CA1187043A - Catalyest cladded electrode at which a slight overvoltage results in oxygen discharge, useable for the electrolysis of water in alkaline media, and manufacture of said electrode - Google Patents

Abstract

The present application relates to a new electrode covered with a catalyst having a low overvoltage for the release of oxygen, usable in particular for the electrolysis of water in an alkaline medium (anode), and a method of manufacturing this electrode. This includes a metallic support covered with a nickel layer made up of nickel particles whose size is from 5 to 150 nm, which has pores with a diameter of 0.5 to 50 nm and which develops a specific surface. from 1 to 120 m2 / g. The nickel layer has an oxide containing cobalt on its surface.

Description

The invention relates to a new electrode covered with a ready catalyst.
feeling a ~ low overvoltage for the release of oxygen, usable notarn-ment for the electrolysis of water in an alkaline medium (anode), and a method of manufacturing this electrode.
The manufacture of thin sheets of highly divided nickel by projection of molten particles of an allia ~ e of Raney is known; the use of these sheets them as electrodes has also been described (US Patent 3,637,437). Under strong anodic polarization, the surface of electrodes of this type is covered with a layer of nickel oxide badly conducting the current and the overvoltages for the oxygen release grow until it becomes greater than that observe on a sheet (or on a grid) of solid nickel.
The use of cobalt-based oxides to reduce the oxygen overvoltage is also known. In English patent 1,352,995, oxides of the pe- type rowskite of formula La1 x Srx Co ~ 3 are prepared in powder form, then applied to a metallic conductor using an organic binder (polyty-trafluoroethylene). When the quantity of binder used is large, the adhesion is good, but the electrical resistance of the catalytic layer is excessive and the oxygen overvoltage that is observed at high current densities is significant. Reducing the amount of binder reduces the adhesion of the product and the service life of the catalytic layer is short.
It has also been proposed to coat the electrodes with galvo-noplasty with layers of nickel sulfide (German patent 28123 ~ 9) or mixed nickel and cobalt sulphide (request ie ~ revet fransais 2 444 083).
It is also known to use electrodes constituted by ~ Ieuil-sintered nickel or by nickel sheets coated with sintered nickel, said sintered nickel comprising oxides of different metals which are incorporated by impregnation of salts in solution and subsequent heat treatment. These sintered nickel layers are obtained by agglomeration of nickel powder and generally have pores with a diameter of 1 to 100 ~ m. The absence of pe-breast pores whose size is less than 0.1 ~ m does not allow re-suitable partitioning of the oxide layer on the base metal.
The release of oxygen inside the pores of this type of electrode moreover leads to their disintegration, sometimes very rapid, when they are used at high current densities.
The low overvoltage electrode according to the invention does not have the in-the well-known nickel-based electrodes of the nickel type Raney or electrodes covered by an oxide powder bound by polyté-trafluorethylene or even electrodes formed by layers of ni-ckel sintered impregnated with oxide. The catalytic layer which covers them has .

excellent adhesion to the current collector support and oxygen release voltages remain low for very long periods of time long t more than 10,000 hours), even at high current densities (up to 1 A / cm or more ~ and at electrolyte temperatures up to 160 or 200GC.
The electrodes according to the invention are covered by a catalytic layer.
that intended to reduce overvoltages and therefore reduce the specific consumption of electrical energy. It was discovered that the deposit on a electrically conductive substrate of a very finely divided porous nickel coating, the surface of which is then treated to fix a small amount of an oxide containing cobalt makes it possible to obtain an electrode with low sur-if we, In the case of alkaline electrolysis of water, the conductive substrate electricity will preferably be made of nickel. Alloys rich in ni-ckel or nickel-plated steels can also be used. This substrate can be presented, for example, in the form of plates, tubes, fabrics or grids.
The catalytic layer according to the invention which is deposited on the substrate conductor of electricity is generally prepared in two main stages:
1 - A layer of nickel is first formed on the metal substrate very finely divided reux ~ or very finely divided porous mixture or alloy with nickel base).
Z - The product of step 1 is subjected to a treatment making it possible to fix on its surface a small amount of an oxide containing cobalt.
By very finely divided porous nickel layer is meant a layer of nickel formed from an assembly of very fine particles whose size ~ measured under the electron microscope or by X-ray scattering, depending on the method described in the book "X-Ray Diffraction Procedures" by Klug and AlexanderJ
pages 542 to 708 edited by J. Wiley and Sons in New York in 1974) is from 5 to 150 nm preferably from 5 to 50 nm.
The arrangement of these small nickel particles will preferably be such that it forms a porous body resembling a sponge with pores of a diameter be from O, S to SO nm and preferably from 2 to 10 nmJ so as to develop a specific surfaceJ measurable for example by the BETJ method from 1 to 120 m / g and preferably from 1 to 80 m / g.
Other coatings suitable for making the first layer of electricity trode according llinvention can be obtained by replacing the coating of ni-finely divided porous ckel applied to the electrodes by a nickel-based coating further containing up to 50 ~ weight of MnJ Ee, Co, Nb or Ta and / or , - 3 -~ '7 ~? ~ 3 up to 15% by weight of Mg, Al, Si, Ti, V, Cu, Zn, Zr, Mo, Sn, La, Hf, W, Pb or Bi, relative to the nickel in the coating.
In general, the thickness of this layer will advantageously be from 5 to 500 ~ m and preferences from SO to 150l ~ m.
A pre ~ erated method to dispossess the nickel-based layer on the elect trodes according to the invention, consists in applying to a solid metallic support, for example in the form of a solid plate, canvas or grid, a layer of nickel-aluminum al-binding preferably containing from 45 to 55% by weight of each metals, by plasma torch projection. The application of this alloy layer can be done using a preformed nickel-aluminum alloy. We can also carry out a simultaneous projection of the two separate metals, a re-baked at temperatures ranging from 200 to 800C, for example 1 to 8 hours can then be pra ~ ique to promote the formation of the alloy between ni-ckel and aluminum. Any other process for forming a layer of nickel-aluminum bonding on the electrode can be used. We can for example forming an aluminum film on a nickel surface by evaporation of aluminum under vacuum and carrying out a subsequent annealing to diffuse the aluminum in the nickel. It is also possible to co-laminate nickel sheets and aluminum followed by heat treatment. The thickness of the layer of alliagenickel-aluminum may advantageously be between 5 and 500 ~ m or da-vantage, and preferably between 50 and 150 ~ m.
This layer of nickel-aluminum alloy is then subjected to attack chemical of known type by an aqueous solution of soda or potash, in order to dissolve the aluminum.
A preferred operating mode is as follows: the attack is made first at cold with a diluted caustic solution (for example 1 to 2N) ~ until cessation of the evolution of hydrogen. The concentration of soda or potash is then increased ~ 6 to 1N) and the temperature is raised to 60 to 80C.

It is advantageous, more particularly when the nickel layer 30 divided was formed by an application of nickel-aluminum alloy followed by a alkaline attack, to perform a depyrophorization of the porous nickel obtained, so as to eliminate the hydrogen which it can retain. This operation can be carried out by contact with hydrogen peroxide with Seil1 from an alkaline medium (for example lN potash solution), it is continued until the potential of the electrode is stabilized. It is also possible to operate by air bubbling.

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7 ~ fL3 Layers of divided nickel suitable for the manufacture of electrodes lon the invention can be obtained analogously from alloys such as nickel-magnesium, nickel-zinc, nickel-silicon, nickel-mercury which is put implemented using suitable proportions and activated by techniques such as those mentioned by WJ KIRKPATRICK ~ Catal ~ sts from alloys of nickel and non-catalytic Metals-publication ICL-1Z - Ths InternationalNickel Company Inc. New ~ ork USA 194 ~) and which include in particular the evapora-selective tion, acid or alkaline hydrolysis, selective chlorination and oxidation.
Other forms of highly ivory porous nickel obtained by electroplating, thermal decomposition of nickel carbonyl or organometallic compounds of nickel, for example acetylacetonate, decomposition and reduction of salts of nickel. for example nitrate, formate, oxalate, carbonate, or by any other process may be used for the manufacture of the electrodes provided that the parameters relating to the particle size, the pore size and the specific surface are as indicated above.
~ The oxides containing cobalt which are deposited in step 2 on the surface ; of the product prepared in step 1 are either the simple cobalt oxides such as CoO, Co304, Co203 or mixed oxides such as for example spinels of type A Co204 where A denotes a metal such as Ti, V, Mn, Fe, Ni, Cu, Zn, Ge or Sn, engaged in the form of a divalent cation, or spinels of the Co type B2 ~ 04 where B denotes a metal such as Al, V, Cr, Mn, Fe, Ga, or In engaged in the form of cation trivalent, or perowskites of the Ln1 M Co 03 type where Ln denotes a metal of transition from the lanthanide series ~ elements of the periodic classification having an atomic number of 57 to 71) engaged in the form of a trivalent cation, M
denotes an alkaline earth element such as Ca, Mg, Sr or Ba and x has a value from 0 to 1 J OR again perowskites of the previous type in which a pro-minor portion of cobalt has been substituted by another element, such as Nb. Mo, Sb, Ta, W, U.
Other cobalt-containing oxides known for their resistance to attack by alkaline solutions and their catalytic activity in reactions using oxygen can be used without departing from the scope of the pre-invention.

. .

The deposition of this oxide layer on the very thin porous nickel layer-ment divided can be done by techniques well known in the art of art.
Electroplating techniques can be used to deposit the oxide metals to form on the surface of the divided nickel layer, then oxidize this deposit electrochemically or chemically.
It is also possible to impregnate the porous layer of ni-ckel by a solution of the metal salt (s) of the oxide to be formed, then, after solvent evaporation, heat treat these salts to decompose and form the oxide. To the solution ~ 'impregnation, we can add, if necessary, various gelifying agents, for example citric acid.

We can also proceed with the formation of the surface oxide layer.
by reactions occurring on the surface to be covered between compounds brought in the gaseous state, such as for example the pyrolysis of organic compounds volatile according to a reaction of the type:

[], ~]
or the reaction between the ~ the) halurets) volatile ~ s) of the metals considered res and a hydrogen-carbon dioxide mixture in contact with the surface of ni-ckel divided, according to a reaction of the type:

MCl ~ + 2 H2 ~ 2 C02 - ~ M02 ~ 4 HCl + 2 CO

The amount of cobalt-containing oxide that is permeated into the layer of divided nickel must be from 1 to 30% of the weight of said layer of nickel and preferably 5 to 15%.
The examples which follow illustrate the invention and should in no way limit it. Examples 1,3,4,8 and 9 are given by way of comparison.

Example 1 (Comparative) , Two 4 x 4 cm grids are cut from an expanded nickel sheet 0.3 mm thick, with diamond-shaped perforations, the large diagonal measures 4.5 mm, these perforat ~ ons being separated by metal strips 1 mm wide.

~ '7 ~ 3 These grilled s ~ n ~ aécapéeS by saDlage, degreased, then my ~ ées in a water electrolysis cell working at 80C at atmospheric pressure with a 36% KOH solution as an electrolyte. These two electrodes are pressed on either side of a diaphragm asbestos ~ asbestos "Ferlam 844", trademark).
One of the electrodes is connected to the pole plus a current generator continuous to serve as an anode. The other electrode is connected to the minus pole of this same generator to serve as cathode.
A mercury-mercury oxide reference electrode containing potash at 36% as electrolyte makes it possible to measure the electro-chemical potential of the ano-thanks to a Luggin capillary emerging near the working face of this anode.
The evolution of the electrochemical potential of this non-activated anode is given in table I as a function of the electrolysis time for a density of constant current equal to 1 A / cm.

Example 2 Again, two grids identical to those described in Example 1.

a) These grids are stripped by sandblasting and then covered with a layer of a nickel-aluminum alloy of average thickness 100 ~ m, by projection using a plasma torch of a powder of a commercial Ni-Al alloy 50-50 with a particle size between 25 and 80 ~ m.

After an annealing of 4 hours under an inert atmosphere (nitrogen) at 400 C, these electrodes are immersed in a 2N potassium hydroxide bath.
When the evolution of hydrogen caused by the chemical attack of aluminum nium has stopped, the 2N potassium hydroxide solution is replaced by a 8N solution and the bath temperature is gradually increased to We use the first electrode to determine its characteristics, as following :

~ - ~ - 7 -~ 7 ~ 3 After washing with water until all traces are completely eliminated residual potassium hydroxide, the surface catalytic layer of the electrode is examined under the electron microscope and by diffrac-tion of the X-rays. The adsorption isotherms are then determined.
desorption of nitrogen at 77K (-196C) and the specific surface is calculated product fique according to Brunauer's equation? Emmett and Teller (J. Am. Chem. Soc. 60, 309, 1938). These various examinations show that the catalytic layer which covers the electrodes is constituted by poorly crystallized nickel containing a small proportion of aluminum (probably alloyed with nickel in Ni Al form and in oxidized form).
The size of the nickel crystallites is between 5 and 50 nm, the pores have a diameter of 2 to 10 nm and the BET surface is 65 m2 / g.

b) the second electrode is also washed with distilled water, then oxidizes the hydrogen remaining in the nickel layer divided by depyro-phorination with hydrogen peroxide. This depyrophorization operation is made by immersing the electrode in a container containing potash lN, and we measure its potential compared to a reference Hg-HgO, while gradually adding a 1M solution of hydrogen peroxide.

The potential of the electrode, which is initially about - 830 mV, lowers when oxygenated water is added. The bill of hydrogen peroxide is stopped when the electrode potential remains at - 590 mV for at least 10 minutes.

This electrode is then immersed in a solution containing 58.20 g of Co (N03) 2.6 H20 per liter for 20 minutes. The electrode is finally drained, then put in an oven under air which one carries the temperature at 500 C for 1 hour.

Examination of the catalytic layer by ray diffraction shows that it contains nickel, a spinel phase C0304 as well as small amounts of NiO and A1203.

This electrode is then used as an anode in the same conditions as in example 1. The electrochemical potential of this electrode and its evolution over time are indicated in the table I.

Example 3 (comparative) The operations of example 2a) are repeated until the attack by potassium hydroxide, to obtain an electrode covered with split nickel.

After washing with distilled water, this electrode is used as an anode under the same conditions as in Example 1. The potential electrochemical of this electrode and its evolution over time under a constant current density of 1 A / cm2 are indicated in the table I.

Example 4 (comparative) .

We repeat again the operations of example 2 a) but we this time uses an alloy powder containing 45% by weight of nickel, 5% cobalt and 50% aluminum.

After washing with distilled water, this electrode is used as anode under the same conditions as in Example 1. A colo-blue ration develops in the electrolyte near the anode from the start of electrolysis indicates a dissolution of cobal-t.
The chemical analysis of the electrolyte effectively confirms that co-balt has gone into solution. The electro-chemical potential of the anode measured during electrolysis is shown in Table I.

Example 5 25 g of Co (CH3CO2) 2, 4 H2O, 12.5 g of Ni (CH3CO2) 2 are dissolved.
4 H20 and 7 9 7 g of NH4CH3C02 in 500 ml of CH30H. We add 4 g of granulated activated carbon and a stream of air and ammonia is bubbled through this solution for 2 hours. It is then filtered to eliminate the coal.

An electrode prepared as in Example 2 a), then depyro-phorinated with hydrogen peroxide as in Example 2b) is immersed in this solution of nickel II hexammine acetate and cobalt III
hexammine for 15 minutes, then drained, air dried then cal-cine at 450 C for 1 hour.

Examination of the catalytic layer by X-ray diffraction shows that it contains nickel, a NiCo2 04 spinel phase as well only small amounts of NiO, Co304 and Al203.

The electrode obtained is used as an anode in the same conditions as in example 1. Its measured electrochemical potential during an electrolysis at 80 C at 1 A / cm2 is indicated in the table I.

Example 6 . .

An electrode is prepared as in Example 2a), then depyrophorized under water by air bubbling for 6 hours. This electrode is then immersed in a solution containing 58.20 g of Co (N03) 2 6 ~ 120, 161.6 g of Fe (N03) 3 9 H20 and 30 g of citric acid per liter. After draining, the electrode is dried under vacuum at 80 ° C.
then calcined in air at a temperature of 450 C for one hour.

Examination of the catalytic layer by X-ray diffraction shows that it contains nickel, a CoFe204 spinel phase as well as a little NiO and Fe304.

~ ~ ~ 7 ~ ~

The evolution of the electrochemical potential of this anode is given in table I as a function of the electrolysis time for a constant current density equal to 1 A / cm2.

Example 7 An electrode covered with divided nickel is prepared as in example 2a). After washing with distilled water, the hydrogen which remains in the electrode is oxidized by hydrogen peroxide, as described in example 2b).
-This electrode is then immersed in a solution containing 21.16 g of Sr ~ N03) 2, 43.30 g of La (NO3) 37 6 H2O, 58.20 g of Co (N03) 26 H2O and 20 g of citric acid per liter ~ for 20 minutes.
The electrode is finally drained, then put in an oven under air which brings the temperature to 500 C for one hour.

Examination of the catalytic layer by X-ray diffraction shows that it contains nickel, a phase of the Lax Sr1_x CoO3 type fairly poorly crystallized, as well as small amounts of NiO, SrO
and Co304.

The electrode obtained is used as an anode in the same conditions as in example 1. Its measured electrochemical potential during an electrolysis at 80 C at 1 A / cm2 is indicated in the table I.

Example 8 (comparison) A powder of a mixed oxide of composition LaO S SrO 5 Co 03 is prepared by dissolving 10.58 g of Sr (N03) 2, 21.65 g of La (N03) 3 6 H20 and 29.10 g of Co (N03) ~, 6 H20 in 500 ml of distilled water then by dropping this solution in rain in an insulated container containing liquid nitrogen at - 196 C. The frozen product beads thus obtained are then dehydrated under reduced pressure -(lyophilization) then thermally decomposed in air in an oven whose temperature is raised to 500 C. The product of calcination is ground in a mortar, then 2 g of the powder obtained are mixed with 0.6 g of PTFE (mar ~ ue ;; Teflon 30 "from Du Pont de Nemours) and 40 cm3 of water. This suspension is then projected by means of a pistol on both sides of a grid identical to those of Example 1 placed on a hot plate. We thus deposit approximately 15 mg of cobalt-based oxide per cm2 of electrode. Cooking under air at 320 C for 30 minutes is finally performed.

This electrode is then used as an anode in the same conditions as in example 1. The electrochemical potential of this electrode and its evolution over time are indicated in the table I.

Example 9 (comparative) An electrode covered with sintered nickel is prepared for deposition.
health on the surface of a grid identical to those used in Example 1 a slurry composed of an ex-carbonyl nickel powder commercial 5 th ~ (Baudier - Poudmet 77 NM 5l ~) and a thickener (nitrocellulose) in solution in acetone. The electrode is first dega ~ ée under air in portan-t gradually its temperature up to 180 C then heat treated under hydrogenated nitrogen at 850 C
for 30 minutes. The thickness of the sintered layer is 95 ~ m.

This electrode is then immersed in a solution containing 21.16 g of Sr (N03) 2, 43.30 g of La (N03) 3, 6 ~ 120, 5 ~ 3.20 g of Co (N03) 2 6 ~ 120 and 20 g of citric acid, per liter, for 20 minutes. The elect trode is finally drained, then put in an oven under air which one carries the temperature at 500 C for one hour.

The electrode obtained is used as an anode in ~ es themselves conditions as in example 1. Its electrochemical potential measures 30 during an electrolysis at 30 C under l A / cm2 is indiqlle in the , ~ Y.
- 1 ~ -3`

table I.

Example_10 An electrode covered with divided nickel is prepared as in Example 2a) using a powder as the starting material of an alloy comprising 48% Ni, 2% Ti and 50% Al by weight.

This electrode is impregnated Gum in Example 7 with a solution comprising nitrates of cobalt, lanthanum and strontium and citric acid, then heat treated under the same conditions.

X-ray diffraction examination shows the presence of the same phases plus some titanium oxide.

The electrode is ultimately used as an anode in the same conditions as in example 1. Its measured electrochemical potential during an electrolysis at 80 C at 1 A / cm2 is indicated in the table I.

TABLE I

Evolution of the potential of the anode (in mV) compared to to a reference Hg - HgO, over time.
¦ Time ~
n (h) l 2 ¦ 20 ¦ 100 ¦ 200 ¦ 300 Example ¦ 1 (comp) ¦ 780 ¦ 785 1,795 ¦ 810 ¦ 820 ¦ 3 (comp) ¦ 735 ¦ 800 ¦ 895 1,930 ¦ 955 ¦ 4 (comp) ¦ 675 ¦ 690 ¦ 840 ¦ 925 ¦ 945 1 5 1,630 1,640 1,665 1,665 1,670 1 7 1,625 1,630 1,640 1,645 1,645 ¦ 8 (comp) ¦ 695 ¦ 710 ¦ 730 ~ 740 1,740 9 (comp) ¦ 720 ¦ 735 ¦ 765 ¦ 770 ¦ 775 lO I 625 1,630 1,635 1,635 1,635 These results show that the electrodes of the examples according to the vention allow the release of oxygen to potentials which are lower, therefore with a lower ~ overvoltage, than the electrodes representative of the prior art used under the same conditions.

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Claims (20)

The embodiments of the invention, concerning the-what an exclusive property right or lien is claimed, are defined as follows: 1. Electrode characterized in that it comprises a metal support covered with a layer of nickel made up of nickel particles whose size is 5 at 150 nm, which has pores with a diameter of 0.5 to 50 nm and which develops a specific surface from 1 to 120 m2 / g, said layer of nickel comprising on its surface a cobalt-containing oxide. 2. Electrode according to claim 1, character-laughed at in that it is obtained by a process in which:
(a) a metal support is deposited on said metal support alloy containing nickel and aluminum;
(b) at least most of aluminum so as to obtain a layer of nickel very finely divided porous according to claim 1;
(c) depositing on the surface of said layer of nickel at least cobalt or at least one cobalt compound;
and (d) the deposit obtained is transformed into oxide containing cobalt. 3. Electrode according to claim 2, character-laughed at in that the nickel aluminum alloy used in step (a) contains 45 to 55% by weight of each metal. 4. Electrode according to claim 2 or 3, characterized in that the alloy deposition in step (a) is carried out using a plasma torch. 5. An electrode according to claim 2 or 3, characterized in that the metal support coated with aluminum bonding in step (a) is annealed at 200 - 800 ° C
for 1 to 8 hours before step (b). 6. Electrode according to claim 2, character-in that in step (b), the elimination of aluminum nium is carried out by attack with soda or potash. 7. An electrode according to claim 2, character-laughed at in that the support coated with the nickel layer porous very finely divided after step (b), is subjected to depyrophorization by contact in alkaline solution with hydrogen peroxide or by bubbling air, before step (c). 8. Electrode according to claim 2, character-laughing at the fact that the support coated with the nickel layer very finely divided porous is impregnated, in step (c), with a solution containing at least one cobalt compound and, after evaporation of the solvent, said cobalt compound is transformed into oxide by thermal decomposition, in step (d). 9. An electrode according to claim 8, character-laughed at in that the solution used for impregnation in step (c) further contains a gelling agent. 10. An electrode according to claim 1 or 2, characterized in that the divided nickel layer has a thickness from 5 to 500 µm. 11. Electrode according to claim 1, character-laughed at in that in said nickel layer a fraction up to 50% by weight of nickel is replaced by the same weight of at least one metal chosen from manganese, iron, cobalt, niobium and tantalum, and / or a fraction up to 15% by weight of nickel is replaced created by the same weight of at least one metal chosen from magnesium, aluminum, silicon, titanium, vanadium, copper, zinc, zirconium, molybdenum, tin, lanthanum, hafnium, tungsten, lead and bismuth. 12. An electrode according to claim 2, character-weighed in that in said layer of nickel a fraction up to 50% by weight of nickel is replaced by the same weight of at least one metal chosen from manganese, iron, cobalt, niobium and tantalum, and / or a fraction up to 15% by weight of nickel is replaced created by the same weight of at least one metal chosen from magnesium, aluminum, silicon, titanium, vanadium, copper, zinc, zirconium, molybdenum, tin, lanthanum, hafnium, tungsten, lead and bismuth. 13. An electrode according to claim 1, 11 or 12, characterized in that in said nickel layer a fraction up to 15% by weight of nickel is replaced created by the same weight of titanium. 14. An electrode according to claim 1 or 2, characterized in that the amount of oxide containing cobalt represents from 1 to 30% by weight of the layer of split nickel. 15. An electrode according to claim 1, character-laughed at in that said cobalt-containing oxide is at less in the form of a selected simple oxide among CoO, Co3O4, Co2O3, of a mixed spinel oxide ACo2O4, where A represents a metal chosen from titanium, vana-dium, manganese, iron, nickel, copper, zinc, germanium and tin, a mixed spinel oxide Co B2O4, where B represents a metal chosen from aluminum, vana-dium, chromium, manganese, iron, gallium and in-dium, or a mixed perowskite oxide Ln1-x Mx Co O3 where Ln represents a metal from the lanthanide series, M represents smells of an alkaline earth metal, x having a value of 0 to 1, or a mixed perowskite oxide of the above type in which a minor proportion of the cobalt is replaced by the same weight of a metal chosen from niobium, the molybdenum, antimony, tantalum, tungsten and uranium. 16. An electrode according to claim 2, character-laughed at in that said cobalt-containing oxide is at less in the form of a simple oxide chosen from CoO, Co3O4, Co2O3, of a mixed spinel oxide ACo2O4, where A
represents a metal chosen from titanium, vanadium, manganese, iron, nickel, copper, zinc, germa-nium and tin, a mixed spinel oxide Co B2O4, where B
represents a metal chosen from aluminum, vanadium, chromium, manganese, iron, gallium and indium, or of a mixed perowskite oxide Ln1-x Mx Co O3 where Ln represents a metal from the lanthanide series, M represents a metal alkaline earth, x having a value of 0 to 1, or a perowskite mixed oxide of the preceding type in which a minor proportion of cobalt is replaced by the same weight of a metal chosen from niobium, molybdenum, anti-monk, tantalum, tungsten and uranium. 17. An electrode according to claim 15 or 16, characterized in that said cobalt-containing oxide is at least partly in the form of a mixed spinel oxide Co B2O4, where B represents iron. 18. An electrode according to claim 15 or 16, characterized in that said cobalt-containing oxide is at least partly in the form of a mixed perowskite oxide Ln1-x Mx CoO3, where Ln represents lanthanum and M represents strontium. 19. An electrode according to claim 1 or 2, characterized in that nickel is present in the form particles from 5 to 50 nm, has pores from 2 to 10 nm and develops a specific surface of 10 to 80 m2 / g. 20. Method of electrolysis of water in the medium alkaline, characterized in that an anode is used an electrode according to claim 1.