Cathode for high-performance water decomposition electrolysis cells. RU patent 2505624.

FIELD: chemistry.

SUBSTANCE: disclosed is a cathode for releasing hydrogen in an electrolysis cell, having a metal base and a coating which consists of pure ruthenium oxide. Described is a method of coating the metal base.

EFFECT: improved performance and longer service life of the electrolysis cell when energy supply is unstable and periodic, such as energy from solar cells, high efficiency of electrolysis of alkaline water.

13 cl, 4 tbl, 3 ex

The technical field

The present invention relates to to produce hydrogen and oxygen from water. More specifically, the present invention relates to for electrolytic decomposition of water with high performance, ensuring high efficiency and long service life, especially when they are used with unstable and (or) periodical source of energy. The present invention also relates to a method of manufacturing of such cathodes.

The level of technology

Electrolysis of water is the well-known process for production of pure hydrogen and oxygen from water. In principle, water is decomposed into its elements by an electric current in accordance with the General chemical edition:

2H 2 O→2H 2 +O 2 ,

that shows that the development of hydrogen and oxygen takes place at a fixed volume ratio, i.e. the amount of oxygen for every two volume of hydrogen.

The reaction is carried out within the so-called electrolysis cells, which generates an electric field between two electrodes, a negative (anode) and positive (cathode), by means of the imposition of electric potential. Water, usually in the form of aqueous solution of a suitable electrolyte (such as salt, acid or base), subjected to electric shocks, and the molecule H 2 O is broken down in accordance with the above reaction and release of hydrogen at the cathode and oxygen at the anode.

Despite the seeming simplicity of the process, its implementation in industrial scale faces a number of technical problems, including the effectiveness of the use of electrical energy and reduce equipment costs.

Electrolysis of water is considered as a key technology for storage and transportation of electric energy in the form of hydrogen (H 2 ). H 2 is highly appreciated as a secondary source of energy as its combustion or reconversion into electrical energy through fuel cells barely out of harmful products. Electrolysis of water, in particular, seems very promising direction in the development of renewable energy sources, providing pure hydrogen, which can be stored, transported and effectively into electrical energy, or to be used as a clean fuel. The increase of polluting emissions and the costs of fossil fuels strongly encourages the promotion of this technology electrolysis of water power from renewable energy sources. Suitable renewable energy sources include , hydroelectric, geothermal, wind, biomass.

Most renewable energy sources, however, have the disadvantage of instability and intermittent. For example, in the case of photovoltaic cells (PV cells or generators working on wind turbines, giving a discontinuous and oscillating energy, heavily dependent on weather conditions.

When such unstable and generated periodically energy is applied to normal electrolysis for decomposition of water, the electrode respectively operates under widely and sometimes rapidly changing conditions of polarization. Accordingly, the electrodes are working in stressful environments, reaching as far as the unusual voltage ranges, which promotes corrosion and even the destruction of the surface of electrodes, reason (s) and bearing structures. It was noted that the harmful impact on the anode is mechanical in nature, while the cathodes are susceptible to chemical corrosion.

There have been several kinds of materials of electrodes to reduce or decisions of the aforementioned technical problems the destruction of electrodes electrolyzers for water decomposition under changing conditions of polarization. Generally speaking, it is known execution electrodes with metal basis, coated with a thin layer of activating material to reduce the surge in the allocation of hydrogen in connection with the electrode reaction. Electrodes with coating, for example, are disclosed in the DE-A-3612790.

More specifically, known by protection anodes is the process of electrochemical porous protective coating with catalyst grains deposited on Nickel basis. Other anode material valued over a relatively long-lasting stability is cobalt. Nickel anodes, covered with a mixture NiO and CO 3 O 4 , or NiCo 2 O 4 , also known as perspective materials. In accordance with the known data mixture of skeletal Nickel catalyst hydrogenation and CO 3 O 4 , applied by means of vacuum-plasma spraying, provide stability for long-term testing under periodic functioning.

On the other hand, and protection of cathodes is very problematic.

Coverage of skeletal Nickel catalyst hydrogenation, popular for water electrolysis steady-state conditions, to demonstrate the effectiveness of the variable polarization, but only while there are traces of metal associated with Nickel in the original alloy (usually Al Zn). As is known, during the preparation of the skeleton of Nickel catalyst hydrogenation, after the application of Ni-Al alloy, or Ni-Zn on the basis of alloyed metal leached alkali, leaving very porous Nickel metal. According to some publications, residual Al Zn provides the cathode relatively good stability to ash alkaline electrolyte. This type of cathode obviously results in a small interest in view of the limited lifetime.

Previously stated that the stability of the skeleton of Nickel catalyst hydrogenation can be increased at the expense of molybdenum additives, i.e. by adding pure molybdenum powder for the preparation of Ni-Al alloy by method of plasma spraying. This method, however, is very expensive and, in addition, during the electrolysis is also a trend to a gradual removal Mo alloy.

Have been tested precious metals alloy Ni/Al/Pt shows a very good baseline indicators surge, while the Pt is not able to prevent the decomposition of the alloy, after full removal Al. Moreover, these electrodes are very expensive because they require relatively large number of Pt. Platinum also dispersed by galvanic method and in small amounts (1 to 2 g/m 2 ) Ni-electrodes, showing very good results in long-term operation when modeling a day-night power cycles, as with conventional installations. However, they have a limit in terms of the need to ensure the security voltage polarization, when the energy supply is terminated, that requires unwanted energy costs.

Thus, prior art does not provide a reliable and effective in terms of cost, solve cathodic protection in the cell to the decomposition of water with unstable and (or) of the periodic submission of the electric power.

Disclosure of the invention

In the basis of the present invention is the task of overcoming the above limitations of prior art, i.e. the task of protection of the cathode cell for decomposition of water from the harmful effects of rapid and significant changes of polarization to improve the performance and service life of the cell, running off and (or) periodic energy supply.

This is achieved through a new type of cathode for the extraction of hydrogen in the electrolytic cell, having:

- metal basis (substrate) and

- thickness of the layer, provided on the specified basis and consisting essentially of pure ruthenium oxide.

The term "essentially pure ruthenium oxide" should be understood ruthenium oxide without doped () or added items. In accordance with the present invention, the Foundation has additional layers of coatings, i.e. the mentioned layer coating essentially pure ruthenium oxide, when used, is in contact with the electrolyte electrolytic cell.

In accordance with the preferred embodiment, the coating layer is a thin layer in the range from 0.1 to 2 mg/cm 2 ; preferably from 0.4 to 1 mg/cm 2 .

The basis of the electrode can be executed in the form of a plate or sheet, perforated or porous, or lattice, depending on the chosen configuration of the electrolytic cell. The substrate electrode is an electrically conductive material, preferably selected from the group consisting of low-carbon steel, alloy steel, Nickel and Nickel alloys.

Cathode in accordance with the present invention is particularly suitable for use in the electrolysis of water carried out in the alkaline environment.

The present invention also relates to the electrolytic cell containing a cathode, and electrolysis, containing electrolytic cell () with cathode.

In accordance with the present invention, electrolysis for hydrogen production has the appropriate number of electrolytic cells, each of which has the cathode with the coverage of ruthenium oxide (RuO 2 ), as defined above, and preferably receives energy from a renewable energy source, such as sun or wind.

Another aspect of the present invention refers to the use of essentially pure ruthenium oxide for coating metal cathode electrolytic cell for hydrogen in the electrolytic cell. In the present invention, in particular, it is offered to use essentially pure ruthenium oxide as a coating material cathodes for high performance, the electrolytic cell unsustainable and existing periodically source of energy, for example, when a cell is powered by a renewable energy source, such as sun or wind, which is usually electricity periodically and in the oscillating mode.

Accordingly, one aspect of the present invention relates to a method for producing pure hydrogen from water via electrolysis alkaline aqueous solution in a suitable device containing at least one of the electrolytic cell, where the hydrogen accumulates at the cathode, which has a metal base and coating essentially pure ruthenium oxide. Cell preferably supplied with energy from a renewable energy source. The term "renewable energy source" means any source, such as , hydroelectric, geothermal, wind, biomass or other renewable energy sources. Preferably use source or wind.

The present invention also relates to a method of manufacture of cathode in accordance with the above, by drawing on a surface of a metal base of the corresponding solution of a covering from a forerunner of ruthenium oxide.

Predecessor may be in the form of soluble salts, later in oxide form. Solution predecessor preferably prepared by dissolving chloride ruthenium, preferably in the form of hydrated RuCl 3 ·nH 2 O in spirtovom solution, preferably on the basis of isopropanol or 2-propanol added via distilled water and aqueous hydrochloric acid.

Coating metal base through ruthenium oxide also called activation framework. In a preferred embodiment of the present invention, the process of activation framework in its basis includes four steps, namely:

a) preliminary processing of the metal base;

b) preparation of activating solution by dissolving the respective predecessor ruthenium oxide in the solvent;

C) application of activating of a solution on a metal base;

g) implementation of the final heat treatment to fix coating on the metal base.

Preferably, pre-treatment includes degreasing and cleaning of metal surface. In accordance with other preferred aspects of the present invention, activating the solution was prepared by dissolving the respective predecessor ruthenium oxide in a solvent; and the drawing is carried out by means of repeated steps with intermediate stages ensure draining surplus solution, if necessary, and drying partially covered with a cathode. The number of such steps is preferably between 5 and 15.

The most preferred parts of the process described above are the following steps. The metal base is degreased and cleaned after preparation of the surface by means of sandblasting or chemical etching; is activating solution by dissolving chloride ruthenium, preferably in the form of hydrated RuCl 3 ·nH 2 O in spirtovom solution, preferably on the basis of isopropanol or 2-propanol added via distilled water and aqueous hydrochloric acid.

Solution predecessor applied by famous as such methods, such as dive pretreated basis in the solution, drawing with a brush or spraying the solution on basis; the best procedure can be selected depending on the size and (or) forms the cathode. The application is then repeated, preferably on both sides of the main cathode, while a specified number of activating substances will not be deposited on its basis; between successive occurrences of the application, as described, if necessary, provide drainage of excess solution or eliminate them through easy blowing air.

Base, coated with a layer of a solution, dried in the oven after each step of the application. Drying perform hot air when 150-350°C, preferably 250-300 C and within a few minutes, usually 3-12 minutes Cathode then extract and allowed to cool before the next drawing of a solution. To achieve adequate performance, many cathodes may be loaded together in the furnace by means of a suitable base frame.

The number of repetitions of the solution is chosen depending on the characteristics of the surface or design element used as a basis until the desired number of coated activating the material, expressed as weight per unit surface of the finished item.

The final heat treatment electrode is in the oven, the same has already been used during the repeated applications of activating a solution or in a separate. Cathodes are left in the oven under moderate circulation of hot air for a time of 1 to 2 hours at a temperature of 250-400°C, preferably 300-350°C.

After the end of the heat treatment, and in accordance with the preferred embodiment, the increase in weight the electrode of the element forming the basis associated with the application of activating material, ranging from 0.1 to 2 mg/cm, preferably from 0.4 to 1 mg/cm 2 activated surface.

Disclosed above process for the manufacture of cathode also provides a reduction in costs, which provides an opportunity of manufacture on an industrial scale.

The present invention also provides reliable and cost-effective way of obtaining pure hydrogen (H 2 ) through the decomposition of water (or a suitable aqueous solution) when using renewable energy sources.

The following are specific limiting claims examples illustrate some of the embodiments of the present invention.

Realization of the invention

Example 1

Used installation for water electrolysis with service elements, containing 60 bipolar cells, equipped with electrodes with 100 cm of the working surface. Electrodes having a circular shape, cut finely perforated Nickel sheet 0.2 mm thick. Perforation have 0.5 mm in diameter and triangular step 1 mm In each cell cathode and anode separated by spaces between them partitions-diaphragms with cloth 0,5 mm thick. Thin nylon mesh placed between each electrode and diaphragm. Bipolar cells are separated from one another by means of bipolar plates with a Nickel sheet 0.5 mm thick. The electrodes are kept in good contact with bipolar plates by Nickel .

The items included in the system to ensure stable circulation through a water solution of potassium hydroxide at a controlled temperature.

Anodes made of pure Nickel, degreased and cleaned with a solvent through the brush with the subsequent drying and short etching in hydrochloric acid.

Cathodes prepared by cleaning the basics as described for anodes, and then plunged in activating solution.

The solution was prepared from 36.5 g hydrated chloride ruthenium, with the content of EN 41,55%dissolved at room temperature, and mechanical stirring in 1 l of isopropanol, to which are added 10 ml of 25% solution of hydrochloric acid, 100 ml water. Mortar mix up within 30 minutes. These conditions are selected to guarantee the complete dissolution of salt ruthenium and ensure the stability of the obtained solution.

Pretreated cathodes kept in the solution about 1 minute, were pinned to the front, allowing to place 10 cathodes in a vertical position, leaving them to ensure draining surplus solution for a few minutes over a suitable flat capacity and then loaded into the furnace at 270 degrees C for 10 minutes with the easy air circulation. At the end of this operation, a rack with a group of cathodes were extracted from the furnace, and were left to cool on the open air at room temperature.

The application of the solution and drying step in the furnace and cooled repeated 6 times. After this hour, carrying 10 cathodes, thermally processed in the oven, where the temperature is regulated in the area of 320 degrees Celsius at a moderate circulation of air within 1,5 hours, with the subsequent extraction of the rack and cooling outdoors.

At the same time, other 5 sets of 10 cathodes were prepared by the same procedure.

Weighing cathodes at the end of treatment shows an increase of the weight of the corresponding application on the basis of 0.8 mg/cm 2 activating the material, related to 100 cm 2 electrodes and distributed on both opposite the main sides of each of the cathode.

Next, going to 60-well plates package through the introduction in the frame cell anodes and cathodes, prepared as described above. The package was installed in the installation of the electrolysis of water, providing all the functions of electrolyte circulation, temperature control process, the emission of the gases generated from the electrolyte and the maintenance of the necessary operational pressure.

The following table 1.1 collected registered and calculated technical and operational data.

Table 1.1

Direct current (A)

Electrolyte temperature (C)

Calculated current density (A/m 2 )

Voltage measured package (B)

Calculated environments. voltage of the cell (B)

Experimental data stresses packages, as appropriate medium voltage cells correspond to energy efficiency, which are significantly higher than the efficiency of alkali electrolytic cells, known from the prior art.

This is confirmed by the following steps comparative example. Given in the table 1.2 data for the same cell, as described above, equipped service elements of the same type, but with the cathodes activated by applying a serial skeletal coverage of Nickel catalyst hydrogenation flaming Nickel coating on the basis of cathode alloy Al-Ni and subsequent leaching of aluminum by boiling in the solution of the COM.

Table 1.2

Direct current (A)

Electrolyte temperature (C)

Calculated current density (A/m 2 )

Voltage measured package (B)

Calculated environments. voltage of the cell (B)

Example 2

Installation for water electrolysis is based on the package containing 48 bipolar cells, which are placed electrodes with 600 cm 2 working area. Electrodes having a circular shape, carved out of porous Nickel sheet 0.2 mm thick and have a diamond-shaped holes, characterized by transverse step 1.3 mm, longitudinal 0.65 mm, extension of 0.25 mm

Electrolytic cells have a configuration with zero gap, this means that in each cell anode and cathode are in direct contact with the opposite side of the diaphragm cell, made of a material Zirfon® 0.6 mm thick. The electrodes are kept in contact with bipolar plates by Nickel .

Package the items proceeds aqueous solution of potassium hydroxide, 30%concentration of circulating under controlled temperature by natural circulation.

Anodes of pure Nickel, degreased, subjected to sand-blasting through crystalline silica usual brand S/6, and finally cleaned jets of compressed air.

Preparation of cathodes was carried out the same treatment as described for anodes, before applying to the two main surface of the activator solution by means of a soft brush. It is prepared in the amount of 2.7 litres, starting with 100 g of industrial hydrated chloride ruthenium, with 41%EN content, and effective addition isopropanol, 270 ml of distilled water and 27 ml of 25% solution of HCl.

Cathodes were pinned to the front, the host set of 24 pieces in a vertical position. After draining surplus solution, they were loaded into the furnace and kept at 300 C, where they became dry for 6 minutes with the easy circulation of air. At the end of this operation hour with a kit of cathodes removed from the furnace and remained cool in the open air at room temperature.

Application of the mortar and stage heating of the furnace and cooled repeated 8 times.

Then, hour, carrier cathodes, is placed on the continuous belt furnaces, in which the length of stay was up to 2 hours at the temperature to 350 degrees C at a moderate air circulation. When you exit the furnace cathodes were left to cool on the open air.

At the end of the heat treatment, the average increase in the weight of one cathode amounted to 430 mg, which is equivalent to 0.36 mg/cm 2 overall effective cathode surface (considering the two opposite of basic surfaces) or about 0.72 mg/cm 2 in respect of the area of the cathode.

Package with 48 cells was going through the introduction in the frame of the cell anodes and cathodes, prepared as described above.

Installation for water electrolysis with service items provided all the necessary functions and control of all parameters of the process, such as process temperature, pressure, fluid levels, the gas analysis.

The items supplied with energy by means of a direct connection to the 30- field of solar photovoltaic cells, which includes 300 photovoltaic panels, consistently connected 100 sections of 3 panels each. Maximum power of direct electric current is up to 300 A, which corresponds to the peak current density cell 5000 A/m 2 .

When the value of the supplied DC power is reduced below 30 A, the energy supply to electrolysis off automatically to avoid the excavation is not enough pure hydrogen. Accordingly, it can occur not only at night but also during the day, when the clouds reduce the solar radiation and the energy supply to the cells can be stopped. Supply the cells with energy automatically resumes when the radiation generates sufficient electric current (>30 (A).

During the 30-day work period, from mid-April to mid-may, 41.5 degrees North latitude, were registered in total 72 interruption of DC, with a maximum of 45 peaks of different intensity in one day.

The following table 2.1 shows the average data recorded at different constant currents at different times during the initial days of the current period and, accordingly, at the end of the current period corresponding to the temperature of the electrolyte 70±1o C, at constant pressure 15 bar.

Table 2.1

The early days of the current period

End of the current period

Instant direct current (A)

Voltage package (B)

The average voltage of the cell (B)

Voltage package (B)

The average voltage of the cell (B)

The results demonstrate good stability.

Example 3

The basis of the electrode the same, sandblasted as in example 2, but a technique of applying predecessor was different.

Anodes were activated by applying a cobalt oxide (Co 3 O 4 ), while activating the cathodes was realized by applying activator solution, prepared by the procedure of the previous examples, by 0.15 M solution of hydrated ruthenium (.Fluka 84050) 2-propanol (.Fluka 59300). The application was ensured through aerial spraying a solution on both the main surface of the cathode.

After a light blow air to remove excess solution with cathodes, they were placed at the front and loaded on 5-6 minutes in a muffle furnace, maintaining temperature of about 330 OC C.

The application of the solution and heating in a muffle furnace repeated 8 times with the final abandonment of the rack with the cathodes for 1 hour at 330 OC C.

The average increase in the weight of the specific cathode in the result of the activation was 105 mg

After the installation inside the electrolysis cells and Assembly of packages elements, the system was filled with a 30% solution of KOH as the electrolyte, maintaining adequate circulation.

The direct current generated through the model of a wind turbine is fed to the package elements, with a consistent repetition for a continuous period of 50 days and daily chart loads, concise as explained above. This means that for a 24 hour cycle repeated 72 times, when the total number of 3600 repetitions, simulating about 10 years of operation of the device. In General, current load interrupted more than 14,000 times.

During the interruption of DC voltage polarization to the cells not committed.

Process pressure was maintained constant about 10 bar for the entire period. Temperature remained vibrating as a result of changes in current density, limited by cooling only in case of reaching 85 C

Evaluation of the effectiveness of cathodes was carried out by comparing the electrical characteristics of the package at the beginning and end of the test. Measurements were performed in the established mode at a temperature of 80±2 degrees C, the pressure of 10 bar, with 30% of the electrolyte CONCENTRATION. The following results were obtained:

Start of the test

The end of the test

Direct current (A)

Voltage measured package (B)

The average voltage of the cell (B)

Voltage measured package (B)

The average voltage of the cell (B)

As shown, the efficiency of the cells is reduced over the test period, while this reduction is limited to the acceptable by any industrial application.

1. Method of water electrolysis for hydrogen (H 2 ) and oxygen (O 2 ) of water, including the stage of electrolysis alkaline water solution in at least one of the electrolytic cell, containing at least the anode and cathode and in which water is decomposed into hydrogen and oxygen so that the resulting hydrogen accumulates on the above at least one cathode mentioned at least one cell, and the cathode has a metal base, which is made from a material selected from mild steel, alloy steel, Nickel and Nickel alloy, and coating layer on the metal base, consisting of ruthenium oxide without alloyed or added items, and the cathode is made by a process that includes at least the following stages: a) pre-treatment referred to the metal base; b) preparation of an activator solution by dissolving hydrated RuCl 3 ·nH 2 O in spirtovom solution based on isopropanol or 2-propanol, added with distilled water and aqueous solution of hydrochloric acid; C) application of the activator solution on a metal basis; d) the final heat treatment to fix coating on the metal base.

2. The method according to claim 1, wherein the said coverage ranged from 0.1 to 2 mg/cm 2 , preferably from 0.4 to 1 mg/cm 2 .

3. The method according to claim 1 in which the said cathode is made in the form of, selected from the group consisting of plate, perforated or porous sheet, grill.

4. The method according to claim 1 in which the said electrolytic cell works from a renewable energy source.

5. The method according to claim 1 in which the said stage (is performed by successive applications of activating of a solution on a metal base, with each application follows the steps draining surplus solution with a metal base, and drying cathode before the next application.

6. The method according to claim 5, where drying is carried out in a hot air oven at temperature of air between 150 and 350 OC and length of stay basics from 3 to 12 minutes

7. The method according to claim 5, in which the application of the activator solution is repeated 5-15 times.

8. The method according to claim 1, 5-7, which referred to the stage (g) the final heat treatment is performed in the hot air oven at a temperature of between 250 and 400 deg C and processing time from 1 to 2 hours

9. Method of manufacture of cathode designed for use in the method according to claim 1, comprising at least the following stages: a) preliminary processing of the metal base; b) the preparation of activating solution by dissolving hydrated RuCl 3 ·nH 2 O in spirtovom solution based on isopropanol or 2-propanol, added with distilled water and aqueous solution of hydrochloric acid; C) application of the mentioned activating the solution on a metal basis; d) implementation of the final heat treatment to fix coating on the metal base.

10. The method of claim 9, in which the said stage (is performed by successive applications of activating of a solution on a metal base, with each application follows the steps draining surplus solution with a metal base, and drying cathode before the next application.

11. The method according to paragraph 10, in which the drying perform in a hot air oven at temperature of air between 150 and 350 OC and length of stay basics from 3 to 12 minutes

12. The method according to paragraph 10, in which the application of the activator solution is repeated 5-15 times.

13. Method according to sub-clause 9-12, in which the mentioned stage (g) the final heat treatment is performed in the hot air oven at a temperature of between 250 and 400 deg C and processing time from 1 to 2 hours