Electrochemical cell

Abstract

The present invention provides an electrochemical cell equipped with a conductive plate in the anode section that does not require surface treatment and offers excellent productivity. [Solution] An electrochemical cell comprising an anode portion and a cathode portion sandwiching an electrolyte membrane, wherein a first fluid mainly composed of water is supplied to the anode portion, and the water is electrolyzed between the anode portion and the cathode portion to generate protons, the anode portion comprising a first conductive plate formed of a composite material containing a first resin and a first carbon material.

Description

[Technical Field]

[0001] This disclosure relates to an electrochemical cell. This application claims priority under Japanese Patent Application No. 2024-051443 dated 27 March 2024, and all provisions contained herein are incorporated herein by reference. [Background technology]

[0002] Patent Document 1 discloses a proton-conducting electrochemical cell that generates protons from water. This electrochemical cell comprises an anode portion and a cathode portion sandwiching an electrolyte membrane. The anode portion comprises an anode facing the first surface of the electrolyte membrane and an electrically conductive end plate. The cathode portion comprises a cathode facing the second surface of the electrolyte membrane and an electrically conductive end plate. Each end plate functions as a conductive plate for applying voltage to the electrochemical cell.

[0003] A first fluid containing water is supplied to the anode section. By applying a direct current between the end plate of the anode section and the end plate of the cathode section, protons are generated from the water contained in the first fluid. In Patent Document 1, hydrogen is stably stored by hydrogenating a hydride such as toluene with the generated protons. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-109986 [Overview of the project]

[0005] The electrochemical cell of the present disclosure comprises an anode portion and a cathode portion sandwiching an electrolyte membrane, and supplies a first fluid mainly composed of water to the anode portion, and generates protons by electrolyzing the water between the anode portion and the cathode portion, wherein the anode portion comprises a first conductive plate formed of a composite material including a first resin and a first carbon material. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a diagram illustrating the operating principle of the electrochemical cell described in the embodiment. [Figure 2] Figure 2 is an exploded perspective view of the electrochemical cell described in the embodiment. [Figure 3] Figure 3 is an explanatory diagram illustrating the arrangement of the second porous layer in the electrochemical cell described in the embodiment. [Figure 4] Figure 4 is a graph showing the relationship between the pH of the electrolyte solution and the corrosion current density in Test Example 2. [Figure 5] Figure 5 is a graph showing the relationship between the electrical conductivity of the electrolyte solution and the corrosion current density in Test Example 2. [Figure 6] Figure 6 is a graph showing the relationship between the operating time of the electrochemical cell and the amount of thinning of the first conductive plate in Test Example 3. [Figure 7] Figure 7 is a schematic diagram of the test apparatus for Test Example 4. [Figure 8] Figure 8 is a graph showing the relationship between compressive strain and surface pressure in Test Example 4. [Modes for carrying out the invention]

[0007] [Issues this disclosure aims to address] The conductive plate, which is the end plate of the anode part in Patent Document 1, is formed of a metal such as titanium. Metals such as titanium are difficult to permeate the first fluid, can prevent the leakage of the first fluid from the anode part, and have excellent mechanical strength. However, for a conductive plate formed of a metal such as titanium, a surface treatment for coating with a metal such as platinum is required to enhance oxidation resistance. Surface treatments such as plating are complicated and reduce the productivity of the electrochemical cell including the cost.

[0008] One of the objectives of the present disclosure is to provide an electrochemical cell including a conductive plate of an anode part that does not require surface treatment and has excellent productivity.

[0009] [Effects of the Present Disclosure] The electrochemical cell of the present disclosure includes a first conductive plate that does not require surface treatment and has excellent productivity.

[0010] [Description of Embodiments of the Present Disclosure] First, the embodiments of the present disclosure will be listed and described.

[0011] <1>The proton-conductive electrochemical cell of the present disclosure includes an anode part and a cathode part sandwiching an electrolyte membrane, and is an electrochemical cell that supplies a first fluid mainly composed of water to the anode part and electrolyzes the water between the anode part and the cathode part to generate protons, wherein the anode part includes a first conductive plate formed of a composite material including a first resin and a first carbon material.

[0012] In the first conductive plate formed of a composite material, the electrical conductivity of the first conductive plate is increased by the first carbon material. This first conductive plate does not require a surface treatment such as plating formed on a metal conductive plate, and is excellent in productivity including cost. In the first conductive plate formed of a composite material, leakage of the first fluid outside the anode portion can be prevented. When a plurality of electrochemical cells are stacked, the first resin of the first conductive plate in the anode portion prevents the first fluid from leaking to the cathode portion adjacent to the anode portion. The first resin improves the strength of the first conductive plate and reduces the oxidation of the first carbon material by the first fluid.

[0013] Since the composite material can be mold-formed, it is easy to obtain a three-dimensional first conductive plate having, for example, grooves formed to smooth the flow of the first fluid.

[0014] <2>In the electrochemical cell described in <1> above, the first carbon material may include graphite, and the graphitization degree in the first conductive plate may be 0.5 or more.

[0015] Although water, which is the main component of the first fluid, is generally an electrical insulator, the electrical conductivity of the first fluid may increase due to impurity ions eluted from the constituent members during operation. When the voltage applied to the first conductive plate is high, for example, when the voltage applied to the first conductive plate is 1.7 V or more, the first carbon material in the composite material may be oxidized by the first fluid mixed with the impurity ions, that is, the first conductive plate may corrode. On the other hand, a first conductive plate having a graphitization degree of 0.5 or more is less likely to corrode. Therefore, the electrical conductivity of the first conductive plate is likely to be maintained. Even with long-term use, the decrease in the thickness of the first conductive plate due to corrosion of the first conductive plate is likely to be small. Therefore, the electrochemical cell described in <2> above is likely to maintain the performance of electrolyzing water.

[0016] <3>In the electrochemical cell described in <1> or <2> above, the electrical conductivity of the first fluid may be 200 μS / cm or less.

[0017] If the electrical conductivity of the first fluid is 200 μS / cm (microsiemens per centimeter) or less, the first carbon material in the composite material is less likely to be oxidized by the first fluid.

[0018] <4> the above <1> from <3> In an electrochemical cell as described in any of the above, the hydrogen ion concentration of the first fluid may be 4 or higher.

[0019] If the hydrogen ion concentration of the first fluid, i.e., the pH, is 4 or higher, the first carbon material in the composite material is less likely to be oxidized by the first fluid.

[0020] <5> the above <1> from <4> In an electrochemical cell as described in any of the above, the content of the first carbon material in the first conductive plate may be 70% by mass or more, when the mass of the first conductive plate is 100% by mass.

[0021] If the content of the first carbon material in the first conductive plate is 70% by mass or more, the first conductive plate has high electronic conductivity and excellent electrical conductivity.

[0022] <6> the above <1> from <5> In an electrochemical cell as described in any of the above, a second fluid containing an organic compound having an unsaturated bond may be circulated in the cathode section.

[0023] the above <6> In the electrochemical cell described herein, an organic compound having an unsaturated bond is supplied to the cathode, and a hydride can be produced by adding a proton generated at the anode to the organic compound. This electrochemical cell can produce hydrides such as methylcyclohexane from toluene, for example. Such an electrochemical cell can be suitably used in a hydrogen carrier production apparatus.

[0024] <7> the above <1> from <6> In an electrochemical cell as described in any of the above, the cathode portion comprises a second conductive plate formed of a composite material containing a second resin and a second carbon material, wherein the second carbon material contains graphite, and the content ratio of the second carbon material in the second conductive plate may be 70% by mass or more when the mass of the second conductive plate is 100% by mass.

[0025] The second conductive plate is formed from a composite material and contains 70% or more by mass of a secondary carbon material containing graphite. This enhances the electrical conductivity of the second conductive plate due to the secondary carbon material, while the secondary resin reduces leakage of the secondary fluid outside the cathode. When multiple electrochemical cells are stacked, the secondary resin of the second conductive plate in the cathode prevents the secondary fluid from leaking to the anode adjacent to the cathode.

[0026] Since the above composite material is moldable, a second conductive plate with a three-dimensional shape, such as a grooved plate, can be molded with high precision. Furthermore, since the resin and graphite are resistant to the above organic compounds, the second conductive plate is less likely to be damaged by the above organic compounds contained in the second fluid.

[0027] When multiple electrochemical cells are stacked, the first conductive plate of one adjacent electrochemical cell and the second conductive plate of the other electrochemical cell are shared. In other words, the front side of one conductive plate functions as the first conductive plate, and the back side functions as the second conductive plate; that is, one conductive plate functions as a dipole plate.

[0028] <8> the above <7> In the electrochemical cell described above, the second resin may be at least one selected from the group consisting of polyester resin, polyamide resin, polyacetal resin, phenolic resin, polyvinylidene chloride resin, polyvinylidene fluoride resin, polytetrafluoroethylene resin, epoxy resin, polyoxymethylene resin, and polyphenylene sulfide resin.

[0029] Since the resins listed above are resistant to the above-mentioned organic compounds, the second conductive plate is less likely to be damaged by the second fluid.

[0030] <9> the above <1> from <8> In an electrochemical cell as described in any of the above, the anode portion comprises a first porous layer formed of a conductive material, and the average thickness of the first porous layer may be 0.20 mm or more and 0.40 mm or less.

[0031] If the potential of the first conductive plate becomes sufficiently high to oxidize the first carbon material within it, the first conductive plate may corrode. If the thickness of the first porous layer at the anode is 0.20 mm or more, the distance over which protons generated by the corrosion reaction of the first conductive plate reach the cathode increases. This increased distance increases the resistance to proton movement. In a first conductive plate with high proton movement resistance, an additional voltage is required to oxidize the first carbon material within it. In an electrochemical cell operating under normal conditions, this voltage is not applied. Therefore, if the average thickness of the first porous layer is 0.20 mm or more, the first conductive plate is less likely to corrode. If the thickness is 0.40 mm or less, the increase in electrical resistance due to the first porous layer is reduced. The first porous layer at the anode can also be expected to have the effect of homogenizing the flow of the first fluid at the anode.

[0032] <10> the above <9> In the electrochemical cell described above, the first porous layer may comprise a substrate formed from a metal and a coating formed on the surface of the substrate. The metal comprises at least one selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, the form of the substrate is a fiber aggregate, a porous sintered body, a foamed molded body, or expanded metal, and the coating comprises platinum.

[0033] the above <10> The first porous layer having the configuration described is resistant to the first fluid. Therefore, the first porous layer is less likely to be damaged by the first fluid.

[0034] <11> the above <1> from <10> In an electrochemical cell as described in any of the above, the cathode portion comprises a second porous layer formed of a conductive material, and the compressive strain of the second porous layer in the cathode portion may be 0.3 or more and 0.8 or less.

[0035] The second porous layer, which satisfies the above compressive strain, exhibits excellent elastic deformability. As described above, even if the thickness of the first conductive plate decreases due to long-term use, the elastic deformation of the second porous layer makes it difficult for gaps to form between adjacent components constituting the electrochemical cell. In other words, the state in which the first conductive plate, the first porous layer, the electrolyte membrane, the second porous layer, and the second conductive plate are in surface contact is easily maintained. If the components of the electrochemical cell are subjected to compressive stress during assembly or stress due to thermal expansion and contraction during operation, it is expected that the second porous layer will alleviate this stress, thereby reducing the stress that can be applied to the first conductive plate. In such an electrochemical cell, damage such as cracking of the first conductive plate is less likely to occur.

[0036] The second porous layer in the cathode section homogenizes the flow of the second fluid in the cathode section. If the second porous layer in the cathode section is not elastically deformable, a gap will form between the second porous layer and the electrolyte membrane during operation, resulting in uneven flow of the second fluid. In contrast, if the second porous layer has excellent elastic deformability, it will adhere closely to the electrolyte membrane, making it less likely for a gap to form between the second porous layer and the electrolyte membrane. If such an electrochemical cell is used in a hydrogen carrier production device, the amount of hydride produced can be increased.

[0037] <12> the above <11> In the electrochemical cell described above, the second porous layer may include a nonwoven fabric having carbon fibers.

[0038] Nonwoven fabrics containing carbon fibers have high elastic deformation capacity. The cushioning properties of the second porous layer make it easier to prevent damage to the first conductive plate, such as cracking.

[0039] [Details of the embodiments of this disclosure] Specific examples of the electrochemical cells of this disclosure will be described with reference to the drawings. Identical reference numerals in the drawings indicate the same or corresponding parts. The dimensions of the components shown in each drawing are for illustrative purposes only and do not necessarily represent actual dimensions. The present invention is not limited to these examples and is intended to include all modifications within the meaning and scope of the claims as indicated by the claims.

[0040] <Embodiment 1> ≪Overview of Organic Hydride Manufacturing Equipment≫ Figure 1 is a schematic diagram of an organic hydride production apparatus 100 equipped with a proton-conducting electrochemical cell 1. In this example, the organic hydride production apparatus 100 supplies a first fluid 101 stored in a first tank 101T and a second fluid 102 stored in a second tank 102T to the electrochemical cell 1. The electrochemical cell 1 comprises an anode section 3 and a cathode section 4 separated by an electrolyte membrane 2. A DC power supply (not shown) is connected to the anode section 3 and the cathode section 4. The anode of the DC power supply is connected to the anode section 3, and the cathode of the DC power supply is connected to the cathode section 4.

[0041] The first fluid 101 is supplied to the anode section 3 through the first supply pipe 101A. The first supply pipe 101A is equipped with a first pump 101P that pressurizes the first fluid 101 to the anode section 3. The anode section 3 is equipped with a first catalyst layer 30. Through an electrochemical reaction, protons (H) are converted from water (H2O) contained in the first fluid 101. + ) and oxygen (O2) and electrons (e - ) and are generated. The protons move to the cathode section 4 through the electrolyte membrane 2. Electrons generated at the anode flow to the cathode via the DC power supply. The first fluid 101 in the anode section 3 is discharged to the first tank 101T through the first discharge pipe 101B.

[0042] The first fluid 101 is a fluid mainly composed of water. The first fluid 101, mainly composed of water, is pure water or water in which the total concentration of impurities is 0.1 mM (millimolar) or less. When the electrochemical cell 1 is started up, the first fluid 101 is, for example, pure water. Commercially available pure water can be used. However, even if the first fluid 101 is pure water when the electrochemical cell 1 is started up, impurity ions originating from the components of the electrochemical cell 1 may be mixed into the first fluid 101 as it circulates to the electrochemical cell 1.

[0043] The second fluid 102 is supplied to the cathode section 4 through the second supply pipe 102A. The second supply pipe 102A is equipped with a second pump 102P that pressurizes the second fluid 102 to the cathode section 4. The cathode section 4 is equipped with a second catalyst layer 40. Through an electrochemical reaction, the hydride substances contained in the second fluid 102 are hydrogenated in the second catalyst layer 40 by combining protons that have permeated the electrolyte membrane 2 with electrons supplied from a DC power source, thereby generating hydrides. The second fluid 102 containing the hydrides is discharged from the cathode section 4 to the second tank 102T through the second discharge pipe 102B.

[0044] The hydrogenated substance contained in the second fluid 102 is, for example, an organic compound having an unsaturated bond. Organic compounds having an unsaturated bond include, for example, monocyclic aromatic compounds, bicyclic aromatic compounds, tricyclic aromatic compounds, or aromatic polymers. Specific examples of these substances include benzene, toluene, xylene, ethylbenzene, mesitylene, naphthalene, methylnaphthalene, anthracene, or tetralin. The hydrogenated substance exemplified in Figure 1 is toluene (indicated as TOL in the figure). The hydride produced by the hydrogenation of toluene is methylcyclohexane (hereinafter referred to as MCH). In this example, the electrochemical cell 1 contains toluene as the second fluid 102 and is also called an MCH electrosynthesis cell. The reactions in the anode 3 and cathode 4 are as follows. 3H2O → 1.5O2 + 6H + +6e - Toluene + 6H + +6e - →Methylcyclohexane

[0045] When water electrolysis is performed in electrochemical cell 1, hydrogen (H2) is generated from protons in the cathode section 4. In electrochemical cell 1 performing water electrolysis, it is not necessary to circulate a second fluid 102 in the cathode section 4. Water that has permeated from the anode section 3 through the electrolyte membrane 2 flows into the cathode section 4. Therefore, electrochemical cell 1 performing water electrolysis is configured to discharge the hydrogen generated from protons along with water from the cathode section 4.

[0046] ≪Basic Configuration of an Electrochemical Cell≫ As shown in Figure 2, the electrochemical cell 1, which comprises an anode 3 and a cathode 4, includes an electrolyte membrane 2, a first flow field 5, a second flow field 6, a first catalyst layer 30, and a second catalyst layer 40.

[0047] The electrolyte membrane 2 is formed of a material that selectively permeates protons. The electrolyte membrane 2 separates the first fluid 101 and the second fluid 102 within the electrochemical cell 1. The thickness of the electrolyte membrane 2 is, for example, 5 μm to 350 μm, 10 μm to 300 μm, or 20 μm to 250 μm.

[0048] The first flow field 5 is the space through which the first fluid 101 flows in the anode section 3. The inlet 5A and outlet 5B of the first flow field 5 are connected to the first supply pipe 101A and the first discharge pipe 101B, respectively, as shown in Figure 1. The first flow field 5 causes the first fluid 101 to flow so as to be in contact with the first surface 21 of the electrolyte membrane 2. The anode section 3 in this example comprises a first conductive plate 31, a first porous layer 32, and a frame seal section 33.

[0049] The first conductive plate 31 is a conductive plate material facing the first surface 21 of the electrolyte membrane 2. The first conductive plate 31 has the function of applying voltage to the electrochemical cell 1. The first conductive plate 31 also has the function of containing the first fluid 101 within the electrochemical cell 1. An electrode plate (not shown) is arranged on the surface of the first conductive plate 31 opposite to the first porous layer 32. The anode of a DC power supply (not shown) is connected to the electrode plate.

[0050] The first porous layer 32 is a conductive plate material having multiple pores, and is placed between the first conductive plate 31 and the first surface 21. Within the electrochemical cell 1, the first porous layer 32 has the function of diffusing the first fluid 101 supplied to the anode 3 throughout the first flow field 5.

[0051] The frame seal portion 33 surrounds the outer periphery of the first porous layer 32. The frame seal portion 33 prevents the first fluid 101 from leaking out from the outer periphery of the first porous layer 32. Therefore, the first flow field 5 in this example is mainly formed from the space between the first surface 21 of the electrolyte membrane 2 and the first conductive plate 31, surrounded by the frame seal portion 33. Because the first porous layer 32 is positioned in this space, the first fluid 101 can utilize the pores of the first porous layer 32 as a flow path.

[0052] The first catalyst layer 30, positioned in the first flow field 5, is in contact with or close to the first surface 21 of the electrolyte membrane 2. The first catalyst layer 30 promotes the electrolysis of water contained in the first fluid 101, generating protons, oxygen, and electrons. In this example, the first catalyst layer 30 is integrally formed with the first surface 21 of the electrolyte membrane 2. The first catalyst layer 30 may also be integrally formed with at least the portion of the first porous layer 32 that is in contact with the electrolyte membrane 2. The first catalyst layer 30 may be a component independent of the electrolyte membrane 2 and the first porous layer 32. In that case, the first catalyst layer 30 is positioned between the electrolyte membrane 2 and the first porous layer 32. The first catalyst layer 30 contains a catalyst. The catalyst is, for example, a noble metal oxide-based catalyst such as RuO2 or IrO2. This catalyst may have a structure in which a noble metal oxide is dispersed and supported on a substrate made of metal wire or metal mesh, or a structure in which a noble metal oxide is coated on the substrate. The first catalyst layer 30 may contain an ionomer that adheres the catalyst to the substrate. The metal constituting the above substrate is, for example, one metal selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ta, and W, or an alloy mainly composed of the above one metal. When IrO2 is used as a catalyst, in a structure in which a thin film of IrO2 is coated on the above substrate, the amount of expensive precious metals used is reduced, thereby lowering manufacturing costs.

[0053] The second flow field 6 is the space through which the second fluid 102 flows in the cathode section 4. The inlet 6A and outlet 6B of the second flow field 6 are connected to the second supply pipe 102A and the second discharge pipe 102B, respectively, as shown in Figure 1. The second flow field 6 causes the second fluid 102 to flow so as to be in contact with the second surface 22 of the electrolyte membrane 2. The second surface 22 is the surface of the electrolyte membrane 2 opposite to the first surface 21. The cathode section 4 in this example comprises a second conductive plate 41, a second porous layer 42, and a frame seal section 43.

[0054] The second conductive plate 41 is a conductive plate material facing the second surface 22 of the electrolyte membrane 2. The second conductive plate 41 has the function of applying voltage to the electrochemical cell 1. The second conductive plate 41 also has the function of containing the second fluid 102 within the electrochemical cell 1. An electrode plate (not shown) is arranged on the side of the second conductive plate 41 opposite to the second porous layer 42. The cathode of a DC power supply (not shown) is connected to the electrode plate.

[0055] The second porous layer 42 is a conductive plate material having a plurality of voids, and is positioned between the second conductive plate 41 and the second surface 22. The second porous layer 42 has the function of diffusing the second fluid 102 supplied to the cathode section 4 throughout the second flow field 6.

[0056] The frame seal portion 43 surrounds the outer periphery of the second porous layer 42. The frame seal portion 43 prevents the second fluid 102 from leaking out from the outer periphery of the second porous layer 42. Therefore, the second flow field 6 in this example is mainly formed from the space between the second surface 22 of the electrolyte membrane 2 and the second conductive plate 41, surrounded by the frame seal portion 43. Because the second porous layer 42 is positioned in this space, the second fluid 102 can utilize the pores of the second porous layer 42 as a flow path.

[0057] The second catalyst layer 40, positioned in the second flow field 6, is in contact with or close to the second surface 22 of the electrolyte membrane 2. The second catalyst layer 40 promotes the reaction between the hydride contained in the second fluid 102 and protons from the anode portion 3, resulting in the production of hydrides. In this example, the second catalyst layer 40 is integrally formed with the second surface 22 of the electrolyte membrane 2. The second catalyst layer 40 may also be integrally formed with at least the portion of the second porous layer 42 that is in contact with the electrolyte membrane 2. The second catalyst layer 40 may be a component independent of the electrolyte membrane 2 and the second porous layer 42. In that case, the second catalyst layer 40 is positioned between the electrolyte membrane 2 and the second porous layer 42. The second catalyst layer 40 contains a catalyst. The catalyst is, for example, a composition containing a first catalyst metal and a second catalyst metal. The first catalyst metal contains at least one of the noble metals Pt and Pd. The second catalyst metal is one or more metals selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Ru, Sn, W, Re, Pb, and Bi. The catalyst may have a carbon support on which the above metal or metal oxide is supported. The second catalyst layer 40 may contain an ionomer that adheres the catalyst to the support. Known catalysts can be used.

[0058] The organic hydride manufacturing apparatus 100 shown in Figure 1 typically comprises a laminate in which multiple electrochemical cells 1 are stacked. In the laminate, the first conductive plate 31 of one of two adjacent electrochemical cells 1 and the second conductive plate 41 of the remaining electrochemical cell 1 form a single dipole plate. In the dipole plate, the first surface of the dipole plate functions as the first conductive plate 31, and the second surface opposite the first surface functions as the second conductive plate 41. Therefore, the first porous layer 32 is placed on the first surface of the dipole plate, and the second porous layer 42 is placed on the second surface of the dipole plate. The first and second ends of the laminate are respectively occupied by the first conductive plate 31 and the second conductive plate 41, rather than a dipole plate.

[0059] <<Components of each part of an electrochemical cell>> The following describes in detail the configuration of each part of electrochemical cell 1.

[0060] [First conductive plate] The first conductive plate 31 is required to be formed from a material that does not readily react with substances contained in the first fluid 101. The first conductive plate 31 is, for example, a plate material formed from a composite material of a first carbon material and a first resin. The first carbon material is, for example, a carbon-based material such as graphite or carbon black. The first resin is, for example, at least one selected from the group consisting of polyester resin, polyamide resin, polyacetal resin, phenolic resin, polyvinylidene chloride resin, polyvinylidene fluoride resin, polytetrafluoroethylene resin, epoxy resin, polyoxymethylene resin, and polyphenylene sulfide resin.

[0061] The first conductive plate 31 can be manufactured, for example, by hot-pressing a mixture of a first carbon material and a first resin. Alternatively, the first conductive plate 31 may be manufactured by impregnating a porous graphite plate made of the first carbon material with the first resin.

[0062] In the first conductive plate 31 formed from a composite material, the electrical conductivity of the first conductive plate 31 is increased by the first carbon material, and the first resin prevents the first fluid 101 from leaking out of the anode portion 3. When multiple electrochemical cells 1 are stacked, the first conductive plate 31 of the anode portion 3 prevents the first fluid 101 from leaking to the cathode portion 4 adjacent to the anode portion 3. The first resin increases the strength of the first conductive plate 31 and reduces the oxidation of the first carbon material by the first fluid 101. By reducing oxidation, the electrical conductivity of the first conductive plate 31 due to the first carbon material is maintained. Furthermore, the first conductive plate 31 formed from a composite material is inexpensive because it does not require coating with platinum or the like, and it can be easily formed by mold molding even if it has a three-dimensional shape with grooves.

[0063] If the first carbon material contains graphite, the degree of graphitization in the first conductive plate 31 containing graphite may be, for example, 0.5 or higher. Graphite has a laminated structure in which multiple planar layer structures are bonded together by van der Waals forces. In each planar layer structure, multiple carbon atoms are connected in a hexagonal shape. The degree of graphitization is an indicator that multiple planar layer structures are regularly stacked. The degree of graphitization is determined by the Franklin P value shown in the following equation (1). (002) This refers to the interplanar spacing of carbon d, measured by XRD (X-ray diffraction). (002) This is the value. In this example, since the first conductive plate 31 is formed from a composite material of graphite and the first resin, the graphitization of the first conductive plate 31 including both graphite and the first resin is evaluated, rather than the graphitization of graphite alone.

[0064]

number

[0065] Graphite is obtained by calcining carbon in an oxygen-free environment. The calcination temperature is, for example, 1500°C or higher. The higher the calcination temperature, for example, 2000°C or above, or 3000°C or above, the higher the degree of graphitization of the graphite.

[0066] The higher the degree of graphitization of graphite, the higher its electrical conductivity. In other words, the higher the degree of graphitization of the first conductive plate 31 containing graphite, the higher the electrical conductivity of the first conductive plate 31. Our studies have shown that the higher the degree of graphitization, the less the graphite contained in the first conductive plate 31 is oxidized by the first fluid 101. Because the graphite is less likely to oxidize, the first conductive plate 31 is less likely to corrode, and the electrical conductivity of the first conductive plate 31 is easier to maintain. Therefore, the performance of the electrochemical cell 1 in electrolyzing water is easier to maintain.

[0067] Oxidation of the first carbon material can occur when the voltage applied to the first conductive plate 31 is high and the electrical conductivity of the first fluid 101 is high. In the electrochemical cell 1, water electrolysis can be performed efficiently if the potential of the first conductive plate 31 is high, such as 1.7V or higher. On the other hand, although water, which is the main component of the first fluid 101, is an insulator, impurity ions may be added to the first fluid 101 as the electrochemical cell 1 operates. These impurity ions increase the electrical conductivity of the first fluid 101. If the electrical conductivity of the first fluid 101 is too high, corrosion of the first conductive plate 31 may progress under the high potential conditions described above. If the electrical conductivity of the first fluid 101 is 200 μS / cm or less, the first carbon material in the first conductive plate 31 is less likely to be oxidized by the first fluid 101. The electrical conductivity of the first fluid 101 may be 100 μS / cm or less, or 50 μS / cm or less.

[0068] Impurity ions lower the pH of the first fluid 101. The pH of the first fluid 101 is an indicator of its electrical conductivity. Measuring the pH of the first fluid 101 is simpler than measuring its electrical conductivity. If the pH of the first fluid 101 is too low, i.e., if the electrical conductivity of the first fluid 101 is too high, corrosion of the first conductive plate 31 may progress. If the pH of the first fluid 101 is 4 or higher, the first carbon material in the first conductive plate 31 is less likely to be oxidized by the first fluid 101. The pH of the first fluid 101 may be 5 or higher, or even 6 or higher. When pure water is used as the first fluid 101 at the start of the electrochemical cell 1, the upper limit of the pH of the first fluid 101 is 7. Since the pH value has an error depending on the measurement method, the pH of the first fluid 101 may slightly exceed 7.

[0069] The electrical conductivity or pH of the first fluid 101 can be measured by sampling the first fluid 101 along its flow path. For example, a sampling path can be provided branching off from the first supply pipe 101A in Figure 1, and a measuring device can be installed in that sampling path, or a measuring device can be installed in the first tank 101T that stores the first fluid 101. With such a configuration, the electrical conductivity or pH of the first fluid 101 can be measured over time.

[0070] To reduce the electrical conductivity of the first fluid 101 in contact with the first conductive plate 31 and bring its pH closer to 7, a filter to remove impurity ions can be placed in the circulation path of the first fluid 101. Alternatively, instead of circulating the first fluid 101, a first fluid 101 with very few impurity ions, such as pure water, can be continuously supplied to the first flow field 5.

[0071] When the mass of the first conductive plate 31 is taken as 100% by mass, the content of the first carbon material in the first conductive plate 31 is, for example, 70% by mass or more. If the content of the first carbon material in the first conductive plate 31 is 70% by mass or more, the first conductive plate 31 has high electrical conductivity. The content of the first carbon material may be 75% by mass or more, or 80% by mass or more. Since the first conductive plate 31 is formed from a composite material, the first conductive plate 31 contains a predetermined amount or more of the first resin. Therefore, the upper limit of the content of the first carbon material is, for example, 95.5% by mass. The range of the content of the first carbon material is, for example, 70% by mass or more and 95.5% by mass or less, 80% by mass or more and 95% by mass or less, or 85% by mass or more and 95% by mass or less. The content of the first resin is the value obtained by subtracting the content of the first carbon material from 100% by mass.

[0072] [First porous layer] The first porous layer 32 in this example is a porous plate material formed from a metallic material. The first porous layer 32 comprises, for example, a three-dimensional mesh structure substrate and a coating formed on the surface of the substrate. The metal includes at least one selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. Alloys are also included in the metal. The first porous layer 32 formed from the above metal is resistant to the first fluid 101. Such a first porous layer 32 is not easily damaged by the first fluid 101. The form of the substrate is a fiber aggregate such as a nonwoven fabric, a porous sintered body, a foamed molded body, or expanded metal. The coating includes, for example, platinum. The substrate may be a stack of multiple mesh plates having meshes of different sizes, or a stack of multiple mesh plates having meshes of different shapes.

[0073] The first porous layer 32 is sandwiched between the electrolyte membrane 2 and the first conductive plate 31. Being sandwiched between the electrolyte membrane 2 and the first conductive plate 31, the first porous layer 32 is pressed against them. Depending on the material of the first porous layer 32, it may be compressed by this pressing. A first porous layer 32 formed from a metallic material has multiple pores but is resistant to deformation.

[0074] The average thickness of the first porous layer 32 sandwiched between the electrolyte membrane 2 and the first conductive plate 31 in the electrochemical cell 1 is, for example, 0.20 mm or more and 0.40 mm or less. If the first porous layer 32 is formed of, for example, a metallic material and is not easily deformed by the above-mentioned pressure, the average thickness of the first porous layer 32 when not sandwiched between the electrolyte membrane 2 and the first conductive plate 31 is substantially equal to the average thickness of the first porous layer 32 when sandwiched between the electrolyte membrane 2 and the first conductive plate 31. The average thickness of the first porous layer 32 is the average of the thicknesses at three or more different points.

[0075] If the average thickness of the first porous layer 32 is 0.20 mm or more, the gap between the first conductive plate 31 and the electrolyte membrane 2 becomes sufficiently large. In other words, a first flow field 5 of sufficient size is formed within the anode portion 3, making it easier for the first fluid 101 to diffuse throughout the first flow field 5. If the thickness of the first porous layer 32 is 0.20 mm or more, the distance over which protons generated by the corrosion reaction of the first conductive plate 31 reach the cathode portion 4 becomes longer. This increased distance increases the resistance to proton movement. In the first conductive plate 31, where the movement resistance is high, an additional voltage equal to the movement resistance is required to oxidize the carbon material in the first conductive plate 31. In an electrochemical cell 1 under normal operation, the above voltage is not applied. Therefore, if the average thickness of the first porous layer 32 is 0.20 mm or more, the first conductive plate 31 is less likely to corrode.

[0076] If the average thickness of the first porous layer 32 is 0.40 mm or less, the increase in electrical resistance due to the first porous layer 32 is reduced. If the average thickness of the first porous layer 32 is 0.40 mm or less, the first flow field 5 does not become too large, so the flow of the first fluid 101 in the anode 3 can be made uniform. Since a thinner metal first porous layer 32 tends to be lighter, the assembly workability of the electrochemical cell 1 is improved. A thin first porous layer 32 can reduce the amount of material used in the electrochemical cell 1 and make the electrochemical cell 1 lighter. The average thickness of the first porous layer 32 may be 0.22 mm or more and 0.40 mm or less, or 0.25 mm or more and 0.40 mm or less.

[0077] The porosity of the first porous layer 32 within the electrochemical cell 1 is, for example, 60% to 90%. Since the elastic deformability of the first porous layer 32 formed from a metallic material is low, the porosity of the first porous layer 32 removed from the electrochemical cell 1 can be considered as the porosity of the first porous layer 32 within the electrochemical cell 1. If the porosity is 60% or more, the first fluid 101 diffuses easily throughout the first flow field 5. If the porosity is 90% or less, the strength of the first porous layer 32 tends to be high. The porosity of the first porous layer 32 may be, for example, 65% to 85%, or 68% to 80%.

[0078] [Frame seal portion of the anode] The size of the frame seal portion 33 of the anode portion 3 should be selected according to the size of the first conductive plate 31 and the first porous layer 32. In this example, the size of the window portion of the frame seal portion 33 roughly corresponds to the size of the first porous layer 32, and the size of the outer edge of the frame seal portion 33 roughly corresponds to the size of the first conductive plate 31. The frame seal portion 33 is formed of an electrically insulating material that has resistance to the first fluid 101. Examples of electrically insulating materials include epoxy resin, phenolic resin, polyamide resin such as PA6 or PA66, polyoxymethylene resin, fluororesin, and polyphenylene sulfide resin.

[0079] [Second conductive plate] In this example, the second conductive plate 41 is required to be formed from a material that does not react easily with the organic compounds contained in the second fluid 102. The second conductive plate 41 is, for example, a plate material formed from a composite material of a second carbon material and a second resin. The second conductive plate 41 formed from the composite material can be manufactured by the same method as the first conductive plate 31. The second carbon material is, for example, a carbon-based material such as graphite or carbon black. The second carbon material imparts electrical conductivity to the second conductive plate 41. The second resin is at least one selected from the group consisting of polyester resin, polyamide resin, polyacetal resin, phenolic resin, polyvinylidene chloride resin, polyvinylidene fluoride resin, polytetrafluoroethylene resin, epoxy resin, polyoxymethylene resin, and polyphenylene sulfide resin. Since the resins listed above are resistant to organic compounds, the second conductive plate 41 is less likely to be damaged by the second fluid 102.

[0080] The second conductive plate 41 contains graphite as a secondary carbon material, and the graphite content in the second conductive plate 41 may be 70% by mass or more, when the mass of the second conductive plate 41 is taken as 100% by mass. By forming the second conductive plate 41 from a composite material and containing 70% by mass or more of a secondary carbon material containing graphite, the electrical conductivity of the second conductive plate 41 is increased by the secondary carbon material, and the leakage of the second fluid 102 outside the cathode portion 4 can be reduced by the second resin. When multiple electrochemical cells 1 are stacked, the second resin of the second conductive plate 41 in the cathode portion 4 prevents the leakage of the second fluid 102 to the anode portion 3 adjacent to the cathode portion 4. The second conductive plate 41 is also strengthened by the second resin and can be easily formed by mold molding even if it has a three-dimensional shape with grooves.

[0081] The second conductive plate 41 may have the same composition as the first conductive plate 31. In this case, one conductive plate can be used as a dipole plate. The dipole plate is a conductive plate that serves as both the first conductive plate 31 and the second conductive plate 41 in two adjacent electrochemical cells 1.

[0082] ≪Composition of the second porous layer≫ The second porous layer 42 is a porous plate material formed from a conductive material. The second porous layer 42 is configured to have high elastic deformability. Inside the electrochemical cell 1, the second porous layer 42, which has high elastic deformability, is compressed by being sandwiched between the electrolyte membrane 2 and the second conductive plate 41. This compression reduces the average thickness of the second porous layer 42. The average thickness of the second porous layer 42 sandwiched between the electrolyte membrane 2 and the second conductive plate 41 inside the electrochemical cell 1 is, for example, 0.15 mm to 3.0 mm. In this specification, the average length between the electrolyte membrane 2 and the second conductive plate 41 in the electrochemical cell 1 is considered to be the average thickness of the second porous layer 42. The number of measurements required to determine the above average length is three or more points, including a measurement at the center position of the electrolyte membrane 2 in a plan view.

[0083] If the average thickness of the compressed second porous layer 42 is 0.15 mm or more, the amount of elastic deformation of the second porous layer 42 within the electrochemical cell 1 tends to be large. As a result, the second porous layer 42 tends to adhere closely to the electrolyte membrane 2 and the second conductive plate 41. If the average thickness of the second porous layer 42 is 0.15 mm or more, the gap between the second conductive plate 41 and the electrolyte membrane 2 becomes sufficiently large. In other words, a second flow field 6 of sufficient size is formed within the cathode section 4, so the second fluid 102 tends to diffuse throughout the second flow field 6. If the average thickness of the compressed second porous layer 42 is 3.0 mm or less, the electrical resistance of the second porous layer 42 and the cell resistance of the electrochemical cell 1 tend not to increase. If the average thickness of the second porous layer 42 is 3.0 mm or less, the gap between the second conductive plate 41 and the electrolyte membrane 2 does not become too large. In other words, the second flow field 6 does not become too large, so the second fluid 102 containing hydrides generated in the second catalyst layer 40 tends to be quickly discharged from the second flow field 6. The average thickness of the second porous layer 42 may be 0.15 mm or more and less than 3.0 mm, 0.2 mm or more and 2.5 mm or less, or 0.25 mm or more and 2.0 mm or less.

[0084] Figure 3 is a schematic diagram showing the stacked state of a part of the electrochemical cell 1. If there are localized gaps at the boundary 1A between the second porous layer 42 and the electrolyte membrane 2, and at the boundary 1B between the second porous layer 42 and the second conductive plate 41, it becomes difficult for the second fluid 102 to spread uniformly across the entire surface of the second catalyst layer 40. When the internal pressure of the second flow field 6 changes during the operation of the electrochemical cell 1, there is a risk that the above-mentioned localized gaps may be formed. If the compressed second porous layer 42 presses the electrolyte membrane 2 and the second conductive plate 41 with a surface pressure of a predetermined level or higher, localized gaps are less likely to form at the above boundaries 1A and 1B. With fewer gaps at boundaries 1A and 1B, the flow of the second fluid 102 tends to become more uniform. As a result, the Faraday efficiency of the electrochemical cell 1 tends to improve. The Faraday efficiency is the ratio of the amount of charge that contributed to the hydrogenation of the hydride, when the total amount of charge introduced into the electrochemical cell 1 is set to 100%. The second porous layer 42, which has high elastic deformation capacity, provides cushioning and easily reduces damage to the first conductive plate 31 and the second conductive plate 41.

[0085] The compressive strain of the second porous layer 42 when compressed within the cathode section 4 of the electrochemical cell 1 is between 0.3 and 0.8. The surface pressure acting on the compressed second porous layer 42 within the electrochemical cell 1 is, for example, 0.5 MPa or more. The upper limit of the surface pressure is, for example, 0.8 MPa. As shown in Figure 8 of Test Example 4 described later, the compressive strain increases as the surface pressure increases. Therefore, if the compressive strain of the second porous layer 42 at a surface pressure of 0.5 MPa is 0.3 or more, then the compressive strain of the second porous layer 42 within the cathode section 4 where a surface pressure of 0.5 MPa or more acts is also 0.3 or more. In this example, the compressive strain is the value obtained by dividing the decrease in thickness λ of the second porous layer 42 compressed by a surface pressure of 0.5 MPa or more and 0.8 MPa or less by the initial thickness t0 of the second porous layer 42 before compression. In other words, the reduction amount λ is expressed as t0-t1, where t0 is the initial thickness of the second porous layer 42 and t1 is the thickness of the second porous layer 42 after compression by a surface pressure of 0.5 MPa to 0.8 MPa. Therefore, the compressive strain can be calculated by (t0-t1) / t0. For example, when a second porous layer 42 with an initial thickness t0 of 1 mm is compressed with a surface pressure of 0.5 MPa, if the thickness t1 of the second porous layer 42 is 0.7 mm, the reduction amount λ is 0.3 mm. Since compressive strain = λ / t0, the compressive strain in this case is 0.3.

[0086] The thicknesses t0 and t1 of the second porous layer 42 are measured in accordance with Method A of JIS L 1096:2010. Specifically, a commercially available thickness measuring device is used to measure the thickness of the second porous layer 42 under a constant time and constant surface pressure. The above time is 10 seconds. The surface pressure used in measuring the initial thickness t0 is 0.7 kPa. The initial thickness t0 is the average value of the thickness measured at five or more points. For the measurement of thickness t1, the surface pressure is changed to, for example, 0.5 MPa, and it can be determined in the same way as the initial thickness t0. Thicknesses t0 and t1 are measured on the second porous layer 42 when it is not assembled into the electrochemical cell 1. The initial thickness t0 of the second porous layer 42 is, for example, 0.3 mm to 3.5 mm.

[0087] The second porous layer 42 having a compressive strain of 0.3 to 0.8 has excellent elastic deformability. When such a second porous layer 42 is compressed between the electrolyte membrane 2 and the second conductive plate 41, it tries to return to its original thickness, pressing the electrolyte membrane 2 and the second conductive plate 41 that sandwich the second porous layer 42 within the cathode portion 4. Therefore, the second porous layer 42 easily makes surface contact with the electrolyte membrane 2 and the second conductive plate 41. Even if the thickness of the first conductive plate 31 decreases due to corrosion from long-term use, the elastic deformation of the second porous layer 42 makes it difficult for gaps to form between adjacent members constituting the electrochemical cell 1. The compressive strain may be 0.4 or more, 0.5 or more, 0.6 or more, or 0.7 or more.

[0088] The second porous layer 42 that satisfies the above compressive strain is, for example, a nonwoven fabric containing carbon fibers. The nonwoven fabric is made by intertwining multiple independent carbon fibers and does not have bonding parts such as binders that fix the carbon fibers together. Nonwoven fabrics that do not have such bonding parts have high elastic deformability. The second porous layer 42 may also be a woven fabric containing carbon fibers, as long as the above compressive strain is satisfied. The woven fabric is made by weaving warp and weft threads of carbon fibers alternately. Woven fabrics containing carbon fibers are also called carbon cloth. Paper containing carbon fibers is not considered to satisfy the above compressive strain. Paper has multiple carbon fibers and a binder that fixes the carbon fibers. For example, when a surface pressure of 0.5 MPa is applied to paper, the compressive strain is less than 0.2 and it hardly deforms.

[0089] The second porous layer 42 may contain members with a compressive strain of less than 0.3, as long as the overall compressive strain is 0.3 or more. For example, the second porous layer 42 may be a configuration in which multiple nonwoven fabrics having different compressive strains are laminated, a configuration in which a nonwoven fabric and a woven fabric are laminated, a configuration in which a nonwoven fabric and paper are laminated, or a configuration in which a nonwoven fabric, a woven fabric and paper are laminated.

[0090] The average diameter of the carbon fibers forming the non-woven fabric is, for example, 5 μm or more and 100 μm or less. When the average diameter is 5 μm or more and 100 μm or less and the basis weight of the second porous layer 42 satisfies the range described below, the second porous layer 42 has a higher elastic deformation ability. The average diameter of the carbon fibers may be, for example, 5 μm or more and 80 μm or less, 5 μm or more and 50 μm or less, or 7 μm or more and 30 μm or less.

[0091] The average diameter of the carbon fibers is a value obtained by determining the diameter of a circle having an area equal to the area of the cross-section of the carbon fibers for each of the plurality of carbon fibers and averaging these diameters. For observing the cross-section, for example, a scanning electron microscope is used. Five or more observation fields are taken from one cross-section. The cross-sectional areas of three or more carbon fibers are determined from each observation field.

[0092] The porosity of the second porous layer 42 in the compressed state in the electrochemical cell 1 is, for example, 40% or more and 98% or less. If the porosity of the second porous layer 42 is within the above range, the second porous layer 42 has excellent elastic deformation ability while having sufficient conductivity and being likely to have pores. The porosity may be, for example, 45% or more and 97% or less, or 50% or more and 96% or less. The porosity is determined from a cross-sectional photograph of the second porous layer 42. The cross-sectional photograph is subjected to binarization processing, and the areas of the solid part and the pore part are determined. The area ratio of the pore part to the total area of the solid part and the pore part is the porosity. If the porosity of the second porous layer 42 before compression and the reduction amount of the thickness of the second porous layer 42 in the electrochemical cell 1 are known, the porosity of the second porous layer 42 in the compressed state can be determined by calculation.

[0093] The basis weight of the second porous layer 42 is, for example, 50 g / m 2 or more and 400 g / m 2 or less. If the basis weight of the second porous layer 42 is within the above range, the second porous layer 42 has excellent elastic deformation ability while having sufficient conductivity and being likely to have pores. The basis weight may be, for example, 55 g / m 2 or more and 395 g / m 2 or less, or 60 g / m 2 or more and 390 g / m 2 or less. The basis weight is, for example, 55 g / m2 More than 200g / m 2 The following, or 60g / m 2 More than 150g / m 2 The following is also acceptable. The basis weight is the mass of the second porous layer 42 per square meter. The basis weight can be obtained by dividing the mass of the second porous layer 42 by the area of ​​the second porous layer 42 when viewed from above.

[0094] [Cathode frame seal] The specifications of the frame seal portion 43 of the cathode portion 4, including its constituent materials and size, are the same as those of the frame seal portion 33 of the anode portion 3.

[0095] [Configuration of the flow path in the first flow field] The first flow field 5 may have a flow channel. By having a flow channel, the flow of the first fluid 101 in the first flow field 5 becomes smoother.

[0096] The flow channels are typically grooves formed in the first conductive plate 31. The shape, size, and arrangement of the grooves can be selected as appropriate. The groove shapes can be, for example, straight, wave-shaped, or meandering. The arrangement of the grooves can be, for example, multiple straight grooves arranged in parallel, or a comb-shaped groove as described later.

[0097] The water contained in the first fluid 101 is rapidly diffused throughout the first flow field 5 by the flow channel. The oxygen generated in the first catalyst layer 30 is rapidly discharged to the outside of the electrochemical cell 1 by the flow channel. The flow channel may also be formed in the first porous layer 32.

[0098] When the first conductive plate 31 has grooves that form a flow path, the contact area between the first conductive plate 31 and the first fluid 101 is larger compared to when it does not have grooves. Because the first conductive plate 31 contains graphite with a high degree of graphitization, the graphite is less likely to oxidize even when the contact area with the first fluid 101 is large.

[0099] [Configuration of the flow path in the second flow field] The second flow field 6 may also have a flow path. The second flow field 6 may have a groove structure comprising a first flow path and a second flow path that are independent of each other, and a region in which grooves forming the first flow path and grooves forming the second flow path are alternately arranged. For example, the first flow path comprises a plurality of parallel first grooves, and the second flow path comprises a plurality of parallel second grooves. In a plan view, at least a portion of the plurality of first grooves and at least a portion of the plurality of second grooves are arranged alternately in parallel in a direction perpendicular to the extending direction of the first and second grooves. The first and second grooves are, for example, longitudinal grooves extending from the lower end to the upper end of the second conductive plate 41.

[0100] The first channel may further include a lower lateral groove connecting the lower ends of a plurality of first grooves, and an inlet groove connecting the lower lateral groove to the inlet 6A (Figure 1). In this case, the first grooves connect to the inlet 6A. Unlike this example, each of the plurality of first grooves may be directly connected to the inlet 6A. In this case, the lower lateral groove and the inlet groove are not formed in the second conductive plate 41. The first channel may be configured such that some of the plurality of first grooves are connected to the lower lateral groove, and each of the remaining grooves is directly connected to the inlet 6A.

[0101] The second flow channel may further include an upper lateral groove connecting the upper ends of a plurality of second grooves, and an outlet groove connecting the upper lateral groove to the outlet 6B (Figure 1). In this case, the second grooves connect to the outlet 6B. Unlike this example, each of the plurality of second grooves may be directly connected to the outlet 6B. In this case, the upper lateral groove and the outlet groove are not formed in the second conductive plate 41. The second flow channel may be configured such that some of the plurality of second grooves are connected to the upper lateral groove, and each of the remaining grooves is directly connected to the outlet 6B. The configuration of the grooves connected to the inlet 6A and the configuration of the grooves connected to the outlet 6B may be the same or different.

[0102] Multiple first grooves and multiple second grooves are arranged to interlock with each other. Since the openings of the first grooves face the second porous layer 42, the second fluid 102 rapidly diffuses from the first grooves throughout the second porous layer 42. As a result, the hydride contained in the second fluid 102 is efficiently supplied to the second catalyst layer 40. Since the openings of the second grooves face the second porous layer 42, the hydride-containing second fluid 102 is rapidly recovered into the second grooves from near the second catalyst layer 40.

[0103] <Test Example 1> In Test Example 1, a first conductive plate 31 was fabricated using the following samples A and B, and the degree of graphitization of the first conductive plate 31 was measured.

[0104] [Sample A] Sample A is a first conductive plate 31 manufactured by mold molding a composite material of graphite particles and phenolic resin. The graphite particle content in Sample A was 88% by mass, and the phenolic resin content was 12% by mass.

[0105] A small piece was sampled from sample A, and the interplanar spacing d of carbon in sample A was determined by XRD. (002) The following measurements were taken. The degree of graphitization of sample A was determined by substituting the measured values ​​into equation (1) described above. The degree of graphitization of sample A was 0.644.

[0106] [Sample B] Sample B is a first conductive plate 31 manufactured by mold molding a composite material of graphite particles and phenolic resin. The graphite particle content in Sample B was 93% by mass, and the phenolic resin content was 7% by mass. The degree of graphitization of Sample B was 0.736.

[0107] <Test Example 2> In this study, we quantitatively investigated the degree to which samples A and B, prepared in Test Example 1, were susceptible to corrosion in electrochemical cell 1. Specifically, a three-electrode measuring cell was prepared with either sample A or sample B as the working electrode, and the current density flowing through samples A and B was measured under predetermined conditions.

[0108] First, several electrolyte solutions were prepared to mimic the first fluid 101, which was contaminated with impurity ions. These electrolyte solutions were sulfuric acid aqueous solutions made by adding sulfuric acid to pure water. The electrical conductivity and pH of the electrolyte solution changed depending on the concentration of sulfuric acid in the solution. The electrical conductivity and pH were calculated from the amount of sulfuric acid added to the pure water. 100% oxygen gas was blown into the electrolyte solution for a predetermined time to bring it to an oxygen-saturated state.

[0109] A three-electrode measurement cell was prepared by immersing a working electrode formed from sample A or sample B, a counter electrode made of a carbon rod, and a reference electrode made of a sulfuric acid / mercury sulfate electrode in the electrolyte solution described above. The working electrode was prepared by covering a portion of a plate material processed from sample A or sample B to a predetermined size with heat-shrink tubing. The heat-shrink tubing is resistant to the electrolyte solution, and the portion of the plate material not covered by the heat-shrink tubing functions as the working electrode in the electrolyte solution. The working electrode had an area of ​​1 cm × 1 cm.

[0110] A potentiogalvanostat (Versa STAT4, Princeton Applied Research) was connected to the measurement cell, and the polarization characteristics of sample A or sample B were measured. Specifically, the voltage was swept at a sweep rate of 1 mV / s (millivolts per second) until the potential of the reference electrode was 1.7 V or higher from the natural potential, and the polarization characteristics were measured. During the measurement of the polarization characteristics, oxygen gas was continuously blown in, taking care not to touch the surface of the working electrode.

[0111] The corrosion current densities of Sample A and Sample B were determined from the test results. The current flowing when a potential is applied to Samples A and B is thought to include not only the corrosion current of graphite but also the oxygen evolution reaction associated with the decomposition of water. Here, the calculations are based on the assumption that the current flowing is entirely the corrosion current of graphite. A smaller corrosion current indicates that the graphite is less likely to oxidize. In this test example, Figures 4 and 5 show the relationship between the corrosion current density (corrosion current divided by the area of ​​the working electrode) and the pH or electrical conductivity of the electrolyte solution. In Figures 4 and 5, the white circle plots represent the results for Sample A, and the black circle plots represent the results for Sample B.

[0112] In Figure 4, the horizontal axis represents the pH of the electrolyte solution, and the vertical axis represents the corrosion current density. Table 1 shows the pH of the electrolyte solutions used for the measurements of samples A and B. The corrosion current densities shown in Figures 4 and 5 are values ​​obtained when the potential of the working electrode is 1.7 V. The unit of corrosion current density is mA / cm². 2 That is the case.

[0113] [Table 1]

[0114] In Figure 5, the horizontal axis represents the electrical conductivity of the electrolyte solution, and the vertical axis represents the corrosion current density. Table 2 shows the electrical conductivity of the electrolyte solutions used for the measurements of samples A and B. The unit of electrical conductivity is μS / cm.

[0115] [Table 2]

[0116] As shown in Figure 4, the corrosion current density of both Sample A and Sample B increased as the pH of the electrolyte solution decreased. Therefore, it can be inferred that in the electrochemical cell 1 of the embodiment, the first conductive plate 31 is more susceptible to corrosion as the pH of the first fluid 101 decreases. Sample B, which has a higher degree of graphitization than Sample A, was found to have a lower corrosion current density and was less susceptible to corrosion. However, the difference in corrosion current density between Sample A and Sample B decreased as the pH of the electrolyte solution decreased. For both Sample A and Sample B, the corrosion current density was sufficiently low when the pH of the electrolyte solution was 4 or higher.

[0117] As shown in Figure 5, the corrosion current density of samples A and B increased as the electrical conductivity of the electrolyte solution increased. Therefore, it can be inferred that in the electrochemical cell 1 of the embodiment, the first conductive plate 31 is more susceptible to corrosion as the electrical conductivity of the first fluid 101 increases. Sample B, which has a higher degree of graphitization than sample A, was found to have a lower corrosion current density and was less susceptible to corrosion. However, the difference in corrosion current density between sample A and sample B decreased as the electrical conductivity of the electrolyte solution increased. For both sample A and sample B, the corrosion current density was sufficiently low when the electrical conductivity of the electrolyte solution was 200 μS / cm or less.

[0118] As shown in Figures 4 and 5, when the pH is less than 4 or the electrical conductivity is greater than 200 μS / cm, the corrosion current density is relatively large even for sample A, which has a graphitization degree of 0.644. Therefore, it can be inferred that when the graphitization degree is less than 0.5, a larger corrosion current density can be obtained than that shown in the graph for sample A.

[0119] On the other hand, as shown in Figures 4 and 5, the corrosion current density decreases as the pH of the electrolyte solution approaches 7 or as the electrical conductivity of the electrolyte solution decreases. Therefore, if there are few impurity ions in the first fluid 101, it is expected that the corrosion current density will be sufficiently low if the degree of graphitization of the first conductive plate 31 is 0.5 or higher.

[0120] <Test Example 3> In Test Example 3, the amount of thinning of the first conductive plate 31 due to the operation of the electrochemical cell 1 was determined by simulation. The corrosion current density obtained in Test Example 2 was used for the simulation.

[0121] The amount of charge flowing through the graphite in samples A and B, and the amount of carbon atoms in the decomposed graphite, can be calculated from the corrosion current density. Since the amount of carbon atoms in samples A and B can be calculated from the composition used during their preparation, the amount of carbon atoms that decompose over time can also be calculated. Based on the amount of carbon atoms that decompose, the amount of thinning of the first conductive plate 31 was determined. Thinning refers to the decrease in the thickness of the first conductive plate 31. The results of this simulation are shown in Figure 6.

[0122] In Figure 6, the horizontal axis represents the operating time of electrochemical cell 1, and the vertical axis represents the amount of wall thinning. The unit of operating time is h (hours). The unit of wall thinning is μm. The black square plots represent the simulation results when the first conductive plate 31 of sample A is in contact with the first fluid 101 at pH 4, and the black circle plots represent the simulation results when the first conductive plate 31 of sample B is in contact with the first fluid 101 at pH 4. The white square plots represent the simulation results when the first conductive plate 31 of sample A is in contact with the first fluid 101 at pH 5, and the white circle plots represent the simulation results when the first conductive plate 31 of sample B is in contact with the first fluid 101 at pH 5.

[0123] As shown in Figure 6, the amount of thinning of the first conductive plate 31 increases with increasing operating time. Comparison of black square plots and white square plots, and black circle plots and white circle plots, shows that the closer the pH is to 7, the smaller the amount of thinning of the first conductive plate 31. Comparison of black square plots and black circle plots, and white square plots and white circle plots, shows that the amount of thinning of the first conductive plate 31 formed by sample B is significantly smaller than that of the first conductive plate 31 formed by sample A. Sample B is a sample with a higher degree of graphitization than sample A. From these results, it was found that increasing the degree of graphitization of the graphite contained in the first conductive plate 31 reduces the amount of thinning associated with the operation of the electrochemical cell 1 more effectively than bringing the pH of the first fluid 101 closer to 7.

[0124] <Test Example 4> The compressive strain of the second porous layer 42 in electrochemical cell 1 was measured. The second porous layer 42 is formed of a nonwoven fabric containing carbon fibers (hereinafter referred to as carbon nonwoven fabric). The average diameter of the carbon fibers forming the carbon nonwoven fabric was 10 μm. The thickness of the carbon nonwoven fabric before compression was 1000 μm, and the basis weight was 90 g / cm². 2 The porosity was 95.6%. When this carbon nonwoven fabric was compressed to a thickness of 300 μm, the basis weight of the carbon nonwoven fabric was 90 g / cm². 2 The porosity is 86.7%. The compressive strain is the decrease in thickness λ (=t0-t1) of the compressed second porous layer 42 divided by the initial thickness t0 of the second porous layer 42 before compression. Thickness t1 is the thickness of the compressed second porous layer 42.

[0125] The initial thickness t0 of the carbon nonwoven fabric was measured using a commercially available thickness measuring device conforming to Method A of JIS L 1096:2010, such as the PG-16J constant pressure thickness measuring instrument (probe diameter: Φ25.2 mm) manufactured by Teclock Co., Ltd. The initial thickness t0 was measured while a surface pressure of 0.7 kPa was applied to the carbon nonwoven fabric for 10 seconds.

[0126] Figure 7 is a schematic diagram of a compression device 9 for measuring the compressive strain of the second porous layer 42. The compression device 9 comprises a lower base 90 and an upper base 91. The upper base 91 is configured to be movable downward. The compression device 9 applies surface pressure to a member sandwiched between the lower base 90 and the upper base 91. The compression device 9 can automatically measure the surface pressure acting between the lower base 90 and the upper base 91, as well as the distance between the lower base 90 and the upper base 91. The compression device 9 is a commercially available strength evaluation device, for example, the micro-strength evaluation tester MST-I type HR manufactured by Shimadzu Corporation.

[0127] For measuring the compressive strain of the carbon nonwoven fabric, the lower protective plate 92, second conductive plate 41, second porous layer 42, first conductive plate 31, and upper protective plate 93 were stacked on the lower base 90 in that order. The lower protective plate 92 and upper protective plate 93 protect the second conductive plate 41 and first conductive plate 31 from damage and apply uniform surface pressure to the second porous layer 42. The lower protective plate 92 and upper protective plate 93 are made of stainless steel. Of the multiple components sandwiched between the lower base 90 and the upper base 91, only the second porous layer 42 has a changing thickness. The lower protective plate 92, second conductive plate 41, first conductive plate 31, and upper protective plate 93 are rigid bodies, and their thicknesses do not change substantially.

[0128] The compression device 9 is activated to apply surface pressure to the second porous layer 42. The surface pressure applied to the second porous layer 42 is gradually increased, and the displacement distance of the upper base 91 corresponding to the magnitude of the surface pressure is measured. The displacement distance can be said to be equal to the decrease in thickness λ of the second porous layer 42. The compressive strain of the second porous layer 42 is determined from the initial thickness t0 and the displacement distance. Specifically, λ / t0 = compressive strain. Compressive strain is dimensionless. The relationship between compressive strain and surface pressure is shown in the graph of Figure 8. The horizontal axis of the graph is compressive strain, and the vertical axis is surface pressure.

[0129] In Test Example 4, the compressive strain of carbon cloth and carbon paper was also measured. The compressive strain of carbon cloth and carbon paper were measured using the same method as for carbon nonwoven fabric. The results are also shown in the graph in Figure 8.

[0130] As shown in Figure 8, the compressive strain of the carbon nonwoven fabric when pressurized with a surface pressure of 0.5 MPa was between 0.3 and 0.8, more specifically between 0.6 and 0.8. Thus, the thickness of the carbon nonwoven fabric changes significantly with compression. The carbon nonwoven fabric has excellent elastic deformation ability. When the second porous layer 42, made of such carbon nonwoven fabric, is compressed between the electrolyte membrane 2 and the second conductive plate 41 as shown in Figure 3, the second porous layer 42 presses the electrolyte membrane 2 and the second conductive plate 41 with a surface pressure equal to the compressive force. As a result, the second porous layer 42 adheres closely to the electrolyte membrane 2 and the second conductive plate 41, and there are almost no local gaps at the boundaries 1A and 1B. Because there are almost no local gaps at the boundaries 1A and 1B, the second fluid 102 can easily spread throughout the second flow field 6. As a result, it is expected that the Faraday efficiency of the electrochemical cell 1 will improve.

[0131] When pressurized with a surface pressure of 0.5 MPa, the compressive strain of the carbon cloth was 0.3 or greater, more specifically 0.4 or greater. In other words, the thickness of the carbon cloth changes to some extent due to the pressurization. When a second porous layer 42 made of such carbon cloth is placed between the electrolyte membrane 2 and the second conductive plate 41 as shown in Figure 3, gaps are less likely to form at the boundaries 1A and 1B.

[0132] As described above, carbon cloth and carbon nonwoven fabric satisfy the compressive strain requirement of 0.3 or higher even when the surface pressure is relatively low, around 0.1 MPa, and even when the surface pressure increases further, the compressive strain remains at 0.3 or higher. Since the surface pressure inside electrochemical cell 1 is greater than 0.1 MPa, it can be said that the compressive strain of carbon cloth and carbon nonwoven fabric in electrochemical cell 1 satisfies the requirement of 0.3 or higher.

[0133] When pressed with a surface pressure of 0.5 MPa, the compressive strain of the carbon paper was less than 0.2, more specifically 0.18 or less. In other words, the thickness of the carbon paper hardly changes under pressure. When such a second porous layer 42 made of carbon paper is placed between the electrolyte membrane 2 and the second conductive plate 41 as shown in Figure 3, gaps tend to form at the boundaries 1A and 1B.

[0134] When the size of the electrochemical cell 1 is increased, or when the number of stacked electrochemical cells 1 is increased, variations may occur in the dimensions of the components constituting the electrochemical cell and in the clamping pressure used to fasten multiple electrochemical cells 1 together. Furthermore, variations in dimensions may also occur due to deformation of the above components over time. In an electrochemical cell 1 equipped with a second porous layer 42 made of carbon paper that is resistant to elastic deformation, these variations are likely to cause gaps at the boundaries 1A and 1B in Figure 3, and it is thought that a decrease in Faraday efficiency due to these gaps is likely to occur.

[0135] Even with the aforementioned variations, the second porous layer 42 made of carbon nonwoven fabric maintains close contact with the electrolyte membrane 2 and the second conductive plate 41 through elastic deformation. As a result, localized gaps are less likely to form at boundaries 1A and 1B in Figure 3. Therefore, it is believed that a high Faraday efficiency can be maintained over a long period of time in the electrochemical cell 1 equipped with the second porous layer 42 made of carbon nonwoven fabric.

[0136] Furthermore, prolonged use may cause a decrease in the thickness of the first conductive plate 31 due to corrosion. Even in this case, the elastic deformation of the second porous layer 42, which is made of carbon nonwoven fabric, helps maintain surface contact between adjacent components constituting the electrochemical cell 1, namely the first conductive plate 31, the first porous layer 32, the electrolyte membrane 2, the second porous layer 42, and the second conductive plate 41. As mentioned above, increasing the degree of graphitization or bringing the pH of the first fluid 101 closer to 7 further helps maintain the above surface contact state.

[0137] <Test Example 4-2> In Test Example 4, multiple carbon nonwoven fabrics X, Y, and Z with different porosity and basis weight were prepared, and the compressive strain of each carbon nonwoven fabric X, Y, and Z was measured under the same conditions as in Test Example 4. The porosity, basis weight, and average diameter of carbon fibers for each carbon nonwoven fabric X, Y, and Z are shown in Table 3. The porosity values ​​in Table 3 are for a carbon nonwoven fabric with a thickness of 1.0 mm that has been compressed to 0.3 mm.

[0138] [Table 3]

[0139] The compressive strains of carbon nonwoven fabrics X, Y, and Z were in the range of 0.6 to 0.8. This test indicated that the porosity in the compressed state was between 80% and 90%, and the basis weight was 70 g / m². 2 More than 130g / m 2 The following shows that if the average diameter of the carbon fibers is in the range of 5 μm to 20 μm, a nonwoven fabric with a compressive strain of 0.6 to 0.8 can be constructed. [Explanation of Symbols]

[0140] 1 Electrochemical cell 1A,1B boundary 2 Electrolyte membrane 21 first page, 22 second page 3. Anode section 30 First catalyst layer, 31 First conductive plate, 32 First porous layer, 33 Frame seal section 4. Cathode section 40 Second catalyst layer, 41 Second conductive plate, 42 Second porous layer, 43 Frame seal section 5. First flow area 5A inlet, 5B outlet 6. Second flow field 6A inlet, 6B outlet 9 Compressor 90 Lower base, 91 Upper base, 92 Lower protective plate, 93 Upper protective plate 100 Organic Hydride Manufacturing Equipment 101 First fluid 101A first supply pipe, 101B first discharge pipe 101P First pump, 101T First tank 102 Second fluid 102A second supply pipe, 102B second discharge pipe 102P Second pump, 102T Second tank

Claims

1. It comprises an anode portion and a cathode portion sandwiching an electrolyte membrane, An electrochemical cell that supplies a first fluid mainly composed of water to the anode and a second fluid containing a hydride to the cathode, and generates protons by electrolyzing the water between the anode and the cathode, The anode portion comprises a first conductive plate formed from a composite material containing a first resin and a first carbon material. The aforementioned first carbon material contains graphite, The degree of graphitization in the first conductive plate is 0.5 or higher. The cathode portion comprises a first channel and a second channel that are independent of each other, and further has a region in which grooves forming the first channel and grooves forming the second channel are arranged alternately. The first flow path is connected to the inlet of the second fluid in the cathode section. The second flow path is connected to the outlet of the second fluid in the cathode section. Electrochemical cell.

2. The cathode portion includes a second conductive plate. The first channel comprises a plurality of first grooves formed in the second conductive plate, The second channel comprises a plurality of second grooves formed in the second conductive plate, At least a portion of the plurality of first grooves and at least a portion of the plurality of second grooves are arranged alternately in parallel in a direction perpendicular to the extension direction of the plurality of first grooves and the plurality of second grooves. The plurality of first grooves and the plurality of second grooves are vertical grooves extending in the direction from the lower end to the upper end of the second conductive plate. The lower end is the end portion that is close to the entrance. The electrochemical cell according to claim 1, wherein the upper end is the end adjacent to the outlet.

3. The electrochemical cell according to claim 2, wherein the plurality of first grooves and the plurality of second grooves are arranged to interlock with each other.

4. The first channel is provided with lower transverse grooves that connect the lower ends of the plurality of first grooves, The electrochemical cell according to claim 2 or 3, wherein the second channel comprises an upper transverse groove connecting the upper ends of the plurality of second grooves.

5. At least a portion of the plurality of first grooves is directly connected to the entrance, The electrochemical cell according to claim 2 or 3, wherein at least a portion of the plurality of second grooves is directly connected to the outlet.

6. The electrochemical cell according to claim 1 or claim 2, wherein the electrical conductivity of the first fluid is 200 μS / cm or less.

7. The electrochemical cell according to claim 1 or claim 2, wherein the hydrogen ion concentration of the first fluid is 4 or higher.

8. The electrochemical cell according to claim 1 or claim 2, wherein the content of the first carbon material in the first conductive plate is 70% by mass or more, when the mass of the first conductive plate is 100% by mass.

9. The electrochemical cell according to claim 1 or claim 2, wherein the hydrogenated substance is an organic compound having an unsaturated bond.

10. The cathode portion comprises a second conductive plate formed from a composite material containing a second resin and a second carbon material. The aforementioned secondary carbon material contains graphite, The electrochemical cell according to claim 1 or claim 2, wherein the content of the second carbon material in the second conductive plate is 70% by mass or more, when the mass of the second conductive plate is 100% by mass.

11. The electrochemical cell according to claim 10, wherein the second resin is at least one selected from the group consisting of polyester resin, polyamide resin, polyacetal resin, phenolic resin, polyvinylidene chloride resin, polyvinylidene fluoride resin, polytetrafluoroethylene resin, epoxy resin, polyoxymethylene resin, and polyphenylene sulfide resin.

12. The anode portion comprises a first porous layer formed of a conductive material, The electrochemical cell according to claim 1 or claim 2, wherein the average thickness of the first porous layer is 0.20 mm or more and 0.40 mm or less.

13. The first porous layer comprises a substrate made of metal and a coating formed on the surface of the substrate. The aforementioned metal includes at least one selected from the group consisting of titanium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. The form of the substrate is a fiber aggregate, a porous sintered body, a foamed molded body, or expanded metal. The electrochemical cell according to claim 12, wherein the coating contains platinum.

14. The cathode portion comprises a second porous layer formed of a conductive material, The electrochemical cell according to claim 1 or claim 2, wherein the compressive strain of the second porous layer in the cathode portion is 0.3 or more and 0.8 or less.

15. The electrochemical cell according to claim 14, wherein the second porous layer includes a nonwoven fabric having carbon fibers.

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