toilets.

[0003] In the above cases, the water to be treated is typically tap water, which is used as the electrolyte. Tap water is characterized by high resistivity, usually well above 1000 Ω, because the concentration of chloride ions dissolved in it is very low (≤10 ppm). Under these conditions, when the battery's operating current density increases above a certain threshold, the oxygen evolution reaction begins to occur at the anode because the competitive chloride evolution reaction is limited by the mass transfer of chloride ions. Oxygen production ultimately leads to electrode corrosion, thus limiting its efficiency and lifespan.

[0004] In addition, water hardness can cause scale to form on the electrode surface, which adversely affects the battery's hypochlorite production efficiency, thus requiring regular electrode cleaning.

[0005] To circumvent this problem, home disinfection applications typically employ bipolar and symmetrical electrode packs, where identical anode-cathode pairs undergo polarity reversal to achieve an effective "self-cleaning" system.

[0006] However, such operating conditions are very detrimental to the catalytic coating of the electrode (if present) because they accelerate its deactivation and delamination process.

[0007] Coated with a large amount of Group 9 precious metal elements (e.g., more than 10 g / m³) 2 Electrodes of Ir and Rh oxides exhibit good corrosion resistance and demonstrate satisfactory free available chlorine (FAC) efficiency (30%). However, from a commercial and industrial perspective, achieving good results requires a large quantity of rare and particularly expensive materials due to associated procurement issues, price fluctuations, scarcity, and total cost.

[0008] On the other hand, the more affordable Ru-Ti oxide active coating compositions exhibit satisfactory behavior when subjected to polarity reversal operation, but are unstable to oxygen corrosion.

[0009] Therefore, it is desirable to have electrodes for hypochlorite precipitation that can withstand the harsh operating conditions seen in domestic water disinfection applications (or other applications characterized by high electrolyte resistivity) while still maintaining industrial and commercial appeal related to the amount of rare and precious metals used. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of electrodes known in the art for hypochlorite precipitation, especially when subjected to polarity reversal conditions and high-resistivity electrolytes (such as tap water).

[0011] As previously mentioned, electrodes with catalytic coatings containing large amounts and high loadings of rare and precious metals, such as Group 9 precious metals (i.e., iridium and / or rhodium), exhibit good corrosion resistance, while active coating compositions containing ruthenium and titanium oxides exhibit satisfactory behavior under polarity reversal conditions.

[0012] It has been observed that mixing iridium oxide with ruthenium oxide can provide materials with the stability of iridium oxide but at a significantly lower cost. This effect is likely due to a shift in the oxidation potential caused by band mixing, a phenomenon known as iridium-ruthenium partialization.

[0013] However, the inventors observed that, in the case of this invention, combinations of Ru-Ti compositions alone with compositions containing Ir and optionally Rh do not produce satisfactory results because the resulting mixtures do not produce stable or controllable materials. Phase segregation was observed at various Ru:Ir ratios, and the durability of the resulting coatings was unsatisfactory. Therefore, in this case, generating a Ru:Ti matrix (which is frequently used in electrochemistry to obtain materials with iridium oxide stability at a lower cost point) does not guarantee the required robustness.

[0014] Surprisingly, the inventors noted that when the two compositions were applied individually and sequentially in one or more thermally decomposed layers, the resulting electrodes exhibited improved corrosion resistance and enhanced FAC. The catalytically coated electrodes obtained via this technique, as inferred from standard-free semi-quantitative SEM / EDAX analysis with ZAF correction, do not accurately reflect the presence of two distinct alternating compositions used in the manufacturing process. While multiple layers may be visually suggested in some SEM images, the elements of the two different coating compositions ultimately exhibit varying degrees of mixing and diffusion across the active coating thickness. Several factors may contribute to this effect: their differing crystallinity affinities, and / or their molecular weights, as well as the sequence and specific heat treatments performed during preparation. The result is a variable and unpredictable profile of elemental concentrations in the final overall coating, as can be observed by scanning the coating composition from the electrode substrate to the outer surface using semi-quantitative standard-free EDAX SEM measurements.

[0015] It has been observed that the complex and specific compositional profile imparted by the preparation method used clearly contributes to electrode performance. Therefore, it can be concluded that electrode performance in the target application depends not only on the elements present in the active coating, but also on the specific properties transferred to the electrode via the preparation method used, and on the subsequent distribution of elements within the active coating.

[0016] In one aspect, the present invention relates to a method for manufacturing an electrode suitable for the precipitation of hypochlorite in tap water. The method comprises at least two sequential stages (I) and (II).

[0017] The first stage (I) includes performing steps a)-b) as defined below on the valve metal substrate.

[0018] Step a) involves applying a first active coating (referred to as "A") comprising at least one layer of a first composition containing precursors of Ta and Ir having the following elemental weight percentages: 20-70% Ta, 30-80% Ir. Each layer is dried at 45-75°C for 5-15 minutes, followed by baking at 480-530°C for 5-15 minutes. Other precursors may be present in the first composition. For example, precursors of Rh, Pt, Nb, and / or W can be successfully used.

[0019] Step b) involves applying a second active coating (referred to as "B") over coating A. Coating B comprises at least one layer of a second composition comprising precursors of Ru and Ti having the following elemental weight percentages: 20-50% Ru, 50-80% Ti.

[0020] Dry each layer at 45-75°C for 5-15 minutes, then bake at 480-530°C for 5-15 minutes.

[0021] In this first stage (I), steps a) and b) should be performed at least once.

[0022] The second stage (II) involves performing step a) as described above on the electrodes from stage (I), and optionally post-baking at 480-530°C for 1-6 hours.

[0023] Therefore, the electrode is prepared according to the following coating sequence: ABA, or ABABA, or ABABABA, etc. For practical reasons, the total number of coatings A and B can preferably be 3 to 31. This number corresponds to performing steps a)-b) 1 to 15 times in stage (I).

[0024] Semi-quantitative, scale-free EDAX SEM measurements of the resulting electrodes showed that the individual coating compositions A and B used in the manufacturing process could not be clearly identified as separate (multi)layers throughout the final coating, but the elemental distribution also differed from that obtained by simply applying a mixture of the first and second compositions. Furthermore, it has been shown that the order in which the two compositions are applied also has a measurable effect on electrode performance (i.e., the order should preferably begin and end with coating A), as will be illustrated in the examples below.

[0025] The inventors have observed that the electrodes obtained therefrom perform particularly well in the execution of the present invention when steps a)-b) in stage (I) are performed 1-6 times.

[0026] The method according to the invention does not exclude the application of an additional coating composition, such as a barrier coating composition, on the electrode substrate before applying coating A, or the application of a top coating composition after stage (II), or the application of other compositions between different stages and steps.

[0027] During each individual execution of step a) in stages (I) and (II) and step b) in stage (I), the number of layers of the corresponding active coating and the total noble metal loading may be different.

[0028] Preferably, those skilled in the art can customize the number of steps performed, the amount of each layer's pick-up and load, and the number of layers based on common sense, until a total final coating thickness of at least 10 micrometers, or even more preferably 10 to 30 micrometers, is achieved.

[0029] Therefore, electrodes can be fabricated according to the following coating sequence: A n -B m -A q Or A n -B m -A o -B p -….-A q , where n, m, o, p, q represent the number of layers applied to each coating A and B, and these numbers can be different from each other.

[0030] To optimally balance the protective effect of the active coating on the contact substrate against corrosion, while reducing the total amount of precious metals used, it may be advantageous to perform step a) by applying a first active coating in 1 to 4 layers, and step b) by applying a second active coating in 2 to 10 layers.

[0031] According to one embodiment, the number of layers of the second active coating is preferably higher than the number of layers of the first active coating.

[0032] Preferably, the noble metal loading of the second active coating is higher than that of the first active coating; even more preferably, the noble metal loading of the second active coating is 2-10 times higher than that of the first active coating.

[0033] Those skilled in the art will understand that steps a) and b) of stages (I) and (II) can be performed until the desired total precious metal loading is achieved.

[0034] According to another embodiment, the total loading of rare precious metals (i.e., precious metals belonging to Group 9 of the periodic table) in the entire final electrode is preferably equal to 2-6 g / m². 2 .

[0035] In another embodiment, the precursors of Ta and Ir in the first composition can advantageously be selected within the range of 20-45% Ta and 55-80% Ir. In this case, the composition may or may not contain other metal precursors. In the latter case, electrode preparation is simplified. Furthermore, the procurement of materials required for electrode preparation is less affected by uncertainties in terms of price fluctuations and the availability of metal precursors, especially when rare and / or precious metals are involved. The resulting electrode advantageously matches the performance of prior art electrodes with much higher precious metal loadings.

[0036] In another embodiment, the first composition preferably further contains a precursor of Rh, wherein the precursors of Ta, Ir, and Rh have the following elemental weight ratio: 20-45% Ta, 30-70% Ir, and 10-25% Rh. The presence of rhodium further improves the durability of the electrode.

[0037] Advantageously, in this embodiment, the total loading of Ir+Rh in step a) is preferably 1-3 g / m³. 2 Choose from the options.

[0038] According to another embodiment, the total Ir+Rh loading in the entire final electrode can preferably be selected to be equal to 2-6 g / m. 2 .

[0039] Typically, for step b), the total loading of Ru can advantageously be 5-10 g / m³. 2 Choose from the options.

[0040] The electrode substrate can be made of any suitable conductive material, preferably a valve metal such as titanium or its alloy. The substrate can have different geometries, any of those shapes suitable for electrochlorination applications, including mesh, sheet, blade, tube, or wire shapes.

[0041] Regardless of the substrate material and shape, the surface of such substrates can advantageously be a clean surface. This can be achieved by any treatment known in the art. Furthermore, the clean surface can be further treated to enhance the adhesion of the active coating composition. This can be achieved by any commonly used method, including intergranular etching of the substrate metal, sharp blasting of the metal surface, or plasma spraying, followed by surface treatment to remove embedded grit.

[0042] To further improve the durability of the material, it is preferable to sandblast the valve metal substrate and then etch it to obtain better roughness and thus better adhesion.

[0043] According to another embodiment of the method of the present invention, the second active composition further comprises a precursor solution of one or more dopants collectively referred to as "X", wherein X is expressed as 0.5-5% by weight of an element and is selected from the following list: scandium, strontium, hafnium, bismuth, zirconium, aluminum and combinations thereof.

[0044] The resulting X-doped composition can provide an efficiency boost under low salinity conditions where the electrode can typically operate.

[0045] According to another embodiment of the method of the present invention, the second active composition may further comprise a precursor solution of one or more dopants collectively referred to as "Y", wherein Y is 0.2-3.2% by weight of element and is selected from the following list: copper, platinum and combinations thereof.

[0046] The resulting Y-doped compositions have been observed to provide improved stability against polarity reversal.

[0047] The X- and Y-doping of the second active composition are not mutually exclusive: they can be performed together or separately.

[0048] As previously stated, compared to other methods of the present invention using the same materials and amounts of Group 9 rare and precious metals, the multilayer preparation method of the alternating coating composition according to the present invention produces electrodes exhibiting higher corrosion resistance and higher FAC efficiency. This method also provides electrodes with high resistance to polarity reversal, which can be used for self-cleaning of symmetrical electrode packs undergoing current reversal without compromising performance.

[0049] As discussed, electrodes obtained using the method of the present invention achieve measurably improved performance compared to electrodes prepared using the same material applied together from the beginning, rather than as alternating and different layers of different compositions as described above. The unique effects of specific heat treatments applied to the two coating compositions, the order, number, and alternation of the layers, and the inherently different volatility of the elements provide products with unique properties and performance.

[0050] In practice, certain elements of the first and second compositions are distributed fairly uniformly along the entire thickness of the catalytic coating, while most other elements are concentrated / consumed closer to the substrate and / or at the top, but still subject to almost unpredictable fluctuations because they can depend on a variety of parameters, such as, but not limited to, the number of times stage (I) is performed, the number of layers used in each of steps a) and b), and their thickness and / or metal loading. This distribution of elements in the final product does not maintain a direct correlation with the AB-…-A pattern performed during electrode fabrication.

[0051] Therefore, while the distribution of the element throughout the final electrode coating is undoubtedly related to the preparation method (which has a measurable effect on electrode performance), it is impossible to define the distribution of the element throughout the final electrode coating without reference to the method unless the scope of the claims is inappropriately limited.

[0052] Therefore, in a second aspect, the present invention relates to an electrode obtainable according to any embodiment of the method described above. Due to the properties imparted by the method employed, by using a relatively reduced total loading of Group 9 noble metal elements (which are scarce and expensive and subject to severe price fluctuations and availability issues), the electrode exhibits improved or comparable lifetime and improved chlorine release efficiency compared to electrodes known in the art.

[0053] It should be understood that the present invention covers all electrodes having similar characteristics to the electrodes described above, regardless of the preparation method used.

[0054] Although, as explained, the aforementioned electrodes cannot be adequately defined in terms of their structural / material properties alone without excessive limitation, the inventors have surprisingly observed that, as described below, certain particularly advantageous embodiments exhibit common characteristics in terms of elemental distribution in coating thickness.

[0055] In a third aspect, the present invention relates to an electrode with improved lifetime and chlorine removal efficiency, which can be obtained by the method according to the invention and is suitable for water disinfection, particularly tap water. The electrode comprises a valve metal substrate, preferably made of Ti or an alloy thereof, and an active coating applied over said substrate, characterized in that the coating has an average thickness “T” of 10-30 micrometers and comprises metal oxides of Ti, Ta, Ir, Ru, and optionally Rh according to the following relative weight percentages: Ir 4-35%, Ta 1.5-22.5%, Ru 10-45.5%, Ti 25-75%, and optionally Rh 0.5-12.5%. The metals diffuse throughout the thickness T, but their relative weight percentages vary with the coating thickness, such that:

[0056] -Ir, Ta and Rh, if present, exhibit a weight percentage peak centered at 2-25% of the coating thickness T, starting from the substrate, with FWHM at 1-10% of T;

[0057] -Ru exhibits an increase in weight percentage until it reaches 10-40% of the coating thickness T, where it is essentially stable (i.e., it does not exhibit any systematic peaks or drops in weight percentage, despite instrumental errors, and does not fluctuate, averaging more than three times its average value, as measured from the substrate between 25% and 100% of T).

[0058] Weight percentages were measured by averaging standard-free semi-quantitative EDAX-SEM line scans with ZAF correction on the sample, with each line scan performed at at least 100 acquisition points along the thickness T of the catalytic coating. For each point, the sum of the weight percentages of all elements present in the catalytic coating was normalized to 100%. The average value of the sample should be measured by taking into account an appropriate number of line scans measured on different regions of the electrode. As will be understood by those skilled in the art, the appropriate number of line scans depends on the overall size and homogeneity of the sample.

[0059] It should be understood that such line scans inherently exhibit fluctuations due to defects or pores in the catalytic coating, the precision and sensitivity of the instrument, impurities, and so on.

[0060] A peak is a relative or absolute maximum value that can be roughly fitted by a Gaussian or skewed normal distribution, and is characterized by the full width at half maximum (FWHM) as described above.

[0061] The weight percentage calculated corresponding to the peak should be at least three times the average value measured at a distance Z from the peak position in the direction toward the outer surface of the active coating (farthest from the substrate), where Z = 1.75 * FWHM - 2.75 * FWHM.

[0062] It should be noted that, in addition to those captured by the above-described SEM / EDAX measurements, the preparation method according to the present invention can provide other structural / chemical properties.

[0063] In a third aspect, the present invention relates to a bipolar electrolyzer employing the electrodes described in the foregoing aspects and embodiments. Preferably, the bipolar electrolyzer uses an electrolyte composed substantially of tap water. Advantageously, the electrolyzer employs at least one pair of identical electrodes, wherein each electrode is one of the electrodes according to the invention as described above.

[0064] In a fourth aspect, the present invention relates to the use of the bipolar electrolyzer according to the invention for hypochlorite-mediated water disinfection. Attached Figure Description

[0065] In the attached diagram:

[0066] Figure 1 Subfigure a) shows an SEM image of the sample prepared according to the method described in Example 1. Subfigure b) plots a label-free semi-quantitative EDAX-SEM line scan of the same sample along the line indicated in subfigure a).

[0067] Figure 2 Subfigure a) shows an SEM image of the sample prepared according to the method described in Example 2. Subfigure b) plots a label-free semi-quantitative EDAX-SEM line scan of the same sample along the line indicated in subfigure a).

[0068] Figure 3 Subfigure a) shows an SEM image of the sample prepared according to the method described in Comparative Example 1. Subfigure b) plots a label-free semi-quantitative EDAX-SEM line scan of the same sample along the line indicated in subfigure a). Detailed Implementation Plan

[0069] Figure 1 Subfigure a) shows a SEM image of the sample prepared according to the method described in Example 1, i.e., by performing stage (I) once according to the application mode of type "ABA". The coating has an average thickness of 20 micrometers.

[0070] Subplot b) of the same sample plots a standard-free semi-quantitative EDAX-SEM line scan at 100 acquisition points along the line indicated in subplot a). ZAF correction was applied to the EDAX measurements. For each point, the sum of the weight percentages of all elements present in the catalytic coating was normalized to 100%. For clarity, only measurements of Ru, Rh, Ta, and Ir are shown.

[0071] Figure 2 Subfigure a) shows a SEM image of the sample prepared according to the method described in Example 2, i.e., by performing stage (I) three times in an application pattern of the type “ABABABA”. The coating exhibits an average thickness of 20 micrometers.

[0072] Subplot b) of the same sample plots a standard-free semi-quantitative EDAX-SEM line scan at 100 acquisition points along the line indicated in subplot a). ZAF correction was applied to the EDAX measurements. For each point, the sum of the weight percentages of all elements present in the catalytic coating was normalized to 100%. For clarity, only measurements of Ru, Rh, Ta, and Ir are shown.

[0073] Figure 3Subfigure a) shows a SEM image of a sample prepared according to the method described in Comparative Example 1, i.e., by mixing compositions A and B together and applying the solution in layers until a coating with an average thickness of 20 micrometers is obtained.

[0074] Subplot b) of the same sample plots a standard-free semi-quantitative EDAX-SEM line scan at 100 acquisition points along the line indicated in subplot a). ZAF correction was applied to the EDAX measurements. For each point, the sum of the weight percentages of all elements present in the catalytic coating was normalized to 100%. For clarity, only measurements of Ru, Rh, Ta, and Ir are shown.

[0075] It can be noted how the method claimed to protect affects the distribution of the semi-quantitative weight percentage of Ir, Rh and Ta content in the resulting coating by favoring a relative increase in the concentration of these elements near the electrode substrate.

[0076] The figures discussed above illustrate the effect of the preparation method used on the structure and elemental concentration within the final coating, while the examples below further demonstrate how this method affects electrode performance.

[0077] The following embodiments are provided to illustrate specific ways of putting the invention into practice, and its practicality has been largely verified within the claimed numerical range.

[0078] Those skilled in the art will understand that the devices, compositions, and techniques disclosed below represent those that the inventors have found to work well in the practice of the present invention; however, based on this disclosure, those skilled in the art will understand that many changes can be made to the specific embodiments disclosed without departing from the scope of the invention, and the same or similar results can still be obtained.

[0079] Example

[0080] Experimental preparation

[0081] In all electrode samples used in the following examples and comparative examples, the electrode substrate was manufactured starting with a Grade 1 titanium plate measuring 100 mm × 100 mm × 1 mm, degreased with acetone in an ultrasonic bath for 10 minutes. The plate was then sandblasted to obtain a surface roughness value Rz greater than 2 μm, followed by annealing at 650 °C for 6 hours. Finally, the plate was etched at boiling temperature in a solution containing 22 wt% HCl for 30 minutes, resulting in a surface roughness of 200 g / m². 2 Total weight loss.

[0082] Unless otherwise stated, all percentages are expressed in weight.

[0083] Example 1

[0084] A pair of electrodes E1-E1 is prepared according to the following procedure:

[0085] Each electrode substrate prepared according to the above "Test Preparation" is coated with a first active coating "A1". This first active coating "A1" is applied by brushing two layers of a first hydrochloride precursor solution "S" consisting of 30% tantalum, 50% iridium, and 20% rhodium in 10% HCl. A To obtain the desired result, each single layer was dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes. The loading of Ir-Rh was 2 g / m³. 2 .

[0086] After applying the first active coating "A1" thus obtained, each electrode is coated with a second active coating "B1", which is applied by brushing with a hydrochloride precursor solution "S" containing 65% titanium, 30% ruthenium, 1% copper and 4% zirconium in 10% HCl. B The coating was obtained by applying nine layers, each dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes; the ruthenium loading was 9 g / m³. 2 .

[0087] Finally, a third coating equal to the first coating "A1" is applied on top of coating "B1".

[0088] Each E1 electrode was further baked at 500°C for 3 hours.

[0089] The final coating, measured using SEM microscopy, had an average thickness of 20 micrometers. Figure 1 Images are provided.

[0090] Under accelerated conditions, by applying frequent polarity reversals to the electrodes compared to nominal conditions and at >7 A / dm 2 The lifetime of the electrode to E1-E1 was tested at a current density of [value missing].

[0091] At room temperature, insert both electrodes into a dedicated beaker containing 1 liter of circulating tap water (maximum 10 ppm Cl). Maintain the pair under the test conditions, and consider it a failure if the measured hypochlorite formation efficiency is below 0.5 ppm.

[0092] Example 2

[0093] A pair of electrodes E2-E2 is prepared according to the following procedure:

[0094] Each electrode substrate prepared according to the above "Experimental Preparation" is coated with a first active coating "A2", which is applied by brushing a layer of the first precursor solution "S" detailed in Example 1. AThe layer was obtained by drying at 60°C for 10 minutes and then baking at 500°C for 10 minutes. The loading of Ir-Rh was 1 g / m³. 2 .

[0095] After applying the first active coating "A2" thus obtained, each electrode is coated with a second active coating "B2", which is obtained by applying the precursor solution "S" described in Example 1. B The coating was obtained by brushing in three layers, each layer dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes; the ruthenium loading was 3 g / m³. 2 .

[0096] In summary, the above coating sequence is performed three times, with the final "A2" coating applied last (thus following the pattern A2-B2-A2-B2-A2-B2-A2).

[0097] Each E2 electrode was further baked at 500°C for 3 hours.

[0098] The final coating, measured using SEM microscopy, had an average thickness of 20 micrometers. Figure 2 SEM images are provided.

[0099] Electrode pair E2-E2 was tested according to the procedure of Example 1, and the lifetime results are provided in Table 1.

[0100] Example 3

[0101] A pair of electrodes E3-E3 is prepared according to the following procedure:

[0102] Each electrode substrate prepared according to the above-described "Experimental Preparation" was coated with a first active coating "A3". This first active coating "A3" was applied by brushing two layers of a first hydrochloride precursor solution "S" in 10% HCl containing 35% tantalum and 65% iridium. A "Obtained. Each single layer was dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes. The loading of Ir was 2 g / m." 2 .

[0103] After applying the first active coating "A3" thus obtained, each electrode is coated with a second active coating "B3", which is obtained by applying the precursor solution "S" described in Example 1. B The coating was obtained by brushing in nine layers, each layer dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes; the ruthenium loading was 9 g / m³. 2 .

[0104] In summary, the above coating sequence is performed once, and finally the last "A3" coating is applied (thus following the pattern A3-B3-A3).

[0105] Each E3 electrode was further baked at 500°C for 3 hours.

[0106] The final coating was measured to be 20 micrometers thick using a SEM microscope.

[0107] Electrode pair E3-E3 was tested according to the procedure of Example 1, and the lifetime results are provided in Table 1.

[0108] Comparative Example 1

[0109] A pair of electrodes C1-C1 is prepared according to the following procedure:

[0110] Each electrode substrate prepared according to the "Experimental Preparation" procedure described above was coated with an active coating, which was obtained by applying 13 layers of a hydrochloride precursor solution containing 9.2% tantalum, 15.4% iridium, 6.1% rhodium, 20.8% ruthenium, 45% titanium, 0.7% copper, and 2.8% zirconium in 10% HCl using a brush. Each layer was dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes. The final loading of Ir-Rh-Ru was 13 g / m³. 2 .

[0111] Using SEM microscopy, the final coating was found to be an average thickness of 20 micrometers. Figure 3 Images are provided.

[0112] Electrode pair C1-C1 was tested according to the procedure of Example 1, and the lifetime results are provided in Table 1.

[0113] Comparative Example 2

[0114] A pair of electrodes C2-C2 is prepared according to the following procedure:

[0115] Each electrode substrate prepared according to the above "Experimental Preparation" is coated with a first active coating "A3", which is applied by brushing a layer of the first precursor solution "S" detailed in Example 1. A The layer was dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes. The loading of Ir-Rh was 4 g / m³. 2 .

[0116] After applying the first active coating "A3" thus obtained, each electrode is coated with a second active coating "B3", which is applied by brushing the precursor solution "S" described in Example 1. BThe second active coating was applied in three layers, each dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes; the ruthenium loading was 9 g / m³. 2 .

[0117] Each electrode was further baked at 500°C for 3 hours.

[0118] The final coating was measured to be 20 micrometers thick using a SEM microscope.

[0119] Electrode pair C2-C2 was tested according to the procedure of Example 1, and the lifetime results are provided in Table 1.

[0120] Comparative Example 3

[0121] A pair of electrodes C3-C3 is prepared according to the following procedure:

[0122] Each electrode substrate prepared according to the "Experimental Preparation" procedure described above was coated with an active coating obtained by applying six layers of a hydrochloride precursor solution containing 30% tantalum, 50% iridium, and 20% rhodium in 10% HCl using a brush. Each layer was dried at 60°C for 10 minutes and then baked at 500°C for 10 minutes. The final Ir-Rh loading was 12 g / m³. 2 .

[0123] The final coating was measured to be 20 micrometers thick using a SEM microscope.

[0124] Electrode pair C3-C3 was tested according to the procedure of Example 1, and the lifetime results are provided in Table 1.

[0125] Electrode pair <![CDATA[Load (g / m 2 )]]> Accelerated lifespan (h) E1-E1 Ir+Rh:4;Ru:9 811 E2-E2 Ir+Rh:4;Ru:9 874 E3-E3 Ir:4;Ru:9 800 C1-C1 Ir+Rh+Ru:13 264 C2-C2 Ir+Rh:4;Ru:9 400 C3-C3 Ir+Rh:12 800

[0126] Table 1

Claims

1. A method for manufacturing an electrode for hypochlorite precipitation, comprising at least two sequential stages (I) and (II): (I) Perform the following steps a)-b) at least once over the valve metal substrate: a) Apply a first active coating comprising at least one layer of a first composition, wherein the first composition comprises precursors of Ta and Ir having the following elemental weight percentages: 20-70% Ta, 30-80% Ir, and wherein each layer is dried at 45-75°C for 5-15 minutes and then baked at 480-530°C for 5-15 minutes. b) Apply a second active coating comprising at least one layer of the second composition onto the first active coating, wherein the second composition comprises precursors of Ru and Ti having the following elemental weight percentages: 20-50% Ru, 50-80% Ti, and wherein each layer is dried at 45-75°C for 5-15 minutes and then baked at 480-530°C for 5-15 minutes. (II) Perform step a) on the electrode from stage (I) and optionally bake at 480-530°C for 1-6 hours.

2. The method of claim 1, wherein the first active coating composition further comprises a precursor solution of Rh, and wherein the precursors of Ta, Ir and Rh have the following element weight percentages: 20-45% Ta, 30-70% Ir, and 10-25% Rh.

3. The method of claim 1, wherein the precursors of Ta and Ir in the first active coating composition have the following elemental weight percentages: 20-45% Ta, 55-80% Ir.

4. The method according to any one of claims 1-3, wherein the first active coating is applied in 1-4 layers and the second active coating is applied in 2-10 layers.

5. The method according to any one of claims 1-4, wherein the second active composition further comprises a precursor solution of one or more dopants X, said dopants X being selected from the list of: scandium, strontium, hafnium, bismuth, zirconium, aluminum and combinations thereof, and X being expressed as 0.5-5% by weight of elements.

6. The method according to any one of claims 1-5, wherein the second active composition further comprises a precursor solution of one or more dopants Y, said dopants Y being selected from the list of copper, platinum and combinations thereof, and Y being expressed as 0.2-3.2% by elemental weight percentage.

7. The method according to any one of claims 1-6, wherein in stage (I), steps a)-b) are performed 1-6 times consecutively before stage (II).

8. The method of claim 2, wherein stages (I) and (II) are performed until 2-6 g / m³ is reached. 2 The total loading of Group 9 precious metal elements.

9. An electrode obtained by the method according to any one of claims 1-8.

10. An electrode for hypochlorite precipitation, comprising a valve metal substrate and an active coating applied over said substrate, characterized in that... The coating has an average thickness "T" of 10-30 micrometers and comprises a metal oxide of Ti, Ta, Ir, Ru, and optional Rh according to the following relative weight percentages of elements: 4-35% Ir, 1.5-22.5% Ta, 10-45.5% Ru, 25-75% Ti, and optional 0.5-12.5% ​​Rh, wherein the relative weight percentages of Ta, Ir, Ru, and optional Rh vary with the coating thickness such that: - Ir, Ta, and Rh, if present, exhibit weight percentage peaks centered at 2-25% of coating thickness T, starting from the substrate, with FWHM at 1-10% of T; - Ru exhibits an increase in weight percentage until it reaches 10-40% of the coating thickness T; The weight percentage was measured by averaging a standard-free semi-quantitative EDAX-SEM line scan of the sample, wherein each line scan was performed over at least 100 acquisition points along the thickness T of the catalytic coating, with ZAF correction.

11. The electrode of claim 10, wherein the valve metal substrate is made of Ti or an alloy thereof.

12. The electrode according to claim 10 or 11, wherein Ru is stable.

13. A bipolar electrolyzer comprising an electrolyte and electrodes according to claim 9, 10, 11, or 12.

14. The bipolar electrolyzer of claim 13, wherein the electrolyte is composed of tap water.

15. Use of the bipolar electrolyzer according to claim 13 or 14 for hypochlorite-mediated water disinfection.

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