Water electrolysis device

Abstract

To provide a water electrolysis device capable of preventing a cell from reaching a high temperature and of achieving high H2 generation efficiency.SOLUTION: The water electrolysis device comprises a power source, a plurality of cells each comprising a cathode, an anode, a cathode terminal, an anode terminal, and an electrolytic solution including water, at least either of a voltage sensor and a temperature sensor, a water level sensor, a water injector injecting water to the electrolytic solution, and a controller controlling the amount of water to be injected from the water injector, causes a water electrolysis reaction to extract H2 gas, and controls so as to increase the amount of water to be injected when the level of the electrolytic solution is lower than the boundary between the cathode and a cathode terminal and the anode and the anode terminal, and controls so as to decrease the amount of water to be injected to the electrolytic solution when it is higher than the boundary, when at least either of (a) and (b) is satisfied. (a) when the cell voltage exceeds 1.7 V. (b) when the temperature of the electrolytic solution exceeds 50°C.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a water electrolysis device.

Background Art

[0002] In recent years, the demand for hydrogen (H2) gas as an energy source for fuel cell vehicles and power generation has been increasing, and research on methods for producing H2 gas has also been progressing. As a method for producing H2 gas, for example, there is a method of separating and recovering water (H2O) into hydrogen (H2) gas and oxygen (O2) gas by a water electrolysis reaction.

[0003] For example, Patent Document 1 discloses a hydrogen gas production device including a water electrolysis cell and a power source, the water electrolysis cell including a first electrode, a second electrode, and an alkaline aqueous solution, the first electrode and the second electrode each being in contact with the alkaline aqueous solution, the first electrode and the second electrode being arranged apart from each other, the first electrode including a hydrogen storage alloy, the hydrogen storage alloy having an equilibrium dissociation pressure of 0.2 MPa or more at 20°C, the first electrode and the second electrode each being connected to the power source, the power source applying a voltage between the two electrodes such that the first electrode becomes the cathode and the second electrode becomes the anode, and hydrogen gas being generated at the first electrode by electrolysis of the alkaline aqueous solution.

[0004] Also, Patent Document 2 discloses a system for generating hydrogen gas from an aqueous solution, comprising: a first compartment including a first working electrode and a first redox-active electrode; and a second compartment including a second working electrode and a second redox-active electrode, each of the first compartment and the second compartment having an inlet configured to receive the aqueous solution, the first working electrode being connectable to a power source and configured to cause reduction of water in the aqueous solution in response to a voltage applied by the power source, thereby generating hydrogen gas and hydroxide ions, the second working electrode being connectable to the power source and configured to cause oxidation of hydroxide ions in response to the voltage applied by the power source, thereby generating oxygen gas and water, and further the second redox-active electrode and the first redox-active electrode being electrically connectable to each other and each being capable of reversibly undergoing oxidation in the presence of hydroxide ions and reduction in the presence of water to thereby generate hydroxide ions, the first compartment and the second compartment being separated from each other.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In addition, when water is consumed by the water electrolysis reaction and the level of the electrolytic solution drops, the positive electrode and the negative electrode immersed in the electrolytic solution are exposed. Further, if a voltage is continuously applied in this state, heat generation occurs. In particular, when the electrolytic solution runs out and the positive electrode and the negative electrode are completely exposed, strong heat generation may occur and the cell may become hot. Therefore, it is expected to manage the amount of the electrolytic solution to be relatively large. However, when the level of the electrolytic solution rises, the positive electrode terminal connected to the positive electrode and the negative electrode terminal connected to the negative electrode are also immersed in the electrolytic solution, and other reactions other than the water electrolysis reaction occur on the surface of the terminals immersed in the electrolytic solution. As a result, charges are consumed in other reactions, and the generation efficiency of H2 gas decreases.

[0007] In view of the above points, an object of the present disclosure is to provide a water electrolysis device that can suppress heat generation and prevent the cell from becoming hot, and can achieve a high generation efficiency of H2 gas.

Means for Solving the Problems

[0008] The means for solving the above problems includes the following aspects. <1> A power source, A cell having a positive electrode, a negative electrode, the power source, a positive electrode terminal connected to the positive electrode, a negative electrode terminal connected to the power source and the negative electrode, and an electrolytic solution containing water, At least one of a voltage sensor that detects the voltage applied to the cell and a temperature sensor that detects the temperature of the electrolytic solution, A water level sensor that detects the level of the electrolytic solution, A water injection unit that injects water into the electrolytic solution, A control unit that controls the injection amount of the water from the water injection unit, And A water electrolysis device that causes a water electrolysis reaction to extract H2 gas, When at least one of the following (a) and (b) is satisfied, if the level of the electrolytic solution detected by the water level sensor is lower than the boundary line between the positive electrode and the positive electrode terminal and the boundary line between the negative electrode and the negative electrode terminal, the control unit controls to increase the amount of water injected from the water injection part, and if the level of the electrolytic solution is higher than the boundary line, the control unit controls to decrease the amount of water injected from the water injection part. A water electrolysis device. (a) When the voltage detected by the voltage sensor exceeds 1.7V (b) When the temperature of the electrolytic solution detected by the temperature sensor exceeds 50°C <2> The water electrolysis device according to <1>, wherein the cell is a nickel-metal hydride battery. <3> The water electrolysis device according to <2>, wherein the nickel-metal hydride battery is a used battery. <4> The water injection amount is controlled by the control unit so that the water injection amount is 80% or more of the case where the level of the electrolytic solution is 100% when the level of the electrolytic solution coincides with the boundary line. The water electrolysis device according to any one of <1> to <3>. <5> When the water is injected from the water injection part into the electrolytic solution, the injection is performed so that the water does not come into contact with the positive electrode terminal and the negative electrode terminal. The water electrolysis device according to any one of <1> to <4>.

Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a water electrolysis device that suppresses heat generation and prevents the cell from becoming hot, and achieves high H2 gas generation efficiency.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0011] Hereinafter, the water electrolysis device according to the present disclosure will be described in detail with reference to the drawings. Each of the drawings shown below is schematically illustrated, and the size and shape of each part are appropriately exaggerated for easy understanding. In addition, in this specification, when expressing the manner of arranging one member with respect to another member, when simply described as "above" or "below", unless otherwise specified, it means that the other member is arranged directly above or directly below so as to be in contact with one member, and also includes the case where another member is arranged above or below one member via another member.

[0012] 〔Water electrolysis device〕 The water electrolysis device according to an embodiment of the present disclosure is a device that causes a water electrolysis reaction to extract H2 gas. Note that O2 gas can also be extracted.

[0013] The water electrolysis device includes a power source and a cell. The cell includes a positive electrode, a negative electrode, a positive electrode terminal connected to the power source and the positive electrode, a negative electrode terminal connected to the power source and the negative electrode, and an electrolytic solution containing water. Further, the water electrolysis device includes at least one of a voltage sensor that detects the voltage applied to the cell and a temperature sensor that detects the temperature of the electrolytic solution, a water level sensor that detects the water level of the electrolytic solution, a water injection unit that injects water into the electrolytic solution, and a control unit that controls the injection amount of water from the water injection unit. Then, when the water electrolysis device satisfies at least one of the following (a) and (b), when the water level of the electrolytic solution detected by the water level sensor is lower than the boundary line between the positive electrode and the positive electrode terminal and the boundary line between the negative electrode and the negative electrode terminal, the control unit controls to increase the injection amount of water from the water injection unit, and when the water level of the electrolytic solution is higher than the boundary line, the control unit controls to decrease the injection amount of water from the water injection unit. (a) When the voltage detected by the voltage sensor exceeds 1.7V (b) When the temperature of the electrolytic solution detected by the temperature sensor exceeds 50°C

[0014] An embodiment of the water electrolysis device according to the present disclosure will be described with reference to FIG. 1. FIG. 1 is a schematic perspective view illustrating a water electrolysis apparatus according to an embodiment of the present disclosure. The water electrolysis apparatus 100 shown in FIG. 1 includes a power source 1 and a cell 2. In the cell 2, a positive electrode 20, a negative electrode 22, the power source 1, a positive electrode terminal 200 connected to the positive electrode 20, a negative electrode terminal 220 connected to the power source 1 and the negative electrode 22, and an electrolytic solution 24 containing water (H2O) 32 are housed in a housing 26. Note that the cell 2 shown in FIG. 1 is a six-cell unit in which six housings 26 that house the positive electrode 20, the negative electrode 22, the positive electrode terminal 200, the negative electrode terminal 220, and the electrolytic solution 24 are arranged. The positive electrode terminal 200 is disposed above the positive electrode 20 in the direction of gravity, and the negative electrode terminal 220 is disposed above the negative electrode 22 in the direction of gravity. In the cell 2 shown in FIG. 1, the positive electrode 20 and the negative electrode 22 are immersed in the electrolytic solution 24, while the positive electrode terminal 200 and the negative electrode terminal 220 are not immersed in the electrolytic solution 24. That is, the water level of the electrolytic solution 24 is adjusted to the same height as the boundary line X between the positive electrode 20 and the positive electrode terminal 200 and between the negative electrode 22 and the negative electrode terminal 220.

[0015] The water electrolysis apparatus 100 has a voltage monitoring device 4A that detects the voltage applied to the cell 2 with a voltage sensor (not shown) and monitors the detected voltage. Note that the water electrolysis apparatus 100 may have a temperature monitoring device 4B that detects the temperature of the electrolytic solution 24 in the cell 2 with a temperature sensor (not shown) and monitors the detected temperature instead of the voltage sensor and the voltage monitoring device 4A. The voltage sensor and the voltage monitoring device 4A detect the voltage applied to the cell 2 adjusted by the power source 1 (and a resistor if necessary) and monitor the voltage. The temperature sensor and the temperature monitoring device 4B detect the temperature of the electrolytic solution 24 in each housing 26 of the cell 2 and monitor the temperature.

[0016] The water electrolysis apparatus 100 has a water level sensor 5 that detects the water level of the electrolytic solution 24, a water injection pipe 30 as a water injection unit that injects water 32 into the electrolytic solution 24, and a control device 3 as a control unit that controls the amount of water injected from the water injection pipe 30. The water level sensor 5 is a sensor that detects the water level of the electrolytic solution 24 in each housing 26 of the cell 2.

[0017] Power supply 1 has a built-in electronic load function. However, a power supply 1 without a built-in electronic load function may also be used. In that case, the water electrolysis device 100 may further have a device (such as a resistor, not shown) with an electronic load function. In the water electrolysis device 100, the voltage is adjusted to increase and decrease by the power supply 1 (and a resistor if necessary), and by maintaining the required voltage, a water electrolysis reaction occurs in the water in the electrolytic solution, and H2 gas can be extracted. Also, the O2 gas generated by the water electrolysis reaction can be collected together. The reaction formulas at the positive and negative electrodes are shown below. (Positive electrode) OH - →1 / 2H2O + 1 / 4O2 + e - (Negative electrode) H2O + e - →1 / 2H2 + OH -

[0018] The water electrolysis device 100 uses a nickel-metal hydride battery as the cell 2. That is, it uses a nickel-metal hydride battery in which six cases 26 containing the positive electrode 20, negative electrode 22, positive electrode terminal 200, negative electrode terminal 220, and electrolytic solution 24 are arranged as the cell 2. This nickel-metal hydride battery may be a used nickel-metal hydride battery. Note that "used" means that the charge capacity is lower than that of the battery immediately after manufacture.

[0019] Here, the water level of the electrolytic solution 24 will be described.

[0020] Note that the water level of the electrolytic solution 24 means the height of the liquid surface of the electrolytic solution 24 in the cell 2. Therefore, in FIG. 1, the water level of the electrolytic solution 24 is adjusted to the same height as the boundary line X between the positive electrode 20 and the positive electrode terminal 200 and between the negative electrode 22 and the negative electrode terminal 220. However, when the water level of the electrolytic solution 24 becomes lower as shown in FIG. 2, a part of the positive electrode 20 and the negative electrode 22 is exposed from the electrolytic solution 24. On the other hand, when the water level of the electrolytic solution 24 becomes higher as shown in FIG. 3, the positive electrode terminal 200 and the negative electrode terminal 220 are also in a state of being immersed in the electrolytic solution 24.

[0021] When performing a water electrolysis reaction with the water electrolysis device 100 shown in FIG. 1, since water in the electrolytic solution 24 is consumed by the reaction, the amount of the electrolytic solution 24 decreases. On the other hand, water 32 is injected into the electrolytic solution 24 from the control device 3 through the water injection pipe 30, and the amount of the electrolytic solution 24 increases. If the consumption amount of water due to this water electrolysis reaction is equal to the injection amount of water 32, the water level of the electrolytic solution 24 is kept constant. If the consumption amount of water due to the water electrolysis reaction is larger, the water level of the electrolytic solution 24 drops. If the injection amount of water 32 is larger, the water level of the electrolytic solution 24 rises.

[0022] However, if the water level of the electrolytic solution 24 continues to drop and the electrolytic solution 24 runs out (i.e., runs dry), and a voltage continues to be applied with the positive electrode 20 and the negative electrode 22 exposed, heat generation may occur and the temperature may become high. Therefore, in order to suppress the electrolytic solution 24 from running out (running dry), it is expected to manage the amount of the electrolytic solution 24 to be larger. However, if the amount of the electrolytic solution 24 increases and the water level of the electrolytic solution 24 becomes high, the positive electrode terminal 200 and the negative electrode terminal 220 will also be in a state of being immersed in the electrolytic solution 24. When a voltage is applied with the positive electrode terminal 200 and the negative electrode terminal 220 immersed in the electrolytic solution 24, other reactions other than the water electrolysis reaction occur on the surface of the terminals, that is, charges are consumed in other reactions, so the generation efficiency of H2 gas will decrease.

[0023] In the present disclosure, as described above, a nickel-metal hydride battery can be used as the cell, and in particular, a used nickel-metal hydride battery can be used. In the future, it is expected that a large amount of used nickel-metal hydride batteries mounted in electric vehicles (BEV), plug-in hybrid vehicles (PHEV), hybrid vehicles (HEV), etc. will be discharged, and it is desirable to divert such used nickel-metal hydride batteries to the water electrolysis device in a form as close to reuse as possible. However, when a used nickel-metal hydride battery is used as the cell of the water electrolysis device, a method of managing the amount of the electrolytic solution to be larger can be considered in order to suppress the electrolytic solution from running dry. However, as described above, in that case, the positive electrode terminal and the negative electrode terminal are immersed in the electrolytic solution, other reactions other than the water electrolysis reaction occur, and the generation efficiency of H2 gas will decrease.

[0024] For the above reasons, it is preferable to continuously adjust the water level of the electrolytic solution so that it is at a height near the boundary lines between the positive electrode and the positive electrode terminal and between the negative electrode and the negative electrode terminal.

[0025] Therefore, when the water electrolysis device according to the embodiment of the present disclosure satisfies at least one of the following (a) and (b), if the water level of the electrolytic solution detected by the water level sensor is lower than the boundary lines between the positive electrode and the positive electrode terminal and between the negative electrode and the negative electrode terminal, the control unit controls to increase the amount of water injected from the water injection part, and if the water level of the electrolytic solution is higher than the boundary lines, the control unit controls to decrease the amount of water injected from the water injection part. (a) When the voltage detected by the voltage sensor exceeds 1.7V (b) When the temperature of the electrolytic solution detected by the temperature sensor exceeds 50°C

[0026] First, the relationship between the water level of the electrolytic solution, the voltage of the cell, and the temperature of the electrolytic solution will be described. As shown in FIG. 1, when the water level of the electrolytic solution is lower compared to the case where it is adjusted to the same height as the boundary lines between the positive electrode and the positive electrode terminal and between the negative electrode and the negative electrode terminal, a part of the positive electrode and the negative electrode is exposed from the electrolytic solution. When a voltage is continuously applied with the positive electrode and the negative electrode exposed, heat generation occurs at the exposed portions of the positive electrode and the negative electrode, the temperature of the electrolytic solution increases, and the voltage applied to the cell also increases. On the other hand, when the water level of the electrolytic solution is higher compared to the case where it is adjusted to the same height as the boundary lines, the positive electrode terminal and the negative electrode terminal are also in a state of being immersed in the electrolytic solution. When a voltage is continuously applied in this state, leakage occurs at the immersed portions of the positive electrode terminal and the negative electrode terminal, the voltage applied to the cell increases, and the temperature of the electrolytic solution also increases. From the above points, it has been found that by detecting at least one of the increase in the voltage of the cell and the increase in the temperature of the electrolytic solution, it can be used as an indicator of the change in the water level of the electrolytic solution.

[0027] When condition (a) is satisfied, the voltage of the cell is detected by a voltage sensor. When the voltage of the cell exceeds 1.7 V, the amount of water injection by the control unit is controlled. Specifically, when the voltage of the cell exceeds 1.7 V, if the level of the electrolytic solution detected by the level sensor is lower than the boundary lines between the positive electrode and the positive terminal and between the negative electrode and the negative terminal, the control unit controls to increase the amount of water injected from the water injection unit. On the other hand, if the level of the electrolytic solution detected by the level sensor is higher than the boundary lines, the control unit controls to decrease the amount of water injected from the water injection unit.

[0028] When condition (b) is satisfied, the temperature of the electrolytic solution is detected by a temperature sensor. When the temperature of the electrolytic solution exceeds 50 °C, the amount of water injection by the control unit is controlled. Specifically, when the temperature of the electrolytic solution exceeds 50 °C, if the level of the electrolytic solution detected by the level sensor is lower than the boundary lines between the positive electrode and the positive terminal and between the negative electrode and the negative terminal, the control unit controls to increase the amount of water injected from the water injection unit. On the other hand, if the level of the electrolytic solution detected by the level sensor is higher than the boundary lines, the control unit controls to decrease the amount of water injected from the water injection unit.

[0029] In this way, by controlling the amount of water injection when at least one of (a) and (b) is satisfied, it is possible to continuously adjust the level of the electrolytic solution to a height near the boundary lines between the positive electrode and the positive terminal and between the negative electrode and the negative terminal. As a result, it is possible to suppress the electrolytic solution from running out (i.e., running dry) and generating heat and becoming high temperature, and to suppress the consumption of charge in reactions other than the water electrolysis reaction, thereby increasing the generation efficiency of H2 gas.

[0030] When condition (a) is satisfied, from the viewpoint of further suppressing the generation of heat and the cell from becoming high temperature and achieving a higher H2 gas generation efficiency, it is preferable that when the voltage of the cell detected by the voltage sensor exceeds 1.6 V, the control unit controls the amount of water injection by the above method, and it is more preferable that when the voltage of the cell exceeds 1.5 V, the control unit controls the amount of water injection by the above method. Further, when the condition (b) is satisfied, from the viewpoint of further suppressing heat generation and preventing the cell from reaching a high temperature and achieving a higher H2 gas generation efficiency, it is preferable to control the amount of water injected by the control unit by the above method when the temperature of the electrolytic solution detected by the temperature sensor exceeds 30°C.

[0031] In any case where either of the above (a) and (b) is satisfied, from the viewpoint of further suppressing heat generation and preventing the cell from reaching a high temperature, when the water level of the electrolytic solution is set to 100% when it coincides with the boundary line between the positive electrode and the positive electrode terminal and between the negative electrode and the negative electrode terminal, it is preferable to control the amount of water injected by the control unit so that the water level is at a height of 80% or more.

[0032] Also, when water is injected into the electrolytic solution from the water injection part (for example, the water injection pipe 30 shown in FIG. 1), from the viewpoint of suppressing the occurrence of electric leakage, it is preferable that the injection is performed so that water does not come into contact with the positive electrode terminal and the negative electrode terminal.

[0033] In FIG. 1, the cell 2 in which the positive electrode 20, the negative electrode 22, the positive electrode terminal 200, and the negative electrode terminal 220 are each accommodated in one housing 26 is shown, but the form of the cell is not limited to this.

[0034] For example, the positive electrode and the negative electrode may be respectively accommodated in different housings, and the housings may be immersed in the same electrolytic solution. That is, the positive electrode and the positive electrode terminal may be accommodated in the first housing, the negative electrode and the negative electrode terminal may be accommodated in the second housing, and the first housing and the second housing may be immersed in the same electrolytic solution to constitute the cell. In this case, oxygen gas is generated from the first housing having the positive electrode, and hydrogen gas is generated from the second housing having the negative electrode, so that the hydrogen gas and the oxygen gas can be easily taken out separately. Note that nickel-metal hydride rechargeable batteries can also be used for the first housing and the second housing, and used nickel-metal hydride rechargeable batteries can also be used.

[0035] In the present disclosure, used nickel-metal hydride rechargeable batteries can be applied to the cell, and the nickel-metal hydride rechargeable batteries can be reused to extract H2 gas and O2 gas.

[0036] Here, the generation of hydrogen gas in the water electrolysis device according to the embodiment of the present disclosure was confirmed by experiments.

[0037] (Preparation of water electrolysis device) A water electrolysis device having the same configuration as the water electrolysis device 100 shown in FIG. 1 and using the following as the cell and the electrolytic solution was prepared. Cell: A used nickel-hydrogen storage battery, with one positive electrode, one negative electrode, one positive electrode terminal, and one negative electrode terminal each, and six cells arranged in parallel, each housing an electrolytic solution. Electrolytic solution: Potassium hydroxide (KOHaq, pH 15), an electrolytic solution containing 64% by mass of water (H2O). In addition, each positive electrode terminal and each negative electrode terminal in the six cells arranged in parallel were connected in series to a power source (one with a built-in function of an electronic load).

[0038] In this water electrolysis device, while injecting water into the electrolytic solution from the water injection pipe, the voltage applied to the cell by the power source was adjusted so as to obtain a voltage at which a water electrolysis reaction occurs.

[0039] (Example 1-1) When causing a water electrolysis reaction by the water electrolysis device, the voltage of the cell was detected by a voltage sensor and the detected voltage was monitored by a voltage monitoring device. When the voltage of the cell exceeded 1.7V, the water injection amount was controlled by the control device. Specifically, when the voltage of the cell exceeded 1.7V, if the water level of the electrolytic solution detected by the water level sensor was lower than the boundary line between the positive electrode and the positive electrode terminal and between the negative electrode and the negative electrode terminal, the control device controlled to increase the water injection amount from the water injection pipe. On the other hand, if the water level of the electrolytic solution detected by the water level sensor was higher than the boundary line, the control device controlled to decrease the water injection amount from the water injection pipe.

[0040] The "temperature of the cell" at 10 minutes, 20 minutes, 30 minutes, and 40 minutes was measured, and the "hydrogen gas generation efficiency" at 40 minutes was also measured. The results are shown in Table 1.

[0041] (Example 1-2) When causing a water electrolysis reaction by a water electrolysis device, the voltage of the cell was detected by a voltage sensor, and when the voltage of the cell exceeded 1.6 V, a water electrolysis reaction was caused in the same manner as in Example 1-1 except that the amount of water injection by the control device was controlled. The results are shown in Table 1.

[0042] (Example 1-3) When causing a water electrolysis reaction by a water electrolysis device, the voltage of the cell was detected by a voltage sensor, and when the voltage of the cell exceeded 1.5 V, a water electrolysis reaction was caused in the same manner as in Example 1-1 except that the amount of water injection by the control device was controlled. The results are shown in Table 1.

[0043] (Example 2-1) When causing a water electrolysis reaction by a water electrolysis device, the temperature of the electrolytic solution was detected by a temperature sensor and the detected temperature was monitored by a temperature monitoring device, and when the temperature of the electrolytic solution exceeded 50 °C, the amount of water injection by the control device was controlled. Specifically, when the temperature of the electrolytic solution exceeded 50 °C, if the level of the electrolytic solution detected by the level sensor was lower than the boundary line between the positive electrode and the positive electrode terminal and the negative electrode and the negative electrode terminal, the control device controlled to increase the amount of water injection from the water injection pipe, while if the level of the electrolytic solution detected by the level sensor was higher than the boundary line, the control device controlled to decrease the amount of water injection from the water injection pipe.

[0044] Similar to Example 1-1, the "temperature of the cell" at 10 minutes, 20 minutes, 30 minutes, and 40 minutes, and the "hydrogen gas generation efficiency" at 40 minutes were measured. The results are shown in Table 1.

[0045] (Example 2-2) When causing a water electrolysis reaction by a water electrolysis device, the temperature of the electrolytic solution was detected by a temperature sensor, and when the temperature of the electrolytic solution exceeded 30 °C, a water electrolysis reaction was caused in the same manner as in Example 2-1 except that the amount of water injection by the control device was controlled. The results are shown in Table 1.

[0046] (Comparative Example 1) When causing a water electrolysis reaction by a water electrolysis device, the voltage of the cell was detected by a voltage sensor, and a water electrolysis reaction was caused in the same manner as in Example 1-1 except that when the voltage of the cell exceeded 2.0 V, the amount of water injection by the control device was controlled. The results are shown in Table 1.

[0047] (Comparative Example 2) When causing a water electrolysis reaction by a water electrolysis device, the temperature of the electrolytic solution was detected by a temperature sensor, and a water electrolysis reaction was caused in the same manner as in Example 2-1 except that when the temperature of the electrolytic solution exceeded 70 °C, the amount of water injection by the control device was controlled. The results are shown in Table 1.

[0048] [Table 1]

[0049] As shown in the examples and comparative examples of Table 1, when detecting the voltage of the cell or the temperature of the electrolytic solution and satisfying at least one of the above (a) and (b), by controlling the amount of water injection by the control device, it can be seen that the cell being heated to a high temperature is suppressed, and a high H2 gas generation efficiency can be achieved.

[0050] Note that when neither the detection of the voltage of the cell nor the detection of the temperature of the electrolytic solution is performed and the water level of the electrolytic solution is simply kept higher than the boundary line continuously, for example, when the water level of the electrolytic solution is 120% while the case where the water level coincides with the boundary line is set to 100%, if the amount of water injection from the water injection pipe is set so as to continue to be maintained, it is presumed that the hydrogen gas generation efficiency deteriorates further compared to Comparative Example 1. Also, when neither the detection of the voltage of the cell nor the detection of the temperature of the electrolytic solution is performed and the water level of the electrolytic solution is simply kept lower than the boundary line continuously, for example, when the water level of the electrolytic solution is 50% while the case where the water level coincides with the boundary line is set to 100%, if the amount of water injection from the water injection pipe is set so as to continue to be maintained, it is presumed that the temperature of the cell rises rapidly, the electrolytic solution boils, and finally the liquid dries up. [Description of Reference Numerals]

[0051] 1 Power supply, 2 Cells, 20 Positive electrode, 200 Positive electrode terminal, 22 Negative electrode, 220 Negative electrode terminal, 24 Electrolyte, 26 Housing, 3 Control device, 30 Water injection pipe, 32 Water, 4 Cells, 4A Voltage monitoring device, 4B Temperature monitoring device, 5 Water level sensor, 100 Water electrolysis device

Claims

1. A power source, a cell having a positive electrode, a negative electrode, an electrolytic solution containing water, a positive electrode terminal connected to the power source and the positive electrode, a negative electrode terminal connected to the power source and the negative electrode, at least one of a voltage sensor for detecting the voltage applied to the cell and a temperature sensor for detecting the temperature of the electrolytic solution, a water level sensor for detecting the water level of the electrolytic solution, a water injection section for injecting water into the electrolytic solution, a control section for controlling the amount of water injected from the water injection section, and a water electrolysis apparatus for causing a water electrolysis reaction to extract H ２ gas, wherein when at least one of the following (a) and (b) is satisfied and the water level of the electrolytic solution detected by the water level sensor is lower than the boundary line between the positive electrode and the positive electrode terminal and the boundary line between the negative electrode and the negative electrode terminal, the control section increases the amount of water injected from the water injection section, and when the water level of the electrolytic solution is higher than the boundary line, the control section decreases the amount of water injected from the water injection section. (a) When the voltage detected by the voltage sensor exceeds 1.7 V (b) When the temperature of the electrolytic solution detected by the temperature sensor exceeds 50°C

2. The water electrolysis apparatus according to claim 1, wherein the cell is a nickel-metal hydride battery.

3. The water electrolysis apparatus according to claim 2, wherein the nickel-metal hydride battery is a used battery.

4. The water electrolysis apparatus according to claim 1, wherein the control section controls the amount of water injection so that the water level is 80% or more when the water level of the electrolytic solution coincides with the boundary line is set to 100%.

5. The water electrolysis apparatus according to claim 1, wherein the water is injected from the water injection section into the electrolytic solution without contacting the positive electrode terminal and the negative electrode terminal.

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