Water electrolysis method

Abstract

To provide a water electrolysis method that uses a single nickel-hydrogen battery, exhibiting high energy conversion efficiency.SOLUTION: A water electrolysis method according to the present disclosure uses a power source, an electrolytic solution that is capable of transferring OH-ions, and a single nickel-hydrogen battery that has a positive electrode connected to the power source and a negative electrode including lanthanum and connected to the power source and that is immersed in the electrolytic solution, applies a potential difference through the power source to make the potential of the positive electrode higher than the potential of the negative electrode, and generates oxygen gas from the positive electrode and hydrogen gas from the negative electrode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a water electrolysis method using a single nickel-metal hydride battery. [Background technology]

[0002] In recent years, hydrogen (H 2 ) Gas demand is increasing, 2 Research into the production of H gas is also underway. 2 Methods for producing gas include, for example, water (H 2 O is converted to hydrogen (H 2 ) gas and oxygen (O 2 ) gas and recover them.

[0003] For example, Patent Document 1 describes a battery that uses platinum (Pt) for the negative electrode and nickel hydroxide (Ni(OH) 2 In one embodiment, a water electrolysis cell using a lithium-ion battery is disclosed, in which oxygen is absorbed and released at the positive electrode, and oxygen is not released when hydrogen is generated at the negative electrode.

[0004] However, in Patent Document 1, platinum (Pt), which has a wide potential window, is used for the negative electrode. In other words, the upper and lower limit potentials of the negative electrode during the electrochemical reaction can be greatly changed (the upper and lower limit potentials do not need to be considered). Therefore, the potential of the paired positive electrode can also be greatly changed. Nickel hydroxide (Ni(OH) 2 ) The reaction continues reversibly so long as the valence of Ni changes between divalent and trivalent. However, if the potential change is increased to, for example, a valence change between divalent and tetravalent, the positive electrode deteriorates irreversibly (an oxide film forms on the positive electrode), and the efficiency of gas generation by water electrolysis may decrease.

[0005] Nickel-metal hydride batteries are already widely used in electric and hybrid vehicles, but the amount of used nickel-metal hydride batteries is expected to increase in the future. Therefore, it is desirable to reuse used nickel-metal hydride batteries as much as possible as water electrolysis cells. However, nickel-metal hydride batteries have a negative electrode containing LaNi5 and a positive electrode containing Ni(OH). 2 In this system, when oxygen is released from the positive electrode and hydrogen is released from the negative electrode as in Patent Document 1, lanthanum (La) has hydrogen storage capacity, so it is necessary to electrochemically deactivate lanthanum first. However, no attention has been paid to the conditions for electrochemical deactivation of La that would not cause deterioration of the positive electrode at the same time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2017-534764 Summary of the Invention [Problem to be solved by the invention]

[0007] In consideration of such conventional demands, an object of the present disclosure is to provide a water electrolysis method using a single nickel-metal hydride battery, which has high energy conversion efficiency. [Means for solving the problem]

[0008] Means for solving the above problems include the following means. <1> Power supply, OH - An electrolyte in which ions can move; a single nickel-metal hydride battery having a positive electrode connected to the power source and a negative electrode including lanthanum and connected to the power source, the single nickel-metal hydride battery being immersed in the electrolyte; A potential difference is applied by the power source such that the potential of the positive electrode is higher than the potential of the negative electrode, thereby generating oxygen gas from the positive electrode and hydrogen gas from the negative electrode. Water electrolysis method. <2> Prior to applying the potential difference, The nickel-metal hydride battery is exposed to the atmosphere at a temperature of 80° C. or less, Thereafter, a voltage is applied to the negative electrode with a potential of −0.6 V or higher in a state where the pH of the electrolytic solution is adjusted to 7 or less, thereby oxidizing the lanthanum. <1> The water electrolysis method according to claim 1. Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a water electrolysis method using at least one nickel-metal hydride battery, which has high energy conversion efficiency. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic perspective view of an apparatus for carrying out a water electrolysis method according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic perspective view of an apparatus for carrying out a water electrolysis method according to another embodiment of the present disclosure. [Diagram 3] 3 is a schematic diagram illustrating a configuration in which a plurality of positive electrodes and a plurality of negative electrodes of a single battery module are connected to a power source in the water electrolysis apparatus shown in FIG. 2. FIG. [Figure 4] This is a potential-pH diagram of Ni at 80°C. [Diagram 5] This is a potential-pH diagram of Ni at 50°C. [Figure 6] FIG. 1 is a schematic diagram showing an example of the configuration of a nickel-metal hydride battery. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The water electrolysis method 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 view, and the size and shape of each part are appropriately exaggerated for ease of understanding.

[0012] In this disclosure, a "single nickel-metal hydride battery" may be a single battery cell or a single battery module having multiple battery cells. A "single battery cell" refers to a battery that is the smallest structural unit that functions as a single, independent battery. A "single battery module" refers to a battery that is made up of multiple cells combined to function as a single, independent battery.

[0013] [Water electrolysis method] The water electrolysis method according to the present disclosure uses a power source, an electrolyte, and a single nickel-metal hydride battery. The nickel-metal hydride battery has a positive electrode connected to the power source and a negative electrode connected to the power source, and is immersed in the electrolyte. The power source applies a potential difference (voltage) such that the potential of the positive electrode is higher than the potential of the negative electrode, and hydrogen gas (H 2 ) from the positive electrode, and oxygen (O 2 ) gas is produced.

[0014] [Battery cell] One embodiment of the water electrolysis method according to the present disclosure will be described with reference to the apparatus illustrated in FIG. 1, in which a single nickel-metal hydride battery is used as a "battery cell." FIG. 1 is a schematic perspective view illustrating a water electrolysis apparatus for carrying out the water electrolysis method of the present disclosure. As shown in FIG. 1, the water electrolysis apparatus 20A includes a power source 3, a resistor 30 which is an example of an electronic load, a housing 4 in which an electrolytic solution 40 is accommodated, a battery cell 100A 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 required voltage can be maintained. A power source with a built-in electronic load function may also be used. The battery cell 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 negative electrode is further connected to the power source 3 and the resistor 30. The battery cell 100A 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 circulate water (H 2The battery cell 100A is supplied with oxygen (O). The battery cell 100A also has a water outlet, to which a water outlet pipe (not shown) is connected, and excess water in the battery cell 100A is discharged from the outlet. 2 The battery cell 100A has a discharge passage 101 for discharging hydrogen (H 2 The distillation device 5 has a discharge passage 102 for discharging water vapor (H 2 ). An electrolytic solution is accommodated in the distillation device 5, and the electrolytic solution in the distillation device 5 and the electrolytic solution 40 in the housing 4 are circulated through a circulation pipe (not shown) equipped with a liquid delivery pump 7. The distillation device 5 is 2 1, a gas flow meter (not shown), a gas pack (not shown), a flashback valve (not shown), and the like may be attached to the exhaust passage 102 as necessary. 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.

[0015] The water electrolysis apparatus 20A uses a nickel-hydrogen battery cell as the battery cell 100A. This nickel-hydrogen battery cell may be a used nickel-hydrogen battery cell. The term "used" refers to a battery whose charging capacity is lower than that of the battery immediately after manufacture.

[0016] In the water electrolysis device 20A, a voltage is applied by the power source 3 and the resistor 30 so that the potential of the positive electrode of the battery cell 100A is higher than the potential of the negative electrode. 2 O) causes a water electrolysis reaction, and O 2 Gas is generated and H 2 Gas is generated. The water electrolysis reaction is shown below. (Positive electrode)OH - →1 / 2H 2 O+1 / 4O 2 +e - (Negative electrode)H 2 O+e - →1 / 2H 2 +OH-

[0017] O from the positive pole of the 100A battery cell 2 Gas is pumped from the negative pole to H 2 When gas is generated, it can be extracted as hydrogen oxyhydroxide (HHO) gas (a mixture of hydrogen and oxygen). 2 From the viewpoint of efficiently causing the water electrolysis reaction in (O), it is preferable to maintain the potential difference between the positive electrode and the negative electrode at 1.48 V or more. From the viewpoint of facilitating the progress of the water electrolysis reaction, the potential difference obtained by subtracting the negative electrode potential from the positive electrode potential in the battery cell 100A is more preferably in the range of 1.48 V to 2.00 V, and from the viewpoint of efficiency, is even more preferably in the range of 1.55 V to 1.80 V. When the generated oxyhydrogen (HHO) gas is to be extracted, the generated gas may be allowed to pass through the exhaust passage 102 using a flow path switching valve or the like (not shown).

[0018] Alternatively, a voltage may be applied so that the potential difference between the positive electrode potential and the negative electrode potential of the battery cell 100A becomes a predetermined potential difference, and only hydrogen gas or only oxygen gas may be generated, in which case a post-process for separating hydrogen gas and oxygen gas is not required.

[0019] The above-mentioned predetermined potential difference varies depending on the type (combination) of electrodes, the pH and temperature of the electrolyte, and other conditions. Here, the positive electrode of the battery cell 100A is Ni(OH). 2 The following description will be given by taking as an example a case where the negative electrode is LaNi5, the pH of the electrolyte is 15, and the temperature is 30° C. Note that, regarding the predetermined potential difference, a potential difference that generates only hydrogen is sometimes called a first potential difference, and a potential difference that generates only oxygen is sometimes called a second potential difference. When oxygen is generated, the potential at which oxygen is generated is 1.48V or more, preferably 1.8V. When hydrogen is generated, the potential at which hydrogen is generated is −0.9V or less, preferably −1.0V. Based on the above potential, a voltage is applied to both electrodes so as to generate only hydrogen, or a voltage is applied to both electrodes with the polarity reversed so as to generate only oxygen (so that a current flows in the opposite direction to that during hydrogen generation). In this way, by repeatedly applying charge and discharge, hydrogen gas and oxygen gas can be generated with time separation. The number of cycles of voltage application is not particularly limited as long as it is at least one, assuming that one cycle is one charge and discharge. It may be 5, 10, 15, 20, or even 100 times. The electrochemical reactions during charge and discharge in a nickel-metal hydride battery are shown below. Charge→ / ←Discharge (Positive electrode)Ni(OH) 2 +OH - ←→NiOOH+H 2 O+e - (Negative electrode)M+H 2 O+e - ←→MH+OH - (Overall)Ni(OH) 2 +M←→NiOOH+MH Furthermore, the time for applying the voltage may be appropriately determined depending on the positive electrode capacity of the battery, for example, 72 seconds / Ah at 30 Acc when charging / discharging the positive electrode capacity of the battery to 20% to 80%, or 24 seconds / Ah at 30 Acc when charging / discharging the positive electrode capacity of the battery to 40% to 60%. The oxygen generating potential (Table 1) and the hydrogen generating potential (Table 2) at an electrolyte pH of 15 and a temperature of −30° C. to 80° C. are shown below. The first potential difference and the second potential difference at each temperature may be appropriately determined with reference to the potentials shown in Tables 1 and 2. [Table 1] [Table 2]

[0020] H 2 If you want to extract only gas, use H 2When gas is generated, the exhaust passage 102 shown in FIG. 1 may be opened and the exhaust passage 101 may be closed. 2 When gas is generated, O 2 The gas is sent to the distillation apparatus 5 through the exhaust passage 101, where it is reduced to water vapor (H 2 O) may be taken out from the outlet 8.

[0021] According to the present disclosure, by applying a voltage so that the potential difference between the positive electrode and the negative electrode becomes the above-mentioned predetermined potential difference, oxygen gas and hydrogen gas can be generated in a manner that does not cause deterioration of the positive electrode and the negative electrode, which leads to improved durability of the water electrolysis device.

[0022] Next, another embodiment will be described.

[0023] [Battery module] Another embodiment of the water electrolysis method according to the present disclosure will be described with reference to the apparatus shown in Fig. 2, in which a "battery module" is used as a single nickel-metal hydride battery. Note that the same components as those in the apparatus shown in Fig. 1 are denoted by the same reference numerals, and duplicated descriptions will be omitted. FIG. 2 is a schematic perspective view illustrating a water electrolysis apparatus for implementing the water electrolysis method 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 containing an electrolytic solution 40, a battery module 100B immersed in the electrolytic solution 40 in the housing 4, and a distillation apparatus 5. The water electrolysis apparatus 20B uses a plurality of nickel-hydrogen battery cells (six-pair nickel-hydrogen battery modules in FIG. 2) as the battery module 100B. Each of the six nickel-hydrogen battery cells in the battery module 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. Furthermore, the negative electrodes are all connected to the power source 3 and the resistor 30. The battery module 100B has a water supply port, to which a water supply pipe (not shown) equipped with a water supply pump 6 is connected, and water (H 2 O is supplied to the battery module 100B. 2The battery module 100B has a discharge passage 101 for hydrogen (H 2 ) a gas exhaust passage 102.

[0024] FIG. 3 shows an example of a configuration in which the multiple (six pairs in FIG. 2) nickel-metal hydride battery cells in the battery module 100B are connected to the power source 3 in the water electrolysis apparatus 20B shown in FIG. 2. Note that FIG. 3 omits configuration other than the battery module 100B and the power source 3, and also omits illustration of an electronic load. As shown in FIG. 3, the positive and negative electrodes in each of the multiple nickel-metal hydride battery cells in the battery module 100B are both connected (shorted) to the power source 3. For example, the power source 3 may be connected to the positive and negative terminals of the battery module 100B, respectively.

[0025] In the water electrolysis apparatus 20B, the nickel-metal hydride battery module used in the battery module 100B may be a used nickel-metal hydride battery module. In addition, in the water electrolysis apparatus 20B, the voltage applied may be the voltage of the water electrolysis apparatus 20A multiplied by the number of cells.

[0026] (Preferred embodiment) [Electrolyte] From the viewpoint of efficiently causing a water electrolysis reaction, the electrolyte in which the nickel-metal hydride battery is 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.

[0027] 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.

[0028] [temperature] From the viewpoint of ease of occurrence of the water electrolysis reaction, the overall temperature of the water electrolysis apparatus is preferably higher with the upper limit being 80° C., and is, for example, preferably from 20° C. to 80° C., more preferably from 40° C. to 80° C., and further preferably from 50° C. to 80° C. The overall temperature of the water electrolysis apparatus is measured by measuring the temperature of the electrolytic solution.

[0029] [Ni 2 O 3 H coating] In the background art of the present application, the change in the valence of Ni between divalent and trivalent continues reversibly, but when the potential change is increased to change the valence between divalent and tetravalent, an oxide film (Ni 2 O 3 However, in this disclosure, the valence of the Ni in the negative electrode is intentionally varied between divalent and tetravalent, and the surface of the negative electrode is coated with Ni 2 O 3 An H coating may be formed. In nickel-metal hydride batteries, the negative electrode contains a hydrogen storage alloy containing misch metal. The hydrogen storage alloy has the characteristic of absorbing hydrogen and releasing hydrogen reversibly. Therefore, in order to prevent the hydrogen storage alloy from absorbing hydrogen generated on the negative electrode side during water electrolysis, Ni 2 O 3 H coating may be formed. 2 O 3 H coating is Ni 2 O 3 It is a film containing H as the main component (the component with the largest mass) and having corrosion resistance and electrical conductivity. The thickness of the film is not particularly limited, but is, for example, 100 to 200 nm. 2 O 3 For details of the H coating, refer to JP 2022-45695 A.

[0030] [Film formation method] In the coating formation method, the material on which the coating is to be formed (for example, LaNi5) is exposed to the atmosphere. Next, the material on which the coating is to be formed (e.g., LaNi5) is immersed in an acidic solution (pH 7 or less), and the first potential (upper potential) and the second potential (lower potential) are applied alternately and repeatedly to the LaNi5. 2 O 3 A H film is formed on the surface of LaNi5. The first potential is Ni-H 2 This is within the potential range in which Ni becomes tetravalent in the O system. The second potential is Ni-H 2 This is within the potential range where Ni becomes divalent in the O system.

[0031] The first potential (upper potential) and the second potential (lower potential) vary depending on the temperature and pH of the solution. 2 This is a potential-pH diagram of the Ni-Ni system (O system) (a diagram showing the existence area of ​​each Ni chemical species in water on a two-dimensional coordinate system of electrode potential and pH). The case of an alkaline solution will be described with reference to Fig. 4. The same applies to the case of an acidic solution. For example, when using an 8M KOH aqueous solution (pH 14.9) at 80°C, the first potential (the potential at which Ni becomes tetravalent) is higher than about 0.48 V (SHE reference potential). The second potential (the potential at which Ni becomes divalent) is within a range of about 0.27 V (SHE reference potential) or less.

[0032] The first potential is preferably about 0.48 V or more. If the first potential is too low within this range, the formation rate will be slow, and if the first potential is too high in combination with the second potential, the formation efficiency will be poor, so it is preferable that the first potential be set appropriately.

[0033] The second potential is preferably about 0.27 V or less. If the second potential is too high, the formation rate becomes slow, and if the second potential is too low, the formation rate becomes slow. 2 O 3 Since the ratio of H to LaNi5 becomes small, it is preferable to set it appropriately.

[0034] Fig. 5 is a potential-pH diagram of Ni at 50° C. As shown in Fig. 5, for example, in the case of using an 8 M KOH aqueous solution at 50° C., the first potential is a potential higher than about 0.57 V. The second potential is a potential lower than about 0.37 V.

[0035] As shown in Figures 4 and 5, the ranges of the first potential and the second potential used in the coating formation method change depending on the pH, temperature, etc. of the solution. Therefore, it is desirable to apply potentials in the appropriate ranges of the first potential and the second potential that satisfy the above conditions according to the pH, temperature, etc. of the solution. The temperature of the solution is preferably 40 to 90°C, more preferably 45 to 85°C. In the case of an alkaline solution, the pH is preferably 10 or more, more preferably 12 or more, and even more preferably 14 or more.

[0036] Specific examples of the alkaline solution include KOH solution, NaOH solution, LiOH solution, etc., and preferably KOH solution and NaOH solution. The concentration of the alkaline solution is preferably a concentration that provides the above-mentioned pH.

[0037] The application time of each of the first voltage and the second voltage is, for example, 5 seconds for the first voltage and 10 seconds for the second voltage, and is appropriately set for each solution condition (type of solution, pH, temperature). The total application time of the first voltage and the second voltage is set to 10 seconds for each solution condition (type of solution, pH, temperature). 2 O 3 The thickness of the H coating is appropriately set.

[0038] [Nickel metal hydride battery] Here, a nickel-metal hydride battery that can be used in the water electrolysis method of the present disclosure will be described. The nickel-metal hydride battery (hereinafter sometimes abbreviated as "battery") may be a used nickel-metal hydride battery that has been used, for example, as a battery for portable devices, an on-board battery, or a battery for renewable energy power generation.

[0039] FIG. 6 is a schematic diagram showing an example of the configuration of a nickel-metal hydride battery cell. The battery cell 1 is a nickel-metal hydride battery cell. The battery cell 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.

[0040] 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.

[0041] [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.

[0042] 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, a Mm-Ni-Mn-Al-Co alloy. "Mm" indicates a mixture of rare earth elements called misch metal. Specifically, La-Ni alloys such as LaNi5 can be used.

[0043] [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. The positive electrode active material may be, for example, nickel hydroxide (Ni(OH) 2 ), cobalt hydroxide (Co(OH) 2), manganese dioxide, silver oxide, etc. The positive electrode active material is preferably nickel hydroxide.

[0044] 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.

[0045] 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.

[0046] [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.

[0047] [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.

[0048] As described above, according to the water electrolysis method of the present disclosure, it is possible to recycle used nickel-metal hydride batteries and produce highly efficient and highly pure H 2 Gas and O 2 Gas can be safely extracted. 2 When gas is generated, H 2 Since the time when gas is generated can be separated from the time when it is generated, high purity H 2 Gas and O 2 The gases can be safely removed separately. Furthermore, according to the present disclosure, when the negative electrode contains an oxygen storage material such as lanthanum, only the negative electrode can be oxidized (lanthanum in the negative electrode can be deactivated) at a potential difference that does not cause the positive electrode to deteriorate. 2 O 3 The lanthanum-containing electrode can then generate hydrogen by electrolysis of water. EXAMPLES

[0049] Here, the generation of hydrogen gas and oxygen gas in the water electrolysis method according to the embodiment of the present disclosure was confirmed by an experiment.

[0050] [Example 1] An experiment was carried out using a water electrolysis apparatus having the same configuration as the water electrolysis apparatus 20B shown in Fig. 2. The following electrolyte and battery module were used. Electrolyte: Potassium hydroxide (KOHaq, pH 15) Battery module: Used battery module NP2, manufactured by Primearth EV Energy Co., Ltd.

[0051] The water electrolysis device had one power source, and a battery module (NP2) had six battery cells, similar to the water electrolysis device 20B shown in Fig. 2. The NP2 was used with the top cover plate removed and each battery cell opened. The positive and negative terminals of the NP2 were both connected to a power source. The positive and negative terminals were also connected to a resistor as an electronic load in addition to the power source.

[0052] In this water electrolysis device, water (H 2 O) was supplied to NP2, and the voltage was maintained by a power supply and a resistor so that the potential of the positive electrode in NP2 was higher than the potential of the negative electrode. After the voltage is held, oxygen (O 2 ) gas and hydrogen (H 2 ) It was confirmed that the gas was being discharged.

[0053] When water electrolysis was performed using used NP2, an extremely high energy conversion efficiency (68.0%) was observed, as shown in Table 3, even though the measurement was performed at room temperature (20°C). [Table 3]

[0054] As mentioned above, hydrogen (H 2 In this way, the water electrolysis method according to the present disclosure can achieve excellent effects and contribute to the transition to a circular economy society. Furthermore, in the water electrolysis method according to the present disclosure, a voltage is applied so as to achieve a predetermined potential difference, and hydrogen (H 2 ) gas and oxygen (O 2) gas can be recovered separately, eliminating the need for a post-process to separate hydrogen gas. Furthermore, by using the specified potential difference, hydrogen (H 2 ) gas and oxygen (O 2 ) gas can be generated, and the durability of the water electrolysis cell can be improved. [Explanation of symbols]

[0055] 1 battery 10. Energy storage element 11 Positive electrode 12 Negative electrode 13 Separator 2. Chassis 3 Power supply 4. Chassis 40 Electrolyte 5. Distillation Apparatus 6. Water supply pump 7 Liquid delivery pump 8 Outlet 20A, 20B water electrolysis equipment 30 resistor 100A battery cell 100B Battery Module 101, 102 Discharge passage

Claims

1. Power supply, O.H. － An electrolyte in which ions can move; a single nickel-metal hydride battery having a positive electrode connected to the power source and a negative electrode including lanthanum and connected to the power source, the single nickel-metal hydride battery being immersed in the electrolyte; A potential difference is applied by the power source such that the potential of the positive electrode is higher than the potential of the negative electrode, thereby generating oxygen gas from the positive electrode and hydrogen gas from the negative electrode. Water electrolysis method.

2. Prior to applying the potential difference, The nickel-metal hydride battery is exposed to the atmosphere at a temperature of 80° C. or less, Thereafter, a voltage is applied to the negative electrode with a potential of −0.6 V or higher in a state where the pH of the electrolytic solution is adjusted to 7 or less, thereby oxidizing the lanthanum. The water electrolysis method according to claim 1.

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