Water electrolysis device

Abstract

To solve the following problem that: in water electrolysis, the place where the reaction proceeds is an extremely limited region at the interface between gas and liquid on the electrode surface, that is, an interface of the three phases of solid, gas, and liquid; the place where the reaction proceeds is therefore limited to a narrow range of the interface between gas and liquid on the electrode surface; and hydrogen molecules or oxygen molecules are not generated unless two molecules of water or four hydroxyl groups simultaneously come into contact with one point in this narrow reaction region, resulting in an extremely limited reaction mechanism.SOLUTION: A water electrolysis device is configured to have at least two sets of electrode groups each having a negative electrode, a positive electrode, and an intermediate electrode, with the intermediate electrode arranged between the negative electrode and the positive electrode, wherein the intermediate electrode is arranged between the negative electrode of one electrode group and the positive electrode of another electrode group. This configuration enabes a reaction surface to expand from a line to a surface to allow efficient water electrolysis.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to an apparatus for generating hydrogen and oxygen by electrolyzing water, and more particularly to a water electrolysis apparatus for producing hydrogen gas and oxygen gas separately. [Background technology]

[0002] Hydrogen is not only an important industrial gas used in the chemical industry and petroleum refining, but in recent years it is expected to play an important role as an energy source that does not produce environmentally hazardous substances. For this reason, the development of hydrogen production technologies is being promoted widely. Hydrogen production methods can be broadly divided into thermochemical methods and electrochemical methods.

[0003] Hydrogen gas has been attracting attention as a clean energy source, and development of electric vehicles, fuel cell vehicles, etc. that use hydrogen gas as fuel, for example, as a highly efficient and clean power source, is progressing worldwide.

[0004] Various methods have been proposed for producing hydrogen gas, but the most well-known method is to produce it by electrolyzing water using a water electrolysis device. The electricity used for the water electrolysis device is renewable energy or nighttime electricity.

[0005] Patent Document 1 discloses a water electrolysis device equipped with electrodes of nickel dioxide and manganese. It discloses a fuel cell technology that has a negative electrode containing a negative electrode active material, a positive electrode made of a mixture of manganese dioxide and nickel hydroxide, and an electrolyte, and that stores hydrogen gas by electrolyzing the electrolyte, and a storage chamber for storing oxygen gas.

[0006] Patent Document 2 discloses a fuel cell capable of generating fuel gas using surplus electricity. Specifically, it discloses a technology that has an oxygen storage chamber for storing oxygen generated at the positive electrode and a hydrogen storage chamber for storing hydrogen generated at the negative electrode, and stores oxygen and hydrogen by electrolyzing an electrolyte using an externally supplied current. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-004868 [Patent Document 2] WO2013 / 145468 publication Summary of the Invention [Problem to be solved by the invention]

[0008] Hydrogen is generated when water molecules that come into contact with the surface of the cathode are reduced to hydrogen atoms and hydroxyl groups. By chance, the same reaction occurs nearby, causing two hydrogen atoms to combine to form hydrogen molecules, which then push aside the electrolyte and generate gas on the electrode surface. Therefore, the reaction occurs in an extremely limited area at the gas-liquid interface on the electrode surface - that is, the three-phase interface (meniscus) of solid, gas, and liquid. In other words, the reaction location is limited to the narrow range of the gas-liquid interface on the electrode surface. Furthermore, unless two water molecules come into contact with one point in this narrow reaction area at the same time, hydrogen molecules will not be generated, and an acrobatic reaction mechanism is required that requires an extremely limited reaction mechanism. As a result, the reaction rate is limited.

[0009] Oxygen generation occurs when four hydroxyl group molecules that come into contact with the surface of the anode are oxidized to form oxygen atoms and water molecules. Again, the reaction takes place at the gas-liquid interface on the electrode surface, which is none other than the three-phase interface (meniscus) of solid, gas, and liquid. This reaction occurs on a closed line that contacts the electrode at the boundary between gas and liquid, and is an extremely narrow reaction surface. Furthermore, it is an acrobatic reaction mechanism in which oxygen molecules are not generated unless four hydroxyl group molecules come into contact with one point on this narrow reaction surface at the same time. As a result, the reaction rate is limited.

[0010] Water electrolysis devices are devices that operate under a constant voltage. They cannot perform as expected under fluctuating voltages. Therefore, it has been thought that electricity from power generation devices using natural energy is not suitable for water electrolysis.

[0011] The present invention has been made in consideration of the above points, and aims to provide a water electrolysis apparatus that has a high reaction rate between hydrogen and oxygen and a high production rate of hydrogen gas and oxygen gas, and that can also utilize electric power from a power generation facility that uses natural energy. [Means for solving the problem]

[0012] In order to achieve the above object, the water electrolysis device according to the present invention includes a negative electrode, a positive electrode, an intermediate electrode, and an electrolyte, and in two electrode groups each having the intermediate electrode disposed between the negative electrode and the positive electrode, the intermediate electrode is disposed between the negative electrode of one of the electrode groups and the positive electrode of the other of the electrode groups. The negative electrode, the positive electrode, and the intermediate electrode each have separate electrolyte circulation paths, and hydrogen gas and oxygen gas are recovered via the electrolyte in the negative electrode circulation path and the electrolyte in the positive electrode circulation path, respectively. .

[0013] In the water electrolysis device according to the present invention, the negative electrode contains a hydrogen storage alloy, the positive electrode contains manganese dioxide, and the intermediate electrode contains nickel hydroxide. Also, in the water electrolysis device according to the present invention, the electrolyte path is isolated from the atmosphere.

[0014] According to this configuration, the electrolyte path is independent of atmospheric pressure, so that by increasing the pressure in the electrolyte system, the hydrogen gas and oxygen gas generated by water electrolysis can be made to be at high pressure.

[0015] In the water electrolysis device according to the present invention, the negative electrodes are electrically connected to each other, and the positive electrodes are are electrically connected to each other, electrode are electrically connected to each other. In the water electrolysis device according to the present invention, the negative electrode is connected to a negative terminal of a power supply, and the positive electrode is connected to the The positive pole of the power source is connected.

[0016] In the water electrolysis device according to the present invention, the electrode group is housed in an insulating cell frame, and the cell frame is provided with a supply path for the electrolyte and a recovery path for the electrolyte. Furthermore, in the water electrolysis device according to the present invention, the cell frame is wrapped in an insulating sheet and housed in a metal case. Furthermore, in the water electrolysis device according to the present invention, the negative electrode, the positive electrode, and the intermediate electrode each have separate electrolyte paths.

[0017] In the water electrolysis device according to the present invention, the negative electrode, the positive electrode, and the intermediate electrode each have a separate path for the electrolyte. Also, in the water electrolysis device according to the present invention, three or more electrode groups are configured via the intermediate electrode. Furthermore, in the water electrolysis device according to the present invention, the power source is electricity obtained from natural energy.

[0018] The inventor's findings can be summarized as follows:

[0019] The reaction that occurs at the interface of the three phases is carried out by first carrying out a solid-liquid two-phase reaction between the solid electrode and the liquid electrolyte, and then the product is captured by the solid and liquid, combined within the solid, and released as a gas.

[0020] Hydrogen is generated when water molecules that come into contact with the surface of the cathode are reduced to hydrogen atoms and hydroxyl groups. The hydrogen atoms diffuse through the hydrogen storage alloy. The hydrogen concentration in the hydrogen storage alloy is at an equilibrium concentration with hydrogen gas, and two atoms combine to form hydrogen molecules, which displace the electrolyte as a gas and are generated on the electrode surface.

[0021] Therefore, the reaction takes place over the entire surface of the electrode, and occurs on a two-dimensional reaction surface consisting of the solid-gas interface and the solid-liquid interface, across the entire surface of the electrode. Hydrogen atoms are generated within the solid, so they are generated at close range. There is a high probability that high-concentration hydrogen atoms will collide and become hydrogen molecules. This is the adsorption and desorption characteristic of hydrogen storage alloys.

[0022] Oxygen is generated when hydroxyl group molecules that come into contact with the surface of the anode are oxidized to form oxygen atoms and hydrogen ions. The oxygen molecules diffuse through the manganese dioxide, becoming oxygen molecules in a peroxidized state and are released from the gas and liquid interfaces. The hydrogen ions combine with the hydroxyl groups to form water molecules.

[0023] The above can be summarized in the chemical reaction formula below. Hydrogen evolution; H2O + e - → H + OH - solid-liquid contact interface H+H → H2 Solid-liquid contact interface and solid-gas contact interface (electrode surface) Oxygen evolution; OH - → O + H + + e - solid-liquid contact interface H + + OH - → H2O O + O → O2 solid-liquid contact interface and solid-gas contact interface (electrode surface)

[0024] As described above, with the water electrolysis device according to the present invention, the reaction region expands from a line to a plane, which is expected to improve the reaction rate and thereby improve productivity.

[0025] Furthermore, in a water electrolysis device that has conventionally been considered unsuitable for operation under a fluctuating voltage, this makes it possible to operate under a fluctuating power supply that uses natural energy. [Effects of the Invention]

[0026] The water electrolysis device of the present invention has an excellent reaction rate. Furthermore, the water electrolysis device of the present invention stores oxygen gas and hydrogen gas generated by the electrolysis of water under high pressure without releasing them into the atmosphere, which makes gas utilization convenient. Furthermore, the water electrolysis device of the present invention enables efficient operation even under fluctuating power sources. [Brief explanation of the drawings]

[0027] [Figure 1A] FIG. 2 is a diagram schematically illustrating an example of a cross-sectional view of an electrode group in a water electrolysis device. [Figure 1B] FIG. 10 is a diagram schematically illustrating another example of a cross-sectional view of an electrode group in a water electrolysis apparatus. [Figure 2] FIG. 2 is a perspective view of a cell frame of the water electrolysis cell. [Figure 3] FIG. 2 is a diagram schematically illustrating the horizontal cross-sectional structure of a water electrolysis unit incorporating a water electrolysis cell. [Figure 4] FIG. 1 is a perspective view showing the appearance of a water electrolysis unit housing a water electrolysis cell therein. [Figure 5] FIG. 2 is a system diagram showing the circulation path of the electrolyte for each electrode. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to this embodiment and various other modifications are possible.

[0029] First, electrodes, which are the main components of the water electrolysis device according to the embodiment, will be described, and then the water electrolysis device will be described in detail.

[0030] The hydrogen storage alloy used as the negative electrode active material is not particularly limited as long as it can absorb and release hydrogen, and examples thereof include alloys such as AB5 type rare earth alloys, AB2 type Laves phase alloys, AB type titanium-zirconium alloys, and A2B type magnesium alloys.

[0031] The positive electrode active material is preferably manganese dioxide, which is inexpensive and has low environmental impact. Furthermore, the positive electrode active material is preferably one with a high bulk density, such as a spherical shape, because this makes it easier to achieve high capacity.

[0032] The active material of the intermediate electrode is preferably nickel oxyhydroxide. Note that the active material of the intermediate electrode is preferably one with a high bulk density, for example, a spherical shape, since this makes it easier to achieve a high capacity.

[0033] The electrodes, which are the main components of the water electrolysis device according to the present invention, will be described with reference to Fig. 1A, which is a cross-sectional view of an electrode group, illustrating a portion thereof. One electrode group 10a includes a positive electrode 12a, which is composed of a negative electrode 11a, an intermediate electrode 13a, and a positive electrode 12a stacked in this order, facing each other. The other electrode group 10b includes a negative electrode 11b, an intermediate electrode 13b, and a positive electrode 12b stacked in this order, facing each other, with an intermediate electrode 13c interposed between them. In other words, from left to right in the figure, the stacking order is negative electrode 11a-intermediate electrode 13a-positive electrode 12a-intermediate electrode 13c-negative electrode 11b-intermediate electrode 13b-positive electrode 12b. Separators 14, which allow ions to pass but not electrons to pass, are interposed between the electrodes. The separators 14 prevent electrical short-circuiting between the electrodes 11, 12, and 13 and also serve to retain the electrolyte.

[0034] By adopting a structure in which an intermediate electrode is placed between the negative and positive electrodes as described above, both sides of the electrodes can contribute to the reaction, whereas previously only one side of the positive and negative electrodes was used, doubling the efficiency of producing hydrogen gas and oxygen gas and increasing productivity.

[0035] 1B shows three electrode groups 10, each of which has a pair of a negative electrode 11, an intermediate electrode 13, and a positive electrode 12. There may be three or more electrode groups, as long as an intermediate electrode is disposed between each electrode group. The inventors fabricated a prototype water electrolysis device consisting of 100 negative electrodes, 100 positive electrodes, and 199 intermediate electrodes.

[0036] The negative electrode 11, positive electrode 12, and intermediate electrode 13 are electrically connected to each other via connection terminals 15a, 15b, and 15c, respectively. By connecting multiple negative and positive electrodes with connection terminals, variations in the reactions at each electrode can be eliminated, and a uniform reaction can be expected. The negative electrode connection terminal 15a is connected to the negative pole of a power supply (not shown), and the positive electrode terminal 15b is connected to the positive pole of the power supply.

[0037] Fig. 2 shows a perspective view of the cell frame 16. The stacked electrode group 10 is housed in the internal space inside the cell frame 16. That is, the electrode group is housed in the cell frame to form a water electrolysis cell 17. Polypropylene is used as the material for the cell frame 16, but insulating materials such as nylon and Zylon may also be used.

[0038] 3 shows a horizontal cross-sectional view of a water electrolysis unit 29 housing a plurality of water electrolysis cells. The water electrolysis cell 17 shown has an electrode group 10, which includes a negative electrode, an intermediate electrode, and a positive electrode, stacked and housed inside a cell frame 16.

[0039] The connection terminals 15 of each electrode are provided between the cell frame 16 and the insulating case 18. The cell frame 16, which has insulating properties, is located inside the connection terminals 15, and the outside is covered by the insulating case 18. Therefore, the connection terminals 15 are insulated from each other.

[0040] Connection terminal 15a is connected to the negative electrode, connection terminal 15b is connected to the positive electrode, and connection terminal 15c is connected to the intermediate electrode. Water electrolysis cell 17 containing electrode group 10 is housed inside metal housing 19, covered with insulating case 18. Iron housing 19 physically protects the water electrolysis cell inside.

[0041] An electrolyte supply hole 21 is provided at the top of the cell frame 16, and an electrolyte return hole 22 is provided at the bottom. The electrolyte supply holes (21a, 21c, 21b) are connected to the negative electrode, intermediate electrode, and positive electrode, respectively, and allow the electrolyte to be supplied to each electrode. The electrolyte return holes (22a, 22c, 22b) at the bottom of the cell frame 16 are connected to the negative electrode, intermediate electrode, and positive electrode, respectively, and allow the electrolyte from each electrode to be returned.

[0042] The electrolyte solution supplied from the electrolyte solution supply hole 21 using a transport pump 23 passes through each electrode and is returned to the electrolyte solution return hole 22. Although a sodium hydroxide solution was used as the electrolyte solution, other types of electrolyte solution may also be used.

[0043] Figure 5 shows a system diagram showing the electrolyte circulation paths for each electrode. The upper part of the diagram is the electrolyte circulation system for the negative electrode, the middle part is the electrolyte circulation system for the intermediate electrode, and the lower part is the electrolyte circulation system for the positive electrode. The electrolyte from each electrolyte reservoir 24 is sent to each electrode by a transport pump 23 from the electrolyte supply path 28 via the electrolyte supply hole 21. The electrolyte from each electrode is returned to the gas-liquid separation box 25 via the electrolyte return hole 22 and the electrolyte return path 26. The returned electrolyte is separated into gas and liquid in the gas-liquid separation box 25, and the gas is sent to the hydrogen gas storage tank 26 or the oxygen gas storage tank 27. The liquid is held in the electrolyte reservoir 24 at the bottom of the gas-liquid separation box 25.

[0044] By sealing the electrolyte system, it becomes a system independent of external pressure, and by maintaining the electrolyte system at high pressure, it is possible to produce high pressure hydrogen gas and oxygen gas. Conventionally, hydrogen gas and oxygen gas produced by water electrolysis are at atmospheric pressure, but this requires a separate compressor to increase the pressure. According to the embodiment of the present invention, the effort required to increase the pressure of the gas can be eliminated.

[0045] In addition, the electrolyte reflux path 26a for hydrogen gas and the electrolyte reflux system 26b for oxygen gas are separated, so the generated hydrogen gas and oxygen gas do not come into contact with each other and are stored separately in the hydrogen gas storage tank and the oxygen gas storage tank, respectively.

[0046] Figure 4 shows the appearance of a water electrolysis unit 29 that houses a large number of water electrolysis cells 17 inside. The water electrolysis unit 29 has a metal housing 19. The front panel of the water electrolysis unit 29 is provided with a cathode terminal 32 connected to the negative electrode of the water electrolysis cell and an anode terminal 33 connected to the positive electrode. An electrolyte supply connection port 30 connected to each electrode is provided at the top of the front face of the panel, and an electrolyte return connection port 31 connected to each electrode is provided at the bottom of the front face of the panel. From left to right, the connection ports are for the negative electrode, intermediate electrode, and positive electrode.

[0047] As mentioned above, a prototype water electrolysis device consisting of 100 negative electrodes, 100 positive electrodes, and 199 intermediate electrodes was fabricated and tested. While a conventional water electrolysis device requires a power supply of 2.2 V, it was confirmed that the water electrolysis device of the present invention operates at 1.289 V. Operation at a low voltage is proof of high efficiency.

[0048] As mentioned above, conventional water electrolysis devices do not perform as expected under a fluctuating power supply. According to the water electrolysis device of the present invention, if the power from the power supply increases, the power that exceeds the fluctuation range is stored between the electrodes as a battery. The power stored between the electrodes is then effectively used for water electrolysis. In other words, when fluctuations occur in the power from the power supply, the unused power is stored between the electrodes. Once the fluctuations settle down, the power stored between the electrodes is used for water electrolysis. Therefore, even power from a power plant that uses natural energy can be effectively used.

[0049] The operation of the water electrolysis device will be explained using reaction formulas for hydrogen gas generation and oxygen gas generation.

[0050] Regarding the hydrogen gas generation reaction, when the negative electrode is connected to the negative pole of a DC power supply (not shown) and the negative electrode is charged, the reaction at the negative electrode is as follows: 2M + 2H2O + 2e - → 2MH + 2OH - (1) In the formula, M represents the hydrogen storage alloy. When the negative electrode is fully charged and the hydrogen storage alloy no longer stores hydrogen, hydrogen is generated from the negative electrode according to reaction formula (2). In this case, the overall reaction equation for the negative electrode is equation (9). 2H2O + 2e - → 2OH - + H2(2)

[0051] Regarding the oxygen gas generation reaction: When a positive electrode is connected to the positive electrode and the positive electrode is charged, the reaction equation at the positive electrode is equation (3). MnOOH + OH - → MnO2 + H2O + e- (3) Here, the positive electrode is in contact with oxygen gas and is in a fully charged state, so oxygen is generated from the positive electrode according to reaction formula (4). 2OH - → 2e - + H2O + 1 / 2O2(4) The overall reaction equation between the negative electrode and the positive electrode, including the hydrogen reaction and the oxygen reaction, is given by equation (5). H2O → H2+ 1 / 2O2(5) [Industrial Applicability]

[0052] The water electrolysis device of the present invention can be suitably used as a water electrolysis device for industrial and consumer use. [Explanation of symbols]

[0053] 10 electrode groups 11 Negative electrode 12 Positive electrode 13 Intermediate electrode 14 Separator 15 Connection terminal 16 Cell Frame 17 Water electrolysis cell 18 Insulation case 19. Cabinet 21 Electrolyte supply hole (21a, 21b, 21c) 22 Electrolyte return hole (22a, 22b, 22c) 23 Transport pump 24 Electrolyte reservoir 25 Gas-liquid separator box 26 Hydrogen gas storage tank 27 Oxygen gas storage tank 28 Electrolyte supply path 26 Electrolyte reflux path 29 Water Electrolysis Unit 30 Electrolyte supply connection port (30a, 30b, 30c) 31 Electrolyte return connection port (31a, 31b, 31c) 32 cathode terminal 33 Anode terminal

Claims

1. The battery includes a negative electrode, a positive electrode, an intermediate electrode, and an electrolyte solution; In two electrode groups in which the intermediate electrode is disposed between the negative electrode and the positive electrode, the intermediate electrode is disposed between the negative electrode of one of the electrode groups and the positive electrode of the other of the electrode groups, the negative electrode, the positive electrode, and the intermediate electrode each have a separate electrolyte circulation path; A water electrolysis device in which hydrogen gas and oxygen gas are recovered via the electrolyte in the circulation path of the negative electrode and the electrolyte in the circulation path of the positive electrode, respectively.

2. A water electrolysis device as described in Claim 1, wherein separate gas-liquid separation means and gas storage tanks are arranged in the negative electrode circulation path and the positive electrode circulation path, respectively.

3. the negative electrode contains a hydrogen storage alloy, the positive electrode comprises manganese dioxide; 2. The water electrolysis apparatus according to claim 1, wherein the intermediate electrode comprises nickel hydroxide.

4. 2. The water electrolysis apparatus according to claim 1, wherein the circulation path of the electrolytic solution is isolated from the atmosphere.

5. The water electrolysis apparatus according to claim 4 , wherein the negative electrodes are electrically connected to each other, the positive electrodes are electrically connected to each other, and the intermediate electrodes are electrically connected to each other.

6. The water electrolysis apparatus according to claim 5, wherein the negative electrode is connected to a negative terminal of a power supply, and the positive electrode is connected to a positive terminal of the power supply.

7. 7. The water electrolysis apparatus according to claim 6, wherein the electrode group is housed in an insulating cell frame, and the cell frame is provided with a supply path for the electrolytic solution and a recovery path for the electrolytic solution.

8. 8. The water electrolysis apparatus according to claim 7, wherein the cell frame is wrapped in an insulating sheet and housed in a metal case.

9. 3. The water electrolysis apparatus according to claim 1, wherein three or more of the electrode groups are configured via the intermediate electrode.

10. 7. The water electrolysis apparatus according to claim 6, wherein the power source is electricity obtained from natural energy.

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