Cathode diffusion layer for organic hydride production

Abstract

The present invention aims to provide a cathode diffusion layer for organic hydride production in an electrolytic cell for organic hydride production using a Dimensionally Stable Electrode (DSE) as the anode, which promotes the removal of water from within the cathode catalyst layer and enables good current efficiency even at high current densities. [Solution] A cathode diffusion layer for organic hydride production in an electrolytic cell for organic hydride production with DSE as the anode, wherein the cathode diffusion layer is provided in direct contact with the cathode catalyst layer, the cathode diffusion layer contains carbon foam, the carbon foam is a porous material having continuous voids, and has linear portions and bonding portions connecting the linear portions, and the surface oxygen concentration measured by X-ray photoelectron spectroscopy is 8.0 atomic% or more and 15 atomic% or less, characterized in that the cathode diffusion layer for organic hydride production.

Description

[Technical Field]

[0001] This invention relates to a technique for electrochemically hydrogenating organic compounds, and more specifically, to a cathode diffusion layer used in an electrolytic cell for the production of organic hydrides. [Background technology]

[0002] Hydrogen is widely used industrially in petroleum refining, chemical synthesis materials, metal refining, and stationary fuel cells. In recent years, its potential uses have expanded to include hydrogen refueling stations for fuel cell vehicles (FCVs), smart communities, and hydrogen power plants. Furthermore, as renewable energy is increasingly introduced, it has become necessary to maintain the supply-demand balance of the power grid, leading to the development of hydrogen carrier technologies that can efficiently store and transport large amounts of electricity.

[0003] Hydrogen carriers primarily include liquefied hydrogen, ammonia, and organic hydrides (hydrogenated organic compounds) in which hydrogen is chemically bonded to organic compounds such as benzene, toluene, and naphthalene. Liquefied hydrogen has the advantage of high hydrogen compression density, but requires low temperature and high pressure for storage and transportation, and the decrease in energy efficiency due to boil-off is a factor that increases costs. Ammonia can store hydrogen at a higher density than liquefied hydrogen, but establishing dehydrogenation technology and handling methods for removing and utilizing the hydrogen is a major challenge. On the other hand, methylcyclohexane, a type of organic hydride in which hydrogen is bonded to toluene, is inferior to liquefied hydrogen and ammonia, but can store hydrogen at a higher density than compressed hydrogen and has the advantage of being able to utilize the same infrastructure technology as gasoline. Furthermore, dehydrogenation catalysts have also been developed, and methylcyclohexane is considered to be the most feasible hydrogen carrier.

[0004] Organic hydrides, used as hydrogen carriers, are produced by introducing hydrogen and hydrogenated organic compound gases into a fixed-bed reactor, where granular catalysts are supported on a mesh-like bed, under high temperature and pressure. However, since the hydrogenation reaction of hydrogenated organic compounds such as benzene and toluene is an exothermic reaction, some of the energy contained in the hydrogen is lost as heat. Furthermore, extracting hydrogen from organic hydrides requires reinjecting the energy lost due to this heat loss, resulting in high energy costs for hydrogen utilization.

[0005] On the other hand, a technology has been developed to directly produce organic hydrides without the need for hydrogen by electrochemically reacting water with hydrogenate organic compounds. This method reduces heat loss due to hydrogenation reactions and eliminates the need for hydrogenation plants, thus enabling significant reductions in equipment. As a result, a reduction in the total cost of hydrogen utilization can be expected.

[0006] In the electrolytic synthesis of organic hydrides, the anode chamber liquid, which is an aqueous solution, and the cathode chamber liquid, which is an organic compound, are separated by a solid polymer electrolyte (PEM) membrane to separate them. At the electrode surface of the cathode chamber, it is necessary to rapidly and uniformly supply the hydrogenated organic compound (the raw material) and discharge the organic hydride (the product). If the supply and discharge are not carried out quickly, it will lead to hydrogen generation due to side reactions, hindering the reduction of the hydrogenated organic compound and resulting in a decrease in current efficiency. From this perspective, increasing the temperature of the organic hydride electrolytic synthesis cell reduces the viscosity of the hydrogenated organic compound and improves the mass transfer of the hydrogenated organic compound. On the other hand, the amount of water (associated water) that permeates the solid polymer electrolyte membrane with protons from the anode chamber and diffuses into the cathode chamber increases, hindering the mass transfer of the hydrogenated organic compound. As a result, the current efficiency, which is the efficiency of the number of electrons contributing to organic hydride purification relative to the number of electrons that pass through the electrolytic synthesis cell, decreases. This tendency becomes more pronounced as the current density increases.

[0007] Therefore, for example, Patent Document 1 discloses an electrolytic cell for producing an organic hydride, which uses a cathode having a cathode catalyst layer and a cathode diffusion layer, and uses a carbon foam having a specific porous structure in the cathode diffusion layer to reduce the mass transfer resistance on the cathode chamber side and improve the current efficiency even at a high current density. In addition, Patent Document 2 discloses an organic hydride production apparatus that uses a cathode having a cathode catalyst layer, a microporous layer, and a diffusion layer in this order, and contains a hydrophilic porous oxide in the microporous layer to suppress the accumulation of accompanying water in the cathode catalyst layer, thereby suppressing the inhibition of the supply of the hydride to the cathode catalyst layer and improving the power efficiency. Patent Document 3 discloses an organic hydride production apparatus that uses a cathode having a cathode catalyst layer and a diffusion layer including a highly hydrophilic region and a low hydrophilic region, arranges the low hydrophilic region of the diffusion layer on the cathode catalyst layer side, and arranges the highly hydrophilic region on the end plate side, thereby inducing the water dispersed near the cathode catalyst layer to the end plate side to promote the discharge of water from the cathode catalyst layer, thereby suppressing the inhibition of the supply of the hydride to the cathode catalyst layer and suppressing the increase in the electrolysis voltage.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] In an organic hydride production apparatus, the requirement for improving the current efficiency is inevitable, and in order to further improve the current efficiency, improvement of the mass transfer on the cathode chamber side is strongly desired.

[0010] Therefore, the present invention has been made in view of the problems of the above-mentioned prior art, and aims to provide a cathode diffusion layer for organic hydride production in an electrolytic cell for organic hydride production using a Dimensionally Stable Electrode (DSE) as the anode, which promotes the removal of water from within the cathode catalyst layer and enables good current efficiency even at high current densities. [Means for solving the problem]

[0011] As a result of diligent research into ways to solve the above problems, the present inventors have found that by using a cathode diffusion layer containing carbon foam having a specific porous structure and a surface oxygen concentration within a specific range, and by ensuring that the cathode catalyst layer and the cathode diffusion layer are in direct contact, the removal of water from within the cathode catalyst layer is promoted, and good current efficiency is observed even at high current densities, thus completing the present invention.

[0012] In other words, the present invention is as follows: [1] In an electrolytic cell for the production of organic hydrides, which uses a dimensionally stable electron (DSE) as the anode, a cathode diffusion layer is provided so as to be in direct contact with the cathode catalyst layer, The cathode diffusion layer comprises carbon foam, The carbon foam is a porous material having continuous voids, comprising linear portions and bonding portions connecting the linear portions, and having a surface oxygen concentration of 8.0 atomic% or more and 15.0 atomic% or less as measured by X-ray photoelectron spectroscopy. A cathode diffusion layer for organic hydride production, characterized by the above features. [2] The cathode diffusion layer for producing organic hydrides according to [1], wherein the carbon foam has an average fiber diameter of 0.5 μm or more and 4.0 μm or less in the linear portion. [3] The carbon foam is a cathode diffusion layer for organic hydride production according to [1] or [2], wherein the Taber bending stiffness measured in accordance with JIS P8125 is 1.0 gf·cm or more and 50.0 gf·cm or less. [4] The carbon foam has a bonding density of 20,000 units / mm³ in at least a portion of it. 3 The above describes a cathode diffusion layer for organic hydride production, wherein the crystallite size determined from the diffraction of the (002) plane in powder X-ray diffraction measurement is 1.50 nm or larger, as described in any of [1] to [3]. [5] The carbon foam has an average carbon frequency of 0.0004 to 0.0035 μm -2 A cathode diffusion layer for the production of organic hydrides, as described in any of [1] to [4]. [6] The carbon foam has a carbon frequency standard deviation of 0.0005 or less, and is a cathode diffusion layer for organic hydride production according to any one of [1] to [5]. [7] The carbon foam has an average carbon area ratio of 0.010 to 0.300, and is a cathode diffusion layer for organic hydride production according to any one of [1] to [6]. [8] The carbon foam has a carbon area ratio standard deviation of 0.030 or less, and is a cathode diffusion layer for organic hydride production according to any one of [1] to [7]. [Effects of the Invention]

[0013] According to the present invention, in an electrolytic cell for organic hydride production using DSE as the anode, it is possible to provide a cathode diffusion layer for organic hydride production that promotes the removal of water from within the cathode catalyst layer and enables good current efficiency even at high current densities. [Brief explanation of the drawing]

[0014] [Figure 1] This is a SEM image of an example of a carbon foam with continuous voids. [Figure 2]This is a flowchart of the method for manufacturing carbon foam according to this embodiment. [Modes for carrying out the invention]

[0015] The following describes in detail an embodiment for carrying out the present invention (hereinafter referred to as "this embodiment"), but the present invention is not limited to the following description and can be implemented in various modifications within the scope of its gist.

[0016] The electrolytic cell for producing organic hydrides according to this embodiment (electrolytic cell for producing organic hydrides) is provided with a proton-conducting solid polymer electrolyte membrane, an anode provided on one side of the solid polymer electrolyte membrane for oxidizing water to generate protons, and a cathode catalyst layer provided on the other side of the solid polymer electrolyte membrane for reducing hydrogenated organic compounds, and the anode chamber for supplying water and the cathode chamber for supplying hydrogenated organic compounds are separated by the solid polymer electrolyte membrane. The cathode diffusion layer is provided within the cathode chamber so as to be in direct contact with the cathode catalyst layer, and together with the cathode catalyst layer, it constitutes the cathode. The cathode diffusion layer plays the role of supplying hydrogenated organic compounds and discharging organic hydrides, as well as acting as a conductor of electrons used in reduction. Direct contact between the cathode diffusion layer and the cathode catalyst layer allows for a significant reduction in contact resistance.

[0017] (Cathode diffusion layer) In this embodiment, the cathode diffusion layer preferably has a three-dimensional continuous structure of conductors, from the viewpoint of efficiently conducting electrons from the current collector to the cathode catalyst layer. Furthermore, the cathode diffusion layer is preferably a porous material with continuous voids, from the viewpoint of rapidly facilitating mass transfer between the hydrogenated organic compound and the organic hydride. From these viewpoints, carbon foam, which is a porous material with continuous voids, is preferably used. Figure 1 is a SEM image of an example of a carbon foam with continuous voids. The carbon foam used in the cathode diffusion layer may be a single layer or a laminate of two or more layers. Furthermore, the carbon foam may be of a single type or a combination of multiple types.

[0018] In this embodiment, the thickness of the cathode diffusion layer is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 150 μm or more, from the viewpoint of reducing mass transfer resistance. Furthermore, from the viewpoint of reducing ohmic resistance, the thickness of the cathode diffusion layer is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less.

[0019] (Carbon foam) The carbon foam of this embodiment has linear portions and connecting portions that join the linear portions. Multiple (two or more, three or more, four or more, etc.) linear portions may be joined at a single connecting portion. In this specification, the fiber diameter of the linear portion is the thickness of the linear portion that connects the connecting portions. Of the portion having a linear shape, the portion in which the fiber diameter is within twice the minimum fiber diameter of the portion is defined as the linear portion, and the portion in which the fiber diameter is more than twice the minimum fiber diameter of the portion is defined as the connecting portion.

[0020] (Average fiber diameter of the linear portion) In this embodiment, the average fiber diameter of the linear portion of the carbon foam is preferably 0.5 μm or more, more preferably 0.8 μm or more, and most preferably 1.2 μm or more, from the viewpoint of good physical strength and conductivity. Furthermore, from the viewpoint of maintaining good deformability and resilience during the compression behavior of the carbon foam, the average fiber diameter of the linear portion is preferably 4.0 μm or less, more preferably 3.5 μm or less, and most preferably 3.0 μm or less.

[0021] (joint density) The density of the bonding portion of the carbon foam in this embodiment is 20,000 units / mm², from the viewpoint of resilience when a compressive load is applied. 3 Preferably, the number is 80,000 or more, and more preferably 80,000 pieces / mm 3 The above, and more preferably 500,000 pieces / mm 3That concludes the explanation. Furthermore, the density of the carbon foam bonds is 5,000,000 / mm², considering the flexibility of the carbon foam. 3 Preferably, the density is as follows, and more preferably 4,000,000 pieces / mm². 3 The following, and more preferably 3,000,000 pieces / mm 3 The following applies:

[0022] It is preferable that at least a portion of the carbon foam in this embodiment contains areas that satisfy the density range of the bonding area, more preferably that the density range is satisfied at 50 volume% or more, even more preferably at 75 volume% or more, and particularly preferably that the density range is satisfied at any part of the carbon foam.

[0023] (Surface oxygen concentration) In this embodiment, the carbon foam has a surface oxygen concentration of 8.0 atomic% or higher, preferably 9.5 atomic% or higher, and more preferably 11.0 atomic% or higher, as determined by surface analysis using X-ray photoelectron spectroscopy. When the surface oxygen concentration is 8.0 atomic% or higher, in an electrolytic cell for organic hydride production using DSE as the anode and carbon foam as the cathode diffusion layer, it has sufficient hydrophilicity to effectively discharge water permeating through the solid polymer electrolyte membrane and can exhibit good current efficiency even at high current densities. Furthermore, the surface oxygen concentration is 15.0 atomic% or lower, preferably 13.5 atomic% or lower, and more preferably 12.0 atomic% or lower. When the surface oxygen concentration is 15.0 atomic% or lower, in an electrolytic cell for organic hydride production using DSE as the anode and carbon foam as the cathode diffusion layer, the resistance is stably kept low for long-term charge and discharge, thereby stably keeping the cell voltage low and enabling efficient production of organic hydrides. Furthermore, when carbon foam is used as the cathode diffusion layer, if the surface oxygen concentration on the surface in direct contact with the cathode catalyst layer is within the above range, good current efficiency can be achieved even at high current densities, as described above. Therefore, for example, when using a laminate of carbon foam with a surface oxygen concentration within the above range and carbon foam with a surface oxygen concentration outside the above range as the cathode diffusion layer, an electrolytic cell exhibiting good current efficiency can be obtained by placing the carbon foam with a surface oxygen concentration within the above range on the side in direct contact with the cathode catalyst layer. Methods for controlling the surface oxygen concentration of carbon foam include, for example, heat treatment of the carbon foam in air, as described later, and oxidizing the surface by immersion in an aqueous potassium permanganate solution. In either method, the surface oxygen concentration can be adjusted by controlling the degree of oxidation by adjusting the temperature and time of the treatment.

[0024] (carbon content) The carbon content of the carbon foam in this embodiment is preferably 51% by mass or more, preferably 60% by mass or more, preferably 70% by mass or more, preferably 80% by mass or more, preferably 85% by mass or more, more preferably 90% by mass or more, and even more preferably 98% by mass or more, from the viewpoint of conductivity. The upper limit of the carbon content is not particularly limited, but may be 100% by mass or less, or 99% by mass or less. The carbon content of the carbon foam can be determined by X-ray fluorescence measurement, and specifically, it shall be measured by the method described in the examples.

[0025] (Ratio of the number of linear parts to the number of joints) In the carbon foam of this embodiment, the ratio of the number of linear sections to the number of joints may be 1.4 or more and 1.55 or less. In other words, this ratio is the average number of branches that branch at the joints. By having a ratio of 1.4 or more, the carbon foam of this embodiment can be excluded from structures in which linear sections do not have a three-dimensional mesh structure where linear sections are joined at the joints, and where unjointed linear sections are in contact, like in nonwoven fabrics. Furthermore, by having a ratio of 1.55 or less, porous structures in which linear sections form strips, such as honeycomb-like walls, can be excluded from the carbon foam of this embodiment. Preferably, this ratio is 1.42 or more and 1.53 or less, and more preferably 1.44 or more and 1.50 or less.

[0026] (Orientation angle of the linear portion) In this embodiment, when carbon foam is carbonized by heat treatment in a heat treatment furnace, for example, by heat treatment of melamine resin foam, the carbon fibers constituting the framework of the carbon foam have an isotropic structure in which they are evenly spread in all directions. In such carbon foam, the difference θ between the average orientation angle in one direction and the average orientation angle in the other directions is usually 1° or less. However, when carbonizing melamine resin foam by heat treatment, applying compressive stress to the resin foam that will be used as the raw material for carbon foam results in a carbon foam with an anisotropic skeletal structure in which the carbon fibers spread. In such a carbon foam, even when a compressive load is applied, the fracture of the carbon fibers (linear parts) can be suppressed, reducing powder shedding and achieving high resilience. To obtain this effect, the carbon foam in this embodiment may have an average difference of 3° or more in orientation angles. This difference is preferably 5° or more, and more preferably 8° or more. The three directions mentioned above may be, for example, the x, y, and z directions, and may be arbitrarily set relative to the carbon foam.

[0027] (porosity) The porosity of the carbon foam in this embodiment may be 50% or more, preferably 60% or more, and more preferably 70% or more, from the viewpoint of flexibility. Furthermore, the porosity of the carbon foam in this embodiment may be 99% or less, preferably 98% or less, and more preferably 95% or less, from the viewpoint of improving surface area and reducing cell resistance. In this embodiment, the porosity is a value obtained from the bulk density and true density. Bulk density is the density based on the volume including the voids contained in the carbon foam. In contrast, true density is the density based on the volume occupied by the material of the carbon foam.

[0028] (Taber bending stiffness) In this embodiment, the carbon foam preferably has a Taber bending stiffness of 1.0 gf·cm or more, more preferably 5.0 gf·cm or more, and most preferably 10.0 gf·cm or more, as measured in accordance with JIS P8125, from the viewpoint of good handling. On the other hand, from the viewpoint of high flexibility and good conformability within the cell, it is preferably 50.0 gf·cm or less, more preferably 45.0 gf·cm or less, and most preferably 40.0 gf·cm or less. The Taber bending stiffness of the carbon foam can be increased, for example, by compressing it during the formation process to adjust the density, or by coating the surface of the carbon foam with a carbon material such as carbon black. The tapered bending stiffness shall be measured specifically by the method described in the examples.

[0029] (crystallite size) In this embodiment, the crystallite size (layer thickness in the c-axis direction of the carbon crystal) Lc of the carbon foam is preferably 1.50 nm or more, and more preferably 1.80 nm or more from the viewpoint of conductivity. Furthermore, from the viewpoint of physical fragility, it is preferably 4.00 nm or less, and more preferably 3.00 nm or less.

[0030] (Average carbon frequency) The average carbon frequency of the carbon form in this embodiment is 0.0004 μm or more from the viewpoint of ensuring good contact with the cathode catalyst layer and the current collector plate (cathode plate) and reducing resistance. -2 More preferably, it is 0.0005 μm or more. -2 Even more preferably, it is 0.0010 μm or more. -2 Also, from the viewpoint of maintaining the strength in the cathode diffusion layer and ensuring flexibility to improve handling properties, the average carbon frequency is preferably 0.0035 μm or less, more preferably 0.0030 μm or less, and even more preferably 0.0028 μm or less. -2 More preferably, it is 0.0030 μm or less. -2 Even more preferably, it is 0.0028 μm or less. -2 (End)

[0031] (Standard deviation of carbon frequency) The standard deviation of the carbon frequency of the carbon form in this embodiment is preferably 0.0005 or less, more preferably 0.0004 or less, and even more preferably 0.0002 or less from the viewpoint of uniform liquid permeability in the cathode diffusion layer, efficient hydrogen addition reaction, and good current efficiency. The lower limit of the standard deviation of the carbon frequency is not particularly limited.

[0032] (Average carbon area ratio) The average carbon area ratio of the carbon form in this embodiment is preferably 0.010 or more, more preferably 0.020 or more, and even more preferably 0.10 or more from the viewpoint of good electrical conductivity of the cathode diffusion layer. Also, from the viewpoint of ensuring liquid permeability in the cathode diffusion layer and reducing resistance in mass transfer, the average carbon area ratio is preferably 0.300 or less, more preferably 0.250 or less, and even more preferably 0.200 or less.

[0033] (Standard deviation of carbon area ratio) The standard deviation of the carbon area ratio of the carbon form in this embodiment is preferably 0.030 or less, more preferably 0.025 or less, and even more preferably 0.020 or less from the viewpoint of uniform liquid permeability in the cathode diffusion layer, efficient hydrogen addition reaction, and good current efficiency. The lower limit of the standard deviation of the carbon area ratio is not particularly limited.

[0034] (Method for measuring surface oxygen concentration) In this specification, the oxygen concentration on the carbon foam surface, determined by surface analysis using X-ray photoelectron spectroscopy, can be calculated using an X-ray photoelectron spectrometer (ULVAC-FI VersaProbe II) as the ratio (percentage) of the area of ​​the O1s peak near 533 eV to the total area of ​​the peaks of the major elements (C1s peak near 285 eV, N1s peak near 400 eV, and O1s peak near 533 eV). If there are peaks of elements other than the major elements listed above that have a high detection intensity, these will also be included in the calculation of the total area.

[0035] (Method for measuring crystallite size) The crystallite size Lc of the carbon foam is determined from the diffraction of the (002) plane obtained by wide-angle X-ray diffraction. After grinding the sample in a mortar, wide-angle X-ray measurements are performed on the ground sample using a benchtop X-ray diffractometer D2 PHASER (Bluker). The specific measurement conditions are as follows. -Measurement conditions- Source: Cu Kα Tube current: 30mA Tube voltage: 40kV Slit: 1mm Sample rotation speed: 10 revolutions / min Measurement time per step: 0.3 seconds Starting angle (2θ): 5.00° Measurement step (2θ): 0.01° End angle (2θ): 90.00° After the above measurements, the obtained data is analyzed to calculate the crystallite size Lc. The crystallite size Lc can be calculated by substituting the full width at half maximum β of the diffraction peak of the (002) plane that appears around 2θ = 25 degrees and the angle θ of the peak's maximum value into the following equation (c) (Scherrer's equation). Generally, the higher the temperature at which carbonization occurs, the higher the crystallinity and the larger the Lc value. Lc = (Kλ) / βcosθ···(c) Here, K is the shape factor and λ is the wavelength of the radiation source. Since the shape factor is (002) plane diffraction, we substitute 0.90. Since we are using CuKα as the radiation source in this case, we substitute 1.541 and perform the calculation.

[0036] (Method for measuring average fiber diameter) In this specification, the fiber diameter of the carbon fibers constituting the carbon foam is determined by image analysis of scanning electron microscope (SEM) images. Specifically, the carbon foam is observed at a magnification of 10,000x using a scanning electron microscope. Assuming a circular cross-sectional shape, the thickness of the carbon fiber is considered to be the fiber diameter. The average fiber diameter is the average value of the fiber diameters measured as described above at any 20 locations.

[0037] (Method for measuring bond density, the number of bonded and linear parts, and orientation angle) In this specification, the bond density, the number of bonds and linear segments, and the orientation angle are values ​​obtained by imaging carbon foam using an X-ray CT (Computerized Tomography) device, preprocessing the obtained tomographic data with a 3D median filter using a filter size of 2 pixels radius, then dividing the region into structure and space using Otsu's binarization algorithm (see Nobuyuki Otsu, "Automatic Threshold Selection Method Based on Discriminant and Least Squares Criteria," IEICE Transactions on Electronics, Information and Communication Engineers, Vol. J63-D, No. 4, pp. 346-356 (1980)), creating a 3D image of the structure including the interior of the carbon foam, and then determining the values ​​using structural analysis software from the obtained 3D image. Specifically, the number of bonds and linear segments is determined by detecting and counting the bonds and linear segments contained in the three-dimensional image obtained as described above. The bond density is determined by counting the number of bonds per unit volume of 1 mm × 1 mm × 1 mm. The ratio of the number of linear segments to the number of bonds is determined based on the number of bonds and linear segments counted as described above for the same carbon foam. Furthermore, the orientation angle θ of the linear portion is the angle between the straight line connecting the two ends of the linear portion and each direction. This angle is calculated for each of the three mutually orthogonal directions in the three-dimensional image, and the average value of the orientation angle of the linear portion can be calculated for each direction. For structural analysis of carbon foam, a CT scanner using low-energy, high-brightness X-rays, such as the nano3DX high-resolution 3DX-ray microscope manufactured by Rigaku Corporation, can be used. Furthermore, for image processing and structural analysis, software such as the Centerline editor from simpleware, manufactured by JSOL Corporation, can be used.

[0038] (Method for measuring average carbon frequency and average carbon area ratio) In this specification, the average carbon frequency and average carbon area ratio of carbon foam are measured as follows. Three-dimensional images obtained using the above-mentioned X-ray CT apparatus are processed with a 3D median filter with a filter size of radius 2 pixels and binarized using Otsu's algorithm. Furthermore, within the analysis area (624 μm × 624 μm) of the cross-sectional image in the thickness direction of the carbon foam (an image of a cross-section cut perpendicular to the thickness direction of the carbon foam), the number of consecutive carbon portions and the sum of the areas of consecutive carbon portions within the analysis area are detected using the particle analysis function of the image processing software ImageJ. By dividing these by the area of ​​the analysis area as shown in the formula below, the carbon frequency and carbon area ratio per 1 μm × 1 μm can be calculated. The same operation is repeated for 1152 cross-sectional images in the thickness direction of the carbon foam (acquired at 0.54 μm / pitch), and the average value of the measured values ​​obtained in the entire area can be calculated to determine the average carbon frequency and average carbon area ratio. Furthermore, during analysis, calculations can be performed using analysis conditions that include the region at the edge of the image. Furthermore, when calculating the average, regions where no carbon sample exists will be excluded, and the average will be calculated using cross-sectional images in which the carbon area ratio in the analysis region is 0.01 or higher. Carbon frequency (μm) -2 ) = Number of consecutive carbon atoms / Area of ​​the analysis region Carbon area ratio = Total area of ​​continuous carbon portions / Area of ​​the analysis region [Image processing conditions] Pixel count: 1152 x 1202 pixels Pixel size: 0.54 μm / pixel Thickness direction: 1152 sheets (0.54 μm / pitch) Software used: ImageJ 1.50i

[0039] (Method for measuring the standard deviation of carbon frequency) Regarding the average carbon frequency of the carbon foam described above, the standard deviation of the carbon frequencies obtained from each cross-sectional image in the thickness direction can be calculated. In doing so, to exclude regions where no carbon sample exists, cross-sectional images in which the carbon area ratio in the analysis region is 0.01 or higher should be used.

[0040] (Method for measuring the standard deviation of the carbon area ratio) Regarding the carbon area ratio of the carbon foam described above, the standard deviation of the carbon area ratio obtained from each cross-sectional image in the thickness direction can be calculated. In this case, in order to exclude regions where no carbon sample is present, cross-sectional images in which the carbon area ratio in the analysis region is 0.01 or greater should be used.

[0041] (Method for measuring surface area) In this specification, the surface area of ​​carbon foam is determined by measuring the surface dimensions using, for example, a caliper, and then calculating the surface area from the obtained dimensions.

[0042] (Calculation of void ratio) In this specification, the porosity Vf,pore can be determined from the bulk density ρbulk and true density ρreal obtained as described below, using the following equation (X). Vf,pore=((1 / ρbulk)-(1 / ρreal)) / (1 / ρbulk)×100 (%) ···(X)

[0043] (Measurement of bulk density) First, the dimensions of the carbon foam are measured using calipers or similar tools, and the bulk volume Vbulk of the carbon foam is determined from these dimensions. Next, the mass M of the carbon foam is measured using a precision balance. From the obtained mass M and bulk volume Vbulk, the bulk density ρbulk of the carbon foam can be calculated using the following equation (Y). ρbulk = M / Vbulk ···(Y)

[0044] (Measurement of true density) The true density (ρreal) of carbon foam can be determined by the buoyancy method using a mixture of n-heptane, carbon tetrachloride, and ethylene dibromide. Specifically, first, a suitable size of carbon foam is placed in a stoppered test tube. Next, the three solvents are mixed appropriately and added to the test tube, which is then immersed in a 30°C constant temperature bath. If the sample floats, low-density n-heptane is added. On the other hand, if the test piece sinks, high-density ethylene dibromide is added. This procedure is repeated until the test piece floats in the liquid. Finally, the density of the liquid is measured using a Gay-Lussac gravity bottle.

[0045] (Manufacturing method of carbon foam) The method for manufacturing carbon foam according to this embodiment may include a raw material foam introduction step of introducing resin foam, which will be the raw material for carbon foam, into a heat treatment furnace; a heating step of raising the temperature inside the heat treatment furnace to a heat treatment temperature at a first heating rate; a carbonization step of carbonizing the resin foam to carbonize it by holding it at the heat treatment temperature for a predetermined time; a cooling step of lowering the temperature inside the heat treatment furnace to room temperature; and a carbon foam removal step of removing the carbon foam from the heat treatment furnace. Here, the heating step may be performed while evacuating the heat treatment furnace under reduced pressure, at least in a first temperature range where the amount of decomposable desorbed gas generated from the resin foam is large. Figure 2 is a flowchart of the method for manufacturing carbon foam according to this embodiment.

[0046] First, in step S1, the resin foam that will be used as the raw material for the carbon foam is introduced into the heat treatment furnace.

[0047] (Raw material foam introduction process) Any resin foam known as a raw material for carbon foam can be used as the resin foam used as the raw material for carbon foam. For example, when using melamine resin foam as the raw material resin foam, a melamine / formaldehyde condensation foam manufactured by the method disclosed in Japanese Patent Application Publication No. 4-349178 can be used as the melamine resin foam. However, the resin foam is not limited to melamine resin foam, and may also be urethane resin foam, phenolic resin foam, etc. According to the above method, a melamine / formaldehyde condensate foam can be obtained by first foaming an aqueous solution or dispersion containing a melamine / formaldehyde precondensate, an emulsifier, a volatile foaming agent, a curing agent, and optionally a well-known filler, and then curing it.

[0048] In the above method, as the melamine / formaldehyde precondensate, for example, a melamine:formaldehyde mixture with a ratio of 1:1.5 to 1:4 and an average molecular weight of 200 to 1000 can be used. As an emulsifier, for example, 0.5 to 5% by mass (based on the melamine / formaldehyde precondensate, the same applies hereinafter) of sodium salts of alkyl sulfonic acid or aryl sulfonic acid can be used. As a volatile blowing agent, for example, 1 to 50% by mass of pentane or hexane can be used. As a curing agent, 0.01 to 20% by mass of hydrochloric acid or sulfuric acid can be used. In the foaming and curing treatments, the solution consisting of the above components should be heated to a temperature set according to the type of volatile blowing agent used.

[0049] Furthermore, the heat treatment furnace used to carbonize the raw material resin foam is not limited to any furnace that can carbonize the resin foam to produce carbon foam. For example, a heat treatment furnace can be used that includes a reaction furnace for containing the raw material resin foam, a heater for heating the inside of the reaction furnace, a gas inlet for introducing inert gas into the reaction furnace, a gas outlet for discharging gas from the inside of the reaction furnace, and a vacuum pump for reducing the pressure inside the reaction furnace to create a vacuum.

[0050] Next, in step S2, the temperature inside the heat treatment furnace is raised to a predetermined heat treatment temperature at a first heating rate (heating step). At this time, it is important to perform the process while evacuating the heat treatment furnace under reduced pressure in the first temperature range where a large amount of decomposable desorbed gas is generated from the resin foam.

[0051] As described above, when the resin foam, which is the raw material for carbon foam, is heated, the active decomposable desorbed gases generated from the resin foam react with the carbon fibers that make up the carbon foam, causing localized decomposition and resulting in heterogeneity in the carbon foam. The amount of decomposable desorbed gases generated depends on the temperature inside the furnace. Therefore, in this embodiment, in the temperature range (first temperature range) during the heating process in which the amount of decomposable desorbed gases generated from the resin foam is large, the inside of the heat treatment furnace is depressurized and evacuated. This promotes the diffusion of the decomposable desorbed gases generated inside the resin foam to the outside of the resin foam, thereby preventing the occurrence of heterogeneity in the carbon foam.

[0052] In this embodiment, the temperature range in which a large amount of decomposable desorbed gas is generated from the resin foam (the first temperature range) is defined as the temperature range in which the mass of the resin foam decreases by 5% or more per 100°C, based on pre-monitoring of the mass of the resin foam in the heating process at intervals of 0°C to 100°C. For example, if the mass of the resin foam decreases by 5% or more per 100°C in all temperature ranges of 300°C to less than 400°C, 400°C to less than 500°C, and 500°C to less than 600°C, then the first temperature range is 300°C to less than 600°C.

[0053] As a result of our investigations, we found that when the resin foam is melamine resin foam, the temperature range in which a large amount of decomposable desorbed gas is generated (first temperature range) is in the temperature range of 200°C to less than 800°C. Therefore, for example, when the resin foam is melamine resin foam, the heat treatment furnace is depressurized and evacuated at least in the above first temperature range.

[0054] The aforementioned depressurized exhaust can be carried out using an exhaust means such as a vacuum pump, and this should be done using a pump that has the capacity to reduce the pressure inside the furnace to 1 Pa or less within 10 minutes.

[0055] The heating rate to the heat treatment temperature (first heating rate) is preferably 10°C / min or less, for example, when the raw material resin foam is melamine resin foam, from the viewpoint of suppressing the generation of decomposable desorbed gases. Furthermore, from the viewpoint of overall productivity, the first heating rate is preferably 1°C / min or more.

[0056] Furthermore, in the temperature range where a large amount of decomposable desorbed gas is generated from the resin foam (first temperature range), it is preferable to perform the heating process at a lower heating rate (second heating rate) than the heating rate to the heat treatment temperature (first heating rate). This reduces the amount of decomposable desorbed gas generated per unit time within the resin foam, thereby further promoting the diffusion of decomposable desorbed gas outside the foam structure. If the heating rate is reduced in the first temperature range (i.e., changed to the second heating rate), after the temperature inside the furnace exceeds the upper limit of the first temperature range, the heating rate should be returned to the first heating rate to increase the temperature.

[0057] Furthermore, it is preferable that the heating process be carried out at a heating rate lower than the second heating rate (third heating rate) in a region (second temperature region) within the first temperature region where the amount of desorbed gas generated is large, and where the rate of increase in the amount of decomposable desorbed gas generated is high. This further reduces the amount of decomposable desorbed gas generated per unit time within the resin foam and further promotes the diffusion of decomposable desorbed gas outside the foam structure.

[0058] In this embodiment, the temperature range (second temperature range) in which the rate of increase in the amount of decomposable desorbed gas generated from the resin foam is high may be defined as the temperature range in which the mass of the resin foam decreases by 20% or more per 100°C, by pre-monitoring the mass of the raw material resin foam in intervals of 0°C to 100°C during the heating process. For example, if the mass of the resin foam decreases by 20% or more per 100°C in the temperature ranges of 300°C to less than 400°C and 400°C to less than 500°C, then the second temperature range is 300°C to less than 500°C.

[0059] When the raw material resin foam is melamine resin foam, the temperature range in which the amount of desorbed gas generated from the resin foam is high (first temperature range) is the temperature range of 200°C to less than 800°C, as described above. Furthermore, as a result of the inventors' investigations, it was found that the temperature range in which the rate of increase in the amount of desorbed gas generated from the resin foam is high (second temperature range) is the temperature range of 300°C to less than 400°C. Therefore, when the raw material resin foam is melamine resin foam, the heating rate is more preferably 5°C / min or less in the first temperature range, and more preferably 3°C / min or less in the second temperature range.

[0060] Furthermore, in this heating process and the carbonization process described later, the atmosphere inside the furnace may be an inert gas atmosphere or a vacuum in order to prevent the decomposition reaction between oxygen and the carbon fibers that make up the carbon foam. Here, a vacuum inside the furnace means that the vacuum level inside the furnace is less than 1 Pa. Alternatively, an inert gas atmosphere can be created by introducing the resin foam, which is the raw material for the carbon foam, into the heat treatment furnace (raw material foam introduction process), then evacuating the furnace under reduced pressure to remove the air containing oxygen. After the furnace reaches a vacuum level of less than 1 Pa and the air has been sufficiently degassed, nitrogen gas is introduced. In this way, the inside of the furnace can be made into a nitrogen gas atmosphere. After creating an inert gas atmosphere or a vacuum inside the furnace in this manner, heating is started, and in the first temperature range, the inside of the furnace is evacuated under reduced pressure.

[0061] Furthermore, in the temperature range of 200°C to less than 800°C (the first temperature range), where the amount of desorbed gas from the melamine resin foam is high, it is preferable to continue depressurizing and evacuating the furnace while introducing an inert gas. This generates a flow of inert gas such as nitrogen gas or argon gas within the furnace, which promotes the discharge of decomposable desorbed gases generated within the resin foam.

[0062] When introducing an inert gas, the flow rate of the inert gas is preferably 1 L / min or more, more preferably 3 L / min or more, and particularly preferably 5 L / min or more. Furthermore, the flow rate of the inert gas is preferably 40 L / min or less, more preferably 30 L / min or less, and particularly preferably 20 L / min or less.

[0063] Next, in step S3, the resin foam is heated and held at the heat treatment temperature reached for a predetermined time to carbonize the resin foam and obtain carbon foam (carbonization step). In this embodiment, the heat treatment temperature is set to a temperature above the softening point of the raw material resin foam. For example, if the resin foam is melamine resin foam, the softening point of melamine resin foam is 300°C to 400°C, so the heat treatment temperature is set to a temperature above the softening point. The heat treatment temperature for melamine resin foam is preferably 800°C or higher, and more preferably 1000°C or higher. Furthermore, from the viewpoint of physical fragility due to high crystallinity, the heat treatment temperature for melamine resin foam is preferably 3000°C or lower, and more preferably 2500°C or lower.

[0064] Furthermore, the holding time at the heat treatment temperature (heat treatment time) may be the time required for the raw material resin foam to be completely carbonized. For example, if the raw material resin foam is melamine resin foam, the holding time should be 0.5 hours or more. The holding time for melamine resin foam is preferably 1 hour or more, and more preferably 2 hours or more. Also, from the viewpoint of productivity, the holding time for melamine resin foam is preferably 5 hours or less, and more preferably 4 hours or less.

[0065] Next, in step S4, the temperature inside the heat treatment furnace is cooled to room temperature (cooling step). The rate of temperature reduction during carbonization of the melamine resin foam is preferably 20°C / min or less from the viewpoint of mitigating damage to the heaters and insulation materials inside the furnace due to rapid cooling. More preferably, the cooling rate for the melamine resin foam is 15°C / min or less. Furthermore, from the viewpoint of overall productivity, the cooling rate for the melamine resin foam is preferably 5°C / min or more. More preferably, the cooling rate for the melamine resin foam is 10°C / min or more.

[0066] Finally, in step S5, the carbon foam is removed from the heat treatment furnace (carbon foam removal step). In this way, the carbon foam of this embodiment described above can be manufactured.

[0067] Furthermore, by performing the heating and carbonization processes while applying a compressive load to the raw resin foam, a carbon foam with an anisotropic skeletal structure in which the carbon fibers expand can be obtained. As described above, anisotropic carbon foam can suppress carbon fiber breakage and reduce powder shedding even when a compressive load is applied, and can also achieve high resilience.

[0068] The above-mentioned compressive load can be applied by placing a weight, such as a graphite plate, on the resin foam material. The applied compressive load is preferably 50 Pa or more, and more preferably 200 Pa or more. Furthermore, the applied compressive load is preferably 2000 Pa or less, and more preferably 1500 Pa or less.

[0069] Furthermore, when compression is performed using a vacuum press or the like, control may be performed not by pressing load, but by determining the film thickness after pressing with a spacer and controlling it by a compression ratio obtained by dividing the original thickness by the thickness of the spacer. In this case, the compression ratio is preferably 4 times or more, and more preferably 10 times or more, in order to provide anisotropy. Also, the compression ratio is preferably 100 times or less, and more preferably 50 times or less, in order to maintain the three-dimensional structure. This vacuum press is not particularly limited as long as it is a device that can discharge active gas and can heat and compress resin foam, or a device that can compress a laminate of carbon foam. For example, a heat treatment furnace equipped with a top plate for pressing the resin foam, a heater for heating the top plate, a gas outlet for discharging gas from inside the device, and a vacuum pump for reducing the pressure inside the device to create a vacuum can be used.

[0070] When a compressive load is applied to the raw material resin foam, the diffusion of decomposable desorbed gases is suppressed by weights such as graphite plates. Therefore, in the heating process, it is particularly preferable to reduce the heating rate and continuously evacuate under reduced pressure while supplying inert gas into the furnace, compared to when no compressive load is applied, in order to promote the removal of decomposable gases.

[0071] For example, when the raw material resin foam is melamine resin foam, it is preferable to set the heating rate to 5°C / min or less in the temperature range of 200°C to less than 800°C (first temperature range), and more preferably to 2°C / min or less in the temperature range of 300°C to less than 400°C (second temperature range) where the rate of increase in the amount of desorbed gas generated is high. Furthermore, it is preferable to supply an inert gas such as nitrogen gas or argon gas into the heat treatment furnace in the temperature range of 200°C to less than 800°C (first temperature range).

[0072] Furthermore, compressive stress on the raw material resin foam may be applied not only in one direction but also in two directions.

[0073] The carbon foam may be subjected to oxidation treatment. By performing oxidation treatment, the surface oxygen concentration of the carbon foam can be increased. Examples of surface oxidation treatment methods include heat treatment of carbon foam in air at 250-700°C for 0.5-5 hours, and immersion of carbon foam in a 1M potassium permanganate aqueous solution at 30-80°C for 0.5-5 hours.

[0074] (Cathode catalyst layer) In this embodiment, the cathode catalyst layer (hereinafter also simply referred to as the "catalyst layer") preferably consists of a noble metal-supported catalyst and a proton-conducting ionomer. The cathode diffusion layer, the cathode catalyst layer, and the solid polymer electrolyte membrane are arranged in this order. The cathode diffusion layer and the cathode catalyst layer are in direct contact with each other from the viewpoint of reducing contact resistance. Furthermore, the cathode catalyst layer and the solid polymer electrolyte membrane are preferably joined to each other or in direct contact with each other from the viewpoint of reducing contact resistance.

[0075] From the viewpoint of reducing charge transfer resistance, the thickness of the catalyst layer in this embodiment is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Furthermore, from the viewpoint of reducing ohmic resistance, the thickness of the catalyst layer is preferably 100 μm or less, more preferably 90 μm or less, and even more preferably 80 μm or less.

[0076] In this embodiment, from the viewpoint of catalytic activity, it is preferable that the catalyst layer contains at least one catalyst metal selected from the group consisting of platinum, ruthenium, rhodium, palladium, iridium, molybdenum, rhenium, tungsten, titanium, nickel, copper, zinc, silver, tin, gold, lead, and lanthanides.

[0077] The catalyst layer of this embodiment preferably has a structure in which the catalyst metal is supported on a conductive carrier. The carrier is not particularly limited, but examples include carbon particles, alumina, silica, zeolite, mesoporous material, etc. By supporting fine particles of the catalyst metal on the carrier, the amount of catalyst metal used is reduced, and the specific surface area per unit volume of the catalyst metal tends to increase, thus tending to improve catalytic activity. In this embodiment, the conductive carrier in the catalyst layer is preferably made of carbon material, from the viewpoint of physical stability when supporting the catalyst metal, conductivity at the contact point with the catalyst metal, chemical stability with respect to the electrolyte, electrochemical stability under electrolytic conditions, and economic efficiency. Furthermore, from the viewpoint of forming the network structure, which is a more preferred form of this embodiment described later, by a catalyst ink coating method, the conductive carrier is preferably in particulate form. From the above viewpoints, it is even more preferable that the conductive carrier be made of carbon particles.

[0078] The catalyst layer of this embodiment has a structure in which the catalyst metal and the conductive carrier are in contact with each other, and this structure will be referred to as a network structure. It is preferable that this network structure exhibits conductivity. Because the catalyst metal and the conductive carrier have a network structure in which they are in contact with each other, they are conductive, which tends to allow electrons to be supplied more efficiently from the external circuit to the catalytic active site.

[0079] The method for obtaining the network structure is not particularly limited, but one example is the catalyst ink coating method described later.

[0080] Furthermore, the method for confirming conductivity based on the network structure is not particularly limited, but examples include a simple method of measuring the resistance value by bringing the electrodes of a tester into contact with the catalyst layer, or, more precisely, a method of measuring the sheet resistance value or volume resistivity using a sheet resistance measuring instrument.

[0081] The method for forming the catalyst layer in this embodiment is not particularly limited, but examples include the catalyst ink coating method described later. In the catalyst ink coating method, first, a catalyst ink is prepared containing the ionomer and the catalyst metal and / or the conductive carrier, and in which the ionomer and the catalyst metal and / or the conductive carrier are uniformly dispersed in water and / or an organic solvent. When preparing the catalyst ink, a dispersant may be used to uniformly disperse the ionomer and the catalyst metal and / or the conductive carrier. Furthermore, the method for uniformly dispersing the ionomer and the catalyst metal and / or the conductive carrier after mixing them in water and / or an organic solvent is not particularly limited, but examples include dispersion using an ultrasonic cleaner, dispersion using a magnetic stirrer, and dispersion using a homogenizer. The catalyst ink prepared as described above is coated onto a substrate to form a wet film. The method for coating the catalyst ink is not particularly limited, but examples include screen printing using a squeegee and coating using an applicator. The water and / or organic solvent contained in the wet film is dried at room temperature, and then heated to bond the ionomer with the catalyst metal and / or the conductive support. The heating temperature is preferably above the glass transition temperature of the ionomer, and more preferably below the decomposition temperature of the ionomer.

[0082] Furthermore, when heating, applying a moderate load perpendicular to the wet film is preferable because it tends to lead to a stronger bond between the ionomer and the catalyst metal and / or the conductive carrier, resulting in a more stable film after heating. After heating the wet film for a sufficient amount of time (e.g., 30 minutes) as described above, the catalyst layer of this embodiment can be obtained by removing the heat at room temperature.

[0083] (Solid polymer electrolyte membrane) The solid polymer electrolyte membrane of this embodiment (hereinafter also simply referred to as the "electrolyte membrane") is made of a proton-conducting material, allowing protons to pass through while separating the cathode chamber and the anode chamber, thereby suppressing the mixing and diffusion of substances.

[0084] The thickness of the electrolyte membrane is preferably 10 μm or more, more preferably 20 μm or more, and most preferably 25 μm or more, from the viewpoint of suppressing the diffusion of the substance. On the other hand, from the viewpoint of lowering resistance, it is preferably 300 μm or less, more preferably 250 μm or less, and most preferably 200 μm or less.

[0085] The electrolyte membrane of this embodiment preferably contains a perfluorocarbon polymer having ion exchange groups. Furthermore, the perfluorocarbon polymer preferably has an equivalent mass EW of ion exchange groups of 600 g / eq to 2000 g / eq.

[0086] (Perfluorocarbon polymer) The electrolyte membrane of this embodiment preferably contains a perfluorocarbon polymer having ion exchange groups. The ion exchange group is not particularly limited, but examples include -COOH groups, -SO3H groups, -PO3H2 groups, or salts thereof. The salt is not particularly limited, but examples include alkali metal salts, alkaline earth metal salts, and amine salts.

[0087] (equivalent mass EW) The perfluorocarbon polymer is preferably 2000 g / eq or less, more preferably 1700 g / eq or less, and most preferably 1500 g / eq or less, from the viewpoint of improving proton conductivity and reducing cell resistance. On the other hand, from the viewpoint of suppressing water movement from the anode chamber to the cathode chamber, it is preferably 600 g / eq or more, more preferably 700 g / eq or more, and most preferably 750 g / eq or more. Note that the equivalent mass EW refers to the dry mass (g) of the perfluorocarbon polymer per equivalent of ion exchange groups. The equivalent mass EW of a perfluorocarbon polymer can be measured by substituting the perfluorocarbon polymer with a salt and back-titrating the solution with an alkaline solution. The equivalent mass EW can be adjusted by the copolymerization ratio of fluorine-based monomers, which are raw materials for perfluorocarbon polymers, and by selecting monomer species.

[0088] The perfluorocarbon polymer preferably contains a structure represented by the following formula (1). -[CF2-CX1X2]a-[CF2-CF(-O-(CF2-CF(CF2X3))b-Oc-(CFR1)d-(CFR2)e-(CF2)f-X4)]g- (1) In equation (1), X1, X2, X3, R1, R2, and a to g are defined as follows: X1, X2, and X3 are each independently a halogen atom or a perfluoroalkyl group having 1 to 3 carbon atoms. The halogen atoms mentioned above are not particularly limited, but examples include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. The perfluoroalkyl groups having 1 to 3 carbon atoms are not particularly limited, but examples include trifluoromethyl groups, pentafluoroethyl groups, perfluoro-n-propyl groups, and perfluoroisopropyl groups. From the viewpoint of chemical stability such as resistance to oxidative degradation of the polymer, X1, X2, and X3 are preferably each independently a fluorine atom or a perfluoroalkyl group having 1 to 3 carbon atoms, and more preferably a fluorine atom. X4 is a -COOZ group, -SO3Z group, -PO3Z2 group, or -PO3HZ group. Z consists of hydrogen atoms, alkali metal atoms, alkaline earth metal atoms, NH4, NH3R11, NH2R11R12, NHR11R12R13, and NR11R12R13R14. Here, R11, R12, R13, and R14 are each independently an alkyl group or an aryl group. The alkyl groups of R11, R12, R13, and R14 are preferably alkyl groups having 1 to 6 carbon atoms, and more preferably a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, or an n-hexyl group. The aryl group is not particularly limited, but examples include a phenyl group and a naphthyl group. In addition, when X4 is a -PO3Z2 group, Z may be the same or different. The alkali metal atom is not particularly limited, and examples thereof include a lithium atom, a sodium atom, and a potassium atom. The alkaline earth metal atom is not particularly limited, and examples thereof include a calcium atom and a magnesium atom. From the viewpoint of chemical stability such as oxidation degradation resistance of the polymer, X4 is preferably SO3Z. R1 and R2 are each independently a halogen atom, a perfluoroalkyl group having 1 to 10 carbon atoms, or a fluorochloroalkyl group. Here, the halogen atom for R1 and R2 is not particularly limited, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these, a fluorine atom is preferable. a and g are numbers satisfying 0 ≦ a < 1, 0 < g ≦ 1, and a + g = 1. b is an integer from 0 to 8. c is 0 or 1. d, e, and f are each independently an integer from 0 to 6. However, d, e, and f are not simultaneously 0. Note that the sequence order of the structural unit of [CF2-CX1X2] and the structural unit of [CF2-CF(-O-(CF2-CF(CF2X3))b-Oc-(CFR1)d-(CFR2)e-(CF2)f-X4)] is not particularly limited, and may be random or a block form.

[0089] As the perfluorocarbon polymer in the present embodiment, since the effects of the present invention tend to be more remarkable, it is preferably a perfluorocarbon sulfonic acid resin (hereinafter also referred to as "PFSA resin"). The PFSA resin in the present embodiment is a resin in which a perfluorocarbon is a side chain and one or more sulfonic acid groups (in some cases, a part may be in the form of a salt) are bonded to each side chain on the main chain composed of a polytetrafluoroethylene (PTFE) backbone chain. The PFSA resin preferably contains a repeating unit represented by -[CF2CF2]- and a repeating unit derived from a compound represented by the following formula (3), (4-1), or (4-2). CF2=CF(-O-(CF2CFXO)n-[A]) (3) (In formula (3), X is F or a perfluoroalkyl group having 1 to 3 carbon atoms, and n is an integer from 0 to 5. [A] is (CF2)m-SO3H, and m is an integer from 0 to 6. However, n and m cannot be 0 at the same time.) CF2=CF-O-(CF2)P-CFX(-O-(CF2)K-SO3H) (4-1) CF2=CF-O-(CF2)P-CFX(-(CF2)LO-(CF2)m-SO3H) (4-2) (In formulas (4-1) and (4-2), X is a perfluoroalkyl group having 1 to 3 carbon atoms, P is an integer from 0 to 12, K is an integer from 1 to 5, L is an integer from 1 to 5, and m is an integer from 0 to 6. However, K and L may be the same or different, and P, K, and L cannot be 0 at the same time.)

[0090] Furthermore, the PFSA resin is a copolymer containing repeating units represented by -[CF2CF2]- and repeating units represented by -[CF2-CF(-O-(CF2CFXO)n-(CF2)m-SO3H)]-(wherein X is F or CF3, n is an integer from 0 to 5, and m is an integer from 0 to 12. However, n and m cannot be 0 at the same time), and it is more preferable that the copolymer contains at least one repeating unit represented by -[CF2-CF(-O-(CF2CFXO)n-(CF2)m-SO3H)]-(wherein X is CF3, n is 0 or 1, and m is an integer from 0 to 12. However, n and m cannot be 0 at the same time). When the PFSA resin is a copolymer having the above structure and has a predetermined equivalent mass EW, the resulting electrolyte membrane tends to have sufficient hydrophilicity and strong resistance to electrolyte active materials, such as pentavalent vanadium.

[0091] Furthermore, when the repeating unit of the PFSA resin represented by -[CF2-CF(-O-(CF2CFXO)n-(CF2)m-SO3H)]- (where n is 0 and m is an integer of 1 to 6) or both repeating units of -[CF2-CF(-O-(CF2)P-CFX(-O-(CF2)K-SO3H))]- and -[CF2-CFX(-O-(CF2)P-CFX(-(CF2)L-O-(CF2)m-SO3H))]- respectively derived from the compound represented by formula (4-1) and the compound represented by formula (4-2) are included, the equivalent weight (EW) tends to be low and the hydrophilicity of the resulting electrolyte membrane tends to be high.

[0092] Since the perfluorocarbon polymer represented by formula (1) in the present embodiment tends to make the effects of the present invention more remarkable, it is more preferable to have a structure represented by the following formula (2). -[CF2CF2]a-[CF2-CF(-O-(CF2)m-SO3H)]g- (2) In formula (2), a and g are numbers satisfying 0≦a<1, 0<g≦1, and a + g = 1, and m is an integer of 1 to 6.

[0093] The perfluorocarbon polymer in the present embodiment is not particularly limited as long as it has a structure represented by formula (1) or formula (2), and may include other structures.

[0094] From the viewpoint of controlling solubility or swelling property, the perfluorocarbon polymer in the present embodiment may be one in which intermolecular partial cross-linking reaction is carried out directly or indirectly with an ion-exchange group. By performing partial cross-linking, for example, even when the equivalent weight EW of the perfluorocarbon polymer is about 500 g / eq, the water solubility of the perfluorocarbon polymer can be reduced (water resistance is improved).

[0095] Also, when the perfluorocarbon polymer has a low melt flow value (when it has a high molecular weight), the above partial cross-linking can increase the entanglement between molecules and reduce solubility and excessive swelling property.

[0096] Examples of the partial crosslinking reaction include reactions between ion exchange groups and functional groups or main chains of other molecules, reactions between ion exchange groups, crosslinking reactions (covalent bonding) via oxidation-resistant low-molecular-weight compounds, oligomers, or polymeric substances, and in some cases, reactions with salt (including ionic bonding with -SO3H groups) forming substances. Examples of oxidation-resistant low-molecular-weight compounds, oligomers, or polymeric substances include polyhydric alcohols and organic diamines.

[0097] The molecular weight of the perfluorocarbon polymer in this embodiment is not particularly limited, but is preferably 0.05 g / 10 min to 50 g / 10 min, more preferably 0.1 g / 10 min to 30 g / 10 min, and even more preferably 0.5 g / 10 min to 20 g / 10 min, based on the melt flow index (MFI) value measured in accordance with ASTM:D1238 (measurement conditions: temperature 270°C, load 2160 g).

[0098] (Method for producing perfluorocarbon polymers) The perfluorocarbon polymer in this embodiment is not particularly limited, but can be obtained, for example, by producing a perfluorocarbon polymer precursor having ion exchange groups (hereinafter also referred to as "resin precursor") and then subjecting it to hydrolysis.

[0099] In the case of PFSA resin, for example, it can be obtained by hydrolyzing a PFSA resin precursor consisting of a copolymer of a vinyl fluoride ether compound represented by formula (6) or formula (7) below and a fluoroolefin monomer represented by formula (8) below. CF2 = CF - O - (CF2CFXO)nA (6) (In formula (6), X is F or a perfluoroalkyl group having 1 to 3 carbon atoms, n is an integer from 0 to 5, A is (CF2)mW, where m is an integer from 0 to 6, n and m cannot be both 0, and W is a functional group that can be converted to a -SO3H group by hydrolysis.) CF2=CF-O-(CF2)P-CFX(-O-(CF2)KW) or CF2=CF-O-(CF2)P-CFX(-(CF2)LO-(CF2)mW) (7) (In formula (7), X is a perfluoroalkyl group having 1 to 3 carbon atoms, P is an integer from 0 to 12, K is an integer from 1 to 5, and L is an integer from 1 to 5, where L, K, and m cannot be 0 simultaneously. m is an integer from 0 to 6, and W is a functional group that can be converted to a -SO3H group by hydrolysis.) CF2 = CFZ (8) (In formula (8), Z is H, Cl, F, a perfluoroalkyl group having 1 to 3 carbon atoms, or a cyclic perfluoroalkyl group which may contain oxygen as a ring constituent atom.) In formulas (6) and (7), W is not particularly limited, but examples include the -SO2F group, the -SO2Cl group, and the -SO2Br group. Furthermore, in formulas (6) and (7), it is preferable that X is CF3 and W is the -SO2F group, and in formula (8), it is preferable that Z is F. Among these, it is more preferable that n=0, m=an integer from 1 to 6, X is CF3, W is the -SO2F group, and Z is F, as this tends to yield a solution with high hydrophilicity and high resin concentration.

[0100] The resin precursor in this embodiment can be synthesized by known means. For example, it can be produced by polymerizing a vinyl fluoride compound having a group (ion exchange precursor group) that can be converted into an ion exchange group (X4 in formula (1)) by hydrolysis or the like in the presence of a radical generator such as a peroxide, with a fluoroolefin such as tetrafluoroethylene (hereinafter also referred to as "TFE"). The polymerization method is not particularly limited, but for example, it can be used to polymerize by filling and dissolving the gas of the vinyl fluoride compound and fluoroolefin in a polymerization solvent such as a fluorine-containing hydrocarbon and reacting them (solution polymerization); to polymerize by using the vinyl fluoride compound itself as the polymerization solvent without using a solvent such as a fluorine-containing hydrocarbon (bulk polymerization); to polymerize by filling and reacting the gas of the vinyl fluoride compound and fluoroolefin in an aqueous solution of a surfactant as a medium (emulsification polymerization); to polymerize by filling and emulsifying the gas of the vinyl fluoride compound and fluoroolefin in an aqueous solution of a surfactant and an emulsifier such as an alcohol and reacting them (emulsion polymerization); and to polymerize by filling and suspending the gas of the vinyl fluoride compound and fluoroolefin in an aqueous solution of a suspension stabilizer and reacting them (suspension polymerization).

[0101] The resin precursor in this embodiment can be prepared by any of the polymerization methods described above. Alternatively, block-shaped or tapered polymers obtained by adjusting polymerization conditions such as the amount of TFE gas supplied may also be used as the resin precursor.

[0102] The resin precursor may be obtained by treating the impure ends generated in the resin molecular structure during the polymerization reaction, or the structurally easily oxidized parts (such as CO groups and H bond parts), under fluorine gas using a known method, thereby fluorinating those parts.

[0103] The resin precursor may have a portion of its ion-exchange group precursor group (e.g., -SO2F group) partially imidized (including intermolecularly) (e.g., alkylimidization).

[0104] The molecular weight of the resin precursor is not particularly limited, but it is preferably 0.05 g / 10 min to 50 g / 10 min, more preferably 0.1 g / 10 min to 30 g / 10 min, and even more preferably 0.5 g / 10 min to 20 g / 10 min, based on the melt flow index (MFI) value measured in accordance with ASTM:D1238 (measurement conditions: temperature 270°C, load 2160 g).

[0105] The shape of the resin precursor is not particularly limited, but from the viewpoint of speeding up the processing rate in the hydrolysis treatment and acid treatment described later, for example, 0.5 cm 3 The following forms are preferable: pellets, a dispersed liquid, or powder particles. Among these, the powdered form after polymerization is more preferable. From a cost standpoint, an extruded film-like resin precursor may also be used.

[0106] The method for producing the perfluorocarbon polymer in this embodiment from a resin precursor is not particularly limited, but for example, the resin precursor may be extruded using an extruder with a nozzle or die and then subjected to hydrolysis treatment, or the polymer product may be used as is, i.e., in a dispersed liquid state, or precipitated and filtered into a powder state, and then subjected to hydrolysis treatment.

[0107] Specifically, the resin precursor obtained as described above and molded as necessary can be further immersed in a basic reaction liquid and subjected to hydrolysis. The basic reaction liquid used for hydrolysis is not particularly limited, but examples include aqueous solutions of amine compounds such as dimethylamine, diethylamine, monomethylamine, and monoethylamine, and aqueous solutions of alkali metal or alkaline earth metal hydroxides. Among these, aqueous solutions of sodium hydroxide or potassium hydroxide are preferred. When alkali metal or alkaline earth metal hydroxides are used, the content is not particularly limited, but it is preferably 10% by mass or more and 30% by mass or less of the total reaction liquid. The above reaction liquid is more preferably further containing swelling organic compounds such as methyl alcohol, ethyl alcohol, acetone, and dimethyl sulfoxide (DMSO). The content of the swelling organic compounds is preferably 1% by mass or more and 30% by mass or less of the total reaction liquid.

[0108] The resin precursor is subjected to hydrolysis in a basic reaction liquid, then thoroughly washed with warm water, and subsequently subjected to acid treatment. The acid used in the acid treatment is not particularly limited, but examples include mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as oxalic acid, acetic acid, formic acid, and trifluoroacetic acid. A mixture of these acids and water is preferred. The above acids may be used individually or in combination of two or more. The basic reaction liquid used in the hydrolysis treatment may be removed beforehand by treatment with a cation exchange resin, etc., before the acid treatment.

[0109] Acid treatment protonates the ion exchange group precursor group of the resin precursor, generating an ion exchange group. For example, in the case of a resin precursor produced using formula (6), the W in formula (6) is protonated by acid treatment to become a -SO3H group. The perfluorocarbon polymer obtained by hydrolysis and acid treatment can be dispersed or dissolved in a protic organic solvent, water, or a mixture of both, and can be prepared as a suspension or solution.

[0110] The perfluorocarbon polymer may contain alkali metals, alkaline earth metals, and other radical-degradable transition metals (such as Ce compounds and Mn compounds) in the form of partial salts with these (approximately 0.01 to 5 equivalents of the total ion exchange group equivalents), or alone, or in combination with the basic polymer described later.

[0111] From the viewpoint of improving electrical resistance and mechanical strength, the electrolyte membrane of this embodiment preferably contains a mixture of two or more perfluorocarbon polymers having ion exchange groups and having different monomer structures.

[0112] By mixing two or more types of perfluorocarbon polymers, it becomes possible to achieve superior properties by combining the functions of each polymer.

[0113] Furthermore, from the viewpoint of achieving better mechanical strength, when mixing two or more perfluorocarbon polymers, it is preferable to have a ratio of polymers with a higher equivalent mass EW greater than 50% by mass, more preferably greater than 55% by mass, and even more preferably greater than 60% by mass. Polymers with a high equivalent mass EW tend to have higher crystallinity, and therefore, when the above ratios are used, higher mechanical strength tends to be achieved.

[0114] (Method for producing raw material films of perfluorocarbon polymers) The raw material membrane used in the production of the electrolyte membrane in this embodiment can be obtained by processing a precursor resin or perfluorocarbon polymer into a film using a known method. For example, a method can be used in which the aforementioned perfluorocarbon polymer precursor is melt-kneaded, a film is formed using an extruder, and then hydrolyzed to form ion exchange groups. Alternatively, the perfluorocarbon polymer may be dispersed in a solvent and then cast onto a substrate to form a film.

[0115] (Ion cluster diameter) The ion cluster diameter of the electrolyte membrane in this embodiment can be measured by small-angle X-ray scattering (SAXS). From the viewpoint of reducing the resistance component when forming an electrolytic cell for organic hydride production, the ion cluster diameter is preferably 2.5 nm or larger, more preferably 2.7 nm or larger, and even more preferably 3.0 nm or larger. Furthermore, from the viewpoint of suppressing swelling of the electrolyte membrane and suppressing the permeation of water from the anode chamber to the cathode chamber, the ion cluster diameter is preferably 3.9 nm or smaller, more preferably 3.7 nm or smaller, and even more preferably 3.6 nm or smaller.

[0116] (crystal long period) The crystal long period measured by small-angle X-ray scattering in the electrolyte membrane of this embodiment is the scattering vector of the small-angle X-ray scattering at 0.1 to 1.0 nm. -1 The location of the peak, which originates from the periodicity of the electron density difference between crystalline and amorphous materials within the specified range, is determined using Bragg's equation.

[0117] The crystal long period measured by small-angle X-ray scattering is preferably 5 nm to 60 nm, more preferably 10 nm to 55 nm, even more preferably 20 nm to 50 nm, and even more preferably 30 nm to 50 nm.

[0118] (anode) The anode in this embodiment is a Dimensionally Stable Electrode (DSE), which is electrically conductive and is an electrode formed by coating or sintering a catalyst onto a support. Examples of support materials include metal fibers (fiber diameter: e.g., 10-30 μm), mesh structures (mesh diameter: e.g., 500-1000 μm), porous metals (sintered bodies), foamed molded bodies (foam), and expanded metal, all composed of metals such as titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, niobium, molybdenum, tantalum, and tungsten, or alloys mainly composed of these metals. From the viewpoint of having sufficient electrical conductivity to carry the current necessary for electrolysis and sufficient mechanical strength, a plate-like material with a thickness of 0.1-2 mm is preferred. Furthermore, from the viewpoint of exhausting oxygen gas generated at the anode, suppressing the increase in resistance due to air bubbles adhering to the surface, and promoting the supply of electrolyte, the support material is preferably a mesh structure (mesh structure) or a porous material, and is preferably excellent in corrosion resistance (acid corrosion resistance) to the electrolyte. From these viewpoints, a titanium mesh structure is preferred. As a catalyst, for example, platinum group precious metal oxide catalysts are preferably used. Among these, iridium oxide-based electrode catalysts are preferred from the viewpoint of durability.

[0119] The anode of this embodiment may further include an anode diffusion layer in addition to the DSE as the anode catalyst layer. The anode diffusion layer is provided on the side opposite to the electrolyte membrane in the anode chamber and plays a role in supplying water and discharging the generated oxygen, as well as acting as a conductor for electrons generated by oxidation. From the viewpoint of reducing contact resistance, it is preferable that the anode catalyst layer and the anode diffusion layer are joined to each other or in direct contact with each other. As the anode diffusion layer, a conductive porous material can be used, such as a titanium fiber sintered body or a titanium powder sintered body with platinum plating on its surface.

[0120] Examples of electrolytes supplied to the anode include aqueous solutions of inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid. The ionic conductivity of the electrolyte is preferably 0.01 S / cm or higher when measured at 20°C. By achieving an ionic conductivity of 0.01 S / cm or higher, an industrially sufficient electrochemical reaction can be generated.

[0121] (Hydrogenated organic compound) In this embodiment, it is preferable that at least part or all of the hydrogenable organic compound is an aromatic compound. The aromatic compound is preferably at least one selected from the group consisting of benzene, naphthalene, anthracene, toluene, xylene, diphenylmethane, diphenylethane, triphenylmethane, triphenylethane, dibenzyltoluene, phenol, pyridine, pyrimidine, pyrazine, quinoline, and isoquinoline. These aromatic compounds may be included individually or as a mixture of two or more. Furthermore, it is more preferable that the hydrogenable organic compound is a liquid at room temperature and pressure. Using a liquid as the electrolyte makes electrochemical hydrogenation by an electrolytic synthesis cell possible without the use of temperature and pressure boosting equipment, and also tends to make it easier to handle as a hydrogen carrier. From this viewpoint, the hydrogenable organic compound is more preferably benzene, toluene, xylene, diphenylethane, or quinoline, with toluene being the most preferred. [Examples]

[0122] The present invention will be described below with reference to specific examples and comparative examples, but it is not limited to these.

[0123] [Measure the score] The thickness (μm) of the carbon foam used in the cathode diffusion layer was measured using a contact-type film thickness gauge (manufactured by Toyo Seiki Seisakusho Co., Ltd.).

[0124] [Measurement of weight] Basis weight (g·m) of carbon foam etc. used in the cathode diffusion layer -2 The mass of the electrode, cut to 50 x 50 mm, was calculated by dividing its mass by its area.

[0125] [Measurement of bulk density] First, measure the dimensions of the carbon foam used in the cathode diffusion layer using a caliper or similar tool, and then calculate its bulk volume V from the obtained dimensions and thickness. bulkNext, the mass M of the carbon foam used in the cathode diffusion layer was measured using a precision balance. The obtained mass M and bulk volume V bulk Therefore, the bulk density ρ of carbon foam, etc. can be calculated using the following formula (Y). bulk (g·cm -3 ) was sought. ρ bulk =M / V bulk ...(Y)

[0126] [Measurement of true density] True density ρ of carbon foam, etc., used in the cathode diffusion layer real (g·cm -3 The density was determined by a buoyancy method using a mixture of n-heptane, carbon tetrachloride, and ethylene dibromide. First, a suitable size of carbon foam or similar material was placed in a stoppered test tube. Next, the three solvents were mixed appropriately and added to the test tube, which was then immersed in a 30°C constant temperature bath. If the sample floated, low-density n-heptane was added. On the other hand, if the test piece sank, high-density ethylene dibromide was added. This procedure was repeated until the test piece floated in the liquid. Finally, the density of the liquid was measured using a Gay-Lussac specific gravity bottle.

[0127] [Calculation of void ratio] The bulk density ρ calculated as described above bulk and true density ρ real Therefore, using the following equation (X), the void ratio V f,pore The percentage was calculated. V f,pore =((1 / ρ bulk )-(1 / ρ real )) / (1 / ρ bulk ) × 100 (%) ...(X)

[0128] [Structural analysis using X-ray CT] Structural analysis of carbon foam and other materials used in the cathode diffusion layer was performed using X-ray CT, with the thickness direction as the x-axis. Specifically, to facilitate X-ray imaging, each material was electroless copper plated, and then test specimens (samples) were taken. Structural analysis of the collected test specimens was performed using a high-resolution 3D X-ray microscope nano3DX (manufactured by Rigaku Corporation). The specific electroless plating conditions and X-ray CT analysis conditions are as follows. The obtained 3D image was processed using a 3D median filter with a filter size of radius 2 pixels, focusing on adjacent pixels, and then binarized using Otsu's algorithm. Next, for the carbon foam, we used JSOL's simpleware software Centerline editor (Ver. 7) with default settings to remove lines smaller than 2.16 μm as noise, and then measured the number of bonds N within a 300 μm × 300 μm × 300 μm measurement field of view. n Number of linear parts N l Detected. Furthermore, the thickness direction of the carbon foam is defined as the x-direction (x-axis), the direction perpendicular to the x-direction as the y-direction (y-axis), and the direction perpendicular to both the x-direction and the y-direction as the z-direction (z-axis). The vectors of each linear portion within the measurement field are calculated, and the average value θ of the degree of orientation of each vector with respect to the x-axis is calculated. avex (deg), the average value of the degree of orientation relative to the y-axis θ avey (deg), θ, the average value of the degree of orientation relative to the z axis avez The (deg) was calculated. During this process, the orientation angle was converted to be within 90 degrees.

[0129] [Electroless plating conditions] The sample was immersed in OPC Condiclean MA (Okuno Pharmaceutical Co., Ltd., diluted with distilled water to 100 mL / L) at 70°C for 5 minutes, then washed with distilled water for 1 minute. Next, it was immersed in OPC Predip 49L (Okuno Pharmaceutical Co., Ltd., diluted with distilled water to 10 mL / L, with 1.5 mL / L of 98% sulfuric acid added) at 70°C for 2 minutes, then washed with distilled water for 1 minute. Next, it was immersed in a solution of OPC Inducer 50AM (Okuno Pharmaceutical Co., Ltd., diluted with distilled water to 100 mL / L) and OPC Inducer 50CM (Okuno Pharmaceutical Co., Ltd., diluted with distilled water to 100 mL / L) mixed in a 1:1 ratio at 45°C for 5 minutes, then washed with distilled water for 1 minute. Next, it was immersed in OPC-150 Crysta MU (Okuno Pharmaceutical Co., Ltd., diluted with distilled water to 150 mL / L) at room temperature for 5 minutes, then washed with distilled water for 1 minute. Next, the samples were immersed in OPC-BSM (manufactured by Okuno Pharmaceutical Co., Ltd., diluted with distilled water to 125 mL / L) at room temperature for 5 minutes. Subsequently, they were immersed in a solution of 1:1 mixed chemical copper 500A (manufactured by Okuno Pharmaceutical Co., Ltd., diluted with distilled water to 250 mL / L) and chemical copper 500B (manufactured by Okuno Pharmaceutical Co., Ltd., diluted with distilled water to 250 mL / L) at room temperature for 10 minutes, followed by washing with distilled water for 5 minutes. After that, they were vacuum-dried at 90°C for 12 hours to remove moisture.

[0130] [X-ray conditions] X-ray target: Cu X-ray tube voltage: 40kV X-ray tube current: 30mA [Shooting conditions] Number of projections: 1500 sheets Rotation angle: 180° Exposure time: 20 seconds / image Pixel count: 1648 x 1202 pixels Pixel size: 0.54 μm / pixel Observation area size: 624 μm × 624 μm × H600 μm Based on the above structural analysis, the number of bonds N for the carbon foam is n Number of linear parts N l , proportion R(N l / N n ), the average value (deg) of the orientation angle for three mutually orthogonal directions (x, y, z), and the density of the joints (number of joints Nn / volume) (pieces / mm³). 3) was sought. The results obtained are shown in Table 1. θ in Table 1 c (deg) is θ avex , θ avey , θ avez This is the difference between the maximum and minimum values ​​within θ. d (deg) is θ avex and θ avey or θ avez This is the smaller of the two differences.

[0131] [Method for measuring average carbon frequency and average carbon area ratio] The 3D images acquired in the above [Structural Analysis by X-ray CT] were processed using a 3D median filter with a filter size of radius 2 pixels, focusing on adjacent pixels, and then binarized using Otsu's algorithm. Furthermore, within the analysis area (624 μm × 624 μm) of the cross-sectional image in the thickness direction of carbon foam, etc. (image of a cross-section cut perpendicular to the thickness direction of carbon foam, etc.), the number of consecutive carbon portions and the sum of the areas of consecutive carbon portions within the analysis area were detected using the particle analysis function of the image processing software ImageJ. By dividing these by the area of ​​the analysis area as shown in the formula below, the carbon frequency per 1 μm × 1 μm and the carbon area ratio per analysis area were calculated. The same operation was repeated for 1152 cross-sectional images in the thickness direction of carbon foam, etc. (acquired at 0.54 μm / pitch), and the average of the measured values ​​obtained across the entire area was calculated to determine the average carbon frequency and average carbon area ratio. During the analysis, the calculations were performed using analysis conditions that included the regions at the edges of the image. Furthermore, when calculating the average, to exclude regions where no carbon sample was present, cross-sectional images with a carbon area ratio of 0.01 or higher in the analysis region were used. Carbon frequency (μm) -2 ) = Number of consecutive carbon atoms / Area of ​​the analysis region Carbon area ratio = Total area of ​​continuous carbon portions / Area of ​​the analysis region [Image processing conditions] Pixel count: 1152 x 1202 pixels Pixel size: 0.54 μm / pixel Thickness direction: 1152 sheets (0.54 μm / pitch) Software used: ImageJ 1.50i

[0132] [Method for measuring the standard deviation of carbon frequency] Regarding the carbon frequency of the carbon foam and other materials mentioned above, the standard deviation of the carbon frequency obtained from each cross-sectional image in the thickness direction was calculated. In doing so, to exclude regions where no carbon sample was present, the calculation was performed using cross-sectional images in which the carbon area ratio in the analysis region was 0.01 or higher.

[0133] [Method for measuring the standard deviation of the carbon area ratio] Regarding the carbon area ratio of the carbon foam and other materials mentioned above, the standard deviation of the carbon area ratio obtained from each cross-sectional image in the thickness direction was calculated. In doing so, to exclude regions where no carbon sample was present, the calculation was performed using cross-sectional images in which the carbon area ratio in the analysis region was 0.01 or higher.

[0134] [Method for measuring average fiber diameter] The average fiber diameter d of the fibrous carbon constituting the cathode diffusion layer ave The (μm) diameter was determined by image analysis of scanning electron microscope images. Specifically, fibrous carbon was observed at a magnification of 10,000x using a scanning electron microscope. From the obtained observation images, the thickness of the fibrous carbon was measured at 20 random locations. Assuming a circular cross-sectional shape, the average thickness was defined as the average fiber diameter d. ave That's what I decided.

[0135] [Carbon content] The carbon content of carbon foam and other materials used in the cathode diffusion layer was determined by X-ray fluorescence analysis. Samples cut into 35 mm squares were placed in a sample holder with an X-ray irradiation diameter of 30 mmφ, and then measured using a Rigaku Corporation ZSX-100E X-ray fluorescence analyzer (wavelength dispersive, Rh tube). Semi-quantitative analysis of all elements was performed with an X-ray irradiation diameter of 30 mmφ to determine the carbon content (wt%) of all elements.

[0136] [Surface oxygen concentration] The oxygen concentration on the surface of carbon foam and other materials used in the cathode diffusion layer was determined using an X-ray photoelectron spectrometer (ULVAC-PHI, VersaProbe II). The ratio of the area of ​​the O1s peak near 533 eV to the total area of ​​the peaks of the major elements (C1s peak near 285 eV, N1s peak near 400 eV, and O1s peak near 533 eV) was calculated as a percentage, and this was defined as the surface oxygen concentration (atomic%). If there were peaks of elements other than the major elements listed above that showed high detection intensity, these were also included in the total area calculation.

[0137] [crystallite size] For carbon foam and other materials used in the cathode diffusion layer, the crystallite size Lc (nm), which is the stacking thickness in the c-axis direction of the carbon crystal, was determined from the diffraction lines of the (002) plane obtained by wide-angle X-ray diffraction. After grinding the carbon foam and other materials used in the cathode diffusion layer in a mortar, wide-angle X-ray measurements were performed on the ground samples using a benchtop X-ray diffractometer D2 PHASER (manufactured by Bluker). The specific measurement conditions are as follows. [Measurement conditions] Source: Cu Kα Tube current: 30mA Tube voltage: 40kV Slit: 1mm Sample rotation speed: 10 revolutions / min Measurement time per step: 0.3 seconds Starting angle (2θ): 5.00° Measurement step (2θ): 0.01° End angle (2θ): 90.00° The crystallite size Lc was determined by applying Scherrer's equation (c) below to the diffraction profile obtained from the above measurements. Lc = (Kλ) / βcosθ···(c) Here, K is the shape factor and λ is the wavelength of the X-ray, set to 0.90 and 1.541 nm, respectively.

[0138] [Taber bending stiffness] The tapered bending stiffness (gf·cm) of carbon foam and other materials used in the cathode diffusion layer was determined according to JIS P 8125-2000 using a tapered stiffness tester No. 2048-D manufactured by Kumagai Riki Kogyo Co., Ltd. A sample cut into a strip 38 mm wide was held so that its free length was 60 mm. The bending stiffness was determined from the average value of the load when this sample was bent to ±15°.

[0139] (Example 1) For the cathode diffusion layer, carbon foam obtained by carbonizing BASF's BASOTECT G+ melamine resin foam was used. A 6mm thick carbon fiber nonwoven fabric and a graphite plate were placed on top of the melamine resin foam (dimensions: 90mm x 120mm x 25mm), and this was introduced into a horizontal tubular furnace with a diameter of 100mm. The mass of the graphite plate was adjusted so that the compressive stress applied to the melamine resin foam was 280 Pa. Next, the furnace was evacuated, and nitrogen gas was introduced. Subsequently, nitrogen gas was introduced at a flow rate of 2.5 L / min. -1 While supplying power, the temperature inside the furnace is raised at a heating rate of 5°C min -1 The temperature was raised to 1100°C and held for 1 hour. Afterward, the temperature inside the furnace was lowered to room temperature. Finally, the resulting carbon foam was heat-treated in air at 300°C for 1 hour to oxidize the surface of the carbon foam. The resulting carbon foam is called air-oxidized 1100°C carbonized foam. The resulting air-oxidized 1100°C carbonized foam consisted of continuous voids and had a structure comprising linear portions with an average fiber diameter of 2.0 μm and bonded portions where these linear portions were joined together. [Electrolytic Cells] For the electrolyte membrane (hereinafter simply referred to as "the membrane") used in the electrolysis test (toluene electrolysis hydrogenation test) described later, Chemors Nafion 115 was used without any pretreatment. The electrolytic cell used was a Chemix Co., Ltd. electrolytic cell with an electrode area of ​​2 x 2 cm. A key feature of this cell is that it has a mechanism consisting of a spring and a retaining rod that allows the pressure of the electrode portion to be adjusted independently of the cell fastening. The electrolytic cell is composed of the following components from the cathode side. Cathode end plate / Cathode plate / Cathode diffusion layer (carbon foam) / Cathode catalyst layer-membrane assembly / Anode catalyst layer / Anode diffusion layer / Anode plate / Anode end plate. The end plates of both electrodes were stainless steel plates with holes for inserting rod-shaped heaters to control the cell temperature. The cathode plate was an impermeable graphite plate without flow channels. On the other hand, the anode plate was a titanium plate with parallel flow channels for circulating sulfuric acid and a platinum-plated surface to suppress corrosion due to electrolysis. For the anode catalyst layer and the anode diffusion layer, Denora Permelec Co., Ltd.'s DSE oxygen generation electrode (iridium oxide-based catalyst coated titanium electrode) and Bekart Totsuna Metal Fiber Co., Ltd.'s platinum-plated titanium fiber sintered body 2GDL5-030-PT02 were used, respectively. A 0.5 mm thick Viton sheet was used as a gasket to maintain airtightness between the cathode plate and the film. On the other hand, a 0.3 mm thick PTFE sheet was used as a gasket to maintain airtightness between the film and the anode plate. The cathode catalyst layer-film assembly was fabricated using a decal method, in which a cathode catalyst layer and film, prepared by spray coating, were joined by hot pressing. First, 0.50 g of platinum-ruthenium supported carbon catalyst particles TEC61E54 manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 2.00 g of distilled water, and 5.00 g of Nafion 117 solution (concentration 5 wt%) manufactured by Sigma-Aldrich were placed in a zirconia pot and mixed using a planetary ball mill to prepare the cathode catalyst ink. Next, the obtained cathode catalyst ink was applied to a PTFE sheet using a small spray coating machine, with a basis weight of 0.5 mg-Ptcm -2 The cathode catalyst layer was fabricated by coating the material in this manner. Next, the obtained cathode catalyst layer and film were hot-pressed at 140°C and 5 MPa for 2 minutes. Finally, the cathode catalyst layer-film bond was fabricated by peeling off the PTFE sheet substrate. After arranging the components of the electrolytic cell in the order described above, they were fastened together with four M4 screws to a torque of 4 Nm. Finally, the compression of the spring was adjusted so that the pressure holding the electrode portion was 0.7 MPa. [Electrolytic Testing] The electrolytic cell assembled as described above was subjected to an electrolytic test according to the following procedure. First, 1M H2SO4 and a mixture of toluene and methylcyclohexane (toluene concentration 10%) were applied to the anode and cathode, respectively, at a flow rate of 10 ml / min. -1 The current was then distributed. Next, the cell was heated to 60°C, and then the current density was set to 0.1 Acm². -2 The cells were aged by applying a constant current for 2 hours. After that, the current density was increased to 0.1 Acm². -2 Width: 0.5Acm -2 It was increased to that point and maintained. The average value of the cell voltage over a holding time of 10 minutes, with a current density of 0.5 Acm². -2 This was defined as the cell voltage (V) at that point. On the other hand, the current efficiency E (%) is given by a current density of 0.5 Acm². -2 The volume V (L) of hydrogen gas produced as a by-product in the cathode during 10 minutes of holding was calculated according to the following formula. E(%)=(1-96485×2×V / (0.5×4×10×60×22.4))×100 = 100 - 717.9 × V

[0140] (Example 2) Except for setting the carbonization temperature of the melamine resin foam and the heat treatment temperature of the carbon foam in air to 2000°C and 600°C, respectively, a carbon foam with an oxidized surface was prepared in the same manner as in Example 1 and used as a cathode diffusion layer. The resulting carbon foam is called air-oxidized 2000°C carbonized foam. All other conditions were the same as in Example 1. The resulting air-oxidized 2000°C carbonized foam consisted of continuous voids and had a structure comprising linear portions with an average fiber diameter of 2.0 μm and bonding portions where these linear portions were joined together.

[0141] (Example 3) A laminate was used in the cathode diffusion layer, consisting of an air-oxidized 1100°C carbonized foam prepared in the same manner as in Example 1, and a carbon foam prepared in the same manner as in Example 2, except that air oxidation was not performed. The latter carbon foam is referred to as the 2000°C carbonized foam. The lamination order was cathode plate / 2000°C carbonized foam / air-oxidized 1100°C carbonized foam / cathode catalyst layer-film assembly. Other conditions were the same as in Example 1. The resulting 2000°C carbonized foam consisted of continuous voids and had a structure comprising linear portions with an average fiber diameter of 2.1 μm and bonding portions where these linear portions were joined together.

[0142] (Comparative Example 1) A carbon foam prepared in the same manner as in Example 1 was used, except that the cathode diffusion layer was not subjected to air oxidation. This carbon foam is called 1100°C carbonized foam. All other conditions were the same as in Example 1. The resulting 1100°C carbonized foam consisted of continuous voids and had a structure comprising linear portions with an average fiber diameter of 2.1 μm and bonding portions where these linear portions were joined together.

[0143] (Comparative Example 2) A 2000°C carbonized foam prepared in the same manner as in Example 3 was used for the cathode diffusion layer. Other conditions were the same as in Example 1.

[0144] (Comparative Example 3) A carbon foam prepared in the same manner as in Example 1 was used for the cathode diffusion layer, except that the heat treatment time in air was 3 hours. All other conditions were the same as in Example 1. The resulting carbon foam consisted of continuous voids and had a structure comprising linear sections with an average fiber diameter of 1.9 μm and bonding sections where these linear sections were joined together.

[0145] (Comparative Example 4) A laminate was used in the cathode diffusion layer, consisting of a 2000°C carbonized foam prepared in the same manner as in Example 3 and an air-oxidized 1100°C carbonized foam prepared in the same manner as in Example 1. The lamination order was cathode plate / air-oxidized 1100°C carbonized foam / 2000°C carbonized foam / cathode catalyst layer-film assembly. Other conditions were the same as in Example 1.

[0146] (Comparative Example 5) For the cathode diffusion layer, carbon fiber paper with a hydrophilic microporous layer containing diatomaceous earth, prepared according to the example in Patent Document 2, was used. The carbon fiber paper was placed on the cathode plate side and the microporous layer on the cathode catalyst layer side. Other conditions were the same as in Example 1. (Comparative Example 6) For the cathode diffusion layer, a laminate was used, which consisted of a low-hydrophilic carbon fiber paper and a high-hydrophilic carbon fiber paper, prepared according to the example in Patent Document 3. The lamination order was cathode plate / high-hydrophilic carbon fiber paper / low-hydrophilic carbon fiber paper / cathode catalyst layer-film assembly. Other conditions were the same as in Example 1.

[0147] [Table 1] [Industrial applicability]

[0148] According to the cathode diffusion layer for organic hydride production of the present invention, an electrolytic cell for organic hydride production using DSE as the anode can exhibit good current efficiency even at high current densities, and is therefore suitable for use in the production of organic hydrides.

Claims

1. In an electrolytic cell for the production of organic hydrides, which uses a Dimensionally Stable Electrode (DSE) as the anode, a cathode diffusion layer is provided so as to be in direct contact with the cathode catalyst layer, The cathode diffusion layer comprises carbon foam, The carbon foam is a porous material having continuous voids, comprising linear portions and bonding portions connecting the linear portions, and having a surface oxygen concentration of 8.0 atomic% or more and 15.0 atomic% or less as measured by X-ray photoelectron spectroscopy. A cathode diffusion layer for organic hydride production, characterized by the above features.

2. The cathode diffusion layer for producing organic hydrides according to claim 1, wherein the carbon foam has an average fiber diameter of 0.5 μm or more and 4.0 μm or less in the linear portion.

3. The cathode diffusion layer for organic hydride production according to claim 1 or 2, wherein the carbon foam has a Taber bending stiffness of 1.0 gf·cm or more and 50.0 gf·cm or less, as measured in accordance with JIS P8125.

4. The carbon foam has a bonding density of 20,000 units / mm² in at least a portion of it. ３ The cathode diffusion layer for producing organic hydrides according to claim 1 or 2, wherein the crystallite size determined from the diffraction of the (002) plane in powder X-ray diffraction measurement is 1.50 nm or more.

5. The carbon foam has an average carbon frequency of 0.0004 to 0.0035 μm －２ The cathode diffusion layer for producing organic hydride according to claim 1.

6. The cathode diffusion layer for producing organic hydrides according to claim 5, wherein the carbon foam has a standard deviation of carbon frequency of 0.0005 or less.

7. The cathode diffusion layer for producing organic hydrides according to claim 5 or 6, wherein the carbon foam has an average carbon area ratio of 0.010 to 0.

300.

8. The cathode diffusion layer for producing organic hydrides according to claim 7, wherein the carbon foam has a standard deviation of 0.030 or less in carbon area ratio.

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