Cleaning method

Abstract

This invention provides a cleaning method and the like that can contribute to improving the lifespan of a PEM-type electrolytic device. [Solution] According to one aspect of the present invention, a method for cleaning a laminate used in a PEM type electrolytic device is provided, wherein the laminate is made up of an anode, an electrolyte membrane, and a cathode stacked in that order, and the cleaning method involves passing a cleaning solution through the object to be cleaned so that one or more of the layers of the anode, electrolyte membrane, and cathode are in contact, while applying ultrasonic vibrations to the object to be cleaned.

Description

Technical Field

[0001] The present invention relates to a cleaning method.

Background Art

[0002] Currently, renewable energy that can be used permanently, such as wind power generation, hydropower generation, and solar power generation, has attracted attention. A system (Power to Gas) that stores and utilizes the power of this renewable energy in the form of hydrogen or methane for a long time is said to be attracting attention. As a method of Power to Gas, there are a method of electrolyzing water with electricity to produce hydrogen, and a method of producing methane using hydrogen and CO2 produced by electrolysis of water. Thus, it can be said that the technology of electrolyzing water to convert it into hydrogen is the core technology in Power to Gas. Water electrolysis is roughly classified into three types. 1) Polymer Electrolyte Membrane (PEM) type water electrolysis, 2) alkaline water electrolysis, 3) Solid Oxide Electrolysis Cell (SOEC) water electrolysis.

[0003] PEM type water electrolysis is typically carried out using a Membrane Electrode Assembly (MEA). Usually, an MEA is composed of an anode and a cathode, which are electrode parts, and an electrolyte membrane sandwiched between them. When water is supplied to the anode side of the MEA and a potential difference occurs between the electrodes, water is decomposed on the anode side, generating oxygen and protons (H + ). The protons move to the cathode side through sulfonic acid groups etc. in the PEM and combine with electrons at the cathode to generate hydrogen. Technologies related to such a PEM type water electrolysis system are disclosed in, for example, Patent Document 1 etc.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] However, our inventors have found that there is room for improvement to extend the lifespan of the PEM-type water electrolysis system (PEM-type water electrolysis device) described above.

[0006] In view of the above circumstances, the present invention aims to provide a cleaning method and the like that can contribute to improving the lifespan of a PEM-type electrolytic device. [Means for solving the problem]

[0007] According to one aspect of the present invention, a method for cleaning a laminate used in a PEM-type electrolytic device is provided, wherein the laminate consists of an anode, an electrolyte membrane, and a cathode stacked in that order, and the cleaning method involves passing a cleaning solution through the object to be cleaned so that one or more of the anode, electrolyte membrane, and cathode layers are in contact, while applying ultrasonic vibrations to the object to be cleaned.

[0008] According to the above embodiment, a cleaning method and the like that can contribute to improving the lifespan of a PEM-type electrolytic device are provided.

[0009] Furthermore, they may be provided in the following embodiments.

[0010] (1) A method for cleaning a laminate used in a PEM type electrolytic device, wherein the laminate is made up of an anode, an electrolyte membrane, and a cathode stacked in that order, and the cleaning method involves passing a cleaning solution through the object to be cleaned so that one or more of the layers of the anode, the electrolyte membrane, and the cathode are in contact, while applying ultrasonic vibrations to the object to be cleaned.

[0011] (2) The cleaning method described in (1) above, wherein the cleaning solution is ultrapure water or pure water.

[0012] (3) The cleaning method described in (2) above, wherein the electrical resistivity of the cleaning solution is in the range of 0.1 to 18 MΩ·cm.

[0013] (4) A cleaning method according to any one of (1) to (3) above, wherein the passage of the cleaning solution is performed with the anode, the electrolyte membrane and the cathode stacked.

[0014] (5) A cleaning method according to any one of (1) to (4) above, wherein the frequency of the ultrasonic waves is in the range of 1 kHz to 100 MHz. Of course, this is not always the case. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram showing an example of a PEM-type electrolytic device in this embodiment. [Figure 2] This graph shows the voltage changes measured in each test example. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described below. The various features shown in the embodiments below can be combined with each other. Furthermore, unless otherwise specified, "~" in this specification represents the following from the above.

[0017] [Washing method] In other words, the cleaning method of this embodiment is as follows. A method for cleaning laminates used in a PEM-type electrolytic device, The aforementioned laminate consists of an anode, an electrolyte membrane, and a cathode, stacked in that order. The cleaning method involves applying ultrasonic vibrations to the object to be cleaned while passing a cleaning solution through it so that one or more layers among the anode, the electrolyte membrane, and the cathode are in contact. Hereinafter, the apparatus related to the cleaning method of the present embodiment, the steps included in the electrolysis method of the present embodiment, etc. will be described.

[0018] (PEM type electrolyzer) In the cleaning method of the present embodiment, one or more layers of the laminate used in the PEM type electrolyzer are cleaned. In this specification, first, the details of this PEM type electrolyzer will be described.

[0019] FIG. 1 is a schematic diagram showing an example of the PEM type electrolyzer in the present embodiment. The PEM type electrolyzer 1 shown in FIG. 1 has a laminate in which an anode 2, an electrolyte membrane 3, and a cathode 4 are laminated in this order. Such a laminate may also be referred to as a membrane electrode assembly (MEA: Mebrane Electrode Assembly). The cleaning method of the present embodiment cleans one or more layers of this laminate. Further, the PEM type electrolyzer 1 of the present embodiment has an anode side cavity 20 on the side where the anode 2 exists, and a cathode side cavity 40 on the side where the cathode 4 exists. These two cavities are isolated via the aforementioned MEA. Further, the anode side cavity 20 is provided with an anode side inlet 21 and an anode side outlet 22, and the cathode side cavity 40 is provided with a cathode side outlet 41. Although the details are not shown in FIG. 1, the anode 2 and the cathode 4 are electrically connected so that a potential difference occurs between the anode 2 and the cathode 4.

[0020] The PEM type electrolyzer 1 of the present embodiment generates oxygen molecules (oxygen gas) and hydrogen molecules (hydrogen gas) by electrolyzing the supplied water. When such electrolysis of water is performed, in the PEM type electrolyzer 1 of the present embodiment, the anode 2 functions as an anode and the cathode 4 functions as a cathode. As shown in the background art section, when water is supplied to the anode side (anode side cavity 20) of the PEM type electrolyzer 1 and a potential difference is generated between the electrodes, water is decomposed at the anode 2, and oxygen molecules (oxygen gas) and protons (H +) will occur. In the PEM electrolyzer 1 shown in FIG. 1, water is typically supplied from the anode-side inlet 21. Also, the oxygen molecules (oxygen gas) generated on the anode 2 side are typically recovered from the anode-side outlet 22. On the other hand, the protons generated on the anode 2 side move to the cathode 4 side through the electrolyte membrane 3 and combine with electrons at the cathode 4 to generate hydrogen molecules (hydrogen gas). In this way, the hydrogen molecules (hydrogen gas) generated at the cathode 4 are recovered from the cathode-side outlet 41.

[0021] Also, the anode 2, electrolyte membrane 3, and cathode 4 of the PEM electrolyzer 1 are appropriately selected and configured from among the materials that enable the electrolysis of water described above. Specifically, the anode 2 and cathode 4 can be selected from among the materials that function as electrodes. Here, as the electrode, a metal catalyst or the like that promotes the gasification reaction described above may be supported on the surface. Such metal catalysts can include various metal atoms such as nickel, copper, palladium, zinc, platinum, gold, silver, ruthenium, iridium, etc. Also, the electrolyte membrane 3 can be constituted by a membrane that permits the movement of protons from the anode 2 to the cathode 4. Such an electrolyte membrane 3 can typically be constituted by a resin material, and the resin material here may have an acid group in its structure. Examples of the acid group here include a sulfonic acid group, carboxylic acid group, phosphonic acid group, phosphoric acid group, etc. Note that the resin material constituting the electrolyte membrane 3 may be a so-called fluororesin. Also, since it is a material with high availability, the electrolyte membrane 3 may be constituted by a fluororesin having a perfluorosulfonic acid group. In particular, Nafion (registered trademark) (manufactured by DuPont), which is a copolymer of a polymerizable perfluorosulfonic acid unit and a tetrafluoroethylene unit, is a typical example of a material suitably used as the electrolyte membrane 3.

[0022] Note that when electrolyzing water with the PEM electrolyzer 1 of the present embodiment, the supplied water may be purified.

[0023] The purification process described here may encompass various purification treatments aimed at reducing the amount of impurities in the water. Typical examples of purification treatments include those using reverse osmosis (RO) membrane separators, degassers, ion exchange systems (such as mixed-bed or 4-bed 5-column systems), electrodeionizers, and oxidation systems such as ultraviolet (UV) irradiation oxidation systems. These treatments remove ions and organic components from the raw water (which may be tap water, etc.). More typical treatments include those combining treatment using an activated carbon (AC) system to treat the raw water with treatment using a reverse osmosis membrane (RO) system equipped with a reverse osmosis membrane to treat the outlet water of the activated carbon system.

[0024] In exemplary embodiments, it is preferable that a process be carried out in which water is brought into contact with a cation exchange resin. This contact with the cation exchange resin may be carried out by bringing water into contact with the cation exchange resin filled in a cartridge, or by passing water through an electrodeionizer (CDI). In a typical embodiment, by bringing water into contact with the cation exchange resin described above, predetermined cations (metal ions, etc.) contained in the water are exchanged for protons (that is, the cation exchange resin may be a resin having a proton-donating group (acid group, etc.).

[0025] (Details of the cleaning process) Next, the details of the process performed in the cleaning method of this embodiment will be described. Specifically, in the cleaning method of this embodiment, ultrasonic vibrations are applied to the object to be cleaned while the cleaning solution is passed through so that one or more layers of the anode 2, electrolyte membrane 3, and cathode 4 are in contact.

[0026] In other words, the cleaning process in this embodiment targets one or more of the layers among the anode 2, electrolyte membrane 3, and cathode 4. The PEM-type electrolytic device 1 can become contaminated with the layers constituting the laminate due to repeated water electrolysis. In this embodiment, by performing a cleaning process on any of these layers, dirt and other contaminants adhering to the layers can be removed.

[0027] Specifically, in the cleaning process of this embodiment, ultrasonic vibrations are applied while a predetermined cleaning solution is brought into contact with one or more of the layers to be cleaned: the anode 2, electrolyte membrane 3, and cathode 4. This cleaning solution may be passed through the anode 2, electrolyte membrane 3, and cathode 4 in a stacked state. Alternatively, the cleaning solution may be passed through the anode 2, electrolyte membrane 3, and cathode 4 after each layer has been separated, so that the cleaning solution comes into contact with any one or more of the layers.

[0028] Furthermore, "fluid flow" may refer to any means by which the cleaning solution is circulated so that dirt adhering to the object to be cleaned is washed away. Specifically, this may include both a method of passing the cleaning solution in the in-plane direction of the layer and a method of passing the cleaning solution in the thickness direction of the layer, with respect to a layer selected from the group consisting of an anode 2, an electrolyte membrane 3, and a cathode 4.

[0029] Furthermore, when passing the cleaning solution through, the anode 2, electrolyte membrane 3, and cathode 4 may be placed in any container. For example, assuming that the cleaning solution is passed through with the anode 2, electrolyte membrane 3, and cathode 4 stacked as described above, this passage of the cleaning solution may be carried out inside the PEM-type electrolytic device 1 shown in Figure 1. That is, a predetermined cleaning solution can be introduced from the anode-side inlet 21 of the PEM-type electrolytic device 1 (in addition, the cleaning solution can be discharged from the anode-side outlet 22 as appropriate), allowing the cleaning solution to come into contact with each of the anode 2, electrolyte membrane 3, and cathode 4. Of course, the container used when cleaning one or more of the anode 2, electrolyte membrane 3, and cathode 4 is not limited to this. For example, even if the anode 2, electrolyte membrane 3, and cathode 4 are stacked, the stack can be transferred to a dedicated cleaning container, and the cleaning solution can be passed through the cleaning container to perform the cleaning process. Furthermore, the cleaning process using such a cleaning container can be performed on any of the layers among the anode 2, electrolyte membrane 3, and cathode 4. That is, the anode 2, electrolyte membrane 3, and cathode 4 can be disassembled, placed in the cleaning container, and the cleaning solution passed through them to perform the cleaning process on each layer.

[0030] Furthermore, when cleaning the laminate within the PEM-type electrolytic device 1, the cleaning solution may be passed through and ultrasonic vibrations applied while the electrolytic treatment is being performed (creating a potential difference between the anode 2 and the cathode 4). In this case as well, since the cleaning is performed while each of the anode 2, electrolyte membrane 3, and cathode 4 functions, efficient cleaning can be performed on each layer.

[0031] Furthermore, in the cleaning method of this embodiment, any cleaning solution can be used. That is, water can be used as the cleaning solution, or an organic solvent that easily dissolves substances that contaminate the laminate can be used. In addition, to promote the dissolution of substances that contaminate the laminate, acids, bases, surfactants, etc. can be added to the water or organic solvent that constitutes the cleaning solution. Note that since the PEM type electrolytic device 1 is expected to undergo electrolytic treatment with water again after cleaning, when using a cleaning solution other than water, it is preferable to pass water through the laminate again before performing the electrolytic treatment. By doing so, components remaining inside the laminate can be efficiently replaced.

[0032] On the other hand, in the cleaning method of this embodiment, the cleaning solution is preferably ultrapure water or pure water. By using water of such high purity, the laminate can be cleaned efficiently, which can contribute to further improving the lifespan of the PEM type electrolytic device 1. Furthermore, it is preferable that the electrical resistivity of the cleaning solution (ultrapure water or pure water) is set within a predetermined range. In a typical embodiment, the electrical resistivity of the cleaning solution (ultrapure water or pure water) may be in the range of 0.1 to 18 MΩ·cm, 0.2 to 16 MΩ·cm, or 0.3 to 12 MΩ·cm. By setting the electrical resistivity of the cleaning solution within such a range, it is possible to use a cleaning solution with an appropriate cost while keeping the electrolytic components remaining in the laminate at a low level.

[0033] Furthermore, the cleaning method of this embodiment is characterized by applying ultrasonic vibrations while passing a cleaning solution through the object to be cleaned. This cleaning method of this embodiment may be performed by placing the object to be cleaned in a container (the PEM-type electrolytic device 1 or cleaning container described above) and applying ultrasonic waves generated by a predetermined device to the object to be cleaned. The frequency of the ultrasonic waves applied to the object to be cleaned may be set appropriately according to the type and size of the laminate, the type of cleaning solution, the type of dirt, etc. To give a typical example, the frequency of the ultrasonic waves used in the cleaning method of this embodiment is preferably in the range of 1kHz to 100MHz, more preferably in the range of 20kHz to 50MHz, and even more preferably in the range of 40kHz to 5MHz. In general ultrasonic cleaning for cleaning various items, ultrasonic waves with a frequency of 20 to 100kHz are often used, but the cleaning method of this embodiment may use ultrasonic waves with a frequency of 0.5 to 5MHz, which is so-called megasonic cleaning.

[0034] As described above, the cleaning method utilizes ultrasonic vibrations to efficiently clean the laminates used in PEM-type electrolytic devices. Furthermore, because the laminates can be cleaned in this way, it can be said that this method contributes to improving the lifespan of the PEM-type electrolytic device 1.

[0035] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention. [Examples]

[0036] The present invention will be described in more detail below with reference to examples (each test example). However, the present invention is not limited to the following examples.

[0037] <Test Example 1> In Test Example 1, a PEM-type electrolytic apparatus with the structure shown in Figure 1 was prepared, and the experiment was carried out as follows: A crystal dish containing the cell (PEM-type electrolytic apparatus 1) was placed inside an ultrasonic cleaner. While supplying ultrapure water to the cell, the cell was driven with current for 4 hours to stabilize the voltage and hydrogen content. The voltage at this time was maintained at approximately 1.8V. After that, the supply water was changed to artificial river water (Soft: containing Na, Mg, Ca, K), and the cell was driven with current until it reached 3.0V, the recommended voltage for MEA replacement.

[0038] Next, the supply water was changed to ultrapure water, and the cells were cleaned while being driven by current. Specifically, without disassembling the cells, tap water was placed in an ultrasonic cleaner and ultrasonic cleaning was performed. Here, the ultrasound reached the ultrapure water being supplied to the cells, and impurities attached to the membrane were cleaned. The cells were placed in a crystal dish so as not to be submerged in water, and were fixed in place to prevent them from shifting during ultrasonic cleaning. The evaluation of Test Example 1 was performed by measuring the voltage at regular intervals during the cleaning process. Specifically, a current of 9V was applied between the anode and cathode of the PEM type electrolytic device 1 every day, and the voltage value at that time was measured. The timing of driving the current was set to only occur when measuring the voltage, and cleaning continued without applying current at other times.

[0039] The model and conditions of the ultrasonic cleaner used in Test Example 1 are as follows. 1) Manufacturer: AS ONE Corporation 2) Model: Large dual-frequency ultrasonic cleaner (separated type) LSD-38D 3) Frequency: 40.0 kHz (Note: The ultrasonic cleaner used is capable of emitting ultrasonic waves at 28.0 kHz and 40.0 kHz.) 4) Washing output (Output Level): Max 5) Washing time: 72 hours

[0040] <Test Example 2> Artificial river water was supplied to the PEM-type electrolytic device 1 using the same procedure as in Test Example 1 until the current drive in the PEM-type electrolytic device 1 reached 3.0V. Thereafter, under the same conditions as in Test Example 1, except that the cells were not subjected to an ultrasonic cleaner, ultrapure water was continuously supplied to the PEM-type electrolytic device 1, and voltage measurements were taken at predetermined intervals.

[0041] Figure 2 shows the changes in the measured voltage in each test example. Figure 2 is a graph showing the changes in the voltage measured in each test example. As can be seen from the results in Figure 2, applying ultrasound to the cell efficiently reduces the voltage. In other words, by cleaning the PEM-type electrolytic device 1 while applying ultrasonic vibrations, it is possible to efficiently clean the components that make up the PEM-type electrolytic device 1.

[0042] Based on these test examples, it is supported that the cleaning method of the present invention can efficiently clean laminates used in PEM-type electrolytic devices by utilizing ultrasonic vibrations. Furthermore, because the laminates can be cleaned in this way, it can be said that this method can contribute to improving the lifespan of PEM-type electrolytic devices. [Explanation of Symbols]

[0043] 1:PEM type electrolyzer 2: Anode 3: Electrolyte membrane 4: Cathode 20: Anode side cavity 21: Anode side entrance 22: Anode side exit 40: Cathode side cavity 41: Cathode side outlet

Claims

1. A method for cleaning laminates used in a PEM type electrolytic device, The aforementioned laminate consists of an anode, an electrolyte membrane, and a cathode, stacked in that order. The cleaning method involves applying ultrasonic vibrations to the object to be cleaned while passing a cleaning solution through it so that one or more layers among the anode, the electrolyte membrane, and the cathode are in contact.

2. In the cleaning method described in claim 1, A cleaning method wherein the cleaning solution is ultrapure water or pure water.

3. In the cleaning method described in claim 2, A cleaning method wherein the electrical resistivity of the cleaning solution is in the range of 0.1 to 18 MΩ·cm.

4. In the cleaning method described in claim 1, A cleaning method in which the cleaning solution is passed through the anode, the electrolyte membrane, and the cathode in a stacked state.

5. In the cleaning method described in claim 1, A cleaning method wherein the frequency of the ultrasonic waves is in the range of 1 kHz to 100 MHz.

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