ELECTRODE FOR ELECTROLYTIC EVOLUTION OF GAS

Abstract

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

Claims

1. An electrode for gas evolution in electrolytic processes 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, obtained from precursors containing said iridium, ruthenium and tin in the form of organometallic complexes, and a second catalytic layer formed on said first catalytic layer containing platinum and tin or their oxides or combinations thereof, wherein said tin of the said second catalytic layer is present in a decreasing concentration from the interface with said first catalytic layer and wherein said platinum of the said first catalytic layer is present in a decreasing concentration from the interface with said second catalytic layer.

2. An electrode for gas evolution in electrolytic processes 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, wherein said platinum-free first precursor solution contains said iridium, ruthenium and tin in the form of organometallic complexes, and wherein said second catalytic layer is obtained from a tin-free second catalytic composition containing platinum, applied said substrate and subjected to a heat treatment.

3. The electrode according to claim 1, wherein said second catalytic layer contains Pt=48-96% in the form of metal, or its oxides, in molar percentage referred to the metal element.

4. The electrode according to claim 1, wherein said second catalytic layer contains Pd=0-24% or Rh=0-24%, in the form of metal, or their oxides, or combinations thereof, in the form of metals or their oxides in molar percentage referred to the metal elements.

5. The electrode according to claim 1, wherein said second catalytic layer contains Sn=4-12% in the form of metal or its oxides, in average molar percentage referred to the metal element.

6. The electrode according to claim 1, wherein said iridium, ruthenium and tin oxides of said first catalytic layer are present in molar percentages Ru=24-34%, Ir=3-13%, Sn=30-70% referring to the metal elements.

7. The electrode according to claim 1, wherein said first catalytic layer also contains titanium oxides in molar percentage Ti=30-40% referred to the metal element.

8. The electrode according to claim 1, wherein said first catalytic layer contains Pt=3-10% in the form of metal or its oxides, in average molar percentage referred to the metal element.

9. The electrode according to claim 1, wherein the valve metal substrate is selected from the group consisting of titanium, tantalum, zirconium, niobium, tungsten, aluminium, silicon, or their alloys.

10. A method for the production of an electrode as defined in claim 1, comprising the following steps: applying to a valve metal substrate a platinum-free first solution comprising a mixture of iridium, ruthenium and tin, subsequently drying at 50-60° C. and carrying out decomposition of said first solution by heat treatment at 400-650° C. for a time of 5 to 30 minutes, wherein said first solution contains said iridium, ruthenium and tin in the form of organometallic complexes; repeating the previous step until a desired specific load of noble metal is reached; applying a tin-free second catalytic solution containing platinum and subsequently drying at 50-60° C. and carrying out decomposition of said second solution by heat treatment at 400-650° C. for a time of 5 to 30 minutes; repeating the previous step until a desired specific load of noble metal is reached.

11. The method according to claim 10, wherein the temperature of said thermal decomposition in steps a) and c) is between 480 and 550° C.

12. (canceled)

13. A cell for the electrolysis of solutions of alkaline chlorides comprising an anodic compartment and a cathodic compartment wherein the anodic compartment is equipped with the electrode according to claim 1.

14. A cell for electrolysis according to claim 13 wherein said anodic compartment and said cathodic compartment are separated by a diaphragm or an ion-exchange membrane.

15. An electrolyzer for the production of chlorine and alkali from alkali chloride solutions comprising a modular arrangement of cells, wherein each cell is the cell according to claim 13.

16. The electrode according to claim 2, wherein said second catalytic layer contains Pt=48-96% in the form of metal, or its oxides, in molar percentage referred to the metal element.

17. The electrode according to claim 2, wherein said second catalytic layer contains Pd=0-24% or Rh=0-24%, in the form of metal, or their oxides, or combinations thereof, in the form of metals or their oxides in molar percentage referred to the metal elements.

18. The electrode according to claim 2, wherein said second catalytic layer contains Sn=4-12% in the form of metal or its oxides, in average molar percentage referred to the metal element.

19. The electrode according to claim 2, wherein said iridium, ruthenium and tin oxides of said first catalytic layer are present in molar percentages Ru=24-34%, Ir=3-13%, Sn=30-70% referring to the metal elements.

20. The electrode according to claim 2, wherein said first catalytic layer also contains titanium oxides in molar percentage Ti=30-40% referred to the metal element.

21. The electrode according to claim 2, wherein said first catalytic layer contains Pt=3-10% in the form of metal or its oxides, in average molar percentage referred to the metal element.

Description

EXAMPLE 1

[0050] A mesh of titanium of dimensions 10 cm×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 HCl at 20%, boiling for 30 minutes.

[0051] 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, 11% Ir and 64% Sn referred to the metals.

[0052] A second solution was also prepared containing a quantity of Pt diamino dinitrate, Pt(NH3)2(NO3)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.

[0053] 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.

[0054] The procedure was repeated until a load expressed as the sum of Ir and Ru referred to the metals equal to 7 g/m.sup.2 was reached.

[0055] 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 before the application of the next coat.

[0056] The procedure was repeated until a total load of Pt equal to 2.5 g/m.sup.2 was reached.

[0057] A final thermal treatment at 500° C. for 100 minutes was lastly carried out.

[0058] The electrode thus obtained was identified as specimen #1.

EXAMPLE 2

[0059] A mesh of titanium of dimensions 10 cm×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 HCl at 20%, boiling for 30 minutes.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.sup.2 was reached.

[0064] Subsequently, 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.

[0065] The procedure was repeated until a total load of noble metal expressed as the sum of Pt and Pd referred to the metals equal to 2.7 g/m.sup.2 was reached.

[0066] Lastly, a final thermal treatment at 500° C. for 100 minutes was carried out.

[0067] The electrode thus obtained was identified as specimen #2.

EXAMPLE 3

[0068] A mesh of titanium of dimensions 10 cm×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 HCl at 20%, boiling for 30 minutes.

[0069] 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.

[0070] 100 ml of a second acetic solution were then prepared containing an organo-metallic complex of platinum, an organo-metallic complex of palladium and RhCl3 and having a molar composition equal to 86% Pt, 10% Pd and 4% Rh referred to the metals.

[0071] 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.

[0072] 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.sup.2 was reached.

[0073] Subsequently, 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.

[0074] 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.sup.2 was reached.

[0075] Lastly, a final thermal treatment at 500° C. for 100 minutes was carried out.

[0076] The electrode thus obtained was identified as specimen #3.

EXAMPLE 4

[0077] A mesh of titanium of dimensions 10 cm×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 HCl at 20%, boiling for 30 minutes.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] The procedure was repeated until a load was reached expressed as the sum of Ir and Ru referred to the metals equal to 6.7 g/m.sup.2.

[0082] Subsequently, 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.

[0083] The procedure was repeated until a total load of noble metal expressed as the sum of Pt and Pd referred to the metals equal to 2.7 g/m.sup.2 was reached.

[0084] Lastly, a final thermal treatment at 500° C. for 100 minutes was carried out. The electrode thus obtained was identified as specimen #4.

EXAMPLE 5

[0085] A mesh of titanium of dimensions 10 cm×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 HCl at 20%, boiling for 30 minutes.

[0086] 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.

[0087] 100 ml of a second acetic solution were also prepared containing an organo-metallic complex of platinum, an organo-metallic complex of palladium and RhCl3 and having a molar composition equal to 86% Pt, 10% Pd and 4% Rh referred to the metals.

[0088] 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.

[0089] 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.sup.2 was reached.

[0090] 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.

[0091] 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 2.7 g/m.sup.2 was reached.

[0092] Lastly, a final thermal treatment at 500° C. for 100 minutes was carried out. The electrode thus obtained was identified as specimen #5.

COUNTER-EXAMPLE 1

[0093] A mesh of titanium of dimensions 10 cm×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 HCl at 20%, boiling for 30 minutes.

[0094] 100 ml of a hydro-alcoholic solution were then prepared containing RuCl3*3H2O, H2IrCl6*6H2O, TiCl3 in a solution of isopropanol, having a molar composition equal to 23% Ru, 22% Ir, 55% Ti.

[0095] 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.

[0096] The procedure was repeated until a total load of noble metal expressed as the sum of Ir and Ru referred to the metals equal to 11 g/m.sup.2 was reached. Then, a final thermal treatment at 500° C. for 100 minutes was carried out.

[0097] The electrode thus obtained was identified as specimen #1C.

COUNTER-EXAMPLE 2

[0098] A mesh of titanium of dimensions 10 cm×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 HCl, boiling for 30 minutes.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] The procedure was repeated until a total load of noble metal expressed as the sum of Ir and Ru referred to the metals equal to 6 g/m.sup.2 was reached.

[0103] Subsequently, 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.

[0104] The procedure was repeated until a total load of noble metal expressed as Pt referred to the metal equal to 2.5 g/m.sup.2 was reached.

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

[0106] The electrode thus obtained was identified as specimen #2C.

COUNTER-EXAMPLE 3

[0107] A mesh of titanium of dimensions 10 cm×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 HCl at 20%, boiling for 30 minutes.

[0108] 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.

[0109] 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.

[0110] The procedure was repeated until a total load of noble metal expressed as the sum of Ir, Ru and Pt referred to the metals equal to 8 g/m.sup.2 was reached.

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

[0112] The electrode thus obtained was identified as specimen #3C.

COUNTER-EXAMPLE 4

[0113] A mesh of titanium of dimensions 10 cm×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 HCl at 20%, boiling for 30 minutes. 100 ml of a first hydro-alcoholic solution were then prepared containing RuCl3*3H2O, H2IrCl6*6H2O, TiOCl2 in a mixture of water and 1-butanol acidified with HCl, having a molar composition equal to 26% Ru, 23% Ir, 51% Ti referred to the metals.

[0114] 100 ml of a second hydro-alcoholic solution were also prepared containing H2PtCl6 and PdCl2.

[0115] 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.

[0116] The procedure was repeated until a total load of noble metal expressed as the sum of Ir and Ru referred to the metals equal to 6 g/m.sup.2 was reached.

[0117] Subsequently, 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.

[0118] The procedure was repeated until a total load of noble metal expressed as the sum Pt+Pd referred to the metals equal to 3 g/m.sup.2 was reached.

[0119] Lastly, a final thermal treatment at 500° C. for 100 minutes was carried out.

[0120] The electrode thus obtained was identified as specimen #4C.

[0121] 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.

[0122] Table 1 reports the over-voltage of chlorine measured at a current density of 4 kA/m.sup.2 and the percentage by volume of oxygen in the chlorine produced.

TABLE-US-00001 TABLE 1 Specimens Cell potential (V) O2/Cl2 (Vol %) 1 2.76 0.9 2 2.76 0.7 3 2.76 0.7 4 2.77 0.8 5 2.77 0.7 1C 2.78 1.2 2C 2.76 1.0 3C 2.77 1.5 4C 2.76 0.8

[0123] The specimens of the preceding examples also underwent a test for operation in beaker. In Table 2, the anode potentials (CISEP) are reported, measured in a sodium chloride solution at a concentration of 200 g/I at a temperature of 80° C., corrected for the ohmic drop at a current density of 3 kA/m.sup.2. Furthermore, in order to evaluate the selectivity for the chlorine reaction, tests were conducted in sulphuric acid at a current density of 3 kA/m.sup.2; the anode potentials reported (CISEP) have been corrected for the ohmic drop. The higher the value of the anode potentials measured in sulphuric acid, the greater the selectivity for the chlorine reaction.

TABLE-US-00002 TABLE 2 ClSEP in NaCl ClSEP in H2SO4 Specimens vs NHE vs NHE 1 1.336 1.820 2 1.336 1.872 3 1.336 1.890 4 1.338 1.872 5 1.338 1.890 1C 1.347 1.693 2C 1.336 1.740 3C 1.336 1.647 4C 1.336 1.872

[0124] Some specimens were, in the end, subjected to a longevity test. 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.sup.2 and the percentage of residual load of the second catalytic layer after a simulated period of a year.

TABLE-US-00003 TABLE 3 Cl O.V Cl O.V. after 1 Specimens Start of test year % residual load 2 0.035 0.035 80% 1C 0.050 0.050 — 4C 0.037 0.060 50%

[0125] The preceding description is not intended to limit the invention, which may be used according to various embodiments without however deviating from the objectives and whose scope is uniquely defined by the appended claims.

[0126] In the description and in the claims of the present application, the terms “comprising”, “including” and “containing” are not intended to exclude the presence of other additional elements, components or process steps.

[0127] The discussion of documents, items, materials, devices, articles and the like is included in this description solely with the aim of providing a context for the present invention. It is not suggested or represented that any or all of these topics formed part of the prior art or formed a common general knowledge in the field relevant to the present invention before the priority date for each claim of this application.