JP6438739B2 - Electrolysis method - Google Patents

Description

  The present invention relates to an electrolysis method. Specifically, it is an electrolysis method that can prevent the occurrence of a reverse current by interrupting a conductive path when energization to an electrolysis cell in an electrolysis system is stopped.

Hydrogen, for example, is very important as a raw material for chemical fertilizer, in addition to being used as a fuel in fuel cell vehicles, a turbine fuel in hydrogen power generation, a fuel such as city gas components, and the like.
Hydrogen can be produced, for example, by electrolysis of water. In particular, with the recent increase in environmental awareness, water electrolysis using renewable energy as a power source has attracted attention. An example of renewable energy is sunlight. Since a power generation system using sunlight has already been put into practical use and there are many commercial products, it is suitable as a power source for electrolysis.
However, a power generation system using renewable energy typified by sunlight has a large amount of power generation. For example, there is a significant difference in the amount of sunshine between clear and rainy days, and between daytime and nighttime, which greatly affects the amount of power generation.

When an electrolysis system that performs electrolysis of water is connected to, for example, a photovoltaic power generation system, sunlight is obtained, and when the electrolysis cell is energized, electrolysis of water is performed to obtain hydrogen as a product. be able to. However, for example, when sunlight is lost due to sunset and energization of the electrolysis cell is stopped, an electromotive force is generated in the electrolysis cell, and so-called “reverse current” is generated. When reverse current is generated in the electrolysis cell, for example, elution of the catalyst layer existing on the surface of the electrode (especially the negative electrode), cracking, peeling, degradation of electrode activity due to oxidation deterioration, etc., and associated increase in hydrogen overvoltage Will cause.
Therefore, when the energization to the electrolytic cell is stopped, it is preferable to block the conductive path as soon as possible to prevent the generation of reverse current.
In this regard, Patent Document 1 proposes a method of obtaining insulation by replacing the electrolyte in the supply passage for supplying electrolyte to the cathode chamber and the anode chamber in the electrolysis system with gas.

JP 2014-95128 A

Specifically, the method of Patent Document 1 is a method of obtaining insulation by performing the replacement by blowing a gas (for example, air) into a supply flow channel installed in a looped state. However, in an ordinary electrolysis system, a plurality of electrolysis cells are often stacked in series. Therefore, the supply channel is also branched and installed in the number of electrolytic cells.
In the electrolysis system having such a configuration, when gas is blown into the supply channel, it is extremely difficult to replace the electrolyte solution quickly and completely without leakage in all of the plurality of loop-shaped supply channels. The electrolytic solution in the supply flow channel far from the gas blowing position remains partly without being replaced. Therefore, in the electrolytic cell to which the flow channel is connected, the concern about the occurrence of reverse current is not wiped out. .

The present invention has been made in view of the above situation.
Therefore, an object of the present invention is to prevent the occurrence of reverse current as much as possible by interrupting the conductive path easily, quickly and reliably when the energization to the electrolysis cell in the electrolysis system is stopped. It is to provide an electrolysis method that can be used.

The above objects of the present invention are achieved by the present invention summarized as follows:
[1] Using an electrolysis system including at least a cathode chamber to which a cathode is attached, an anode chamber to which an anode is attached, and an electrolysis cell having a diaphragm partitioning the cathode chamber and the anode chamber,
An electrolysis method comprising flowing an electrolyte through the cathode and the anode when energizing the electrolysis cell.
[2] The electrolysis method according to [1], wherein a flow rate of the electrolytic solution is 0.001 to 100 L / (m ² · min) per unit time per surface area of the cathode or anode.

[3] The electrolysis method according to [1] or [2], wherein when the energization to the electrolysis cell is stopped, the flow of the electrolyte solution to the cathode chamber and the anode chamber is stopped to obtain electrical insulation. .
[4] An electrolytic cell comprising at least a cathode chamber to which a cathode is attached, an anode chamber to which an anode is attached, and a diaphragm partitioning the cathode chamber and the anode chamber;
A system comprising: the cathode and means for pouring electrolyte over the anode and used for electrolysis of water.
[5] The system according to [4], which is also used as a fuel cell.
[6] The system according to [4] or [5], wherein the diaphragm is a porous membrane subjected to hydrophilic treatment.

According to the present invention, when energization to the electrolysis cell in the electrolysis system is stopped, it is possible to easily, quickly and surely cut off the conductive path and prevent the occurrence of reverse current as much as possible. An electrical isolation method is provided.
Since the method of the present invention can prevent the occurrence of reverse current when the amount of sunshine changes and the energization of the electrolysis cell is stopped, for example, in an electrolysis system connected to a photovoltaic power generation system, It becomes possible to suppress deterioration of the cathode with time as much as possible.

FIG. 1 is a schematic view for explaining an electrolysis system of the present invention.

The electrolysis system used in the present invention is at least:
A cathode chamber with a cathode attached,
An electrolytic cell is provided that includes an anode chamber to which an anode is attached, and a diaphragm that partitions the cathode chamber and the anode chamber.
The above electrolysis system performs electrolysis in a state where the cathode chamber and the anode chamber are not filled with the electrolytic solution. When electrolysis is performed using the above-described electrolysis system, energization is ensured by flowing an electrolyte solution through the cathode and the anode. Here, “spraying” means creation of a state in which the cathode and the anode are always wetted by the flowing electrolyte. Therefore, it is preferable that the electrolysis system according to the present invention further includes means for pouring the electrolyte solution through the cathode and the anode in addition to the electrolysis cell.

In the present specification, “spreading” does not include the meaning of “disposable”. Therefore, the electrolytic solution poured in the method of the present invention may be recycled.
As the cathode, the anode, the diaphragm, and the electrolytic solution, known materials used in water electrolysis can be used without limitation. Specific examples are as follows, for example.

Examples of the cathode and the anode include soluble electrodes such as carbon electrodes, Al electrodes, Cu electrodes, Sn electrodes, and Pb electrodes;
Insoluble electrodes such as metal plated electrodes, Pt / Ti electrodes, metal fired electrodes, IrO ₂ / Ti electrodes;
A gas diffusion electrode etc. can be mentioned.
Application of voltage between the cathode and the anode can be performed using a power feeding member appropriately selected from known ones. As this electric power feeder, for example,
A power feeder made of a sintered metal fiber;
A power feeding body formed by forming a metal particle layer on the surface of the sintered body;
Power feeding body made of a porous material such as foam metal;
Power supply body made of metal woven fabric with fine metal wires;
A power feeder consisting of a punching mesh with holes in a metal plate;
Examples of the power supply include an expanded metal that is cut into a metal plate in a zigzag pattern and simultaneously spread and processed into a rhombus or turtle-shaped mesh.

As the diaphragm, an ion permeable membrane is preferably used, and for example, a cation exchange membrane having fluorine atoms can be exemplified. These films may be subjected to hydrophilic treatment.
The diaphragm is preferably always wet with the electrolyte during operation in order to facilitate the permeation of ions (especially potassium ions and sodium ions) and to ensure the conductivity thereof. Therefore, the diaphragm in the present embodiment is preferably a porous film that has been subjected to a water immersion treatment. The method of hydrophilization is not particularly limited, and examples thereof include a method of modifying the porous film with a hydrophilic inorganic material or the like. Examples of the hydrophilic inorganic material include TiO ₂ and ZrO ₂ . In order to bind these modifiers to the porous membrane, for example, a binder such as a conductive ion exchange resin can be used.
Examples of the electrolytic solution include an alkali halide aqueous solution and an alkali hydroxide aqueous solution.

  The electrolysis system in the present invention may have only one electrolysis cell as described above, or may have a cell stack structure in which two or more electrolysis cells are laminated. When the cell stack structure is adopted, each unit electrolysis cell may be installed through the diaphragm as described above, or a conductive path made of a conductive material is formed between each unit electrolysis cell. Also good.

When performing electrolysis using the electrolysis system according to the present invention, the cathode chamber and the anode chamber are not filled with the electrolyte solution, and the electrolyte is flowed through the cathode and the anode, thereby ensuring energization and the raw material for the electrolysis. Water (electrolyte solvent) is supplied. As an example of this pouring, for example, when the electrolyte supplied from the vicinity of the upper ends of the cathode and the anode comes into contact with the cathode and the anode and then flows downward by gravity, the entire surface of the cathode and the anode is wetted. It can be illustrated preferably. Examples of means for pouring the electrolyte include a method in which a nozzle is provided in the electrolysis cell and the liquid is dropped from the nozzle. For example, a spray nozzle can be mentioned.
As the spray nozzle, for example, one nozzle (supply port) showing an arbitrary spray pattern such as a dot shape, a full circle shape, an annular shape, an elliptical shape, a polygonal shape, a flat shape, a spiral shape, a film shape, or the like Mention may be made of spray nozzles having two or more nozzles (groups).

The means for pouring the electrolytic solution is preferably installed at a position where the entire surface of the cathode and the anode is wetted by the electrolytic solution supplied from the supply means. Specifically, the electrolyte solution supply port is installed near the upper ends of the cathode and the anode. The supply port for the electrolytic solution may be installed as a cathode supply port and an anode supply port as separate independent ports, or may be installed as a common cathode anode supply port.
If the amount of electrolyte flowed is small, the water necessary for electrolysis will be insufficient, and electrolysis will not proceed. In addition, since the electrolytic solution has an effect of cooling, if the amount of flowing of the electrolytic solution is small, the effect is reduced, and the electrode generates heat. As a result, not only the electrode itself but also the diaphragm in contact with the electrode may be damaged. The over flow quantity of the electrolytic solution, per surface area of the cathode and anode, as the flow rate per unit time, it is preferable to 0.001~100L / ^{(m 2} · min), 0.01~10L / ^{(m 2} Min), more preferably 0.02 to 1.0 L / (m ² · min).
Flowing of the electrolyte solution (including the case of reusing the electrolyte solution) can be performed by, for example, a liquid feed pump.

In the electrolysis method of the present invention, it is preferable to stop pouring the electrolyte into the cathode chamber and the anode chamber. As a result, electrical insulation between the cathode and the anode can be obtained, so that no reverse current flows even when the energization of the electrolysis cell is stopped. The pouring can be stopped by an arbitrary method, for example, by stopping the liquid feeding pump or closing the flow path.
In a preferred embodiment of the present invention, it is preferable to recover and reuse the electrolytic solution supplied from the vicinity of the upper ends of the cathode and the anode and flowing down due to gravity after contacting the cathode and the anode. Therefore, it is preferable that the electrolytic system used in the present invention has an electrolytic solution storage tank for collecting the electrolytic solution after use. The electrolytic solution recovered in the electrolytic solution storage tank can be reused for flowing over the cathode and the anode. Most preferably, the electrolyte storage tank is located below the cathode chamber and the anode chamber, and the electrolyte after being used for pouring is stored in the electrolyte storage tank under its own weight.

The electrolyte storage tank may comprise a single tank for commonly collecting the catholyte discharged from the cathode chamber and the anolyte discharged from the anode chamber; or discharged from the cathode chamber. A catholyte storage tank for recovering the prepared catholyte,
You may consist of the anolyte storage tank for collect | recovering the anolyte discharged | emitted from the anode chamber. Since the electrolyte storage tank is composed of such two tanks, mixing of the gas generated from the cathode and the gas generated from the anode can be avoided. Contributes to improving the purity of certain hydrogen (and oxygen or halogen). Since the gas generated from each electrode is vaporized while the electrolyte is stored in the storage tank and returns to each electrode chamber, even if the electrolyte storage tank has two tank configurations, When reusing the electrolyte, the reuse line may be common to both electrodes.

The electrolytic system in the present invention aims to obtain hydrogen (and oxygen or halogen) as a product. Therefore, it is preferable to have gas-liquid separation means for separating and recovering hydrogen or the like generated in the vicinity of the electrode from the electrolytic solution.
In a known electrolysis system, a cathode tank and an anode tank provided above the electrolysis cell serve as the gas-liquid separation means. However, since these tanks are filled to the middle with electrolyte, using these tanks as a gas-liquid separation means is intended to obtain insulation between the cathode and anode by stopping pouring. It is not preferable from the gist of the invention.

Therefore, in the present invention, it is preferable to provide a gas-liquid separation chamber that has gas-liquid separation ability but does not substantially have liquid storage ability, instead of these tanks. This gas-liquid separation chamber can be realized, for example, by providing a vertically elongated chamber above the cathode chamber and the anode chamber. The volume of the gas-liquid separation chamber is preferably 1,000 times or less, more preferably 1 to 100 times the volume of the cathode chamber and the anode chamber. The aspect ratio of the gas-liquid separation chamber is preferably about 10 to 1,000 as the ratio of the height (length) to the width of the chamber.
The gas-liquid separation chamber preferably includes a cathode gas-liquid separation chamber connected to the cathode chamber and an anode gas-liquid separation chamber connected to the anode chamber from the viewpoint of product purity.
When flowing the electrolyte solution through the cathode and the anode, the electrolyte solution preferably pumped out from the electrolyte storage tank by the liquid feed pump may be directly flowed from the flow path to the cathode and anode, or the gas-liquid separation chamber It may flow over the cathode and the anode via

As described above, the electrolysis system according to the present invention is suitably used for electrolyzing water to produce hydrogen (and oxygen or halogen). However, in the electrolysis system of the present invention, when the electrolyte is stored in the electrolyte storage tank and hydrogen is supplied to the cathode side and oxygen is supplied to the anode side, it can be used as a fuel cell.
By using the electrolysis system according to the present invention as a fuel cell, it is possible to generate electric power on-site using hydrogen generated from the electrolysis system according to the present invention. Such a usage mode enables energy self-sufficiency by using only the system of the present invention even in an isolated area where it is difficult to supply energy.

The fuel cell can generate electric power by causing an electrochemical reaction at a three-phase interface where the fuel gas, the electrolytic solution, and the catalyst are simultaneously in contact. If it takes time for the fuel gas to reach this three-phase interface, the power generation efficiency of the fuel cell will deteriorate. Therefore, when the system of the present invention is also used as a fuel cell, it is preferable to use a gas diffusion electrode capable of quickly feeding fuel gas to the three-phase interface as an electrode.
The gas diffusion electrode is an electrode made of a conductive material having a porous structure configured so that a large number of three-phase interfaces where the fuel gas, the electrolyte solution, and the catalyst are simultaneously in contact are formed. The material of the gas diffusion electrode applied to the system of the present invention is not particularly limited. For example, a porous structure made of carbon, iron, stainless steel, titanium, nickel, or the like can be used.
As the diaphragm in the case where the system of the present invention is also used as a fuel cell, the above-described water-immersed porous membrane can be preferably used.

Hereinafter, the configuration of the electrolysis system of the present invention will be specifically described with reference to the drawings.
FIG. 1 shows a schematic diagram of a system preferably used in the present invention.
1 includes a cathode chamber 1 having a cathode 11, an anode chamber 2 having an anode 21, and an electrolysis cell 10 having a diaphragm 3, a cathode gas-liquid separation chamber 12 connected to the cathode chamber 1, A catholyte storage tank 31, an anode gas-liquid separation chamber 22 and an anolyte storage tank 32 connected to the anode chamber 2, a cathode-side stop valve 41, an anode-side stop valve 42, and a circulation pump 50 are provided. Each of the cathode gas-liquid separation chamber 12 and the anode gas-liquid separation chamber 22 has an elongated shape, and is installed vertically above the cathode chamber 1 and the anode chamber 2. These gas-liquid separation chambers contribute to increasing the purity of the product because they have gas-liquid separation ability, but since they do not substantially have liquid storage ability, energization to the electrolysis cell is stopped, and the cathode In addition, it contributes to securing insulation when the flow of the electrolyte solution to the anode is stopped. The catholyte storage tank 31 and the anolyte storage tank 32 are disposed below the cathode chamber 1 and the anode chamber 2, respectively. An electrolyte supply line 60 for circulating and reusing the electrolyte is common to the catholyte storage tank 31 and the anolyte storage tank 32.

  When electrolysis is performed using the system of FIG. 1, the electrolyte pump (for example, potassium hydroxide aqueous solution, not shown) is pumped from the catholyte storage tank 31 and the anolyte storage tank 32 by the function of the circulation pump 50, It is supplied to the cathode 11 and the anode 21 through the electrolytic solution supply line 60 to carry out pouring. In this system, the electrolytic solution is supplied from the top to the cathode 11 via the cathode gas-liquid separation chamber 12 and to the anode electrode 20 via the anode gas-liquid separation chamber 22. The supplied electrolyte solution wets the entire surfaces of the cathode 11 and the anode 21 when descending by its own weight, and enables electrolysis of water by energizing the electrolytic cell 10. Thereafter, the electrolytic solution is reused by the function of the circulation pump 50.

  When energization of the electrolysis cell 10 is stopped, for example, by stopping the circulation pump 50, closing the stop valves 41 and 42, or both, the flow of the electrolyte solution to the cathode 11 and the anode 21 is stopped. As a result, insulation between the cathode 11 and the anode 21 can be easily obtained, so that no reverse current flows even when the energization is stopped. When energization to the electrolysis cell 10 is resumed, the electrolysis can be continued by opening the stop valves 41 and 42 and restarting the circulation pump 50.

  The system shown in FIG. 1 stores the electrolytic solution in the catholyte storage tank 31 and the anolyte storage tank 32, and supplies hydrogen to the cathode chamber 1 and oxygen to the anode chamber 2, respectively. Can be used.

DESCRIPTION OF SYMBOLS 1 Cathode chamber 2 Anode chamber 3 Diaphragm 11 Cathode 21 Anode 10 Electrolysis cell 12 Cathode gas-liquid separation chamber 22 Anode gas-liquid separation chamber 31 Catholyte storage tank 32 Anode solution storage tank 41 Cathode side stop valve 42 Anode side stop valve 50 Liquid sending Pump 60 Electrolyte supply line

Claims (7)

Using an electrolysis system comprising at least a cathode chamber to which a cathode is attached, an anode chamber to which an anode is attached, and an electrolysis cell comprising a diaphragm partitioning the cathode chamber and the anode chamber;
An electrolysis method comprising supplying an electrolyte to the cathode and the anode when the electrolysis cell is energized so that the cathode and the anode are always wetted by the flowing electrolyte. ^2. The electrolysis method according to claim 1, wherein the supply amount of the electrolytic solution to the cathode and the anode is 0.001 to 100 L / (m ² · min) per unit time per surface area of the cathode or anode. . The electrolysis method according to claim 1 or 2, wherein when the energization to the electrolysis cell is stopped, the supply of the electrolyte solution to the cathode chamber and the anode chamber is stopped to obtain electrical insulation. An electrolysis cell comprising at least a cathode chamber to which a cathode is attached, an anode chamber to which an anode is attached, and a diaphragm partitioning the cathode chamber and the anode chamber;
Means for supplying an electrolytic solution to the cathode and the anode, and creating a state in which the cathode and the anode are always wet by the flowing electrolytic solution , and used for electrolysis of water And the system.   The system according to claim 4, which is also used as a fuel cell. An electrolysis cell comprising at least a cathode chamber to which a cathode is attached, an anode chamber to which an anode is attached, and a diaphragm partitioning the cathode chamber and the anode chamber;
Means for supplying an electrolyte to the cathode and the anode, and creating a state in which the cathode and the anode are always wet by the flowing electrolyte , and used as a fuel cell. ,system.   The system according to any one of claims 4 to 6, wherein the diaphragm is a porous membrane subjected to a hydrophilic treatment.

Images