Hypochlorite generation electrode

Abstract

The present invention relates to a hypochlorite generation electrode comprising a conductive substrate and a catalytic coating applied over said substrate, and a multi-layer method for the manufacture thereof.

Description

[Technical field]

[0001] The present invention relates to a hypochlorite generating electrode and a method for producing the same. [Background technology]

[0002] The hypochlorite generation electrodes, used alone or in combination with other methods (UV, ozone), may be advantageously used in cells and systems for water treatment applications. In particular, these electrodes may be successfully used in the field of domestic water disinfection, including pools and toilets.

[0003] In the above example, the water to be treated, usually tap water, serves as the electrolyte. Tap water is characterized by a high electrical resistivity, usually well above 1000 Ω, due to the very low concentration of chloride ions dissolved in it (≦10 ppm). Under these conditions, when the operating current density of the cell is increased beyond a certain threshold, the oxygen evolution reaction begins to take place at the anode, as the competing chlorine evolution reaction is limited by the mass transport of chloride ions. Oxygen production ultimately contributes to electrode corrosion, thereby limiting its efficiency and lifespan.

[0004] Additionally, water hardness can cause scale to form on the electrode surfaces which adversely affects the hypochlorite production efficiency of the cell and thus necessitates regular cleaning of the electrodes.

[0005] To circumvent this problem, home disinfection applications typically use bipolar and symmetric electrode packs, i.e., identical anode-cathode pairs that undergo polarity reversal to obtain an effective "self-cleaning" system.

[0006] However, this operating condition, if present, is very detrimental to the catalytic coating of the electrode, since it accelerates its deactivation and delamination processes.

[0007] Large amounts of Group 9 precious metal elements (e.g., 10 g / m 2Electrodes coated with Ir and Rh oxides (above 10 ...

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

[0009] It would therefore be desirable to have a hypochlorite generation electrode that could withstand the harsh operating conditions that may be found in household water disinfection applications (or other applications characterized by high electrolyte resistivity), while maintaining industrial and commercial attractiveness in terms of the amount of rare precious metal used. Summary of the Invention

[0010] Description of the invention It is an object of the present invention to overcome the shortcomings of hypochlorite generation electrodes known in the art, especially when exposed to polarity reversal conditions and high resistance electrolytes such as tap water.

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

[0012] It has often been observed that mixing iridium oxide with ruthenium oxide can result in a material that has the stability of iridium oxide, but is significantly cheaper. This effect is likely due to a shift in the oxidation potential caused by band mixing, and is called partialisation of iridium by ruthenium.

[0013] However, the inventors have observed that in this case the simple combination of a Ru-Ti composition with a composition containing Ir and optionally Rh does not give satisfactory results, since the mixture obtained does not produce a stable or controllable material. Phase separation is observed at various Ru:Ir ratios and the coatings thus obtained are not of satisfactory durability. Thus, the creation of a Ru:Ti matrix, often utilized in electrochemistry to obtain materials with the stability of iridium oxide at a lower price point, does not guarantee the robustness required in this case.

[0014] Surprisingly, the inventors have noted that when the two compositions are applied separately and sequentially, the resulting electrodes exhibit improved corrosion resistance and increased FAC in one or more layers that undergo thermal decomposition. As may be inferred by standardless semi-quantitative SEM / EDAX analysis with ZAF correction, the catalyst-coated electrodes obtained by this technique do not accurately reflect the presence of the two different alternating compositions used in the fabrication method. Although the presence of multiple layers may be visually suggested in certain SEM images, ultimately, the elements of the two different coating compositions intermingle and diffuse differently throughout the active coating thickness. Several factors may contribute to this effect, namely, their different crystal affinities, and / or their molecular weights, as well as the successive and specific heat treatments performed during fabrication. The result is an unexpected profile that varies in the concentration of elements in the final overall coating, as can be observed by scanning the coating composition from the electrode substrate to the outer surface with semi-quantitative standardless EDAX SEM measurements.

[0015] This complex and specific composition profile imparted by the fabrication method used has been observed to contribute clearly to the electrode performance. It may therefore be concluded that the electrode performance in the targeted application does not only depend on the elements present in the active coating, but is also related to the specific properties conveyed to the electrode via the fabrication method used, and the resulting distribution of the elements within the active coating.

[0016] In one aspect, the present invention relates to a method for producing an electrode suitable for hypochlorite generation in tap water, the method comprising at least two successive steps (I) and (II).

[0017] The first stage (I) comprises carrying out steps a) to b) defined below on a valve metal substrate.

[0018] Step a) involves applying a first active coating ("A" for brevity) comprising at least one layer of a first composition containing precursors of Ta and Ir with the following weight percentages in terms of elements: 20-70% Ta, 30-80% Ir. Each layer is dried at 45-75°C for 5-15 minutes and subsequently calcined 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 may be used successfully.

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

[0020] Each layer is dried at 45-75°C for 5-15 minutes and then fired at 480-530°C for 5-15 minutes.

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

[0022] The second stage (II) involves carrying out step a) above on the electrode obtained from stage (I) and optionally post-baking at 480-530° C. for 1-6 hours.

[0023] Thus, the electrode is made according to the following coating sequence: ABA, or ABABA, or ABABABA, etc., where the total number of coatings A and B may, for practical reasons, preferably range from 3 to 31. This number corresponds to carrying out steps a) to b) in stage (I) 1 to 15 times.

[0024] Semi-quantitative standardless EDAX SEM measurements on the resulting electrodes show that, although the separate coating compositions A and B used in the manufacturing process are not clearly identifiable as separate (multi)layers in the overall final coating, the elemental distribution is also different from that which might be obtained by simply applying a mixture of both 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 the electrode performance (i.e., the sequence should preferably start and end with coating A), as shown in the examples below.

[0025] The inventors have observed that if steps a) to b) in stage (I) are carried out 1 to 6 times, the electrode thus obtained works particularly well in the practice of the invention.

[0026] The method according to the invention does not preclude the application of additional coating compositions, such as a barrier coating composition on the electrode substrate prior to application of coating A, or a top coating composition after step (II), or other compositions between different steps and processes.

[0027] During each single run of step a) in both stages (I) and (II), and step b) in stage (I), the number of layers of the corresponding active coating, and the total precious metal loading, may vary.

[0028] Preferably, the skilled person may adjust the number of steps performed, the pick-up and load of each layer, as well as the number of layers according to general knowledge, until an overall final coating thickness of at least 10 microns, and even more preferably 10 to 30 microns, is reached.

[0029] Thus, the electrodes are coated with the following sequence: n -B m -A q Or A n -B m -A o -B p -...-A q where n, m, o, p, q indicate the number of layers in which each coating A and B is applied, which numbers may be different from each other.

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

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

[0032] Preferably, the precious metal loading of the second active coating is higher than the precious metal loading of the first active coating, and even more preferably, the precious metal loading of the second active coating is 2 to 10 times higher than the precious metal loading of the first active coating.

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

[0034] According to another embodiment, the total loading of rare precious metals, i.e. precious metals belonging to group 9 of the periodic table, is preferably between 2 and 6 g / m2 for the entire final electrode. 2 is equal to.

[0035] In another embodiment, the precursors of Ta and Ir in the first composition may be advantageously selected within the following ranges: 20-45% Ta and 55-80% Ir. In this case, the composition may or may not contain further metal precursors. In the latter case, the fabrication of the electrode is simplified. Moreover, the procurement of materials required for the electrode fabrication is less subject to uncertainties regarding price fluctuations and availability of metal precursors, especially when rare and / or precious metals are involved. The resulting electrodes advantageously match 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, the precursors of Ta, Ir and Rh having the following weight ratios of the elements: 20-45% Ta, 30-70% Ir, 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 between 1 and 3 g / m 2 may be selected between.

[0038] According to another embodiment, the total loading of Ir+Rh in the entire final electrode is preferably between 2 and 6 g / m 2 may be selected to be equal to

[0039] Generally, for step b), the total loading of Ru is advantageously between 5 and 10 g / m 2 may be selected between.

[0040] The electrode substrate may be made of any suitable conductive material, preferably a valve metal such as titanium or an alloy thereof. The substrate may be in any of the different geometric shapes that may be used in electrochlorination applications, including mesh, sheet, blade, tube or wire shapes.

[0041] Regardless of the material and shape of the substrate, the surface of such substrate may advantageously be a cleaned surface. This may be obtained by any of the processes known in the art. Furthermore, the cleaned surface may be further treated to enhance adhesion of the active coating composition. This may be achieved by any conventional means, including intergranular etching of the substrate metal, sharp grit blasting of the metal surface, or plasma spraying, followed by surface treatment to remove embedded grit.

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

[0043] According to a further embodiment of the method according to the invention, the second active composition further comprises a precursor solution of one or more doping agents collectively identified as "X", where X is between 0.5 and 5%, expressed as a weight percent with respect to the element, and is selected from the following list: scandium, strontium, hafnium, bismuth, zirconium, aluminum, and combinations thereof.

[0044] The resulting X-doped composition may provide improved efficiency in the low salinity conditions in which the electrodes may typically operate.

[0045] According to a further embodiment of the method according to the invention, the second active composition may further comprise a precursor solution of one or more doping agents collectively identified as "Y", Y being 0.2-3.2% by weight percent with respect to the element and selected from the following list: copper, platinum and combinations thereof.

[0046] The resulting Y-doped composition has been observed to provide improved robustness against polarity reversal.

[0047] The X and Y doping of the second active composition are not mutually exclusive and they may be carried out together or separately.

[0048] As previously discussed, the multi-layer fabrication method of the alternative coating composition according to the present invention results in electrodes that exhibit higher corrosion resistance and higher FAC efficiency compared to other methods utilizing the same materials and amounts of rare precious metals from Group 9. The method also provides electrodes with high resistance to polarity reversal that can be utilized for self-cleaning of symmetrical electrode packages subjected to current reversal without compromising performance.

[0049] As explained, the electrodes obtainable by this method achieve measurably improved performance with respect to electrodes made of the same materials applied together from the beginning, instead of alternating different layers of different compositions as described above. The unique effects of the specific heat treatments applied to the two coating compositions, the order, number and alternation of the layers, combined with the inherent different volatilities of the elements, provide a product with unique properties and performance.

[0050] Indeed, certain elements of the first and second compositions are fairly uniformly distributed along the overall catalyst coating thickness, while other elements are mostly enriched / depleted near and / or at the top of the substrate, but are nevertheless subject to hard-to-predict variations likely depending on a wide 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), as well as their thicknesses and / or metal loadings. This distribution of elements in the final product has no direct relationship to the AB-...-A pattern performed during the electrode fabrication.

[0051] Thus, while the distribution of elements throughout the final electrode coating is certainly related to the preparation method which provides a measurable effect on electrode performance, it cannot be defined without reference to said method without unduly limiting the scope of the claims.

[0052] Thus, in a second aspect, the present invention relates to an electrode obtainable by any of the above process embodiments, which, due to the properties conferred by the process used, exhibits an improved or comparable lifespan and an improved efficiency of chlorine evolution compared to electrodes known in the art, using as a comparison a reduced total loading of precious metal elements belonging to group 9, which are rare, expensive and subject to dramatic price fluctuations and availability problems.

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

[0054] As explained, the above electrodes cannot be adequately defined solely in terms of their structural / material properties without undue limitations, however, the inventors have surprisingly observed that certain particularly advantageous embodiments exhibit common features in the distribution of elements through the coating thickness, as explained below.

[0055] In a third aspect, the invention relates to an electrode with improved life span and chlorine generation efficiency, which may be obtained using the method according to the invention and is suitable for water disinfection, in particular for tap water. The electrode comprises a valve metal substrate, preferably made of Ti or an alloy thereof, and an active coating applied onto said substrate, characterized in that said coating has an average thickness "T" of 10 to 30 microns and comprises metal oxides of Ti, Ta, Ir, Ru and optionally Rh according to the following relative weight percentages for the elements: Ir 4-35%, Ta 1,5-22,5%, Ru 10-45,5%, Ti 25-75% and optionally Rh 0,5-12,5%. The metals are diffused throughout the thickness T, but their relative weight percentages are: Ir, Ta, and Rh, when present, exhibit weight percent peaks centered at 2-25% of the coating thickness, T, starting from the substrate, and have a FWHM of 1-10% of T; -Ru shows an increase in weight percent until it reaches 10-40% of the coating thickness T, where it essentially stabilizes (i.e., starting from the substrate, it does not show any systematic peaks or dips in weight percent and does not fluctuate, despite instrumental error, beyond an average of three times the average value measured from 25% to 100% of T). So it varies with the coating thickness.

[0056] The weight percentage is measured by averaging over a sample of standardless semi-quantitative EDAX-SEM line scans with ZAF correction, with each line scan taken over 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 is normalized to 100%. The average over a sample should be measured by considering an appropriate number of line scans measured over different regions of the electrode. As one skilled in the art may appreciate, the appropriate number of line scans depends on the overall size and uniformity of the sample.

[0057] It should be understood that such line scans will inherently exhibit variations due to defects or pores in the catalyst coating, instrument precision and sensitivity, impurities, and the like.

[0058] By peak we mean a relative or absolute maximum that can be approximately fitted by a Gaussian or skewed normal distribution and is characterized by a full width at half maximum (FWHM) as described above.

[0059] The calculated weight percentage corresponding to said peak should be at least three times the average value measured at a distance Z from the position of the peak in the direction towards the outer surface of the active coating (farthest from the substrate), where Z=1.75*FWHM-2.75*FWHM.

[0060] It should be noted that other structural / chemical properties may be imparted by the fabrication method according to the invention beyond those captured by the SEM / EDAX measurements above.

[0061] In a third aspect, the present invention relates to a bipolar electrolyzer using the electrodes according to the above aspects and embodiments. Preferably, the bipolar electrolyzer uses an electrolyte consisting essentially of tap water. Advantageously, the electrolyzer uses at least a pair of identical electrodes, each electrode being one of the electrodes according to the invention described above.

[0062] In a fourth aspect, the present invention relates to the use of a bipolar electrolysis device according to the invention for hypochlorite mediated water disinfection. [Brief description of the drawings]

[0063] [Figure 1] Panel a) of Figure 1 depicts an SEM image of a sample prepared according to the method described in Example 1. Panel b) plots a standardless semi-quantitative EDAX-SEM line scan performed on the same sample along the line indicated in panel a). [Diagram 2] Panel a) of Figure 2 depicts an SEM image of a sample prepared according to the method described in Example 2. Panel b) plots a standardless semi-quantitative EDAX-SEM line scan performed on the same sample along the line indicated in panel a). [Diagram 3] Panel a) of Figure 3 represents an SEM image of a sample prepared according to the method described in Counter Example 1. Panel b) plots a standardless semi-quantitative EDAX-SEM line scan performed on the same sample along the line indicated in panel a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0064] Detailed Description of the Drawings Panel a) of Figure 1 represents an SEM image of a sample prepared according to the method described in Example 1, i.e. by performing step (I) once according to an "ABA" type application pattern. The coating had an average thickness of 20 microns.

[0065] Panel b), referring to the same sample, plots a standardless semi-quantitative EDAX-SEM line scan taken over 100 acquisition points along the line indicated in panel a). A ZAF correction is applied to the EDAX measurements. For each point, the sum of the weight percentages of all elements present in the catalyst coating is normalized to 100%. For clarity, only measurements of Ru, Rh, Ta and Ir are shown.

[0066] Panel a) of Figure 2 represents an SEM image of a sample prepared according to the method described in Example 2, i.e. by carrying out step (I) three times according to an "ABABABA" type application pattern. The coating exhibited an average thickness of 20 microns.

[0067] Panel b), referring to the same sample, plots a standardless semi-quantitative EDAX-SEM line scan taken over 100 acquisition points along the line indicated in panel a). A ZAF correction is applied to the EDAX measurements. For each point, the sum of the weight percentages of all elements present in the catalyst coating is normalized to 100%. For clarity, only measurements of Ru, Rh, Ta and Ir are shown.

[0068] Panel a) of Figure 3 represents an SEM image of a sample prepared according to the method described in Counter Example 1, i.e. by mixing compositions A and B together and applying the solution in layers until a coating of average thickness of 20 microns is obtained.

[0069] Panel b), referring to the same sample, plots a standardless semi-quantitative EDAX-SEM line scan taken over 100 acquisition points along the line indicated in panel a). A ZAF correction is applied to the EDAX measurements. For each point, the sum of the weight percentages of all elements present in the catalyst coating is normalized to 100%. For clarity, only measurements of Ru, Rh, Ta and Ir are shown.

[0070] It is possible to note how the claimed method affects the semi-quantitative weight percent distribution of Ir, Rh and Ta contents in the obtained coating by favoring a relative increase in the concentration of these elements near the electrode substrate.

[0071] The figures above show the effect of the preparation method used on the structure and concentration of elements in the final coating, while the examples below further show how this method affects electrode performance.

[0072] The following examples are included to demonstrate specific ways of practicing the invention, the utility of which has been verified for the most part within the ranges of values ​​claimed.

[0073] Those of skill in the art should appreciate that the devices, compositions, and techniques disclosed below represent devices, compositions, and techniques discovered by the inventors to function well in the practice of the invention. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the scope of the invention. EXAMPLES

[0074] Experimental preparation For all electrode samples used in the following examples and counter examples, starting from a titanium grade 1 plate of size 100 mm x 100 mm x 1 mm, the electrode substrate was prepared by degreasing with acetone in an ultrasonic bath for 10 minutes. The plate was then subjected to grit blasting to obtain a surface roughness value Rz of more than 2 μm, followed by annealing at 650 °C for 6 hours. Finally, the plate was etched in a solution containing 22 wt. % HCl at boiling temperature for 30 minutes to obtain a roughness of 200 g / m 2 This resulted in a total weight loss of 1.0 kg / kg.

[0075] Unless otherwise indicated, all percentages are expressed by weight.

[0076] Example 1 A pair of electrodes E1-E1 was prepared according to the following procedure.

[0077] Each electrode substrate prepared according to the above "Experimental Preparation" was immersed in a first hydrochloride precursor solution of 30% tantalum, 50% iridium, and 20% rhodium in 10% HCl, "S A The first active coating, "A1", was obtained by applying two layers of "Ir-Rh" by brush. Each monolayer was dried at 60 °C for 10 min and subsequently calcined at 500 °C for 10 min. The loading of Ir-Rh was 2 g / m 2 It was.

[0078] After applying the first active coating "A1" thus obtained, each electrode was immersed in a hydrochloride precursor solution "S" of 65% titanium, 30% ruthenium, 1% copper and 4% zirconium in 10% HCL. B The coating was applied in nine layers, each layer dried at 60°C for 10 minutes, followed by calcination at 500°C for 10 minutes. The ruthenium loading was 9 g / m 2 It was.

[0079] Finally, a third coating equivalent to the first coating "A1" above was applied over coating "B1".

[0080] Furthermore, each E1 electrode was baked at 500° C. for 3 hours.

[0081] The resulting final coating had an average thickness of 20 microns as measured by SEM microscopy, and the image is shown in Figure 1.

[0082] The life of the electrode pair E1-E1 is increased by subjecting the electrodes to frequent polarity reversals compared to nominal conditions, at current densities >7A / dm 2 The test was performed under accelerated conditions.

[0083] Both electrodes were inserted at room temperature into a dedicated beaker containing 1 I of circulating tap water (max 10 ppm Cl). The couple was maintained at the test conditions and was considered to have failed if the measured hypochlorite generation efficiency was less than 0.5 ppm.

[0084] Example 2 A pair of electrodes E2-E2 was prepared according to the following procedure.

[0085] Each electrode substrate prepared according to the above "Experimental Preparation" was dissolved in the first precursor solution "S A The substrate was coated with a first active coating "A2" obtained by applying with a brush one layer of "Ir-Rh". The layer was dried at 60°C for 10 min and subsequently calcined at 500°C for 10 min. The loading of Ir-Rh was 1 g / m 2 It was.

[0086] After applying the first active coating "A2" thus obtained, each electrode is then immersed in the precursor solution "S" described in Example 1. B The coating was applied by brush in three layers, each layer dried at 60°C for 10 minutes, followed by calcination at 500°C for 10 minutes. The ruthenium loading was 3 g / m 2 It was.

[0087] In total, the above coating sequence was performed three times, concluding with one final application of the "A2" coating (thereby following the pattern A2-B2-A2-B2-A2-B2-A2).

[0088] Furthermore, each E2 electrode was calcined at 500° C. for 3 hours.

[0089] The resulting final coating had an average thickness of 20 microns as measured by SEM microscopy, and the SEM image is shown in FIG.

[0090] Electrode pair E2-E2 was tested according to the procedure of Example 1 and the lifetime results are shown in Table 1.

[0091] Example 3 A pair of electrodes E3-E3 was prepared according to the following procedure.

[0092] Each electrode substrate prepared according to the above “Experimental Preparation” was immersed in a first hydrochloride precursor solution of 35% tantalum and 65% iridium in 10% HCl, “S A The first active coating, "A3", was obtained by applying two layers of "Ir" by brush. Each single layer was dried at 60 °C for 10 min and subsequently calcined at 500 °C for 10 min. The Ir loading was 2 g / m 2 It was.

[0093] After applying the first active coating "A3" thus obtained, each electrode was then immersed in the precursor solution "S" described in Example 1. B The coating was applied by brush in nine layers, each layer dried at 60°C for 10 minutes, followed by calcination at 500°C for 10 minutes. The ruthenium loading was 9 g / m 2 It was.

[0094] Overall, the above coating sequence was performed once, culminating with the application of one final "A3" coating (thereby following the pattern A3-B3-A3).

[0095] Furthermore, each E3 electrode was calcined at 500° C. for 3 hours.

[0096] The resulting final coating had an average thickness of 20 microns as measured by SEM microscopy.

[0097] Electrode pair E3-E3 was tested according to the procedure of Example 1 and the lifetime results are shown in Table 1.

[0098] Counterexample 1 A pair of electrodes C1-C1 was prepared according to the following procedure.

[0099] Each electrode substrate prepared according to the "Experimental Preparation" above was coated with an active coating obtained by applying with a brush 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. Each layer was dried at 60 °C for 10 min and subsequently calcined at 500 °C for 10 min. The final loading of Ir-Rh-Ru was 13 g / m 2 It was.

[0100] The final coating obtained was an average of 20 microns thick as measured by SEM techniques, and the image is shown in FIG.

[0101] Electrode pair C1-C1 was tested according to the procedure of Example 1 and the lifetime results are shown in Table 1.

[0102] Counterexample 2 A pair of electrodes C2-C2 was fabricated according to the following procedure.

[0103] Each electrode substrate prepared according to the above "Experimental Preparation" was dissolved in the first precursor solution "S A The substrate was coated with a first active coating "A3" obtained by applying with a brush one layer of "Ir-Rh". The layer was dried at 60°C for 10 minutes and subsequently baked at 500°C for 10 minutes. The loading of Ir-Rh was 4 g / m 2 It was.

[0104] After applying the first active coating "A3" thus obtained, each electrode was then immersed in the precursor solution "S" described in Example 1. B The second active coating was applied in three layers, each layer dried at 60°C for 10 minutes, followed by calcination at 500°C for 10 minutes. The ruthenium loading was 9 g / m 2 It was.

[0105] Furthermore, each electrode was sintered at 500° C. for 3 hours.

[0106] The resulting final coating had an average thickness of 20 microns as measured by SEM microscopy.

[0107] Electrode pair C2-C2 was tested according to the procedure of Example 1 and the lifetime results are shown in Table 1.

[0108] Counterexample 3 A pair of electrodes C3-C3 was fabricated according to the following procedure.

[0109] Each electrode substrate prepared according to the "Experimental Preparation" above was coated with an active coating obtained by applying with a brush six layers of a hydrochloride precursor solution containing 30% tantalum, 50% iridium and 20% rhodium in 10% HCL. Each layer was dried at 60 °C for 10 min and subsequently calcined at 500 °C for 10 min. The final loading of Ir-Rh was 12 g / m 2 It was.

[0110] The resulting final coating had an average thickness of 20 microns as measured by SEM microscopy.

[0111] Electrode pair C3-C3 was tested according to the procedure of Example 1 and the lifetime results are shown in Table 1. TIFF2024540996000001.tif57170

Claims

1. A method for manufacturing an electrode for hypochlorite generation, comprising at least two successive steps (I) and (II): (I) on a valve metal substrate, the following steps a) to b): a) applying a first active coating comprising at least one layer of a first composition, wherein said first composition comprises precursors of Ta and Ir having the following weight ratios in terms of elements: 20-70% Ta, 30-80% Ir, each layer being dried at 45-75°C for 5-15 minutes and subsequently calcined at 480-530°C for 5-15 minutes; b) applying a second active coating comprising at least one layer of a second composition over the first active coating, wherein the second composition comprises precursors of Ru and Ti having the following weight ratios in terms of elements: 20-50% Ru, 50-80% Ti, each layer being dried at 45-75°C for 5-15 minutes and subsequently calcined at 480-530°C for 5-15 minutes. at least once; (II) carrying out step a) on the electrode obtained from step (I), and optionally post-baking at 480-530° C. for 1-6 hours; A method comprising:

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

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

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

5. 3. The method of claim 1 or 2, wherein the second active composition further comprises a precursor solution of one or more doping agents X selected from the following list: scandium, strontium, hafnium, bismuth, zirconium, aluminum, and combinations thereof, wherein X is between 0.5 and 5% expressed in weight percent with respect to the element.

6. 3. The method of claim 1 or 2, wherein the second active composition further comprises a precursor solution of one or more doping agents Y selected from the following list: copper, platinum and combinations thereof, wherein Y is between 0.2 and 3.2% expressed in weight percent with respect to the element.

7. 3. The method according to claim 1, wherein in step (I), steps a) and b) are carried out 1 to 6 times in succession before step (II).

8. Steps (I) and (II) are from 2 to 6 g / m ２ 3. The method of claim 2, wherein the total loading of Group 9 noble metal element is reached.

9. Electrode obtainable by the method according to claim 1 or 2.

10. 1. A hypochlorite generation electrode, comprising a valve metal substrate, preferably made of Ti or an alloy thereof, and an active coating applied onto said substrate, said coating having an average thickness "T" of 10 to 30 microns and comprising metal oxides of Ti, Ta, Ir, Ru and optionally Rh according to the following relative weight percentages for the elements: 4-35% Ir, 1.5-22.5% Ta, 10-45.5% Ru, 25-75% Ti, and optionally 0.5-12.5% ​​Rh, wherein the relative weight percentages of Ta, Ir, Ru and optionally Rh are: Ir, Ta, and Rh, when present, exhibit a weight percent peak starting from the substrate centered at 2-25% of the coating thickness, T, with a FWHM of 1-10% of T; Ru shows an increase in weight percent until it reaches 10-40% of the coating thickness T, at which point it essentially stabilizes. Varies depending on coating thickness, The weight percent is determined by averaging standardless semi-quantitative EDAX-SEM line scans on the sample, each line scan being taken over at least 100 acquisition points along the thickness T of the catalyst coating using ZAF correction. An electrode for generating hypochlorite, characterized by:

11. A bipolar electrolyzer comprising the electrode of claim 9 and an electrolyte.

12. 12. The bipolar electrolyzer of claim 11, wherein the electrolyte consists essentially of tap water.

13. 12. Use of a bipolar electrolyzer according to claim 11 for hypochlorite-mediated water disinfection.

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