Water electrolysis device, water electrolysis method, and nickel-metal hydride storage battery recycling method

Abstract

To provide a water electrolysis device capable of safely taking out H2 gas and O2 gas having high purity.SOLUTION: A water electrolysis device 20A includes a power source 3, an electrolyte 40, a first tank 100A which has a positive electrode connected to the power source 3, a supply port and a discharge port of H2O and a take-out port of O2 gas, and is immersed in the electrolyte 40, and a second tank 200A which has a negative electrode to the power source 3, the supply port and the discharge port of H2O and a take-out port of H2 gas, and is immersed in the electrolyte 40, holds a voltage so that the potential of the positive electrode becomes higher than the potential of the negative electrode by the power source 3, thereby takes out the O2 gas from the first tank 100A, and takes out the H2 gas from the second tank 200A.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a water electrolysis device, a water electrolysis method, and a method for recycling a nickel-metal hydride storage battery. [Background technology]

[0002] In recent years, the demand for hydrogen (H2) gas has increased as an energy source for fuel cell vehicles and power generation, and research into H2 gas production methods is also underway. One method for producing H2 gas is, for example, to separate water (H2O) into hydrogen (H2) gas and oxygen (O2) gas through a water electrolysis reaction and then recover the gas.

[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 being each in contact with the alkaline aqueous solution and disposed apart from each other, the first electrode including a hydrogen storage alloy having an equilibrium dissociation pressure of 0.2 MPa or more at 20°C, the first electrode and the second electrode being each connected to the power source, the power source applying a voltage between the first electrode as a cathode and the second electrode as an anode, and hydrogen gas being generated at the first electrode by electrolysis of the alkaline aqueous solution. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-017628 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when recovering hydrogen (H2) gas and oxygen (O2) gas through a water electrolysis reaction, the generated H2 gas and O2 gas will react explosively when mixed together, so it is necessary to recover the H2 gas and O2 gas safely and in a highly pure state.

[0006] In light of such conventional demands, the present disclosure has an object to provide a water electrolysis device and a water electrolysis method capable of safely extracting high-purity H2 gas and O2 gas, and a method for recycling nickel-metal hydride storage batteries capable of reusing used nickel-metal hydride storage batteries and safely extracting high-purity H2 gas and O2 gas. [Means for solving the problem]

[0007] Means for solving the above problems include the following aspects. <1> Power supply, An electrolyte; a first tank having a positive electrode connected to the power source, an H2O supply port and an exhaust port, and an O2 gas outlet port, and being immersed in the electrolytic solution; a second tank having a negative electrode connected to the power source, an H2O supply port and an exhaust port, and an H2 gas outlet port, and being immersed in the electrolytic solution; having A water electrolysis apparatus in which the power supply maintains a voltage such that the potential of the positive electrode is higher than the potential of the negative electrode, thereby extracting O2 gas from the first tank and H2 gas from the second tank. <2> At least one of the first tank and the second tank is a nickel-metal hydride battery; <1> The water electrolysis device according to claim 1. <3> The nickel-metal hydride storage battery is a used storage battery. <2> The water electrolysis device according to claim 1. <4> The O2 gas outlet and the H2 gas outlet are provided at the upper part of the first tank or the second tank in the gravity direction, <1> ~ <3> 13. The water electrolysis apparatus according to claim 12 . <5> The supply port and the discharge port in the first tank, and the supply port and the discharge port in the second tank are provided so that the HO flows from the bottom to the top in the direction of gravity. <1> ~ <4> 13. The water electrolysis apparatus according to claim 12 . <6> The electrolyte has a pH of 15 or more. <1> ~ <5> 13. The water electrolysis apparatus according to claim 12 . <7> The shortest distance between the positive electrode and the negative electrode is more than 0 mm and 35 mm or less; <1> ~ <6> 13. The water electrolysis apparatus according to claim 12 . <8> The temperature of the entire water electrolysis apparatus is 40° C. or more and 80° C. or less. <1> ~ <7> 13. The water electrolysis apparatus according to claim 12 . <9> Power supply, An electrolyte; a first tank having a positive electrode connected to the power source, an H2O supply port and an exhaust port, and an O2 gas outlet port, and being immersed in the electrolytic solution; a second tank having a negative electrode connected to the power source, an H2O supply port and an exhaust port, and an H2 gas outlet port, and being immersed in the electrolytic solution; For a water electrolysis device having a voltage maintained by the power source so that the potential of the positive electrode is higher than the potential of the negative electrode, and O2 gas is extracted from the first tank and H2 gas is extracted from the second tank. <10> A nickel-metal hydride battery is used as at least one of the first tank and the second tank. <9> The water electrolysis method according to claim 1. <11> The nickel-metal hydride storage battery is a used storage battery. <10> The water electrolysis method according to claim 1. <12> The O2 gas outlet and the H2 gas outlet are provided at the upper part of the first tank or the second tank in the gravity direction, <9> ~ <11> 13. The water electrolysis method according to claim 12. <13> The supply port and the discharge port in the first tank, and the supply port and the discharge port in the second tank are provided so that the HO flows from the bottom to the top in the direction of gravity. <9> ~ <12> 13. The water electrolysis method according to claim 12. <14> The electrolyte has a pH of 15 or more. <9> ~ <13> 13. The water electrolysis method according to claim 12. <15> The shortest distance between the positive electrode and the negative electrode is more than 0 mm and 35 mm or less; <9> ~ <14> 13. The water electrolysis method according to claim 12. <16> The temperature of the entire water electrolysis apparatus is 40° C. or more and 80° C. or less. <9> ~ <15> 13. The water electrolysis method according to claim 12. <17> Power supply, An electrolyte; a first tank having a positive electrode connected to the power source, an H2O supply port and an exhaust port, and an O2 gas outlet port, and being immersed in the electrolytic solution; a second tank having a negative electrode connected to the power source, an H2O supply port and an exhaust port, and an H2 gas outlet port, and being immersed in the electrolytic solution; having A water electrolysis apparatus in which a voltage is maintained by the power source so that a potential of the positive electrode is higher than a potential of the negative electrode, thereby extracting O2 gas from the first tank and extracting H2 gas from the second tank, A method for recycling nickel-metal hydride storage batteries, comprising using a used nickel-metal hydride storage battery as at least one of the first tank and the second tank. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a water electrolysis device and a water electrolysis method capable of safely extracting high purity H2 gas and O2 gas, and also to provide a method for recycling nickel-metal hydride storage batteries capable of reusing used nickel-metal hydride storage batteries and safely extracting high purity H2 gas and O2 gas. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic perspective view illustrating a water electrolysis device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic perspective view illustrating a water electrolysis device according to another embodiment of the present disclosure. [Diagram 3] 3 is a schematic diagram showing a connection configuration between a plurality of positive electrodes in a first tank and a plurality of negative electrodes in a second tank in the water electrolysis apparatus shown in FIG. 2. FIG. [Figure 4] FIG. 11 is a schematic diagram showing a connection configuration between multiple positive electrodes in a first tank and multiple negative electrodes in a second tank in a water electrolysis device in another embodiment of the present disclosure. [Diagram 5] FIG. 1 is a schematic diagram showing an example of the configuration of a nickel-metal hydride storage battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The water electrolysis device, the water electrolysis method, and the method for recycling a nickel-metal hydride battery according to the present disclosure will be described in detail below with reference to the drawings. Each of the drawings shown below is a schematic illustration, and the size and shape of each part are appropriately exaggerated for ease of understanding. In addition, in this specification, when expressing an aspect in which another member is arranged relative to a certain member, the term "above" or "below" simply refers to both a case in which another member is arranged directly above or below a certain member so as to be in contact with the certain member, and a case in which another member is arranged above or below a certain member via another member, unless otherwise specified.

[0011] [Water electrolysis device and water electrolysis method] The water electrolysis device according to the present disclosure includes a power source, an electrolytic solution, a first tank having a positive electrode connected to the power source, an H2O supply port and an exhaust port, and an O2 gas outlet, and being immersed in the electrolytic solution, and a second tank having a negative electrode connected to the power source, an H2O supply port and an exhaust port, and an H2 gas outlet, and being immersed in the electrolytic solution. The power source maintains a voltage such that the potential of the positive electrode is higher than the potential of the negative electrode, thereby extracting O2 gas from the first tank and H2 gas from the second tank.

[0012] One embodiment of a water electrolysis device according to the present disclosure will be described with reference to FIG. FIG. 1 is a schematic perspective view illustrating a water electrolysis apparatus according to an embodiment of the present disclosure. As shown in FIG. 1, the water electrolysis apparatus 20A includes a power source 3, a resistor 30 as an example of an electronic load, a housing 4 in which an electrolytic solution 40 is accommodated, a first tank 100A and a second tank 200A immersed in the electrolytic solution 40 in the housing 4, and a distillation device 5. The power source 3 and the resistor 30 adjust the increase and decrease of the voltage, and the voltage can be maintained at a desired voltage. A power source having a built-in electronic load function may be used. The first tank 100A has a positive electrode and a negative electrode, and the positive electrode is connected to the power source 3 and the resistor 30. The second tank 200A has a positive electrode and a negative electrode, and the negative electrode is connected to the power source 3 and the resistor 30. The first tank 100A has a water supply port, and a water supply pipe (not shown) equipped with a water supply pump is connected to the supply port, and the water supply pump (not shown) is driven to supply water (H2O). The first tank 100A has a water outlet, to which a water outlet pipe (not shown) is connected, and excess water in the first tank 100A is discharged from the outlet. The second tank 200A has a water supply port, to which a water supply pipe (not shown) equipped with a water supply pump 6 is connected, and the water supply pump 6 is driven to supply water (H2O). The second tank 200A has a water outlet, to which a water outlet pipe (not shown) is connected, and excess water in the second tank 200A is discharged from the outlet. The first tank 100A has an oxygen (O2) discharge passage 101, which is connected to the distillation device 5. The second tank 200A has a hydrogen (H2) discharge passage 201. An electrolyte is contained in the distillation apparatus 5, and the electrolyte in the distillation apparatus 5 and electrolyte 40 in the housing 4 are circulated through a circulation pipe (not shown) equipped with a liquid delivery pump 7. The distillation apparatus 5 has an outlet 8 for water vapor (H2O). In the above, an example was given in which a resistor was used as the electronic load, but a variable resistor, for example, may also be used instead of a resistor.

[0013] The water electrolysis apparatus 20A uses nickel-metal hydride batteries as the first tank 100A having a positive electrode and the second tank 200A having a negative electrode. These nickel-metal hydride batteries may be used nickel-metal hydride batteries. The term "used" refers to a battery whose charging capacity is lower than that of the battery immediately after manufacture.

[0014] In the water electrolysis device 20A, the power supply 3 and the resistor 30 maintain a voltage so that the potential of the positive electrode in the first tank 100A is higher than the potential of the negative electrode in the second tank 200A. As a result, a water electrolysis reaction occurs in the water (H2O) supplied to the first tank 100A and the second tank 200A, and O2 gas is generated from the first tank 100A. The generated O2 gas is sent to the distillation device 5 through the discharge passage 101, where it is reduced in the distillation device 5 and taken out from the discharge port 8 as water vapor (H2O). In addition, a water electrolysis reaction occurs in the second tank 200A, and H2 gas is generated, and this H2 gas is taken out from the discharge passage 201. From the viewpoint of efficiently causing a water electrolysis reaction in the water (H2O) supplied to the first tank 100A and the second tank 200A, it is preferable to maintain the potential difference between the positive electrode and the negative electrode at 1.48 V or more. The reaction formula at the positive electrode and the negative electrode is shown below. (Positive electrode)OH - →1 / 2H2O+1 / 4O2+e - (Negative electrode) H2O+e - →1 / 2H2+OH -

[0015] From the viewpoint of allowing the water electrolysis reaction to proceed more easily, the potential difference obtained by subtracting the potential of the negative electrode in the second tank from the potential of the positive electrode in the first tank is more preferably in the range of 1.48 V or more and 2.00 V or less, and from the viewpoint of efficiency, is even more preferably in the range of 1.55 V or more and 1.80 V or less.

[0016] From the viewpoint of ease of extracting O2 gas, the O2 gas outlet of the first tank 100A, i.e., the inlet of the exhaust passage 101 from the first tank 100A, is preferably provided at the upper part of the first tank 100A in the direction of gravity. Also, from the viewpoint of ease of extracting H2 gas, the H2 gas outlet of the second tank 200A, i.e., the inlet of the exhaust passage 201 from the second tank 200A, is preferably provided at the upper part of the second tank 200A in the direction of gravity.

[0017] The water (H2O) supply port and discharge port of the first tank 100A and the water supply port and discharge port of the second tank 200A are preferably provided so that H2O flows from the bottom to the top in the direction of gravity. For example, in the first tank 100A and the second tank 200A, the water supply port is preferably provided on the bottom side in the direction of gravity, and the water discharge port is preferably provided on the top side in the direction of gravity.

[0018] Next, another embodiment will be described.

[0019] Another embodiment of the water electrolysis apparatus according to the present disclosure will be described with reference to Fig. 2. Note that the same components as those in the water electrolysis apparatus shown in Fig. 1 are denoted by the same reference numerals. FIG. 2 is a schematic perspective view illustrating a water electrolysis apparatus according to an embodiment of the present disclosure. As shown in FIG. 2, the water electrolysis apparatus 20B includes a power source 3, a resistor 30, a housing 4 in which an electrolytic solution 40 is accommodated, a first tank 100B and a second tank 200B immersed in the electrolytic solution 40 in the housing 4, and a distillation apparatus 5. In the water electrolysis apparatus 20B, a plurality of nickel-hydrogen storage batteries (six-pair nickel-hydrogen storage batteries in FIG. 2) are used as both the first tank 100B and the second tank 200B. Each of the six nickel-hydrogen storage batteries in the first tank 100B has a positive electrode and a negative electrode, and the positive electrodes are all connected to the power source 3 and the resistor 30. Each of the six nickel-hydrogen storage batteries in the second tank 200B has a positive electrode and a negative electrode, and the negative electrodes are all connected to the power source 3 and the resistor 30. The first tank 100B has a water supply port, to which a water supply pipe (not shown) equipped with a water supply pump is connected, and water (H2O) is supplied by driving the water supply pump (not shown). The second tank 200B has a water supply port, to which a water supply pipe (not shown) equipped with a water supply pump 6 is connected, and water (H2O) is supplied by driving the water supply pump 6. The first tank 100B has an oxygen (O2) exhaust passage 101, which is connected to the distillation device 5. The second tank 200B has a hydrogen (H2) exhaust passage 201. The distillation device 5 contains an electrolyte, and the electrolyte in the distillation device 5 and the electrolyte 40 in the housing 4 are circulated through a circulation pipe (not shown) equipped with a liquid delivery pump 7. The distillation device 5 has a water vapor (H2O) exhaust port 8.

[0020] In the water electrolysis apparatus 20B shown in Fig. 2, the connection configuration between the multiple (six pairs in Fig. 2) nickel-metal hydride batteries in the first tank 100B, the multiple (six pairs in Fig. 2) nickel-metal hydride batteries in the second tank 200B, and the electrodes 3 is shown in Fig. 3. Note that Fig. 3 omits configuration other than the first tank 100B, the second tank 200B, and the electrodes 3, and also omits the illustration of the electronic load. As shown in Fig. 3, the positive electrodes of the multiple nickel-metal hydride batteries in the first tank 100B are all connected (shorted) to the power source 3, and the negative electrodes of the multiple nickel-metal hydride batteries in the second tank 200B are all connected (shorted) to the power source 3.

[0021] In the water electrolysis apparatus 20B, the nickel-metal hydride storage batteries used in the first tank 100B and the second tank 200B may be used nickel-metal hydride storage batteries.

[0022] In the water electrolysis device 20B, the power supply 3 and resistor 30 maintain a voltage such that the potential of the positive electrode in the first tank 100B is higher than the potential of the negative electrode in the second tank 200B. As a result, a water electrolysis reaction occurs in the water (H2O) supplied to the first tank 100B and the second tank 200B, and O2 gas is generated from the first tank 100B. The generated O2 gas is sent to the distillation device 5 through the discharge passage 101, where it is reduced in the distillation device 5 and taken out as water vapor (H2O) from the discharge port 8. In addition, a water electrolysis reaction occurs in the second tank 200B, and H2 gas is generated, and this H2 gas is taken out from the discharge passage 201. From the viewpoint of efficiently causing a water electrolysis reaction in the water (H2O) supplied to the first tank 100B and the second tank 200B, it is preferable to maintain the potential difference between the positive electrode and the negative electrode at 1.48 V or more. The potential difference between the positive electrode and the negative electrode is more preferably in the range of 1.48V or more and 2.00V or less, and further preferably in the range of 1.55V or more and 1.80V or less.

[0023] From the viewpoint of ease of extracting O2 gas, the O2 gas outlet of the first tank 100B, i.e., the inlet of the exhaust passage 101 from the first tank 100B, is preferably provided at the upper part of the first tank 100B in the direction of gravity. Also, from the viewpoint of ease of extracting H2 gas, the H2 gas outlet of the second tank 200B, i.e., the inlet of the exhaust passage 201 from the second tank 200B, is preferably provided at the upper part of the second tank 200B in the direction of gravity.

[0024] The water (H2O) supply port and discharge port of the first tank 100B and the water supply port and discharge port of the second tank 200B are preferably provided so that H2O flows from the bottom to the top in the direction of gravity. For example, in the first tank 100B and the second tank 200B, the water supply port is preferably provided on the bottom side in the direction of gravity, and the water discharge port is preferably provided on the top side in the direction of gravity.

[0025] In an embodiment in which the first tank contains multiple positive electrodes and the second tank contains multiple negative electrodes, the positive electrodes, negative electrodes, and power source may be connected in a different configuration, in addition to the short-circuit connection configuration shown in FIG. Fig. 4 is a schematic diagram showing a connection configuration between a plurality of nickel-hydrogen storage batteries in a first tank, a plurality of nickel-hydrogen storage batteries in a second tank, and electrodes. In the water electrolysis apparatus 20C shown in Fig. 4, the first tank 100C has a plurality (six in Fig. 4) of nickel-hydrogen storage batteries, and the second tank 200C has a plurality (six in Fig. 4) of nickel-hydrogen storage batteries. Furthermore, the water electrolysis apparatus 20C has a plurality (six in Fig. 4) of power sources 31, 32, 33, 34, 35, 36. One power source 31 is connected (normally connected) to the positive electrode of one nickel-hydrogen storage battery included in the first tank 100C and the negative electrode of one nickel-hydrogen storage battery included in the second tank 200C to form one circuit. Similarly, the remaining power sources 32, 33, 34, 35, and 36 are each connected (normally connected) to the positive electrode of one nickel-metal hydride battery included in the first tank 100C and the negative electrode of one nickel-metal hydride battery included in the second tank 200C, forming one circuit. In other words, the water electrolysis apparatus 20C has multiple circuits (six circuits in FIG. 4) in which the power sources, positive electrodes, and negative electrodes are separately connected. Each circuit is separated by a separator 9. Note that FIG. 4 omits configuration other than the first tank 100C, the second tank 200C, and the electrodes 31, 32, 33, 34, 35, and 36. Therefore, in each circuit of the water electrolysis apparatus 20C, the positive electrode and the negative electrode are connected to an electronic load in addition to the power source.

[0026] As described above, in the water electrolysis method and water electrolysis device according to the present disclosure, a first tank in which O2 gas is generated by a water electrolysis reaction and a second tank in which H2 gas is generated are separately provided in the electrolytic solution. Therefore, O2 gas and H2 gas can be taken out separately from the gas outlets of the first tank and the second tank, respectively, and high-purity H2 gas and O2 gas can be safely taken out.

[0027] In the present disclosure, a nickel-metal hydride storage battery can be applied to one or both of the first tank and the second tank. The nickel-metal hydride storage battery may be a used nickel-metal hydride storage battery. In other words, according to the present disclosure, the used nickel-metal hydride storage battery can be reused to safely extract high-purity H2 gas and O2 gas.

[0028] (Preferred embodiment) ·Electrolyte From the viewpoint of efficiently causing a water electrolysis reaction, the electrolyte in which the first tank and the second tank are immersed preferably has a pH of 14 or more, more preferably a pH of 15 or more, and even more preferably a pH of 16 or more. The pH is a value measured at 25° C. using a pH meter.

[0029] The electrolyte is not particularly limited, but is preferably an aqueous electrolyte. For example, an alkaline aqueous solution can be suitably used as the aqueous electrolyte. The alkaline aqueous solution contains, for example, water and an alkali metal hydroxide dissolved in the water. The alkali metal hydroxide may have a concentration of, for example, 1 mol / L to 45 mol / L. For example, the alkali metal hydroxide includes potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), etc.

[0030] ·Voltage From the viewpoint of efficiently causing the water electrolysis reaction, it is preferable to maintain the voltage so that the potential difference between the positive electrode and the negative electrode is 1.48 V or more.

[0031] Water supply From the viewpoint of easiness of extracting the generated O2 gas and H2 gas, it is preferable that water (H2O) is supplied to the first tank and the second tank from below (from the direction of gravity to the direction against gravity) in both cases. For example, it is preferable to supply water from the bottom surface of the tank to the top surface by capillary action. Furthermore, it is preferable that the outlets for discharging excess water in the first tank and the second tank are provided on the upper side in the direction of gravity.

[0032] ·distance From the viewpoint of ease of occurrence of the water electrolysis reaction, the distance between the positive electrode in the first tank and the negative electrode in the second tank is preferably 0 mm or more and 50 mm or less, more preferably 0 mm or more and 35 mm or less, even more preferably 0 mm or more and 25 mm or less, and even more preferably 0 mm or more and 15 mm or less. The distance between the positive electrode and the negative electrode refers to the shortest distance between the positive electrode and the negative electrode. When the water electrolysis device has multiple first tanks and multiple second tanks, that is, when the water electrolysis device has multiple positive electrodes and multiple negative electrodes, the distance refers to the shortest distance between the nearest positive electrodes and nearest negative electrodes.

[0033] ·temperature From the viewpoint of ease of occurrence of the water electrolysis reaction, the temperature of the entire water electrolysis apparatus is preferably higher with an upper limit of 80° C., and is, for example, preferably from 20° C. to 80° C., more preferably from 40° C. to 80° C., and even more preferably from 50° C. to 80° C. In order to control the temperature of the entire water electrolysis apparatus within the above range, it is preferable to perform a constant temperature treatment in which the water electrolysis apparatus is left in a temperature environment within the above range before starting the water electrolysis reaction. The overall temperature of the water electrolysis device is measured by measuring the temperature of the electrolyte.

[0034] 1 and 2, from the viewpoint of transportability of O2 gas generated in first tank 100B to distillation apparatus 5, it is preferable that the temperature and pressure inside distillation apparatus 5 are lower than those inside casing 40. From the same viewpoint, it is preferable that distillation apparatus 5 is arranged lower in the direction of gravity than casing 40.

[0035] (Nickel metal hydride battery) Here, a nickel-metal hydride storage battery that can be used for the first and second tanks will be described. The nickel-metal hydride storage battery (hereinafter sometimes abbreviated as "battery") may be a used nickel-metal hydride storage battery that has been used, for example, as a battery for portable devices, an in-vehicle battery, or a storage battery for renewable energy power generation.

[0036] FIG. 5 is a schematic diagram showing an example of the configuration of a nickel-metal hydride storage battery. The battery 1 is a nickel-metal hydride storage battery. The battery 1 includes a housing 2. The housing 2 is a cylindrical case. The housing 2 is made of metal. However, the housing 2 may have any shape. The housing 2 may be, for example, a rectangular case. The housing 2 may be, for example, a pouch made of an aluminum laminate film. The housing 2 may be, for example, made of resin.

[0037] The housing 2 houses an electricity storage element 10 and an electrolyte. The electricity storage element 10 includes a positive electrode 11, a negative electrode 12, and a separator 13. The illustrated electricity storage element 10 is a wound type. The electricity storage element 10 is formed by winding a strip-shaped electrode in a spiral shape. The electricity storage element 10 may be, for example, a laminated type. The electricity storage element 10 may be formed, for example, by laminating sheet-shaped electrodes.

[0038] 《Negative electrode》 The negative electrode 12 is in the form of a sheet. The negative electrode 12 may have a thickness of, for example, 10 μm to 1 mm. The negative electrode 12 has a lower potential than the positive electrode 11.

[0039] The negative electrode includes, for example, a negative electrode current collector and a negative electrode active material. The negative electrode current collector can be, for example, a nickel mesh. The negative electrode active material can be, for example, a hydrogen storage alloy. The composition of the hydrogen storage alloy is not limited as long as it can store and release hydrogen. The hydrogen storage alloy can be, for example, an Mm-Ni-Mn-Al-Co alloy. "Mm" indicates a mixture of rare earth elements called misch metal.

[0040] 《Positive electrode》 The positive electrode 11 is in the form of a sheet. The positive electrode 11 may have a thickness of, for example, 10 μm to 1 mm. The positive electrode 11 has a higher potential than the negative electrode 12. The positive electrode 11 includes a positive electrode active material. The positive electrode active material may include any component. Examples of the positive electrode active material include nickel hydroxide (Ni(OH)2), cobalt hydroxide (Co(OH)2), manganese dioxide, and silver oxide. The positive electrode active material is preferably nickel hydroxide.

[0041] The positive electrode 11 may be substantially composed of only a positive electrode active material. The positive electrode 11 may further include a current collector, a conductive material, a binder, and the like, in addition to the positive electrode active material. The current collector may include, for example, a porous metal sheet, and the like. The current collector is made of, for example, Ni.

[0042] For example, the positive electrode 11 can be formed by applying a positive electrode active material, a conductive material, and a binder to a current collector. The conductive material has electronic conductivity. The conductive material can include any component. The conductive material can include, for example, carbon black, Co, cobalt oxide, etc. The amount of the conductive material can be, for example, 0.1 parts by mass to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material. The binder bonds the current collector and the positive electrode active material. The binder can include any component. The binder can include, for example, ethylene vinyl acetate (EVA), etc. The amount of the binder can be, for example, 0.1 parts by mass to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.

[0043] <Separator> The separator 13 is in the form of a sheet. The separator 13 is disposed between the positive electrode 11 and the negative electrode 12. The separator 13 physically separates the positive electrode 11 and the negative electrode 12. The separator 13 may have a thickness of, for example, 50 μm to 500 μm. The separator 13 is porous. The separator 13 may include, for example, a stretched porous film, a nonwoven fabric, or the like. The separator 13 is electrically insulating. The separator may be made of, for example, polyolefin, polyamide, or the like.

[0044] 《Electrolyte》 The electrolyte is not particularly limited, but is preferably an aqueous electrolyte. For example, an alkaline aqueous solution can be suitably used as the aqueous electrolyte. The alkaline aqueous solution contains, for example, water and an alkali metal hydroxide dissolved in the water. The alkali metal hydroxide may have a concentration of, for example, 1 mol / L to 20 mol / L. For example, the alkali metal hydroxide includes potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), etc.

[0045] [Method of recycling nickel-metal hydride batteries] A method for recycling nickel-metal hydride batteries according to the present disclosure includes a water electrolysis device comprising: a power source, an electrolytic solution, a first tank having a positive electrode connected to the power source, an H2O supply inlet and an exhaust outlet, and an O2 gas outlet, and being immersed in the electrolytic solution; and a second tank having a negative electrode connected to the power source, an H2O supply inlet and an exhaust outlet, and an H2 gas outlet, and being immersed in the electrolytic solution, wherein the power source maintains a voltage such that a potential of the positive electrode is higher than a potential of the negative electrode, thereby extracting O2 gas from the first tank and H2 gas from the second tank, and a used nickel-metal hydride battery is used as at least one of the first tank and the second tank.

[0046] According to the method for recycling nickel-metal hydride storage batteries according to the present disclosure, used nickel-metal hydride storage batteries can be reused, and highly pure H 2 gas and O 2 gas can be safely extracted.

[0047] Here, the generation of hydrogen gas in the water electrolysis device according to the embodiment of the present disclosure was confirmed by an experiment.

[0048] (Experimental Examples A1-A4, B1-B3) A water electrolysis apparatus was prepared that had the same configuration as the water electrolysis apparatus 20A shown in FIG. 1, but used the following as the electrolytic solution, and the first and second tanks, and connected the positive electrode in the first tank and the negative electrode in the second tank to a power source and a resistor (electronic load). Electrolyte: Potassium hydroxide (KOHaq, pH 15) First tank and second tank: used nickel-metal hydride storage battery

[0049] In this water electrolysis apparatus, water (H2O) was supplied to the first tank from a water supply pump, and water (H2O) was supplied to the second tank from a water supply pump, and the voltage was maintained by a power supply and resistor so that the potential of the positive electrode in the first tank was higher than the potential of the negative electrode in the second tank. The conditions for maintaining the voltage, specifically, the voltage, average current, time, capacity, input power, amount of electricity, amount of hydrogen generated, efficiency, electrode distance (distance between the positive and negative electrodes), and temperature (overall temperature of the water electrolysis apparatus), are shown in Tables 1 and 2. After the voltage started to be held, it was confirmed that oxygen (O2) gas was discharged from the exhaust passage of the first tank, and hydrogen (H2) gas was discharged from the exhaust passage of the second tank.

[0050] [Table 1]

[0051] [Table 2]

[0052] As shown in Table 1, the amount of hydrogen generated increases as the electrode distance decreases from 40 mm to 30 mm, 20 mm, and 10 mm. Furthermore, as shown in Table 2, the amount of hydrogen generated increases as the temperature increases to 30°C, 45°C, and 60°C.

[0053] (Experimental Examples C1 to C5) Experiments were conducted using a water electrolysis apparatus having the same configuration as the water electrolysis apparatus 20C shown in Fig. 4 (hereinafter referred to as "Pattern 1") and the same configuration as the water electrolysis apparatus 20B shown in Fig. 2 and Fig. 3 (hereinafter referred to as "Pattern 2") The following were used as the electrolyte, the six storage batteries in the first tank, and the six storage batteries in the second tank. Electrolyte: Potassium hydroxide (KOHaq, pH 15) First tank and second tank: used nickel-metal hydride storage battery

[0054] In Experimental Example C1, a water electrolysis apparatus of Pattern 1 was used, and in Experimental Examples C2 to C5, a water electrolysis apparatus of Pattern 2 was used. The water electrolysis apparatus of Pattern 1 has six power sources, similar to the water electrolysis apparatus 20C shown in Fig. 4, with the first tank having six nickel-hydrogen storage batteries and the second tank having six nickel-hydrogen storage batteries. Each power source is connected to the positive electrode of one nickel-hydrogen storage battery included in the first tank and the negative electrode of one nickel-hydrogen storage battery included in the second tank to form one circuit, that is, the apparatus has six circuits. Each circuit is separated by a separator. In each circuit, the positive electrode and the negative electrode are connected to a resistor as an electronic load in addition to the power source. 2 and 3, the water electrolysis apparatus of Pattern 2 has one power source, and the first tank has six nickel-metal hydride batteries, and the second tank has six nickel-metal hydride batteries. The positive electrodes of the six nickel-metal hydride batteries in the first tank are all connected to a power source, and the negative electrodes of the six nickel-metal hydride batteries in the second tank are all connected to a power source. The positive and negative electrodes are connected to a resistor as an electronic load in addition to the power source.

[0055] In this water electrolysis apparatus, water (H2O) was supplied to the first tank from a water supply pump, and water (H2O) was supplied to the second tank from a water supply pump, and the voltage was maintained by a power supply and resistor so that the potential of the positive electrode in the first tank was higher than the potential of the negative electrode in the second tank. The conditions for maintaining the voltage, specifically, the voltage, average current, time, capacity, input power, amount of electricity, amount of hydrogen generated, efficiency, electrode immersion height (height at which the positive and negative electrodes are immersed in the electrolyte), electrode distance (distance between the positive and negative electrodes), and temperature (overall temperature of the water electrolysis apparatus), are shown in Table 3. After the voltage started to be held, it was confirmed that oxygen (O2) gas was discharged from the exhaust passage of the first tank, and hydrogen (H2) gas was discharged from the exhaust passage of the second tank.

[0056] [Table 3]

[0057] As shown in Experimental Examples C1 and C2 in Table 3, the amount of hydrogen generated in the water electrolysis apparatus of Pattern 2 was greater than that in the water electrolysis apparatus of Pattern 1. Furthermore, as shown in Experimental Examples C2 to C5 in Table 3, it can be seen that the amount of hydrogen generated increases as the electrode immersion height decreases to 80 mm, 40 mm, 10 mm, and 5 mm. [Explanation of symbols]

[0058] 1 battery 10. Energy storage element 11 Positive electrode 12 Negative electrode 13 Separator 2. Chassis 3, 31, 32, 33, 34, 35, 36 power supply 4. Chassis 40 Electrolyte 5. Distillation Apparatus 6. Water supply pump 7 Liquid delivery pump 8 Outlet 9 Separator 20A, 20B, 20C water electrolysis equipment 30 resistor 100A, 100B, 100C First tank 200A, 200B, 200C Second tank 101, 201 Discharge passage

Claims

1. Power supply, An electrolyte; A positive electrode connected to the power supply, H ２ A supply port and a discharge port for O, and ２ a first tank having a gas outlet and immersed in the electrolyte; A negative electrode connected to the power supply, H ２ O supply and discharge ports, and H ２ a second tank having a gas outlet and immersed in the electrolyte; having The power source maintains a voltage such that the potential of the positive electrode is higher than the potential of the negative electrode, thereby discharging O from the first tank. ２ Remove gas and H from the second vessel. ２ A water electrolysis device that extracts gas.

2. 2. The water electrolysis apparatus according to claim 1, wherein at least one of the first tank and the second tank is a nickel-metal hydride battery.

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

4. The above O ２ Gas outlet and the H ２ 2. The water electrolysis apparatus according to claim 1, wherein a gas outlet is provided at an upper portion of the first tank or the second tank in the direction of gravity.

5. The supply port and the discharge port in the first tank and the supply port and the discharge port in the second tank are ２ The water electrolysis apparatus according to claim 1 , wherein the O flows from the lower part to the upper part in the direction of gravity.

6. The water electrolysis device according to claim 1 , wherein the electrolytic solution has a pH of 15 or more.

7. The water electrolysis apparatus according to claim 1 , wherein the shortest distance between the positive electrode and the negative electrode is greater than 0 mm and is equal to or less than 35 mm.

8. The water electrolysis apparatus according to claim 1 , wherein the temperature of the entire water electrolysis apparatus is 40° C. or higher and 80° C. or lower.

9. Power supply, An electrolyte; A positive electrode connected to the power supply, H ２ A supply port and a discharge port for O, and ２ a first tank having a gas outlet and immersed in the electrolyte; A negative electrode connected to the power supply, H ２ O supply and discharge ports, and H ２ a second tank having a gas outlet and immersed in the electrolyte; For a water electrolysis device having The power supply maintains a voltage such that the potential of the positive electrode is higher than the potential of the negative electrode, and O is supplied from the first tank. ２ Remove gas and H from the second vessel. ２ A water electrolysis method to extract gas.

10. The water electrolysis method according to claim 9, wherein at least one of the first tank and the second tank is a nickel-metal hydride storage battery.

11. The water electrolysis method according to claim 10, wherein the nickel-metal hydride storage battery is a used storage battery.

12. The above O ２ The water electrolysis method according to claim 9 , wherein the gas outlet and the H2 gas outlet are provided at an upper portion of the first tank or the second tank in the direction of gravity.

13. The supply port and the discharge port in the first tank and the supply port and the discharge port in the second tank are ２ The method for water electrolysis according to claim 9 , wherein the O flows from a lower portion to an upper portion in a direction of gravity.

14. The water electrolysis method according to claim 9 , wherein the electrolytic solution has a pH of 15 or more.

15. The water electrolysis method according to claim 9, wherein the shortest distance between the positive electrode and the negative electrode is more than 0 mm and 35 mm or less.

16. The water electrolysis method according to claim 9, wherein the temperature of the entire water electrolysis apparatus is 40° C. or higher and 80° C. or lower.

17. Power supply, An electrolyte; A positive electrode connected to the power supply, H ２ A supply port and a discharge port for O, and ２ a first tank having a gas outlet and immersed in the electrolyte; A negative electrode connected to the power supply, H ２ O supply and discharge ports, and H ２ a second tank having a gas outlet and immersed in the electrolyte; having The power source maintains a voltage such that the potential of the positive electrode is higher than the potential of the negative electrode, thereby discharging O from the first tank. ２ Remove gas and H from the second vessel. ２ For water electrolysis equipment that extracts gas, A method for recycling nickel-metal hydride storage batteries, comprising using a used nickel-metal hydride storage battery as at least one of the first tank and the second tank.

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