Water treatment device

Abstract

Provided is a water treatment device comprising: an electrolytic cell capable of storing water to be treated; a first electrode and a second electrode immersed in the water to be treated in the electrolytic cell; and a control unit for controlling energization of the first electrode and the second electrode. In this water treatment device, the first electrode and the second electrode include a catalyst layer on the electrode surface. The control unit is configured to be capable of switching to either an electrolysis mode in which the water to be treated is electrolyzed or a coating formation mode in which an oxide film is formed by the catalyst layer of the anode among the first electrode and the second electrode. When switching from the electrolysis mode to the coating formation mode, the control unit is configured to be capable of reversing the polarity between the first electrode and the second electrode.

Description

Water treatment equipment

[0001] The present disclosure relates to a water treatment device.

[0002] BACKGROUND ART Conventionally, devices such as alkaline ionized water purifiers, hypochlorous acid generators, and electrolytic water softeners are known as water treatment devices that electrolyze water using electrodes equipped with a catalyst layer to obtain products that can be used for various purposes.

[0003] JP 2000-42551 A JP 2007-260492 A WO 2003 / 000957 A JP 2005-74307 A JP 2012-81449 A

[0004] In conventional water treatment devices, the polarity of the electrodes is switched to prevent the deposition of insulating solid matter called scale on the electrode surfaces, thereby preventing electrolysis from being hindered (Patent Documents 1 to 5).The present inventors have newly discovered that in such water treatment devices, the switching of the electrode polarity and the subsequent application of electricity for electrolysis can wear out the catalyst layer disposed on the electrode surface, resulting in a decrease in the efficiency of water electrolysis.

[0005] The present disclosure has been made in view of the above-mentioned problems. That is, a main object of the present disclosure is to provide a water treatment device that can suitably suppress wear of a catalyst layer.

[0006] The inventors of the present invention attempted to solve the above problems by taking a new approach rather than simply extending the conventional technology, and as a result, they have invented a water treatment device that achieves the above-mentioned main object.

[0007] The water treatment device according to the present disclosure comprises an electrolytic cell capable of accommodating water to be treated, first and second electrodes immersed in the water to be treated within the electrolytic cell, and a control unit that controls the flow of electricity between the first and second electrodes, wherein the first and second electrodes have catalytic layers on their surfaces, and the control unit is configured to be switchable between either an electrolysis mode in which the water to be treated is electrolyzed, or a coating formation mode in which an oxide coating is formed on the catalytic layer of the anode of the first and second electrodes, and is configured to be able to reverse the polarity between the first and second electrodes when switching from the electrolysis mode to the coating formation mode.

[0008] According to the water treatment device according to an embodiment of the present disclosure, wear of the catalyst layer can be suitably suppressed.

[0009] FIG. 1 is a schematic diagram showing a water treatment device according to a first embodiment of the present disclosure. FIG. 2A is a schematic cross-sectional view of an electrode used in the water treatment device according to the first embodiment of the present disclosure. FIG. 2B is a schematic cross-sectional view of an electrode having an oxide film according to the first embodiment of the present disclosure. FIG. 3A is a current profile of a water treatment device according to an embodiment of the present disclosure. FIG. 3B is a current profile of a water treatment device according to an embodiment of the present disclosure. FIG. 3C is a typical current profile of a conventional water treatment device. FIG. 4 is a schematic diagram showing a water treatment device according to a second embodiment of the present disclosure. FIG. 5 is a bar graph showing the results of the film thickness retention rate of the catalyst layer obtained in a water treatment device according to an embodiment of the present disclosure and a conventional water treatment device. FIG. 6 is a bar graph showing the lifespan of the catalyst layer obtained in a water treatment device according to an embodiment of the present disclosure and a conventional water treatment device.

[0010] The following describes specific embodiments of the present disclosure. The applicant provides the following description and examples to enable those skilled in the art to fully understand the present disclosure, and it should be noted that these are not intended to limit the subject matter described in the claims. In other words, the present disclosure is not particularly limited to the preferred embodiments described below, and can be implemented with appropriate modifications within the scope of its purpose. For convenience, the present disclosure may be divided into embodiments and examples to facilitate explanation or understanding of the key points. However, partial substitution and / or combination of the configurations shown in different embodiments is possible. In describing such embodiments, redundant explanations of substantially identical features may be omitted, and only differences may be described. In particular, similar effects resulting from similar configurations may not be mentioned in each embodiment.

[0011] Furthermore, references to directions or orientations in the description of this specification are merely for the convenience of explanation and are not intended to limit the scope of the present disclosure unless otherwise explicitly stated. For example, relative terms such as "outside" (or "external"), "inside" (or "internal"), and their derivatives should be understood to refer to the directions as described or illustrated. Similarly, "on" an element includes not only contact with the top surface of the element but also non-contact with the top surface of the element. In other words, "on" an element includes not only a position above the element, i.e., a position above the element via another object or a position above the element with a gap, but also a position directly above the element. Furthermore, "on" does not necessarily mean above in the vertical direction. "On" merely indicates the relative positional relationship of an element. In other words, unless otherwise explicitly stated, the invention is not limited to a specific direction, orientation, shape, or the like.

[0012] The same applies to terms such as "provided," "disposed," "connected," and "attached," as well as their derivatives, and unless otherwise explicitly stated, may not be limited to a direct manner, but may also refer to a manner in which other elements, such as intervening elements, are present.

[0013] The various numerical ranges referred to herein are intended to include the lower and upper numerical limits themselves unless otherwise specified, and the term "about" means that there may be a variation or difference of a few percent, e.g., ±10%.

[0014] First Embodiment A water treatment device 1 according to a first embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the water treatment device 1 according to the first embodiment.

[0015] The water treatment device 1 mainly comprises an electrolytic cell 10 capable of containing the water to be treated 20, a plurality of electrodes 40A, 40B immersed in the water to be treated 20 contained in the electrolytic cell 10, and a control unit 60 that controls the flow of electricity to the plurality of electrodes 40A, 40B.

[0016] Hard water, such as city water (e.g., water containing hardness components) supplied from an external source, may be used as the water to be treated 20. Hard water is defined as water with a hardness of 120 mg / L or more. The water treatment device 1 of the present disclosure can be used, for example, as an electrolyzed water generator for producing acidic electrolyzed water and alkaline electrolyzed water by electrolyzing hard water.

[0017] (Electrolytic Cell 10) The electrolytic cell 10 may be configured as a container for accommodating the water to be treated 20 therein and for electrolyzing the water to be treated 20 using a plurality of electrodes 40A, 40B.

[0018] Although not shown, the electrolytic cell 10 may have an inlet for allowing untreated water 20 (also referred to as "raw water") to flow into the electrolytic cell 10, and an outlet for removing treated water (also referred to as "treated water" or "electrolyzed water") from the electrolytic cell 10. The water 20 to be treated may be supplied to the electrolytic cell 10 via the inlet, undergo electrolysis in the electrolytic cell 10, and then removed from the outlet as treated water. The treated water may be removed separately, for example, as acidic water obtained on the anode side and alkaline water obtained on the cathode side.

[0019] For example, the water to be treated 20 may be continuously supplied from an inlet into the electrolytic cell 10 and then flowed from the electrolytic cell 10 toward an outlet, thereby being continuously electrolyzed. The treated water may be continuously removed from the outlet. In such a configuration, the flow rate of the water to be treated 20 supplied from the inlet to the electrolytic cell 10 may be the same as the flow rate of the treated water removed from the electrolytic cell 10 via the outlet.

[0020] (Electrodes 40A, 40B) A plurality of electrodes including a first electrode 40A and a second electrode 40B are immersed in the water to be treated 20 contained in the electrolytic cell 10. The first electrode 40A and the second electrode 40B may be fixed inside the electrolytic cell 10 so that at least a portion of the electrodes can be immersed in the water to be treated 20 contained in the electrolytic cell 10.

[0021] The first electrode 40A and the second electrode 40B may be disposed opposite each other inside the electrolytic cell 10. When current is applied, one of the first electrode 40A and the second electrode 40B functions as an anode, and the other functions as a cathode.

[0022] The first electrode 40A and the second electrode 40B each include a substrate 42 made of carbon, nickel, titanium, or the like, and a catalyst layer 45 positioned on the surface of the substrate (see FIG. 2A ). The catalyst layer 45 may be provided so as to cover the surface of the substrate 42. The catalyst layer 45 of one electrode 40 may be provided so as to cover at least the surface of the substrate 42 that faces the other electrode, or may be provided so as to cover the entire surface of the substrate 42.

[0023] The catalyst layer 45 may be made of, for example, a material in the form of a metal, alloy, and / or metal oxide. While merely illustrative, specific examples of the catalyst layer 45 include at least one selected from the group consisting of precious metals such as platinum, iridium, palladium, gold, silver, ruthenium, and rhodium, as well as copper, iron, nickel, lead, tantalum, and carbon. Considering the electrolysis efficiency during electrolysis, the catalyst layer 45 preferably contains at least a precious metal, and more preferably contains at least platinum. That is, the first electrode 40A and the second electrode 40B may be platinum-based electrodes having a catalyst layer 45 containing at least platinum.

[0024] The first electrode 40A and the second electrode 40B may be made of the same material, or substrates and / or catalyst layers made of different materials may be used. Preferably, the first electrode 40A and the second electrode 40B may be made of the same material.

[0025] (Control unit 60) Control unit 60 controls the current flow state of first electrode 40A and second electrode 40B immersed in to-be-treated water 20. Water treatment device 1 may further include power supply 50 electrically connected to first electrode 40A and second electrode 40B to supply current to each of them, and control unit 60 may control the current flow state of first electrode 40A and second electrode 40B via power supply 50.

[0026] The water treatment device of the present disclosure is particularly characterized by the control of the power supply state by the control unit 60. The control of the power supply state in the water treatment device of the present disclosure will be described in detail below.

[0027] The water treatment device 1 according to the first embodiment of the present disclosure is characterized in that it is capable of implementing a current conduction mode for forming an oxide film during a treatment cycle, separate from a current conduction mode for electrolysis of the water 20 to be treated.

[0028] The control unit 60 is configured to be able to switch between an electrolysis mode in which the water to be treated 20 is electrolyzed and a coating mode in which an oxide coating is formed on the catalytic layer of the electrode. That is, the control unit 60 is configured to be able to implement two different current conduction modes: an electrolysis mode in which current is applied to generate electrolyzed water, and a coating mode in which current is applied to form an oxide coating on the catalytic layer. For example, the electrolysis mode can also be referred to as an "electrolyzed water generation mode" or a "water treatment mode." The coating mode can also be referred to as an "oxide coating formation mode," "catalytic layer oxidation mode," "anodic oxidation mode," or the like. Alternatively, the two different current conduction modes can simply be referred to as the coating formation mode as a "first current conduction mode" and the electrolysis mode as a "second current conduction mode."

[0029] Furthermore, when switching between the electrolysis mode and the coating mode, the control unit 60 can reverse the polarity between the first electrode 40A and the second electrode 40B. More specifically, the control unit 60 can switch between the coating mode, the electrolysis mode, and the polarity reversal in this order.

[0030] In the electrolysis mode, the control unit 60 applies a current to either the first electrode 40A or the second electrode 40B as a cathode and the other as an anode at a potential required for electrolysis of the water to be treated. This generates hydroxide ions at the cathode, producing alkaline electrolyzed water near the cathode. Meanwhile, hydrogen ions are generated at the anode, producing acidic electrolyzed water near the anode.

[0031] During electrolysis of the water to be treated 20, hydroxide ions are generated at either the first electrode 40A or the second electrode 40B, whichever electrode functions as the cathode. When these hydroxide ions react with metal ions and the like contained in the water to be treated 20, insulating solid compounds called scale are generated, which adhere to the electrode surface and form a passivation film. Such a passivation film increases the resistance of the electrode, which can cause a decrease in the electrolysis efficiency during electrolysis.

[0032] Scale adhering to the electrodes can be removed by reversing the polarity of the electrodes. Specifically, by reversing the polarity of the electrodes and passing current through them, a localized acidic atmosphere is created near the electrodes where the scale is adhering, causing the adhering scale to dissolve and peel off from the electrodes. The water treatment device 1 of the present disclosure performs electrolysis for a predetermined time, and then reverses the polarity of the first electrode 40A and the second electrode 40B, thereby enabling the removal of scale from the electrode surfaces. For example, the control unit 60 may perform electrolysis for a predetermined time with the first electrode 40A as the cathode and the second electrode 40B as the anode, and then switch the first electrode 40A to the anode and the second electrode 40B to the cathode.

[0033] After the polarity is switched, the current may be passed again. By passing current while reversing the polarity at predetermined time intervals, the water to be treated 20 can be continuously electrolyzed while removing scale.

[0034] In this current control, the inventors have newly discovered that the catalytic layer 45 of the electrode that functions as the anode after polarity reversal may be consumed during the polarity reversal and the electrolysis after polarity reversal. Specifically, components contained in the catalytic layer 45 (e.g., metal components such as platinum) are eluted during electrolysis of the water to be treated 20 and during polarity reversal, thereby reducing the amount of catalytic layer 45 covering the electrode substrate surface, which may result in a decrease in the electrolysis efficiency of the water treatment device 1. Thus, in this specification, "consumption of the catalytic layer" broadly includes a decrease in the reactivity of the catalytic layer 45 due to alteration of the catalytic layer 45 and at least refers to a physical reduction in the amount of catalytic layer 45 contributing to electrolysis. Performing electrolysis immediately after polarity reversal may shorten the life of the electrode due to consumption of the catalytic layer 45.

[0035] On the other hand, in the water treatment device 1 of the present disclosure, a film formation mode is performed after polarity reversal and before electrolysis. Fig. 2A is a partial cross-sectional view schematically showing the anode before film formation mode is performed. Fig. 2B is a partial cross-sectional view schematically showing the anode after film formation mode is performed. In the film formation mode, an oxide film 46 of a metal component contained in the catalyst layer 45 is formed on the catalyst layer 45 of the electrode 40, which functions as the anode in the subsequent electrolysis. For example, if a platinum-based electrode is used as the electrode 40, a platinum oxide film 46 may be formed on the catalyst layer 45 in the film formation mode.

[0036] The oxide film 46 formed on the catalytic layer 45 can effectively suppress elution of the catalytic layer 45 in the subsequent electrolysis mode. Furthermore, the oxide film 46 can also suppress wear of the catalytic layer 45 during polarity reversal performed after the electrolysis mode. That is, the oxide film 46 can function as a protective film that effectively suppresses elution and wear of the catalytic layer 45 during electrolysis and polarity reversal. Alternatively, the oxide film 46 can be interpreted as a protective film that suppresses elution and deterioration of the catalytic layer 45 when a high potential is applied. According to the present disclosure, by including a film formation mode in which such an oxide film 46 is formed, a water treatment device that can effectively suppress wear of the catalytic layer 45 is provided.

[0037] The electrolysis mode, in which the water to be treated 20 is electrolyzed, and the film formation mode, in which an oxide film is formed, are energized at different electrode potentials. The potential difference between the first electrode 40A and the second electrode 40B required for electrolysis of the water to be treated is relatively large, and the electrode potential of the anode in the film formation mode can be lower than the electrode potential of the anode in the subsequent electrolysis mode. Therefore, according to the water treatment device 1 of the present disclosure, by performing the film formation mode after polarity reversal, energization is performed at a lower electrode potential before the electrolysis mode is performed, allowing the formation of an oxide film 46 on the anode catalytic layer 45. This means that a sudden change in electrode potential can be avoided by performing gradual energization, transitioning from the film formation mode to the electrolysis mode via the film formation mode, at an electrode that has become an anode due to polarity reversal. This can suppress wear of the catalytic layer due to polarity reversal.

[0038] The water treatment device disclosed herein can repeatedly perform a treatment cycle including a film formation mode, an electrolysis mode, and polarity reversal. More specifically, after electrolysis in the electrolysis mode, the first electrode is switched from a cathode to an anode by polarity reversal, and the film formation mode is performed, where an oxide film is formed on the surface of the catalytic layer. The electrolysis mode is then performed using the first electrode with the oxide film as the anode, and the water to be treated is electrolyzed. After a predetermined period of electrolysis, the polarity is reversed again, whereby the first electrode with the oxide film is switched from an anode to a cathode. Meanwhile, the second electrode, which had been functioning as a cathode, is switched to an anode. The device then transitions to the film formation mode, where an oxide film is formed on the catalytic layer of the second electrode. The device then switches to the electrolysis mode, whereby electrolysis is performed using the second electrode with the oxide film as the anode.

[0039] In this manner, the control unit may continuously electrolyze the water to be treated by repeating a treatment cycle including a film formation mode, an electrolysis mode, and polarity reversal. The oxide film formed on the catalytic layer can be reduced and removed by reversing the polarity again after the subsequent electrolysis mode is performed and energizing the catalytic layer as a cathode. In the present disclosure, in continuous electrolysis involving polarity reversal, an oxide film is formed on the anode before the electrolysis mode is performed by including a film formation mode in the treatment cycle. As a result, even if an oxide film formed once is reduced and removed when energized as a cathode, an oxide film is formed again before electrolysis when energized as an anode in the next cycle. In other words, in the electrolysis mode, electrolysis can be performed using an electrode with an oxide film as the anode at all times. This extends the life of the electrodes used in electrolysis, thereby realizing a water treatment device that enables continuous treatment operation for longer periods of time.

[0040] As described above, the water treatment device of the present disclosure can implement a coating mode for forming an oxide film, separate from the electrolysis mode for electrolyzing the water to be treated. This reduces the wear on the catalyst layer and results in a longer electrode life. Typically, implementing a current application mode other than the electrolysis mode during electrolysis increases the overall treatment cycle time and potentially reduces the electrolysis efficiency per cycle, so this is avoided. However, the water treatment device of the present disclosure intentionally implements the coating mode to reduce the wear on the catalyst layer and prevent a decrease in electrolysis efficiency over long-term treatment. In other words, the water treatment device of the present disclosure can maintain favorable electrolysis efficiency over a larger number of treatment cycles. Therefore, the water treatment device of the present disclosure can be particularly useful for continuous treatment of water to be treated.

[0041] The oxide film 46 is preferably formed on the outer surface of the catalyst layer 45 so as to cover the catalyst layer 45 (see FIG. 2B ). That is, the oxide film 46 may be positioned as the outermost layer of the electrode 40. The oxide film 46 may be formed, for example, so as to cover at least 50% of the outer surface area of ​​the catalyst layer 45. Preferably, the catalyst layer 45 may be entirely covered by the oxide film 46 formed on the outermost layer of the electrode 40. This means that the oxide film 46 is formed over the entire outer surface of the catalyst layer 45. By covering the catalyst layer 45 extensively in this manner, wear and elution of the catalyst layer 45 during polarity reversal and the subsequent electrolysis mode can be suitably suppressed.

[0042] In addition, in the water treatment device according to one aspect of the present disclosure, the control unit is configured to be able to perform the film formation mode not only during the treatment cycle but also before the start of the electrolysis treatment.

[0043] In this aspect, the coating mode may be performed before the start of electrolysis. For example, in the first cycle of the treatment cycle, the coating mode may be performed before the electrolysis mode is performed. In other words, after the water treatment device is started, current may be applied to form an oxide coating on the catalytic layer of the electrode functioning as the anode before electrolysis is performed in the first cycle of treatment. This makes it possible to suitably suppress wear of the catalytic layer of the electrode functioning as the anode during current application in the electrolysis mode in the first cycle.

[0044] The control unit may perform the film formation mode by controlling the electrode potential of the electrode used as the anode in the subsequent electrolysis mode to a predetermined value. That is, in the film formation mode, the control unit applies a predetermined electrode potential to the anode, thereby forming an oxide film on the catalytic layer of the anode. Typically, in the electrolysis mode, the control unit performs electrolysis of the water to be treated by applying a voltage between the first electrode and the second electrode that is equal to or greater than the voltage required for electrolysis of the water to be treated. On the other hand, in the film formation mode, the control unit may form an oxide film on the catalytic layer by controlling the electrode potential of the anode to be near the oxidation potential of the components contained in the catalytic layer. For example, if the catalytic layer is a platinum-based electrode mainly containing platinum, a platinum oxide film may be formed on the catalytic layer by controlling the electrode potential of the anode to be near the oxidation potential of platinum.

[0045] The electrode potential of the anode in the coating formation mode may be determined based on the oxidation potential of the metal that is the main component of the catalytic layer. That is, the control unit is configured to apply an electrode potential to the anode that is close to the oxidation potential of the metal component that is most abundant in the catalytic layer. This allows an oxide coating to be formed on the catalytic layer of the anode.

[0046] As used herein, the "oxidation potential" of a component refers to the potential at which the component is oxidized. The oxidation potential may be determined by electrochemical measurement such as cyclic voltammetry, or a literature value may be used.

[0047] In addition, in this specification, "near the oxidation potential" means a value of an electrode potential that is equal to or higher than the oxidation potential of the metal component contained in the catalyst layer and is close to the oxidation potential. Specifically, the oxidation potential based on the standard hydrogen electrode (SCE) at a predetermined temperature is E ｏｘ (mV vs. SCE), the electrode potential corresponding to "near the oxidation potential" is E ｏｘ (mV vs. SCE) or more, and E ｏｘ This corresponds to an electrode potential of +1000 (mV vs. SCE) or less. In other words, the electrode potential E applied to the anode ａ is the oxidation potential E of the metal component mainly contained in the catalyst layer ｏｘ Based on E ｏｘ ≦E ａ ≦(E ｏｘ If the efficiency of oxide film formation is important, the electrode potential E applied to the anode may be in the range of +1000 mV. ａ Is E ｏｘ ≦E ａ ≦(E ｏｘ +800 mV), and E ｏｘ ≦E ａ ≦(E ｏｘ It is more preferable that the value be in the range of +600 mV. Note that the above-mentioned numerical range may vary depending on the quality of the water to be treated, etc.

[0048] For example, the catalyst layer can be a platinum-based electrode containing platinum. Platinum oxides include PtOH, PtO, and PtO ２ Specifically, PtOH is generated at low potential, and at higher potentials, PtOH is oxidized to generate PtO, and when PtO is further oxidized, PtO ２ Thus, platinum has a plurality of oxidation potentials corresponding to different oxidation states. In the water treatment device of the present disclosure using a platinum-based electrode, the type of platinum oxide formed in the catalyst layer is not particularly limited. In other words, the oxide film may contain one type of metal oxide or multiple types of metal oxides. For example, the oxide film may contain PtOH, PtO, and PtO. ２Therefore, in a water treatment device using a platinum-based electrode, the electrode potential of the anode in the film formation mode may be at least one selected from the group consisting of PtOH, PtO, and PtO. ２ For example, the electrode potential of the anode in the film formation mode may be in the range of 800 mV to 1500 mV, or 800 mV to 1400 mV, relative to a standard hydrogen electrode at 25° C. When the electrode potential of the anode is in the above range, platinum contained in the catalytic layer is oxidized, and a platinum oxide film can be suitably formed.

[0049] As described above, in the coating mode, the anode is controlled so as to be energized at a desired electrode potential. For example, the electrode potential of the anode in the coating mode may be achieved by current value control. That is, the control unit may adjust the electrode potential of the anode to a desired value by controlling the current value applied to the first electrode and the second electrode. For example, the control unit may store in advance in a memory or the like a current value that will result in a desired electrode potential, and energize the anode at the stored current value in the coating mode to achieve the desired electrode potential.

[0050] Alternatively, the electrode potential of the anode in the coating mode may be achieved by voltage value control. That is, the control unit may adjust the electrode potential of the anode to a desired value by controlling the voltage values ​​applied to the first electrode and the second electrode. For example, the control unit may pre-store in a memory or the like a voltage value that will result in a desired electrode potential, and apply the stored voltage in the coating mode to achieve the desired electrode potential.

[0051] 3A and 3B show current profiles for the first electrode or the second electrode in a water treatment device according to the present disclosure. In the water treatment device according to the present disclosure, the cycle time C1 of the treatment cycle includes an electrolysis mode implementation time P1 and a coating mode implementation time Q1. For example, the control unit may switch between the electrolysis mode and the coating mode by stepwise changing the current between the electrolysis mode current value A1 and the coating mode current value B1 (see FIG. 3A ). That is, an oxide coating may be formed by maintaining the current at B1 for a predetermined time (Q1), and then, after the coating mode ends, current may be applied at the electrolysis mode current value A1.

[0052] Alternatively, the control unit may gradually change the current value. For example, as shown in FIG. 3B , in the coating mode, the control unit may control the current value so that it gradually increases from a certain current value B1′ to B1. In such a control mode, the amount of change in the current value per unit time (i.e., the sweep rate of the current value) may or may not be constant over the duration Q1 of the coating mode. For example, the current profile in the coating mode may include a sweep portion in which the current value gradually changes and a holding portion in which the current value is held at a predetermined value.

[0053] 3A and 3B show an embodiment in which a desired electrode potential in the coating mode is achieved by controlling the current value, but a similar profile may also be applied to an embodiment in which a voltage value is controlled. That is, when transitioning from the electrolysis mode to the coating mode via polarity reversal, the control unit may control the potential applied to the electrode so that it changes in a stepwise manner. Alternatively, the control unit may control the voltage value using a profile including a sweep-like potential change so that the potential applied to the electrode changes gradually.

[0054] The control unit controls the current flow to perform the film formation mode for a predetermined time before switching to the electrolysis mode, thereby forming an oxide film on the catalytic layer of the anode. Generally, the longer the current flow time at the electrode potential required for forming the oxide film, the more the oxide film formation reaction progresses. This can result in effects such as an improved coverage of the catalytic layer with the oxide film and / or an increased thickness of the oxide film. Therefore, the longer the processing time in the film formation mode, the more oxide film is formed, and the more effectively the catalytic layer is protected. When prioritizing the prevention of elution and wear of the catalytic layer, the processing time in the film formation mode may be 1% or more, 3% or more, or 5% or more of the current flow time in the electrolysis mode.

[0055] On the other hand, from the viewpoint of more efficiently electrolyzing the water to be treated, it is preferable that the operation time of the film formation mode is shorter. When emphasis is placed on efficient water treatment, the treatment time of the film formation mode may be 65% or less, 60% or less, or 50% or less of the current application time of the electrolysis mode.

[0056] Furthermore, the cycle time of a treatment cycle including the electrolysis mode, the coating mode, and the polarity switching between the electrolysis mode and the coating mode is not particularly limited, but can be, for example, 0.5 minutes or more and 60 minutes or less, 1 minute or more and 30 minutes or less, or 1.5 minutes or more and 15 minutes or less.

[0057] For example, the amount of oxide film formed in the film formation mode can be converted into the amount of electricity required to reduce the oxide film and evaluated as the oxide film capacity. Specifically, the oxide film capacity can be determined by measuring the current value when a potential of -0.1 V is applied for 180 seconds to an electrode on which an oxide film has been formed, and integrating the resulting current-time curve with respect to time. The oxide film capacity per unit area can be determined by dividing this oxide film capacity by the electrode area.

[0058] For example, the oxide film capacitance per unit area at the end of the film formation mode is 0.05 μC m －２ or more, or 0.15 μC m －２ It can be more than 0.3 μC m －２If the oxide film capacity per unit area is within the above range, it is possible to suitably suppress the consumption of the catalyst layer that accompanies the electrolysis mode and polarity reversal that follow the film formation mode. On the other hand, although there is no particular limitation on the upper limit, if emphasis is placed on the current flow efficiency in the film formation mode, it is preferable to set the upper limit to, for example, 5.0 μC m －２ Less than or equal to 1.5 μC m －２ It can be:

[0059] The electrode with the oxide film formed in the film formation mode undergoes electrolysis in the subsequent electrolysis mode, and then becomes a cathode by polarity reversal. Thereafter, by being energized as a cathode in the film formation mode and the electrolysis mode, at least a portion of the oxide film formed on the catalytic layer can be reduced. The electrode is then switched to an anode by polarity reversal again, and a new oxide film is formed by being subjected to the film formation mode. In this manner, in the water treatment device disclosed herein, the formation and reduction removal of an oxide film on the catalytic layer are repeated by repeating the treatment cycle. Because the treatment cycle includes the film formation mode, even if an oxide film formed once by polarity reversal is reduced and removed, the oxide film can be re-formed by performing the film formation mode after polarity reversal again. This allows the catalytic layer of the electrode, whose polarity is reversed with each treatment cycle, to be suitably protected by the oxide film formed with each treatment cycle. Therefore, the present disclosure provides a water treatment device capable of performing electrolytic treatment involving polarity reversal while suitably suppressing wear on the catalytic layer.

[0060] Second Embodiment Next, a water treatment device 1′ according to a second embodiment will be described (see FIG. 4). The water treatment device 1′ differs from the water treatment device 1 according to the first embodiment in that it further includes a pre-treatment device 70 upstream of the electrolytic cell 10.

[0061] 4 is a schematic diagram showing the configuration of a water treatment device 1' according to a second embodiment of the present disclosure. As shown in the figure, the water treatment device 1' includes a pretreatment unit 70 upstream of the electrolytic bath 10. In this configuration, the water to be treated 20A is supplied to the electrolytic bath 10 via the pretreatment unit 70. That is, the pretreatment unit 70 receives the water to be treated 20A before it is supplied to the electrolytic bath 10. The water to be treated discharged from the pretreatment unit 70 may then be supplied to the electrolytic bath 10.

[0062] The pretreatment unit 70 is configured to be able to remove at least a portion of the metal components contained in the water to be treated 20A. In other words, at least a portion of the metal components contained in the water to be treated 20A are removed in the pretreatment unit 70. The water to be treated is supplied to the electrolytic cell 10 in a state in which at least a portion of the metal components have been removed in the pretreatment unit 70.

[0063] The present inventors have newly discovered that the presence of metal components in the water being treated is one of the causes of the wear of the catalyst layer. Without being limited by a particular theory, this may be due to the generation of highly reactive radicals such as hydroxyl radicals from hydrogen peroxide produced during electrolysis, using the metal components present in the water as a catalyst.

[0064] In the water treatment device 1' according to the second embodiment of the present disclosure, the above-described pretreatment unit 70 is provided upstream of the electrolytic bath 10, thereby further effectively suppressing wear of the catalyst layer. Specifically, the pretreatment unit 70 reduces the amount of metal components contained in the water to be treated 20 supplied to the electrolytic bath 10, thereby reducing the amount of radicals generated during electrolysis. This effectively suppresses wear of the catalyst layer due to the presence of these radicals.

[0065] The metal components removed in the pretreatment unit 70 are preferably transition metals. In particular, transition metal components that can assume a reduced form in the water to be treated are more preferably removed in the pretreatment unit 70 because they can promote the generation of hydroxyl radicals through the Fenton reaction.

[0066] Metal components may be mixed in, for example, by elution from materials contained in pipes for transporting the water to be treated 20A. Considering that the water treatment device of the present disclosure can be used to treat city water, the metal components removed in the pretreatment unit 70 are preferably metal components used in materials such as pipes through which city water can pass.

[0067] Examples of preferred metal components removed by the pretreatment unit 70 include metals such as Fe (iron), Cu (copper), Cr (chromium), Mn (manganese), and Ni (nickel), or compounds thereof. In other words, the pretreatment unit 70 may be configured to be capable of removing metal components including at least one selected from the group consisting of Fe, Cu, Cr, Mn, and Ni.

[0068] The configuration of the pretreatment unit 70 is not particularly limited as long as it is capable of performing a process for removing at least a portion of the metal components contained in the water to be treated 20A. In other words, any means capable of removing at least a portion of the metal components may be used to remove the metal components in the pretreatment unit 70. For example, the pretreatment unit 70 may be capable of removing metal components by various means, such as coagulation sedimentation, coprecipitation, sulfide separation, ion flotation, ion exchange, or adsorption. The pretreatment unit 70 may also be equipped with a filter to capture solids, such as precipitated compounds and aggregates containing metal components. Examples of the filter that can be used include a coarse filtration membrane, a microfiltration membrane (MF membrane), and / or an ultrafiltration membrane (UF membrane).

[0069] The total concentration of transition metal components in the water to be treated 20 contained in the electrolytic cell 10 may be, for example, 0.5 mg / L or less, and more preferably 0.01 mg / L or less.

[0070] Furthermore, to further suppress wear of the catalyst layer due to the presence of metal components, measures may be taken to suppress the incorporation of metal components into the water to be treated supplied to the electrolytic cell 10. For example, components of the water treatment device 1′ that may come into contact with the water to be treated, such as piping for transporting the water to be treated, may be made of a resin material. If the piping is made of a metal such as iron, metal components may be mixed in or eluted during transport of the water to be treated. By making the components of the water treatment device 1′, such as the piping, out of resin, it is possible to prevent the incorporation of metal components into the water to be treated from these components. This suppresses the generation of radicals due to the presence of metal components during electrolysis of the water to be treated, thereby making it possible to effectively suppress wear of the catalyst layer.

[0071] Although the embodiments of the present disclosure have been described above, they are merely typical examples. Those skilled in the art will readily understand that the present disclosure is not limited thereto, and that various modifications are possible within the scope of the present disclosure.

[0072] For example, a diaphragm may be provided between the first electrode and the second electrode. For example, the interior of the electrolytic cell may be divided into a plurality of regions (chambers) by ion-permeable diaphragms disposed between the electrodes.

[0073] For example, a plurality of pre-treatment units may be disposed upstream of the electrolytic cell, and another component may be provided between the pre-treatment units and the electrolytic cell.

[0074] Furthermore, the above effects are merely exemplary, and the present disclosure is not limited to the above, and additional effects may also be achieved.

[0075] Note that one embodiment of the present disclosure as described above includes the following preferred aspects: <1> A water treatment device comprising: an electrolytic cell capable of accommodating water to be treated; first and second electrodes immersed in the water to be treated within the electrolytic cell; and a controller that controls the flow of current to the first and second electrodes, wherein the first and second electrodes have catalytic layers on their surfaces, and the controller is configured to be switchable between an electrolysis mode in which the water to be treated is electrolyzed and a coating mode in which an oxide coating is formed on the catalytic layer of the anode of the first and second electrodes, and is configured to be able to reverse polarity between the first and second electrodes when switching from the electrolysis mode to the coating mode. <2> The water treatment device according to <1>, wherein the coating mode, the electrolysis mode, and the polarity reversal are performed in this order. <3> The water treatment device according to <1> or <2>, wherein the electrolysis mode is performed after the film formation mode, and one of the first electrode and the second electrode, which has the catalytic layer on which the oxide film is formed in the film formation mode, functions as an anode in the electrolysis mode. <4> The water treatment device according to any one of <1> to <3>, wherein an electrode potential different from that in the electrolysis mode is applied in the film formation mode. <5> The water treatment device according to any one of <1> to <4>, wherein the control unit applies a predetermined electrode potential to the first electrode and the second electrode by controlling a current value. <6> The water treatment device according to any one of <1> to <4>, wherein the control unit applies a predetermined electrode potential to the first electrode and the second electrode by controlling a voltage value. <7> The water treatment device according to any one of <1> to <6>, wherein the catalytic layer contains at least one noble metal selected from the group consisting of platinum, iridium, palladium, gold, silver, ruthenium, and rhodium. <8> The water treatment device according to any one of <1> to <7>, wherein the catalytic layer is a noble metal catalytic layer containing at least platinum. <9> The water treatment device according to <8>, wherein in the film formation mode, the electrode potential of the anode of the first electrode and the second electrode is 800 mV or more and 1500 mV or less based on the standard hydrogen electrode potential.<10> The water treatment device according to any one of <1> to <9>, wherein the control unit repeats a treatment cycle in which the coating mode, the electrolysis mode, and the polarity reversal are carried out in this order. <11> The water treatment device according to any one of <1> to <10>, wherein the energization time of the coating mode is set to be 3% to 60% of the energization time of the electrolysis mode. <12> The water treatment device according to any one of <1> to <11>, further comprising a pretreatment unit through which the to-be-treated water passes before being supplied to the electrolytic cell, wherein the pretreatment unit removes at least a portion of metal components contained in the to-be-treated water. <13> The water treatment device according to <12>, wherein the metal components are transition metal components contained in a pipe through which the to-be-treated water passes. <14> The water treatment device according to <12> or <13>, wherein the metal components include at least one selected from the group consisting of Fe, Cu, Cr, Mn, and Ni. <15> The water treatment device according to any one of <1> to <14>, further comprising a pipe through which the water to be treated supplied to the electrolytic cell passes, and at least a portion of the pipe that comes into contact with the water to be treated is made of a resin material.

[0076] A demonstration test was conducted in accordance with the present disclosure.

[0077] (Demonstration Test 1) A demonstration test was carried out using the water treatment device 1 having the configuration shown in FIG.

[0078] The electrolytic cell used had a capacity of 26.4 mL. The first and second electrodes were made of titanium substrates measuring 110 mm x 60 mm x 0.5 mm, with a 0.2 μm-thick platinum catalyst layer sintered onto the entire surface of the substrate. The first and second electrodes were placed inside the electrolytic cell so that their major surfaces, which were the widest surfaces of the electrodes, faced each other. The distance between the opposing major surfaces of the first and second electrodes was 4 mm.

[0079] The treated water was Kadoma City water, and NaHCO ３ (Nacalai Tesque, Inc.), CaC ｌ２ ・2H ２ O (Wako Pure Chemical Industries, Ltd.), and MgSO ４ ・7H ２The hardness of the water to be treated after preparation was about 350 mg / L.

[0080] The electrolysis was carried out in a flow system. The control conditions for the electrolysis were as follows: Flow rate of the water to be treated: 500 to 2000 mL / min Temperature of the water to be treated in the electrolytic cell: approximately 10 to 20°C Current density in electrolysis mode: 2.4 A / dm ２ Current application time in electrolysis mode: 2 minutes. Electrode potential of the anode in film formation mode: 800 mV (vs. SHE (standard hydrogen electrode)). Current application time in film formation mode: 20 to 120 seconds.

[0081] The electrode potential of the anode in the film formation mode was adjusted by controlling the current value. Switching between the electrolysis mode and the film formation mode, including polarity reversal, was performed using the current profile shown in FIG. 3A.

[0082] The electrode potential of the anode in the film formation mode was measured with a digital multimeter (digital power meter, WT200, manufactured by Yokogawa Electric Corporation) using a platinum wire (manufactured by Nilaco Corporation) as the measurement electrode. An oxide film was formed on the catalytic layer of the anode by passing a current of a value that would result in a predetermined electrode potential when converted from the measured value to a standard hydrogen electrode at 25°C.

[0083] The film formation mode was performed with various current application times, and the capacitance of the oxide film formed on the catalyst layer after the first cycle of electrolysis in the film formation mode was evaluated. The oxide film capacitance was determined by measuring the current value when a potential of -0.1 V was applied for 180 seconds to the electrode on which the oxide film had been formed using a potentiostat (ALS760E, manufactured by BAS Co., Ltd.) and integrating the resulting current-time curve with respect to time. The oxide film capacitance per unit area was determined by dividing this oxide film capacitance by the electrode area.

[0084] The following table shows the measurement results of the oxide film capacitance per unit area of ​​the anode when the film formation mode was carried out with various current application times.

[0085]

[0086] As shown in Table 1, it was confirmed that the inclusion of the film formation mode resulted in the formation of an oxide film on the catalyst layer. In other words, it was found that the water treatment device of the present disclosure can effectively form an oxide film on the catalyst layer. It was also found that the longer the current flow time, the more oxide film was formed.

[0087] (Demonstration Test 2) The effect of suppressing wear of the catalyst layer in the water treatment device of the present disclosure was evaluated.

[0088] In Examples 6 to 11, electrolysis was carried out using a water treatment device having control conditions including a film formation mode at various electrode potentials and various current application times. In these demonstration tests, the same configuration as the water treatment device in Example 1 was used, except for the control conditions of the electrode potential and current application time shown in Table 2. Table 2 below shows the control conditions for the film formation mode in Examples 6 to 11.

[0089]

[0090] In Comparative Example 1, electrolysis was performed under control conditions that did not include a film formation mode in the treatment cycle using a water treatment device with the same configuration as that of Example 1. That is, the control conditions for Comparative Example 1 were the same as those for Example 1, except that the film formation mode was not included. The current in the Comparative Example was applied according to the current profile shown in FIG. 3C.

[0091] In the examples and comparative examples, the treatment cycle was repeated 10,000 times, and the film thickness of the catalyst layer after 10,000 cycles was measured. The film thickness of the catalyst layer was measured using a fluorescent X-ray analyzer (EDX7000, manufactured by Shimadzu Corporation). The percentage of the film thickness of the catalyst layer after 10,000 cycles relative to the film thickness of the catalyst layer before treatment was calculated as the "film thickness retention rate (%)," and the degree of consumption of the catalyst layer was evaluated. The electrode potential and current flow time in the film formation mode were evaluated for the film thickness retention rate in the examples and comparative examples. The evaluation results are shown in Figure 5.

[0092] As shown in Figure 5, all of Examples 1 to 6 showed higher film thickness retention rates than the water treatment device of Comparative Example 1. These results demonstrate that performing electrolysis in a treatment cycle that includes the film formation mode can effectively suppress wear on the catalyst layer. Therefore, the water treatment device of the present disclosure that performs a current application cycle that includes the film formation mode can effectively suppress wear on the catalyst layer.

[0093] (Demonstration Test 3) Furthermore, the life of the catalyst layer in the electrolysis treatment using the water treatment device according to the first embodiment and the water treatment device according to the second embodiment of the present disclosure was evaluated.

[0094] As Example 12, a water treatment device similar to that of Example 1 was used, except that the electrode potential in the film formation mode was 975 mV (vs. SHE) and the current application time was 60 seconds. Furthermore, as Example 13, a water treatment device similar to that of Example 12 was used, except that a cartridge filter (manufactured by AS ONE Corporation, 1-5741-01) was provided as a pretreatment unit upstream of the electrolytic cell, and the components of the piping for delivering the water to be treated and the electrolytic cell were changed to resin components, as shown in FIG. As Comparative Example 2, a water treatment device having the same configuration as that of the water treatment device of Example 1 was used, except that the control conditions did not include the film formation mode in the treatment cycle.

[0095] Treatment cycles were repeated for the water treatment devices of Examples 12 and 13 and Comparative Example 2. The number of treatment cycles at the point when the voltage in the electrolysis mode exceeded the upper limit (50 V) of the power supply setting and the control shifted from constant current control to constant voltage control was recorded as the life of the catalytic layer of the water treatment device. The results of evaluating the life of the catalytic layer in each of the water treatment devices of the Examples and Comparative Example are shown in Figure 6.

[0096] As shown in FIG. 6, the life of the catalyst layer in the water treatment device of Example 12, in which electrolysis including the film formation mode was performed, was significantly longer than that of the water treatment device of Comparative Example 2, which did not include the film formation mode.

[0097] Furthermore, the water treatment device of Example 13, which includes a coating mode and is further equipped with a pretreatment device capable of removing metal components, exhibited a longer catalyst layer life than the water treatment device of Example 12, which does not include a pretreatment device. From these results, it is presumed that the installation of the pretreatment device and the replacement of the water treatment device components, such as piping, with resin materials reduced the amount of metal components in the water to be treated supplied to the electrolytic cell, thereby further suppressing the wear of the catalyst layer. In other words, it is presumed that the reduced content of metal components suppressed the generation of active species such as radicals during electrolysis, further suppressing the wear of the catalyst layer.

[0098] From the above, it was found that the water treatment device of the present disclosure can suppress the wear of the catalytic layer of the anode during polarity reversal and subsequent energization by performing a treatment cycle including a film formation mode. Furthermore, it was found that the provision of a pretreatment unit capable of removing metal components can also suppress the wear of the catalytic layer due to the generation of active species during electrolysis, thereby enabling the electrode to have a longer life.

[0099] The water treatment device of the present disclosure can be used in various fields that require electrolytic treatment of water.

[0100] REFERENCE SIGNS LIST 1, 1' WATER TREATMENT APPARATUS 10 ELECTROLYZER 20 WATER TO BE TREATED 40 ELECTRODE 40A FIRST ELECTRODE 40B SECOND ELECTRODE 42 SUBSTRATE 45 CATALYST LAYER 46 OXIDE COATING FILM 50 POWER SUPPLY 60 CONTROL UNIT 70 PRE-TREATMENT UNIT

Claims

1. A water treatment device comprising: an electrolytic cell capable of containing water to be treated; first and second electrodes immersed in the water to be treated within the electrolytic cell; and a control unit that controls the flow of electricity between the first and second electrodes, wherein the first and second electrodes have catalytic layers on their surfaces; the control unit is configured to be switchable between either an electrolysis mode in which the water to be treated is electrolyzed, or a coating formation mode in which an oxide coating is formed on the catalytic layer of the anode of the first and second electrodes, and is configured to be able to reverse polarity between the first and second electrodes when switching from the electrolysis mode to the coating formation mode.

2. The water treatment device according to claim 1, wherein the film formation mode, the electrolysis mode, and the polarity reversal are carried out in this order.

3. The water treatment device according to claim 1, wherein the electrolysis mode is carried out after the film formation mode, and the electrode among the first electrode and the second electrode that has the catalytic layer on which the oxide film is formed in the film formation mode functions as an anode in the electrolysis mode.

4. The water treatment device according to claim 1, wherein an electrode potential applied in the film formation mode is different from that applied in the electrolysis mode.

5. The water treatment device according to claim 1, wherein the control unit applies a predetermined electrode potential to the first electrode and the second electrode by controlling a current value.

6. The water treatment device according to claim 1, wherein the control unit applies a predetermined electrode potential to the first electrode and the second electrode by controlling a voltage value.

7. The water treatment device of claim 1, wherein said catalyst layer comprises at least one precious metal selected from the group consisting of platinum, iridium, palladium, gold, silver, ruthenium and rhodium.

8. The water treatment device according to claim 1, wherein the catalyst layer is a precious metal catalyst layer containing at least platinum.

9. The water treatment device according to claim 8, wherein in the film formation mode, the electrode potential of the anode out of the first electrode and the second electrode is 800 mV or more and 1500 mV or less based on the standard hydrogen electrode potential.

10. The water treatment device according to claim 1, wherein the control unit repeats a treatment cycle in which the film formation mode, the electrolysis mode, and the polarity reversal are carried out in this order.

11. The water treatment device according to claim 1, wherein the energization time of the film formation mode is set to be 3% or more and 60% or less of the energization time of the electrolysis mode.

12. The water treatment device according to claim 1, further comprising a pretreatment device through which the water to be treated passes before being supplied to the electrolytic cell, the pretreatment device removing at least a portion of the metal components contained in the water to be treated.

13. The water treatment device according to claim 12, wherein the metal component is a transition metal component contained in a pipe through which the water to be treated passes.

14. The water treatment device of claim 12, wherein the metal component comprises at least one selected from the group consisting of Fe, Cu, Cr, Mn, and Ni.

15. The water treatment device according to claim 1, further comprising a pipe through which the water to be treated supplied to the electrolytic cell passes, and at least a portion of the pipe that comes into contact with the water to be treated is made of a resin material.