TWI862529B - Electrode for electrolytic evolution of gas - Google Patents

Abstract

The invention relates to an electrode for evolution of gas in electrolytic processes comprising a substrate of valve metal and a catalytic coating comprising two layers. A first layer comprising oxides of valve metal, ruthenium and iridium and a second layer comprising one or more metals chosen from amongst elements of the platinum group.

Description

Electrode for releasing gas in electrolysis and its preparation method and electrolytic cell and electrolytic tank

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

The field of the invention relates to the manufacture of catalyst coatings for electrodes used in brine electrolysis processes. The coatings are applied to metal substrates, typically titanium or other valve metals.

Over the years, the technology of brine electrolysis has been evolving towards efficient implementation from an energy point of view and cost/benefit of resource use. In this increasingly challenging context, the optimization of the anode plays a key role. In particular, efforts have been made to reduce the overvoltage of the anode during chlorine production and to reduce the oxygen concentration in the produced chlorine, thus producing high-purity chlorine.

Another challenge is to obtain electrodes that can maintain high performance for a long time.

Generally speaking, the electrolysis of alkaline chloride brine, such as sodium chloride, to produce chlorine and caustic soda is carried out at an anode made of titanium or another valve metal, with a surface layer of ruthenium dioxide (RuO ₂ ), optionally mixed with tin dioxide (SnO ₂ ) and another precious metal, activated, for example, as described in EP 0153586. As a result, the overvoltage of the chlorine-releasing anode reaction can be reduced, thereby saving overall energy consumption.

The above data, as well as other formulations containing tin, also have the problem of reducing the overvoltage of oxygen reaction at the same time, resulting in the production of chlorine gas mixed with excess oxygen.

Another method that has achieved some improvement is to use a RuO ₂ and SnO ₂ formulation for the metal substrate with reduced IrO ₂ , such as described in WO2016083319. Such a formulation allows for a moderate battery potential and allows for a moderate amount of oxygen.

Other coatings of the prior art, such as the formulation described in WO2012081635, include two catalyst coatings, the first containing titanium and precious metal oxides, and the second containing platinum and palladium alloys, which also allow for an appropriate battery potential and reduce the amount of oxygen in the resulting chlorine gas; however, they fail to impart an appropriate resistance to the electrode to maintain a high level of performance in terms of catalyst activity and selectivity for an appropriate period of time.

US 2013/0186750 A1 describes an electrode suitable for releasing chlorine, which has two layers of alternating and distinct components, namely, the first layer includes iridium, ruthenium and valve metal, and the second layer includes oxides of iridium, ruthenium and tin.

[10] US 2013/0334037 A1 describes an electrode for electrolysis, comprising 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.

[11] US 4,626,334 describes an anode comprising a conductive substrate having a (Ru—Sn)O ₂ solid solution coating for brine electrolysis.

【12】JP S62243790 describes an electrode having a first coating layer including a mixture of platinum and iridium oxide, and a second coating layer including a mixture of ruthenium oxide and tin oxide.

[13] It is therefore evident that there is a need for new catalyst coatings for electrodes used in brine electrolysis processes to release gaseous products in electrolytic cells, characterized by a higher level of catalyst activity and a high electrical resistance capable of maintaining a higher level of performance for a long period of time under normal operating conditions of prior art formulations.

【14】The various gist of the present invention is described in the attached patent application.

[15] The present invention relates to an electrode for releasing a gaseous product in an electrolytic cell, such as a brine electrolytic cell for releasing chlorine, comprising a catalyst coating applied to a metal substrate. In the context of this case, the term catalyst coating refers to two different catalyst layers having different catalyst compositions, wherein the first catalyst layer is formed on the substrate and comprises at least iridium, ruthenium, tin and platinum, or a mixture of oxides thereof, or individual combinations thereof, and the second catalyst layer is formed on the first catalyst layer and comprises platinum and tin, or oxides thereof, or individual combinations thereof. The concentration of tin in the second catalyst layer decreases from the interface with the first catalyst layer toward the upper surface of the second catalyst layer, that is, the opposite surface of the interface with the first catalyst layer, while the concentration of platinum in the first catalyst layer decreases from the interface with the second catalyst layer toward the substrate.

[16] The present invention also relates to an electrode for releasing gaseous products in an electrolytic cell, such as chlorine in an alkaline brine electrolytic cell, comprising a valve metal substrate, and a coating, comprising a first catalyst layer formed on the substrate, containing iridium, ruthenium, tin and platinum, or a mixture of oxides thereof, or a combination thereof, and a second catalyst layer formed on the first catalyst layer, containing platinum and tin, or oxides thereof, or a combination thereof, wherein the first catalyst layer is obtained from a first precursor solution that does not contain platinum, comprising a mixture of iridium, ruthenium and tin, applied to the substrate and subjected to heat treatment, and wherein the second catalyst layer is obtained from a second catalyst solution that does not contain tin, containing platinum, applied to the first catalyst layer and subjected to heat treatment. The "platinum-free" and "tin-free" mentioned in the present invention mean that the platinum concentration in the first solution is at least lower than the average platinum concentration in the first layer obtained from the first solution, and the tin concentration in the second solution is at least lower than the average tin concentration in the second layer obtained from the second solution. Preferably, the platinum-free solution contains platinum as impurities at most, and the tin-free solution contains tin as impurities at most.

【17】A double-layer structure applied to a metal substrate, typically titanium, a titanium alloy or another valve metal, which saves energy consumption and produces chlorine gas of extremely high purity while maintaining the appropriate performance characteristics of catalyst activity and selectivity for a long time.

[18] The first catalyst layer formed on the substrate preferably includes ruthenium oxide, iridium oxide, tin oxide, and metallic titanium or its oxide. _RuO2 is known to have excellent catalytic activity and stability in alkaline media, which is improved by the presence of _IrO2 ; the presence of _SnO2 can ensure that the noble metal is consumed more slowly.

[19] The second catalyst layer formed on the first layer includes tin or its oxide, one or more metals selected from the platinum group, especially platinum itself, which is known to improve selectivity and reduce energy consumption.

[20] The inventors have observed that electrodes having similar catalyst coatings, wherein the second catalyst layer comprises platinum, in the form of a metal or its oxide, in a molar percentage ranging between 48 and 96% of the metal element (or 50 to 99.999% excluding the tin component), have the advantage of a concomitant reduction in the overvoltage in the chlorine release reaction.

【21】In the context of the present invention, the ranges referred to by “from” and “between…” include specific upper and lower limits, respectively.

[22] In another embodiment, in addition to platinum and tin, the second catalyst layer includes palladium or rhodium in the form of a metal or its oxide, or a combination thereof, in a range between 0 and 24% (or between 0 and 25% excluding the tin component) in terms of molar percentage of the metal element, wherein the element is in the form of a metal or its oxide. In this way, due to the presence of two or more noble metals in combination, a high catalytic activity can be ensured.

[23] The second catalyst layer preferably includes tin or its oxide, with an average molar percentage ranging from 4 to 12% in terms of the metal element. Since the concentration of the tin component varies in the vertical direction of the interface between the first and second layers, the tin concentration is the average value of the concentration cross section of the second catalyst layer.

[24] Therefore, in a preferred embodiment, the second catalyst layer is composed of platinum and tin, and optionally palladium and/or rhodium, excluding unavoidable impurities, and the molar percentage range of the metal elements is 48-96% platinum, 4-12% tin, 0-24% palladium, and 0-24% rhodium.

[25] According to a preferred embodiment of the above-mentioned electrode, the first catalyst layer includes metal or metal oxide of iridium, rhodium, and tin, and the molar percentage of metal elements is Ru = 24-34%, Ir = 3-13%, and Sn = 30-70%.

[26] The first catalyst layer preferably includes platinum or its oxide, with an average percentage in the range of 3-10% as a metal element. Since the concentration of the platinum component varies in the vertical direction of the interface between the first and second layers, the platinum concentration is the average value of the concentration cross section through the first catalyst layer.

[27] Needless to say, all technical experts will choose the molar percentages of the individual elements in such a way that the total molar percentages of the components add up to 100. In particular, if no other metal is present in the first catalyst layer, the concentration of Sn and Sn oxides is preferably 55-70% of the metal element.

[28] In another embodiment, the first catalyst layer comprises another valve metal selected from titanium, tantalum and niobium in an amount ranging between 30 and 40% in terms of molar percentage of the metal element; it has been observed that the presence of another valve metal such as titanium can improve the catalyst activity and substantially increase the resistance of the electrode in the process, requiring current reversal.

[29] In a preferred embodiment, the first catalyst layer contains iridium, ruthenium, tin and platinum, and optionally titanium, excluding unavoidable impurities, and the molar percentages of the metal elements range from 3-13% iridium, 24-34% ruthenium, 30-70% tin, 3-10% platinum, and 30-40% titanium.

[30] The inventors of the present invention unexpectedly observed that in the above-mentioned catalyst coating, diffusion occurs between layers: the tin in the first catalyst layer diffuses into the second layer, and the platinum in the second catalyst layer diffuses into the first layer. The diffusion of tin into the second catalyst layer creates a gradient across the concentration, so that the amount of tin in the second catalyst layer is the largest at the interface between the two catalyst layers and decreases toward the outer surface of the second catalyst layer.

【31】The presence of tin diffused into the second catalyst layer is beneficial to slow down the consumption of precious metals in the second catalyst layer, so that the optimal performance characteristics of catalyst activity and selectivity can be maintained for a longer period of time without damaging the catalyst performance. Similarly, platinum diffuses from the second catalyst layer into the first catalyst layer, so that the amount of platinum in the first catalyst layer is the largest at the interface between the two catalyst layers and gradually decreases toward the inner surface of the first catalyst layer.

【32】Platinum diffuses into the first catalyst layer to enhance the activity of the catalyst. This allows the catalyst to maintain better performance characteristics during the use of the electrode. Extended use will cause the second layer to wear out over time. The existing elements and the special structure of the catalyst coating can achieve better performance characteristics than previous technologies, ensuring another advantage of increasing the operating life of the electrode.

【33】The electrode of the present invention can unexpectedly maintain excellent performance characteristics such as activity and selectivity for a long time.

【34】The presence of tin has a significant impact on selectivity; however, if tin is present in large quantities on the outer surface of the catalyst coating, the addition of platinum will weaken the catalytic activity of platinum itself.

【35】Sn diffuses from the first catalyst layer into the second catalyst layer, producing a concentration cross section of the element between the layers, which can maintain a high catalyst activity with optimal selectivity and slow down the consumption of precious metals in the second catalyst layer. The concentration cross section between the two catalyst layers is characterized by a monotonically decreasing element concentration in the second layer in the opposite direction of the first layer.

[36] In another embodiment, the specific loading of the precious metal in the first catalyst layer is between 3 and 8 g/m ² , and the specific loading of the precious metal in the second catalyst layer is between 0.8 and 4 g/m ^2. The inventors have found that the reduction in the precious metal loading is sufficient to impact the optimal catalyst activity.

[37] According to another aspect, the present invention relates to a method for preparing an electrode for releasing a gaseous product in an electrolytic cell, such as releasing chlorine in an alkaline brine electrolytic cell, comprising the following stages:

a. Apply a first catalyst solution that does not contain platinum, including a mixture of iridium, ruthenium and tin, to the valve metal substrate, then dry at 50-60°C, and heat treat at 400-650°C for 5-30 minutes to decompose the first solution;

b. Repeat stage a until the first catalyst composition obtains the required specific loading of precious metals;

c. Apply a second catalyst solution that does not contain tin but contains platinum, then dry at 50-60°C and heat treat at 400-650°C for 5-30 minutes, the second solution decomposing;

d. Repeat stage c until the second catalyst composition obtains the required specific loading of precious metals.

[38] In one embodiment, the thermal decomposition temperature of stages a and c is between 480 and 550°C.

[39] In one embodiment, the first solution further includes titanium.

[40] In another embodiment, the second solution includes palladium and rhodium, either alone or in combination.

[41] In a preferred embodiment of the present invention, the second electrode layer undergoes a final heat treatment. In one embodiment, the final heat treatment is performed at a temperature between 400 and 650°C, preferably around 500°C, for at least 60 minutes, preferably 60-180 minutes, and more preferably 80-120 minutes.

[42] Preferably, the first solution comprises iridium, ruthenium and tin compounds, and optionally a titanium compound, to form an organic metal complex. In one embodiment, the organic metal complex is a hydroxyacetate chloride complex of tin, ruthenium, iridium and optionally titanium.

[43] Without wishing to be bound by a particular scientific theory, the heat treatment and decomposition of the above method can be carried out in stages a and c, with the addition that the elements present in the first and second solutions, and their concentrations, because their diffusion coefficients depend on the temperature, favor the intermediate diffusion of the tin and platinum present, respectively, from the first catalyst layer to the second catalyst layer, or vice versa.

[44] According to another aspect, the present invention relates to an electrolytic cell for an alkaline chloride solution, comprising an anodic chamber and a cathodic chamber, wherein the anodic chamber is provided with an electrode of one of the above-mentioned types as an anode for releasing chlorine gas.

[45] According to another aspect, the invention relates to an industrial electrolytic cell for producing chlorine and alkali from an alkaline chloride solution, and in the absence of a bias protection device, comprises a modular arrangement of an electrolytic cell having an anode chamber and a cathode chamber separated by an ion exchange membrane or by a diaphragm, wherein the anode chamber comprises an electrode of one of the above-mentioned types as an anode.

【46】The following examples are used to demonstrate the specific embodiments of the present invention and can fully demonstrate the numerical range of the scope of the patent application. It is obvious to any technical expert that the compositions and technologies contained in the following examples represent the compositions and technologies encountered in the actual good operation of the present invention; however, in view of the description of this case, technical experts can also know that the above-mentioned various compositions can have various changes and still obtain the same or similar results without violating the scope of the present invention.

【47】Implementation Example 1

【48】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

[49] Prepare 100 ml of a first acetic acid solution containing tin complex acetyl hydroxy chloride, ruthenium complex acetyl hydroxy chloride and iridium complex acetyl hydroxy chloride, with a molar composition equal to 25% Ru, 11% Ir and 64% Sn, based on the metals.

[50] A second solution was prepared containing platinum diamino dinitrate Pt(NH ₃ ) ₂ (NO ₃ ) ₂ in an amount equivalent to 40 g of Pt dissolved in 160 ml of glacial acetic acid, to make a 10% by weight solution of acetic acid in a volume of 1 liter.

【51】The first acetic acid solution was applied to the titanium mesh and the paint was applied in 8 times. After each application, a drying step was performed at 50-60°C for about 10 minutes, and then a heat treatment was performed at 500°C for 10 minutes. The mesh was cooled in the wind each time before the next application.

[52] This procedure was repeated until the loading, expressed as a total of Ir and Ru, reached 7 g/m ² on a metal basis.

【53】Then, the second solution was applied and the paint was applied in 4 times. After each application, a drying step was carried out at 50-60℃ for about 10 minutes, and then heat-treated at 500℃ for 10 minutes. The net was cooled in the air each time before the next application.

[54] This procedure was repeated until the total Pt loading was equal to 2.5 g/m ² .

【55】Finally, a final heat treatment was performed at 500°C for 100 minutes.

【56】The obtained electrode is labeled as sample No. 1.

【57】Implementation Example 2

【58】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

[59] Prepare 100 ml of a first acetic acid solution containing tin complex acetyl hydroxy chloride, ruthenium complex acetyl hydroxy chloride and iridium complex acetyl hydroxy chloride, with a molar composition equal to 26% Ru, 10% Ir and 64% Sn, based on the metals.

【60】Prepare 100 ml of a second acetic acid solution containing an organometallic complex of platinum and an organometallic complex of palladium with a molar composition of 87% Pt and 13% Pd, based on the metals.

【61】The first acetic acid solution was applied to the titanium mesh and the paint was applied in 8 times. After each application, a drying step was carried out at 50-60℃ for about 10 minutes, and then a heat treatment was carried out at 500℃ for 10 minutes. The mesh was cooled in the wind each time before the next application.

[62] This procedure was repeated until the loading, expressed as a total of Ir and Ru, reached 6.7 g/m ² on a metal basis.

【63】Then, a second acetic acid solution was applied, and the paint was applied in 4 passes. After each pass, a drying step was performed at 50-60°C for about 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The net was cooled in the wind each time before the next pass was applied.

[64] This procedure was repeated until the total precious metal loading, calculated as Pt and Pd, reached 2.7 g/m ² .

【65】Finally, a final heat treatment was performed at 500°C for 100 minutes.

【66】The obtained electrode is labeled as sample No. 2.

【67】Implementation Example 3

【68】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

[69] Prepare 100 ml of a first acetic acid solution containing tin complex acetyl hydroxy chloride, ruthenium complex acetyl hydroxy chloride and iridium complex acetyl hydroxy chloride, with a molar composition equal to 26% Ru, 10% Ir and 64% Sn, based on the metals.

[70] A second acetic acid solution (100 ml) was prepared containing an organometallic complex of platinum, an organometallic complex of palladium and RhCl ₃ , with a molar composition equal to 86% Pt, 10% Pd and 4% Rh, based on the metals.

【71】The first acetic acid solution was applied to the titanium mesh and the paint was applied in 8 times. After each application, a drying step was carried out at 50-60℃ for about 10 minutes, and then heat treated at 500℃ for 10 minutes. The mesh was cooled in the wind each time before the next application.

[72] This procedure was repeated until the loading, expressed as a total of Ir and Ru, reached 6.7 g/m ² on a metal basis.

【73】Then, a second acetic acid solution was applied, and the paint was applied in 4 passes. After each pass, a drying step was performed at 50-60°C for about 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The net was cooled in the wind each time before the next pass was applied.

[74] This procedure was repeated until the total precious metal loading, expressed as the sum of Pt, Pd and Rh, reached 2.8 g/m ² for each metal.

【75】Finally, a final heat treatment was performed at 500°C for 100 minutes.

【76】The obtained electrode is labeled as sample No. 3.

【77】Implementation Example 4

【78】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

[79] Prepare 100 ml of a first acetic acid solution containing tin complex acetyl hydroxy chloride, ruthenium complex acetyl hydroxy chloride, iridium complex acetyl hydroxy chloride, and titanium complex acetyl hydroxy chloride, with a molar composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Ti, calculated on a metal basis.

[80] Prepare a second acetic acid solution (100 ml) containing an organometallic complex of platinum and an organometallic complex of palladium with a molar composition of 87% Pt and 13% Pd, based on the metals.

【81】The first acetic acid solution was applied to the titanium mesh and the paint was applied in 8 times. After each application, a drying step was carried out at 50-60℃ for about 10 minutes, and then heat treated at 500℃ for 10 minutes. The mesh was cooled in the wind each time before the next application.

[82] This procedure was repeated until the loading, expressed as a total of Ir and Ru, reached 6.7 g/m ² on a metal basis.

【83】Then, a second acetic acid solution was applied, and the paint was applied in 4 passes. After each pass, a drying step was performed at 50-60°C for about 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The net was cooled in the wind each time before the next pass was applied.

[84] This procedure was repeated until the total precious metal loading, expressed as the sum of Pt and Pd, reached 2.7 g/m ² , calculated as metal.

【85】Finally, a final heat treatment was performed at 500°C for 100 minutes.

【86】The obtained electrode is labeled as sample No. 4.

【87】Implementation Example 5

【88】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

[89] Prepare 100 ml of a first acetic acid solution containing tin complex acetyl hydroxy chloride, ruthenium complex acetyl hydroxy chloride, iridium complex acetyl hydroxy chloride, and titanium complex acetyl hydroxy chloride, with a molar composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Ti, calculated on a metal basis.

[90] A second acetic acid solution (100 ml) was prepared containing an organometallic complex of platinum, an organometallic complex of palladium and RhCl ₃ , the molar composition of which, based on the metals, was equal to 86% Pt, 10% Pd and 4% Rh.

【91】The first acetic acid solution was applied to the titanium mesh and the paint was applied in 8 times. After each application, a drying step was carried out at 50-60℃ for about 10 minutes, and then heat treated at 500℃ for 10 minutes. The mesh was cooled in the wind each time before the next application.

[92] This procedure was repeated until the loading, expressed as a total of Ir and Ru, reached 6.7 g/m ² on a metal basis.

【93】Then, the second solution was applied in 4 coats. After each coat, a drying step was carried out at 50-60°C for about 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The net was cooled in the wind each time before the next coat was applied.

[94] This procedure was repeated until the total precious metal loading, expressed as the sum of Pt, Pd and Rh, reached 2.7 g/m ² for each metal.

【95】Finally, a final heat treatment was performed at 500°C for 100 minutes.

【96】The obtained electrode is labeled as sample No. 5.

【97】Comparison Example 1

【98】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

【99】Prepare 100 ml of an alcohol-water solution containing RuCl ₃ ． 3H ₂ O, H ₂ IrCl _{6 ．} 6H ₂ O and TiCl ₃ in propanol solution, with a molar composition equal to 23% Ru, 22% Ir and 55% Ti.

【100】This solution was applied to the titanium mesh and the paint was applied in 14 times. After each application, a drying step was performed at 50-60°C for about 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The workpiece was cooled in the wind each time before the next application.

[101] This procedure was repeated until the precious metal loading, expressed as the sum of Ir and Ru, reached 11 g/m ² on a metal basis. A final heat treatment was then carried out at 500°C for 100 minutes.

【102】The obtained electrode is labeled as sample 1C.

【103】Comparison Example 2

【104】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

[105] Prepare 100 ml of a first acetic acid solution containing tin complex acetyl hydroxy chloride, ruthenium complex acetyl hydroxy chloride and iridium complex acetyl hydroxy chloride, with a molar composition equal to 26% Ru, 10% Ir and 64% Sn, based on the metals.

[106] Prepare a second acetic acid solution of 100 ml containing an organometallic complex of platinum and a tin complex acetylhydroxy chloride having a molar composition equal to 87% Pt and 13% Sn, based on the metals.

[107] The first acetic acid solution was applied to the titanium mesh and the paint was applied in 6 times. After each application, a drying step was carried out at 50-60℃ for about 10 minutes, and then heat treated at 500℃ for 10 minutes. The mesh was cooled in the wind each time before the next application.

[108] This procedure was repeated until the total precious metal loading, expressed as the sum of Ir and Ru, reached 6 g/m ² , calculated on a metal basis.

【109】Then, a second acetic acid solution was applied, and the paint was applied in 4 passes. After each pass, a drying step was performed at 50-60°C for about 10 minutes, and then a heat treatment was performed at 500°C for 10 minutes. The net was cooled in the wind each time before the next pass was applied.

[110] This procedure was repeated until the total precious metal loading, expressed as Pt, reached 2.5 g/m ² .

【111】Finally, a final heat treatment was performed at 500°C for 100 minutes.

【112】The obtained electrode is labeled as sample 2C.

【113】Comparison Example 3

【114】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

[115] Prepare 100 ml of a first acetic acid solution containing an organometallic complex of tin complex acetyl hydroxy chloride, ruthenium complex acetyl hydroxy chloride, iridium complex acetyl hydroxy chloride and platinum, with a molar composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Pt, based on the metals.

【116】Acetic acid solution was applied to the titanium mesh and the paint was applied in 10 times. After each application, a drying step was carried out at 50-60℃ for about 10 minutes, and then heat treated at 500℃ for 10 minutes. The mesh was cooled in the wind each time before the next application.

[117] This procedure was repeated until the total precious metal loading, expressed as the sum of Ir, Ru and Pt, reached 8 g/m ² .

【118】Finally, a final heat treatment was performed at 500°C for 100 minutes.

【119】The obtained electrode is labeled as sample 3C.

【120】Comparison Example 4

【121】Take a titanium mesh of size 10cm×10cm and wash it three times in deionized water at 60℃, changing the liquid each time. After washing, heat treat it at 350℃ for 2 hours. The mesh is then treated in a 20% HCl solution and boiled for 30 minutes.

[122] A first alcoholic aqueous solution (100 ml) containing RuCl _{3 .} 3H ₂ O, H ₂ IrCl _{6 .} 6H ₂ O and TiCl ₃ was prepared in a mixture of water and 1-butanol, acidified with HCl, and having a molar composition, based on the metals, equal to 26% Ru, 23% Ir and 51% Ti.

【123】Prepare 100 ml of a second alcohol aqueous solution containing H ₂ PtCl ₆ and PdCl ₂ .

【124】The first acetic acid solution was applied to the titanium mesh and the paint was applied in 8 times. After each application, a drying step was carried out at 50-60°C for about 10 minutes, and then a heat treatment was carried out at 500°C for 10 minutes. The mesh was cooled in the wind each time before the next application.

[125] This procedure was repeated until the total precious metal loading, expressed as the sum of Ir and Ru, reached 6 g/m ² , calculated on a metal basis.

【126】Then, a second acetic acid solution was applied, and the paint was applied in 4 passes. After each pass, a drying step was performed at 50-60°C for about 10 minutes, followed by a heat treatment at 500°C for 10 minutes. The net was cooled in the wind each time before the next pass was applied.

[127] This procedure was repeated until the total precious metal loading, expressed as Pt+Pd, reached 3 g/m ² , calculated on a metal basis.

【128】Finally, a final heat treatment was performed at 500°C for 100 minutes.

【129】The obtained electrode is labeled as sample 4C.

[130] The samples of the embodiment and comparative example were tested as anodes for releasing chlorine gas in a laboratory cell filled with a sodium chloride aqueous solution with a concentration of 200 g/l.

【131】Table 1 lists the chlorine overvoltage measured at a current density of 4 kA/m ² and the oxygen content percentage in the produced chlorine.

【132】The samples in the above example were also tested in a beaker.

【133】Table 2 lists the anodic potential (CISEP) measured in a sodium chloride solution with a concentration of 200 g/l at a temperature of 80°C, corrected for the resistance drop at a current density of 3 kA/m ^2. Furthermore, to evaluate the selectivity of the chlorine reaction, the test was carried out in sulfuric acid at a current density of 3 kA/m ² ; the anodic potential (CISEP) listed has been corrected for the resistance drop. The higher the anodic potential measured in sulfuric acid, the greater the selectivity of the chlorine reaction.

[134] At the end of the test, some samples were subjected to a life test. The so-called life test simulates the separation of industrial electrolysis conditions in the battery. Table 3 lists the battery voltage of the samples at the beginning of the test and after a simulation period of one year, as an index of the catalyst activity measured as the chlorine released (Cl OV) at a current density of 8 kA/m ² , and the residual load percentage of the second catalyst layer after a simulation period of one year.

[135] The above description is not intended to limit the present invention, which can be used in various specific embodiments without violating its purpose, and its scope is solely limited by the scope of the attached patent application.

[136] In the description and scope of the patent application in this case, the words "include", "comprise" and "contain" are not intended to exclude other additional elements, ingredients or manufacturing steps.

【137】The documents, items, materials, equipment, papers, etc. contained in this specification are for the sole purpose of providing the content of the present invention. They do not advocate or represent that any or all of these issues formed part of the prior art or common knowledge in the field related to the present invention before the priority date of the patent application scope of this case.

Claims (15)

An electrode for releasing gas in an electrolytic process includes a valve metal substrate and a coating, the latter including a first catalyst layer formed on the substrate, containing iridium, ruthenium, tin and platinum, or a mixture of their oxides or combinations thereof, and a second catalyst layer formed on the first catalyst layer, containing platinum and tin, or their oxides or combinations thereof, wherein the concentration of the tin in the second catalyst layer decreases from the interface with the first catalyst layer, and wherein the concentration of the platinum in the first catalyst layer decreases from the interface with the second catalyst layer. An electrode for releasing gas in an electrolytic process includes a valve metal substrate and a coating, the latter including a first catalyst layer formed on the substrate, containing iridium, ruthenium, tin and platinum, or a mixture of their oxides or combinations thereof, and a second catalyst layer formed on the first catalyst layer, containing platinum and tin, or their oxides or combinations thereof, wherein the first catalyst layer is obtained from a first matrix solution without platinum, including a mixture of iridium, ruthenium and tin, applied to the substrate and heat-treated, and wherein the second catalyst layer is obtained from a second catalyst composition containing platinum but not tin, containing platinum, applied to the substrate and heat-treated. For example, the electrode in item 1 of the patent application, wherein the second catalyst layer contains Pt = 48-96%, in the form of metal or its oxide, expressed as a molar percentage of the reference metal element. For an electrode of any one of items 1 to 3 of the patent application, wherein the second catalyst layer contains Pd = 0-24% or Rh = 0-24%, in the form of metal, its oxide or combination, in the form of metal or its oxide, expressed as a molar percentage of the metal element. For an electrode as claimed in any one of items 1 to 3 of the patent application, the second catalyst layer contains Sn=4-12% in the form of metal or its oxide, expressed as an average molar percentage of the metal element. For an electrode of any one of items 1 to 3 of the patent application scope, the oxides of iridium, ruthenium and tin in the first catalyst layer are present in molar percentages of metal elements such as Ru=24-34%, Ir=3-13%, and Sn=30-70%. For an electrode in any of items 1 to 3 of the patent application, the first catalyst layer contains titanium oxide, and the molar percentage of the metal element is Ti = 30-40%. For an electrode as claimed in any one of items 1 to 3 of the patent application, the first catalyst layer contains Pt=3-10% in the form of metal or its oxide, expressed as an average molar percentage of the metal element. For an electrode of any one of items 1 to 3 of the patent application scope, the valve metal substrate is selected from the group consisting of titanium, tantalum, zirconium, niobium, tungsten, aluminum, silicon, or an alloy thereof. A method for producing an electrode defined in one of the aforementioned patent applications, comprising the following steps: (a) applying a first solution containing no platinum, including a mixture of iridium, ruthenium and tin, to a valve metal substrate, followed by drying at 50-60°C and heat treating at 400-650°C for 5 to 30 minutes to decompose the first solution; (b) repeating step (a) until the desired specific loading of the precious metal is achieved; (c) applying a second solution containing no tin, including platinum, followed by drying at 50-60°C and heat treating at 400-650°C for 5 to 30 minutes to decompose the second solution; (d) repeating step (c) until the desired specific loading of the precious metal is achieved. For example, in the method of claim 10, the temperature of the heat treatment in steps (a) and (c) is between 480 and 550°C. A method as claimed in claim 10 or 11, wherein the first solution contains the iridium, ruthenium and tin in the form of an organometallic complex. An electrolytic cell for an alkaline chloride solution, comprising an anode chamber and a cathode chamber, wherein the anode chamber is equipped with any electrode of items 1 to 8 of the patent application scope. For example, in the electrolytic cell of claim 13, the anode chamber and the cathode chamber are separated by a diaphragm or an ion exchange membrane. An electrolytic cell for producing chlorine and alkaline metal from an alkaline metal chloride solution, comprising a modular arrangement of electrolytic cells, wherein each electrolytic cell is an electrolytic cell as defined in claim 13.