Electrodes for electrolytic generation of gases

Abstract

The present invention relates to an electrode for generating gas in an electrolytic process, comprising a valve metal substrate and a catalytic coating comprising two layers: a first layer comprising oxides of a valve metal, ruthenium, and iridium, and a second layer comprising one or more metals selected from the platinum group of elements.

Description

[Technical Field]

[0001] The present invention relates to an electrode for generating gas in an electrolytic process, comprising a valve metal substrate and a catalytic coating comprising two layers: a first layer comprising a valve metal, an oxide of ruthenium, and an oxide of iridium, and a second layer comprising one or more metals selected from the platinum group of elements. [Background technology]

[0002] The field of the invention relates to the preparation of catalytic coatings for electrodes used in brine electrolysis processes, which coatings are applied to metal substrates, typically titanium or other valve metals.

[0003] Over the years, the science and technology of brine electrolysis has evolved towards efficient implementation from an energy standpoint and a cost / benefit standpoint of resource use. In this ever more challenging situation, anode optimization plays a key role. In particular, significant efforts have been made to reduce the anode overpotential during chlorine generation and to reduce the concentration of oxygen in the generated chlorine gas, thereby producing high-purity chlorine gas.

[0004] Additional challenges exist in obtaining electrodes that can maintain higher performance over extended periods of time.

[0005] Generally speaking, processes for electrolyzing brines, e.g., brines of alkali chlorides such as sodium chloride, to produce chlorine and caustic soda are carried out with anodes made of titanium or other valve metals activated with a surface layer of ruthenium dioxide (RuO2) optionally mixed with tin dioxide (SnO2) and other noble metals, such as those described in EP 0 153 586. Thereby, it is possible to obtain a reduction in the overpotential of the chlorine evolution anode reaction, and thus a reduction in overall energy usage.

[0006] However, the formulation just described, along with other formulations containing tin, suffers from the problem of producing excessive amounts of oxygen-contaminated chlorine gas in order to reduce the overpotential of the concomitant oxygen evolution reaction.

[0007] Another partial improvement in performance can be obtained by applying to the metal substrate a formulation based on RuO2 and SnO2 in combination with a reduced amount of IrO2, such as that described in WO2016083319. Similar formulations can provide optimal values ​​of cell potential and a moderate amount of oxygen.

[0008] Other prior art coatings, such as the formulation described in WO2012081635, which include two catalytic coatings, i.e., a first catalytic coating containing oxides of titanium and precious metals and a second catalytic coating containing platinum and palladium alloys, can also achieve optimal values ​​of cell potential and reduced amounts of oxygen in chlorine gas, but do not provide the electrode with optimal durability to maintain higher levels of performance in terms of catalytic activity and selectivity for a reasonable period of time.

[0009] US2013 / 0186750A1 describes an electrode suitable for chlorine evolution having alternating layers of two distinct compositions, namely one type of layer comprising iridium, ruthenium, and a valve metal and another type of layer comprising oxides of iridium, ruthenium, and tin.

[0010] US2013 / 0334037A1 describes an electrode for electrolysis, which includes a conductive substrate, a first layer formed on the conductive substrate and containing at least one oxide selected from ruthenium oxide, iridium oxide, and titanium oxide, and a second layer formed on the first layer and containing an alloy of platinum and palladium.

[0011] No. 4,626,334 describes an anode comprising an electrically conductive substrate with a (Ru-Sn)O2 solid solution coating for brine electrolysis.

[0012] JPS 62243790 describes an electrode having a first coating layer comprising a mixture of platinum and iridium oxide and a second coating layer comprising a mixture of ruthenium oxide and tin oxide.

[0013] Thus, there is a clear need to identify new electrode catalytic coatings for generating gaseous products in electrolysis cells in brine electrolysis processes that are characterized by a high level of catalytic activity compared to prior art formulations and a high durability that allows for sustained high levels of performance over extended periods under normal operating conditions. Summary of the Invention

[0014] Various aspects of the invention are set forth in the following claims.

[0015] The present invention relates to an electrode comprising a catalytic coating applied to a metal substrate for generating gaseous products in an electrolysis cell, e.g., for generating chlorine in an alkaline brine electrolysis cell. In the context of the present invention, the term catalytic coating refers to two distinct catalytic layers having different catalytic compositions, where a first catalytic layer formed on a substrate contains a mixture of at least iridium, ruthenium, tin, and platinum, or oxides thereof, or combinations thereof, and a second catalytic layer formed on the first catalytic layer contains platinum and tin, or oxides thereof, or combinations thereof. The tin in the second catalytic layer is present in a decreasing concentration from the surface in contact with the first catalytic layer toward the upper surface of the second catalytic layer, i.e., the surface opposite the surface in contact with the first catalytic layer, and the platinum in the first catalytic layer is present in a decreasing concentration from the surface in contact with the second catalytic layer toward the substrate.

[0016] The present invention also relates to an electrode for generating gaseous products in an electrolysis cell, for example, for generating chlorine in an alkaline brine electrolysis cell, comprising a valve metal substrate and a coating, the coating comprising: a first catalytic layer formed on the substrate and containing a mixture of iridium, ruthenium, tin, and platinum, or oxides thereof, or combinations thereof; and a second catalytic layer formed on the first catalytic layer and containing platinum and tin, or oxides thereof, or combinations thereof, the first layer being obtained from a platinum-free first precursor solution containing a mixture of iridium, ruthenium, and tin that is applied to the substrate and subjected to a heat treatment; and the second catalytic layer being obtained from a platinum-containing, tin-free second catalytic solution that is applied to the first catalytic layer and subjected to a heat treatment. The terms "platinum-free" and "tin-free" in the sense of the present invention mean that the platinum concentration in a first solution is at least one order of magnitude lower than the average platinum concentration in a first layer obtained from said first solution, and the tin concentration in a second solution is at least one order of magnitude lower than the average tin concentration in a second layer obtained from the second solution. Preferably, a platinum-free solution contains platinum as at most an impurity, and a tin-free solution contains tin as at most an impurity.

[0017] This dual layer structure applied to a metal substrate, typically titanium, a titanium alloy, or another valve metal, allows for energy savings to be combined with excellent purity of the chlorine gas produced, while maintaining optimal performance characteristics in terms of catalytic activity and selectivity over long periods of time. DETAILED DESCRIPTION OF THE INVENTION

[0018] The first catalytic layer formed on the substrate preferably contains ruthenium oxide, iridium oxide, tin oxide, and platinum metal or its oxide. RuO2 is widely known for its excellent catalytic activity and its stability in alkaline media, which is improved by the presence of IrO2, while the presence of SnO2 ensures that the consumption of the precious metals present is slow.

[0019] The second catalyst layer formed on the first layer comprises tin or its oxide and one or more metals selected from the platinum group elements, particularly platinum itself, which are known to increase selectivity and reduce energy usage.

[0020] The inventors have observed that an electrode having a similar catalytic coating, wherein the second catalytic layer comprises platinum in the form of metal or its oxide in a molar percentage ranging between 48 and 96% on a metallic element basis (or 50 and 99.999% if the tin content is not taken into account), can provide the advantage of resulting in a reduction in the overpotential of the reaction for generating chlorine.

[0021] In the context of the present invention, ranges indicated either by "from" or "between" include the specified upper and lower limits, respectively.

[0022] In another embodiment, in addition to platinum and tin, the second catalytic layer contains palladium or rhodium in the form of metal, their oxide, or a combination thereof, in a molar percentage range of 0-24% (or 0-25% if the tin component is not taken into account) based on the metallic element, where these elements are in the form of metal or their oxide, which can ensure high catalytic activity due to the combined presence of two or more noble metals.

[0023] The second catalyst layer preferably contains tin or its oxide at an average molar percentage in the range of 4 to 12% on a metal element basis. The concentration of the tin component varies perpendicular to the interface between the first and second layers, so the tin concentration is the average of the concentration profile through the second catalyst layer.

[0024] Thus, in a preferred embodiment, excluding unavoidable impurities, the second catalyst layer consists of platinum and tin, and optionally palladium and / or rhodium, with molar percentages on a metal element basis in the ranges of 48-96% platinum, 4-12% tin, 0-24% palladium, and 0-24% rhodium.

[0025] According to a preferred embodiment of the above-mentioned electrode, the first catalyst layer contains metals or metal oxides of iridium, ruthenium, and tin in molar percentages of Ru=24-34%, Ir=3-13%, and Sn=30-70% based on the metal elements.

[0026] The first catalyst layer preferably contains platinum or its oxide in an average molar percentage in the range of 3 to 10% on a metal elemental basis. The concentration of the platinum component varies perpendicular to the interface between the first and second layers, so the platinum concentration is the average of the concentration profile through the first catalyst layer.

[0027] Of course, one skilled in the art would select the mole percentages of the individual elements so that the sum of the mole percentages of the components equals 100. In particular, if no other metals are present in the first catalyst layer, Sn or Sn oxides are preferably present in a concentration of 55-70% on a metal element basis.

[0028] In another embodiment, the first catalytic layer comprises another valve metal selected from titanium, tantalum, and niobium in an amount, expressed as a mole percentage, of between 30 and 40% of the metal element. It has been observed that the presence of another valve metal, such as titanium, can combine excellent catalytic activity with a substantial increase in the resistance of the electrode in processes requiring current reversal.

[0029] In a preferred embodiment, excluding unavoidable impurities, the first catalyst layer consists of iridium, ruthenium, tin, and platinum, and optionally titanium, with molar percentages on a metal element basis in the ranges of 3-13% iridium, 24-34% ruthenium, 30-70% tin, 3-10% platinum, and 30-40% titanium.

[0030] The inventors have surprisingly observed that in the above catalytic coating, a phenomenon of interlayer diffusion occurs: tin from the first catalytic layer diffuses into the second layer, while platinum from the second catalytic layer diffuses into the first layer. The diffusion of tin into the second catalytic layer occurs in an end-to-end concentration gradient, with the amount of tin in the second catalytic layer being greatest at the interface between the two catalytic layers and decreasing toward the outer surface of the second catalytic layer.

[0031] The presence of diffused tin in the second catalyst layer can advantageously slow down the consumption of the precious metal present in the second catalyst layer, allowing optimal performance characteristics in terms of catalytic activity and selectivity to be maintained for a longer period of time without compromising catalytic performance.

[0032] Similarly, the diffusion of platinum from the second catalyst layer into the first catalyst layer is such that the amount of platinum in the first catalyst layer is greatest at the interface between the two catalyst layers and gradually decreases toward the inner surface of the first catalyst layer.

[0033] The diffusion of platinum into the first catalytic layer makes it possible to enhance catalytic activity, which further makes it possible to maintain better catalytic performance characteristics throughout the life of the electrode and even when prolonged use of the electrode causes wear of the second layer over time. The elements present and the specific structure of the catalytic coating make it possible to guarantee better performance characteristics compared to the prior art, with the added benefit of increasing the operating life of the electrode.

[0034] The electrode according to the invention also surprisingly makes it possible to maintain better performance characteristics in terms of activity and selectivity over time.

[0035] The presence of tin has a large effect on selectivity, but if tin is present in large amounts on the outer surface of the catalytic coating along with platinum, it counteracts the increased catalytic activity of the platinum itself.

[0036] As tin diffuses from the first catalyst layer to the second, a concentration profile of the element is created between the layers, which allows for maintaining high catalytic activity with optimal selectivity and slowing down the consumption of the precious metal present in the second catalyst layer. The tin concentration profile between the two catalyst layers is characterized by a monotonically decreasing concentration of the element in the second layer in the opposite direction to that in the first layer.

[0037] In another embodiment, the first catalyst layer has a coating weight of 3 to 8 g / m 2 and the second catalyst layer has a specific precious metal loading in the range of 0.8 to 4 g / m 2 The present inventors have found that such reduced precious metal loadings are more than sufficient to provide optimum catalytic activity.

[0038] According to another aspect, the present invention provides a method for producing a method of manufacturing a semiconductor device comprising: a. applying a platinum-free first solution containing a mixture of iridium, ruthenium, and tin to a valve metal substrate, followed by drying at 50-60°C and decomposing the first solution by heat treatment at 400-650°C for 5-30 minutes; b. repeating step a) until said first catalyst composition having a desired specific precious metal loading is obtained; c. applying a tin-free second catalytic solution containing platinum, followed by drying at 50-60°C and decomposing the first solution by heat treatment at 400-650°C for 5-30 minutes; d. repeating step c) until the first catalyst composition having the desired specific precious metal loading is obtained. The present invention relates to a method for obtaining an electrode for generating gaseous products in an electrolytic cell, for example for generating chlorine in an alkaline brine electrolytic cell, comprising:

[0039] In one embodiment, the temperature of the pyrolysis in steps a) and c) is between 480 and 550°C.

[0040] In one embodiment, the first solution further comprises titanium.

[0041] In another embodiment, the second solution comprises palladium and rhodium, either alone or in combination with each other.

[0042] In a preferred embodiment of the invention, the two-layer electrode is subjected to a final heat treatment, which in one embodiment is carried out at a temperature between 400 and 650°C, preferably at a temperature of approximately 500°C, for at least 60 minutes, preferably between 60 and 180 minutes, more preferably between 80 and 120 minutes.

[0043] Preferably, the first solution comprises iridium, ruthenium, and tin compounds, and optionally titanium compounds, in the form of organometallic complexes, hi one embodiment, the organometallic complexes are aceto-hydroxychloride complexes of tin, ruthenium, iridium, and optionally titanium, respectively.

[0044] Without wishing to be limited to a particular scientific theory, since the diffusion coefficients of the elements present in said first and said second solutions also depend on the temperature, the heat treatment or decomposition steps a and c of the above method, together with the elements present and their concentrations, may contribute to the interdiffusion of the tin and platinum present from the first catalyst layer to the second catalyst layer and vice versa, respectively.

[0045] According to another aspect, the present invention relates to a cell for the electrolysis of alkaline chloride solutions, comprising an anodic compartment and a cathodic compartment, the anodic compartment being equipped with an electrode of one of the above-described configurations, the electrode being used as an anode for generating chlorine.

[0046] According to another aspect, the present invention relates to an industrial electrolytic cell for producing chlorine and alkali from an alkali chloride solution, even if it does not include a bias protection device and comprises a modular arrangement of electrolytic cells having an anode compartment and a cathode compartment separated by an ion exchange membrane or diaphragm, the anode compartment comprising an electrode of one of the above-described forms used as an anode.

[0047] The following examples are included to demonstrate specific embodiments of the invention, the feasibility of which is fully verified within the scope of the claimed values. It will be apparent to those skilled in the art that the compositions and techniques described in the following examples represent compositions and techniques that the inventors have found to work well in practice for the present invention. However, those skilled in the art will further appreciate in light of the description of the invention that various modifications can be made to the various embodiments described and still produce the same or similar results without departing from the scope of the invention. [Example]

[0048] Example 1 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0049] A 100 ml first acetic acid solution was then prepared containing an acetate-hydroxychloride complex of tin, an acetate-hydroxychloride complex of ruthenium, and an acetate-hydroxychloride complex of iridium, having a molar composition equal to 25% Ru, 11% Ir, and 64% Sn on a metals basis.

[0050] A second solution was also prepared containing an amount of Pt diaminodinitrate, Pt(NH3)2(NO3)2, equivalent to 40 g of Pt dissolved in 160 ml of glacial acetic acid, then made up to a volume of 1 liter with 10 wt% acetic acid.

[0051] The first acetic acid solution was applied to the titanium mesh in eight coats, each followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes, with the mesh being cooled in air each time before the next coat was applied.

[0052] The metal loading expressed as the sum of Ir and Ru is 7 g / m 2 This procedure was repeated until it was equal to

[0053] The second solution was then applied in four coats, each followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. After each coat, the mesh was cooled in air before applying the next coat.

[0054] Total Pt loading was 2.5 g / m 2 This procedure was repeated until

[0055] A final heat treatment at 500°C for 100 minutes was finally carried out.

[0056] The electrode thus obtained was designated as sample no.

[0057] Example 2 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0058] A 100 ml first acetic acid solution was then prepared containing an acetate-hydroxychloride complex of tin, an acetate-hydroxychloride complex of ruthenium, and an acetate-hydroxychloride complex of iridium, having a molar composition equal to 26% Ru, 10% Ir, and 64% Sn on a metals basis.

[0059] A second 100 ml acetic acid solution was also prepared containing an organometallic complex of platinum and an organometallic complex of palladium, with a molar composition equal to 87% Pt and 13% Pd on a metals basis.

[0060] The first acetic acid solution was applied to the titanium mesh in eight coats. After each coat, a drying step was performed at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The mesh was cooled in air before each subsequent coat.

[0061] The metal loading, expressed as the sum of Ir and Ru, is 6.7 g / m 2 This procedure was repeated until it was equal to

[0062] The second acetic acid solution was then applied in four coats, each followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. After each coat, the mesh was cooled in air before applying the next coat.

[0063] Total precious metal loading, expressed as the sum of Pt and Pd, is 2.7 g / m 2 This procedure was repeated until it was equal to

[0064] Finally, a final heat treatment was carried out at 500°C for 100 minutes.

[0065] The electrode thus obtained was designated as sample no. 2.

[0066] Example 3 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0067] A 100 ml first acetic acid solution was then prepared containing an acetate-hydroxychloride complex of tin, an acetate-hydroxychloride complex of ruthenium, and an acetate-hydroxychloride complex of iridium, having a molar composition equal to 26% Ru, 10% Ir, and 64% Sn on a metals basis.

[0068] A second 100 ml acetic acid solution was then prepared containing an organometallic complex of platinum, an organometallic complex of palladium, and RhCl3, with a molar composition equal to 86% Pt, 10% Pd, and 4% Rh on a metals basis.

[0069] The first acetic acid solution was applied to the titanium mesh in eight coats. After each coat, a drying step was performed at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The mesh was cooled in air before each subsequent coat.

[0070] The metal loading, expressed as the sum of Ir and Ru, is 6.7 g / m 2 This procedure was repeated until it was equal to

[0071] The second acetic acid solution was then applied in four coats, each followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. After each coat, the mesh was cooled in air before applying the next coat.

[0072] Total precious metal loading, expressed as the sum of Pt, Pd, and Rh, is 2.8 g / m 2 This procedure was repeated until it was equal to

[0073] Finally, a final heat treatment was carried out at 500°C for 100 minutes.

[0074] The electrode thus obtained was designated as sample no.

[0075] Example 4 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0076] A 100 ml first acetic acid solution was then prepared containing an acetate-hydroxychloride complex of tin, an acetate-hydroxychloride complex of ruthenium, an acetate-hydroxychloride complex of iridium, and an acetate-hydroxychloride complex of titanium, having a molar composition equal to 25% Ru, 10% Ir, 35% Sn, and 30% Ti on a metals basis.

[0077] A second 100 ml acetic acid solution was also prepared containing an organometallic complex of platinum and an organometallic complex of palladium, with a molar composition equal to 87% Pt and 13% Pd on a metals basis.

[0078] The first acetic acid solution was applied to the titanium mesh in eight coats. After each coat, a drying step was performed at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The mesh was cooled in air before each subsequent coat.

[0079] The metal loading expressed as the sum of Ir and Ru was 6.7 g / m 2 This procedure was repeated until it was equal to

[0080] The second acetic acid solution was then applied in four coats, each followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. After each coat, the mesh was cooled in air before applying the next coat.

[0081] Total precious metal loading, expressed as the sum of Pt and Pd, is 2.7 g / m 2 This procedure was repeated until it was equal to

[0082] Finally, a final heat treatment was carried out at 500°C for 100 minutes.

[0083] The electrode thus obtained was designated as sample no.

[0084] Example 5 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0085] A 100 ml first acetic acid solution was then prepared containing an acetate-hydroxychloride complex of tin, an acetate-hydroxychloride complex of ruthenium, an acetate-hydroxychloride complex of iridium, and an acetate-hydroxychloride complex of titanium, having a molar composition equal to 25% Ru, 10% Ir, 35% Sn, and 30% Ti on a metals basis.

[0086] A second 100 ml acetic acid solution was also prepared containing an organometallic complex of platinum, an organometallic complex of palladium, and RhCl3, with a molar composition equal to 86% Pt, 10% Pd, and 4% Rh on a metals basis.

[0087] The first acetic acid solution was applied to the titanium mesh in eight coats. After each coat, a drying step was performed at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The mesh was cooled in air before each subsequent coat.

[0088] The metal loading, expressed as the sum of Ir and Ru, is 6.7 g / m 2 This procedure was repeated until it was equal to

[0089] The second solution was then applied in four coats, each followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. After each coat, the mesh was cooled in air before applying the next coat.

[0090] Total precious metal loading, expressed as the sum of Pt, Pd, and Rh, is 2.7 g / m 2 This procedure was repeated until it was equal to

[0091] Finally, a final heat treatment was carried out at 500°C for 100 minutes.

[0092] The electrode thus obtained was designated as sample no.

[0093] Counterexample 1 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0094] Then, RuCl3 * 3H2O, H2IrCl6 * A 100 ml aqueous alcoholic solution was prepared containing a solution of 6H2O, TiCl3 in isopropanol, with a molar composition equal to 23% Ru, 22% Ir, and 55% Ti.

[0095] The solution was applied to a titanium mesh by painting it in 14 coats, each of which was followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The workpiece was cooled in air before each subsequent coat.

[0096] The total loading of precious metals, expressed as the sum of Ir and Ru, is 11 g / m 2 This procedure was repeated until the temperature reached a value equal to 100° C. A final heat treatment was then carried out at 500° C. for 100 minutes.

[0097] The electrode thus obtained was designated specimen number 1C.

[0098] Counterexample 2 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0099] A 100 ml first acetic acid solution was then prepared containing an acetate-hydroxychloride complex of tin, an acetate-hydroxychloride complex of ruthenium, and an acetate-hydroxychloride complex of iridium, having a molar composition equal to 26% Ru, 10% Ir, and 64% Sn on a metals basis.

[0100] A second 100 ml acetic acid solution was also prepared containing an organometallic complex of platinum and an acetato-hydroxychloride complex of tin, with a molar composition equal to 87% Pt and 13% Sn on a metals basis.

[0101] The first acetic acid solution was applied to the titanium mesh in six coats. After each coat, a drying step was performed at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The mesh was cooled in air before each subsequent coat.

[0102] The total loading of precious metals expressed as the sum of Ir and Ru is 6 g / m 2 This procedure was repeated until it was equal to

[0103] The second acetic acid solution was then applied in four coats, each followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. After each coat, the mesh was cooled in air before applying the next coat.

[0104] Total metal loading of precious metal expressed as Pt is 2.5 g / m 2 This procedure was repeated until it was equal to

[0105] Finally, a final heat treatment was carried out at 500°C for 100 minutes.

[0106] The electrode thus obtained was designated sample number 2C.

[0107] Counterexample 3 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0108] A 100 ml first acetic acid solution was then prepared containing an acetate-hydroxychloride complex of tin, an acetate-hydroxychloride complex of ruthenium, an acetate-hydroxychloride complex of iridium, and an organometallic complex of platinum, having a molar composition equal to 25% Ru, 10% Ir, 35% Sn, and 30% Pt on a metals basis.

[0109] The acetic acid solution was applied to the titanium mesh in ten coats. After each coat, a drying step was carried out at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The mesh was cooled in air before each coat.

[0110] Total precious metal loading, expressed as the sum of Ir, Ru, and Pt, is 8 g / m 2 This procedure was repeated until it was equal to

[0111] Finally, a final heat treatment was carried out at 500°C for 100 minutes.

[0112] The electrode thus obtained was designated sample number 3C.

[0113] Counterexample 4 A titanium mesh measuring 10 cm x 10 cm was washed three times in deionized water at 60 °C, changing the liquid each time. After washing, it was heat-treated at 350 °C for 2 hours. The mesh was then boiled in a solution of 20% HCl for 30 minutes.

[0114] Then, RuCl3 in a mixture of water and 1-butanol acidified with HCl * 3H2O, H2IrCl6 * A 100 ml aqueous alcoholic solution was prepared containing 6H2O, TiOCl2, and having a molar composition equal to 26% Ru, 23% Ir, and 51% Ti on a metals basis.

[0115] A second 100 ml aqueous alcoholic solution containing H2PtCl6 and PdCl2 was also prepared.

[0116] The first acetic acid solution was applied to the titanium mesh in eight coats. After each coat, a drying step was performed at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The mesh was cooled in air before each subsequent coat.

[0117] The total loading of precious metals expressed as the sum of Ir and Ru is 6 g / m 2 This procedure was repeated until it was equal to

[0118] The second acetic acid solution was then applied in four coats, each followed by a drying step at 50-60°C for approximately 10 minutes, followed by a heat treatment at 500°C for 10 minutes. After each coat, the mesh was cooled in air before applying the next coat.

[0119] Total precious metal loading expressed as the sum of Pt and Pd is 3 g / m 2 This procedure was repeated until it was equal to

[0120] Finally, a final heat treatment was carried out at 500°C for 100 minutes.

[0121] The electrode thus obtained was designated sample number 4C.

[0122] The example and counter example specimens were characterized as anodes for chlorine generation in a laboratory cell filled with a brine solution of sodium chloride at a concentration of 200 g / l.

[0123] Table 1 shows the 2 The chlorine overpotential measured at a current density of 1000 kJ / s and the volume percentage of oxygen in the chlorine produced are reported. TIFF0007814931000001.tif103170

[0124] The specimens from the previous examples were also tested for operation in a beaker. Table 2 shows the results measured in a 200 g / l sodium chloride solution at a temperature of 80°C, with a resistance of 3 kA / m 2 The ohmic drop corrected anodic potential (CISEP) at a current density of 3 kA / m is reported. Furthermore, to evaluate the selectivity towards chlorine reaction, the test was performed in sulfuric acid at 3 kA / m 2 The anodic potentials (CISEP) reported were corrected for ohmic drop. The higher the anodic potential measured in sulfuric acid, the greater the selectivity for the chlorine reaction. TIFF0007814931000002.tif109170

[0125] Finally, some specimens were subjected to a service life test, which simulated the conditions of industrial electrolysis in separate cells. Table 3 shows the 8 kA / m of the specimens at the start of the test and after a simulated period of one year, as an indicator of their catalytic activity for chlorine evolution. 2 The cell voltage (Cl 0V) measured at a current density of 1000 kJ / cm 2 and the percentage loading remaining in the second catalyst layer after a simulated one year period are reported. TIFF0007814931000003.tif49170

[0126] The foregoing description is not intended to limit the present invention, which can be utilized in various embodiments without departing from its scope, the scope of which is uniquely defined by the appended claims.

[0127] In the description and claims of this application, the terms "comprising," "including," and "containing" are not intended to exclude the presence of other additional elements, components, or process steps.

[0128] The discussion of documents, items, materials, devices, articles and the like is included in this description solely for the purpose of providing a context for the invention, and is not intended to suggest or represent that any or all of these topics formed part of the prior art or common general knowledge in the art to which this invention pertains prior to the priority date of each claim of this application.

Claims

1. a) applying a platinum-free first solution containing a mixture of iridium, ruthenium, and tin to a valve metal substrate, followed by drying at 50-60°C and decomposing the first solution by heat treatment at 400-650°C for 5-30 minutes, wherein the first solution contains the iridium, ruthenium, and tin in the form of an organometallic complex; b) repeating step a) until the desired specific precious metal loading is reached; c) applying a tin-free second catalytic solution containing platinum, followed by drying at 50-60°C and decomposing the second catalytic solution by heat treatment at 400-650°C for 5-30 minutes; d) repeating step c) until the desired specific precious metal loading is reached; and e) subjecting the electrode to a final heat treatment at a temperature of 400-650°C for at least 60 minutes; 1. A method for producing an electrode for generating gas in an electrolytic process, comprising:

2. 2. The method of claim 1, wherein the temperature of the heat treatment in steps a) and c) is between 480 and 550°C.

3. 1. An electrode for generating gas in an electrolysis process, comprising a valve metal substrate and a coating, the coating comprising: a first catalyst layer formed on the substrate, the first catalyst layer containing iridium, ruthenium, tin, and platinum, or an oxide thereof, or a combination thereof, the first catalyst layer being obtained from a precursor containing the iridium, ruthenium, and tin in the form of an organometallic complex; and a second catalyst layer formed on the first catalyst layer, the second catalyst layer containing platinum and tin, or an oxide thereof, or a combination thereof, the tin in the second catalyst layer being present in a concentration that decreases from a surface in contact with the first catalyst layer, and the platinum in the first catalyst layer being present in a concentration that decreases from a surface in contact with the second catalyst layer; 3. An electrode, wherein the electrode is obtainable by the method of claim 1 or 2.

4. 1. An electrode for generating gas in an electrolysis process, comprising a valve metal substrate and a coating, the coating comprising: a first catalytic layer formed on the substrate and containing a mixture of iridium, ruthenium, tin, and platinum, or oxides thereof, or combinations thereof; and a second catalytic layer formed on the first catalytic layer and containing platinum and tin, or oxides thereof, or combinations thereof; 3. An electrode, wherein the electrode is obtainable by the method of claim 1 or 2.

5. 5. The electrode according to claim 3, wherein the second catalyst layer contains Pt in the form of metal or its oxide in an amount of 48 to 96% by mole percentage based on the metal element.

6. 6. The electrode according to claim 3, wherein the second catalyst layer contains, in molar percentages based on the metal elements, Pd=0 to 24% or Rh=0 to 24% in the form of a metal or an oxide thereof, or a combination thereof.

7. 7. The electrode according to claim 3, wherein the second catalyst layer contains, in an average molar percentage based on the metal element, Sn=4 to 12% in the form of metal or its oxide.

8. 8. The electrode according to claim 3, wherein the oxides of iridium, ruthenium, and tin in the first catalytic layer are present in the following molar percentages based on metal elements: Ru=24 to 34%, Ir=3 to 13%, and Sn=30 to 70%.

9. 9. The electrode according to claim 3, wherein the first catalyst layer also contains an oxide of titanium in a molar percentage based on the metal element of Ti=30 to 40%.

10. 10. The electrode according to claim 3, wherein the first catalyst layer contains Pt=3 to 10% in the form of metal or its oxide, in an average molar percentage based on the metal element.

11. 11. The electrode of any one of claims 3 to 10, wherein the valve metal substrate is selected from the group consisting of titanium, tantalum, zirconium, niobium, tungsten, aluminum, silicon, or alloys thereof.

12. A cell for electrolysis of an alkali chloride solution, comprising an anode chamber and a cathode chamber, the anode chamber being equipped with an electrode according to any one of claims 3 to 11.

13. 13. The electrolysis cell according to claim 12, wherein the anode chamber and the cathode chamber are separated by a diaphragm or an ion exchange membrane.

14. 13. An electrolytic cell for producing chlorine and alkali from an alkali chloride solution, comprising a modular arrangement of cells, each cell being a cell according to claim 12.

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