ELECTRODE ASSEMBLY AND ELECTROLYSER

Abstract

The present invention relates to an electrode assembly and an electrolyser using one or more of said assemblies, in particular the present invention provides an electrode assembly for the production of hydrogen comprising: i) an anode structure which comprises an anode located within an electrolysis compartment, ii) a cathode structure which comprises a cathode located within an electrolysis compartment containing a solution of an alkali metal hydroxide, characterised in that the cathode comprises: a) An electrically conductive metal substrate, and b) An electrocatalytic layer on the substrate and comprising a, at least one metal selected from platinum group metals, rhenium, nickel, cobalt and molybdenum and b. at least 50% by volume of an electrically conductive support material, wherein the electrically conductive support material is formed from particles having an average particle size of less than 5 microns (5 μm) and which are not metallic particles.

Claims

1-19. (canceled)

20. An electrode assembly for the production of hydrogen comprising: i) an anode structure which comprises an anode located within an electrolysis compartment, ii) a cathode structure which comprises a cathode located within an electrolysis compartment containing a solution of an alkali metal hydroxide, characterised in that the cathode comprises: a) An electrically conductive metal substrate, and b) An electrocatalytic layer on the substrate said layer comprising at least one metal supported on an electrically conductive support material, wherein a. the at least one metal is selected from platinum group metals, rhenium, nickel, cobalt and molybdenum, and b. the electrocatalytic layer comprises at least 50% by volume of the electrically conductive support material, and wherein the electrically conductive support material is formed of particles having an average particle size of less than 5 μm (5 microns) and which are not metallic particles.

21. An assembly according to claim 20 wherein the at least one metal comprises at least one platinum group metal.

22. An assembly according to claim 21 wherein the at least one metal comprises ruthenium.

23. An assembly according to claim 22 wherein the at least one metal comprises ruthenium and platinum.

24. An assembly according to claim 20 wherein the electrically conductive support material comprises an electrically conductive carbon material.

25. An assembly according to claim 20 wherein the electrocatalytic layer comprises 0.2 to 10% by volume of the at least one metal and 90 to 99.8% by volume of the electrically conductive support material.

26. An assembly according to claim 20 wherein the electrically conductive support material has a surface area of at least 50 m.sup.2/g, preferably 200 to 1000 m.sup.2/g.

27. An assembly according to claim 20 wherein the electrically conductive support material is formed of particles having an average particle size of less than 1 μm (1 micron), especially 10 to 250 nanometers, such as 20 to 100 nanometers.

28. An assembly according to claim 20 wherein the cathode further comprises a binder, preferably which has been coated with the electrocatalytic layer.

29. An assembly according to claim 20 wherein the cathode comprises two or more electrocatalytic layers as defined in the preceding claims, but where the layers as deposited differ in composition.

30. An assembly according to claim 20 which is for the production of hydrogen and a halogen and wherein the anode compartment contains a solution of an alkali metal halide.

31. An assembly according to claim 20 which is for the production of hydrogen and oxygen and wherein the anode compartment contains a solution of an alkali metal hydroxide.

32. A modular or filter press electrolyser comprising a plurality of electrode assemblies as claimed in claim 20, and preferably comprising 5-300 electrode assemblies.

33. A process for electrolysis which comprises performing electrolysis in an electrode assembly according to claim 20, and preferably in a modular or filter press electrolyser comprising a plurality of said electrode assemblies, to produce hydrogen.

34. Use of an electrocatalytic layer on an electrode, said electrode comprising a) An electrically conductive metal substrate, and b) An electrocatalytic layer on the substrate, said layer comprising at least one metal supported on an electrically conductive support material, wherein a. the at least one metal is selected from platinum group metals, rhenium, nickel, cobalt and molybdenum, and b. the electrocatalytic layer comprises at least 50% by volume of the electrically conductive support material, and wherein the electrically conductive support material is formed of particles having an average particle size of less than 5 μm (5 microns) and which are not metallic particles, to provide at least one of: i) a reduced overpotential of the electrode, ii) an overpotential of the electrode which is stable over prolonged periods of operation, and iii) an improved reverse current tolerance of an electrode.

35. Use according to claim 34 wherein the electrode is a cathode in a process for the production of hydrogen from said cathode.

36. Use according to claim 35 wherein the process for the production of hydrogen from said cathode is a process for production of hydrogen from an alkali metal hydroxide at the cathode and either (1) a halogen from an alkali metal halide or (2) oxygen from an alkali metal hydroxide at the anode.

37. A method which comprises: i) Producing an electrode comprising a) An electrically conductive metal substrate, and b) An electrocatalytic layer on the substrate said layer comprising at least one metal supported on an electrically conductive support material, wherein a. the at least one metal is selected from platinum group metals, rhenium, nickel, cobalt and molybdenum, and b. the electrocatalytic layer comprises at least 50% by volume of the electrically conductive support material, and wherein the electrically conductive support material is formed of particles having an average particle size of less than 5 μm (5 microns) and which are not metallic particles, and ii) Supplying said electrode for use as a cathode in a process for electrolysis of an alkali metal hydroxide to produce hydrogen.

38. A method according to claim 37 wherein the process for electrolysis of an alkali metal hydroxide to produce hydrogen is a process for the production of hydrogen from the cathode and either (1) a halogen from an alkali metal halide or (2) oxygen from an alkali metal hydroxide at the anode.

Description

[0200] FIG. 1 shows the cell voltage versus the number of shutdown cycles for Comparative Example 4D and Example 5D. Table 4 provides a summary of the data presented in FIG. 1.

[0201]

TABLE-US-00004 Cell Voltage Cell Voltage Before After Number of Shutdown Shutdown Shutdowns Example Coating Type Cycling Cycling Completed Comparative Carbon-free −2.85 −3.04 7 Example 4D Ru Example 5D Carbon- −2.82 −2.82 43 supported Ru

[0202] Comparative Example 4D demonstrates a start-up cell voltage of −2.85V while Example 5D demonstrates an improvement of 30 mV with a cell voltage of −2.82V. This demonstrates ruthenium carbon coating is also more active than just the ruthenium coating, at an equivalent coat weight on Electrode “Type D”.

[0203] Comparative Example 4D shows a dramatic change of cell voltage during only 7 shutdown cycles, degrading to −3.04V (equivalent to a cell voltage change of 190 mV).

[0204] Example 5D on the other hand shows no significant change of cell voltage during 43 shutdown cycles. This Example demonstrates the carbon-ruthenium coating has significantly better tolerance to shutdowns.