JP2019194349A - Electrolytic solution for water electrolysis, water electrolysis device and water electrolysis method employing the same - Google Patents

Abstract

To provide an electrolytic solution, a water electrolysis device and a water electrolysis method, capable of improving the efficiency of producing hydrogen by water electrolysis by virtue of an effect of magnetic buoyancy even in a micro-gravitational field.SOLUTION: An electrolytic solution 3 for water electrolysis is characterized by containing a water-based magnetic nano fluid that contains an electrolyte and magnetic nanoparticles. A water electrolysis device 1 is characterized by comprising a power source 2, the electrolytic solution 3 for water electrolysis that contains a water based magnetic nano fluid containing an electrolyte and magnetic nanoparticles, a pair of electrodes 4 each constituting an anode and a cathode respectively, a magnetic field applying means 5 that applies a non-uniform magnetic field at least to one electrode of the pair of electrodes 4, and a container 6 that stores the electrolytic solution 3 for water electrolysis.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrolytic solution for water electrolysis containing magnetic nanoparticles, a water electrolysis apparatus and a water electrolysis method using the same.

Products using hydrogen energy fuel cell vehicle and the representative is commercialized, efficient hydrogen production due to the growing demand for hydrogen energy is important, the high-purity hydrogen without discharging the CO ₂ in the manufacturing process The resulting water electrolysis has attracted attention (Non-Patent Document 1).

In water electrolysis, generated hydrogen and oxygen adhere to the electrode and the resistance value increases, so that the amount of electrolysis is suppressed. Therefore, Non-Patent Document 2 describes electrolysis using MHD convection. Patent Document 1 discloses a gas in a porous gas diffusion electrode seal portion of a fuel cell in which a small amount of magnetic nanofluid is used as an electrolyte and the magnetic nanofluid is moved along a gas-impermeable insulating seal portion by an external magnetic force. An apparatus related to impermeability is described.

However, there has been no disclosure of using a water-based magnetic nanofluid as an electrolytic solution for water electrolysis. As for the electrode used for water electrolysis, for example, a lithium ion battery uses a porous electrode having a large electrolytic surface area in order to improve efficiency. In water electrolysis, bubbles (oxygen and hydrogen) generated are constrained inside the porous electrode. Therefore, there is a problem that the porous electrode cannot be used and it is difficult to increase the efficiency of hydrogen production by the electrolyzed water.

On the other hand, the technology related to the moon, which is the target of space development, will continue to attract attention in the future.For example, water electrolysis promotion technology is expected to become more important in relation to propellant generation technology and oxygen generation system, In a microgravity field such as outer space, there is a problem in that the difficulty becomes remarkable due to the above-mentioned restriction of bubbles.

JP 2000-323160 A

Masato Yoshino, an energy storage and supply system using hydrogen that uses renewable energy, Electrochemistry Vol. 84, pp620-625, 2016 H. Matsushima, T .; Iida, and Y. Fukunaka, “Observation of bubble layer formed on hydrogen and oxygen gas-evolving electrode in a magnetic field,” J. Solid State Electrochem, vol. 16, no. 2, pp. 617-623, 2012 H. Matsushima, T .; Nishida, Y. Konishi, Y. Fukunaka, Y. Ito, K. Kuribayashi “Water electrolysis under microgravity Part 1. Experimental technique” Electrochimica Acta (2003) 4119-4125

An object of the present invention is to solve the conventional problems as described above, and to provide an electrolytic solution, a water electrolysis apparatus, and a water electrolysis method capable of increasing the efficiency of hydrogen production by water electrolysis by the action of magnetic buoyancy even in a microgravity field Is to provide.

(1) An electrolytic solution for water electrolysis comprising a water-based magnetic nanofluid containing an electrolyte and magnetic nanoparticles.
(2) The electrolyte for water electrolysis according to (1) (hereinafter sometimes referred to as “electrolyte”), wherein the electrolyte is a neutral salt.
(3) a power source, an electrolytic solution for water electrolysis containing a water-based magnetic nanofluid containing an electrolyte and magnetic nanoparticles, a pair of electrodes constituting an anode and a cathode, and at least one of the pair of electrodes A water electrolysis apparatus comprising: a magnetic field application unit that applies a non-uniform magnetic field; and a container that stores the electrolytic solution for water electrolysis.
In order for the water electrolysis apparatus to function, it is necessary that the pair of electrodes and the power source are electrically connected.
(4) The water electrolysis apparatus according to (3), wherein the magnetic field applying means is a magnet or an electromagnetic coil.
(5) The water electrolysis apparatus according to (3) or (4), wherein the pair of electrodes is a porous electrode.
(6) The water electrolysis apparatus according to (5), wherein the porous electrode is a sponge-like electrode.
(7) an electrolytic solution for water electrolysis containing a water-based magnetic nanofluid containing an electrolyte and magnetic nanoparticles, a power source, a pair of electrodes constituting an anode and a cathode, and at least one of the pair of electrodes A water electrolysis method characterized in that at least hydrogen is obtained by energizing a water electrolysis device comprising a magnetic field applying means for applying a non-uniform magnetic field and a container for storing the water electrolysis electrolyte.
(8) The water electrolysis method according to (7), wherein the pair of electrodes has an inclination of 15 ° to 45 ° with respect to the vertical direction.

According to the present invention, a water-based magnetic nanofluid can be used to form an electrolytic solution for water electrolysis, and hydrogen can be efficiently produced by the action of magnetic buoyancy even in a microgravity field.

It is a figure which shows typically the description of the magnetic exclusion effect in the water electrolysis apparatus which is one embodiment of this invention, and a cathode and an anode. It is a figure which shows the state (A) under a gravitational environment and (B) under the microgravity environment in a state where bubbles (hydrogen, oxygen) generated by water electrolysis are attached to an electrode (cathode, anode). It is a figure which shows the state in (A) static system, (B) MDH convection, and (C) magnetic buoyancy about the bubble produced | generated by water electrolysis. Regarding hydrogen generated by water electrolysis, (A) only the cathode, that is, buoyancy, (B) the state of the cathode that received a non-uniform magnetic field by the magnet, that is, buoyancy and the state of hydrogen that received magnetic buoyancy due to the magnetic exclusion effect, FIG. (A) It is a figure which shows typically the state of a bubble when a magnetic field acts on a magnetic nanofluid which is electrolyte solution, and a magnetic field acts on a pair of electrode which (B) bubble generate | occur | produced. About the bubble which generate | occur | produced in the porous electrode, the state when a magnetic exclusion effect acts in (A) microgravity environment (1 / 6G) and (B) microgravity environment (1 / 6G) is each shown typically. FIG. It is a figure which shows the liquid appearance at the room temperature of Examples 1-6 (water-based magnetic nanofluid whose electrolyte is sodium sulfate) and Comparative Example 1 (around 3 months). It is a figure which shows typically the experimental apparatus which measures the amount of electrolysis of water. It is a figure which shows the electrolysis cell which comprises the experimental apparatus of FIG. (A) A device part in which a magnet (neodymium magnet) for applying a magnetic field to an electrolytic cell containing an electrolytic solution is disposed, (B) a pattern of applied voltage to the device part, (C) a magnetic field intensity in a space region near the magnet It is a figure which shows a state, respectively. It is a figure which shows the relationship between the electric current value i [A / cm < ² >] and time passage t [s] in the case of L = 7, 9, 11, 13 mm of FIG. FIG. 12 is a diagram illustrating a relationship between a total charge amount and a time response in which a current value is integrated with respect to time and a time course of the total charge amount is calculated. It is a figure which shows typically the case where a sponge-like electrode is used for an electrode in the electrolytic cell of FIG. It is a figure which shows the actual thing of the schematic diagram of FIG. It is a figure which shows the state of a bubble when a convection acts on (A) electrolyte solution about the sponge-like electrode and the bubble which generate | occur | produced in the sponge-like electrode, respectively (B) when a magnetic buoyancy acts. In the electrolysis of water using the experimental apparatus shown in FIG. 13, regarding the current value with respect to time, the difference between the case where the electrolyte is a magnetic field in Example 3 and the case where the electrolyte is water and no magnetic field is shown. It is a figure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be added without departing from the scope of the invention.

A water-based magnetic nanofluid containing magnetic nanoparticles is a fluid in which magnetic nanoparticles such as iron powder particles and a surfactant are dispersed in water. In the present invention, in order to use the water-based magnetic nanofluid as an electrolytic solution for water electrolysis, an electrolyte is contained to increase electrical conductivity.
The electrolyte has high electrical conductivity, is easy to dispose of, and is neutral, so there is no risk of breaking the bond between the magnetic nanoparticles and the surfactant adsorbed on the magnetic nanoparticles. From this viewpoint, a neutral salt is preferably used. As the neutral salt, sodium sulfate, potassium nitrate and the like are preferable.

As shown in FIG. 1, the water electrolysis apparatus (1) includes a power source (2), an electrolytic solution for water electrolysis (3), a pair of electrodes (4) constituting an anode and a cathode, and a pair of electrodes ( 4) includes a magnetic field applying means (5) for applying a non-uniform magnetic field and a container (6) for storing the electrolytic solution (3) for water electrolysis. Here, the electrolytic solution (3) for water electrolysis contains a water-based magnetic nanofluid containing an electrolyte and magnetic nanoparticles.

As the magnetic field applying means (5), for example, a magnet or an electromagnetic coil can be used. When the electromagnetic coil is used, the magnitude of the non-uniform magnetic field can be controlled by adjusting the current to be energized, and the amount of electrolysis can be adjusted to an arbitrary amount. The magnitude of the non-uniform magnetic field is preferably 4T or less from the viewpoint of feasibility, and is preferably 50 mT to 350 mT from the viewpoint of economical and efficient application.

The place where the magnetic field applying means (5) is arranged is a position where a magnetic field gradient due to a non-uniform magnetic field can efficiently act on at least one of the pair of electrodes (4). That is, the magnetic field applying means (5) should be arranged at a position where the magnetic field gradient is as large as possible. The magnetic field applying means (5) may be disposed on both electrodes as shown in FIG. Further, the place where the magnetic field applying means (5) is arranged is preferably a position where a magnetic field is applied perpendicularly to the surface of the electrode acting on electrolysis. Furthermore, if the magnetic field application means (5) is corrosive with respect to moisture, a position where it does not touch the electrolyte is preferable.

In FIG. 1, the magnetic field applying means (5) is arranged on each of the anode and the cathode, but the magnetic field applying means (5) is arranged on either the anode or the cathode or on either of them. In this case, the surface area of the electrode on which the magnetic field applying means (5) is not arranged or not arranged is made sufficiently larger than the surface area of the electrode on which the magnetic field applying means (5) is arranged. Can promote water electrolysis (see Examples 7 to 14).

In FIG. 1, for example, water is reduced at the cathode to generate hydroxide ions and hydrogen, and the generated hydrogen gas forms hydrogen bubbles and adheres to the cathode surface. Receive buoyancy. As will be described in detail later, since the elimination of bubbles is promoted by the magnetic exclusion effect, the electrical resistance of the cathode is reduced and the oxidation-reduction reaction is promoted, so that the amount of generated hydrogen increases. The same applies to oxygen generated when water is oxidized at the anode.

In FIG. 2, a gravity environment and a microgravity environment are compared between hydrogen bubbles generated at the cathode and attached to the cathode surface, and oxygen bubbles generated at the anode and attached to the anode surface. In a gravitational environment, the buoyancy that acts to detach hydrogen bubbles from the electrode hardly acts in a microgravity environment, so the hydrogen bubbles remain attached to the cathode, etc., and there is no contact between water and the electrode. This hinders water electrolysis (Non-Patent Document 3).

As shown in FIG. 3, in MHD convection, Lorentz force acts on ions in the electrolyte, and the size of bubbles generated in the electrode is reduced compared to a stationary system (system in which buoyancy acts on bubbles). The buoyancy and convection facilitates the detachment of bubbles from the electrode. However, the electrical conductivity of the electrolyte solution of MHD convection is small, and the detachment of bubbles from the electrode is due solely to the convection of ions in the electrolyte solution, not to the magnetic field gradient acting on the bubbles themselves. A magnetic field (1T or more) is required.

On the other hand, when magnetic buoyancy acts on bubbles generated in the electrodes, as shown in FIG. 1, the magnetic buoyancy acts along a magnetic field gradient. Therefore, since the direction of the bubbles desorbed from the electrode is a direction away from the electrode above the electrode as shown in FIG. 3C, the desorption of bubbles from the electrode is further promoted. As a result, an apparatus required for MHD convection is unnecessary, the apparatus can be simplified, and it is not necessary to have a strong magnetic field.

Based on FIG. 4, the magnetic buoyancy acting on the non-magnetic hydrogen bubbles will be further described. With respect to hydrogen bubbles in the electrolyte, it is gravity and buoyancy that acts on the hydrogen bubbles in FIG. 4 (A), so the desorption of hydrogen bubbles from the cathode is caused by the force obtained by subtracting gravity from buoyancy. . On the other hand, in FIG. 4B, the hydrogen bubbles act on gravity (not shown) and buoyancy, and also on the magnetic field gradient (gradient due to the magnetic field changing from strong to weak as it moves away from the magnet). Based on magnetic buoyancy.

The magnetic buoyancy is the area of the magnetic pressure that the magnetic nanoparticles give to the hydrogen bubbles, and acts in the direction from the region where the magnetic pressure is large to the region where it is small. Since the magnetic pressure is higher in the high magnetic field gradient region than in the low magnetic field region, the magnetic buoyancy acts in the direction from the high magnetic pressure region to the small region, for example, away from the cathode. . As a result, the resultant force of gravity, buoyancy and magnetic buoyancy acts above the electrode, which is an efficient direction for hydrogen bubbles to desorb from the electrode, and the hydrogen bubble moves above the electrode, i.e. away from the electrode. It will be.

FIG. 5A shows that when the magnetic field gradient by the magnet acts on the bubble (8) in the electrolyte solution (7), the bubble (8) moves away from the magnet based on the magnetic field gradient. ing. FIG. 5B also shows the effect of the magnetic field gradient on the bubbles generated at the electrode even when the electrode is arranged in the electrolytic solution (7).

FIG. 6 (A) shows that bubbles (8) generated in the electrolyte solution under microgravity environment (1 / 6G) are adsorbed on the electrode surface when the electrode is a porous electrode (9). When the bubbles (8) are retained inside the porous electrode (9), the electrochemical reaction is lowered and the electrolysis is slowed down. On the other hand, FIG. 6B shows that, even in a microgravity environment (1 / 6G), when a magnetic field by a magnet acts on the porous electrode (9), the bubbles (8) are formed into the porous electrode due to the magnetic exclusion effect. (9) It shows that electrolysis is promoted without leaving the inside and reducing the electrochemical reaction.

The pair of electrodes provided in the water electrolysis device is preferably a porous electrode from the viewpoint of dramatically expanding the electrolysis surface. And when an electrode is a porous electrode, it is preferable that the magnitude | size (diameter) of a porous average void | hole exceeds 10 nm. This is because it is necessary for the magnetic nanoparticles to move to the inside of the porous electrode in order to move the bubbles generated inside the porous body from the inside of the porous electrode to the outside by magnetic buoyancy. Here, since the general size (diameter) of the magnetic nanoparticles is 10 nm, the porous electrode preferably has an average pore exceeding 10 nm.

The electrical conditions of the water electrolysis method can be appropriately determined based on the standard electrode potential E ° (1.229 V) of water.

(Preparation of electrolytic solution for water electrolysis, Examples 1 to 6 and Comparative Example 1)
Electrolysis for water electrolysis using ferri1003s (Ichinen Chemicals) as a water-based magnetic nanofluid containing magnetic nanoparticles (Fe ₃ O ₄ ) and sodium sulfate (Na ₂ SO ₄ , Wako Pure Chemicals) as a neutral salt as an electrolyte A liquid was prepared. As shown in Table 1, Examples 1 to 6 and Comparative Example 1 were prepared by mixing 1.0 mol / L Na ₂ SO ₄ aqueous solution prepared separately and ferri 1003s.

Examples 1 to 6 and Reference Example 1 were each dispensed in 10 mL screw test tubes and allowed to stand at room temperature for 3 months. As shown in FIG. The appearance was stable and stable.

(Electrolysis of electrolytic solution, Examples 7 to 10, Examples 11 to 14)
Using the experimental apparatus shown in FIG. 8, the electrolytic solution was electrolyzed using 10 mL of Example 3 as the electrolytic solution. The experimental apparatus is a three-electrode electrolytic cell (hereinafter referred to as “electrolytic cell”, manufactured by BAS), a potentiostat (HAL3001 manufactured by Hokuto Denko Co., Ltd.), a multi-function generator (WF circuit 1973 manufactured by NF Circuit Design Block Co., Ltd.). ), An oscilloscope (Yokogawa Meter & Instruments DLM 2024).
The potential output from the potentiostat was controlled with a function generator, and electrolysis was performed while the potential of the working electrode with respect to the reference electrode was maintained at a set value with the potentiostat. The current value and potential measured with a potentiostat were recorded through an oscilloscope.
8 is a potentiostat (corresponding to a power source), Example 3 (corresponding to an electrolytic solution for water electrolysis), the electrolytic cell (corresponding to a container and a pair of electrodes) and a neodymium magnet shown in FIG. (Corresponding to magnetic field applying means). That is, the experimental apparatus shown in FIG. 8 is an embodiment of the water electrolysis apparatus of the present invention.

FIG. 9 shows a detailed view of a combination of an electrolytic cell and a neodymium magnet. The electrolytic cell includes a working electrode (cathode electrode), a counter electrode (counter electrode, anode), a reference electrode (reference electrode), and a container 11 for storing an electrolytic solution therein. Regarding the material, the working electrode and the counter electrode were platinum, and the reference electrode was silver-silver chloride. The fact that the working electrode is a cathode and the counter electrode is an anode is that a step potential is set to −2.0 V at a set potential described later, and hydrogen bubbles are generated from the working electrode. On the other hand, oxygen bubbles were generated from the cathode.

From the arrangement relationship between the neodymium magnet and the working electrode or the counter electrode, the neodymium magnet was biased toward the working electrode or arranged with respect to the working electrode. The electrode area of the working electrode, ie, the cathode (electrode surface 13) was 7.1 mm ² (= 1.5 × 1.5 × π), whereas the electrode area of the counter electrode, ie, the anode, was 95 mm ² (= The area of the circle + the area of the cylindrical portion = 0.5 × 0.5 × π + 30 × π), and the neodymium magnets are not arranged biased, or the anodes that are not arranged are sufficiently larger than the cathodes It had an electrode area. The electrode area is determined from the portion where the electrode is immersed in the electrolytic solution was the electrode area of the electrode area / cathode anode ⁼ 95mm ^{2 /7.1mm} 2 ⁼ 13.4.

In order to investigate the influence of the strength of the magnetic field on the amount of electrolysis, the amount of electrolysis was measured by a chronoamperometry (hereinafter sometimes referred to as CA) method.
As shown in FIG. 10, the magnetic field intensity was changed by adjusting the distance between the electrolytic cell and the neodymium magnet. The magnet used was a Magfine cylindrical neodymium magnet with a diameter of 25 mm and a height of 10 mm (magnetic flux density B = 373.3 mT). The surface of the neodymium magnet was directed perpendicular to the electrode surface of the working electrode, and the distance Lmm from the center of the electrode surface was changed with a spacer. (7 mm (Example 7), 9 mm (Example 8), llmm (Example 9), 13 mm (Example 10)) from the center of the electrode surface. As for the set potential when performing CA, the initial potential was 0.43 V which is a natural potential, and the step potential was −2.0 V (Examples 11 to 14). That is, Examples 11 to 14 related to the water electrolysis method corresponded to Examples 7 to 10 related to the water electrolysis apparatus.

Regarding the electrolytic cell, the CA method was intended to measure the amount of electrolysis, and an experiment was conducted with the entire electrolytic cell tilted by about 30 ° from the horizontal plane in order to prevent hydrogen bubbles from accumulating on the surface of the working electrode. That is, the working electrode was inclined at about 60 ° with respect to the vertical direction. This inclination is a preferable mode for the electrode surface (working electrode) 13 being perpendicular to the vertical direction, and is not necessarily required if the electrode surface does not have such a condition.

FIG. 11 shows the current value-time response obtained from the experiment, and FIG. 12 shows the total charge amount-time response obtained by integrating the current value over time and calculating the time course of the total charge amount. From FIG. 11, the time response of the current value was large under the condition closest to the neodymium magnet, that is, under the condition of high magnetic field strength. The result was similarly seen in FIG. 12, and the results of increasing the amount of electrolysis were obtained in order from the condition with the highest magnetic field strength. Even under low magnetic field and low magnetic field gradient conditions using permanent magnets, the effect of magnetic buoyancy was clearly generated, indicating that the electrolysis process was promoted continuously and easily. Theoretically, the magnetic field gradient is important for the generation of magnetic buoyancy, and if the shape and application method of the neodymium magnet can be optimized, the effect of magnetic buoyancy is expected to increase.
On the other hand, when the electrolytic solution of Comparative Example 1 was used, water electrolysis occurred and no current that generated hydrogen bubbles flowed.

(Electrolysis of electrolyte, Examples 15 and 16, Comparative Example 2)
Experimental apparatus (Example 15) using the electrode cell of FIG. 13 instead of the electrolytic cell shown in FIG. 9, 450 mL of Example 3 as the electrolytic solution, the initial potential is 0.43 V of the natural potential, step Electrolysis was performed by the CA method at a potential of −2.0 V (Example 16). In FIG. 13, a carbon sponge-like electrode 9 is used as a pair of electrodes (working electrode (WE) and counter electrode (CE)), and a neodymium magnet is used as a magnetic field applying means inside each carbon sponge-like electrode 9. Arranged. The reference electrode was silver silver chloride. Further, the carbon sponge-like electrode 9 is as shown in FIG. 15 and is formed of a three-dimensional mesh-like carbon fiber, which is an example of a porous electrode. 14 also shows the carbon sponge-like electrode 9 and the experimental apparatus using it.
On the other hand, in the experimental apparatus of Example 15, electrolysis was performed by the CA method in the same manner as in Example 16 except for the neodymium magnet and using water instead of Example 3 as the electrolytic solution (Comparative Example 2).

As shown in FIG. 15, when bubbles are constrained inside the porous electrode, (C) in the convection toward the spongy electrode, the convection is blocked by the porous, and the accumulated bubbles from the inside of the porous It is difficult to disengage. On the other hand, (D) the magnetic field gradient acting on the sponge-like electrode is not obstructed by the sponge-like electrode, so that the retained bubbles are separated from the inside of the sponge-like shape by magnetic buoyancy due to the magnetic field gradient Can do it.

FIG. 16 shows the current value iA measured in Example 16 (with a magnetic field at ferrl003s) and Comparative Example 2 (without a magnetic field in water) minus 0 to 40 s obtained by subtracting Comparative Example 2 from Example 16. It was shown by the energizing time. Since the amount of hydrogen generated from the cathode is proportional to the current value, it was found that the amount of hydrogen generated in Example 16 was larger.

Even in a microgravity field, hydrogen can be produced efficiently by the action of magnetic buoyancy.

1: Water electrolysis device 2: Power supply 3, 7, 10: Electrolyte for water electrolysis (electrolyte)
4: Pair of electrodes 5: Magnetic field applying means 6, 11: Container 8: Bubble 9: Spongy electrode 13: Electrode surface (working electrode)

Claims (8)

An electrolytic solution for water electrolysis comprising a water-based magnetic nanofluid containing an electrolyte and magnetic nanoparticles. The electrolyte for water electrolysis according to claim 1, wherein the electrolyte is a neutral salt. A power source, an electrolytic solution for water electrolysis containing a water-based magnetic nanofluid containing electrolyte and magnetic nanoparticles, a pair of electrodes constituting an anode and a cathode, and at least one of the electrodes of the pair of electrodes A water electrolysis apparatus comprising: a magnetic field application unit that applies a uniform magnetic field; and a container that stores the water electrolysis electrolyte. The water electrolysis apparatus according to claim 3, wherein the magnetic field applying unit is a magnet or an electromagnetic coil. The water electrolysis apparatus according to claim 3 or 4, wherein the pair of electrodes are porous electrodes. The water electrolysis apparatus according to claim 5, wherein the porous electrode is a sponge-like electrode. Electrolyte for water electrolysis containing water-based magnetic nanofluid containing electrolyte and magnetic nanoparticles, power supply, pair of electrodes constituting anode and cathode, and non-uniformity on at least one of said pair of electrodes A water electrolysis method characterized in that at least hydrogen is obtained by energizing a water electrolysis apparatus comprising a magnetic field application means for applying a magnetic field and a container for storing the water electrolysis electrolyte. The water electrolysis method according to claim 7, wherein the pair of electrodes are inclined at 15 ° to 45 ° with respect to the vertical direction.