Nickel electrode, self-supporting nickel layer, method for production thereof, and use thereof

Abstract

Nickel electrodes comprising an electrically conductive nickel sheet and a nickel layer deposited thereon which consists of spherical, porous nickel particles which adhere to each other, made by the method of partially reducing spherical nickel hydroxide particles in a reducing atmosphere at elevated temperatures to obtain partially reduced spherical Ni/NiO particles, preparing a paste from the Ni/NiO particles obtained and an organic and/or inorganic binder as well as further excipients as required, applying the paste in a layer to one or both sides of the electrically conductive nickel sheet, and tempering the coated nickel sheet in a reducing atmosphere at elevated temperatures. Self-supporting nickel layers of spherical, porous nickel particles which adhere to each other. Producing nickel electrodes and the self-supporting nickel layer, and use thereof, particularly as an electrode for water electrolysis.

Claims

1. A nickel electrode, comprising an electrically conductive nickel sheet and a nickel layer consisting of spherical, porous nickel particles adhering to each other deposited thereon, obtainable with a method comprising the following steps: a) providing spherical nickel hydroxide particles, b) partially reducing the spherical nickel hydroxide particles in a reducing atmosphere at elevated temperatures to obtain partially reduced spherical Ni/NiO particles, c) preparing a paste from the Ni/NiO particles obtained and an organic and/or inorganic binder as well as further excipients as required, d) applying the paste in a layer to one or both sides of the electrically conductive nickel sheet, and e) tempering the coated nickel sheet in a reducing atmosphere at elevated temperatures.

2. A self-supporting nickel layer consisting of spherical, porous nickel particles which adhere to each other, obtainable with a method comprising the following steps: a) providing spherical nickel hydroxide particles, b) partially reducing the spherical nickel hydroxide particles in a reducing atmosphere at elevated temperatures to obtain partially reduced spherical Ni/NiO particles, c) preparing a paste from the Ni/NiO particles obtained and an organic and/or inorganic binder as well as further excipients as required, d) applying the paste in a layer to a carrier, e) tempering the coated carrier in a reducing atmosphere at elevated temperatures, and f) separating the carrier to obtain the self-supporting porous nickel layer.

3. The nickel electrode according to claim 1, wherein the spherical nickel hydroxide particles provided in step a) have an average particle size from 0.3-75 m.

4. The nickel electrode according to claim 1, wherein the partial reduction in step b) is carried out at temperatures from 270-330 C.

5. The nickel electrode according to claim 1, wherein the partial reduction in step b) and the tempering in step e) are carried out in a reducing atmosphere containing 10-100% hydrogen and optionally an inert gas.

6. The nickel electrode according to claim 1, wherein in step c) natural and/or synthetic polymers or derivatives thereof are used as organic binders, and ammonium salts or hydrazine salts are used as inorganic binders.

7. The nickel electrode according to claim 1, wherein the nickel layer of the nickel electrode has a thickness in the range from 1-1,000 m.

8. The nickel electrode according to claim 1, wherein the spherical, porous nickel particles have an average particle size of 0.1-25 m.

9. The self-supporting nickel layer according to claim 2, wherein metal foils, metal foams, metal meshes, expanded metals, carbon foils, carbon foams, polymer foils or ceramic carriers are used as the carrier in step d).

10. A method for producing a nickel electrode according to claim 1, comprising the following steps: a) providing spherical nickel hydroxide particles, b) partially reducing the spherical nickel hydroxide particles in a reducing atmosphere at elevated temperatures to obtain partially reduced spherical Ni/NiO particles, c) preparing a paste from the Ni/NiO particles obtained and an organic and/or inorganic binder as well as further excipients as required, d) applying the paste in a layer to one or both sides of the electrically conductive nickel sheet, and e) tempering the coated nickel sheet in a reducing atmosphere at elevated temperatures.

11. A method for producing a self-supporting nickel layer according to claim 2, comprising the following steps: a) providing spherical nickel hydroxide particles, b) partially reducing the spherical nickel hydroxide particles in a reducing atmosphere at elevated temperatures to obtain partially reduced spherical Ni/NiO particles, c) preparing a paste from the Ni/NiO particles obtained and an organic and/or inorganic binder as well as further excipients as required, d) applying the paste in a layer to a carrier, e) tempering the coated carrier in a reducing atmosphere at elevated temperatures, and f) separating the carrier to obtain the self-supporting porous nickel layer.

12. The nickel electrode according to claim 3, wherein the spherical nickel hydroxide particles provided in step a) have an average particle size from 3-30 m.

13. The nickel electrode according to claim 12, wherein the spherical nickel hydroxide particles provided in step a) have an average particle size from 9-12 m.

14. The nickel electrode according to claim 13, wherein the spherical nickel hydroxide particles provided in step a) have an average particle size of about 10 m.

15. The self-supporting nickel layer according to claim 2, wherein the spherical nickel hydroxide particles provided in step a) have an average particle size from 0.3-75 m.

16. The self-supporting nickel layer according to claim 15, wherein the spherical nickel hydroxide particles provided in step a) have an average particle size from 3-30 m.

17. The self-supporting nickel layer according to claim 16, wherein the spherical nickel hydroxide particles provided in step a) have an average particle size from 9-12 m.

18. The self-supporting nickel layer according to claim 17, wherein the spherical nickel hydroxide particles provided in step a) have an average particle size of about 10 m.

19. The nickel electrode according to claim 4, wherein the partial reduction in step b) is carried out at temperatures from 290-310 C.

20. The self-supporting nickel layer according to claim 2, wherein the partial reduction in step b) is carried out at temperatures from 270-330 C.

21. The self-supporting nickel layer according to claim 20, wherein the partial reduction in step b) is carried out at temperatures from 290-310 C.

22. The self-supporting nickel layer according to claim 2, wherein the partial reduction in step b) and the tempering in step e) are carried out in a reducing atmosphere containing 10-100% hydrogen and optionally an inert gas.

23. The self-supporting nickel layer according to claim 2, wherein in step c) natural and/or synthetic polymers or derivatives thereof are used as organic binders, and ammonium salts or hydrazine salts are used as inorganic binders.

24. The nickel electrode according to claim 7, wherein the nickel layer of the nickel electrode has a thickness in the range from 10-900 m.

25. The nickel electrode according to claim 24, wherein the nickel layer of the nickel electrode has a thickness in the range from 20-200 m.

26. The self-supporting nickel layer according to claim 2, wherein the self-supporting nickel layer has a thickness in the range from 1-1,000 m.

27. The self-supporting nickel layer according to claim 26, wherein the self-supporting nickel layer has a thickness in the range from 10-900 m.

28. The self-supporting nickel layer according to claim 27, wherein the self-supporting nickel layer has a thickness in the range from 20-200 m.

29. The nickel electrode according to claim 8, wherein the spherical, porous nickel particles have an average particle size of 1-10 m.

30. The nickel electrode according to claim 29, wherein the spherical, porous nickel particles have an average particle size of 2-6 m.

31. The nickel electrode according to claim 30, wherein the spherical, porous nickel particles have an average particle size of 3-4 m.

32. The self-supporting nickel layer according to claim 2, wherein the spherical, porous nickel particles have an average particle size of 0.1-25 m.

33. The self-supporting nickel layer according to claim 32, wherein the spherical, porous nickel particles have an average particle size of 1-10 m.

34. The self-supporting nickel layer according to claim 33, wherein the spherical, porous nickel particles have an average particle size of 2-6 m.

35. The self-supporting nickel layer according to claim 34, wherein the spherical, porous nickel particles have an average particle size of 3-4 m.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows an REM (raster electron microscope) image of the surface of a commercial nickel sintered electrode magnified 1000-fold. (from Morioka Y., Narukawa S., Itou T., Journal of Power Sources 100 (2001): 107-116);

(2) FIG. 2 shows an REM image of the surface of a commercial nickel foam electrode with honeycomb structure magnified 150-fold;

(3) FIG. 3 shows an REM image of the surface of a commercial nickel fibre electrode magnified 500-fold. (from Ohms D., Kohlhase M., Benczur-Urmossy G., Schadlich G., Journal of Power Sources 105 (2002): 127-133);

(4) FIG. 4 shows an REM image of the surface of a nickel electrode according to the invention magnified 500-fold;

(5) FIG. 5 shows an REM image of the surface of a nickel electrode according to the invention magnified 10,000-fold;

(6) FIG. 6a shows a quasistationary cyclic voltammogram with a scan rate of 50 V s.sup.1 on a 1 cm.sup.2 nickel electrode for water electrolysis according to the invention in an electrolyte of 5.5 M KOH; 2.5M NaOH and 0.5M LiOH at room temperature. The rear of the electrode is coated with epoxy resin for electrical insulation;

(7) FIG. 6b shows a quasistationary cyclic voltammogram with a scan rate of 100 V s.sup.1 on a 1 cm.sup.2 nickel electrode for water electrolysis according to the invention in an electrolyte of 5.5 M KOH; 2.5M NaOH and 0.5M LiOH at room temperature. The rear of the electrode is coated with epoxy resin for electrical insulation;

(8) FIG. 6c shows a quasistationary cyclic voltammogram with a scan rate of 50 V s.sup.1 on a flat, untreated 1 cm.sup.2 nickel electrode for water electrolysis in an electrolyte of 5.5 M KOH; 2.5M NaOH and 0.5M LiOH at room temperature. The rear of the electrode is coated with epoxy resin for electrical insulation;

(9) FIG. 6d shows a quasistationary cyclic voltammogram with a scan rate of 100 V s.sup.1 on a flat, untreated 1 cm.sup.2 nickel electrode for water electrolysis in an electrolyte of 5.5 M KOH; 2.5M NaOH and 0.5M LiOH at room temperature. The rear of the electrode is coated with epoxy resin for electrical insulation.

PREFERRED EMBODIMENTS AND EXEMPLARY EMBODIMENT

(10) Production of a Nickel Electrode According to the Invention

(11) 50 g spherical -Ni(OH).sub.2 particles are partially reduced for 4 hours at a temperature of 300 C. in an atmosphere of 50 vol. % hydrogen in nitrogen in an annealing furnace, wherein the average particle diameter of about 10 m was preserved. These partially reduced, spherical Ni/NiO particles already have an internal pore structure.

(12) 5 g of the partially reduced, spherical Ni/NiO particles are converted into a paste with 3 ml of a 7.5 wt. % aqueous solution of polyvinyl alcohol, which paste is then applied to one side of a 125 m thick nickel sheet.

(13) After a final tempering stage in the annealing furnace at a temperature of 620 C. in a reducing atmosphere of 50 vol. % hydrogen in nitrogen, the electrode formed is ready for use. The spherical nickel particles which were applied to the nickel sheet have an average diameter of 3.4 m and have an internal pore structure.

(14) The following Table 1 summarises the average particle sizes of the nickel hydroxide particles used, of the partially reduced Ni/NiO particles and of the spherical, porous nickel particles of the nickel layer.

(15) TABLE-US-00001 TABLE 1 Sample Average particle size [m] -Ni(OH).sub.2 10.1 Partially reduced Ni/NiO 10.3 Ni particles coated on Ni sheet 3.4
Oxygen Development

(16) Because of its large internal surface area, the transition resistance between the electrode according to the invention and the surrounding medium is very low, which means that the current density that can be attained during water hydrolysis for example is greater than that provided by uncoated nickel sheets. In uncoated nickel sheets, current densities in the range of 144 mA/cm.sup.2 with a voltage of 0.819 V against the Hg/HgO reference electrode, and voltage changes in the range from 50 to 100 V/s in an electrolyte consisting of 5.5 M KOH, 2.5 M NaOH and 0.5 M LiOH are obtained. The low voltage change may be considered a quasistatic measurement. The selected potential of 0.819 V against the Hg/HgO reference is attributable solely to oxygen development. With nickel electrodes having large surface areas produced with the method according to the invention, current densities of between 218-232 mA/cm.sup.2 are found under the same conditions. This corresponds to an average amplification of the current density by a factor of about 1.5 (see Tab. 2). The corresponding cyclic voltammograms are shown in FIG. 6 a-d.

(17) TABLE-US-00002 TABLE 2 Current density Current density [mA/cm.sup.2] [mA/cm.sup.2] Sample at 50 V/s at 100 V/s Ni sheet uncoated; 144.65 144.81 rear insulated with epoxy resin Ni sheet coated with 3.4 m 218.67 232.81 Ni particles; rear insulated with epoxy resin Average amplification factor 1.5 1.6
Hydrogen Development

(18) A significantly greater gas generation amplification effect due to the nickel electrodes with large surface area according to the invention may be observed for hydrogen generation. In uncoated nickel sheets, current densities in the range of 5 mA/cm.sup.2 for a voltage of 1.231 V against the Hg/HgO reference electrode and a a voltage change of 50 to 100 V/s in an electrolyte of 5.5 M KOH, 2.5 M NaOH and 0.5 M LiOH were obtained. The low voltage change may be considered as a quasistatic measurement. The selected potential of 1.231 V against the Hg/HgO reference is attributable solely to the hydrogen development. With nickel electrodes having large surface areas produced with the method according to the invention, current densities of between 86-91 mA/cm.sup.2 are found under the same conditions. This corresponds to an average amplification of the current density by a factor of about 17 (see Tab. 3). The corresponding cyclic voltammograms are shown in FIG. 6 a-d.

(19) TABLE-US-00003 TABLE 3 Current density Current density [mA/cm.sup.2] [mA/cm.sup.2] Sample at 50 V/s at 100 V/s Ni sheet uncoated; 5.35 4.92 rear insulated with epoxy resin Ni sheet coated with 3.4 m 86.49 91.29 Ni particles; rear insulated with epoxy resin Average amplification factor 16.2 18.55