Seawater electrolysis device

Abstract

In a seawater electrolysis device for seawater electrolysis at sea, the pH decrease around the anode is eliminated, and the generation of chlorine is inhibited. The seawater electrolysis device (1) for seawater electrolysis at sea includes: a cathode (20); an anode (10) disposed opposite to the cathode (20); a diaphragm (21) disposed between the cathode (20) and the anode (10); a power source (30) for applying a voltage between the cathode (20) and the anode (10); and a control device (40) for controlling the voltage application from the power source (30) to the cathode (20) and the anode (10). The control device (40) stops applying the voltage after a first predetermined period has elapsed after the voltage application has started, and restarts applying the voltage after a second predetermined period has elapsed after the voltage application has stopped.

Description

Technical Field

[0001] This invention relates to a seawater electrolysis apparatus for electrolyzing seawater at sea. Background Technology

[0002] The demand for green hydrogen is increasing. To meet this demand, producing hydrogen through seawater electrolysis is the best method in terms of both cost and scale of production. However, when electrolyzing chlorine-containing solutions such as seawater, chlorine gas with environmental impact is also generated from the anode during electrolysis.

[0003] Patent document 1 describes that in an electrolysis device for producing slightly acidic electrolyzed water by electrolyzing a chlorine-containing composition, chlorine gas is sometimes released when the hydrogen ion concentration is below pH 4.

[0004] To avoid the generation of chlorine gas, various types of anodes have been developed. For example, Patent Document 2 describes the use of an anti-corrosion electrode with manganese dioxide deposited by electrodeposition, which keeps the chlorine generation rate extremely low.

[0005] Non-patent document 1 describes how the selectivity of oxygen generation reaction (OER) relative to chlorine generation reaction (CER) is improved by setting a manganese dioxide film with intercalated sodium ions on a fluorine-doped tin oxide (FTO) electrode.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: International Publication No. 2011 / 158279

[0009] Patent Document 2: Japanese Patent Application Publication No. 11-100686

[0010] Non-patent literature

[0011] Non-patent literature 1: Hikaru Abe, Ai Murakami, Shun Tsunekawa, Takuya Okada, Toru Wakabayashi, Masaaki Yoshida, and Masaharu Nakayama, "Selective Catalyst for Oxygen Evolution in Neutral Brine Electrolysis: An Oxygen-DeficientManganese Oxide Film", ACS Catal. 2021,11,11, pp.6390-6397<URL: https: / / doi.org / 10.1021 / acscatal.0c05496> Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Around the anode, due to the electrolysis of water, the concentration of hydrogen ions increases along with oxygen (O2), and the pH decreases. Even if a film is placed on the anode surface as described in Patent Document 2 and Non-Patent Document 1, the pH decrease caused by water electrolysis cannot be avoided. When the pH around the anode decreases excessively, the selectivity of the chlorination reaction (CER) becomes high, and chlorine is easily produced.

[0014] The objective of this invention is to continuously generate hydrogen while suppressing chlorine production in a hydrogen generation apparatus for electrolyzing seawater at sea to produce hydrogen by eliminating excessive pH reduction around the anode.

[0015] Methods for solving problems

[0016] The present invention provides a seawater electrolysis apparatus for electrolyzing seawater at sea, comprising: a cathode; an anode disposed opposite to the cathode; a diaphragm disposed between the cathode and the anode; a power source for applying a voltage between the cathode and the anode; and a control device for controlling the application of the voltage from the power source to the cathode and the anode, wherein the control device stops the application of the voltage after the application of the voltage begins when a first predetermined period has elapsed, and restarts the application of the voltage after the application of the voltage has stopped when a second predetermined period has elapsed.

[0017] Invention Effects

[0018] According to the present invention, in a seawater electrolysis apparatus for seawater electrolysis at sea, when a first predetermined period has elapsed, the decrease in pH around the anode is eliminated by stopping the voltage application from the power source to the cathode and anode, and then the voltage application is restarted after the pH rises, thus enabling the continuous generation of hydrogen while suppressing the generation of chlorine. Attached Figure Description

[0019] Figure 1 This is a circuit diagram of a seawater electrolysis device 1 for producing hydrogen by electrolyzing seawater at sea.

[0020] Figure 2 This is a schematic plan view of seawater electrolysis unit 1.

[0021] Figure 3 yes Figure 2 Cross-sectional view in the direction of arrow III-III.

[0022] Figure 4 This is a schematic diagram of the hydrogen recovery unit 70.

[0023] Figure 5 This is a time series diagram showing the relationship between the timing of applying voltage between the anode 10 and the cathode 20 and the pH around the anode 10.

[0024] Figure 6 This is a schematic diagram showing the setup of Experiment 1.

[0025] Figure 7 This is a schematic diagram showing the setup of Experiment 2.

[0026] Figure 8 This is a graph showing the relationship between the amount of chlorine generated and the electrolysis time in Experiment 1 and Experiment 2.

[0027] Figure 9 This is a graph showing the relationship between oxygen generation rate and electrolysis time in Experiment 1 and Experiment 2.

[0028] Figure 10 This is a graph showing the relationship between pH and electrolysis time in Experiment 1 and Experiment 2. Detailed Implementation

[0029] The embodiments of the present invention will be described in detail below.

[0030] In this specification, "sea" includes brackish estuaries, brackish lakes, saltwater lakes, salt lakes, and other waters containing chlorine-containing compositions.

[0031] In this specification, "seawater" includes brackish water, a mixture of fresh and seawater.

[0032] In this specification, "water flow" includes the flow of rivers, tides, and ocean currents.

[0033] Implementation Method 1

[0034] Figure 1 This is a circuit diagram of the seawater electrolysis device 1 used in this embodiment for electrolyzing seawater at sea. Figure 1 As shown, the seawater electrolysis device 1 includes an anode 10, a cathode 20, a power supply 30, and a control device 40. Additionally, although not shown in... Figure 1 As shown in the figure, but as Figure 2 , Figure 3 As shown, a diaphragm 21 is provided between the anode 10 and the cathode 20.

[0035] Anode 10 and cathode 20 are arranged opposite each other in the sea. By applying a voltage from power source 30 between anode 10 and cathode 20, oxygen is generated at anode 10 through an oxidation reaction, and hydrogen is generated at cathode through a reduction reaction.

[0036] With the anode 10 and cathode 20 immersed in seawater, the power source 30 applies a voltage between the anode 10 and cathode 20. Power is supplied to the power source 30 from an external power source, such as a wind turbine or solar generator located at sea.

[0037] The control device 40 includes a processor, a storage device storing the software (programs, firmware, etc.) executed by the processor, etc. The control device 40 controls the voltage applied from the power supply 30 between the anode 10 and the cathode 20. Furthermore, as described later, when a moving mechanism 60 is provided, the control device 40 controls the moving mechanism 60.

[0038] Furthermore, as described later, when a pH sensor 41 is provided around the anode 10, a signal from the pH sensor 41 is input to the control device 40. In this case, the control device 40 can control the power supply 30 or the moving mechanism 60 based on the output of the pH sensor 41.

[0039] Figure 2 This is a schematic plan view of seawater electrolysis unit 1. Figure 3 yes Figure 2 Elevation view with arrow III-III pointing in the direction of the arrow. Additionally, Figures 1-3 The document describes a seawater electrolysis device 1 having three pairs of anodes 10 and cathodes 20, but the number of pairs of anodes 10 and cathodes 20 is arbitrary. Furthermore, although not shown, it is preferable to provide a net or similar device around the seawater electrolysis device 1 to prevent the intrusion of fish and seaweed.

[0040] like Figure 2 , Figure 3 As shown, a spacer 11 is provided on the upper part of the anode 10. The spacer 11 is made of an insulator or covered by an insulating film.

[0041] The anode 10 can be a flat plate, or a perforated mesh, stretched metal mesh, or other mesh shapes.

[0042] On the surface of the anode 10, a catalyst layer is provided to improve the selectivity of the oxygen generation reaction (OER) relative to the chlorine generation reaction (CER) during seawater electrolysis. Specifically, the anode 10 is formed by providing a manganese dioxide (MnO2) layer on the surface of a conductive substrate.

[0043] As a conductive substrate for the anode 10, titanium (Ti), titanium-tantalum alloy (TiTa), iridium-tantalum alloy (IrTa), and TiTa-IrTa alloy (TIR) ​​can be used, for example. Alternatively, a material in which an oxide layer of an iridium-tantalum alloy (IrTaO) is formed on titanium can also be used as a conductive substrate.

[0044] By electrodepositing the above-mentioned conductive substrate in an aqueous solution of manganese sulfate (MnSO4) and sulfuric acid (H2SO4), a manganese dioxide (MnO2) layer can be formed on the surface of the conductive substrate.

[0045] After a manganese dioxide (MnO2) layer is deposited onto the surface of a conductive substrate by electrodeposition, a vanadium (V)-doped layer (Mn-VO) can be formed on the manganese dioxide layer. For example, after forming a manganese dioxide layer on a conductive substrate, electrodeposition can be performed in an aqueous solution of manganese sulfate (MnSO4), sodium orthovanadate (Na3VO4), and sulfuric acid (H2SO4) to form a Mn-VO layer on the manganese dioxide layer.

[0046] like Figure 2 , Figure 3 As shown, a cover 22 is provided on the upper part of the cathode 20. The cover 22 is made of an insulator or covered by an insulating film.

[0047] The cathode 20 can be a flat plate, or a perforated mesh, stretched metal mesh, or other mesh-like structures. When the seawater electrolysis device 1 is installed at sea, the cathode 20 is suspended on the support rod 51 and installed vertically.

[0048] The upper end of the diaphragm 21 is positioned above the sea surface S, as shown below. Figure 2 As shown, the diaphragm 21 surrounds the outer periphery of the cover 22 and is held between the spacer 11 and the cover 22. Therefore, the diaphragm 21 is arranged to surround the cathode 20 in the horizontal direction. In addition, the lower part of the diaphragm 21 may be open.

[0049] The vertical length of the diaphragm 21 is preferably longer than the vertical length of the cathode 20. That is, as... Figure 3 As shown, a diaphragm is preferably provided such that the lower end of the diaphragm 21 is located at a position lower than the lower end of the cathode 20.

[0050] The width of the diaphragm 21 is preferably greater than the width of the opposing surfaces of the cathode 20 and the anode 10.

[0051] Additionally, the diaphragm 21 can be located at both ends of the cathode 20 in the width direction. Figure 2 The diaphragm 21 is located at the left and right ends of the cathode 20, below the sea surface S. That is, the diaphragm 21 does not need to completely surround the cathode 20 in the horizontal direction; it is sufficient to place the diaphragm 21 between the cathode 20 and the anode 10. In this case, the width of the diaphragm 21 needs to be sufficient to prevent the gases generated at the anode 10 and cathode 20 from mixing in the seawater; for example, it is preferably more than twice the width of the face of the cathode 20 facing the anode 10.

[0052] A hydrogen trap 23 is installed on the upper part of the cover 22. The hydrogen trap 23 is connected to the hydrogen recovery device 70 (see reference). Figure 4 )connect.

[0053] Hydrogen (H2) generated by reduction reaction on the surface of cathode 20 through seawater electrolysis rises towards the sea surface S inside diaphragm 21 and is captured in the space enclosed by the sea surface S, diaphragm 21, and cover 22. The captured hydrogen (H2) is removed from hydrogen capture nozzle 23 and sent to hydrogen recovery device 70.

[0054] Figure 4 This is a schematic diagram of the hydrogen recovery unit 70. The hydrogen recovery unit 70 includes a water seal tank 71, a hydrogen refiner 72, etc.

[0055] Hydrogen extracted from hydrogen collection nozzle 23 is transported to the next process via water seal tank 71, hydrogen refiner 72, etc.

[0056] The seawater electrolysis apparatus 1 includes a holding section 50 for holding an anode 10 and a cathode 20. The holding section 50 holds the anode 10 and the cathode 20 in such a way that a space is left between the anode 10 and the cathode 20 for seawater flow.

[0057] For example, the retaining part 50 includes a support rod 51 and a float 52.

[0058] The support rod 51 supports the anode 10 and cathode 20 while being insulated from the anode 10 and cathode 20. Specifically, as... Figure 2 and Figure 3 As shown, with the diaphragm 21 sandwiched between the spacer 11 disposed on the upper part of the anode 10 and the cover 22 disposed on the upper part of the cathode 20, the spacer 11, the cover 22 and the diaphragm 21 are supported by the support rod 51 and fastened by fasteners (not shown). Thus, the anode 10 and the cathode 20 are arranged at a predetermined interval, and the diaphragm 21 is disposed between the anode 10 and the cathode 20.

[0059] The two ends of the support rod 51 are fixed to the float 52. The seawater electrolysis device 1 is positioned at sea via the float 52.

[0060] As described above, a catalyst layer is provided on the surface of the anode 10 to improve the selectivity of the oxygen generation reaction (OER) relative to the chlorination generation reaction (CER) during seawater electrolysis. However, around the anode 10, the hydrogen ion concentration increases and the pH decreases along with the generation of oxygen (O2) as shown in equation (1).

[0061] 2H₂O→O₂+4H + +4e - (4OH) - →2H₂O + O₂ + 4e - (1)

[0062] When the pH decreases, the selectivity of the chlorine reaction (CER) increases, making it easier to produce chlorine gas.

[0063] In this embodiment, the voltage applied from the power source 30 to the anode 10 and cathode 20 is switched on / off at predetermined intervals to stop electrolysis during the pH decrease around the anode 10.

[0064] Figure 5 This is a time series diagram showing the relationship between the timing of applying voltage between the anode 10 and the cathode 20 and the pH around the anode 10.

[0065] like Figure 5 As shown in the upper paragraph, the following process is repeated: during the specified application period T1, a voltage is applied between the anode 10 and the cathode 20; during the specified stop period T2, the application of voltage between the anode 10 and the cathode 20 is stopped.

[0066] Here, the application period T1 is as follows: Figure 5 As shown in the lower section, the time T1 is set from the start of applying voltage between the anode 10 and the cathode 20 until the pH around the anode 10 decreases to a specified value pHβ (e.g., pH=4) or less. The application period T1 is appropriately set according to the shape of the anode 10, the distance between the anode 10 and the cathode 20, the surface area of ​​the anode 10 and the cathode 20, the current, the seawater temperature, the water flow velocity, etc. Therefore, the application period T1 can vary each time it is set.

[0067] In addition, the shutdown period T2 is set as the sufficient time required from the cessation of seawater electrolysis until the pH around the anode 10 rises to a specified value pHα (e.g., pH=6). The shutdown period T2 is appropriately set according to the shape of the anode 10, the distance between the anode 10 and the cathode 20, the surface area of ​​the anode 10 and the cathode 20, the seawater temperature, the water flow velocity, etc. Therefore, the shutdown period T2 can vary each time it is set.

[0068] Additionally, the pH rise around anode 10 during the shutdown period T2 occurs through seawater exchange around anode 10. This seawater exchange can occur, for example, by a water flow that circulates seawater around anode 10. In this case, the shutdown period T2 can be set to a value larger than the width of anode 10 divided by the water flow velocity.

[0069] For example, the application period T1 can be set to 5 minutes, the stop period T2 can be set to 1 minute, and the voltage applied from the power source 30 to the anode 10 and cathode 20 can be switched on / off in a 6-minute cycle.

[0070] In this way, by switching on / off the voltage applied from the power source 30 to the anode 10 and the cathode 20 at predetermined intervals, excessive pH reduction around the anode 10 can be suppressed, preventing chlorine ionization.

[0071] Alternatively, the control device 40 can install a pH sensor 41 on or around the surface of the anode 10 and control the power supply 30 such that when the pH of the seawater on the surface of the anode 10 reaches a predetermined lower limit value pHβ, the voltage applied between the anode 10 and the cathode 20 is stopped, and when the pH of the surface of the anode 10 reaches a predetermined upper limit value pHα, the voltage applied between the anode 10 and the cathode 20 is started. Here, "the pH of the seawater on the surface of the anode 10" can also be the pH of the seawater between the anode 10 and the diaphragm 21. The "prescribed lower limit value pHβ" can be set to a value higher than the pH value at which chlorine is freed through seawater electrolysis (e.g., pH=4). If chlorine generation is permissible to a certain extent, the pH value set according to that extent can be used as the "pH value at which chlorine is freed". In addition, the "prescribed upper limit value pHα" can be set to a sufficiently high pH value (e.g., pH=6) required for the oxygen generation reaction (OER) to be more selective than the chlorine generation reaction (CER) during seawater electrolysis through the anode 10.

[0072] Furthermore, the values ​​of α and β can be the measured values ​​of pH sensor 41, or values ​​calculated based on the measured values ​​of pH sensor 41. Specifically, this embodiment illustrates a case where there is only one pH sensor 41, but multiple pH sensors 41 can be installed at appropriate locations depending on the scale of the seawater electrolysis device 1, the conditions of the installation site, etc. In this case, the values ​​of α and β can be appropriately calculated based on the measured values ​​of each pH sensor 41. This calculation is performed by the control device 40, which serves as a calculation unit.

[0073] The seawater electrolysis device 1 may include a moving mechanism 60, which moves the anode 10, cathode 20, and diaphragm 21 along the direction of the anode 10 facing the cathode 20. Figure 1 The anode 10, cathode 20, and diaphragm 21 move in a direction intersecting each other (vertically). By moving the anode 10, cathode 20, and diaphragm 21, the seawater surrounding the anode 10 can be exchanged. Therefore, without waiting for the surrounding seawater to be exchanged via water flow, the anode 10 and other components can be moved to a position where the pH of the surrounding seawater is sufficiently high, and seawater electrolysis can be restarted. The control device 40 can control the moving mechanism 60 to move the anode 10, cathode 20, and diaphragm along the width direction of the opposing surfaces of the anode 10 and cathode 20 (vertically). Figure 2 (lateral) movement.

[0074] The moving mechanism 60 may, for example, be along the width direction of the face of the anode 10 opposite to the cathode 20. Figure 1 The float 52 is positioned along a horizontal slide rail. Alternatively, the float 52 can be moved along the slide rail. Alternatively, a rope (not shown) can be installed on the float 52, and the entire seawater electrolysis device 1 can be moved by pulling the rope from the outside. Alternatively, a propeller or other propulsion device can be installed on the float 52, allowing the seawater electrolysis device 1 to be moved by self-propulsion.

[0075] The anode 10 needs to be moved to a location where the pH of the surrounding seawater is sufficiently high; therefore, the preferred moving distance of the anode 10 is the width of the face of the anode 10 facing the cathode 20. Figure 1 (horizontal width) or more.

[0076] The moving mechanism 60 moves the anode 10, cathode 20, and diaphragm 21. For example, this can be achieved by moving the float 52 along... Figure 2 The lateral movement is used to move the entire seawater electrolysis device 1.

[0077] The moving mechanism 60 preferably moves the anode 10, cathode 20, and diaphragm 21 during the stop period T2. In this case, the moving speed is preferably greater than or equal to the value obtained by dividing the moving distance of the anode 10 by the stop period T2.

[0078] Alternatively, not limited to the stop period T2, the anode 10, cathode 20 and diaphragm 21 can be moved during the application period T1.

[0079] Alternatively, a pH sensor 41 can be installed around the anode 10. When the pH measured by the pH sensor 41 reaches a predetermined lower limit, the control device 40 starts moving the anode 10 via the moving mechanism 60. When the pH measured by the pH sensor 41 reaches a predetermined upper limit, the control device 40 stops moving the anode 10 via the moving mechanism 60. Here, the methods for setting the "predetermined lower limit" and "predetermined upper limit" are as described above.

[0080] Furthermore, the upper and lower limits of pH can be the values ​​measured by pH sensor 41, or values ​​calculated based on the values ​​measured by pH sensor 41 as described above. Alternatively, instead of controlling the movement of anode 10 based on pH value, the movement distance can be pre-calculated. For example, the movement distance up to a point where the pH of the seawater surrounding anode 10 is sufficiently high can be pre-calculated based on the scale of the seawater electrolysis device 1 and the conditions of the installation site. Furthermore, the pre-calculated movement distance can be corrected based on the values ​​measured by pH sensor 41.

[0081] The following electrolysis experiment based on sodium chloride aqueous solution illustrates the relationship between the pH decrease caused by electrolysis and the generation of chlorine at the anode.

[0082] Experiment 1

[0083] Production Figure 6 The electrolytic cell shown undergoes electrolysis while circulating an aqueous sodium chloride solution.

[0084] like Figure 6As shown, an anode chamber 110 containing an anode 101, a cathode chamber 120 containing a cathode 102, a diaphragm 103, and a spacer 104 are arranged and fastened in the order of anode chamber 110, spacer 104, diaphragm 103, and cathode chamber 120 to form an electrolytic cell.

[0085] As anode 101, a material is used in which a layer of manganese dioxide (MnO2) is formed by electrodepositing a layer of manganese dioxide (Mn-VO) by doping vanadium (V) onto the surface of a titanium conductive substrate.

[0086] As the cathode 102, a nickel-based conductive substrate is used.

[0087] As the separator 103, an alkali-resistant anion exchange membrane (AHA, manufactured by Astom Co., Ltd.) is used.

[0088] The thickness of spacer 104 ( Figure 6 The horizontal length is set to 15mm.

[0089] Anode solution is supplied from an anolyte tank 111 located outside the electrolytic cell to the anode chamber 110 via a pump 112, while simultaneously recovering anolyte from the anode chamber 110 back to the anolyte tank 111, thus circulating the solution. The anolyte is an aqueous sodium chloride solution with an initial concentration of 30 g / L. The pump 112 delivers 104 mL / min at a rate of 0.5 cm / s within the anode chamber 110.

[0090] Cathodic solution is supplied from a cathodic solution tank 121 located outside the electrolytic cell to the cathode chamber 120 via a feed pump 112, while simultaneously recovering cathodic solution from the cathode chamber 120 back to the cathodic solution tank 121, thus circulating the solution. The cathodic solution is an aqueous sodium chloride solution with an initial concentration of 30 g / L. The feed rate by the feed pump 122 is 104 mL / min, and the linear flow velocity within the cathode chamber 120 is 0.5 cm / s.

[0091] Electrolysis is performed by circulating the anolyte and catholyte while applying a voltage from the power supply 130 between the anode 101 and the cathode 102. The power supply 130 is a DC power supply (PMC35-2A, manufactured by Kikusui Electronics Industry Co., Ltd.). The current value is set to 0.1 A / cm² relative to the surface area of ​​the anode 101 and the cathode 102. 2 .

[0092] During the 30-minute electrolysis process, a portion of the anolyte was removed from the anolyte tank 111 every 5 minutes, and the chlorine generation and pH were measured.

[0093] The amount of chlorine generated was determined by the diethyl-p-phenylenediamine method (DPD method).

[0094] pH was measured using pH test paper.

[0095] In addition, the oxygen generation rate is calculated based on the amount of chlorine generated and the equivalent of electrons flowing through.

[0096] Here, the generation of oxygen in the anode chamber is represented by the following formula (1), while the generation of chlorine is represented by the following formula (2).

[0097] 2H₂O → O₂ + 4H + + 4e - (4OH) - → 2H₂O + O₂ + 4e - …(1)

[0098] 2Cl - → Cl2 + 2e - …(2)

[0099] When the amount of oxygen generated in equation (1) is set as n_O2 and the amount of chlorine generated in equation (2) is set as n_Cl2, the number of electrons generated in equation (1) is 4 × n_O2 and the number of electrons generated in equation (2) is 2 × n_Cl2. If the total amount of electrons generated in equations (1) and (2) is set as the equivalent of the flowing electrons n_e - If , then the following formula is true.

[0100] 4 × n_O2 + 2 × n_Cl2 = n_e -

[0101] Therefore, the amount of oxygen generated is expressed by the following formula.

[0102] n_O2 = (n_e - -2 × n_Cl2) / 4

[0103] The oxygen generation rate is calculated using the following formula.

[0104] Oxygen generation rate = 4 × n_O2 / n_e - = (n_e - -2×n_Cl2) / n_e -

[0105] Therefore, it is possible to obtain the electron equivalent (n_e) supplied by a DC power source. - The oxygen generation rate was calculated from the chlorine generation (n_Cl2) determined by the DPD method.

[0106] Experiment 2

[0107] Production Figure 7 The electrolytic cell shown undergoes electrolysis while circulating an aqueous sodium chloride solution.

[0108] like Figure 7As shown, an anode chamber 110 containing an anode 101, a cathode chamber 120 containing a cathode 102, and a diaphragm 103 are arranged and fastened in the order of anode chamber 110, diaphragm 103, and cathode chamber 120, thereby forming an electrolytic cell. Figure 7 The only difference in the electrolytic cell of Experiment 1 shown is the absence of spacer 104.

[0109] The relationship between chlorine generation and electrolysis time in Experiments 1 and 2 is shown in the figure. Figure 8 The relationship between oxygen generation rate and electrolysis time is shown in... Figure 9 The relationship between pH and electrolysis time is shown in Figure 10 .

[0110] like Figure 8 , Figure 9 As shown, in either Experiment 1 or Experiment 2, no chlorine was detected until 5 minutes after the start of electrolysis. On the other hand, as... Figure 10 As shown, the pH was 6 before electrolysis began, and decreased to 4 5 minutes after electrolysis began.

[0111] like Figure 8 , Figure 9 As shown, chlorine was detected in both Experiment 1 and Experiment 2 10 minutes after electrolysis began. Figure 10 As shown, the pH dropped to 3 10 minutes after the start of electrolysis.

[0112] After that, as Figure 8 As shown, the amount of chlorine produced increases with increasing electrolysis time. Figure 9 As shown, the oxygen generation rate remained slightly below 80% after 15 minutes of electrolysis. Figure 10 As shown, the pH was 3 from 10 to 25 minutes after the start of electrolysis, but dropped to 2 30 minutes after the start of electrolysis.

[0113] The results of Experiments 1 and 2 show that when the pH of the anolyte decreases to the specified value, only oxygen is produced without the formation of chlorine. Therefore, it can be concluded that eliminating the pH decrease around the anode can inhibit the formation of chlorine.

[0114] Although experiments 1 and 2 used saline solution, even in seawater electrolysis, chlorine formation can be suppressed by eliminating excessive pH reduction around the anode. Therefore, in a seawater electrolysis device, the application period for applying voltage between the anode and cathode, and the period for stopping voltage application can be appropriately set according to the size of the cathode and anode, the distance between the cathode and anode, the voltage, the current, the seawater temperature, and the water flow velocity. By alternating between applying and stopping voltage application, it is possible to suppress chlorine formation while continuously generating hydrogen.

[0115] This application claims priority based on Japanese Patent Application No. 2024-050672, filed on March 27, 2024.

Claims

1. A seawater electrolysis device for electrolyzing seawater at sea, comprising: cathode; An anode arranged opposite to the cathode; A diaphragm disposed between the cathode and the anode; A power source that applies a voltage between the cathode and the anode; A control device for controlling the voltage applied from the power source to the cathode and the anode; The control device stops applying the voltage after a first predetermined period has elapsed after the voltage application begins, and restarts applying the voltage after a second predetermined period has elapsed after the voltage application has stopped.

2. The seawater electrolysis apparatus according to claim 1, comprising a moving mechanism that moves the anode, the cathode and the diaphragm during the second specified period.

3. In the seawater electrolysis apparatus according to claim 2, the moving direction of the anode by the moving mechanism is the width direction of the opposing surface of the anode and the cathode, and the moving distance of the anode is greater than or equal to the width of the opposing surface.

4. The seawater electrolysis apparatus according to claim 1, further comprising: A cover disposed on the upper part of the cathode and connected to the upper end of the diaphragm; A hydrogen trapping nozzle that captures hydrogen produced from the cathode through the electrolysis of seawater.

5. The seawater electrolysis apparatus according to claim 1, wherein the width of the diaphragm is greater than the width of the cathode facing the anode.

6. In the seawater electrolysis apparatus according to claim 1, the vertical height of the diaphragm is higher than the vertical height of the cathode.

7. The seawater electrolysis apparatus according to claim 4 further includes a recovery device for recovering hydrogen captured by the hydrogen trap nozzle.

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