Conductive porous base material, gas diffusion electrode base material, electrochemical device, and vehicle

Abstract

The present invention addresses the problem of providing a conductive porous base material having high water repellency without containing fluorine.　The present invention is a conductive porous base material containing carbon fibers, wherein a resin containing nanocarbon aggregates is supported on the carbon fibers, the sliding angle is 2° to 60° inclusive, and the mass ratio F / C of the fluorine content to the carbon content is 0.01 or less.

Description

Conductive porous substrate, gas diffusion electrode substrate, electrochemical device and vehicle

[0001] The present invention relates to a conductive porous substrate suitable for use in electrochemical devices such as fuel cells, particularly polymer electrolyte fuel cells; a gas diffusion electrode substrate having a porous layer on the conductive porous substrate; an electrochemical device having the gas diffusion electrode substrate; and a vehicle using the electrochemical device.

[0002] Polymer electrolyte fuel cells are expected to become widespread as a clean energy source because they are highly energy efficient and emit only water as an exhaust. One of the most promising applications of polymer electrolyte fuel cells is as a power source for vehicles such as automobiles.

[0003] The basic components of a polymer electrolyte fuel cell are a polymer electrolyte membrane, catalyst layers formed on both sides of the polymer electrolyte membrane, a gas diffusion electrode substrate formed on the outside of the catalyst layer, and separators sandwiching these.

[0004] Fuel cells are systems that electrically extract the energy generated when hydrogen and oxygen react to produce water. Therefore, when the electrical load increases and the current output from the cell increases, a large amount of water (water vapor) is generated. When this water vapor cools, it condenses into droplets, blocking the pores of the gas diffusion electrode substrate, reducing the amount of gas (oxygen gas and / or hydrogen gas) supplied to the catalyst layer. Finally, when all the pores of the gas diffusion electrode substrate are blocked, power generation stops, a phenomenon known as flooding. Conventionally, gas diffusion electrode materials for fuel cells have required high drainage performance to effectively suppress flooding.

[0005] To achieve high drainage, gas diffusion electrode substrates may have a porous layer called a microporous layer (MPL) on one side of a water-repellent conductive porous substrate. To impart water repellency to a conductive porous substrate, fluororesins with excellent water repellency have been added, and combinations with carbon materials have also been considered. For example, Patent Document 1 discloses a gas diffusion electrode substrate for use in fuel cells, in which a microporous layer composed of a carbon-based filler and a fluororesin is formed on one side of the electrode substrate. The gas diffusion electrode substrate has a water sliding angle of 30 degrees or less on the surface opposite to the surface on which the microporous layer is formed, and a surface-perpendicular gas permeation resistance of 15 to 190 mmAq.

[0006] International Publication No. 2015 / 125750

[0007] Water repellents containing organic fluorine compounds, commonly known as PFAS (Per- and PolyfluoroAlkyl Substances), have been used for conductive porous substrates for gas diffusion electrode substrates, which require high water repellency. However, fluorine compounds are known as "eternal chemicals," and are substances with low decomposition properties, raising concerns about their impact on the environment and human body. PFAS is a group of more than 4,730 organic fluorine compounds, and future scientific verification of the impact of each compound on the human body and the environment is awaited. However, from a preventative perspective, there is a demand for conductive porous substrates with high water repellency without using PFAS.

[0008] Although Patent Document 1 achieves high water repellency, this effect is only observed when a fluorine compound is used, and no consideration has been given to conductive porous substrates that do not use a fluorine compound.

[0009] Furthermore, the inventors of the present invention have conducted extensive research and found that it is difficult to impart sufficient water repellency to a conductive porous substrate simply by using a water repellent agent that does not contain fluorine.

[0010] Therefore, an object of the present invention is to provide a conductive porous substrate that does not contain fluorine and has high water repellency, and an electrochemical device that is capable of stable power generation.

[0011] The present invention and its preferred embodiments have the following configurations. (1) A conductive porous substrate containing carbon fibers, wherein a resin containing nanocarbon aggregates is supported on the carbon fibers, the conductive porous substrate having a sliding angle of 2° to 60° and a mass ratio F / C of the fluorine content to the carbon content of 0.01 or less. (2) The conductive porous substrate according to (1), further containing a water repellent. (3) The conductive porous substrate according to (1) or (2), wherein the primary particles of the nanocarbon aggregates are spherical. (4) The conductive porous substrate according to any one of (1) to (3), wherein the primary particles of the nanocarbon aggregates have a particle size of 10 nm to 200 nm. (5) The conductive porous substrate according to any one of (1) to (4), wherein the nanocarbon aggregates are made of carbon black. (6) The conductive porous substrate according to (1) or (2), wherein the nanocarbon aggregates are fibrous nanocarbon aggregates having a diameter of 5 nm to 200 nm. (7) The conductive porous substrate according to any one of (1) to (6), wherein the proportion of the nanocarbon aggregates in 100% by mass of the conductive porous substrate is 0.5% by mass or more and 16.0% by mass or less. (8) The conductive porous substrate according to (2), wherein the water repellent agent has a non-fluorinated alkyl group. (9) The conductive porous substrate according to (8), wherein the number of carbon atoms constituting the non-fluorinated alkyl group is 8 to 40. (10) The conductive porous substrate according to (2), wherein the sliding angle increases by 10° or more or the water repellency is lost when heat-treated at 400°C for 1 hour in an air atmosphere. (11) A gas diffusion electrode substrate comprising a porous layer containing carbonaceous particles and a binder resin on one surface of the conductive porous substrate according to any one of (1) to (10). (12) The gas diffusion electrode substrate according to (11), wherein the mass ratio F / C of the fluorine content to the carbon content in the porous layer is 0.01 or less. (13) An electrochemical device having the conductive porous substrate according to any one of (1) to (10) or the gas diffusion electrode substrate according to (11) or (12). (14) A vehicle using the electrochemical device according to (13) as a power source.

[0012] The present invention provides a conductive porous substrate that is fluorine-free and has high water repellency. The conductive porous substrate obtained can be suitably used in electrochemical devices such as gas diffusion electrode substrates and fuel cells.

[0013] An embodiment of the present invention will now be described in detail.

[0014] <Conductive Porous Substrate> The conductive porous substrate of the present invention contains carbon fibers.

[0015] Examples of the carbon fiber include polyacrylonitrile (PAN)-based, pitch-based, rayon-based, etc. Among these, PAN-based and pitch-based carbon fibers are preferred because of their excellent mechanical strength.

[0016] The carbon fibers preferably have an average fiber diameter of 3 μm or more and 20 μm or less. By setting the average fiber diameter to 3 μm or more, more preferably 5 μm or more, the pore size of the conductive porous substrate can be increased, improving drainage when used in a fuel cell and more effectively suppressing flooding. On the other hand, by setting the average diameter to 20 μm or less, more preferably 12 μm or less, and even more preferably 10 μm or less, water vapor diffusivity can be reduced, more effectively improving power generation performance at high temperatures when used in a fuel cell.

[0017] It is also preferable to use two or more types of carbon fibers having different average diameters, which can improve the surface smoothness of the conductive porous substrate.

[0018] The average fiber diameter of carbon fibers can be determined by taking photographs of the carbon fibers at 1,000x magnification or more using a microscope such as a scanning electron microscope, randomly selecting 30 different single fibers, measuring their diameters, and calculating the average value. As the scanning electron microscope, for example, an S-5500 manufactured by Hitachi, Ltd. or an equivalent product can be used.

[0019] The carbon fibers preferably have an average length of 3 mm or more and 20 mm or less. By setting the average length to 3 mm or more, more preferably 5 mm or more, the mechanical strength, electrical conductivity, and thermal conductivity of the electrode substrate can be improved. On the other hand, by setting the average length to 20 mm or less, more preferably 15 mm or less, the dispersibility of the carbon fibers when made into a carbon fiber paper sheet can be improved, and a homogeneous electrode substrate can be obtained. The carbon fibers can be obtained by, for example, cutting continuous carbon fibers to the desired length.

[0020] The average length of carbon fibers can be determined by taking photographs of the carbon fibers at 50x magnification or more using a microscope such as a scanning electron microscope, randomly selecting 30 different single fibers, measuring their lengths, and calculating the average length. As the scanning electron microscope, for example, an S-5500 manufactured by Hitachi, Ltd. or an equivalent product can be used.

[0021] The average fiber diameter and average length of the carbon fibers may be measured and calculated by directly observing the carbon fibers that are the raw material for the conductive porous substrate, or may be measured and calculated by observing the conductive porous substrate.

[0022] Examples of the form of the carbon fiber in the conductive porous substrate include carbon fiber woven fabric, carbon fiber paper, carbon fiber nonwoven fabric, carbon felt, carbon paper, and carbon cloth. Among these, carbon paper, which is a substrate containing carbide obtained by binding a carbon fiber paper with a carbide, is preferred because it has excellent "spring properties" that allow it to absorb dimensional changes in the thickness direction of the electrolyte membrane when used in a fuel cell. Hereinafter, a substrate composed of carbon fiber will also be referred to as a "carbon fiber substrate."

[0023] In the conductive porous substrate, a resin containing nanocarbon aggregates is supported on the carbon fibers. "Supported" here refers to a state in which the resin containing nanocarbon aggregates is placed on the carbon fibers and immobilized. Whether or not the resin is immobilized can be determined by whether or not 30% by mass or more of the supported nanocarbon aggregates are retained without falling off from the carbon fiber substrate after performing the operation of immersing the conductive porous substrate in water and removing it three times.

[0024] The nanocarbon aggregates have the function of increasing the effect of a water repellent agent described later and increasing the amount of the water repellent agent attached by imparting irregularities to the surface of the conductive porous substrate. The nanocarbon aggregates do not need to be in an aggregated form before being supported on the carbon fiber substrate, but from the viewpoint of handling, they are preferably aggregated before being supported.

[0025] Examples of nanocarbon constituting the nanocarbon aggregate include carbon black and fibrous nanocarbon.

[0026] Carbon black is preferred in that it can be obtained with high purity. Examples of carbon black include acetylene black, ketjen black, furnace black, etc. Among them, acetylene black is preferred in that it contains less impurities such as iron, which can reduce the power generation performance when used in a fuel cell.

[0027] The fibrous nanocarbon is preferably a carbon nanotube.

[0028] The shape of the primary particles of the nanocarbon is preferably spherical from the viewpoint of smooth gas diffusion when used in a fuel cell.

[0029] When the primary particles of the nanocarbon are spherical, the particle size of the primary particles is preferably 10 nm or more and 200 nm or less. By setting the particle size of the primary particles to 10 nm or more, handling properties can be improved. On the other hand, by setting the particle size of the primary particles to 200 nm or less, a small amount of addition can impart numerous irregularities to the conductive porous substrate, thereby increasing the specific surface area.

[0030] The particle size of nanocarbon primary particles can be measured and calculated by observing them at a magnification of 200,000 or more using a scanning electron microscope (e.g., S-5500 manufactured by Hitachi, Ltd.) or a transmission electron microscope. Specifically, 100 primary particles constituting the nanocarbon aggregate are randomly observed and their particle sizes are measured, and the average particle size of the obtained individual primary particles is calculated to determine the particle size of the primary particles. The particle size of each primary particle is calculated from the average of the minimum circumscribed circle diameter and the maximum inscribed circle diameter. Because nanocarbon aggregates are composed of an aggregation of multiple primary particles, the boundary lines between the individual primary particles may be unclear. In such cases, the particle size of each primary particle is measured, assuming that the constricted portion where the primary particles abut is the boundary line.

[0031] The diameter of the fibrous nanocarbon is preferably 5 nm or more and 200 nm or less. By setting the diameter to 200 nm or less, a small amount of the nanocarbon aggregate can be added to impart numerous irregularities to the conductive porous substrate, thereby increasing the specific surface area. On the other hand, by setting the diameter to 5 nm or more, entanglement of the fibrous nanocarbons with each other can be suppressed, making it easier to form irregularities on the conductive porous substrate.

[0032] The diameter of the fibrous nanocarbon can be measured and calculated by observation using a scanning electron microscope (for example, S-5500 manufactured by Hitachi, Ltd.). Specifically, the conductive porous substrate is photographed at a magnification of 100,000 times or more, 100 different fibrous nanocarbons are randomly selected and their diameters are measured, and the average value is calculated from the diameters of the individual fibrous nanocarbons obtained, which is the diameter of the fibrous nanocarbon. The diameter of each fibrous nanocarbon may be calculated from the average value of the minimum circumscribed circle diameter and the maximum inscribed circle diameter after observing the cross section, or the width (thickness) of the fiber when observed from above may be used as the diameter.

[0033] The nanocarbon aggregate preferably has a diameter of 10 μm or less. The diameter of the nanocarbon aggregate can be measured by observing it at a magnification of 5,000 times or more using a scanning electron microscope. Specifically, 100 nanocarbon aggregates are randomly observed, and the diameter of the circumscribed sphere is measured, which is defined as the diameter of the nanocarbon aggregate. A scanning electron microscope (e.g., S-5500 manufactured by Hitachi, Ltd.) can be used as a microscope capable of such observation.

[0034] The content of the nanocarbon aggregates in 100% by mass of the conductive porous substrate is preferably 0.5% by mass or more and 16.0% by mass or less. By setting the proportion of the nanocarbon aggregates to 0.5% by mass or more, it is possible to form unevenness that is more effective in increasing the water repellency of the conductive porous substrate. On the other hand, by setting the proportion of the nanocarbon aggregates to 16.0% by mass or less, it is possible to suppress the nanocarbon aggregates from interfering with gas diffusion inside the conductive porous substrate.

[0035] The resin is an amorphous organic compound that functions to bind the nanocarbon aggregate to the carbon fiber substrate. As the resin, those that can bind the nanocarbon aggregate to the carbon fiber substrate, for example, polyester resin, polyethylene, polypropylene, polystyrene, acrylic resin, ABS resin, polyvinyl chloride, nylon, polyacetal, polycarbonate, polybutylene terephthalate, polyarylate, phenol resin, epoxy resin, polyurethane resin, melamine resin, unsaturated polyester resin, etc. can be used. Among them, polyester resin is preferred because it has excellent heat resistance and is easy to obtain a water dispersion.

[0036] The conductive porous substrate preferably further contains a water repellent agent. The water repellent agent in the present invention refers to an agent that, when contained in the conductive porous substrate, has the effect of reducing the sliding angle (described later) of the conductive porous substrate by 10° or more.

[0037] The water repellent preferably has a non-fluorinated alkyl group. The non-fluorinated alkyl group refers to an alkyl group that does not contain a fluorine atom. By having a non-fluorinated alkyl group, it is possible to impart high water repellency to the conductive porous substrate without containing PFAS, which is a concern for its impact on the human body and the environment.

[0038] The number of carbon atoms constituting the non-fluorinated alkyl group is preferably 8 or more and 40 or less, and more preferably 12 or more and 30 or less.

[0039] The presence of a non-fluorinated alkyl group in the water repellent attached to the conductive porous substrate can be confirmed by the following procedure: (i) The conductive porous substrate is shredded into 1-2 cm square pieces, immersed in hexane, and irradiated with ultrasonic waves while heating to 50°C to extract soluble matter. (ii) IR or 1H NMR of the soluble matter extracted in (i) is measured. (iii) The CH of the non-fluorinated alkyl group is measured. ３ - and -CH ２ - Check for the presence of peaks and absorption lines. ３ or CH ２ 2800-3000 cm due to stretching vibration －１Check for the presence or absence of a peak in the CH ３ - absorption lines observed in the range of 0.95 to 0.85 due to the chemical shift of -CH ２ The presence of absorption lines observed in the range of 1.35 to 1.20 due to the chemical shift of - is confirmed.

[0040] The number of carbon atoms in the non-fluorinated alkyl group of the water repellent agent attached to the conductive porous substrate can be identified by the following procedure: (i) The conductive porous substrate is shredded into 1-2 cm square pieces, immersed in hexane, and heated to 50°C while being irradiated with ultrasound to extract soluble matter. (ii) The number of carbon atoms in the soluble matter extracted in (i) is calculated using GC / MS.

[0041] The water repellent is preferably an organic compound and does not contain fluorine atoms. The absence of fluorine atoms in the water repellent can be confirmed by measuring the sliding angle after heat-treating the conductive porous substrate in an air atmosphere at 400 ° C for 1 hour. Unlike resins containing fluorine atoms, so-called fluororesins, many water repellents that do not contain fluorine atoms significantly lose their water repellency when heat-treated at 400 ° C for 1 hour. Specifically, when the conductive porous substrate containing a water repellent that does not contain fluorine atoms is heat-treated in an air atmosphere at 400 ° C for 1 hour, the sliding angle described below increases by 10 ° or more compared to before the heat treatment, or the water repellency is lost. When a droplet of purified water is placed on the conductive porous substrate, the water droplet penetrates into the conductive porous substrate, making it impossible to measure the sliding angle. That is, it is preferable that the conductive porous substrate of the present invention has a sliding angle that increases by 10 ° or more when heat-treated in an air atmosphere at 400 ° C for 1 hour, or loses its water repellency.

[0042] Examples of the fluorine-free water repellent agent include hydrocarbon-based water repellents such as XF-5003, XF-5005, and XF-5007 (all manufactured by Daikin Industries, Ltd.), Rakuguard NOF (manufactured by Rakuto Chemical Industry Co., Ltd.), Modiper (registered trademark) FP100 (manufactured by NOF Corporation), Rikenpalan PG-70 (manufactured by Miki Riken Kogyo Co., Ltd.), Meishield (registered trademark) Z-1, and Meishield (registered trademark) Z-210 (all manufactured by Meisei Chemical Industry Co., Ltd.), and examples of silicone-based water repellents include Rikenpalan SG-54 (manufactured by Miki Riken Kogyo Co., Ltd.), Neoseed (registered trademark) NR7080, and Neoseed (registered trademark) NR8800 (all manufactured by Nicca Chemical Co., Ltd.). Examples of paraffin-based water repellents include SDX-5100 (trade name) (manufactured by Sumika Chemtex Co., Ltd.) and Paragit ZS (manufactured by Meisei Chemical Industry Co., Ltd.).

[0043] The resin and the water repellent agent may contain the same material, in which case the same material serves both to improve water repellency and to immobilize the nanocarbon aggregates.

[0044] In the conductive porous substrate, the mass ratio F / C of the fluorine content to the carbon content is 0.01 or less. Here, "the mass ratio F / C is 0.01 or less" means that the conductive porous substrate does not substantially contain fluorine. Since the conductive porous substrate does not substantially contain fluorine, it is possible to reduce the concern of unintentionally releasing fluorine compounds into the environment, and it is also possible to reduce the management costs required to prevent fluorine compounds from being released into the environment from production to disposal.

[0045] The mass ratio F / C of the conductive porous substrate can be measured and calculated by the following procedure. (i) The surface of the conductive porous substrate is observed at 2,000 times magnification using a scanning electron microscope (SEM). (ii) The area observed at magnification in (i) is irradiated with an electron beam at an acceleration voltage of 20 kV using energy dispersive X-ray analysis (EDX), and reflected characteristic X-rays are detected. (iii) The characteristic X-rays detected in (ii) are quantified to derive the mass fractions of fluorine and carbon, and the ratio obtained by dividing the mass fraction of fluorine by the mass fraction of carbon is calculated. (iv) The measurements and calculations in (i) to (iii) above are performed 10 times in randomly selected different fields of view, and of the 10 calculated ratios, the two largest and two smallest values, a total of four values, are excluded, and the average of the remaining six values ​​is calculated to obtain the mass ratio F / C.

[0046] When the conductive porous substrate is used in a fuel cell, its thickness is preferably 70 μm or more and 220 μm or less. By making the thickness 220 μm or less, more preferably 150 μm or less, and even more preferably 120 μm or less, gas diffusivity can be improved. On the other hand, by making the thickness 70 μm or more, mechanical strength can be maintained and handling during the manufacturing process can be facilitated.

[0047] The conductive porous substrate has a sliding angle of 2° or more and 60° or less. By setting the sliding angle to 60° or less, more preferably 40° or less, and even more preferably 30° or less, flooding can be suppressed when used in a fuel cell. Furthermore, by setting the sliding angle to 40° or less, and even more preferably 30° or less, flooding can be suppressed even under higher humidity. On the other hand, by setting the sliding angle to 2° or more, excessive water repellency can be prevented, preventing the conductive porous substrate from becoming a wall that does not allow water to pass through, and the water discharge function can be maintained.

[0048] The sliding angle can be determined by placing a 10 μL droplet of purified water on a horizontally placed conductive porous substrate, tilting the conductive porous substrate at a speed of 1 ° / sec, and measuring the angle at which the water droplet starts to roll at 10 sample points. The sliding angle can be determined by calculating the average value. The sliding angle can be measured using an automatic contact angle meter (e.g., DM-501 manufactured by Kyowa Interface Science Co., Ltd., or an equivalent product). In addition, as described below, when the conductive porous substrate has a porous layer on one side, the sliding angle is measured and calculated for the side on which the porous layer is not provided.

[0049] Whether or not a gas diffusion electrode substrate described below contains a fluorine-free water repellent agent can be confirmed by heat-treating the gas diffusion electrode substrate in an air atmosphere at 400°C for 1 hour, and then measuring the sliding angle on the surface on which the conductive porous substrate, on which no porous layer is formed, is exposed.

[0050] <Gas Diffusion Electrode Substrate> The gas diffusion electrode substrate of the present invention has a porous layer containing carbonaceous particles and a binder resin on one surface of the conductive porous substrate.

[0051] The carbonaceous particles preferably have a large specific surface area so as to easily form a porous structure. Specifically, carbon black is preferred, and more specifically, acetylene black, ketjen black, furnace black, etc. are preferred. Among these, acetylene black is more preferred because it contains less impurities such as iron, which can reduce the power generation performance when used in a fuel cell.

[0052] The binder resin can hold the carbonaceous particles on the conductive porous substrate, and examples of the binder resin that can be used include polyester resin, polyethylene, polypropylene, polystyrene, acrylic resin, ABS resin, polyvinyl chloride, nylon, polyacetal, polycarbonate, polybutylene terephthalate, polyarylate, phenol resin, epoxy resin, polyurethane resin, melamine resin, unsaturated polyester resin, etc. Among these, polyester resin is more preferred because it has excellent heat resistance and is easy to obtain an aqueous dispersion.

[0053] The binder resin may be the same material as the resin containing the nanocarbon aggregates in the conductive porous substrate.

[0054] The porous layer preferably contains a fluorine-free water repellent agent to further improve water repellency. In particular, when the gas diffusion electrode substrate is used in a fuel cell, the porous layer is preferred because it easily improves all of the following: high gas diffusivity in the perpendicular direction for diffusing gas supplied from the separator to the catalyst; drainage performance for discharging liquid water generated by electrochemical reactions to the separator; and conductivity for extracting the generated current. Furthermore, the porous layer is preferred because it also has the function of promoting back-diffusion of water into the electrolyte membrane in the fuel cell and wetting the electrolyte membrane.

[0055] The binder resin and the fluorine-free water repellent agent contained in the porous layer may be the same material, in which case the material serves both to improve the water repellency as a water repellent agent and to hold the carbonaceous particles.

[0056] The mass ratio F / C of the fluorine content to the carbon content in the porous layer is preferably 0.01 or less. Here, "the mass ratio F / C being 0.01 or less" means that the porous layer is substantially free of fluorine. The porous layer being substantially free of fluorine not only reduces concerns about unintentional release of fluorine compounds into the environment, but also reduces the management costs required to prevent release of fluorine compounds into the environment from production to disposal.

[0057] The mass ratio F / C can be measured and calculated by the following procedure: (i) The surface of the porous layer is observed at 2,000x magnification using a scanning electron microscope (SEM). (ii) The area observed at magnification in (i) is irradiated with an electron beam at an accelerating voltage of 20 kV using energy dispersive X-ray analysis (EDX), and the reflected characteristic X-rays are detected. (iii) The characteristic X-rays detected in (ii) are quantified to derive the mass fractions of fluorine and carbon, and the ratio obtained by dividing the mass fraction of fluorine by the mass fraction of carbon is calculated. (iv) The measurements and calculations in (i) to (iii) above are performed 10 times in randomly selected different fields of view, and of the 10 calculated ratios, the two largest and two smallest values, a total of four values, are excluded, and the average of the remaining six values ​​is calculated to obtain the mass ratio F / C.

[0058] <Method for producing conductive porous substrate> An example of a method for producing the conductive porous substrate of the present invention will be described. However, the following description should not be construed as limiting the embodiments of the conductive porous substrate of the present invention.

[0059] (Resin supporting step) The step of supporting a resin containing nanocarbon aggregates on a carbon fiber substrate is also called a “resin supporting step”. Examples of the method for the resin supporting step include a method of immersing the carbon fiber substrate in a liquid composition in which the resin containing the nanocarbon aggregates is dispersed in a solvent, a method of applying the liquid composition to the carbon fiber substrate, and a method of spraying the liquid composition onto the carbon fiber substrate.

[0060] The water repellency of the conductive porous substrate can be controlled by adjusting the amount of water repellent attached by changing the concentration of the water repellent in the water repellent attaching step described below, but can also be controlled by adjusting the amount of the resin containing the nanocarbon aggregates carried in the resin carrying step. As the amount of nanocarbon aggregates carried increases, the surface area of ​​the conductive porous substrate increases, and therefore the amount of water repellent attached increases, resulting in improved water repellency.

[0061] The liquid composition can be prepared by dispersing the nanocarbon or nanocarbon aggregate together with the resin in a solvent. In this method, a dispersant may be further added to the solvent. As the dispersant, a nonionic dispersant is preferred because it does not leave unnecessary ions remaining in the conductive porous substrate.

[0062] (Heating step) If the dispersant remains on the conductive porous substrate, it may cause a decrease in water repellency, so after the nanocarbon aggregate is attached to the surface of the carbon fiber substrate, it is preferable to heat it at 200°C or higher. This step is also called the "heating step". The heating step can burn off the dispersant.

[0063] (Water-repellent agent application process) It is also preferable to apply the water-repellent agent after the resin supporting process or the heating process. This process is also called the "water-repellent agent application process." By applying an appropriate amount of water-repellent agent in the water-repellent agent application process, it becomes easy to make the sliding angle of the conductive porous substrate 2 ° or more and 60 ° or less. Methods for applying the water-repellent agent include, for example, a method of impregnating the conductive porous substrate after the resin supporting process or the heating process with a dispersion of the water-repellent agent and then drying, or a method of applying a dispersion of the water-repellent agent to the conductive porous substrate after the resin supporting process or the heating process and then drying.

[0064] <Method for producing gas diffusion electrode substrate> An example of a method for producing the gas diffusion electrode substrate of the present invention will be described. However, the following description should not be construed as limiting the aspects of the gas diffusion electrode substrate of the present invention.

[0065] (Porous layer forming step) The gas diffusion electrode substrate of the present invention is obtained by forming the porous layer containing the carbonaceous particles and the binder resin on one surface of the conductive porous substrate. This step is also called the porous layer forming step.

[0066] Examples of the method for the porous layer formation step include applying a dispersion liquid in which the carbonaceous particles and the binder resin are dispersed onto the conductive porous substrate, followed by drying and baking. It is preferable that the dispersion liquid is water, as this is easy to handle. In this case, a dispersant may be used to uniformly disperse the carbonaceous particles in the water dispersion medium. A nonionic dispersant is preferred as the dispersant, as it does not leave unnecessary ions remaining in the porous layer.

[0067] (Porous layer heating step) If the dispersant in the porous layer forming step remains in the porous layer, it may cause a decrease in the water repellency of the porous layer, so after the porous layer forming step, it is preferable to heat the porous layer in the atmosphere at 200°C or higher to burn off the dispersant. This step is also called the "porous layer heating step."

[0068] (Water-repellent agent application step) From the viewpoint of further improving water repellency, it is preferable to apply a fluorine-free water-repellent agent to the porous layer. This step is also called the "water-repellent agent application step."

[0069] Examples of the water repellent application step include a method of immersing the gas diffusion electrode substrate in a dispersion of the water repellent and then drying it, or a method of applying a dispersion of the water repellent to the surface of the porous layer, or to the surface of the porous layer and the surface of the conductive porous substrate, and then drying it.

[0070] <Electrochemical Device> The electrochemical device of the present invention has the conductive porous substrate of the present invention or the gas diffusion electrode substrate of the present invention. Examples of the electrochemical device include a fuel cell, a water electrolysis device, a CO ２ Examples of the electrolytic device include various storage batteries, etc. Among these, the conductive porous substrate and the gas diffusion electrode substrate are suitable for fuel cells.

[0071] The vehicle of the present invention, such as an automobile, an aircraft, or a ship, uses the electrochemical device as a power source. Among these, a fuel cell, which is one of the electrochemical devices, and a polymer electrolyte fuel cell are particularly suitable as a power source for vehicles such as an automobile, an aircraft, or a ship.

[0072] The present invention will be specifically explained below with reference to examples, but the present invention should not be construed as being limited to these examples.

[0073] <Evaluation> (1) Basis Weight For the carbon fiber substrate, the conductive porous substrate without water repellent treatment, and the conductive porous substrate after water repellent treatment (hereinafter collectively referred to as "substrate"), three test pieces of 10 cm x 10 cm were taken from the substrate to be measured. The mass of the test pieces was measured, and the mass per unit area of ​​each test piece was calculated by the following formula. Mass per unit area (g / m ２ ) = mass of test piece (g) / area of ​​test piece (m ２ ) The arithmetic mean value of the mass per unit area of ​​the three test pieces (g / m ２ ) was rounded off to the nearest whole number, and the value obtained was taken as the basis weight of the substrate.

[0074] (2) Sliding Angle A 10 μL droplet of purified water was placed on a horizontally placed conductive porous substrate, and the angle at which the water droplet began to roll when the conductive porous substrate was tilted at a rate of 1° / sec was measured using an automatic contact angle meter (DM-501 manufactured by Kyowa Interface Science Co., Ltd.). The measurement was performed 10 times at different measurement points on the conductive porous substrate, and the average value was taken as the sliding angle.

[0075] (3) Mass Ratio F / C A portion observed at 2,000 times magnification using a scanning electron microscope (SEM) (S-5500 manufactured by Hitachi, Ltd.) was irradiated with an electron beam at an acceleration voltage of 20 kV using energy dispersive X-ray analysis (EDX), and reflected characteristic X-rays were detected. By quantifying this characteristic X-ray, the mass fractions of fluorine and carbon were derived, and the ratio obtained by dividing the mass fraction of fluorine by the mass fraction of carbon was calculated. This measurement and calculation were performed 10 times at different randomly selected locations, and of the 10 calculated ratios, the two largest and two smallest, a total of four values, were excluded, and the average of the remaining six values ​​was calculated to obtain the mass ratio F / C.

[0076] [Example 1] (Carbon fiber substrate) A carbon fiber substrate cut into a square with a side length of 10 cm, a thickness of 190 μm, and a basis weight of 84 g / m ２ Carbon paper (TGP-H-060 manufactured by Toray Industries, Inc.) was used as the carbon fiber substrate.

[0077] (Resin Supporting Step) To 200 g of pure water, 3 g of acetylene black (DENKA BLACK (registered trademark) Li-100 manufactured by Denka Co., Ltd.) as nanocarbon aggregates, 7 g of a nonionic dispersant, and 3 g of an aqueous dispersion of polyethylene resin (Vylonal (registered trademark) MD-2000 manufactured by Toyobo MC Co., Ltd.) were added, and the mixture was stirred at 2,000 rpm for 5 minutes using a stirrer (ARE-310 manufactured by Thinky Corporation) to obtain a dispersion of nanocarbon and resin.

[0078] The carbon fiber substrate was immersed in the obtained dispersion and then dried at 100°C for 2 minutes.

[0079] (Heating Step) Thereafter, the substrate was heated at 320° C. for 10 minutes to obtain a conductive porous substrate that had not been subjected to water repellency treatment.

[0080] (Water-repellent agent attachment step) 5 g of a water-repellent agent having a non-fluorinated alkyl group and not containing fluorine ("Meisei Chemical Industry Co., Ltd." "Meishield (registered trademark)" Z-210) was added to 95 g of pure water to prepare a water-repellent treatment solution, and the conductive porous substrate that had not been subjected to the water-repellent treatment was immersed in the solution, then pulled out, dried at 100 ° C. for 1 minute, and then dried at 180 ° C. for 10 minutes to obtain a conductive porous substrate after the water-repellent treatment.

[0081] The evaluation results are shown in Table 1. Although no fluororesin-based water repellent agent was used, the water repellency was comparable to that of a conductive porous substrate using a fluororesin-based water repellent agent.

[0082] [Example 2] In the resin supporting step, the amount of acetylene black added was changed to 6 g, the amount of nonionic dispersant added to 14 g, and the amount of polyethylene resin aqueous dispersion added to 6 g. Except for these, the same procedure as in Example 1 was carried out to obtain a conductive porous substrate before and after the water-repellent treatment.

[0083] The evaluation results are shown in Table 1. Although no fluororesin-based water repellent agent was used, the water repellency was comparable to that of a conductive porous substrate using a fluororesin-based water repellent agent.

[0084] Example 3 A conductive porous substrate before and after the water-repellent treatment was obtained in the same manner as in Example 1, except that carbon nanotubes (MWCNT, LB220-84 manufactured by Cnano Corp.) were used as the nanocarbon aggregates in the resin supporting step.

[0085] The evaluation results are shown in Table 1. As with the case of using carbon black, the case of using carbon nanotubes also showed water repellency equivalent to that of a conductive porous substrate using a fluororesin-based water repellent, despite the absence of a fluororesin-based water repellent.

[0086] Comparative Example 1 (Carbon Fiber Substrate) The same carbon fiber substrate as used in Example 1 was used.

[0087] (Resin Supporting Step) In Comparative Example 1, the resin supporting step was not performed.

[0088] (Water-repellent agent application step) A water-repellent treated conductive porous substrate was obtained in the same manner as in Example 1, except that the carbon fiber substrate was immersed in the water-repellent treatment liquid.

[0089] The evaluation results are shown in Table 1. Water repellency comparable to that of a conductive porous substrate using a fluororesin-based water repellent agent was not obtained.

[0090] Comparative Example 2 (Carbon Fiber Substrate) The same carbon fiber substrate as used in Example 1 was used.

[0091] (Resin Supporting Step) In Comparative Example 2, the resin supporting step was not performed.

[0092] (Water repellent agent attachment process) 5 g of an aqueous dispersion of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) as a fluororesin-based water repellent agent was added to 95 g of pure water to prepare a water repellent treatment liquid, and the carbon fiber base material was immersed in the water repellent treatment liquid, and then dried at 100°C for 1 minute.

[0093] (Heating Step) Thereafter, the substrate was baked at 400° C. for 30 minutes to obtain a water-repellent treated conductive porous substrate.

[0094] The evaluation results are shown in Table 1.

[0095] [Comparative Example 3] (Carbon fiber substrate, resin supporting step and heating step) Using the same carbon fiber substrate as used in Example 1, a non-water-repellent treated conductive porous substrate was obtained through the resin supporting step and heating step in the same manner as in Example 1.

[0096] (Water-repellent agent application process) 6 g of an aqueous dispersion of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) as a fluororesin-based water-repellent agent was added to 94 g of pure water to prepare a water-repellent treatment liquid, and the conductive porous substrate that had not been subjected to water-repellent treatment was immersed in the liquid, then removed and dried at 100°C for 1 minute.

[0097] (Heating Step) Thereafter, the substrate was baked at 400° C. for 30 minutes to obtain a water-repellent treated conductive porous substrate.

[0098] The evaluation results are shown in Table 1. In the conductive porous substrate containing a water repellent agent containing fluorine atoms, the sliding angle of this comparative example, in which a resin containing nanocarbon aggregates was supported on carbon fibers, was 8° smaller than that of comparative example 2, in which the resin was not supported.

[0099] On the other hand, in the conductive porous substrate containing a water repellent agent that does not contain fluorine atoms, Example 1, in which a resin containing nanocarbon aggregates was supported on carbon fibers, had a sliding angle that was 60° smaller than that of Comparative Example 1, in which a resin containing nanocarbon aggregates was not supported. This shows that the effect of the nanocarbon aggregates in the present invention on improving water repellency is significantly manifested when a water repellent agent that does not contain fluorine atoms is used.

[0100] Comparative Example 4 A conductive porous substrate before and after the water-repellent treatment was obtained in the same manner as in Example 1, except that acetylene black in the resin supporting step was changed to graphite particles (average particle size 5 μm, manufactured by Chuetsu Graphite Industries, Ltd., flake graphite BF-5A).

[0101] The evaluation results are shown in Table 1. In this comparative example, in which a resin containing graphite particles was supported on a carbon fiber substrate, the sliding angle was 22° lower than in comparative example 1, in which a resin containing graphite particles was not supported, but the sliding angle was still 61°, and the water repellency was not improved to a level that would allow for the suppression of flooding when used in a fuel cell. This shows that the effect of the resin supported on carbon fiber in the present invention on improving water repellency is particularly evident when nanocarbon aggregates are used.

[0102]

[0103] The conductive porous substrate of the present invention can be used as a gas diffusion electrode substrate or a component of a gas diffusion electrode substrate in electrochemical devices such as polymer electrolyte fuel cells.

Claims

1. A conductive porous substrate comprising carbon fibers, wherein a resin containing nanocarbon aggregates is supported on the carbon fibers, the sliding angle is 2° or more and 60° or less, and the mass ratio F / C of the fluorine content to the carbon content is 0.01 or less.

2. The conductive porous substrate of claim 1, further comprising a water repellent agent.

3. The conductive porous substrate according to claim 1 or 2, wherein the primary particles of the nanocarbon aggregates are spherical.

4. The conductive porous substrate according to claim 1 or 2, wherein the primary particle diameter of the nanocarbon aggregate is 10 nm or more and 200 nm or less.

5. The conductive porous substrate according to claim 1 or 2, wherein the nanocarbon aggregates are composed of carbon black.

6. The conductive porous substrate according to claim 1 or 2, wherein the nanocarbon aggregates are aggregates of fibrous nanocarbons having a diameter of 5 nm or more and 200 nm or less.

7. A conductive porous substrate according to claim 1 or 2, wherein the proportion of the nanocarbon aggregates in 100% by mass of the conductive porous substrate is 0.5% by mass or more and 16.0% by mass or less.

8. The conductive porous substrate of claim 2, wherein the water repellent agent has a non-fluorinated alkyl group.

9. The conductive porous substrate according to claim 8, wherein the number of carbon atoms constituting said non-fluorinated alkyl group is 8 or more and 40 or less.

10. The conductive porous substrate according to claim 2, which, when heat-treated at 400°C for 1 hour in an air atmosphere, exhibits an increase in sliding angle of 10° or more, or loses water repellency.

11. A gas diffusion electrode substrate comprising the conductive porous substrate according to claim 1 and a porous layer containing carbonaceous particles and a binder resin on one surface of the conductive porous substrate.

12. The gas diffusion electrode substrate according to claim 11, wherein the mass ratio F / C of the fluorine content to the carbon content in said porous layer is 0.01 or less.

13. An electrochemical device comprising the conductive porous substrate according to claim 1 or the gas diffusion electrode substrate according to claim 11.

14. A vehicle using the electrochemical device according to claim 13 as a power source.

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