JP2017199546A - Fuel cell and conductive member for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell having a water repellent layer capable of improving conductivity while suppressing reduction in strength and change in characteristics.SOLUTION: In the fuel cell, a part of an anode part 91 and/or a part of a cathode part 92 is composed of conductive nanofibers 1 having conductivity. The conductive nanofiber 1 includes: a sheet-like nanofiber 2 composed of a plurality of polymeric fibers 21; and a plurality of linear conductive nano materials 3 having a cross-sectional area smaller than a cross-sectional area of the fiber 21 and arranged in the fiber 21. On the surface of the fiber 21, a protruding portion 31 is formed in which one end portion of the conductive nano material 3 protrudes from the surface.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fuel cell and a conductive member for a fuel cell.

  The fuel cell includes an anode part, a cathode part, and an electrolyte layer disposed between the anode part and the cathode part. The configuration of the fuel cell is described in, for example, Japanese Patent Laid-Open No. 2002-203569 (Patent Document 4). The electrolyte layer is, for example, a solid polymer electrolyte membrane. Each of the anode part and the cathode part includes a catalyst layer disposed on the electrolyte side and a gas diffusion layer disposed on the gas phase side. In recent fuel cells, a water repellent layer is provided between the catalyst layer and the gas diffusion layer in the anode part and the cathode part (particularly the cathode part). As the material of the water repellent layer of the cathode portion, a material having oxygen permeability, water repellency, and conductivity is adopted. Since the water-repellent layer plays an important role in water management in the fuel cell, the material and composition thereof have been studied.

  Here, recently, research has been conducted on conductive nanofibers used in various applications. For example, Japanese Unexamined Patent Application Publication No. 2007-273190 (Patent Document 1) describes a composite material in which a carbonized nanofiber layer is formed on a substrate by carbonization firing. Further, for example, JP 2009-138305 A (Patent Document 2) describes a conductive nanofiber in which conductivity is expressed by irradiating the nanofiber with ions. Moreover, for example, Japanese Patent Laying-Open No. 2015-35291 (Patent Document 3) describes conductive nanofibers whose surfaces are plated with metal.

JP 2007-273190 A JP 2009-138305 A JP-A-2015-35291 Japanese Patent Laid-Open No. 2002-20369

  However, the nanofiber according to Patent Document 1 is low in strength because it uses carbonized firing, and has a carbonized nanofiber layer formed on the surface, and thus its characteristics are likely to change due to oxidation or water immersion. In addition, the nanofiber according to Patent Document 2 has low conductivity, and has a problem in terms of practicality (for example, application to battery materials). In addition, the nanofiber according to Patent Document 3 has a problem in strength because the metal plating is easily peeled off. For example, graphite is originally a water-repellent material, but its surface is highly active and easily becomes hydrophilic. As described above, the conventional material has room for improvement in terms of compatibility between conductivity and strength and change in characteristics with respect to wetting in order to use the material as a fuel cell material.

  The present invention has been made in view of such circumstances, and a conductive member for a fuel cell capable of improving conductivity while suppressing a decrease in strength and a change in characteristics, and a fuel cell using the same. The purpose is to provide.

  A fuel cell according to the present invention is a fuel cell comprising an anode part, a cathode part, and an electrolyte membrane disposed between the anode part and the cathode part, wherein a part of the anode part and one part of the cathode part are provided. At least one of the parts is composed of conductive nanofibers having conductivity, the conductive nanofibers are sheet-like nanofibers composed of a plurality of polymer fibers, and the cross-sectional area is the cross-sectional area of the fibers And a plurality of linear conductive nanomaterials arranged in the fiber, and one end of the conductive nanomaterial protrudes from the surface on the surface of the fiber. The part is formed.

  According to the present invention, the electrical conductivity in the longitudinal direction of the fiber is ensured by the conductive nanomaterial disposed in the fiber, and further, the end of the conductive nanomaterial protruding from the surface of the fiber (protrusion) The conductivity in the direction (thickness direction, stacking direction) crossing the longitudinal direction of the film is also ensured. That is, by having the protruding portion, the probability that the protruding portions are in contact with each other between the fibers adjacent in the thickness direction is increased. Thereby, the electroconductivity of electroconductive nanofiber can be improved and it can be suitably used in a fuel cell. Moreover, since electrical conductivity can be ensured even if the ratio of the conductive nanomaterial in the whole is reduced, a decrease in the strength of the conductive nanofiber can be suppressed. In addition, since many parts of the conductive nanomaterial are arranged inside the nanofiber, the influence of exfoliation (separation), water immersion, or oxidation is also suppressed, which is advantageous in terms of suppressing strength reduction and property change. It is. Further, this structure does not require carbonization firing. That is, according to the present invention, it is possible to improve conductivity while suppressing a decrease in strength and a change in characteristics of a member used in a fuel cell.

It is a conceptual diagram for demonstrating the electroconductive nanofiber of this embodiment. It is a conceptual diagram for demonstrating the detailed structure of the electroconductive nanofiber of this embodiment. It is a flowchart for demonstrating the manufacturing method of the electroconductive nanofiber of this embodiment. It is a SEM photograph (100,000 times) of the conductive nanofiber of this embodiment. It is a SEM photograph (50000 times) of the electroconductive nanofiber of this embodiment. It is a SEM photograph (50000 times) of the electroconductive nanofiber of this embodiment. 2 is a SEM photograph (30000 times) of Example 1. 3 is a SEM photograph (30000 times) of Example 2. It is a conceptual diagram (description figure seen from the direction orthogonal to a longitudinal direction) for demonstrating the electroconductive nanofiber of this embodiment. It is a conceptual diagram (description figure seen from the direction orthogonal to a longitudinal direction) for demonstrating the electroconductive nanofiber of this embodiment. It is explanatory drawing for demonstrating an Example and a comparative example. It is explanatory drawing for demonstrating an Example and a comparative example. It is a conceptual diagram for demonstrating the measuring method of surface resistivity. It is a conceptual diagram for demonstrating the structure of the fuel cell of this embodiment. It is explanatory drawing for demonstrating the electric power generation characteristic of the fuel cell of this embodiment. It is a conceptual diagram for demonstrating the measuring method of a penetration resistivity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that some of the drawings are conceptual diagrams, and the shape of each part may not always be exact. As shown in FIGS. 1 and 2, the conductive nanofiber 1 constituting the fuel cell conductive member of this embodiment includes a nanofiber 2 and a conductive nanomaterial 3.

  The nanofiber 2 is composed of a plurality of fibers 21 of a polymer (polymer compound). In other words, the nanofiber 2 is composed of a polymer material that is converted into a nanofiber. The nanofiber 2 is formed in a sheet shape by a plurality of fibers 21. The raw material of the nanofiber 2 may be a polymer material, but assuming a general application (for example, various battery materials), for example, poly (vinylidene fluoride) (PVDF), polyacrylonitrile (PAN), polyamide, polyimide, etc. Is preferred. The nanofiber is a non-woven fabric (sheet) composed of a plurality of fibers having a fiber diameter of nano order. The thickness may be adjusted to the thickness required for the member to be applied, if necessary, but is generally about 0.1 to 1000 μm. However, the thickness is not limited to this.

  The conductive nanomaterial 3 is a nanomaterial that has a cross-sectional area smaller than the cross-sectional area of the fiber 21 and is linear and disposed in the fiber 21. The term “linear” means that the shape is not spherical or particulate (non-spherical and non-particulate), and means a shape having a longitudinal direction, such as a thread shape, a tubular shape, or a crimp shape. The cross-sectional area is an area of a cross section (hereinafter also referred to as “orthogonal cross section”) obtained by cutting the nanomaterial or fiber 21 in a direction orthogonal to the longitudinal direction (stretching direction). That the cross-sectional area of the conductive nanomaterial 3 is smaller than the cross-sectional area of the fiber 21 is the same meaning that the diameter (converted diameter) of the conductive nanomaterial 3 is smaller than the fiber diameter (converted diameter) of the fiber 21. The converted diameter is a diameter when the orthogonal cross section of the object is converted into a circle. It can be said that the orthogonal cross sections of the fibers 21 and the conductive nanomaterial 3 are substantially circular. A plurality of conductive nanomaterials 3 are arranged in the fiber 21.

  One end 31 of the conductive nanomaterial 3 protrudes from the surface of the fiber 21 to the outside of the fiber 21. In other words, the conductive nanomaterial 3 includes a main body portion 30 disposed in the fiber 21 and a protruding portion (one end portion) 31 connected to the main body portion 30 and disposed outside the fiber 21. That is, on the surface of the fiber 21, a protruding portion 31 is formed in which one end portion of the conductive nanomaterial 3 protrudes from the surface. The protruding portion 31 is one in which one end portion of the conductive nanomaterial 3 protrudes from the surface of the fiber 21. It can be said that the conductive nanofiber 1 has the conductive nanomaterial 3 in which a part is disposed in the fiber 21 and the other part is disposed outside the fiber 21. In other words, it can be said that the conductive nanomaterial 3 partially exposed from the fiber 21 and the conductive nanomaterial 3 entirely disposed in the fiber 21 exist.

  The conductive nanomaterial 3 is preferably a carbon-based conductive nanomaterial from the viewpoint of manufacturing cost and oxidation suppression. Examples of the carbon-based conductive nanomaterial include carbon black, carbon nanotube, carbon nanofiber, graphene, fullerene, carbon nanohorn, and carbon nanocoil. Among these, a linear thing corresponds to the electroconductive nanomaterial 3 of this embodiment. In addition, two or more names may be applied to one material, and the materials may overlap each other in meaning (for example, carbon nanohorns may be a kind of carbon nanotube).

  Since the carbon-based conductive nanomaterial is difficult to function as a catalyst, an unintended reaction is suppressed, and the carbon-based conductive nanomaterial is also suitable inside a battery where chemical reactions frequently occur. Among the carbon-based conductive nanomaterials described above, those that are in a normal state (for example, carbon nanotubes, carbon nanohorns, and carbon nanocoils) that are linear (a shape having a longitudinal direction) From the viewpoint of

  Particularly preferable as the conductive nanomaterial 3 is a carbon nanotube. Carbon nanotubes have a diameter of 100 nm or less and a relatively large aspect ratio (length / diameter), and therefore are suitable for improving conductivity. Furthermore, since many carbon nanotubes have a crimp shape, the carbon nanotube is more suitable in terms of formation of the protruding portion 31 and expression of conductivity. It can be said that the conductive nanomaterial 3 is preferably a carbon-based conductive nanomaterial having a diameter of 100 nm or less and having a crimp shape. More specifically, the conductive nanomaterial 3 is preferably a metal-type single-walled carbon nanotube (SWCNT) or a metal-type multi-walled carbon nanotube (MWCNT). In terms of conductivity and cost, multi-walled carbon nanotubes are more preferable. The length (full length) of the carbon nanotubes is preferably 1 μm or more. In this case, the conductivity can be expressed with a small blending ratio. That is, the aspect ratio (length / diameter) of the conductive nanomaterial 3 is more preferably 10 or more.

  In addition, in the conductive nanofiber 1, it can be said that as shown in FIG. 7A, a current-carrying portion Z in a state where the protruding portions 31 are in contact with each other is formed between the adjacent fibers 21. For example, it can be said that between the fibers 21 adjacent to each other in the thickness direction of the nanofiber 2, the energization part Z in a state where the protruding parts 31 are in contact with each other is formed. The energizing part Z is configured such that the protruding parts 31 are in contact with each other. The energization part Z can be said to be a part where the protrusions 31 are in contact with each other. In other words, as shown in FIG. 7B, the energization part Z is in contact with the first protruding part 31a and the first protruding part 31a formed on the first fiber 21a and the second protruding part 31a. Second projecting portion 31b. The energization part Z is formed between the first fiber 21a and the second fiber 21b adjacent to the first fiber 21a. Thereby, the electroconductivity of the thickness direction of the electroconductive nanofiber 1 expresses. When conductivity develops in the thickness direction, it can be estimated that the energization part Z is formed between the fibers 21 adjacent in the thickness direction. The conductive nanofiber 1 has a plurality of energization parts Z.

  In the present embodiment, a plurality of protrusions 31 are formed on each fiber 21 (one per fiber). When a plurality of protrusions 31 are formed on one fiber 21, at least one of the protrusions 31 and the protrusions 31 of the other fibers 21 are likely to come into contact with each other. The energization part Z is formed between the fibers 21.

(Production method)
In the present embodiment, the conductive nanofiber 1 is manufactured using an electrospinning method. The electrospinning method is a known method, for example, filling a nozzle with a raw material solution and applying a voltage (for example, 20 kV) between a nozzle (collecting site) where nanofibers are deposited and collected, This is a method of drawing a raw material solution from a nozzle to form nanofibers and generating nanofibers on a collection site. As shown in FIG. 3, the manufacturing method of the conductive nanofiber 1 of the present embodiment is performed by electrospinning using a raw material solution creating step S1 for creating a raw material solution and the raw material solution created in the raw material solution creating step S1. And a nanofiber production step S2 for producing a nanofiber (conductive nanofiber 1) by the method.

  The raw material solution creation step S1 includes a first solution creation step S11 and a second solution creation step S12. The first solution creation step S11 is a step in which, for example, an operator creates a first solution in which a polymer material is dissolved in a solvent. The solvent is required to have a drying property that can dissolve the polymer material to be converted into nanofibers and can be spun by an electrospinning method. The solvent may be a single solvent or a mixture of a plurality of solvents. When the polymer material that is the main raw material of the nanofiber is poly (vinylidene fluoride) (PVDF), polyacrylonitrile (PAN), polyamide, or polyimide, the solvent is, for example, NN dimethylformamide (DMF), NN dimethylacetamide (DMAc), or N methylpyrrolidone (NMP) or the like is preferable.

  In the second solution preparation step S12, for example, the operator can add the conductive nanomaterial 3 (for example, carbon nanotubes here) and the dispersant to the first solution during or after the preparation of the first solution. It is a process of creating. The second solution is a dispersion of carbon nanotubes and is a raw material solution. In the second solution preparation step S12, the second solution may be prepared using a known device such as a ball mill, a bead mill, a jet mill, or an ultrasonic disperser according to the purpose. As the dispersant, a dispersant that can be coordinated on the surface of the conductive nanomaterial 3 (carbon nanotube) and is soluble in a solvent is preferable. Examples of the dispersant include an anionic surfactant such as sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfate (SDBS), sodium cholate (SC), or sodium deoxycholate (DOC). Moreover, as a dispersing agent, for example, a cationic surfactant (such as various amines and quaternary ammonium salts) can be used. In recent literatures, it is also described that salts of weak acids (for example, acetates such as ammonium and potassium, carbonates, and phosphates) can be used as a dispersant. By appropriately adding a dispersant to create the second solution, aggregation of the conductive nanomaterial 3 can be suppressed.

  In the nanofiber production step S2, for example, an operator uses a general electrospinning apparatus (an apparatus having a nozzle and a collection part) and uses nanofibers (conductive nanofibers) from a raw material solution (second solution) by an electrospinning method. This is a step of creating 1). The electrospinning apparatus is set and operated so that the diameter of the nanofiber is 900 nm or less (for example, 400 to 500 nm).

  Here, in the nanofiber creation step S2 of the present embodiment, in order to create the conductive nanofiber 1, the electrospinning method is performed under the following conditions. That is, the applied voltage applied between the nozzle and the collection site (hereinafter also referred to as “between the nozzle and the collection site”) is 30 kV or more, and more preferably 35 kV or more. Since the raw material solution contains carbon nanotubes, a current easily flows between the nozzle and the collection site, and the applied voltage is set to be about 10 kV higher than the case where no carbon nanotubes are blended.

  The atmospheric temperature at the time of nanofiber production is 25 ° C. or higher, more preferably 30 ° C. or higher. Thereby, the drying property of resin can be improved. If this temperature is low, the drying property of the solution will be poor, and it will be difficult to collect the fibers unless the distance between the nozzle and the collection site is increased. On the other hand, when the distance between the nozzle and the collection site is increased, a larger voltage is required to blow the solution from the nozzle. If the applied voltage is too large, the electrical insulation between the nozzle and the collection site will be broken, making spinning difficult and causing damage to the sheet due to sparks. Is disadvantageous. Therefore, when using a raw material solution containing carbon nanotubes, it is preferable to increase the spinning temperature to improve the spinning property.

  The solvent used in the raw material solution (the solvent of the first solution) is an organic solvent, which makes the solution non-conductive, so that a potential difference is likely to occur between the nozzle and the collection site, and spinning is easy. In addition, when a solvent is water, since an electric current will flow when an applied voltage will be 20 kV or more, a spinning property may deteriorate and there exists a possibility that the fiber production amount per unit time may fall.

  The relative humidity is 35% or less, which suppresses segregation of the resin. In general, spinning is possible at a relative humidity of 50% or less. Here, when the relative humidity is higher than 35%, the fiber collecting property deteriorates. That is, in this case, the fiber tends to rise from the collection site and extend to the nozzle side, the nozzle and the collection site are connected by a conductive material (conductive nanofiber), and an overcurrent is generated between the nozzle and the collection site. May flow and short circuit, making spinning difficult to continue. When water is added to the resin solution, the phenomenon that the resin precipitates can be seen, so if water (humidity) is present in the process of evaporating the solvent and forming nanofibers while the solution popping out from the nozzle is stretched, The resin will precipitate before the solvent evaporates. For this reason, it is considered that the product has a partially rigid portion and rises when collected at the collection site. When carbon nanotubes are blended in the solution, this tendency becomes remarkable. Therefore, the relative humidity is preferably set to 35% or less. Under such conditions, the electrospinning method is performed, and the conductive nanofiber 1 of the present embodiment is manufactured.

  Normally, the fiber in which the conductive material is arranged in the fiber can ensure the conductivity in the longitudinal direction (stretching direction) of each fiber by the conductive material. The conductivity tends to deteriorate. This is because the outermost surface of the fiber is covered with a resin, and the contact portion between the fibers becomes a non-conductive resin. Similarly, since the nanofiber is a sheet deposited in a non-woven fabric at the collection site, the conductivity tends to be poor if it is normal. On the other hand, according to this embodiment, the electroconductive nanofiber 1 with favorable electroconductivity is obtained.

  As shown in FIG. 4, the carbon nanotube generally has a bent crimp shape instead of a linear shape. For this reason, as shown in FIG. 5A and FIG. 5B, the carbon nanotubes are distributed in the nanofibers, and the fiber diameter of the produced nanofibers 2 is controlled to be small (less than 500 nm). In addition, a structure is formed in which the fiber 21 is bent finely under the influence of the crimp shape of the carbon nanotube and one end of the carbon nanotube protrudes from the surface of the fiber 21 (for example, the surface of the corner of the fiber 21). Thereby, even if the fibers 21 overlap, as shown in FIG. 7, the projecting end portions (projections) 31 of the carbon nanotubes that are the conductive nanomaterials 3 come into contact with each other, and an energization portion Z is formed there. It is possible to develop good conductivity. Note that FIG. 5B is a photograph of the conductive nanofiber 1 stretched. In a state where the conductive nanofibers 1 are not stretched (for example, in a general use state), for example, as shown in another photograph, a plurality of fibers 21 are intricate.

  Thus, according to the electroconductive nanofiber 1 of this embodiment, since the electricity supply part Z is formed between the fibers 21 by the protrusion part 31, the electroconductivity improvement of the whole sheet | seat including a thickness direction is possible. Become. In other words, by forming the conductive nanofiber 1 in which the protruding portions 31 are formed on the surfaces of the plurality of fibers 21, the energization portion Z is formed in various places, and the conductivity of the conductive nanofiber 1 can be improved. it can.

  FIG. 4 is an SEM photograph of 100,000 times of the aggregate of carbon nanotubes, which are defective sites formed in a part of the conductive nanofiber 1. The diameter of the carbon nanotube of FIG. 4 is 30 nm or less (approximately 10 nm or more and 30 nm or less), and has a twisted crimp shape. 5A and 5B are 50,000 times SEM photographs of the conductive nanofiber 1 of FIG. 4, and the circles in the drawing indicate the positions of the protrusions 31. These SEM photographs are SEM photographs of Example 2 described later.

(Example)
Examples 1 to 3, which are examples of this embodiment, will be described. In Examples 1 to 3, Solef 21216 (manufactured by Solvay) is used as a polymer material that is a main raw material of nanofibers, and NC7000 (manufactured by Nanosil), which is a carbon nanotube, is used as a conductive nanomaterial 3, and as a dispersant. Ajisper PB821 (manufactured by Ajinomoto Fine Techno Co., Ltd.) was used, and a solvent in which DMF and acetone were mixed at a ratio of 1: 1 was used. In the comparative example, Toka Black # 4500 (manufactured by Tokai Carbon Co., Ltd.), which is carbon black, was used as the conductive nanomaterial 3 under the above conditions.

  A wet jet mill JN20 (manufactured by Joko) was used for the preparation of the raw material solution. As shown in FIG. 8, in Example 1, the concentration of the polymer material in the raw material solution is 5.4 wt%, the conductive material (carbon nanotube) concentration in the raw material solution is 0.39 wt%, The percentage was 7.2%. In Example 2, the polymer material concentration in the raw material solution is 5.4 wt%, the conductive material (carbon nanotube) concentration in the raw material solution is 0.73 wt%, and the ratio of the conductive material to the resin is 13.5%. there were. In Example 3, the polymer material concentration in the raw material solution is 7 wt%, the conductive material (carbon nanotube) concentration in the raw material solution is 0.14 wt%, and the ratio of the conductive material to the resin (conductive material concentration / polymer material) Concentration) was 2%.

  The “ratio of the conductive material to the resin” is a value obtained by dividing the conductive material concentration by the polymer material concentration (conductive material concentration / polymer material concentration). As shown in FIG. 6A (30,000 times SEM photograph of Example 1) and 6B (30,000 times SEM photograph of Example 2), the nanofibers of Examples 1 and 2 have protrusions 31. Was formed. A circle in the figure represents the protrusion 31.

  In the comparative example, the polymer material concentration in the raw material solution was 5.4 wt%, the conductive material (carbon black) concentration in the raw material solution was 3.24 wt%, and the ratio of the conductive material to the resin was 60%. When the conductive material is carbon black, if the ratio of the conductive material to the resin is larger than 60%, it becomes difficult to make nanofibers.

  Using the raw material solution, sheet-like nanofibers were prepared by electrospinning under the same conditions. As the electrospinning apparatus, an electrospinning apparatus NF-103 (manufactured by MEC) was used. The preparation conditions were an applied voltage of 35 kV, an ambient temperature of 36 ° C., and a relative humidity of 30%.

  As shown in FIG. 9, the surface resistivity of the nanofiber thus prepared is 9022Ω / □ (Ω □, Ω / sq, ohm per square) in Example 1, and 55.8Ω / in Example 2. □, Example 3 was 3682000Ω / □, and the comparative example was not measurable (a value larger than the measurement upper limit value). The penetration resistance (volume resistivity), which is the resistivity in the thickness direction of the sheet, is 1503 Ω · cm in Example 1, 6.1 Ω · cm in Example 2, and 490900 Ω · cm in Example 3. The comparative example was not measurable (infinite). In Examples 1 to 3, conductivity was expressed, but not in Comparative Example. The penetration resistance is more preferably 5 kΩ · cm or less (0 <penetration resistivity ≦ 5 kΩ · cm) from the viewpoint of industrial use of conductivity, and further 2 kΩ · cm or less as in Examples 1 and 2. It is preferable. In particular, Example 2 has a penetration resistance of 100 Ω · cm or less, which is extremely effective for industrial use.

  In the comparative example using particulate carbon black, conductivity was not expressed even at a high conductive material blending ratio (ratio of conductive material). On the other hand, in Examples 1-3, conductivity was exhibited at a low conductive material blending ratio. In Examples 1 to 3, since the conductive material blending ratio is low, sufficient strength can be maintained, and the strength is also advantageous. Further, in Examples 1 and 2, the surface resistivity is 10 kΩ / □ or less (0 <surface resistivity ≦ 10 kΩ / □), and excellent conductivity is exhibited. For example, it is suitable as a material for various batteries. In particular, in Example 2, the surface resistivity is 100Ω / □ or less, and extremely excellent conductivity is exhibited. As described above, Examples 1 and 2 have both high conductivity and high strength.

  The ratio of the conductive material to the resin is preferably 2% or more from the viewpoint of conductivity, and preferably 50% or less from the viewpoint of strength. Furthermore, the ratio is more preferably 5% or more including Examples 1 and 2 and 30% or less (more preferably 20% or less). Further, the ratio may be 7% or more. The said ratio can be set by the relationship of desired intensity | strength and resistivity, making the ratio which can be nanofiber-ized into an upper limit. The upper limit of the ratio can be set based on the required strength (depending on the application). For example, when higher strength is required, such as when used in a battery having a severe usage environment (for example, a fuel cell), according to this embodiment, the ratio can be set to 15% or less, and this ratio (2 to 15%) ) Can exhibit electrical conductivity. According to this embodiment, in expressing conductivity, the ratio of the conductive nanomaterial to the polymer can be set to 2% or more and 20% or less as in Examples 1 to 3, for example. Both strength maintenance is possible.

The number of the protrusions 31 is preferably one or more per 10,000 μm ³ of the conductive nanofiber 1. Furthermore, it is preferable that the number of the protrusions 31 is, for example, 5 or more per 10,000 μm ^{3 of the} conductive nanofiber 1.

  In addition, the KTEC method (JEF techno research method) was used for the measuring method of surface resistivity. Specifically, as shown in FIG. 10, two electrodes (copper plate of 15 mm × 5 mm × thickness 1 mm) are arranged on the surface of the measurement target sheet, the distance between the electrodes is 15 mm, and the electrical resistance between the electrodes is measured by a tester ( Measured with Yokogawa Meter & Instruments TY720 Digital Multimeter). Then, the surface resistivity ρ is calculated based on the equation of resistance R = surface resistivity ρ × distance L ÷ electrode width D (average value of 5-point measurement).

  The penetration resistivity was measured using current collectors Y1 and Y2 as shown in FIG. 13 in order to separate the measured resistance value and the contact resistance. The current collectors Y1 and Y2 are formed in a plate shape by covering the plate electrode with a resin member, and the plate electrode can be energized through the exposed terminal. The surface of the current collector Y1 is planar, and irregularities are formed on the surface of the current collector Y2. First, as a first measurement, the conductive nanofiber 1 is sandwiched between two current collectors Y1 in the thickness direction, a predetermined surface pressure is applied in the thickness direction, and a voltage is applied to the terminal of one current collector Y1. As a result, a first measurement value of the penetration resistivity was obtained. As a second measurement, the conductive nanofiber 1 is sandwiched between the current collector Y1 and the current collector Y2 in the thickness direction, a predetermined surface pressure is applied in the thickness direction, and one current collector Y2 (or A voltage was applied to the terminals of the current collector Y1) to obtain a second measured value of the penetration resistance. In the second measurement, due to the unevenness of the current collector Y2, the contact area between the current collector Y2 and the conductive nanofiber 1 is halved compared to the first measurement.

The breakdown of the first measurement value (resistance) is R ₁ = r / S + r / S + Rs, and the breakdown of the second measurement value (resistance) is R ₂ = r / S + 2r / S + Rs. Each of R ₁ and R ₂ is a measured value, r is a contact resistance, S is a contact area, and Rs is a sample resistance (that is, a penetration resistivity of the conductive nanofiber 1). The contact resistance r can be calculated from the difference between the above two formulas, thereby obtaining the sample resistance Rs.

  In this specification, “having conductivity” or “expressing conductivity” means that the surface resistivity and penetration resistivity can be measured numerically by the above method (that is, each resistance is infinite). Is equivalent to In this example, each resistance was measurable (the measurement result of each resistance was a numerical value), the surface resistivity was 4000 kΩ / □ or less, and the penetration resistivity was 500 kΩ · cm or less.

(Fuel cell)
The conductive nanofiber 1 of the present embodiment can be used as a member of a fuel cell (solid polymer fuel cell). As an example, the fuel cell 9 includes an anode portion 91, a cathode portion 92, an electrolyte membrane 93 disposed between the anode portion 91 and the cathode portion 92, and separators X1 and X2, as shown in FIG. I have. The anode portion 91 is configured by forming a gas diffusion layer 911, a water repellent layer 912, and a catalyst layer 913 from one surface to the other surface on the electrolyte membrane 93 side. The cathode portion 92 is configured by forming a gas diffusion layer 921, a water repellent layer 922, and a catalyst layer 923 from the other surface toward one surface on the electrolyte membrane 93 side. The anode part (fuel electrode) 91, the cathode part (air electrode) 92, and the electrolyte membrane 93 constitute an electrode assembly (MEA).

  The gas diffusion layers (GDL) 911 and 921 are layers for uniformly distributing the gas to the catalyst layers 913 and 923. The gas diffusion layer 911 is also a layer for sending electrons received from the water repellent layer 912 to the separator X1. That is, the gas diffusion layer 911 is a layer for supplying hydrogen to the catalyst layer 913 and transferring electrons, and is disposed on the gas phase side of the anode portion 91. The gas diffusion layer 921 is a layer for supplying an oxidant gas to the catalyst layer 923 and transferring electrons, and is disposed on the gas phase side of the cathode portion 92. The gas diffusion layers 911 and 921 only need to be porous and conductive. For example, the gas diffusion layers 911 and 921 are formed by solidifying carbon particles having a pore diameter of several μm. In the fuel cell 9, for example, a configuration in which the reaction gas is humidified and a configuration in which water generated by a chemical reaction is used is employed. The gas diffusion layers 911 and 921 constitute a water or water vapor passage and, together with the water repellent layers 912 and 922, play a role of appropriately sucking and discharging moisture necessary for the reaction system. The separators (bipolar plates) X1 and X2 are conductive members that form gas flow paths, and are conductive members having a plurality of grooves formed on the surface, for example.

  The water repellent layer 912 of the anode portion 91 is a layer for sending water to the gas diffusion layer 911 without condensing water, and is a layer for transferring electrons. The water repellent layer 912 of the cathode portion 92 is a layer for suppressing the formation of a liquid film on the surface of the gas diffusion layer 921 on the catalyst layer 923 side, and is a layer for transferring electrons. The water repellent layer 912 is provided from the viewpoint of moisture retention (preventing dryout), and the water repellent layer 922 is provided from the viewpoint of improving drainage (preventing flooding). The water repellent layers 912 and 922 are disposed between the catalyst layers 913 and 923 and the gas diffusion layers 911 and 921 so as to cover the gas phase side surfaces of the catalyst layers 913 and 923. It can be said that the water-repellent layers 912 and 922 are microporous layers (MPL). The conventional water-repellent layer is formed by, for example, solidifying carbon particles having a pore diameter of several nm. The conventional water repellent layer is a thin film mainly composed of a water repellent resin and carbon black, for example.

  For example, the water repellent layer 922 of the cathode portion 92 has oxygen permeability that can supply oxygen contained in the oxidant gas to the catalyst layer 923 and discharge of water from the catalyst layer 923 to the gas diffusion layer 921. It is required to have water repellency (for example, drainage) that can be adjusted to an appropriate amount. Similarly, the water repellent layer 912 of the anode portion 91 is required to have hydrogen permeability and appropriate water repellency (for example, moisture retention). The cathode portion 92 is a portion where a relatively large amount of water is generated by operation (reaction) in terms of configuration, and thus the role (performance) of the water repellent layer 922 becomes more important.

  The catalyst layers 913 and 923 are layers that serve as reaction fields for the battery reaction, and are provided at portions of the anode portion 91 and the cathode portion 92 that are in contact with the electrolyte membrane 93. The catalyst layer 913 is a layer for decomposing hydrogen into protons and electrons. The catalyst layer 923 is a layer for generating water from protons, electrons, and oxygen. Although not shown, the catalyst layers 913 and 923 include, for example, a carrier, a catalyst supported on the carrier, and an in-layer electrolyte. The catalyst layers 913 and 923 are formed by, for example, covering carbon particles having a pore diameter of several μm with platinum particles having a diameter of several nm, covering the polymer particles with a polymer, and solidifying them. Further, for example, the catalyst layers 913 and 923 are formed by supporting platinum particles having several nm on carbon particles having a particle diameter of several μm. The electrolyte membrane 93 is a polymer electrolyte membrane (PEM), which can be made of various materials, and may be, for example, a fluorinated polymer or a hydrocarbon polymer. The electrolyte membrane 93 can be said to be a member for moving protons from the anode portion 91 side to the cathode portion 92 side and blocking the passage of electrons and gases. In addition, a well-known thing can be referred for the structure and function of each part in the conventional fuel cell before applying the electroconductive nanofiber 1. FIG.

  Here, the conductive nanofiber 1 is preferably used as the water-repellent layer 922. That is, in the fuel cell 9 of the present embodiment, at least the water repellent layer 922 of the cathode portion 92 is the conductive nanofiber 1. The conductive nanofiber 1 has good conductivity (for example, a penetration resistance of 10 kΩ · cm or less), has a low compounding ratio, and the conductive nanomaterial 3 is disposed in the fiber 21, thereby improving the strength. It is excellent in terms of improvement in durability and suppression of influence during flooding.

  For example, a fuel cell in which the conductive nanofibers 1 are disposed as the water repellent layer 922 has an output (voltage) that is increased in a high current region, compared with a fuel cell in which a conventional water repellent layer is disposed. The output is easy to stabilize. In the conventional water-repellent layer, characteristics (wetting properties) change under the influence of water immersion or oxidation, but this embodiment can suppress this. Since most of the exposed conductive nanofibers 1 are fibers 21, the conductive nanofiber 1 can withstand the internal atmosphere (strong acid atmosphere) of the fuel cell 9. Thus, it is very effective to use the conductive nanofiber 1 as a layer of the fuel cell 9.

For example, as shown in FIG. 12, when a conventional fuel cell is compared with a fuel cell using the conductive nanofibers 1 of the present embodiment for the water-repellent layer on the cathode side, the region where the electron flow (current) is increased. (About 1.7 A / cm ² or more), in the conventional fuel cell, the cathode side layer is covered with a water film, which makes power generation difficult. The decrease is suppressed. A conventional fuel cell is a conventional fuel cell as a gas diffusion layer and a water repellent layer. In this test, a fuel cell using a carbon fiber nonwoven fabric coated with a conventional conductive nanofiber is used. In the power generation test that obtained the results of FIG. 12, the humidity on the anode side was 88% RH, and the humidity on the cathode side was 130% RH. In general, when the fuel cell generates power, water is generated on the cathode side and the humidity increases. When the power generation load is high, the cathode side tends to be overhumidified. This power generation test is a test in a state where the cathode humidity is increased and a load is applied to the fuel cell. In addition, in order to evaluate the gas diffusibility, drainage property, wettability, etc. of the conductive nanofiber 1, the test was performed by placing the conductive nanofiber 1 on the cathode side. On the cathode side, the arrangement of the conductive nanofibers 1 is particularly effective because of its function.

(Other)
As described above, in the present embodiment, carbonization firing is not necessary in the production, which is advantageous in terms of cost and yield. In this embodiment, since the conductive nanomaterial 3 is not a gold or platinum but a carbon-based conductive nanomaterial, it is advantageous in terms of cost. Further, in the method of applying metal plating, plating that can withstand the strong acid atmosphere of the battery must be generated, and complicated processes (treatments) are required. In addition, wrinkles easily occur and yield is poor. Then they don't happen.

  The present invention is not limited to the above embodiment. For example, both the water repellent layer 912 of the anode portion 91 and the water repellent layer 922 of the cathode portion 92 may be composed of the conductive nanofiber 1. Depending on the operating conditions, the water repellent layer 911 of the anode portion 91 is required to have severe strength and characteristic change resistance, so this configuration is also effective. Moreover, the anode part 91 may have a two-layer structure of a gas diffusion layer and a catalyst layer without providing a water repellent layer. Further, the water repellent layer of the anode portion 91 may have a conventional configuration. Further, the water repellent layer of the anode portion 91 may be the conductive nanofiber 1, and the water repellent layer of the cathode portion 92 may have a conventional configuration. However, in view of the configuration of the fuel cell, it is preferable that at least the water repellent layer 922 of the cathode portion 92 is composed of the conductive nanofiber 1.

  The water-repellent layers 912 and 922 may be provided for the purpose of holding a large amount of moisture in the electrolyte membrane 93 or for discharging excess moisture in the cell depending on the operating conditions. . Regardless of the purpose, the water-repellent layers 912 and 922 are required to have conductivity and strength that can withstand practical use and a configuration in which changes in characteristics with respect to wetting are suppressed, and the present invention is effective. The water repellent layers 912 and 922 are preferably designed according to the operating conditions of the fuel cell, such as a humidifying operation. In addition, the nanofiber may be generated by a method other than the electrospinning method. Each fiber 21 and each carbon nanotube can also be said to be a hair.

  In addition, the conductive nanofiber 1 may be used as the gas diffusion layers 911 and 921. Even in this case, the conductive nanofiber 1 is effective because it has a conductivity, strength, and characteristic change suppression configuration. That is, the conductive nanofiber 1 of the present invention includes at least the water repellent layer 912 of the anode portion 91, the water repellent layer 921 of the cathode portion 92, the gas diffusion layer 911 of the anode portion 91, and the gas diffusion layer 921 of the cathode portion 92. One can be configured. Thus, the conductive nanofiber 1 can constitute at least one of a part of the anode part 91 and a part of the cathode part 92. The part of the anode part 91 and the part of the cathode part 92 can be said to be at least one of a plurality of layers constituting each part 91, 92. Specifically, a part of the anode portion 91 is a portion excluding the catalyst layer 913, for example, a portion constituted by the gas diffusion layer 911 and the water repellent layer 912 or a portion constituted only by the gas diffusion layer 911. means. Similarly, a part of the cathode portion 92 is a portion excluding the catalyst layer 923, for example, a portion constituted by the gas diffusion layer 921 and the water repellent layer 922 or a portion constituted only by the gas diffusion layer 921. To do. It is effective that the conductive nanofiber 1 is used as the water-repellent layers 912 and 922 (further, the water-repellent layer 922) because of its properties.

1: Conductive nanofiber (conductive member for fuel cell),
2: nanofiber, 21: fiber,
3: conductive nanomaterial, 30: main body, 31: protrusion (one end),
9: Fuel cell 91: Anode part 92: Cathode part
911, 912: gas diffusion layer, 912, 922: water repellent layer,
913, 923: catalyst layer, 93: electrolyte membrane, Z: current-carrying part

Claims (13)

A fuel cell comprising an anode part, a cathode part, and an electrolyte membrane disposed between the anode part and the cathode part,
At least one of the part of the anode part and the part of the cathode part is composed of conductive nanofibers having conductivity,
The conductive nanofiber is:
A sheet-like nanofiber composed of a plurality of polymer fibers; and
A plurality of linear conductive nanomaterials having a cross-sectional area smaller than that of the fiber and disposed in the fiber;
With
A fuel cell in which a projecting portion in which one end portion of the conductive nanomaterial projects from the surface is formed on the surface of the fiber. A fuel cell comprising an anode part, a cathode part, and an electrolyte membrane disposed between the anode part and the cathode part,
At least one of the part of the anode part and the part of the cathode part is composed of conductive nanofibers having conductivity,
The conductive nanofiber is:
A sheet-like nanofiber composed of a plurality of polymer fibers; and
A plurality of linear conductive nanomaterials having a cross-sectional area smaller than that of the fiber and disposed in the fiber;
With
One end of the conductive nanomaterial protrudes from the surface of the fiber to form a protrusion,
Between the first fiber and the second fiber adjacent to the first fiber, the first protrusion formed on the first fiber and the second fiber are formed. And the fuel cell in which the electricity supply part comprised by the said 2nd protrusion part which contacted the said 1st protrusion part was formed.   At least one of the anode part and the cathode part is a water repellent layer composed of the conductive nanofibers, a gas diffusion layer disposed on one side of the water repellent layer, and the other side of the water repellent layer. The fuel cell according to claim 1, further comprising: a catalyst layer disposed on the electrolyte membrane side.   The fuel cell according to claim 1, wherein the conductive nanomaterial is a carbon nanotube.   The fuel cell according to any one of claims 1 to 4, having a surface resistivity of 10 kΩ / □ or less.   The fuel cell according to claim 5, wherein the surface resistivity is 100Ω / □ or less.   The fuel cell according to any one of claims 1 to 6, wherein a penetration resistivity which is a resistivity in a thickness direction is 5 kΩ · cm or less.   The fuel cell according to claim 7, wherein the penetration resistivity is 2 kΩ · cm or less.   The fuel cell according to claim 7, wherein the penetration resistivity is 100 Ω · cm or less.   The fuel cell according to any one of claims 1 to 9, wherein a ratio of the conductive nanomaterial to the polymer is 2% or more and 20% or less.   The fuel cell according to any one of claims 1 to 10, wherein a plurality of the protrusions are formed on each of the fibers.   The fuel cell according to any one of claims 1 to 11, wherein the cathode portion includes the water-repellent layer. A conductive fuel used as a constituent member of at least one of the anode part and the cathode part in a fuel cell comprising an anode part, a cathode part, and an electrolyte membrane disposed between the anode part and the cathode part A conductive member for a battery,
A sheet-like nanofiber composed of a plurality of polymer fibers; and
A plurality of linear conductive nanomaterials having a cross-sectional area smaller than that of the fiber and disposed in the fiber;
With
A conductive member for a fuel cell, wherein one end of the conductive nanomaterial protrudes from the surface on the surface of the fiber.