Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
  • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
  • C25B11/093—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds at least one noble metal or noble metal oxide and at least one non-noble metal oxide
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/24—Halogens or compounds thereof
  • C25B1/26—Chlorine; Compounds thereof
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/055—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material
  • C25B11/057—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the substrate or carrier material consisting of a single element or compound
  • C25B11/061—Metal or alloy
  • C25B11/063—Valve metal, e.g. titanium
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
  • C25B11/097—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds comprising two or more noble metals or noble metal alloys
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B13/00—Diaphragms; Spacing elements
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
  • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms
  • C25B9/23—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms comprising ion-exchange membranes in or on which electrode material is embedded

Definitions

• the invention relates to an electrode for evolution of gas in electrolytic processes comprising a valve metal substrate and a catalytic coating comprising two layers.
• a first layer comprising valve metal, ruthenium and iridium oxides and a second layer comprising one or more metals chosen from amongst the elements of the platinum group.
• the field of the invention relates to the preparation of a catalytic coating for electrodes used in brine electrolysis processes. This coating is applied to a metal substrate, typically titanium or other valve metal.
• a further difficulty resides in the obtaining of an electrode capable of maintaining higher performance for a long period of time.
• the processes for electrolysis of brines for example alkaline chloride brines such as sodium chloride, for the production of chlorine and caustic soda, are carried out with anodes made of titanium or another valve metal, activated with a superficial layer of ruthenium dioxide (Ru02) optionally mixed with tin dioxide (Sn02) and another noble metal, such as for example described in EP0153586.
• Ru02 ruthenium dioxide
• Sn02 tin dioxide
• EP0153586 another noble metal
• Another partial improvement in the performance is obtained by applying to a metal substrate a formulation based on Ru02 and Sn02 combined with a reduced quantity of Ir02 such as for example described in WO2016083319.
• a similar formulation allows optimum values of cell potential and moderate quantities of oxygen to be obtained.
• coatings of the prior art such as for example the formulation described in WO2012081635 comprising two catalytic coatings, the first containing titanium and noble metal oxides and the second containing a platinum and palladium alloy, also allow optimum values of cell potential and reduced quantities of oxygen in chlorine gas to be obtained; however, they do not endow the electrode with an optimum resistance capable of maintaining higher levels of performance, with regard to catalytic activity and selectivity, for an adequate period of time.
• US 2013/0186750 A1 describes an electrode suitable for chlorine evolution which has alternate layers of two distinct compositions, namely one type of layers comprising iridium, ruthenium and valve metals and another type of layer comprising oxides of iridium, ruthenium and tin.
• US 2013/0334037 A1 describes an electrode for electrolysis including a conductive substrate, a first layer formed on the conductive substrate containing at least one oxide selected from ruthenium oxide, iridium oxide and titanium oxide and a second layer formed on the first layer containing an alloy of platinum and palladium.
• US 4,626,334 describes an anode comprising an electroconductive substrate provided with a (Ru-Sn)02 solid solution coating for brine electrolysis.
• JP S62243790 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.
• the present invention relates to an electrode for evolution of gaseous products in electrolytic cells, for example for evolution of chlorine in alkaline brine electrolysis cells, comprising a catalytic coating applied on a metal substrate.
• the term catalytic coating indicates two different catalytic layers with different catalytic compositions in which the first catalytic layer formed on the substrate comprises at least a mixture of iridium, of ruthenium, of tin and of platinum or their oxides or respective combinations and a second catalytic layer formed on the first catalytic layer comprises platinum and tin or their oxides or respective combinations thereof.
• the tin of the second catalytic layer is present in a concentration decreasing from the interface with said first catalytic layer towards the upper surface of the second catalytic layer, i.e. surface opposite the interface with the first catalytic layer, and the platinum of the said first catalytic layer is present in a concentration decreasing from the interface with said second catalytic layer towards the substrate.
• the present invention also relates to an electrode for evolution of gaseous products in electrolytic cells, for example for evolution of chlorine in alkaline brine electrolysis cells, comprising a valve metal substrate and a coating comprising a first catalytic layer formed on said substrate containing a mixture of iridium, ruthenium, tin and platinum or their oxides or combinations thereof and a second catalytic layer formed on said first catalytic layer containing platinum and tin or their oxides or combinations thereof, wherein said first layer is obtained from a platinum-free first precursor solution comprising a mixture of iridium, ruthenium and tin, applied said substrate and subjected to a heat treatment, and wherein said second catalytic layer is obtained from a tin-free second catalytic solution containing platinum, applied to said first catalytic layer and subjected to a heat treatment.
• platinum-free and“tin-free” in the sense of the present invention mean that the platinum concentration in the first solution is at least an order of magnitude lower that the average platinum concentration in the first layer obtained from said first solution and that the tin concentration in the second solution is at least an order of magnitude lower that the average tin concentration in second layer obtained from the second solution.
• a platinum-free solution contains platinum at most as an impurity and a tin- free solution contains tin at most as an impurity.
• This double-layer structure applied to a metal substrate, typically titanium, titanium alloy or another valve metal, allows a saving in the energy consumption to be combined with an excellent purity of chlorine gas produced while maintaining optimal performance characteristics in terms of catalytic activity and of selectivity for a long period of time.
• the first catalytic layer, formed on the substrate preferably comprises ruthenium oxide, iridium oxide, tin oxide and metallic platinum or its oxides.
• Ru02 is widely known for its excellent catalytic activity and its stability in an alkaline medium which is improved by the presence of Ir02; the presence of Sn02 guarantees a slower consumption of the noble metals present.
• the second catalytic layer formed on the first layer, comprises tin or its oxides and one or more metals chosen from amongst the elements of the platinum group, especially platinum itself, which are known for increasing the selectivity and for reducing the energy consumption.
• an electrode with a similar catalytic coating where said second catalytic layer comprises platinum in a molar percentage referred to the metal element in the range between 48 and 96% (or, when taking the tin component not into account, from 50 and 99.999%) in the form of the metal or its oxide, can offer the advantage of subsequently reducing the over-voltage of the reaction for evolution of chlorine.
• ranges denoted by either“from” or“between” include the specified upper and lower limits, respectively.
• said second catalytic layer comprises palladium or rhodium in the form of metals or their oxides, or combinations thereof, in molar percentage referred to the metal elements in the range between 0 and 24% (or, when taking the tin component not into account, between 0 and 25%), where the elements are in the form of metals or oxides thereof.
• the second catalytic layer preferably comprises tin or its oxide in an average molar percentage referred to the metal element in a range from 4 to 12%.
• concentration of the tin component varies in a direction perpendicular to the interface between the first and second layers, the tin concentration is an average of the concentration profile through the second catalytic layer.
• the second catalytic layer consists of platinum and tin, and optionally palladium and/or rhodium, in molar percentage referred to the metal elements in the ranges from 48 to 96% platinum, from 4 to 12% tin, from 0 to 24% palladium and from 0 to 24% rhodium.
• the first catalytic layer preferably comprises platinum or its oxide in an average molar percentage referred to the metal element in a range from 3 to 10%. As the concentration of the platinum component varies in a direction perpendicular to the interface between the first and second layers, the platinum concentration is an average of the concentration profile through the first catalytic layer.
• said first catalytic layer comprises another valve metal chosen from amongst titanium, tantalum and niobium, in a quantity, expressed in molar percentage, in the range between 30 and 40% referred to the metal element; it has in fact been observed how the presence of another valve metal such as titanium allows a good catalytic activity to be combined with a substantial increase in the resistance of the electrode in processes that require current inversion.
• the first catalytic layer consists of iridium, ruthenium, tin and platinum and optionally titanium, in molar percentage referred to the metal elements in the ranges from 3 to 13% iridium, from 24 to 34% ruthenium, from 30 to 70% tin, from 3 to10% platinum and from 30 to 40% titanium.
• the inventors have observed that, surprisingly, in the catalytic coating described above, a phenomenon of diffusion between layers takes place: the tin of the first catalytic layer diffuses into the second layer, while the platinum of the second catalytic layer diffuses into the first layer.
• the diffusion of tin into the second catalytic layer takes place across a gradient of concentration such that the quantity of tin in the second catalytic layer is maximum at the interface between the two catalytic layers and decreases towards the external surface of the second catalytic layer.
• the presence of tin diffused into the second catalytic layer can advantageously slow the consumption of the noble metals present in the second catalytic layer, enabling optimum performance characteristics in terms of catalytic activity and of selectivity to be maintained for a longer period of time, without compromising the catalytic performance.
• the diffusion of platinum from the second catalytic layer into the first catalytic layer is such that the quantity of platinum in the first catalytic layer is maximum at the interface between the two catalytic layers and decreases gradually toward the internal surface of the first catalytic layer.
• the diffusion of the platinum into the first catalytic layer allows the catalytic activity to be enhanced. This furthermore allows better catalytic performance characteristics to be maintained throughout the lifetime of the electrode, also where the prolonged use of the same causes wear of the second layer over time.
• the elements present and the particular structure of the catalytic coating allow better performance characteristics with respect to the prior art to be guaranteed with the further advantage of increasing the operating lifetime of the electrode.
• the electrode according to the invention furthermore surprisingly allows the better performance characteristics in terms of activity and of selectivity to be maintained over time.
• tin has a high impact on the selectivity; however, if the tin is present in high quantities on the external surface of the catalytic coating, in combination with the platinum, it attenuates the increase in catalytic activity of the platinum itself.
• the diffusion of tin from the first catalytic layer to the second produces a profile of concentration of the element between the layers which enables a high catalytic activity together with an optimum selectivity to be maintained, furthermore allowing the consumption of the noble metals present in the second catalytic layer to be slowed.
• the profile of concentration of tin between the two catalytic layers is characterized by a monotonic decrease in concentration of the element within the second layer in the opposite direction to the first layer.
• the first catalytic layer has a specific load of noble metal in the range between 3 and 8 g/m 2 and the second catalytic layer has a specific load of noble metal in the range between 0.8 and 4 g/m 2 .
• the inventors have found that loads thus reduced of noble metal are more than sufficient to impart an optimum catalytic activity.
• the present invention relates to a method for obtaining an electrode for evolution of gaseous products in electrolytic cells, for example for evolution of chlorine in alkaline brine electrolysis cells, comprising the following stages: application to a valve metal substrate of a platinum-free first solution comprising a mixture of iridium, ruthenium and tin, subsequent drying at 50-60°C and decomposition of said first solution by heat treatment at 400-650 ° C for a period of 5 to 30 minutes; repetition of the stage a) until said first catalytic composition is obtained with a desired specific load of noble metal; application of a tin-free second catalytic solution containing platinum being subsequently dried at 50-60°C and decomposition of said first solution by heat treatment at 400-650 ° C for a period of 5 to 30 minutes; repetition of the stage c) until said first catalytic composition is obtained with a desired specific load of noble metal.
• the temperature of said thermal decomposition in steps a) and c) is between 480 and 550°C.
• said first solution furthermore comprises titanium.
• said second solution comprises palladium and rhodium on their own or in combination with each other.
• the two-layers electrode is subjected to a final thermal treatment.
• the final thermal treatment is effected at a temperature between 400 and 650 °C, preferably at a temperature of around 500 °C, for at least 60 minutes, preferably between 60 and 180 minutes, more preferably between 80 and 120 minutes.
• the first solution comprises the iridium, ruthenium and tin compounds and optionally the titanium compounds in the form of organometallic complexes.
• the organometallic complexes are aceto-hydroxychloride complexes of tin, ruthenium, iridium and optionally titanium, respectively.
• stages a and c for thermal treatment or decomposition of the method described above, together with the elements present and with the concentrations thereof within said first and said second solution, because their coefficient of diffusion is also dependent on the temperature, to contribute to the inter-diffusion of the tin and of the platinum present respectively from the first catalytic layer to the second catalytic layer and vice versa.
• the invention relates to a cell for the electrolysis of solutions of alkaline chlorides comprising an anode compartment and a cathode compartment in which the anode compartment is equipped with the electrode in one of the forms such as described above, used as an anode for evolution of chlorine.
• the invention relates to an industrial electrolyser for the production of chlorine and alkali from alkali chloride solutions, when also lacking biasing protection devices and comprising a modular arrangement of electrolytic cells with the anode and cathode compartments separated by ion-exchange membranes or by diaphragms, where the anode compartment comprises an electrode in one of the forms such as described above used as an anode.
• a mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution of HCI at 20%, boiling for 30 minutes.
• tin complex acetato- hydroxichloride 100 ml of a first acetic solution were then prepared containing tin complex acetato- hydroxichloride, ruthenium complex acetato-hydroxichloride and iridium complex acetato- hydroxichloride and having a molar composition equal to 25% Ru, 1 1 % Ir and 64% Sn referred to the metals.
• a second solution was also prepared containing a quantity of Pt diamino dinitrate, Pt(NH3)2(N03)2 corresponding to 40 g of Pt dissolved in 160 ml of glacial acetic acid and then made up to a volume of one litre with acetic acid at 10% by weight.
• the first acetic solution was applied to the mesh of titanium by painting on in 8 coats. After each coat, a drying step at 50-60°C was carried out for around 10 minutes, then a thermal treatment for 10 minutes at 500°C, the mesh being each time cooled in air prior to the application of the next coat.
• the second solution was applied by painting on in 4 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air before the application of the next coat.
• the electrode thus obtained was identified as specimen #1 .
• EXAMPLE 2 A mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution of HCI at 20%, boiling for 30 minutes.
• a first acetic solution 100 ml of a first acetic solution were then prepared containing tin complex acetato- hydroxichloride, ruthenium complex acetato-hydroxichloride and iridium complex acetato- hydroxichloride and having a molar composition equal to 26% Ru, 10% Ir and 64% Sn referred to the metals.
• 100 ml of a second acetic solution were also prepared containing an organo-metallic complex of platinum and an organo-metallic complex of palladium and having a molar composition equal to 87% Pt and 13% Pd referred to the metals.
• the first acetic solution was applied to the mesh of titanium by painting on in 8 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the second acetic solution was applied by painting on in 4 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• a mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution of HCI at 20%, boiling for 30 minutes.
• a first acetic solution 100 ml of a first acetic solution were then prepared containing tin complex acetato- hydroxichloride, ruthenium complex acetato-hydroxichloride and iridium complex acetato- hydroxichloride and having a molar composition equal to 26% Ru, 10% Ir and 64% Sn referred to the metals.
• the first acetic solution was applied to the mesh of titanium by painting on in 8 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the second acetic solution was applied by painting on in 4 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat. The procedure was repeated until a total load of noble metal expressed as the sum of Pt, Pd and Rh referred to the metals equal to 2.8 g/m 2 was reached.
• the electrode thus obtained was identified as specimen #3.
• a mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution of HCI at 20%, boiling for 30 minutes.
• tin complex acetato- hydroxichloride 100 ml of a first acetic solution were then prepared containing tin complex acetato- hydroxichloride, ruthenium complex acetato-hydroxichloride, iridium complex acetato- hydroxichloride and titanium complex acetato-hydroxichloride and having a molar composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Ti referred to the metals.
• 100 ml of a second acetic solution were also prepared containing an organo-metallic complex of platinum and an organo-metallic complex of palladium and having a molar composition equal to 87% Pt and 13% Pd referred to the metals.
• the first acetic solution was applied to the mesh of titanium by painting on in 8 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the second acetic solution was applied by painting on in 4 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the electrode thus obtained was identified as specimen #4.
• a mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution of HCI at 20%, boiling for 30 minutes.
• tin complex acetato- hydroxichloride 100 ml of a first acetic solution were then prepared containing tin complex acetato- hydroxichloride, ruthenium complex acetato-hydroxichloride, iridium complex acetato- hydroxichloride and titanium complex acetato-hydroxichloride and having a molar composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Ti referred to the metals.
• 100 ml of a second acetic solution were also prepared containing an organo-metallic complex of platinum, an organo-metallic complex of palladium and RhCI3 and having a molar composition equal to 86% Pt, 10% Pd and 4% Rh referred to the metals.
• the first acetic solution was applied to the mesh of titanium by painting on in 8 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the procedure was repeated until a load expressed as the sum of Ir and Ru referred to the metals equal to 6.7 g/m 2 was reached. Subsequently, the second solution was applied by painting on in 4 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the electrode thus obtained was identified as specimen #5.
• a mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution of HCI at 20%, boiling for 30 minutes.
• the solution was applied to the mesh of titanium by painting on in 14 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the work piece was cooled in air prior to the application of the next coat.
• a mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution at 20% of HCI, boiling for 30 minutes.
• a first acetic solution 100 ml of a first acetic solution were then prepared containing tin complex acetato- hydroxichloride, ruthenium complex acetato-hydroxichloride and iridium complex acetato- hydroxichloride and having a molar composition equal to 26% Ru, 10% Ir and 64% Sn referred to the metals.
• 100 ml of a second acetic solution were also prepared containing an organo-metallic complex of platinum and a tin complex acetato-hydroxichloride and having a molar composition equal to 87% Pt and 13% Sn referred to the metals.
• the first acetic solution was applied to the mesh of titanium by painting on in 6 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the second acetic solution was applied by painting on in 4 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the electrode thus obtained was identified as specimen #2C.
• a mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution of HCI at 20%, boiling for 30 minutes.
• tin complex acetato- hydroxichloride 100 ml of a first acetic solution were then prepared containing tin complex acetato- hydroxichloride, ruthenium complex acetato-hydroxichloride, iridium complex acetato- hydroxichloride and organo-metallic complex of platinum and having a molar composition equal to 25% Ru, 10% Ir, 35% Sn and 30% Pt referred to the metals.
• the acetic solution was applied to the mesh of titanium by painting on in 10 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the electrode thus obtained was identified as specimen #3C.
• a mesh of titanium of dimensions 10 cm x 10 cm was washed three times in de-ionized water at 60°C, changing the liquid each time. The washing was followed by a thermal treatment for 2 hours at 350°C. The mesh was then subjected to a treatment in a solution of HCI at 20%, boiling for 30 minutes. 100 ml of a first hydro-alcoholic solution were then prepared containing RuCI3 * 3H20, H2lrCI6 * 6H20, TiOCI2 in a mixture of water and 1 -butanol acidified with HCI, having a molar composition equal to 26% Ru, 23% Ir, 51 % Ti referred to the metals.
• the first acetic solution was applied to the mesh of titanium by painting on in 8 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the second acetic solution was applied by painting on in 4 coats. After each coat, a drying step at 50-60°C for around 10 minutes was carried out, then a thermal treatment for 10 minutes at 500°C. Each time, the mesh was cooled in air prior to the application of the next coat.
• the electrode thus obtained was identified as specimen #4C.
• the specimens of the examples and of the counter-examples were characterized as anodes for evolution of chlorine in a laboratory cell filled with a brine solution of sodium chloride at a concentration of 200 g/l.
• Table 1 reports the over-voltage of chlorine measured at a current density of 4 kA/m 2 and the percentage by volume of oxygen in the chlorine produced.
• the specimens of the preceding examples also underwent a test for operation in beaker.
• the anode potentials (CISEP) are reported, measured in a sodium chloride solution at a concentration of 200 g/l at a temperature of 80°C, corrected for the ohmic drop at a current density of 3 kA/m 2 .
• tests were conducted in sulphuric acid at a current density of 3 kA/m 2 ; the anode potentials reported (CISEP) have been corrected for the ohmic drop.
• the longevity test in question is the simulation, in a cell divided by the conditions of industrial electrolysis.
• Table 3 reports the cell voltage for the specimens at the start of the test and after a simulated period of a year, as an indicator of their catalytic activity for the evolution of chlorine (Cl O.V.) measured at a current density of 8 kA/m 2 and the percentage of residual load of the second catalytic layer after a simulated period of a year.

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• Measuring Oxygen Concentration In Cells (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

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