Pretreatment method and cell

Abstract

This pretreatment method comprises, prior to incorporating a mesh plate (80) into a cell, exposing the mesh plate (80) to ultrasonic waves while the mesh plate (80) is immersed in water. Hydrophilicity of the mesh plate (80) is thereby improved. Stagnation of gas in the mesh plate (80) when an electrochemical reaction is performed in a cell can therefore be suppressed. The efficiency of an electrochemical reaction in a cell can be improved as a result.

Description

Pretreatment method and cell

[0001] The present invention relates to a method for pretreating a mesh plate used in a cell that performs an electrochemical reaction, and to a cell equipped with the mesh plate.

[0002] Conventionally, water (H ２ Hydrogen (H ２ A solid polymer water electrolysis device that produces hydrogen is known. The water electrolysis device has a cell stack in which cells and separators are alternately stacked. Each cell has an electrolyte membrane and a catalyst layer formed on both sides of the electrolyte membrane. When the water electrolysis device is in use, a voltage is applied between the anode-side catalyst layer and the cathode-side catalyst layer, and water is supplied to the anode-side catalyst layer. This causes the following electrochemical reaction between the anode-side catalyst layer and the cathode-side catalyst layer: As a result, hydrogen is discharged from the cathode-side catalyst layer. (Anode side) 2H ２ O → 4H ＋ + O ２ + 4e － (Cathode side) 2H ＋ + 2e － → H ２

[0003] A conventional water electrolysis device is described in, for example, Patent Document 1.

[0004] Japanese Patent Application Laid-Open No. 2022-023996

[0005] The cell of the water electrolysis device has a porous transport layer laminated on the outside of the anode-side catalytic layer. The porous transport layer is required to perform three functions: supply water to the catalytic layer, discharge oxygen generated in the catalytic layer, and conduct electricity between the catalytic layer and the separator. For this reason, a mesh plate with water permeability, air permeability, and electrical conductivity is used for the porous transport layer. The mesh plate is made of, for example, titanium, and its surface is plated with platinum.

[0006] However, mesh plates have low hydrophilicity, especially in the initial stage of use. Therefore, during water electrolysis, gaseous oxygen generated in the anode-side catalytic layer may accumulate in the porous transport layer. In this case, the accumulated oxygen in the porous transport layer inhibits the flow of water through the porous transport layer, making it difficult for water to be supplied to the catalytic layer. This results in a problem of reduced efficiency of electrolysis in the catalytic layer.

[0007] Therefore, an object of the present invention is to provide a technique that can improve the efficiency of the electrochemical reaction in the cell by improving the hydrophilicity of the mesh plate.

[0008] In order to solve the above problems, the first invention of the present application is a pretreatment method for treating a mesh plate that has water permeability, breathability, and conductivity and is used in a cell that performs an electrochemical reaction before being incorporated into the cell, and includes an ultrasonic treatment step in which ultrasonic waves are applied to the mesh plate while the mesh plate is immersed in water.

[0009] A second invention of the present application is the pretreatment method of the first invention, wherein the mesh plate has a plating on its surface, and the intensity of the ultrasonic waves is 2000 W / m ２ or more and 3500 W / m ２ The following is the result.

[0010] A third invention of the present application is the pretreatment method of the first or second invention, further comprising a storage step of storing the mesh plate immersed in water after the ultrasonic treatment step.

[0011] A fourth aspect of the present invention is the pretreatment method of any one of the first to third aspects, wherein the mesh plate is made of titanium or a titanium alloy and has a platinum-plated surface.

[0012] A fifth aspect of the present invention is the pretreatment method of any one of the first to fourth aspects, wherein the mesh plate is used as an anode-side porous transport layer in a cell for performing water electrolysis.

[0013] A sixth invention of the present application is a cell for performing an electrochemical reaction, comprising an electrolyte membrane, a catalyst layer formed on the surface of the electrolyte membrane, and a mesh plate laminated on the surface of the catalyst layer, the mesh plate having water permeability, air permeability, and electrical conductivity, wherein when E1 is the moving average value of the voltage value 10 hours after the start of current flow and E2 is the moving average value of the voltage value 50 hours after the start of current flow, E1 / E2 is 1.5 or less.

[0014] According to the first to fifth aspects of the present invention, the hydrophilicity of the mesh plate is improved by applying ultrasonic waves to the mesh plate while it is immersed in water. This makes it possible to prevent gas from remaining on the mesh plate when an electrochemical reaction is carried out in the cell. As a result, the efficiency of the electrochemical reaction in the cell can be improved.

[0015] In particular, according to the second aspect of the present invention, the hydrophilicity of the mesh plate can be improved and the plating can be prevented from peeling off from the surface of the mesh plate.

[0016] In particular, according to the third aspect of the present invention, the mesh plate can be maintained in a highly hydrophilic state.

[0017] Furthermore, according to the sixth aspect of the present invention, the efficiency of the electrochemical reaction in the cell can be improved.

[0018] FIG. 1 is a schematic diagram of a water electrolysis device. FIG. 2 is a schematic diagram of one cell and a pair of separators located on both sides of the cell. FIG. 3 is a flowchart showing the procedure for producing a stacked structure on the anode side. FIG. 4 is a diagram showing the configuration of a pretreatment device. FIG. 5 is a flowchart showing the flow of pretreatment. FIG. 6 is a graph showing the current-voltage characteristics of a comparative example. FIG. 7 is a graph showing the current-voltage characteristics of an example. FIG. 8 is a graph showing the change in voltage value over time in an example.

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] <1. Overall Configuration of the Water Electrolysis Apparatus> Fig. 1 is a schematic diagram of a solid polymer water electrolysis apparatus 1 according to one embodiment of the present invention. The water electrolysis apparatus 1 is an apparatus for producing hydrogen by water electrolysis. As shown in Fig. 1, the water electrolysis apparatus 1 includes a cell stack 30 composed of a plurality of cells 10 and a plurality of separators 20, and a power supply device 40 that applies a voltage to the cell stack 30. The cells 10 and the separators 20 are alternately stacked to form the cell stack 30.

[0021] 2 is a schematic diagram illustrating only one cell 10 and a pair of separators 20 located on either side of the cell 10 in the cell stack 30 of the water electrolysis device 1. As shown in FIG. 2 , one cell 10 has an electrolyte membrane 51, an anode catalyst layer 61, a porous transport layer 62, a cathode catalyst layer 71, and a gas diffusion layer 72.

[0022] The stacked body formed by the electrolyte membrane 51, the anode catalyst layer 61, and the cathode catalyst layer 71 is called a catalyst-coated membrane (CCM). The cell 10 formed by the electrolyte membrane 51, the anode catalyst layer 61, the porous transport layer 62, the cathode catalyst layer 71, and the gas diffusion layer 72 is also called a membrane-electrode-assembly (MEA).

[0023] The electrolyte membrane 51 is a thin plate-like membrane (ion exchange membrane) having ion conductivity. The electrolyte membrane 51 of this embodiment is a membrane that exchanges hydrogen ions (H ＋ ) is a proton exchange membrane that conducts the electrolyte membrane 51. A fluorine-based or hydrocarbon-based polymer electrolyte membrane is used as the electrolyte membrane 51. Specifically, for example, a polymer electrolyte membrane containing perfluorocarbon sulfonic acid is used as the electrolyte membrane 51. The thickness of the electrolyte membrane 51 is, for example, 5 μm to 200 μm.

[0024] The anode catalyst layer 61 is a catalyst layer that causes an electrochemical reaction on the anode side. The anode catalyst layer 61 is formed on the anode side surface of the electrolyte membrane 51. The anode catalyst layer 61 contains a plurality of catalyst particles and an ionomer.

[0025] The catalyst particles are particles that have catalytic activity for causing the electrolysis of water. The catalyst particles are made of, for example, iridium (Ir), ruthenium (Ru), iridium oxide (IrOx), platinum (Pt), or an alloy of iridium (Ir) and ruthenium (Ru). The catalyst particles may be supported by a support. In this case, the support may be, for example, titanium dioxide (TiO ２ ) or carbon (C) is used.

[0026] The ionomer is an electrolyte polymer that covers the catalyst particles. The ionomer plays a role in transporting hydrogen ions generated by the electrolysis of water within the anode catalyst layer 61. For example, Nafion (perfluorocarbon sulfonic acid) is used as the ionomer. The ionomer has a polymer chain structure with ion exchange groups such as sulfonic groups. The hydrogen ions bond with water within the anode catalyst layer 61 to form oxonium ions (H ３ O ＋ ) Then, the oxonium ion propagates through the ion exchange groups of the ionomer.

[0027] When the water electrolysis device 1 is in use, water (H ２ O) is supplied. Then, a voltage is applied between the anode catalyst layer 61 and the cathode catalyst layer 71 by the power supply device 40. Then, due to the action of the voltage and the catalyst particles, water is converted into hydrogen ions (H ＋ ), oxygen (O ２ ), and electrons (e － That is, the following electrochemical reaction occurs in the anode catalyst layer 61: ２ O → 4H ＋ + O ２ + 4e －

[0028] The porous transport layer (PTL) 62 is a layer that uniformly supplies water from the separator 20 to the anode catalyst layer 61 and transports oxygen and electrons generated in the anode catalyst layer 61 to the separator 20. The porous transport layer 62 is laminated on the outer surface of the anode catalyst layer 61 (the side opposite to the electrolyte membrane 51). A mesh plate 80 is used for the porous transport layer 62.

[0029] The mesh plate 80 is a porous plate having many small holes that communicate with each other. Therefore, the mesh plate 80 has water permeability and air permeability. The mesh plate 80 is made of, for example, titanium or a titanium alloy. The surface of the mesh plate 80 is plated with platinum. Therefore, the mesh plate 80 has electrical conductivity.

[0030] The cathode catalyst layer 71 is a catalyst layer that causes an electrochemical reaction on the cathode side. The cathode catalyst layer 71 is formed on the cathode side surface of the electrolyte membrane 51 (the surface opposite to the surface on which the anode catalyst layer 61 is formed). The cathode catalyst layer 71 includes a large number of carbon particles supporting catalyst particles. The catalyst particles are, for example, platinum particles. However, the catalyst particles may also be platinum particles mixed with trace amounts of ruthenium or cobalt particles.

[0031] When the water electrolysis device 1 is in use, hydrogen ions (H ＋ ) and electrons (e － ) is supplied to the anode catalyst layer 61. Then, a voltage is applied between the anode catalyst layer 61 and the cathode catalyst layer 71 by the power supply device 40. Then, due to the voltage and the action of the catalyst particles, a reduction reaction occurs in the cathode catalyst layer 71, and hydrogen gas (H ２ That is, the following electrochemical reaction occurs in the cathode catalyst layer 71: ＋ + 2e － → H ２

[0032] The gas diffusion layer (GDL) 72 is a layer that transfers electrons from the separator 20 to the cathode catalyst layer 71 and transfers hydrogen generated in the cathode catalyst layer 71 to the separator 20. The gas diffusion layer 72 is laminated on the outer surface of the cathode catalyst layer 71 (the side opposite to the electrolyte membrane 51). The gas diffusion layer 72 is made of a conductive and porous material. For example, a porous substrate made of carbon (carbon paper) is used for the gas diffusion layer 72.

[0033] The separator 20 is a layer that transfers electrons between adjacent cells 10 and also forms paths for water, oxygen, and hydrogen. The separator 20 is interposed between the porous transport layer 62 and the gas diffusion layer 72 of adjacent cells 10. The separator 20 is made of a material that is electrically conductive and impermeable to gases and liquids. For example, a metal plate is used as the separator 20.

[0034] Separator 20 has an anode surface 21 in contact with porous transport layer 62 and a cathode surface 22 in contact with gas diffusion layer 72. A plurality of anode grooves 23 are formed on anode surface 21. Water is supplied from outside cell stack 30 to porous transport layer 62 through anode grooves 23 of separator 20. Oxygen generated in anode catalyst layer 61 passes through porous transport layer 62 and anode grooves 23 of separator 20, before being discharged to outside cell stack 30.

[0035] Additionally, a plurality of cathode grooves 24 are formed on the cathode surface 22 of the separator 20. Hydrogen produced in the cathode catalyst layer 71 passes through the gas diffusion layer 72 and the cathode grooves 24 of the separator 20, and is discharged to the outside of the cell stack 30.

[0036] The power supply 40 is a device that applies a voltage to the cell stack 30. As shown in Fig. 1, the positive terminal of the power supply 40 is electrically connected to the separator 20 located at the end of the cell stack 30 closest to the anode. The negative terminal of the power supply 40 is electrically connected to the separator 20 located at the end of the cell stack 30 closest to the cathode. The power supply 40 applies a voltage required for water electrolysis to the cell stack 30.

[0037] The power supply device 40 has a control circuit 41 that controls the applied voltage. The control circuit 41 measures the value of the current supplied from the power supply device 40 to the cell stack 30 and controls the value of the voltage applied to the cell stack 30 so that the current value becomes a predetermined value. Therefore, when the resistance value of the cell 10 changes, the value of the voltage applied from the power supply device 40 to the cell stack 30 also changes accordingly.

[0038] When the water electrolysis device 1 is in use, water is supplied from the anode groove 23 of the separator 20 to the anode catalyst layer 61 via the porous transport layer 62. Then, due to the voltage applied from the power supply 40 and the action of the catalyst particles in the anode catalyst layer 61, the water is decomposed into hydrogen ions, oxygen, and electrons. The hydrogen ions propagate through the electrolyte membrane 51 to the cathode catalyst layer 71. The oxygen passes through the porous transport layer 62 and the anode groove 23 and is discharged to the outside of the cell stack 30. The electrons flow through the porous transport layer 62 and the separator 20 to the adjacent cell 10.

[0039] In the adjacent cell 10, the electrons pass through the gas diffusion layer 72 and reach the cathode catalyst layer 71. Then, in the cathode catalyst layer 71, the hydrogen ions and electrons combine to generate hydrogen. The generated hydrogen passes through the gas diffusion layer 72 and the cathode groove 24 and is discharged to the outside of the cell stack 30. In this way, hydrogen is produced.

[0040] 3 is a flowchart showing the steps for fabricating the anode-side stack structure of the above-described cell 10. As shown in Fig. 3, when fabricating the anode-side stack structure, first, an anode catalyst layer 61 is formed on one surface of the electrolyte membrane 51 (step S1).

[0041] In step S1, a catalyst ink prepared by adding catalyst particles and an ionomer to water or alcohol is ejected from a nozzle toward one surface of the electrolyte membrane 51. The nozzle may eject the catalyst ink in the form of a film from a slit-shaped ejection opening, or may eject the catalyst ink in the form of a spray.

[0042] Next, the catalyst ink applied to the electrolyte membrane 51 is dried. For example, the electrolyte membrane 51 on which the catalyst ink has been applied is carried into a drying oven. Because the temperature inside the drying oven is higher than the ambient temperature, the solvent in the catalyst ink evaporates. This dries the catalyst ink and turns it into the anode catalyst layer 61.

[0043] Meanwhile, in parallel with step S1, a pretreatment is performed on the mesh plate 80 to be used as the porous transport layer 62 (step S2). Fig. 4 is a diagram showing the configuration of a pretreatment device 90 that pretreats the mesh plate 80. As shown in Fig. 4, the pretreatment device 90 includes a pretreatment tank 91, an ultrasonic vibrator 92, and a controller 93.

[0044] The pretreatment tank 91 is a container capable of storing a liquid. The pretreatment tank 91 is large enough to accommodate the entire mesh plate 80. The ultrasonic vibrator 92 is a device that generates ultrasonic vibrations. The ultrasonic vibrator 92 is disposed at the bottom of the pretreatment tank 91. The controller 93 is electrically connected to the ultrasonic vibrator 92. The controller 93 can switch the ultrasonic vibrator 92 on and off. The controller 93 can also adjust the intensity of the ultrasound by adjusting the power supplied to the ultrasonic vibrator 92.

[0045] FIG. 5 is a flowchart showing the flow of pretreatment of the mesh plate 80. When pretreatment of the mesh plate 80 is performed, water is first stored in the pretreatment tank 91 (step S21). The water stored in the pretreatment tank 91 is, for example, pure water or ultrapure water. Next, as shown in FIG. 4, the mesh plate 80 is immersed in the water in the pretreatment tank 91 (step S22). At this time, the entire mesh plate 80 is immersed in water. Then, with the mesh plate 80 immersed in water, the controller 93 operates the ultrasonic vibrator 92. Then, ultrasonic waves generated from the ultrasonic vibrator 92 are applied to the mesh plate 80 via the water in the pretreatment tank 91 (step S23: ultrasonic treatment process).

[0046] This improves the hydrophilicity of the surface of the mesh plate 80. In other words, the wettability of the surface of the mesh plate 80 is improved. Furthermore, by applying ultrasonic waves to the mesh plate 80 instead of simply immersing it in water, the gas held in the pores in the mesh plate 80 is replaced with water. This improves the hydrophilicity not only of the outermost surface of the mesh plate 80 but also of the surfaces of the pores in the mesh plate 80.

[0047] When a predetermined time has elapsed since the operation of the ultrasonic vibrator 92 was started, the controller 93 stops the operation of the ultrasonic vibrator 92. This ends the application of ultrasonic waves to the mesh plate 80.

[0048] After the ultrasonic treatment process in step S23 is completed, the mesh plate 80 is stored immersed in water in the pretreatment tank 91 until the next step S3 (step S24: storage step). This prevents the surface of the mesh plate 80 from drying out. Therefore, the mesh plate 80 can be maintained in a highly hydrophilic state.

[0049] Thereafter, the mesh plate 80 is removed from the pretreatment tank 91 and placed on the surface of the anode catalyst layer 61 formed in step S1 (step S3). This forms a porous transport layer 62 using the mesh plate 80. As a result, an anode-side laminate structure consisting of the electrolyte membrane 51, anode catalyst layer 61, and porous transport layer 62 is produced.

[0050] When the water electrolysis device 1 is in use, water is supplied from outside the cell 10 to the anode catalyst layer 61 through the porous transport layer 62. Furthermore, oxygen generated by electrolysis of water is discharged to the outside of the cell 10 through the porous transport layer 62. At this time, if gaseous oxygen remains in the pores in the porous transport layer 62, it becomes difficult for water to be supplied from outside the cell 10 to the anode catalyst layer 61 through the porous transport layer 62. This reduces the efficiency of electrolysis in the anode catalyst layer 61. Furthermore, since the resistance value of the cell 10 increases, the voltage applied to the cell 10 from the power supply device 40 also increases, reducing the energy efficiency of the water electrolysis device 1.

[0051] However, in this embodiment, before the mesh plate 80 used as the porous transport layer 62 is incorporated into the cell 10, the mesh plate 80 is subjected to a pretreatment in step S3. In the pretreatment, ultrasonic waves are applied to the mesh plate 80 while the mesh plate 80 is immersed in water. This can improve the hydrophilicity of the mesh plate 80.

[0052] The improved hydrophilicity of mesh plate 80 allows water and oxygen to circulate efficiently in porous transport layer 62 when water electrolysis is performed using manufactured cell 10. That is, oxygen can be efficiently discharged from anode catalyst layer 61 to the outside of cell 10 via porous transport layer 62. Furthermore, gaseous oxygen can be prevented from remaining in the pores in porous transport layer 62, allowing water to be efficiently supplied from the outside of cell 10 to anode catalyst layer 61 via porous transport layer 62.

[0053] In this way, by improving the hydrophilicity of the mesh plate 80, it is possible to promote the exchange of water and oxygen in the porous transport layer 62. As a result, electrolysis can be carried out efficiently in the anode catalyst layer 61. Furthermore, since the voltage applied to the cell 10 from the power supply device 40 can be reduced, the energy efficiency of the water electrolysis device 1 can be improved.

[0054] In this embodiment, the hydrophilicity is improved by applying ultrasonic waves to the mesh plate 80 in water, which reduces the time and cost required for pretreatment compared to when chemically treating the surface of the mesh plate 80 for hydrophilicity.

[0055] In the ultrasonic treatment process of step S33, if the intensity of the ultrasonic waves applied to the mesh plate 80 is too strong, there is a possibility that the platinum plating will peel off from the surface of the mesh plate 80. On the other hand, if the intensity of the ultrasonic waves applied to the mesh plate 80 is too weak, the effect of improving the hydrophilicity of the mesh plate 80 will be reduced. For this reason, it is desirable that the intensity of the ultrasonic waves generated from the ultrasonic vibrator 92 is set to a level that sufficiently improves the hydrophilicity of the mesh plate 80 and prevents the platinum plating from peeling off from the surface of the mesh plate 80.

[0056] From the above viewpoint, the intensity per unit area of ​​the ultrasonic waves generated from the ultrasonic transducer 92 is, for example, 2000 W / m ２ or more and 3500 W / m ２ It is desirable that the intensity per unit area of ​​the ultrasonic waves generated from the ultrasonic transducer 92 is 2500 W / m or less. ２ or more and 3000 W / m ２ It is more preferable to do the following:

[0057] 6 is a graph showing the current-voltage characteristics of a cell 10 using a mesh plate 80 that has not been pretreated as described above as a porous transport layer 62, when a voltage is applied from the power supply 40 while a constant amount of water is supplied to the anode side (Comparative Example). FIG. 7 is a graph showing the current-voltage characteristics of a cell 10 using a mesh plate 80 that has been pretreated as described above as a porous transport layer 62, when a voltage is applied from the power supply 40 while a constant amount of water is supplied to the anode side (Example). The cell 10 in FIG. 6 and the cell 10 in FIG. 7 were fabricated under the same conditions except for the presence or absence of pretreatment.

[0058] The horizontal axis in Figures 6 and 7 represents the current value (current density) I per unit area flowing through the cell 10. The vertical axis in Figures 6 and 7 represents the voltage value E applied by the power supply device 40 between the anode and cathode of the cell 10. As described above, the power supply device 40 controls the voltage value E applied to the cell 10 so that the current flowing through the cell 10 becomes a specified current value. Therefore, as shown in Figures 6 and 7, when the specified current density I is changed, the voltage value E changes accordingly.

[0059] In the comparative example of FIG. 6, measurements were taken three times for the same cell 10, and in each measurement, the voltage value E increased relatively significantly as the current density I increased. In other words, in the comparative example of FIG. 6, the slope of the voltage value E relative to the current density I is large. In particular, in the first measurement, when the current density I was 3 A / cm ２ When this occurs, the voltage value E rises sharply as indicated by the dashed arrow in FIG.

[0060] In the first measurement shown in Figure 6, the slope of the voltage value E versus current density I increases sharply because water has not completely permeated the mesh plate 80. If water has not completely permeated the mesh plate 80, the mesh plate 80 has low hydrophilicity, making it difficult for water to move within the mesh plate 80. Under these circumstances, the rate at which water is supplied to the surfaces of the catalyst particles in the anode catalyst layer 61 decreases, and the amount of water present on the surfaces of the catalyst particles decreases. Therefore, even if the voltage value E is increased, the reaction rate of water electrolysis does not increase easily. As a result, the slope of the voltage value E versus current density I increases.

[0061] On the other hand, in the second and subsequent measurements shown in FIG. 6 , water infiltration into the mesh plate 80 progresses. As a result, the hydrophilicity of the mesh plate 80 becomes higher than in the first measurement, and water moves more easily through the mesh plate 80. Under these circumstances, the rate at which water is supplied to the surfaces of the catalyst particles in the anode catalyst layer 61 increases, and water is more easily supplied to the surfaces of the catalyst particles than in the first measurement. Therefore, the higher the voltage value E, the greater the reaction rate of water electrolysis. As a result, the slope of the voltage value E relative to the current density I becomes stable. Therefore, in order to operate the device at a stable voltage value E, it is effective to pretreat the mesh plate 80 and promote water infiltration into the mesh plate 80 in advance.

[0062] In contrast, in the example of Fig. 7 , the increase in voltage value E when the current density I is increased is smaller than in the comparative example of Fig. 6 . In other words, in the example of Fig. 7 , the slope of the voltage value E with respect to the current density I is smaller than in the comparative example of Fig. 6 . This indicates that water electrolysis was performed efficiently at a lower voltage than in the comparative example of Fig. 6 . The comparative example of Fig. 6 and the example of Fig. 7 were under the same conditions except for the presence or absence of pretreatment, and therefore it is believed that the improvement in the efficiency of water electrolysis in the example of Fig. 6 is due to the effect of pretreatment.

[0063] Figure 8 is a graph showing the change in voltage value E over time when a voltage is applied from power supply 40 to cell 10 using pretreated mesh plate 80 as porous transport layer 62 while a constant amount of water is supplied to the anode side (Example). The vertical axis of Figure 8 represents voltage value E applied by power supply 40 between the anode and cathode of cell 10. The horizontal axis of Figure 8 represents the elapsed time t after the start of current flow.

[0064] In the embodiment of FIG. 8, the voltage value E rises approximately 15 hours after the start of power supply, and thereafter, operation can be continued at a stable voltage value E within a certain range (voltage value E within the range from Emin to Emax in FIG. 8).

[0065] 8, the change in voltage value E when a mesh plate 80 that has not been pretreated is used for the porous transport layer 62 (comparative example) is shown by the two-dot chain line. Even in the comparative example, after 30 hours or more have passed since the start of current application, the voltage value E falls within the range from Emin to Emax. However, in the comparative example, in the early stages up to 30 hours, the voltage value E reaches a high value that far exceeds Emax.

[0066] This is thought to be because in the comparative example in which mesh plate 80 was not pretreated, the hydrophilicity of mesh plate 80 was low, especially in the initial stage after starting use, causing oxygen to accumulate in porous transport layer 62. In contrast, in the example in which mesh plate 80 was pretreated, oxygen was less likely to accumulate in porous transport layer 62 even in the initial stage after starting use, so the voltage value E did not exceed Emax, allowing for efficient driving.

[0067] In this way, by pretreating the mesh plate 80, it is possible to provide a cell 10 that can suppress the voltage value E, particularly in the initial stage after starting use. Specifically, when the moving average value of the voltage value E 10 hours after the start of current application is E1 and the moving average value of the voltage value E 50 hours after the start of current application is E2, it is possible to provide a cell 10 in which E1 / E2 is 1.5 or less. More preferably, it is possible to provide a cell 10 in which E1 / E2 is 1.2 or less. This allows the energy efficiency of electrolysis in the cell 10 to be improved.

[0068] In the water electrolysis system 1, the reaction rate of electrolysis in the anode catalyst layer 61 is often slower than the reaction rate of the reduction reaction in the cathode catalyst layer 71. For this reason, there are situations in which the treatment rate of the entire water electrolysis system 1 is rate-limited by the reaction rate on the anode side. As in the above embodiment, if the hydrophilicity of the mesh plate 80 used in the anode-side porous transport layer 62 is improved to increase the reaction rate of electrolysis in the anode catalyst layer 61, the treatment rate of the entire water electrolysis system 1 can be improved.

[0069] 4. Modifications Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0070] In the above embodiment, in the ultrasonic treatment step of step S23, ultrasonic waves are applied from the ultrasonic vibrator 92 to the mesh plate 80 via the pretreatment tank 91 and water. However, ultrasonic waves may be applied directly to the mesh plate 80 by connecting the ultrasonic vibrator 92 to the mesh plate 80, without passing through the pretreatment tank 91 and water.

[0071] In the above embodiment, in the storage step of step S23, the mesh plate 80 is stored in the pretreatment tank 91. However, the mesh plate 80 may be transferred to a water tank other than the pretreatment tank 91 and stored in a state where it is immersed in water stored in the water tank.

[0072] In the above embodiment, the present invention has been described as being applied to a PEM (Proton Exchange Membrane) type water electrolysis apparatus 1. However, the present invention may also be applied to water electrolysis apparatuses other than the PEM type, such as an AEM (Anion Exchange Membrane) type water electrolysis apparatus.

[0073] Furthermore, when the present invention is applied to an AEM-type water electrolysis apparatus, the liquid stored in the pretreatment tank 91 when pretreatment of the mesh plate 80 is performed may be a KOH aqueous solution.

[0074] In the above embodiment, the mesh plate 80 used in the water electrolysis apparatus 1 is pretreated. However, a similar method may be used to pretreat a mesh plate used in a fuel cell. In a fuel cell, oxygen is supplied from the outside and water generated in the catalyst layer is discharged from the cathode side. Therefore, even when the present invention is applied to a mesh plate used on the cathode side of a fuel cell, the exchange of water and oxygen can be promoted, thereby improving the efficiency of the electrochemical reaction.

[0075] Furthermore, a mesh plate used in a liquid organic hydrogen carrier (LOHC) process for producing an organic hydride (e.g., toluene-methylcyclohexane) by hydrogenating an aromatic compound such as toluene may be subjected to a pretreatment similar to that described above.

[0076] Furthermore, the elements appearing in the above-described embodiments and modifications may be combined as appropriate or some may be deleted within the scope of not causing any contradiction.

[0077] 1: Water electrolysis device 10: Cell 20: Separator 30: Cell stack 40: Power supply device 41: Control circuit 51: Electrolyte membrane 61: Anode catalyst layer 62: Porous transport layer 71: Cathode catalyst layer 72: Gas diffusion layer 80: Mesh plate 90: Pretreatment device 91: Pretreatment tank 92: Ultrasonic vibrator 93: Controller E: Voltage value I: Current density t: Elapsed time

Claims

1. A pretreatment method for treating a mesh plate, which is used in a cell for performing an electrochemical reaction and has water permeability, air permeability, and electrical conductivity, before being incorporated into the cell, the pretreatment method comprising an ultrasonic treatment step of applying ultrasonic waves to the mesh plate while immersing the mesh plate in water.

2. A pretreatment method according to claim 1, wherein the mesh plate has a plating on its surface, and the intensity of the ultrasonic waves is 2000 W / m ２ or more and 3500 W / m ２ The pre-processing method is as follows.

3. A pretreatment method according to claim 1 or 2, further comprising a storage step of storing the mesh plate immersed in water after the ultrasonic treatment step.

4. A pretreatment method according to any one of claims 1 to 3, wherein the mesh plate is made of titanium or a titanium alloy and has a platinum-plated surface.

5. A pretreatment method according to any one of claims 1 to 4, wherein the mesh plate is used as a porous transport layer on the anode side of a cell for performing water electrolysis.

6. A cell for performing an electrochemical reaction, comprising: an electrolyte membrane; a catalyst layer formed on the surface of said electrolyte membrane; and a mesh plate laminated on the surface of said catalyst layer, said mesh plate having water permeability, air permeability, and electrical conductivity, wherein, when E1 is the moving average value of the voltage value 10 hours after the start of current flow and E2 is the moving average value of the voltage value 50 hours after the start of current flow, E1 / E2 is 1.5 or less.

Images