Electrochemical cell

Abstract

This electrochemical cell comprises an anode part and a cathode part that sandwich an electrolyte membrane, the electrochemical cell being such that a first fluid mainly composed of water is supplied to the anode part, and the water is electrolyzed between the anode part and the cathode part to generate protons, wherein the anode part is provided with a first electroconductive plate formed from a composite material containing a first resin and a first carbon material.

Description

electrochemical cell

[0001] The present disclosure relates to an electrochemical cell. This application claims priority to Japanese Patent Application No. 2024-051443 filed on March 27, 2024, the entire contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses a proton-conducting electrochemical cell that generates protons from water. This electrochemical cell includes an anode section and a cathode section that sandwich an electrolyte membrane. The anode section includes an anode facing a first surface of the electrolyte membrane and an electrically conductive end plate. The cathode section includes a cathode facing a second surface of the electrolyte membrane and an electrically conductive end plate. Each end plate functions as a conductive plate that applies a 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, the generated protons are used to hydrogenate a substance to be hydrogenated, such as toluene, thereby stably storing hydrogen.

[0004] Japanese Patent Application Laid-Open No. 2021-109986

[0005] The electrochemical cell disclosed herein comprises an anode section and a cathode section sandwiching an electrolyte membrane, a first fluid mainly composed of water is supplied to the anode section, and the water is electrolyzed between the anode section and the cathode section to generate protons, and the anode section comprises a first conductive plate formed from a composite material containing a first resin and a first carbon material.

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

[0007] [Problem to be Solved by the Present Disclosure] The conductive plate serving as the end plate of the anode section in Patent Document 1 is made of a metal such as titanium. Metals such as titanium are less permeable to the first fluid, can prevent leakage of the first fluid from the anode section, and have excellent mechanical strength. However, conductive plates made of metals such as titanium require surface treatment, such as coating with a metal such as platinum, to improve oxidation resistance. Surface treatments such as plating are complicated and reduce the productivity of the electrochemical cell, including costs.

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

[0009] [Advantages 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, embodiments of the present disclosure will be listed and described.

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

[0012] In a first conductive plate formed from a composite material, the first carbon material increases the electrical conductivity of the first conductive plate. This first conductive plate does not require surface treatment such as plating that is applied to metal conductive plates, resulting in excellent productivity, including cost. A first conductive plate formed from a composite material can prevent the first fluid from leaking outside the anode section. When multiple electrochemical cells are stacked, the first resin of the first conductive plate in the anode section prevents the first fluid from leaking to the cathode section adjacent to the anode section. The first resin improves the strength of the first conductive plate and reduces oxidation of the first carbon material by the first fluid.

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

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

[0015] Although water, which is the main component of the first fluid, is generally an electrical insulator, impurity ions eluted from components during operation may increase the electrical conductivity of the first fluid. When a high voltage is applied to the first conductive plate, for example, when the voltage applied to the first conductive plate is 1.7 V or higher, the first carbon material in the composite material may be oxidized by the first fluid containing the impurity ions, i.e., the first conductive plate may corrode. In contrast, a first conductive plate having a graphitization degree of 0.5 or higher is less susceptible to corrosion. Therefore, the electrical conductivity of the first conductive plate is more likely to be maintained. Even with long-term use, the reduction in the thickness of the first conductive plate due to corrosion of the first conductive plate is also likely to be small. Therefore, the electrochemical cell described in <2> above is more likely to maintain its water electrolysis performance.

[0016] <3> In the electrochemical cell according to the above <1> or <2>, the first fluid may have an electrical conductivity of 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> In the electrochemical cell according to any one of <1> to <3> above, the first fluid may have a hydrogen ion exponent of 4 or more.

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

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

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

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

[0023] In the electrochemical cell described in <6> above, an organic compound having an unsaturated bond is supplied to the cathode, and protons generated in the anode are added to the organic compound to produce a hydride. This electrochemical cell can produce a hydride such as methylcyclohexane from toluene, for example. Such an electrochemical cell can be suitably used in a hydrogen carrier production device.

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

[0025] When the second conductive plate is formed from a composite material and contains 70 mass % or more of a second carbon material including graphite, the second carbon material increases the electrical conductivity of the second conductive plate, and the second resin reduces leakage of the second fluid outside the cathode section. When multiple electrochemical cells are stacked, the second resin of the second conductive plate in the cathode section prevents leakage of the second fluid to the anode section adjacent to the cathode section.

[0026] The composite material can be molded into a mold, allowing for high-precision molding of a three-dimensional second conductive plate, such as a grooved plate. Furthermore, since the resin and graphite are resistant to the organic compounds, the second conductive plate is less likely to be damaged by the 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 adjacent electrochemical cell are shared, i.e., the front side of one conductive plate functions as the first conductive plate and the back side functions as the second conductive plate, i.e., one conductive plate functions as a bipolar plate.

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

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

[0030] <9> In the electrochemical cell according to any one of <1> to <8> above, the anode part may include a first porous layer formed of a conductive material, and the first porous layer may have an average thickness of 0.20 mm or more and 0.40 mm or less.

[0031] If the potential of the first conductive plate becomes sufficiently large to oxidize the first carbon material in the first conductive plate, the first conductive plate may corrode. If the thickness of the first porous layer in the anode section is 0.20 mm or more, the distance that protons generated by the corrosion reaction of the first conductive plate must travel to the cathode section increases. This increase in distance increases the resistance to proton migration. In order to oxidize the first carbon material in the first conductive plate when the migration resistance is high, an additional voltage is required to compensate for the migration resistance. This voltage is not applied in an electrochemical cell operating normally. 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 in the anode section can also be expected to have the effect of uniforming the flow of the first fluid in the anode section.

[0032] <10> In the electrochemical cell described in <9> above, the first porous layer may include a substrate made of a metal and a coating formed on a 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, the substrate is in the form of a fiber aggregate, a porous sintered body, a foamed molded body, or an expanded metal, and the coating includes platinum.

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

[0034] <11> In the electrochemical cell described in any one of <1> to <10> above, the cathode part may include a second porous layer formed of a conductive material, and the compressive strain of the second porous layer in the cathode part 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. Even if the thickness of the first conductive plate decreases with long-term use as described above, 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 first conductive plate, first porous layer, electrolyte membrane, second porous layer, and second conductive plate are likely to maintain surface contact. If the components of the electrochemical cell are subjected to compressive stress during assembly or stress due to thermal expansion and contraction during operation, the second porous layer is expected to relieve the stress, thereby reducing the stress that may be applied to the first conductive plate. In such an electrochemical cell, the first conductive plate is less likely to be damaged, such as cracked.

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

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

[0038] The nonwoven fabric containing carbon fibers has high elastic deformability. The cushioning properties of the second porous layer make it easier to prevent damage to the first conductive plate, such as cracking of the first conductive plate.

[0039] [Details of the embodiments of the present disclosure] Specific examples of electrochemical cells according to the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or equivalent parts. The dimensions of the components shown in the drawings are expressed for the purpose of clarity and do not necessarily represent the actual dimensions. The present invention is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope of the claims are intended to be included.

[0040] <First Embodiment> <Overview of Organic Hydride Manufacturing Apparatus> Fig. 1 is a principle diagram of an organic hydride manufacturing apparatus 100 including a proton-conductive electrochemical cell 1. The organic hydride manufacturing apparatus 100 of this example 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 includes 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 section 3 is connected to the anode of the DC power supply, and the cathode section 4 is connected to the cathode of the DC power supply.

[0041] The first fluid 101 is supplied to the anode section 3 through a first supply pipe 101A. A first pump 101P is disposed in the first supply pipe 101A to pump the first fluid 101 to the anode section 3. A first catalyst layer 30 is disposed in the anode section 3. Water (H ２ O) to proton (H ＋ ) and oxygen (O ２ ) and electrons (e － ) are generated. The protons move through the electrolyte membrane 2 to the cathode section 4. Electrons generated at the anode flow to the cathode via a DC power supply. The first fluid 101 in the anode section 3 is discharged to a first tank 101T through a 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 with a total impurity concentration of 0.1 mM (millimolar) or less. The first fluid 101 at the start of the electrochemical cell 1 is, for example, pure water. Commercially available pure water can be used. However, even if the first fluid 101 at the start of the electrochemical cell 1 is pure water, impurity ions derived from the components of the electrochemical cell 1 may be mixed into the first fluid 101 as it circulates through the electrochemical cell 1.

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

[0044] The substance to be hydrogenated contained in the second fluid 102 is, for example, an organic compound having an unsaturated bond. Examples of organic compounds having an unsaturated bond include monocyclic aromatic compounds, bicyclic aromatic compounds, tricyclic aromatic compounds, and aromatic polymers. Specific substance names are benzene, toluene, xylene, ethylbenzene, mesitylene, naphthalene, methylnaphthalene, anthracene, and tetralin. The substance to be hydrogenated illustrated in FIG. 1 is toluene (denoted as TOL in the figure). The hydride produced by hydrogenating toluene is methylcyclohexane (hereinafter denoted as MCH). In the electrochemical cell 1 of this example, the second fluid 102 contains toluene, and the cell is also referred to as an MCH electrosynthesis cell. The reactions in the anode section 3 and cathode section 4 are as follows: 3H ２ O → 1.5O ２ +6H ＋ +6e － Toluene + 6H ＋ +6e － →Methylcyclohexane

[0045] When water electrolysis is performed in the electrochemical cell 1, hydrogen (H ２ ) is generated. In the electrochemical cell 1 that performs water electrolysis, a configuration for circulating the second fluid 102 in the cathode section 4 is not necessary. Water that has permeated the electrolyte membrane 2 from the anode section 3 flows into the cathode section 4. Therefore, the electrochemical cell 1 that performs water electrolysis has a configuration for discharging hydrogen generated from protons from the cathode section 4 together with water.

[0046] <<Basic Configuration of Electrochemical Cell>> As shown in FIG. 2 , an electrochemical cell 1 including an anode portion 3 and a cathode portion 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 allows protons to permeate. 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 a space in the anode section 3 through which the first fluid 101 flows. As shown in FIG. 1 , the inlet 5A and the outlet 5B of the first flow field 5 are connected to a first supply pipe 101A and a first discharge pipe 101B, respectively. The first flow field 5 allows the first fluid 101 to flow so as to contact the first surface 21 of the electrolyte membrane 2. The anode section 3 of this example includes 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 that faces the first surface 21 of the electrolyte membrane 2. The first conductive plate 31 has a function of applying a voltage to the electrochemical cell 1. The first conductive plate 31 also has a function of confining the first fluid 101 within the electrochemical cell 1. An electrode plate (not shown) is disposed on the surface of the first conductive plate 31 opposite the first porous layer 32. The electrode plate is connected to the anode of a DC power supply (not shown).

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

[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 by the space between the first surface 21 of the electrolyte membrane 2 and the first conductive plate 31 and surrounded by the frame seal portion 33. By disposing the first porous layer 32 in this space, the first fluid 101 can use the pores of the first porous layer 32 as a flow path.

[0052] The first catalyst layer 30 disposed 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, resulting in the generation of protons, oxygen, and electrons. In this example, the first catalyst layer 30 is formed integrally with the first surface 21 of the electrolyte membrane 2. The first catalyst layer 30 may be formed integrally with at least a portion of the first porous layer 32 that contacts the electrolyte membrane 2. The first catalyst layer 30 may be a member independent of the electrolyte membrane 2 and the first porous layer 32. In this case, the first catalyst layer 30 is disposed between the electrolyte membrane 2 and the first porous layer 32. The first catalyst layer 30 includes a catalyst. The catalyst may be, for example, RuO ２ , IrO ２ The catalyst may be a precious metal oxide-based catalyst such as IrO. This catalyst may have a structure in which a precious metal oxide is dispersed and supported on a substrate made of a metal wire or metal mesh, or a structure in which the substrate is coated with a precious metal oxide. The first catalyst layer 30 may contain an ionomer that adheres the catalyst to the substrate. The metal constituting the 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 containing the above metal as a main component. IrO ２ When the catalyst is used, the substrate is provided with IrO ２ In the structure coated with a thin film made of, for example, a reduction in the amount of expensive precious metals used reduces the manufacturing cost.

[0053] The second flow field 6 is a space in the cathode section 4 through which the second fluid 102 flows. As shown in FIG. 1 , the inlet 6A and the outlet 6B of the second flow field 6 are connected to the second supply pipe 102A and the second discharge pipe 102B, respectively. The second flow field 6 causes the second fluid 102 to flow so as to contact 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 of this example includes a second conductive plate 41, a second porous layer 42, and a frame seal portion 43.

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

[0055] The second porous layer 42 is a conductive plate having a plurality of pores, and is disposed 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 by the space between the second surface 22 of the electrolyte membrane 2 and the second conductive plate 41 and surrounded by the frame seal portion 43. By disposing the second porous layer 42 in this space, the second fluid 102 can use the pores of the second porous layer 42 as a flow path.

[0057] The second catalyst layer 40 disposed in the second flow field 6 is in contact with or adjacent to the second surface 22 of the electrolyte membrane 2. The second catalyst layer 40 promotes a reaction between the substance to be hydrided contained in the second fluid 102 and protons from the anode section 3, resulting in the production of hydrides. In this example, the second catalyst layer 40 is integrally formed on the second surface 22 of the electrolyte membrane 2. The second catalyst layer 40 may be integrally formed on at least a portion of the second porous layer 42 that contacts 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 this case, the second catalyst layer 40 is disposed between the electrolyte membrane 2 and the second porous layer 42. The second catalyst layer 40 includes a catalyst. The catalyst is, for example, a composition including a first catalytic metal and a second catalytic metal. The first catalytic metal includes at least one of the precious 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 be 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 of FIG. 1 typically includes a stack of multiple electrochemical cells 1. In the stack, of two adjacent electrochemical cells 1, the first conductive plate 31 of one electrochemical cell 1 and the second conductive plate 41 of the remaining electrochemical cell 1 form a single bipolar plate. In the bipolar plate, a first surface of the bipolar plate functions as the first conductive plate 31, and a second surface opposite the first surface functions as the second conductive plate 41. Accordingly, a first porous layer 32 is disposed on the first surface of the bipolar plate, and a second porous layer 42 is disposed on the second surface of the bipolar plate. At a first end and a second end of the stack, the first conductive plate 31 and the second conductive plate 41, rather than bipolar plates, are disposed, respectively.

[0059] <Configuration of Each Part of Electrochemical Cell> The configuration of each part of the electrochemical cell 1 will be described in detail below.

[0060] [First Conductive Plate] The first conductive plate 31 is required to be made of a material that is unlikely to react with substances contained in the first fluid 101. The first conductive plate 31 is, for example, a plate formed of 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] First conductive plate 31 can be produced, for example, by hot pressing a mixture of a first carbon material and a first resin. First conductive plate 31 may also be produced 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 the composite material, the first carbon material increases the electrical conductivity of the first conductive plate 31, and the first resin prevents the first fluid 101 from leaking out of the anode section 3. When multiple electrochemical cells 1 are stacked, the first conductive plate 31 of the anode section 3 prevents the first fluid 101 from leaking to the cathode section 4 adjacent to that anode section 3. The first resin increases the strength of the first conductive plate 31 and reduces oxidation of the first carbon material by the first fluid 101. The reduced oxidation allows the electrical conductivity of the first carbon material to be maintained in the first conductive plate 31. Furthermore, the first conductive plate 31 formed from the composite material is inexpensive because it does not require a coating such as platinum, and can be easily formed by molding even into a three-dimensional shape, such as one having grooves.

[0063] When the first carbon material includes graphite, the degree of graphitization of the first conductive plate 31 including the graphite may be, for example, 0.5 or more. Graphite has a layered structure in which a plurality of planar layer structures are bonded by van der Waals forces. In each planar layer structure, a plurality of carbon atoms are connected in a hexagonal shape. The degree of graphitization is an index showing whether a plurality of planar layer structures are regularly layered. The degree of graphitization is calculated by the Franklin P value shown in the following formula 1. The value of "d" in the following formula (1) is （００２） ' is the carbon interplanar spacing d measured by XRD (X-ray diffraction) （００２） In this example, since first conductive plate 31 is formed from a composite material of graphite and the first resin, the graphitization degree of first conductive plate 31 including the graphite and the first resin is evaluated, rather than the graphitization degree of graphite alone.

[0064]

[0065] Graphite can be obtained by firing carbon in an oxygen-free state. The firing temperature is, for example, 1500° C. or higher. The higher the firing temperature, for example, 2000° C. or higher or 3000° C. or higher, the higher the graphitization degree of the graphite.

[0066] The higher the graphitization degree of graphite, the higher the electrical conductivity of the graphite. In other words, the higher the graphitization degree of first conductive plate 31 containing graphite, the higher the electrical conductivity of first conductive plate 31. Studies by the present inventors have revealed that the higher the graphitization degree, the more resistant the graphite contained in first conductive plate 31 is to oxidation by first fluid 101. Because graphite is less resistant to oxidation, first conductive plate 31 is less susceptible to corrosion, and the electrical conductivity of first conductive plate 31 is more likely to be maintained. Therefore, the performance of electrochemical cell 1 in electrolyzing water is more likely to be maintained.

[0067] Oxidation of the first carbon material can occur when a high voltage is applied to the first conductive plate 31 and the electrical conductivity of the first fluid 101 is high. In the electrochemical cell 1, water electrolysis can be performed efficiently when the potential of the first conductive plate 31 is a high potential, such as 1.7 V or higher. Meanwhile, although water, which is the main component of the first fluid 101, is an insulator, impurity ions may be contained in 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 when the above-described high potential is applied. 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 may be 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 the electrical conductivity of the first fluid 101. Measuring the pH of the first fluid 101 is easier than measuring the electrical conductivity of the first fluid 101. 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. Because 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 may be measured by sampling the first fluid 101 midway through the flow path of the first fluid 101. For example, a sampling path branching from the first supply pipe 101A in Fig. 1 may be provided, and a measuring device may be provided on the sampling path, or a measuring device may be provided 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] In order to reduce the electrical conductivity of the first fluid 101 in contact with the first conductive plate 31 and bring the pH closer to 7, a filter that removes impurity ions may be placed in the circulation path of the first fluid 101. Instead of circulating the first fluid 101, it is also possible to continuously supply the first fluid 101 with an extremely small amount of impurity ions, such as pure water, 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. Because 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 content of the first carbon material ranges, for example, from 70% by mass to 95.5% by mass, from 80% by mass to 95% by mass, or from 85% by mass to 95% by mass. 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] In this example, the first porous layer 32 is a porous plate made of a metal material. The first porous layer 32 includes, for example, a substrate with a three-dimensional mesh structure 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. The metal also includes alloys. The first porous layer 32 made of the above metal is resistant to the first fluid 101. Such a first porous layer 32 is less likely to be damaged by the first fluid 101. The substrate may be in the form of a fiber aggregate such as a nonwoven fabric, a porous sintered body, a foam molded body, or an expanded metal. The coating includes, for example, platinum. The substrate may be a stack of multiple mesh plates with different mesh sizes or a stack of multiple mesh plates with different mesh shapes.

[0073] The first porous layer 32 is sandwiched between the electrolyte membrane 2 and the first conductive plate 31. By being sandwiched between the electrolyte membrane 2 and the first conductive plate 31, the first porous layer 32 is pressed by them. Depending on the material of the first porous layer 32, the first porous layer 32 may be compressed by the above-mentioned pressing force. The first porous layer 32 formed from a metal material has a plurality of pores but is difficult to deform.

[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 made of, for example, a metal material and therefore 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 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 is sufficiently large. In other words, a sufficiently large first flow field 5 is formed within the anode section 3, allowing the first fluid 101 to easily diffuse throughout the entire 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 section 4 is increased. This increase in distance increases the resistance to proton migration. In order to oxidize the carbon material in the first conductive plate 31 when the migration resistance is high, an additional voltage is required to compensate for the migration resistance. This voltage is not applied in an electrochemical cell 1 operating normally. Therefore, if the average thickness of the first porous layer 32 is 0.20 mm or more, the first conductive plate 31 is less susceptible to corrosion.

[0076] If the average thickness of the first porous layer 32 is 0.40 mm or less, an 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, and the flow of the first fluid 101 in the anode section 3 can be made uniform. The thinner the metal first porous layer 32, the lighter it tends to be, improving the assembly workability of the electrochemical cell 1. A thin first porous layer 32 can reduce the material of 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 in the electrochemical cell 1 is, for example, 60% or more and 90% or less. Because the first porous layer 32 formed from a metal material has low elastic deformability, the porosity of the first porous layer 32 removed from the electrochemical cell 1 can be considered to be the porosity of the first porous layer 32 in the electrochemical cell 1. If the porosity is 60% or more, the first fluid 101 is likely to diffuse throughout the entire first flow field 5. If the porosity is 90% or less, the strength of the first porous layer 32 is likely to be high. The porosity of the first porous layer 32 may be, for example, 65% or more and 85% or less, or 68% or more and 80% or less.

[0078] [Frame Seal Portion of Anode Portion] The size of the frame seal portion 33 of the anode portion 3 may be selected according to the sizes 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 is resistant to the first fluid 101. Examples of the electrically insulating material 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 is not easily reactive with the organic compounds contained in the second fluid 102. The second conductive plate 41 is, for example, a plate formed from a composite material of a second carbon material and a second resin. The second conductive plate 41 formed from a composite material can be manufactured using 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. The above-listed resins are resistant to organic compounds, making the second conductive plate 41 less likely to be damaged by the second fluid 102.

[0080] The second conductive plate 41 contains graphite as the second 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 100% by mass. When the second conductive plate 41 is formed from a composite material and contains 70% by mass or more of the second carbon material including graphite, the second carbon material increases the electrical conductivity of the second conductive plate 41, and the second resin reduces leakage of the second fluid 102 outside the cathode section 4. When multiple electrochemical cells 1 are stacked, the second resin of the second conductive plate 41 in the cathode section 4 prevents leakage of the second fluid 102 to the anode section 3 adjacent to that cathode section 4. The strength of the second conductive plate 41 is also increased by the second resin, and even a three-dimensional shape having grooves can be easily formed by molding.

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

[0082] <Configuration of the Second Porous Layer> The second porous layer 42 is a porous plate made of a conductive material. The second porous layer 42 is configured to have high elastic deformability. In the electrochemical cell 1, the second porous layer 42, which has high elastic deformability, is sandwiched between the electrolyte membrane 2 and the second conductive plate 41, thereby compressing the second porous layer 42. 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 in the electrochemical cell 1 is, for example, 0.15 mm or more and 3.0 mm or less. 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 average length is three or more, including a measurement at the center position of the electrolyte membrane 2 in a plan view.

[0083] If the average thickness of the second porous layer 42 in the compressed state is 0.15 mm or more, the amount of elastic deformation of the second porous layer 42 within the electrochemical cell 1 is likely to be large. As a result, the second porous layer 42 is likely 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 is sufficiently large. In other words, a sufficiently large second flow field 6 is formed within the cathode section 4, and the second fluid 102 is likely to diffuse throughout the second flow field 6. If the average thickness of the second porous layer 42 in the compressed state is 3.0 mm or less, the electrical resistance of the second porous layer 42 and the cell resistance of the electrochemical cell 1 are unlikely 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 is not too large. In other words, because the second flow field 6 is not too large, the second fluid 102 containing hydrides produced in the second catalyst layer 40 is likely 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] FIG. 3 is a schematic diagram showing the stacked state of a portion of the electrochemical cell 1. Localized gaps at the boundary 1A between the second porous layer 42 and the electrolyte membrane 2 and the boundary 1B between the second porous layer 42 and the second conductive plate 41 make it difficult for the second fluid 102 to uniformly distribute across the entire surface of the second catalyst layer 40. If the internal pressure of the second flow field 6 changes during operation of the electrochemical cell 1, these localized gaps may form. If the compressed second porous layer 42 presses the electrolyte membrane 2 and the second conductive plate 41 with a surface pressure equal to or greater than a predetermined value, localized gaps are unlikely to form at the boundaries 1A and 1B. The lack of gaps at the boundaries 1A and 1B facilitates uniform flow of the second fluid 102. As a result, the Faraday efficiency of the electrochemical cell 1 is likely to be improved. The Faraday efficiency is the ratio of the amount of charge contributed to the hydrogenation of the substance to be hydrogenated to the total amount of charge input to the electrochemical cell 1, which is taken as 100%. Second porous layer 42 having high elastic deformability exhibits cushioning properties and is likely to reduce damage to first conductive plate 31 and second conductive plate 41 .

[0085] The compressive strain of the second porous layer 42 in a compressed state within the cathode section 4 of the electrochemical cell 1 is 0.3 or more and 0.8 or less. 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 FIG. 8 of Test Example 4 described below, the greater the surface pressure, the greater the compressive strain. Therefore, if the compressive strain of the second porous layer 42 at a surface pressure of 0.5 MPa is 0.3 or more, the compressive strain of the second porous layer 42 within the cathode section 4, to which a surface pressure of 0.5 MPa or more acts, is also 0.3 or more. The compressive strain in this example is the value obtained by dividing the thickness reduction amount 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 compressed with a surface pressure of 0.5 MPa or more and 0.8 MPa or less. Therefore, the compressive strain can be calculated by (t0 - t1) / t0. For example, when a second porous layer 42 having 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, the thickness of the second porous layer 42 is measured for a fixed time and under a fixed surface pressure using a commercially available thickness measuring device. The time is 10 seconds. The surface pressure in measuring the initial thickness t0 is 0.7 kPa. The initial thickness t0 is an average value of thicknesses measured at five or more points. The thickness t1 is measured in the same manner as the initial thickness t0, but by changing the surface pressure to, for example, 0.5 MPa. The thicknesses t0 and t1 are measured for the second porous layer 42 in a state not assembled into the electrochemical cell 1. The initial thickness t0 of the second porous layer 42 is, for example, 0.3 mm or more and 3.5 mm or less.

[0087] The second porous layer 42 having the compressive strain of 0.3 to 0.8 has excellent elastic deformability. When compressed between the electrolyte membrane 2 and the second conductive plate 41, the second porous layer 42 attempts to return to its original thickness before compression, pressing the electrolyte membrane 2 and the second conductive plate 41, which sandwich the second porous layer 42, within the cathode section 4. Therefore, the second porous layer 42 is likely to come into 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 caused by long-term use, the elastic deformation of the second porous layer 42 makes it difficult for gaps to form between adjacent components 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 entangling multiple independent carbon fibers and does not have bonding parts such as binders that secure the carbon fibers together. Nonwoven fabrics that do not have bonding parts have high elastic deformability. As long as the second porous layer 42 satisfies the above compressive strain, it may be a woven fabric containing carbon fibers. The woven fabric is made by alternately weaving warp and weft threads of carbon fibers. Woven fabric containing carbon fibers is also called carbon cloth. Paper containing carbon fibers is considered not to satisfy the above compressive strain. The paper contains multiple carbon fibers and a binder that secures the carbon fibers. For example, the paper has a compressive strain of less than 0.2 when a surface pressure of 0.5 MPa is applied, and is hardly deformed.

[0089] As long as the compressive strain of the second porous layer 42 as a whole is 0.3 or greater, the second porous layer 42 may include a member having a compressive strain of less than 0.3. For example, the second porous layer 42 may be configured by laminating a plurality of nonwoven fabrics having different compressive strains, by laminating a nonwoven fabric and a woven fabric, by laminating a nonwoven fabric and a paper, or by laminating a nonwoven fabric, a woven fabric, and a paper.

[0090] The carbon fibers forming the nonwoven fabric have an average diameter of, 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 higher elastic deformability. 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 carbon fibers is calculated by averaging the diameters of circles having the same area as the cross-sections of a plurality of carbon fibers. The cross-sections are observed using, for example, a scanning electron microscope. Five or more observation fields are taken from one cross-section. The cross-sectional areas of three or more carbon fibers are calculated from each observation field.

[0092] The porosity of the second porous layer 42 in its compressed state within the electrochemical cell 1 is, for example, 40% to 98%. If the porosity of the second porous layer 42 is within the above range, the second porous layer 42 is likely to have sufficient conductivity and pores while maintaining excellent elastic deformability. The porosity may be, for example, 45% to 97%, or 50% to 96%. The porosity is determined from a cross-sectional photograph of the cross section of the second porous layer 42. The cross-sectional photograph is binarized to determine the areas of the solid portion and pore portion. The porosity is the ratio of the area of ​​the pore portion to the total area of ​​the solid portion and pore portion. If the porosity of the second porous layer 42 before compression and the amount of reduction in thickness of the second porous layer 42 within the electrochemical cell 1 are known, the porosity of the second porous layer 42 in its compressed state can be calculated.

[0093] The basis weight of the second porous layer 42 is, for example, 50 g / m ２ More than 400g / m ２ If the basis weight of the second porous layer 42 is within the above range, the second porous layer 42 is likely to have sufficient electrical conductivity and pores while having excellent elastic deformability. ２ 395g / m or more ２ or less than 60 g / m ２ 390g / m or more ２ The weight per unit area may be, for example, 55 g / m ２ More than 200g / m ２or less than 60 g / m ２ 150g / m or more ２ The basis weight is the mass of the second porous layer 42 per square meter. The basis weight can be calculated by dividing the mass of the second porous layer 42 by the area of ​​the second porous layer 42 in a plan view.

[0094] [Frame Seal Portion of Cathode Portion] The specifications such as the constituent material and size of the frame seal portion 43 of the cathode portion 4 are the same as the specifications such as the constituent material and size of the frame seal portion 33 of the anode portion 3 .

[0095] [Configuration of Flow Channel in First Flow Field] The first flow field 5 may be provided with a flow channel. By providing the flow channel, the flow of the first fluid 101 in the first flow field 5 becomes smooth.

[0096] The flow paths are typically grooves formed in first conductive plate 31. The shape, size, and arrangement of the grooves can be selected as appropriate. The grooves may be, for example, linear, wavy, or serpentine. The grooves may be arranged, for example, in the form of a plurality of linear grooves arranged in parallel, or in the form of grooves with a comb-tooth structure, as described below.

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

[0098] When first conductive plate 31 has grooves that form flow paths, first conductive plate 31 has a larger contact area with first fluid 101 compared to when first conductive plate 31 does not have grooves. First conductive plate 31 contains graphite with a high degree of graphitization, so that the graphite is less likely to be oxidized even when the contact area with first fluid 101 is large.

[0099] [Configuration of Flow Channels in Second Flow Field] The second flow field 6 may also have flow channels. The second flow field 6 may include first flow channels and second flow channels that are independent of each other, and may have a groove structure including an area in which grooves forming the first flow channels and grooves forming the second flow channels are alternately arranged. For example, the first flow channel includes a plurality of first grooves arranged in parallel, and the second flow channel includes a plurality of second grooves arranged in parallel. In a plan view, at least some of the plurality of first grooves and at least some of the plurality of second grooves are alternately arranged in parallel in a direction perpendicular to the extension direction of the first grooves and the second grooves. The first grooves and the second grooves are, for example, vertical grooves extending in a direction from the lower end to the upper end of the second conductive plate 41.

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

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

[0102] The plurality of first grooves and the plurality of second grooves are arranged to interdigitate with each other. Because the openings of the first grooves face the second porous layer 42, the second fluid 102 is quickly diffused from the first grooves throughout the second porous layer 42. As a result, the substance to be hydrided contained in the second fluid 102 is efficiently supplied to the second catalyst layer 40. Because the openings of the second grooves face the second porous layer 42, the second fluid 102 containing the hydride is quickly collected in the second grooves from near the second catalyst layer 40.

[0103] Test Example 1 In Test Example 1, first conductive plates 31 formed from the following Sample A and Sample B were produced, and the degree of graphitization of first conductive plates 31 was measured.

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

[0105] A small piece was sampled from sample A, and the carbon lattice spacing d （００２） The measured value was substituted into the above-mentioned formula (1) to determine the degree of graphitization of Sample A. The degree of graphitization of Sample A was 0.644.

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

[0107] Test Example 2 The susceptibility of Sample A and Sample B prepared in Test Example 1 to corrosion in the electrochemical cell 1 was quantitatively investigated. Specifically, a three-electrode measurement cell was prepared in which Sample A or Sample B was placed as the working electrode, and the density of the current flowing through Sample A and Sample B under predetermined conditions was measured.

[0108] First, several types of electrolyte solutions were prepared to simulate the first fluid 101 containing impurity ions. These electrolyte solutions were aqueous sulfuric acid solutions prepared by adding sulfuric acid to pure water. The electrical conductivity and pH of the electrolyte solutions varied depending on the sulfuric acid concentration in the electrolyte solutions. 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 solutions for a predetermined period of time, and the electrolyte solutions were saturated with oxygen.

[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 above-described electrolyte solution. The working electrode was prepared by covering a portion of a plate material obtained by processing Sample A or Sample B to a predetermined size with a heat-shrinkable tube. The heat-shrinkable tube was resistant to the electrolyte solution, and the portion of the plate material not covered by the heat-shrinkable tube functioned as a working electrode in the electrolyte solution. The area of ​​the working electrode was 1 cm x 1 cm.

[0110] A potentiogalvanostat (Versa STAT4 manufactured by 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 reached 1.7 V or more from the natural potential, to measure the polarization characteristics. During the measurement of the polarization characteristics, oxygen gas was continuously blown in so as not to hit the surface of the working electrode.

[0111] From the test results, the corrosion current densities of Sample A and Sample B were determined. The current that flows 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 generation reaction associated with the decomposition of water. Here, the calculations are made assuming that all of the current that flows is the corrosion current of graphite. It can be determined that the smaller the corrosion current, the less likely the graphite is to oxidize. In this test example, the relationship between the corrosion current density, which is the corrosion current divided by the area of ​​the working electrode, and the pH or electrical conductivity of the electrolyte solution is shown in Figures 4 and 5. In Figures 4 and 5, the open circles plot the results for Sample A, and the closed circles plot the results for Sample B.

[0112] The horizontal axis of Fig. 4 represents the pH of the electrolyte solution, and the vertical axis represents the corrosion current density. The pH of the electrolyte solution used in the measurements of Samples A and B is shown in Table 1. The corrosion current densities shown in Figs. 4 and 5 are values ​​when the potential of the working electrode is 1.7 V. The unit of corrosion current density is mA / cm. ２ is.

[0113]

[0114] 5, the horizontal axis represents the electrical conductivity of the electrolyte solution, and the vertical axis represents the corrosion current density. The electrical conductivities of the electrolyte solutions used in the measurements of Samples A and B are shown in Table 2. The unit of electrical conductivity is μS / cm.

[0115]

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

[0117] As shown in Figure 5, the corrosion current density of Sample A and Sample B increased as the electrical conductivity of the electrolyte solution increased. Therefore, it is presumed that in the electrochemical cell 1 of the embodiment, the first conductive plate 31 becomes more susceptible to corrosion as the electrical conductivity of the first fluid 101 increases. It was found that Sample B, which has a higher degree of graphitization than Sample A, had 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. In both Sample A and Sample B, the corrosion current density was sufficiently small when the electrical conductivity of the electrolyte solution was 200 µS / cm or less.

[0118] 4 and 5 , when the pH is less than 4 or the electrical conductivity is more 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 is presumed that when the graphitization degree is less than 0.5, a corrosion current density larger than that shown in the graph for Sample A can be obtained.

[0119] On the other hand, as shown in FIGS. 4 and 5 , the closer the pH of the electrolyte solution is to 7 or the lower the electrical conductivity of the electrolyte solution is, the smaller the corrosion current density becomes. Therefore, when first fluid 101 contains a small amount of impurity ions, it is expected that the corrosion current density will be sufficiently small if the graphitization degree of 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 operation of the electrochemical cell 1 was determined by simulation. The corrosion current density determined in Test Example 2 was used in the simulation.

[0121] From the corrosion current density, the amount of charge flowing through the graphite contained in Sample A and Sample B, and the amount of carbon atoms in the graphite that decomposes can be calculated. Because the amount of carbon atoms contained in Sample A and B can be calculated from the composition of Sample A and B when they are produced, the amount of carbon atoms that decomposes over time can also be calculated. The amount of metal loss in first conductive plate 31 was calculated based on the amount of carbon atoms that decomposes. The amount of metal loss refers to the amount of reduction in the thickness of first conductive plate 31. The results of this simulation are shown in FIG. 6.

[0122] The horizontal axis of Figure 6 represents the operating time of the electrochemical cell 1, and the vertical axis represents the amount of metal loss. The operating time is measured in hours (h). The amount of metal loss is measured in μm. The black squares represent the simulation results when the first fluid 101 of pH 4 comes into contact with the first conductive plate 31 of sample A, and the black circles represent the simulation results when the first fluid 101 of pH 4 comes into contact with the first conductive plate 31 of sample B. The white squares represent the simulation results when the first fluid 101 of pH 5 comes into contact with the first conductive plate 31 of sample A, and the white circles represent the simulation results when the first fluid 101 of pH 5 comes into contact with the first conductive plate 31 of sample B.

[0123] As shown in FIG. 6 , the amount of thinning of first conductive plate 31 increases as the operating time increases. A comparison between the filled square plots and the open square plots, and a comparison between the filled circle plots and the open circle plots, reveals that the amount of thinning of first conductive plate 31 decreases as the pH approaches 7. A comparison between the filled square plots and the filled circle plots, and a comparison between the open square plots and the open circle plots, reveals that the amount of thinning of first conductive plate 31 formed from sample B is significantly smaller than that of first conductive plate 31 formed from sample A. Sample B has a higher degree of graphitization than sample A. These results reveal that increasing the degree of graphitization of the graphite contained in first conductive plate 31 is more effective at reducing the amount of thinning caused by operation of electrochemical cell 1 than bringing the pH of first fluid 101 closer to 7.

[0124] Test Example 4 The compressive strain of the second porous layer 42 in the electrochemical cell 1 was measured. The second porous layer 42 was 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 / cm. ２ When this carbon nonwoven fabric was compressed to a thickness of 300 μm, the weight per unit area of ​​the carbon nonwoven fabric was 90 g / cm ２ The porosity is 86.7%. The compressive strain is the value obtained by dividing the reduction in thickness λ (=t0-t1) of the compressed second porous layer 42 by the initial thickness t0 of the second porous layer 42 before compression. The thickness t1 is the thickness of the compressed second porous layer 42.

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

[0126] 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 includes a lower pedestal 90 and an upper pedestal 91. The upper pedestal 91 is configured to be movable downward. The compression device 9 applies a surface pressure to a member sandwiched between the lower pedestal 90 and the upper pedestal 91. The compression device 9 can automatically measure the surface pressure acting between the lower pedestal 90 and the upper pedestal 91 and the distance between the lower pedestal 90 and the upper pedestal 91. The compression device 9 is a commercially available strength evaluation device, for example, a micro strength evaluation tester MST-I type HR manufactured by Shimadzu Corporation.

[0127] When measuring the compressive strain of the carbon nonwoven fabric, a lower protective plate 92, second conductive plate 41, second porous layer 42, first conductive plate 31, and upper protective plate 93 were stacked in this order on lower pedestal 90. The lower protective plate 92 and upper protective plate 93 protect second conductive plate 41 and first conductive plate 31 from damage and apply uniform surface pressure to second porous layer 42. The lower protective plate 92 and upper protective plate 93 are made of stainless steel. Of the multiple members sandwiched between lower pedestal 90 and upper pedestal 91, only the second porous layer 42 changes 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 substantially change.

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

[0129] In Test Example 4, the compressive strains of the carbon cloth and carbon paper were also measured. The compressive strains of the carbon cloth and carbon paper were measured in the same manner as for the carbon nonwoven fabric. The results are also shown in the graph of FIG.

[0130] As shown in FIG. 8 , the compressive strain of the carbon nonwoven fabric when compressed at a surface pressure of 0.5 MPa was 0.3 to 0.8, more specifically, 0.6 to 0.8. Thus, the thickness of the carbon nonwoven fabric changes significantly with compression. Carbon nonwoven fabric has excellent elastic deformability. When the second porous layer 42 made of such a carbon nonwoven fabric is compressed between the electrolyte membrane 2 and the second conductive plate 41 as shown in FIG. 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. Therefore, the second porous layer 42 adheres closely to the electrolyte membrane 2 and the second conductive plate 41, and almost no local gaps are formed at the boundaries 1A and 1B. The almost complete absence of local gaps at the boundaries 1A and 1B facilitates the second fluid 102 to circulate throughout the entire second flow field 6. As a result, the Faraday efficiency of the electrochemical cell 1 is expected to be improved.

[0131] The compressive strain of the carbon cloth when pressed with a surface pressure of 0.5 MPa was 0.3 or more, more specifically, 0.4 or more. That is, the thickness of the carbon cloth changes to some extent depending on the pressure. When second porous layer 42 made of such carbon cloth is disposed between electrolyte membrane 2 and second conductive plate 41 as shown in FIG. 3, gaps are unlikely to form at boundaries 1A and 1B.

[0132] As described above, the carbon cloth and carbon nonwoven fabric satisfy a compressive strain of 0.3 or more even when the surface pressure is relatively small, at about 0.1 MPa, and even when the surface pressure is greater, the compressive strain remains 0.3 or more. Because the surface pressure within the electrochemical cell 1 is greater than 0.1 MPa, it can be said that the compressive strain of the carbon cloth and carbon nonwoven fabric in the electrochemical cell 1 satisfies 0.3 or more.

[0133] The compressive strain of the carbon paper when pressed with a surface pressure of 0.5 MPa was less than 0.2, more specifically, 0.18 or less. That is, the thickness of the carbon paper hardly changes due to the pressure. When second porous layer 42 made of such carbon paper is disposed between electrolyte membrane 2 and second conductive plate 41 as shown in FIG. 3, gaps are likely to form at boundaries 1A and 1B.

[0134] When the electrochemical cell 1 is enlarged or 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 clamp the multiple electrochemical cells 1. Furthermore, variations in dimensions may occur due to deformation of the components over time. In an electrochemical cell 1 including 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 FIG. 3, and the gaps are likely to cause a decrease in the Faraday efficiency.

[0135] Even if the above-described variations occur, the second porous layer 42 made of carbon nonwoven fabric maintains a state of close contact between the electrolyte membrane 2 and the second conductive plate 41 due to elastic deformation. As a result, local gaps are unlikely to occur at the boundaries 1A and 1B in Figure 3. Therefore, it is believed that the electrochemical cell 1 including the second porous layer 42 made of carbon nonwoven fabric can maintain high Faraday efficiency for a long period of time.

[0136] Furthermore, corrosion may occur over long-term use, resulting in a reduction in the thickness of first conductive plate 31. Even in this case, elastic deformation of second porous layer 42 made of carbon nonwoven fabric tends to maintain a state of surface contact between adjacent components that make up electrochemical cell 1, i.e., first conductive plate 31, first porous layer 32, electrolyte membrane 2, second porous layer 42, and second conductive plate 41. Increasing the degree of graphitization or bringing the pH of first fluid 101 closer to 7, as described above, makes it even easier to maintain the above-mentioned state of surface contact.

[0137] <Test Example 4-2> A plurality of carbon nonwoven fabrics X, Y, and Z were prepared, each having a different porosity and basis weight from those in Test Example 4, and the compressive strain of each of the carbon nonwoven fabrics X, Y, and Z was measured under the same conditions as in Test Example 4. The porosity, basis weight, and average diameter of the carbon fibers of each of the carbon nonwoven fabrics X, Y, and Z are shown in Table 3. The porosity in Table 3 is the value when a carbon nonwoven fabric with a thickness of 1.0 mm was compressed to 0.3 mm.

[0138]

[0139] The compression strain of the carbon nonwoven fabrics X, Y, and Z was in the range of 0.6 to 0.8. This test confirmed that the porosity in the compressed state was 80% to 90%, and the basis weight was 70 g / m ２ 130g / m or more ２ It was shown below that if the average diameter of the carbon fibers is in the range of 5 μm or more and 20 μm or less, a nonwoven fabric having a compression strain of 0.6 or more and 0.8 or less can be constructed.

[0140] REFERENCE SIGNS LIST 1 Electrochemical cell 1A, 1B Boundary 2 Electrolyte membrane 21 First surface, 22 Second surface 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 field 5A Inlet, 5B Outlet 6 Second flow field 6A Inlet, 6B Outlet 9 Compression device 90 Lower base, 91 Upper base, 92 Lower protective plate, 93 Upper protective plate 100 Organic hydride manufacturing apparatus 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. The fuel cell has an anode section and a cathode section sandwiching an electrolyte membrane, An electrochemical cell in which a first fluid mainly composed of water is supplied to the anode section, and the water is electrolyzed between the anode section and the cathode section to generate protons, the anode portion includes a first conductive plate formed of a composite material including a first resin and a first carbon material; The first conductive plate satisfies the following conditions in a three-electrode measuring cell using the first conductive plate as a working electrode: the hydrogen ion exponent of the electrolyte solution in the measuring cell is 4 or more, and the corrosion current density when the potential of the working electrode is 1.7 V is 0.1 mA / cm 2 or less. Electrochemical cell.

2. An electrochemical cell as described in claim 1, wherein the electrical conductivity of the electrolyte solution is 200 μS / cm or less.

3. the first carbon material comprises graphite; 3. The electrochemical cell of claim 1, wherein the first conductive plate has a degree of graphitization of 0.5 or more.

4. 3. The electrochemical cell of claim 1, wherein the first fluid has an electrical conductivity of 200 μS / cm or less.

5. 3. The electrochemical cell of claim 1, wherein the first fluid has a hydrogen ion exponent of 4 or greater.

6. 3 . The electrochemical cell according to claim 1 , wherein a content of the first carbon material in the first conductive plate is 70% by mass or more when a mass of the first conductive plate is 100% by mass.

7. 3. The electrochemical cell according to claim 1, wherein a second fluid containing an organic compound having an unsaturated bond is circulated through the cathode section.

8. the cathode portion includes a second conductive plate formed of a composite material including a second resin and a second carbon material; the second carbon material comprises graphite; 3. The electrochemical cell according to claim 1, wherein a content of the second carbon material in the second conductive plate is 70% by mass or more when a mass of the second conductive plate is 100% by mass.

9. 9. The electrochemical cell according to claim 8, wherein the second resin is at least one selected from the group consisting of polyester resin, polyamide resin, polyacetal resin, phenol resin, polyvinylidene chloride resin, polyvinylidene fluoride resin, polytetrafluoroethylene resin, epoxy resin, polyoxymethylene resin, and polyphenylene sulfide resin.

10. the anode assembly includes a first porous layer formed of a conductive material; 3. The electrochemical cell according to claim 1, wherein the first porous layer has an average thickness of 0.20 mm or more and 0.40 mm or less.

11. the first porous layer includes a substrate made of metal and a coating formed on a 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; The substrate is in the form of a fiber aggregate, a porous sintered body, a foamed molded body, or an expanded metal, 11. The electrochemical cell of claim 10, wherein the coating comprises platinum.

12. the cathode portion includes a second porous layer formed of a conductive material; 3. The electrochemical cell according to claim 1, wherein the second porous layer in the cathode section has a compressive strain of 0.3 to 0.

8.

13. 13. The electrochemical cell of claim 12, wherein the second porous layer comprises a nonwoven fabric having carbon fibers.