JP5332554B2 - Gas diffusion layer for fuel cell, method for producing the same, and fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion layer for a fuel cell and its manufacturing method, which provide both high conductivity and a low cost. <P>SOLUTION: The gas diffusion layer for the fuel cell includes a porous material layer, and a conductive carbon layer existing on the surface of or inside the porous material layer or a conductive carbon particles. An intensity ratio R (I<SB>D</SB>/I<SB>G</SB>) between D-band peak intensity I<SB>D</SB>and G-band peak intensity I<SB>G</SB>measured with Raman scattering spectral analysis is 1.3 or more in the conductive carbon layer or the conductive carbon particles. In addition, an average peak measured by rotary anisotropy measurement on the basis of the Raman scattering spectral analysis of the conductive carbon layer shows a twice symmetry pattern. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a gas diffusion layer for a fuel cell, a method for producing the same, and a fuel cell using the same.

The gas diffusion layer (GDL) conventionally used uses a sheet-like base material using carbon fiber (CF) having high conductivity that has been subjected to graphitization. Patent Document 1 discloses carbon paper or carbon cloth having electrical conductivity and air permeability as GDL. More specifically, it is disclosed that carbon fiber processed into a woven fabric, non-woven fabric, paper, or cloth is used as a material having both gas permeability and conductivity. A technique is disclosed in which a carbon layer is provided on the surface of such GDL, and a metal catalyst is disposed thereon by sputtering.
JP 2008-153200 A

  However, in such a case, since the high temperature treatment at 2000 ° C. or higher is performed, there is a problem that the cost of the gas diffusion layer (GDL) itself increases significantly. If the graphitization is reduced and the process is completed in the previous stage (carbonization), the cost can be reduced, but there is also a problem that it is difficult to ensure conductivity. On the other hand, the GDL made of metal fibers also has a problem that the conductivity is insufficient due to the oxide film formed on the metal surface.

  Therefore, an object of the present invention is to provide a fuel cell gas diffusion layer that achieves both high conductivity and low cost. Another object of the present invention is to provide a method for producing the gas diffusion layer for a fuel cell.

In order to achieve the above object, a gas diffusion layer for a fuel cell according to the present invention comprises a porous material layer and a conductive carbon layer or conductive carbon particles present on or in the surface of the porous material layer. Including. Then, in the conductive carbon layer or a conductive carbon particles, the intensity ratio of the measured from the Raman scattering spectroscopy D- band peak intensity I _D and G- band peak intensity _{I G R (I D / I} G) is 1 .3 or more. In addition, the average peak measured by rotational anisotropy measurement by Raman scattering spectroscopy of the conductive carbon layer shows a two-fold symmetrical pattern.

  According to the present invention, it is possible to cover insufficient conductivity by surface treatment while realizing cost reduction by suppressing the treatment until carbonization. In addition, even in a gas diffusion layer (GDL) made of metal fibers, the lack of conductivity due to the oxide film formed on the metal surface can be secured by the surface treatment.

[First Embodiment]
The gas diffusion layer for fuel cells (GDL for fuel cells) according to the first embodiment of the present invention includes a porous material layer and a conductive carbon layer or conductive carbon existing on or in the surface of the porous material layer. It is a gas diffusion layer for fuel cells containing particles. Then, in the conductive carbon layer or a conductive carbon particles, the intensity ratio of the measured from the Raman scattering spectroscopy D- band peak intensity I _D and G- band peak intensity _{I G R (I D / I} G) is 1 .3 or more. In addition, the average peak measured by rotational anisotropy measurement by Raman scattering spectroscopy of the conductive carbon layer shows a two-fold symmetrical pattern.

  As will be described later, the porous material layer may include one or more selected from the group consisting of carbon fibers, metal fibers, and organic fibers. Carbon fibers that are not graphitized with carbon fiber but have been carbonized are considered as those having insufficient conductivity. Such carbon fibers are mainly used for strength reinforcing members of buildings and the like, and are significantly cheaper than graphitized carbon fibers, but have a technical problem of poor conductivity. On the other hand, in the case of a metal fiber, for example, if the fiber is made of a noble metal, the conductivity is sufficiently high, but it is very expensive and not practical. On the other hand, in the metal fiber itself comprised with an inexpensive metal, the electroconductivity lack by surface oxide film formation may arise. In other words, the lack of conductivity due to the oxide film is a technical problem when using metal fibers.

  In view of such technical problems, the technical principle of the present invention is as follows. That is, even if the porous material layer is formed of inexpensive fibers that are not sufficiently conductive, it can be applied to a fuel cell by coating (surface treatment) the conductive carbon layer or conductive carbon particles on the fibers. To get a good GDL. That is, the GDL for a fuel cell according to the present invention is a GDL that realizes both high conductivity and low cost.

  In the present specification, the conductive carbon constituting the fiber in the case where the porous material layer includes carbon fiber is referred to as “conductive carbon constituting the porous material layer”. On the other hand, the conductive carbon (conductive carbon layer or conductive carbon particles) coated on the porous material layer is also simply referred to as “conductive carbon” to distinguish both conductive carbons.

  According to the present embodiment, the contact resistance between the fuel cell GDL formed by disposing the conductive carbon layer or the conductive carbon particles on the porous material layer and the adjacent member is significantly reduced. Further, the arrangement of the conductive carbon layer or the conductive carbon particles makes it possible to control the pore diameter of the porous material constituting the porous material layer, which is effective in improving gas-liquid discharge in the fuel cell. The conductive carbon layer is present on the surface of the porous material layer or in (inside) the porous material layer (fiber). On the other hand, in most cases, the conductive carbon particles are present in (inside) the porous material layer (fiber).

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments to which the invention is applied will be described with reference to the accompanying drawings. In addition, this invention is not restrict | limited only to the following embodiment. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention.

  An anode catalyst layer 3a and a cathode catalyst layer 3c are disposed in close contact with both surfaces of the solid polymer electrolyte membrane 2 that selectively transports hydrogen ions. The catalyst layers (3a, 3c) are generally composed mainly of carbon powder carrying a platinum-based metal catalyst. Furthermore, the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c, which have both gas permeability and conductivity, are disposed in close contact with the outer surfaces of the catalyst layers (3a, 3c), respectively. The gas diffusion layer constitutes a gas diffusion electrode. A membrane electrode assembly (MEA) 10 is constituted by the gas diffusion layers (4a, 4c) and the solid polymer electrolyte membrane 2.

  The gas diffusion layers (4a, 4c) promote the diffusion of the gas (fuel gas or oxidant gas) supplied through the gas flow paths (6a, 6c) of the separator to the catalyst layers (3a, 3c). And function as an electron conduction path.

  A membrane electrode assembly (MEA) 10 is mechanically joined to the outside of the gas diffusion electrode, and adjacent MEAs are electrically connected to each other so as to be electrically in series with each other, a conductive anode separator 5a and a cathode separator 5c. Is arranged. On one surface of the anode separator 5a and the cathode separator 5c, a reaction gas is supplied to the gas diffusion electrode, and an anode gas flow path 6a and a cathode gas flow for carrying away water and excess gas generated by the reaction. A path 6c is formed. The unit cells thus produced are stacked in one direction to constitute a laminate.

  Here, by using the GDL for fuel cell according to the present embodiment as the gas diffusion layers (4a, 4c), both high conductivity and low cost can be realized. As a result, a high performance and inexpensive polymer electrolyte fuel cell (PEFC) 1 can be obtained.

  FIG. 2 is a cross-sectional view showing a schematic configuration of the gas diffusion layers (4a, 4c) in FIG. In the present embodiment, the gas diffusion layer 51 essentially includes a porous material layer 52 and a conductive carbon layer 54 as conductive members. An intermediate layer 56 is interposed between these layers, although it is not essential. Here, the sectional view of the gas diffusion layer in FIG. 2 shows a structure in which an intermediate layer and a conductive carbon layer are laminated on the porous material layer. However, the cross-sectional view of the present embodiment is not limited to this, and in addition, a structure in which an intermediate layer and a conductive carbon layer are “laminated” in (inside) a porous material layer composed of fibers is also possible. It is possible. Here, “lamination” in this specification is not limited to a layer stacked on (or under) a certain layer, but refers to a layer configured in (inside) a certain layer. There is also. In the present embodiment, not only one “laminated” form but also one gas diffusion layer having both “laminated” forms may be used.

  FIG. 2 also shows a hydrophilic layer 58, which will be described later. In PEFC1, the separators (5a, 5c) are arranged so that the conductive carbon layer 54 is located on the MEA 10 side. Hereinafter, each component of the fuel cell GDL will be described in detail.

<Porous material layer>
The porous material layer 52 is basically composed of a sheet-like porous material. In some cases, the porous material layer includes a conductive carbon layer and / or conductive carbon particles as described later, and / or an intermediate layer composed of a metal and / or the metal.

  The porous material layer 52 preferably contains one or more selected from the group consisting of carbon fibers, metal fibers, and organic fibers. In such a case, the electrical resistance at the interface between the fibers can be reduced when the fibers are fused in the firing step in the production of the porous material layer. In other words, in such a case, there is an advantage that the conductivity is significantly increased by the fusion of the fibers.

  FIG. 3 is a schematic view microscopically showing the surface of the porous material layer. In the formation (lamination) of the conductive carbon layer by sputtering, the target (conductive carbon) is linearly directed to the porous material layer by sputtering. Therefore, the conductive carbon layer or the conductive carbon particles can be laminated (deposited) only on the fiber surface exposed to the sputtering direction. Therefore, by changing the angle of the fiber substrate itself, in other words, by appropriately adjusting the pore diameter, the conductive carbon layer or the conductive carbon particles can be disposed on a wider surface among the surfaces.

  Further, as shown in FIG. 3, the porous material layer 52 composed of carbon fibers or the like is in a state where a large number of fibers (carbon fibers (CF) 53) are overlapped. When the conductive carbon layer 54 is deposited (laminated) on the porous material layer 52 by sputtering, a target (conductive carbon) is placed on the main surface of the porous material layer 52 as shown in FIG. It will be sputtered. That is, the conductive carbon layer can be formed not only on the outermost surface of the porous material layer but also in the vicinity thereof (portion exposed on the surface of the porous material layer). In other words, the conductive carbon layer is not only in the form laminated on the surface of the porous material layer as shown in FIG. 2, but also in the form existing only in the porous material layer, and in the porous material layer. Forms that exist both on the surface and in the porous material layer may also be employed.

  Further, by appropriately adjusting the fiber diameter (thickness) as the positional relationship between the fibers constituting the porous material layer, both improvement in conductivity and prevention of pressure loss can be realized. Specifically, the larger the fiber diameter (the thicker one of the fibers), the larger the voids in the fiber, but the number of contacts per fiber decreases. Therefore, the electrical conductivity is further reduced, but the pressure loss can be further prevented. On the other hand, the smaller the fiber diameter (the thinner one of the fibers), the smaller the voids in the fiber, but the number of contacts per fiber increases. Therefore, the conductivity is further increased, but the influence of the pressure loss can be further increased. Therefore, it is preferable to adjust the fiber diameter to an appropriate range.

  The “carbon fiber” in the present specification means a fiber obtained by firing a raw material fiber in an inert atmosphere at a temperature of 1000 ° C. or higher. Examples of such carbon fibers include, but are not limited to, polyacrylonitrile (PAN) based carbon fibers, pitch based carbon fibers, phenol based carbon fibers, and vapor grown carbon fibers. The PAN-based carbon fiber is a fiber made of synthetic fiber whose main component is PAN. On the other hand, the pitch-based carbon fiber is a fiber made from petroleum, coal, synthetic pitch or the like.

  The preferred range of the average fiber diameter of the carbon fibers varies depending on the specifications of the PAN and pitch as a raw material and the manufacturing method. Among the commercially available products, the average fiber diameter may be 5 to 10 μm for PAN, 5 to 20 μm for pitch, and several μm for vapor phase growth. On the other hand, the average fiber length of carbon fibers that can be used in the GDL for fuel cells according to the present invention is not particularly limited, but paper made from generally used chopped fibers of 10 mm or less (more preferably 3 to 6 mm) is used. Can do.

  Since the carbon fiber has a low electric resistivity, when it is contained in the porous material layer, the electric charge generated in the catalyst layer can be collected more efficiently. Carbon fiber has been industrially used as a reinforcing material for various composite materials in a wide range of fields such as aerospace due to its excellent specific strength and specific elastic modulus. Of these, PAN-based carbon fibers or pitch-based carbon fibers are preferred because they are carbon fibers widely used in industry.

  Furthermore, from the viewpoint of versatility, cost performance, and high conductivity, the porous material layer is carbonized that does not include PAN-based or pitch-based carbon fibers and graphitized (decarbonized) fibers. A fiber is particularly preferred. Here, “not containing graphitized (decarbonized) fibers” means that elements other than carbon (N, O, etc.) are not included in the middle of the carbon atom chain forming the fibers. . Hereinafter, the reason why such a fiber is particularly preferable will be described.

  While PAN-based carbon fibers are mainly excellent in strength and elongation, they have a problem of low elastic modulus because they are non-graphitizable. In order to improve the elastic modulus, generally, firing at a high temperature of about 2200 to 3000 ° C. is indispensable, but there is a problem that the strength is reduced at the same time. In addition, it is extremely difficult to avoid high costs such as shortening the life of the furnace by high-temperature firing, which can be disadvantageous on an industrial scale.

  On the other hand, pitch-based carbon fibers can be broadly classified into those derived from isotropic pitches and those derived from anisotropic pitches, but anisotropic pitches are generally used in order to develop high performance. The carbon fiber derived from anisotropic pitch is excellent in elasticity and strength due to the graphitizable nature of the raw material (anisotropic pitch), but has a problem of low elongation. Therefore, industrially, there is a possibility that the productivity of carbon fiber and the handling property at the time of compounding are inferior.

  In view of the problems existing in these PAN-based carbon fibers and pitch-based carbon fibers, various studies have been made on combining the PAN-based carbon fibers and the pitch-based carbon fibers in order to compensate for the disadvantages of both the PAN-based carbon fibers and the pitch-based carbon fibers. However, there are many problems such as an increase in cost and a decrease in quality due to the complexity of the process, and the reality is that it is difficult to use industrially.

  On the other hand, in the present embodiment, the porous material layer is composed of carbonized fibers that do not include graphitized (decarbonized) fibers that are PAN-based or pitch-based carbon fibers. Such a problem does not occur. And, in the porous material layer composed of PAN-based or pitch-based carbon fiber not containing graphitized fiber, the decrease in conductivity as a compensation for reducing the cost is covered by the presence of the conductive carbon layer described later. Can do. In this way, the fuel cell gas diffusion layer according to the present embodiment can achieve both high conductivity and low cost. The “graphitized fiber” in the present specification means a fiber obtained by firing at a temperature of 2000 ° C. or higher in an inert gas atmosphere for the purpose of improving the elastic modulus of the carbon fiber.

  FIG. 4 is a schematic view showing changes in fibers in each step of manufacturing PAN-based carbon fibers. Conventionally, in order to impart high conductivity to the PAN-based carbon fiber, it is finally crystallized by performing a graphitization treatment. In the production of such a PAN-based carbon fiber, the graphitization treatment that has been conventionally performed realizes a significant improvement in the conductivity of the porous material layer, while the cost of the porous material itself greatly increases. . That is, most of the cost is spent on the graphitization treatment in the production of the PAN-based carbon fiber. On the other hand, when the gas diffusion layer according to the present embodiment includes PAN-based carbon fibers, no graphitization treatment is performed in the manufacture of the PAN-based carbon fibers. Therefore, as shown in FIG. 4, the changed fibers can be referred to as carbonized fibers rather than graphitized fibers. However, since the carbonized fiber has a nitrogen atom in the middle of the “carbon-carbon” bond, the conductivity of the PAN-based carbon fiber is much lower than that of the graphitized fiber.

  Therefore, according to the present embodiment, by including the conductive carbon layer or the conductive carbon particles present on or in the surface of the porous material layer, the result is high even without performing graphitization treatment. Conductivity can be obtained. Thereby, both high conductivity and a significant cost reduction can be realized. Furthermore, the porosity in the porous material layer may be excessively increased by the graphitization treatment that has been conventionally performed. On the other hand, according to the present embodiment, the configuration including the conductive carbon layer or the conductive carbon particles present on or in the surface of the porous material layer enables the graphitization treatment to be omitted, which is unnecessary. High porosity can be prevented.

  The organic fiber means a conductive resin fiber. The conductive resin fiber is a fiber that contains many carbon atoms and is easily carbonized by firing to form a carbon fiber, and as a result, exhibits conductivity. Examples of the organic fiber include, but are not limited to, phenolic resin fiber, polyacrylonitrile fiber, polyethylene terephthalate fiber, and polybutylene terephthalate fiber. Especially, it is preferable that a porous material layer contains a phenol-type resin fiber from a viewpoint that electrical conductivity can be ensured more reliably.

  The range of the fiber diameter of the organic fiber is not limited to the following, but is preferably 50 to 5 μm, more preferably 30 to 10 μm. On the other hand, the fiber length of the organic fiber that can be used in the fuel cell GDL according to the present invention is not particularly limited because it is not chopped in the state of the organic fiber.

  The metal fiber is not limited to the following, and examples thereof include iron, titanium, aluminum, copper and alloys thereof; stainless steel; and fibers of noble metals such as gold and silver. Among these, from the viewpoint of mechanical strength, versatility, cost, ease of processing, and high conductivity, the porous material layer 52 preferably includes stainless steel, aluminum, or aluminum alloy fibers. In particular, the porous material layer 52 contains stainless steel fibers in order to have not only mechanical strength, versatility, cost, ease of processing and high conductivity, but also sufficient resistance to an acidic atmosphere in the fuel cell. Is more preferable. In addition, when a porous material layer contains a stainless fiber, the electroconductivity of a contact surface with the porous material layer which comprises a separator can fully be ensured. As a result, the durability of the separator can be maintained by the corrosion resistance of the oxide film formed on the porous material layer itself made of stainless steel even if moisture enters the gaps in the rib shoulder film. Has an effect.

  Although it does not limit to the following as a range of the fiber diameter of a metal fiber, Preferably it is 100-1 micrometer, More preferably, it is 50-5 micrometers, More preferably, it is 20-5 micrometers. On the other hand, the fiber length of the metal fiber that can be used in the GDL for fuel cell according to the present invention is not particularly limited, but it is possible to make a paper of chopped fiber of 10 mm or less (more preferably 10 to 5 mm) that is generally used. it can.

  Examples of stainless steel include austenite, martensite, ferrite, austenite / ferrite, and precipitation hardening. Examples of austenite include SUS201, SUS202, SUS301, SUS302, SUS303, SUS304, SUS305, SUS316 (L), and SUS317. Examples of the austenite-ferrite type include SUS329J1. Examples of the martensite system include SUS403 and SUS420. Examples of the ferrite type include SUS405, SUS430, and SUS430LX. Examples of the precipitation hardening system include SUS630. Among these, it is more preferable to use austenitic stainless steel such as SUS304 and SUS316. Moreover, the content rate of iron (Fe) in stainless steel becomes like this. Preferably it is 60-84 mass%, More preferably, it is 65-72 mass%. Furthermore, the content of chromium (Cr) in the stainless steel is preferably 16 to 20% by mass, and more preferably 16 to 18% by mass.

  Examples of the aluminum alloy include pure aluminum, aluminum / manganese, and aluminum / magnesium. The elements other than aluminum in the aluminum alloy are not particularly limited as long as they are generally usable as an aluminum alloy. For example, copper, manganese, silicon, magnesium, zinc and nickel can be included in the aluminum alloy. Specific examples of the aluminum alloy include A1050 and A1050P as the pure aluminum system, A3003P and A3004P as the aluminum / manganese system, and A5052P and A5083P as the aluminum / magnesium system. On the other hand, since the separator is also required to have mechanical strength and formability, the tempering of the alloy can be appropriately selected in addition to the above alloy types. When the porous material layer 52 is composed of a simple substance of titanium or aluminum, the purity of the titanium or aluminum is preferably 95% by mass or more, more preferably 97% by mass or more, and further preferably 99%. It is at least mass%.

  Here, the porous material layer may include two or more selected from the group consisting of carbon fibers, metal fibers, and organic fibers. The case where the fiber which comprises the said porous material layer consists of a carbon fiber and a metal fiber is demonstrated to an example. The relationship between these carbon fibers and metal fibers may be such that any one of the fibers is a carbon fiber and the other one is a metal fiber. The form in which a metal fiber exists in the periphery may be sufficient.

  In addition, the porous material layer may include fibers and other components that do not have conductivity. However, from the viewpoint that the gas diffusion layer according to this embodiment has sufficient conductivity, when the constituent component of the porous material layer is 100% by mass, the content of the component having no conductivity is 50. It is preferable that it is below mass%. Moreover, it is more preferable that it is 10 mass% or less, and it is especially preferable that a porous material layer does not contain the component which does not have electroconductivity substantially.

<Conductive carbon layer>
The conductive carbon layer 54 is a layer containing conductive carbon. And as above-mentioned, the electroconductive fall as a price which aims at low cost in a porous material layer can be covered by presence of an electroconductive carbon layer. This is particularly the case for carbon fibers (in particular, PAN-based or pitch-based carbon fibers). Further, when metal fibers are used as the porous material layer, the presence of the conductive carbon layer ensures corrosion resistance as compared with the case of only the porous material layer 52 while ensuring the conductivity as the gas diffusion layer. It can be improved.

In the conductive carbon layer or a conductive carbon particles in the present embodiment, the intensity ratio of the measured from the Raman scattering spectroscopy D- band peak intensity I _D and G- band peak intensity _{I G R (I D / I} G) is 1.3 or more. In addition, the average peak measured by rotational anisotropy measurement by Raman scattering spectroscopy of the conductive carbon layer shows a two-fold symmetrical pattern.

As will be described later, most of the conductive carbon layer or the conductive carbon particles having an intensity ratio R (I _D / I _G ) of 1.3 or more is formed on or in the surface of the porous material layer. And exists as polycrystalline graphite. The “polycrystalline graphite” has an anisotropic graphite crystal structure (graphite cluster) in which graphene surfaces (hexagonal network surfaces) are laminated. Therefore, at least most of the conductive carbon layer or the conductive carbon particles have a strength ratio R (I _D / I _G ) of 1.3 or more, and thus constitute a conductive carbon layer. A laminate having a graphene surface is formed.

When the carbon material is analyzed by Raman spectroscopy, peaks are usually generated around 1350 cm ⁻¹ and 1584 cm ⁻¹ . Highly crystalline graphite has a single peak near 1584 cm ⁻¹ , and this peak is usually referred to as the “G band”. On the other hand, a peak near 1350 cm ⁻¹ appears as the crystallinity decreases (crystal structure defects increase). This peak is usually referred to as the “D band” (note that the peak of diamond is strictly 1333 cm ⁻¹ and is distinct from the D band). The intensity ratio R (I _D / I _G ) between the D band peak intensity (I _D ) and the G band peak intensity (I _G ) is the graphite cluster size of the carbon material and the disorder of the graphite structure (crystal structure defect), Used as an index such as sp ² bond ratio. That is, in the present invention, it can be used as an index of contact resistance of the conductive carbon layer 54 and can be used as a film quality parameter for controlling the conductivity of the conductive carbon layer 54.

The R (I _D / I _G ) value is calculated by measuring the Raman spectrum of the carbon material using a microscopic Raman spectrometer. Specifically, the peak intensity of 1300～1400Cm ^-1 called the D band _{(I D),} the relative intensity ratio of the peak intensity of 1500～1600Cm ^-1 called G band _{(I G)} (peak area ratio ( I _D / I _G )).

  As described above, in this embodiment, the R value is 1.3 or more. Moreover, in preferable embodiment, R value becomes like this. Preferably it is 1.4-2.0, More preferably, it is 1.4-1.9, More preferably, it is 1.5-1.8. When the R value is 1.3 or more, a conductive carbon layer in which the conductivity in the stacking direction is sufficiently secured can be obtained. Moreover, if R value is 2.0 or less, the reduction | decrease of a graphite component, ie, the disorder degree of a graphite structure, can be suppressed effectively. Furthermore, an increase in internal stress of the conductive carbon layer itself can be suppressed, and adhesion with a porous material layer (an intermediate layer when an intermediate layer described later) exists can be further improved.

  In addition, the mechanism by which the above-mentioned effect is acquired by making R value 1.3 or more like this embodiment is estimated as follows. However, the following estimation mechanism does not limit the technical scope of the present invention.

As described above, increasing the D-band peak intensity (that is, increasing the R value) means an increase in crystal structure defects in the graphite structure. In other words, it means that the sp ³ carbon increases in the highly crystalline graphite consisting of only sp ² carbon. Here, a photograph (magnification: 400,000 times) of a cross section of a conductive member (conductive member A) having a conductive carbon layer with R = 1.0 to 1.2 observed with a transmission electron microscope (TEM) is shown in FIG. 5A. Shown in Similarly, FIG. 5B shows a photograph (magnification: 400,000 times) of a cross section of a conductive member (conductive member B) having a conductive carbon layer with R = 1.6 observed by TEM. The conductive member A and the conductive member B use SUS316L as a porous material layer, and an intermediate layer (thickness: 0.2 μm) made of chromium (Cr) and a conductive carbon layer (thickness :) on the surface. 0.2 μm) was sequentially formed by sputtering. In addition, the bias voltage applied to the porous material layer when the conductive carbon layer in the conductive member A is manufactured is 0 V, and is applied to the porous material layer when the conductive carbon layer in the conductive member B is manufactured. The bias voltage applied was -140V.

  As shown in FIG. 5B, it can be seen that the conductive carbon layer of the conductive member B has a structure of polycrystalline graphite. On the other hand, such a structure of polycrystalline graphite cannot be confirmed in the conductive carbon layer of the conductive member A shown in FIG. 5A.

  Here, “polycrystalline graphite” microscopically has an anisotropic graphite crystal structure (graphite cluster) in which graphene surfaces (hexagonal network surfaces) are laminated, but macroscopically, a large number of such graphite structures. Is an isotropic crystal. Therefore, it can be said that the polycrystalline graphite is one type of diamond-like carbon (DLC). Normally, single crystal graphite has a disordered structure in which graphene surfaces are laminated even when viewed macroscopically, as represented by HOPG (highly oriented pyrolytic graphite). On the other hand, the polycrystalline graphite has a graphite structure as an individual cluster, and has a turbostratic structure. By controlling the R value to the above-mentioned value, this degree of disturbance (graphite cluster amount and size) can be ensured appropriately, and a conductive path from one surface of the conductive carbon layer 54 to the other surface can be secured. As a result, it is considered that a decrease in conductivity due to the separate provision of the conductive carbon layer 54 in addition to the porous material layer 52 can be prevented.

In polycrystalline graphite, since the graphene surface is formed by the bonding of sp ² carbon atoms constituting the graphite cluster, conductivity is ensured in the plane direction of the graphene surface. Polycrystalline graphite is substantially composed of only carbon atoms, has a small specific surface area, and a small amount of bonded functional groups. For this reason, polycrystalline graphite has excellent resistance to corrosion by acidic water or the like. In addition, even in powders such as carbon black, primary particles are often formed by aggregates of graphite clusters, thereby exhibiting electrical conductivity. However, since the individual particles are separated, there are many functional groups formed on the surface, and corrosion due to acidic water or the like is likely to occur. In addition, even when a conductive carbon layer is formed with carbon black, there is a problem that the denseness as a protective film is lacking.

  Here, when the conductive carbon layer 54 of the present embodiment is made of polycrystalline graphite, the size of the graphite cluster constituting the polycrystalline graphite is not particularly limited. As an example, the average diameter of the graphite cluster is preferably about 1 to 50 nm, more preferably 2 to 10 nm. When the average diameter of the graphite cluster is in such a range, it is possible to prevent the conductive carbon layer 54 from being thickened while maintaining the crystal structure of the polycrystalline graphite. Here, the “diameter” of the graphite cluster means the maximum distance among the distances between any two points on the contour line of the cluster. Moreover, the average diameter value of the graphite cluster is expressed as an average value of the diameter of the cluster observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Can be calculated.

  In the present embodiment, the conductive carbon layer 54 may be composed of only polycrystalline graphite, but the conductive carbon layer 54 may include materials other than polycrystalline graphite. Examples of carbon materials other than polycrystalline graphite that can be included in the conductive carbon layer 54 include graphite particles such as carbon black, fullerenes, carbon nanotubes, carbon nanofibers, carbon nanohorns, and carbon fibrils. Specific examples of carbon black include, but are not limited to, ketjen black, acetylene black, channel black, lamp black, oil furnace black, and thermal black. Carbon black may be subjected to a graphitization treatment. As materials other than carbon that can be included in the conductive carbon layer 54, gold (Au), silver (Ag), platinum (Pt), ruthenium (Ru), palladium (Pd), rhodium (Rh), indium (In ) And the like. Moreover, water-repellent substances such as polytetrafluoroethylene (PTFE), conductive oxides, and the like can also be given. As for materials other than polycrystalline graphite, only 1 type may be used and 2 or more types may be used together. It goes without saying that materials other than polycrystalline graphite may be used in combination with polycrystalline graphite.

  The thickness of the conductive carbon layer 54 is not particularly limited. However, Preferably it is 1-1000 nm, More preferably, it is 2-500 nm, More preferably, it is 5-200 nm. If the thickness of the conductive carbon layer is within such a range, sufficient conductivity can be secured between the porous material layer constituting the gas diffusion layer and the separator. Moreover, there can be an advantageous effect that the porous material layer can have a high corrosion resistance function.

  Hereinafter, although more preferable embodiment is described about the conductive carbon layer 54 in this embodiment, the technical scope of this invention is not limited only to the following form.

  First, regarding the Raman scattering spectroscopic analysis of the conductive carbon layer 54, from another viewpoint, the average peak measured by the rotational anisotropy measurement of the Raman scattering spectroscopic analysis shows a two-fold symmetry pattern. Hereinafter, the measurement principle of rotational anisotropy measurement will be briefly described.

  The rotational anisotropy measurement of the Raman scattering spectroscopic analysis is performed by performing the Raman scattering spectroscopic measurement while rotating the measurement sample 360 degrees in the horizontal direction. Specifically, the surface of the measurement sample is irradiated with laser light, and a normal Raman spectrum is measured. Next, the measurement sample is rotated by 10 °, and the Raman spectrum is measured in the same manner. This operation is performed until the measurement sample rotates 360 °. And the average peak is obtained by calculating the average value of the peak intensities obtained in the measurement at each angle and displaying the 360 ° polar coordinate with one peak at the center. For example, when the graphite layer is present on the sample surface so that the graphene surface is parallel to the surface direction of the sample, a three-fold symmetry pattern as shown in FIG. 6A can be seen. On the other hand, when the graphite layer is present on the sample surface so that the graphene surface is perpendicular to the surface direction of the sample, a two-fold symmetry pattern as shown in FIG. 6B can be seen. When an amorphous carbon layer having no clear crystal structure is present on the surface of the sample, a pattern having no symmetry as shown in FIG. 6C is seen. Therefore, the average peak measured by rotational anisotropy measurement shows a two-fold symmetry pattern. This means that the surface direction of the graphene surface constituting the conductive carbon layer 54 is substantially the same as the stacking direction of the conductive carbon layer 54. Means you are doing it. According to such a form, the conductivity in the conductive carbon layer 54 is ensured by the shortest path, which is preferable.

  Here, the result of the rotational anisotropy measurement performed on the conductive member B described above is shown in FIGS. 7A and 7B. FIG. 7A shows a Raman spectrum when the conductive member B is used as a measurement sample and the rotation angles of the sample are 0 °, 60 °, and 180 °, respectively. FIG. 7B shows an average peak of rotational anisotropy measurement for the conductive member B obtained by the above-described method. As shown in FIG. 7B, in the measurement of rotational anisotropy of the conductive member B, peaks were observed at 0 ° and 180 ° positions. This corresponds to the two-fold symmetry pattern shown in FIG. 7B. In addition, in this specification, the definition that the average peak measured by the rotational anisotropy measurement of Raman scattering spectroscopic analysis “shows a two-fold symmetry pattern” is shown below. That is, as shown in FIG. 6B and FIG. 7B, this means that there are two peaks that face each other by 180 ° with respect to the point where the peak intensity is 0 in the average peak. Since the peak intensity seen in the 3-fold symmetrical pattern and the peak intensity seen in the 2-fold symmetrical pattern are supposed to show the same value in principle, such a definition is possible.

  In a preferred embodiment, the Vickers hardness of the conductive carbon layer 54 is defined. “Vickers hardness (Hv)” is a value that defines the hardness of a substance, and is a value inherent to the substance. In this specification, the Vickers hardness means a value measured by a nanoindentation method. The nanoindentation method is a method in which the diamond indenter is continuously loaded and unloaded with a very small load on the sample surface, and the hardness is measured from the obtained load-displacement curve. Larger means that the substance is harder. In a preferred embodiment, specifically, the Vickers hardness of the conductive carbon layer 54 is preferably 1500 Hv or less, more preferably 1200 Hv or less, further preferably 1000 Hv or less, and particularly preferably 800 Hv or less. . When the Vickers hardness is within such a range, excessive mixing of sp3 carbon having no conductivity can be suppressed, and a decrease in conductivity of the conductive carbon layer 54 can be prevented. On the other hand, the lower limit value of the Vickers hardness is not particularly limited, but if the Vickers hardness is 50 Hv or more, the hardness of the conductive carbon layer 54 is sufficiently ensured. As a result, it is possible to provide a conductive member (separator) that can withstand impacts such as external contact and friction and has excellent adhesion to the porous material layer 52. From such a viewpoint, the Vickers hardness of the conductive carbon layer 54 is more preferably 80 Hv or more, further preferably 100 Hv or more, and particularly preferably 200 Hv or more.

  Here, SUS316L is prepared as a metal base layer of the conductive member, and an intermediate layer (thickness: 0.2 μm) made of Cr and a conductive carbon layer (thickness: 0.2 μm) are sequentially formed on the surface by a sputtering method. It produced by forming. At this time, the Vickers hardness of the conductive carbon layer was changed by controlling the bias voltage and the film formation method. FIG. 8 shows the relationship between the Vickers hardness of the conductive carbon layer in the conductive member thus obtained and the value of the sp3 ratio in the conductive carbon layer. In FIG. 8, diamond has an sp3 ratio = 100% and becomes Hv10000. From the results shown in FIG. 8, it can be seen that when the Vickers hardness of the conductive carbon layer is 1500 Hv or less, the value of the sp3 ratio is greatly reduced. Moreover, it is estimated that the value of the contact resistance of a conductive member also falls along with this, when the value of sp3 ratio falls.

  From another point of view, it is preferable to consider the amount of hydrogen atoms contained in the conductive carbon layer 54 as well. That is, when the conductive carbon layer 54 includes a hydrogen atom, the hydrogen atom is bonded to the carbon atom. Then, the hybrid orbital of the carbon atom to which the hydrogen atom is bonded changes from sp2 to sp3 and loses conductivity, so that the conductivity of the conductive carbon layer 54 is lowered. Further, when the C—H bond in the polycrystalline graphite is increased, the continuity of the bond is lost, the hardness of the conductive carbon layer 54 is lowered, and finally the mechanical strength and corrosion resistance of the conductive member are lowered. . From such a viewpoint, the content of hydrogen atoms in the conductive carbon layer 54 is preferably 30 atomic percent or less, more preferably 20 atomic percent or less, with respect to all atoms constituting the conductive carbon layer 54. More preferably, it is 10 atomic% or less. Here, as the value of the hydrogen atom content in the conductive carbon layer 54, a value obtained by elastic recoil scattering analysis (ERDA) is adopted. In this method, a measurement sample is tilted, and a helium ion beam is incident shallowly, thereby detecting an element ejected forward. Since the nucleus of a hydrogen atom is lighter than the incident helium ion, if a hydrogen atom is present, the nucleus is ejected forward. Since such scattering is elastic scattering, the energy spectrum of the ejected atom reflects the mass of the nucleus. Therefore, the content of hydrogen atoms in the measurement sample can be measured by measuring the number of nuclei of ejected hydrogen atoms with a solid detector.

  Here, FIG. 9 is a graph showing the results of measuring the contact resistance of several conductive members having conductive carbon layers having different hydrogen atom contents although the R value is 1.3 or more. is there. As shown in FIG. 9, when the content of hydrogen atoms in the conductive carbon layer is 30 atomic% or less, the value of the contact resistance of the conductive member is significantly reduced. In the experiment shown in FIG. 9, SUS316L was used as the metal base layer of the conductive member, and an intermediate layer (thickness: 0.2 μm) made of Cr and a conductive carbon layer (thickness: 0.2 μm) on this surface. ) Were sequentially formed by a sputtering method. At this time, the hydrogen atom content in the conductive carbon layer was changed by controlling the film formation method and the amount of hydrocarbon gas.

  In the present embodiment, the entire surface of the porous material layer 52 is covered (surface treatment) with the conductive carbon layer 54 directly or indirectly through the intermediate layer 56. In other words, in this embodiment, the ratio (coverage) of the area where the porous material layer 52 is covered with the conductive carbon layer 54 is 100%. However, it is not limited only to such a form, and the coverage may be less than 100%.

  When the porous material layer 52 contains metal fibers (particularly when the porous material layer 52 is made of metal fibers), the coverage of the porous material layer 52 by the conductive carbon layer 54 is preferably 50% or more. In other words, 50% or more of the surface of the porous material layer 52 containing metal fibers (particularly the porous material layer 52 made of metal fibers) is made of “conductive carbon”, that is, conductive carbon layers or conductive carbon particles. It is preferable to coat. Further, it is more preferably 80% or more, further preferably 90% or more, and most preferably 100%. By adopting such a configuration, it is possible to effectively suppress a decrease in conductivity and corrosion resistance due to the formation of an oxide film on the exposed portion of the porous material layer 52 that is not covered with the conductive carbon layer 52.

  On the other hand, when the porous material layer 52 contains carbon fibers (particularly when the porous material layer 52 is made of carbon fibers), the coverage of the porous material layer 52 by the conductive carbon layer 54 is preferably 85% or more. is there. Further, it is more preferably 90% or more, and most preferably 92%. By adopting such a configuration, in particular, when the carbon fiber is a PAN-based or pitch-based carbon fiber, it is possible to ensure contact resistance comparable to that of a porous material composed of graphitized carbon fiber.

  When the intermediate layer 56 described later is interposed between the porous material layer 52 and the conductive carbon layer 54 as in the present embodiment, the coverage ratio is determined by the gas diffusion layers (5a, 5c) in the stacking direction. It means the ratio of the area of the porous material layer 52 that overlaps with the conductive carbon layer 54 when viewed from the above.

<Intermediate layer>
First, as shown in FIG. 2 described above, the conductive carbon layer 54 in the present embodiment is present on the surface of the porous material layer 52, and between the conductive carbon layer 54 and the porous material layer. The intermediate layer 56 made of metal may be further included. Second, the metal may exist in (inside) at least one of the porous material layer 52 and the conductive carbon layer 54 (not shown).

  Thus, the fuel cell gas diffusion layer (fuel cell GDL) of this embodiment may include the intermediate layer 56 as a conductive member. The intermediate layer 56 has a function of improving adhesion between the porous material layer 52 and the conductive carbon layer 54 and a function of preventing elution of ions from the porous material layer 52. In particular, when the R value exceeds the upper limit value of the preferable range described above, the effect of providing the intermediate layer 56 is remarkably exhibited. However, it is a matter of course that an intermediate layer can be provided even when the R value is included in the preferred range described above. From another point of view, the above-described operation and effect due to the installation of the intermediate layer 56 are also remarkably exhibited when the porous material layer 52 is made of aluminum or an alloy thereof. In the present invention, the intermediate layer is an arbitrary layer, and the intermediate layer does not necessarily exist. Hereinafter, a preferable form in the case where the conductive member includes an intermediate layer will be briefly described.

  The material constituting the intermediate layer 56 is not particularly limited as long as it provides the above adhesion. For example, Group 4 metals (Ti, Zr, Nf) of the periodic table, Group 5 metals (V, Nb, Ta), Group 6 metals (Cr, Mo, W), and their carbides, Examples thereof include nitrides and carbonitrides. Among these, metals with low ion elution such as chromium (Cr), tungsten (W), titanium (Ti), molybdenum (Mo), niobium (Nb) or hafnium (Hf), or their nitrides, carbides or charcoal are preferable. Nitride is used. More preferably, Cr or Ti, or a carbide or nitride thereof is used. In particular, when the above-described metal with little ion elution or a carbide or nitride thereof is used, the corrosion resistance of the separator can be significantly improved.

  The thickness of the intermediate layer 56 is not particularly limited, but is preferably 0.005 to 10 μm, more preferably 0.005 to 0.1 μm, and further preferably 0.005 to 0.01 μm. preferable. The intermediate layer itself is effective in terms of suppressing peeling due to thermal expansion between the conductive carbon layer and the fiber, and preventing corrosion when the metal constituting the fiber has low corrosion resistance. When the thickness is 10 μm or more, there is a high possibility that the pores of the porous layer are blocked by the thickness of the intermediate layer. Note that the thickness of the intermediate layer is measured by AES depth analysis.

  In addition, the surface of the intermediate layer 56 on the conductive carbon layer 54 side is preferably rough at the nano level. According to such an embodiment, the adhesion of the conductive carbon layer 54 formed on the intermediate layer 56 to the intermediate layer 56 can be further improved.

Furthermore, when the thermal expansion coefficient of the intermediate layer 56 is close to the thermal expansion coefficient of the metal constituting the porous material layer 52, the adhesion between the intermediate layer 56 and the porous material layer 52 is improved. However, in such a form, the adhesion between the intermediate layer 56 and the conductive carbon layer 54 may decrease. Similarly, if the thermal expansion coefficient of the intermediate layer 56 is close to the thermal expansion coefficient of the conductive carbon layer 54, the adhesion between the intermediate layer 56 and the porous material layer 52 may be reduced. Considering these, the thermal expansion coefficient (α _mid ) of the intermediate layer, the thermal expansion coefficient (α _sub ) of the porous material layer, and the thermal expansion coefficient (α _c ) of the conductive carbon layer are expressed by α _sub ≧ α It is preferable to satisfy the relationship of _mid > α _c . The case where α _sub and α _mid are the same value corresponds to the case where the constituent metal of the metal fiber and the constituent metal of the intermediate layer are both the same in the porous material layer.

  The intermediate layer 56 may be present on at least one surface of the porous material layer 52. Moreover, when a conductive carbon layer exists in both surfaces of a porous material layer, it is preferable to interpose an intermediate | middle layer between a porous material layer and both conductive carbon layers, respectively. When the intermediate layer exists only between the porous material layer and one of the conductive carbon layers, the intermediate layer is disposed on the MEA side of the PEFC and the porous layer. It is preferable to exist between the material layers.

<Hydrophilic layer>
As described above, the conductive carbon layer 54 may exist on the surface of the porous material layer 52. In this case, as shown in FIG. 2, a hydrophilic layer 58 composed of at least one selected from the group consisting of metal, metal nitride, metal carbide, and metal oxide is further provided on the conductive carbon layer 54. May be. And it is preferable that the hydrophilization layer 58 is arrange | positioned in the state adjacent to a separator on the conductive carbon layer which exists in the side facing the separator of the porous material layer 52. FIG. If it shows in FIG. 1, it is preferable that a hydrophilization layer is arrange | positioned in the surface of the side in which a separator (5a, 5c) exists among gas diffusion layers (4a, 4c). The function of such a hydrophilic layer will be described below. Although water is generated by the power generation of the battery, it is highly desirable that this water be quickly transported to the separator and discharged. At that time, if the hydrophilic layer is disposed on the surface of the gas diffusion layer (4a, 4c) where the separator (5a, 5c) is present, the hydrophilicity at the separator interface is improved and the catalyst layer ( The rapid discharge of water from 3a, 3c) to the separator side can be promoted.

  From the viewpoint of the function of such a hydrophilic layer, in FIG. 1, a groove-like flow path constituted by a plurality of concave portions present in the separators (5a, 5c) is involved in drainage. Therefore, in the hydrophilic layer of the gas diffusion layer (4a, 4c) on the separator (5a, 5c) side, the portion of the hydrophilic layer in contact with the recess is made of metal so as to have a high degree of hydrophilicity. It is preferable. On the other hand, since the hydrophilicity of the portion of the hydrophilic layer that is in contact with the convex portion is not important, if it is composed of one or more selected from the group consisting of metals, metal nitrides, metal carbides, and metal oxides. Good. Furthermore, such a hydrophilic layer does not have to exist in the portion of the hydrophilic layer in contact with the convex portion. In such a case, the hydrophilization layer may take the form of a partial (discontinuous) “layer” in which the metal is dispersed and exists on the surface of the gas diffusion layer.

  The said metal may have 1 or more types selected from the group which consists of a metal element which comprises a noble metal or a metal separator base material, and the surface treatment of a separator. Although it does not limit to the following as a metal element which comprises a metal separator base material, For example, iron, titanium, aluminum, copper, and these alloys are mentioned. Here, the iron alloy includes stainless steel. Regarding the examples of each element and each alloy (including stainless steel), the above-mentioned examples are cited as they are. When the metal is a noble metal, not only can hydrophilicity be improved, but contact resistance can be significantly reduced. In addition, when the metal is a metal element constituting the metal separator base material or a metal element included in the surface treatment of the separator, corrosion that may occur when dissimilar metals come into contact with each other can be effectively prevented. The metal nitride, metal carbide, and metal oxide can include all of the above-described metal nitride, carbide, and oxide.

  FIG. 2 described above shows the hydrophilic layer 58. In FIG. 2, as an example, the hydrophilization layer 58 is shown as a continuous layer. However, a discontinuous layer form, that is, a metal dispersed layer form as described above may be adopted. In FIG. 2, essential porous material layer 52 and conductive carbon layer 54, and optional intermediate layer 56 and hydrophilic layer 58 exist as conductive members. However, in the present embodiment, neither the intermediate layer 56 nor the hydrophilized layer 58 may exist, or at least one of them may exist.

  Here, the sectional view of the gas diffusion layer in FIG. 2 shows a structure in which an intermediate layer and a conductive carbon layer are laminated on the porous material layer. However, the cross-sectional view of the present embodiment is not limited to this, and in addition, a structure in which an intermediate layer and a conductive carbon layer are “laminated” in (inside) a porous material layer composed of fibers is also possible. It is possible. Although it is as above-mentioned until now, supplementary description is required about a hydrophilization layer. In other words, since the function of the hydrophilic layer is to promote the rapid drainage of water to the separator side, the positional relationship of the conductive carbon layer (and the intermediate layer) with respect to the porous material layer is taken. Even so, only the hydrophilic layer needs to be present on the porous material layer.

<Gas diffusion electrode (gas diffusion layer)>
The gas diffusion electrode (gas diffusion layer) preferably has an electric resistance value in the thickness direction of 1 mΩ · cm ² or less. When the electric resistance value in the thickness direction of the gas diffusion electrode is 2.0 mΩ or less, the battery performance is likely to be improved, and embrittlement of the components of the gas diffusion electrode due to heat generation can be effectively prevented. Here, the electrical resistance value in the thickness direction is an electrical resistance value measured between two test electrodes with a gas diffusion electrode sandwiched between two gold-plated 50 mm square test electrodes (thickness 10 mm) at a pressure of 1 MPa. (MΩ).

  The gas diffusion layer generally has a thickness of 300 to 100 μm, but the thickness can be appropriately adjusted in view of the shape and performance of the cell.

  In the gas diffusion layer (gas diffusion electrode) as described above, the fiber component has conductivity, and since the fibers are fused to each other, the conductivity of the gas diffusion layer can be increased.

[Second Embodiment]
There is no restriction | limiting in particular about the method of manufacturing the gas diffusion layer of 1st Embodiment mentioned above, It can manufacture by referring a conventionally well-known method suitably. Hereinafter, although preferable embodiment for manufacturing a gas diffusion layer is described, the technical scope of this invention is not limited only to the following form. In addition, since various conditions such as the material of each member constituting the gas diffusion layer are as described above, the description thereof is omitted here.

  The method for producing a gas diffusion layer for fuel cell (GDL for fuel cell) according to the second embodiment of the present invention is a step of forming a conductive carbon layer or conductive carbon particles on or in the surface of the porous material layer. including. In addition, about a porous material layer, a commercial item can be used. However, some of the porous material layers in the present invention, such as PAN-based or pitch-based carbon fibers that are not subjected to graphitization, are not currently distributed as commercial products. Therefore, the manufacturing method and conditions of the special PAN-based or pitch-based carbon fiber will be described later.

  In the step (a) of forming the conductive carbon layer or the conductive carbon particles, a layer containing conductive carbon is stacked on the porous material layer at the atomic level using conductive carbon (for example, graphite) as a target ( By conducting film formation, a conductive carbon layer can be formed. In this way, the adhesion (including the vicinity thereof) between the directly attached conductive carbon layer and porous material layer can be maintained for a long period of time due to intermolecular force or slight carbon atom penetration.

  Suitable methods for laminating (depositing) conductive carbon include, for example, physical vapor deposition (PVD) such as sputtering or ion plating, or filtered cathodic vacuum arc (FCVA). Examples include ion beam evaporation. Examples of the sputtering method include a magnetron sputtering method, an unbalanced magnetron sputtering (UBMS) method, a dual magnetron sputtering method, and an ECR sputtering method. Examples of the ion plating method include an arc ion plating method. Especially, it is preferable to use sputtering method and an ion plating method, and it is especially preferable to use sputtering method. According to such a method, a carbon layer with a low hydrogen content can be formed. As a result, the ratio of bonds between carbon atoms (sp2 hybrid carbon) can be increased, and excellent conductivity can be achieved. In addition, there is an advantage that the film can be formed at a relatively low temperature, and damage to the porous material layer can be minimized. Furthermore, the sputtering method has an advantage that the film quality of the deposited film can be controlled by controlling the bias voltage and the like. Further, there is an advantage that the conductive carbon layer can be continuously and efficiently manufactured by forming (forming a film) by the sputtering method.

  When the porous material layer contains metal fibers, it is preferable to remove the oxide film on the surface of the porous material layer (metal fibers) by sputtering with argon (Ar) plasma.

  FIG. 10 is a schematic view showing an apparatus for forming (lamination) an intermediate layer or a conductive carbon layer on or in the surface of a porous material layer using a sputtering method. When the conductive carbon layer is formed by sputtering, the degree of vacuum in the chamber 64 is not limited to the following, but is preferably exhausted from the gas exhaust port 66 to about 3 to 10 Pa. Thereafter, Ar is introduced preferably through the atmospheric gas inlet 68 at about 0.1 to 1 Pa. The temperature of the fuel cell gas diffusion layer (GDL) itself is not particularly limited as long as it is in the range of room temperature to about 200 ° C., but is preferably appropriately selected according to the material of the GDL (particularly the porous material layer). Set the temperature. Sputtering is performed by ejecting a target material (such as Cr or graphite) from the target 70 to the porous material layer 72.

  Here, when the conductive carbon layer is formed by a sputtering method, a negative bias voltage may be applied to the porous material layer during sputtering. According to such a form, a conductive carbon layer having a structure in which graphite clusters are densely assembled can be formed by the ion irradiation effect. Since such a conductive carbon layer can exhibit excellent conductivity, a conductive member (gas diffusion layer) having a small contact resistance with other members (for example, MEA) can be provided. In this embodiment, the magnitude (absolute value) of the negative bias voltage to be applied is not particularly limited, and a voltage capable of forming a conductive carbon layer can be adopted. As an example, the magnitude of the applied voltage is preferably 50 to 500V, more preferably 100 to 300V. In addition, specific forms, such as other conditions at the time of film-forming, are not restrict | limited, A conventionally well-known knowledge can be referred suitably. Further, when the conductive carbon layer 54 is formed by the UBMS method, it is preferable to form an intermediate layer in advance and form the conductive carbon layer thereon. Thereby, the conductive carbon layer excellent in adhesiveness with the underlayer can be formed. However, when the conductive carbon layer is formed by another method, a conductive carbon layer having excellent adhesion to the porous material layer can be formed even when the intermediate layer is not present.

  According to the above-described method, a conductive member in which the conductive carbon layer 54 is formed on one surface of the porous material layer 52 can be manufactured. In order to manufacture a conductive member in which the conductive carbon layer 54 is formed on both surfaces of the porous material layer 52, the other surface of the porous material layer 52 is made conductive by the same method as described above. A carbon layer may be formed.

  In order to manufacture the gas diffusion layer having the intermediate layer 56 as shown in FIG. 2, the intermediate layer is formed on at least one surface of the porous material layer before the conductive carbon layer forming step described above. The process to do is performed. At this time, as the method for forming the intermediate layer, the same method as described above for the formation of the conductive carbon layer may be employed. However, it is necessary to change the target to the constituent material of the intermediate layer.

  Subsequently, a step of forming a conductive carbon layer on a surface different from the surface facing the conductive carbon layer of the intermediate layer formed by the above step may be performed. As a method for forming the conductive carbon layer on the surface of the intermediate layer, the same method as described above for the formation of the conductive carbon layer on the surface of the porous material layer may be employed.

  In addition, after the step (a), a sputtering method targeting one or more selected from the group consisting of metal, metal nitride, metal carbide and metal oxide, or after the step (a), Either method (treatment) of plating treatment is used. And you may perform the process (b) of forming a hydrophilization layer by such a method (process). When forming a hydrophilic layer on the surface of the gas diffusion layer on the side facing the separator, steps (A) to (B) can be performed easily and continuously by sputtering a predetermined metal or the like. On the other hand, when the step (b) is performed by plating, if the porous material layer is a continuous sheet, it can be processed in a roll-to-roll manner in a solution. There is an advantage that it can be manufactured at a low cost.

  Further, regarding the order of the steps, a desired gas diffusion layer can be formed by performing the step (b) after the step (a). On the other hand, the step (b) and the step (b) can also be performed (almost) simultaneously to form a hydrophilic layer on the separator-side surface of the gas diffusion layer, and further have the advantage of greatly reducing the production time. is there. In addition, when performing simultaneously, the hydrophilization member which comprises a hydrophilization layer may exist in not only the separator side surface of a gas diffusion layer but the whole gas diffusion layer. However, as described in the first embodiment, the hydrophilization layer may take a discontinuous layer form, that is, a metal dispersed layer form. Therefore, it can be said that it is sufficiently meaningful to perform the step (b) and the step (b) simultaneously (almost simultaneously) in view of the advantages of cost and labor reduction resulting from a significant reduction in manufacturing time.

  The metal used in the plating process is preferably a noble metal or a metal element constituting a metal separator substrate. As the metal element constituting the metal separator substrate, the examples mentioned in the first embodiment are cited as they are. When the metal is a noble metal, not only can hydrophilicity be improved, but contact resistance can be significantly reduced. In addition, when the metal is a metal element constituting the metal separator substrate, it is possible to effectively prevent corrosion that may occur when dissimilar metals come into contact with each other.

  Said process (I) and process (B) can be paraphrased as follows. First, a conductive carbon layer or conductive carbon particles, and / or a hydrophilic layer (a layer formed of a hydrophilic member) can be formed using a sputtering method. On the other hand, for the formation of the hydrophilic layer, a plating process can be used instead of the sputtering method.

  As described in the first embodiment (FIG. 4), when a porous material layer is obtained by producing a polyacrylonitrile (PAN) -based or pitch-based carbon fiber, carbonization is not performed until the graphitization treatment. It is preferable to end the process. This can result in a significant cost reduction. FIG. 11 is a diagram showing a general PAN-based carbon fiber manufacturing process and a PAN-based carbon fiber manufacturing process in the present invention. In FIG. 11, this embodiment has the greatest feature in that no graphitization is performed. To put it more succinctly than the flowchart of FIG. 11, after the carbonization treatment, the finishing (filament cutting) treatment including surface treatment and sizing is performed without performing the graphitization treatment. When the chopped fiber obtained by this treatment is made into paper, the surface of the fiber is preferably subjected to a water repellent treatment using a conventionally known fluorine-based liquid. And it can calcinate at the end and can obtain the roll-shaped sheet of a gas diffusion layer. For the method and conditions of each manufacturing step (treatment) of “special PAN-based carbon fiber” (hereinafter also referred to as “PAN-based carbonized fiber”) in the present invention, a conventionally known one as shown in FIG. 11 is applied. do it. Hereinafter, although an example of the method and conditions of each manufacturing process (treatment) of the PAN-based carbon fiber in the present invention will be shown, the manufacturing method of the PAN-based carbon fiber in the present invention is not limited to the following, and the method and conditions appropriately. Changes may be made.

  First, a monomer having acrylonitrile as a main component is polymerized to obtain a PAN polymer. Subsequently, a PAN-based precursor fiber is produced by spinning the PAN-based polymer by a wet method, a dry method, or a dry-wet method.

  Although not limited to the following, the PAN-based polymer preferably contains 90% by weight or more, more preferably 95% by weight or more of acrylonitrile, which is the main component of the monomers. If necessary, other monomers copolymerizable with acrylonitrile may be added for copolymerization. The polymer (including a copolymer) can be used as a stock solution for spinning dissolved in a solvent during spinning. The other monomer is not particularly limited as long as it is copolymerizable with acrylonitrile, and examples thereof include butadiene and styrene.

  Examples of the solvent for the polymer include, but are not limited to, inorganic salt solvents such as zinc chloride and sodium thiocyanate, and organic solvents such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. It is done.

  A spinning solution in which such a polymer is dissolved in a solvent is generally spun into fibers by wet, dry or dry wet methods. If necessary, the film is stretched in a heating heat medium such as pressurized steam to adjust the orientation, or in some cases, further subjected to a heat treatment at 130 to 200 ° C. and wound to obtain a PAN-based precursor fiber. The basic skeleton of the PAN-based precursor fiber is shown in FIG. 4 (top). Here, the weight average molecular weight (Mw) of the PAN-based precursor fiber is not limited to the following.

  Subsequently, the PAN-based carbon fiber in the present invention is produced from the PAN-based precursor fiber.

More specifically, first, the PAN-based precursor fiber is stabilized. The stabilization treatment is not limited to the following in an oxidizing atmosphere such as air, but preferably is 200 to 350 ° C., more preferably 200 to 300 ° C., and even more preferably 230 to 270 ° C. Stretch 1.05 times. Thereby, the PAN-based precursor fiber is converted into a flame-resistant fiber. At that time, the treatment time is not particularly limited, but is, for example, 80 to 160 minutes, and the degree of pressurization is not particularly limited, but is, for example, more than 1.3 g / cm ³ . The basic skeleton of the flameproof fiber is shown in FIG. 4 (second from the top). Thereafter, as an optional step, the obtained flame-resistant fiber is not limited to the following in an oxidizing atmosphere such as air, but preferably activated carbon fiber is obtained by activation while heating at 800 to 1200 ° C.

  Subsequently, the obtained activated carbon fiber (or flame-resistant fiber) is carbonized. In an inert atmosphere such as nitrogen, the maximum temperature is not limited to the following, but it is preferably 600 to 900 ° C, more preferably 700 to 800 ° C, while stretching 1.0 to 1.1 times. Next, in an inert atmosphere such as nitrogen, the maximum temperature is not limited to the following, but is preferably 0.91 to 1800 ° C, more preferably 1200 to 1500 ° C, while stretching 0.95 to 1.0 times. By doing so, a carbonized fiber is obtained. The basic skeleton of the flameproof fiber is shown in FIG. 4 (third from the top). As shown in FIG. 4, since carbonized fibers have nitrogen atoms in the middle of the “carbon-carbon” bond, their conductivity is compared with the conductivity of graphitized fibers (crystals) after graphitization. Significantly lower.

  Although not performed in the method for producing a PAN-based carbon fiber in the present invention, a graphitization treatment that is essential in a general method for producing a PAN-based carbon fiber will be described just in case. While the carbonized fiber is not limited to the following as the maximum temperature in an inert atmosphere such as nitrogen, it is preferably 2000 to 3000 ° C, more preferably 2200 to 3000 ° C, and even more preferably 2200 to 2800 ° C. 1.01 to 1.2 times. At that time, the processing time is not particularly limited, but is, for example, 150 to 400 seconds. The basic skeleton of the graphitized fiber is shown in FIG. 4 (bottom). The graphitized fiber thus obtained is subjected to a surface oxidation treatment, preferably an electrolytic oxidation treatment of 10 to 200 coulomb / g in an acid or alkaline aqueous solution, to produce a functional group that enhances adhesion on the fiber surface. There is a case to let you.

  In the present invention, as described above, after the carbonization treatment, the finishing (filament cutting) treatment including surface treatment and sizing is performed as it is. The chopped fiber obtained by this treatment is made into paper as in the case of making paper. A conventionally known method may be applied to the papermaking method and conditions. Examples of the material to be used include, but are not limited to, constituents of the porous material layer (such as carbon fiber), activated carbon, pulp (such as cellulose fiber), and artificial graphite fine powder. The addition ratio of each material is not particularly limited as long as it can be made into paper. There are no particular restrictions on the size and weight of the paper (sheet) obtained. The conditions for the subsequent papermaking (sheet) firing are not particularly limited as long as the conditions are set at an optimum temperature and time for realizing graphitization of the material contained in the papermaking. As an example, there may be 1-48 hours at 1000-2500 ° C.

Here, when making the paper, the surface of the fiber is preferably subjected to a water repellent treatment using a conventionally known fluorine-based liquid. The paper-made sheet is not limited to the following, but preferably has a thickness of 0.2 to ² mm / sheet and a density of 100 to 250 g / m ² . Preferably 1 to 5 sheets are laminated and fired in an atmosphere of an inert gas such as nitrogen or argon. Firing may be performed, for example, between graphite plates in order to prevent warpage of the sheet. Although the temperature rise of baking is not limited to the following, it is preferably performed at a temperature of about 800 ° C. or lower (maximum temperature reached) for 5 to 100 hours. The final temperature for firing is not particularly limited. Thereby, the roll-shaped sheet of a gas diffusion layer can be obtained.

  Here, the water repellent treatment will be described in more detail. For the gas diffusion layer, it is preferable to use a water repellent for the purpose of further improving the water repellency and preventing the flooding phenomenon. Although it does not specifically limit as a water repellent, Fluorine-type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Examples thereof include molecular materials, polypropylene, and polyethylene.

  In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent agent on the catalyst layer side of the substrate. You may have.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle diameter of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  Examples of the water repellent used in the carbon particle layer include the same water repellent as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

  The mixing ratio of the carbon particles and the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) in mass ratio in consideration of the balance between water repellency and electron conductivity. It is good. In addition, there is no restriction | limiting in particular also about the thickness of a carbon particle layer, What is necessary is just to determine suitably in consideration of the water repellency of the gas diffusion layer obtained.

[Third Embodiment]
Each constituent member of the polymer electrolyte fuel cell according to the second embodiment of the present invention will be described. First, a solid polymer electrolyte membrane having an anode (oxidant side) catalyst layer formed on one surface and a cathode (fuel gas agent side) catalyst layer formed on the other surface is provided. Next, a gas diffusion layer is provided outside each catalyst layer. Here, at least one of the gas diffusion layers arranged outside the anode catalyst layer and the cathode catalyst layer is a gas obtained by the gas diffusion layer of the first embodiment or the manufacturing method of the second embodiment. It is a diffusion layer. Preferably, the gas diffusion layer disposed outside the Pt catalyst layer is at least the gas diffusion layer of the first embodiment or the gas diffusion layer obtained by the manufacturing method of the second embodiment. Moreover, the gasket provided in each of the both sides of the said gas diffusion layer is provided. In addition, a gas impermeable carbon separator or a metal separator provided on each side of the gasket and having a performance as an anode or cathode current collector is provided.

  Especially, the gas diffusion layer for fuel cells in this embodiment can be used for various uses. A typical example is the gas diffusion layer (4a, 4c) of PEFC shown in FIG.

  As shown in FIG. 1, the PEFC 1 first includes a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the solid polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state.

  In PEFC1, the MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5 a, 5 c) are illustrated so as to be positioned at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another adjacent PEFC. These descriptions are omitted in FIG.

  The separators (5a, 5c) are obtained, for example, by forming a concavo-convex shape as shown in FIG. 1 by subjecting a thin plate having a thickness of 0.5 mm or less to a press treatment. The convex part seen from the MEA side of the separator (5a, 5c) is in contact with the MEA 10. Thereby, the electrical connection with MEA10 is ensured. Further, a recess (space between the separator and the MEA generated due to the concavo-convex shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for circulating gas during operation of the PEFC 1 Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) is circulated through the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated through the gas flow path 6c of the cathode separator 5c.

  On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) serves as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  However, the use of the fuel cell gas diffusion layer in the present embodiment is not limited to this. For example, in addition to PEFC, various fuel cell gases such as phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), solid electrolyte fuel cell (SOFC) or alkaline fuel cell (AFC) It can also be suitably used as a diffusion layer. In common with these fuel cells, the conductivity can be improved and the cost can be greatly reduced.

  Hereinafter, the components of the PEFC using the gas diffusion layer formed of the conductive member of the present embodiment will be described with reference to FIG. However, the present invention is characterized by the gas diffusion layer. Therefore, the specific form such as the shape of the gas diffusion layer in the PEFC and the specific form of the members other than the gas diffusion layer constituting the fuel cell are appropriately modified with reference to conventionally known knowledge. Can be done.

<Separator>
It is a plate-like member sandwiched between cells in a fuel cell stack (a stack of cells). It has the role of blocking fuel gas and air while transmitting electricity. In addition to sealing the cell, it also has the function of ensuring the gas flow and sending fuel gas and air.

  Conventionally, metals, carbon, conductive resins, and the like are known as constituent materials for fuel cell separators that require high conductivity. In recent years, a separator that can reduce the size of a fuel cell stack in an in-vehicle PEFC or the like, and that improves corrosion resistance while ensuring conductivity is preferably used. As the separator such as the above-described metal, carbon, or conductive resin, since a conventionally known separator can be used, description thereof is omitted here.

<Electrolyte layer>
The electrolyte layer is composed of, for example, a solid polymer electrolyte membrane 2 as shown in FIG. The solid polymer electrolyte membrane 2 has a function of selectively permeating protons generated in the anode catalyst layer 3a during operation of the PEFC 1 to the cathode catalyst layer 3c along the film thickness direction. The solid polymer electrolyte membrane 2 also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  The solid polymer electrolyte membrane 2 is roughly classified into a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane depending on the type of ion exchange resin that is a constituent material. Examples of ion exchange resins constituting the fluorine-based polymer electrolyte membrane include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride- Examples include perfluorocarbon sulfonic acid polymers. From the viewpoint of improving power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. A membrane is used.

  Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon polymer electrolyte membranes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the material selectivity is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

  The thickness of the electrolyte layer may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte layer is usually about 5 to 300 μm. When the thickness of the electrolyte layer is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

<Catalyst layer>
The catalyst layers (the anode catalyst layer 3a and the cathode catalyst layer 3c) are layers in which the cell reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer 3a, and the reduction reaction of oxygen proceeds in the cathode catalyst layer 3c.

  The catalyst layer includes a catalyst component, a conductive catalyst carrier that supports the catalyst component, and an electrolyte. Hereinafter, a composite in which a catalyst component is supported on a catalyst carrier is also referred to as an “electrode catalyst”.

  The catalyst component used in the anode catalyst layer is not particularly limited as long as it has a catalytic action in the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. The catalyst component used in the cathode catalyst layer is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specifically, it can be selected from metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof. .

  Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. Although the composition of the alloy depends on the type of metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the anode catalyst layer and the catalyst component used for the cathode catalyst layer can be appropriately selected from the above. In the present specification, unless otherwise specified, descriptions of the catalyst components for the anode catalyst layer and the cathode catalyst layer have the same definition for both. Therefore, they are collectively referred to as “catalyst components”. However, the catalyst components of the anode catalyst layer and the cathode catalyst layer do not have to be the same, and can be appropriately selected so as to achieve the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be adopted. However, the shape of the catalyst component is preferably granular. At this time, the average particle diameter of the catalyst particles is preferably 1 to 30 nm. When the average particle diameter of the catalyst particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading can be appropriately controlled. The “average particle diameter of catalyst particles” in the present invention is the average of the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction or the average particle diameter of the catalyst component determined from a transmission electron microscope image. It can be measured as a value.

  The catalyst carrier functions as a carrier for supporting the above-described catalyst component, and an electron conduction path involved in the transfer of electrons between the catalyst component and another member.

  Any catalyst carrier may be used as long as it has a specific surface area for supporting the catalyst component in a desired dispersion state and sufficient electron conductivity, and the main component is preferably carbon. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. Note that “substantially consisting of carbon atoms” means that contamination of about 2 to 3 mass% or less of impurities can be allowed.

The BET specific surface area of the catalyst carrier may be a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. When the specific surface area of the catalyst carrier is in such a range, the balance between the dispersibility of the catalyst component on the catalyst carrier and the effective utilization rate of the catalyst component can be appropriately controlled.

  The size of the catalyst carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the catalyst layer within an appropriate range, the average particle size is about 5 to 200 nm, preferably 10 to 10 nm. About 100 nm is preferable.

  In the electrode catalyst in which the catalyst component is supported on the catalyst carrier, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 70% by mass with respect to the total amount of the electrode catalyst. When the supported amount of the catalyst component is within such a range, the balance between the degree of dispersion of the catalyst component on the catalyst support and the catalyst performance can be appropriately controlled. The amount of the catalyst component supported on the electrode catalyst can be measured by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst layer includes an ion conductive polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. For example, the ion exchange resin which comprises the electrolyte layer mentioned above can be added to a catalyst layer as a polymer electrolyte.

<Fuel cell manufacturing method>
The manufacturing method of the fuel cell is not particularly limited, and conventionally known knowledge can be appropriately referred to in the field of the fuel cell.

  The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used in that high output is possible.

  Furthermore, a fuel cell stack having a structure in which a plurality of membrane electrode assemblies are stacked and connected in series via a separator may be formed so that the fuel cell can exhibit a desired voltage. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

[Fourth Embodiment]
The vehicle according to the fourth embodiment of the present invention uses the polymer electrolyte fuel cell (PEFC) of the third embodiment. In other words, the PEFC 1 of the present embodiment and the fuel cell stack using the PEFC 1 can be mounted on the vehicle as a driving power source.

  FIG. 12 is a schematic view of a vehicle equipped with the fuel cell stack of the above-described embodiment. As shown in FIG. 12, in order to mount the fuel cell stack 62 on a vehicle such as the fuel cell vehicle 61, for example, the fuel cell stack 62 may be mounted under the seat at the center of the vehicle body of the fuel cell vehicle 61. If it is installed under the seat, the interior space and the trunk room can be widened. In some cases, the place where the fuel cell stack 62 is mounted is not limited to the position under the seat, but may be the lower part of the rear trunk room or the engine room in front of the vehicle. Thus, a vehicle equipped with the PEFC 1 and the fuel cell stack 62 of the above-described form is also included in the technical scope of the present invention.

  Here, the above-described PEFC 1 and the fuel cell stack use the gas diffusion layers (4a, 4c) described in the above embodiment. Therefore, the PEFC 1 and the fuel cell stack can maintain good power generation performance over a long period of time, and can achieve a significant cost reduction. The PEFC 1 and the fuel cell stack using the PEFC 1 in the present embodiment can be suitably mounted on a vehicle as a driving power source. Thus, a vehicle equipped with the PEFC 1 and the fuel cell stack of the above-described form is also included in the technical scope of the present invention. The PEFC 1 and the fuel cell stack described above are particularly excellent in power generation performance. Therefore, a low-cost and highly reliable fuel cell vehicle can be provided over a long period of time.

  Hereinafter, although the effect by this invention is demonstrated using an Example and a comparative example, the technical scope of this invention is not limited to these Examples.

[Example 1]
First, carbonized GDL was prepared. The carbonized GDL is a “special” PAN-based carbon fiber (PAN-based carbonized fiber) that has been subjected to carbonization treatment as a material for the porous material layer, and then the conductive carbon layer is made porous. It is GDL for fuel cells laminated | stacked on the surface of the material layer.

<Lamination of chromium (Cr) layer and conductive carbon layer>
First, an intermediate layer (Cr layer) was laminated by UBMS sputtering. The degree of vacuum of the chamber was evacuated to about 3 to 10 Pa, and then argon (Ar) gas was introduced to about 1 Pa. The temperature of the fuel cell gas diffusion layer (fuel cell GDL) itself was set to 80 ° C. without considering the GDL material.

  During UBMS sputtering, a bias voltage of 140 V was applied to the gas diffusion layer without considering the material of the porous material layer. 99% or more of Cr was used as a target. In this way, a Cr layer having a thickness of 20 nm was laminated as an intermediate layer on the surface of the porous material layer.

  Subsequently, a conductive carbon layer was stacked by UBMS sputtering. Except for using 99% or more of graphite as a target, a conductive carbon layer was laminated by the same method and conditions as the lamination of the intermediate layer (Cr layer). The obtained conductive carbon layer was confirmed to have a laminated structure with a graphene surface, and its thickness was 7 μm.

[Comparative Example 1]
As a comparative example, TGP-H-90 (manufactured by Toray Industries, Inc.), which is a commercially available graphitized GDL, was used.

[Comparative Example 2]
A GDL for a fuel cell was produced using a “special” PAN-based carbon fiber subjected to carbonization treatment as a material for the porous material layer. Note that the chromium (Cr) layer and the conductive carbon layer are not stacked. Therefore, the obtained GDL for a fuel cell does not have a graphene-surface stacked body structure.

<Manufacture of porous material layer>
A porous material layer was produced by the same method and conditions as in the production of the porous material layer in Example 1.

[Measurement of R value]
In the gas diffusion layers produced in the above examples and comparative examples, the R value of the conductive carbon layer was measured. Specifically, first, the Raman spectrum of the conductive carbon layer was measured using a microscopic Raman spectrometer. Then, the peak intensity of the bands (D-band) located 1300~1400cm ^-1 _{(I D),} the peak area ratio of the peak intensity _{(I G)} of band (G-band) located 1500~1600cm ^-1 ( I _D / I _G ) was calculated and used as the R value. The obtained results are shown in Table 1 below.

[Measurement of contact resistance]
The contact resistance between the gas diffusion layer for fuel cells and the separator obtained in the above Examples and Comparative Examples was measured. FIG. 13 is a diagram showing a method for measuring the contact resistance between the fuel cell gas diffusion layer and the separator obtained in Examples and Comparative Examples. As shown in FIG. 13, as the separator 60, a stainless steel plate (flat plate) having a surface plated with gold plating on the surface of the fuel cell gas diffusion layer 62 side was used. Then, the produced fuel cell gas diffusion layer 62 is sandwiched between a pair of separators 60, power is connected to both ends thereof, and held while applying a 1 MPa load from the vertical direction to the main surfaces of the separators 60 on both sides. And configured a measuring device. A constant current of 1 A was passed through both ends of this measuring apparatus, and the contact resistance value of the laminate was calculated from the voltage value and Ohm's law at that time. The obtained results are shown in Table 1 below.

  As shown in Table 1, since the contact resistance values of Example 1 and Comparative Example 1 are almost the same, according to the present invention, it is equivalently high compared to the conventional gas diffusion layer for fuel cells. It was confirmed that the cost could be significantly reduced while ensuring conductivity. In addition, since the measuring method and conditions of contact resistance in this specification are the same as the above-mentioned method and conditions, detailed description regarding the measurement of contact resistance is abbreviate | omitted hereafter.

  Moreover, the graph corresponding to the result regarding the contact resistance of Example 1 shown in Table 1 is shown in FIG. The graph shows the value of contact resistance when the horizontal axis represents the ratio of “conductive carbon” to PAN-based carbonized fiber (conductive carbon / PAN-based carbonized fiber). That is, FIG. 14 shows a GDL for a fuel cell in which a PAN-based carbonized fiber that has been subjected to carbonization treatment is used as a material for a porous material layer, and then a conductive carbon layer is laminated on the surface of the porous material layer. The sensitivity of contact resistance is shown. As shown in FIG. 14, the PAN-based carbonized fiber according to one embodiment of the present invention is significantly inferior in terms of conductivity to a normal PAN-based carbon fiber subjected to graphitization treatment. However, the contact resistance is significantly reduced in proportion to the amount of the conductive carbon layer laminated on the porous material layer composed of such PAN-based carbonized fibers. In other words, the gas diffusion layer according to the present invention can be equivalent to a gas diffusion layer made of a conventional porous material layer (made of PAN-based carbon fiber) from the viewpoint of conductivity. In addition, unlike the normal PAN-based carbon fiber, the PAN-based carbonized fiber in the present invention does not perform graphitization, and thus can greatly reduce the cost.

  Both the carbon fiber and “conductive carbon” are detected as carbon (C) by Auger electron spectroscopy (AES). Therefore, the two cannot be distinguished. Therefore, on the premise that the conductive carbon layer is necessarily formed on the constituent elements of the intermediate layer when the intermediate layer before forming (stacking) the conductive carbon layer is formed (laminated), AES surface mapping was performed on the carbon fibers and the constituent metals of the intermediate layer. Through such a process, the ratio of “conductive carbon” to the carbon fiber was calculated.

[Reference Example 1]
The ratio of Au to conductive carbon (Au / conductive carbon) and contact angle when a hydrophilic layer made of gold (Au) was stacked on the conductive carbon layer were determined.

  The chamber was evacuated to about 3 to 10 Pa with respect to the gas diffusion layer obtained in Example 1, and then argon (Ar) gas was introduced to about 1 Pa. The temperature of the fuel cell gas diffusion layer (fuel cell GDL) itself was set to 80 ° C. without considering the GDL material.

  During UBMS sputtering, a bias voltage of 140 V was applied to the gas diffusion layer without considering the material of the porous material layer. And 99% or more of Au was used as a target. In this way, an Au layer (hydrophilic layer) having a thickness of 5 nm was laminated on the surface of the conductive carbon layer.

  Since the base material (porous material layer) is porous, the arrangement of Au was calculated by Auger electron spectroscopy (AES) surface mapping and image analysis. And the static contact angle of water with respect to the area ratio of electroconductive carbon and Au was measured. Here, the contact angle was measured in accordance with JIS K6768. More specifically, the static contact angle was measured using pure water (6 μL) under the conditions of 24 ° C. (room temperature) and humidity (RH) 49%. As a measuring device, DM700 (θ / 2 method) manufactured by Kyowa Interface Science Co., Ltd. was used. A graph of the measurement results is shown in FIG. The unit of the contact angle on the vertical axis is “degree”.

  In the absence of Au (negative control), the known and known carbon contact angle was around 85 degrees. In contrast, it was confirmed that the hydrophilicity increased in proportion to the amount of Au arranged.

[Reference Example 2]
The resistance reduction effect when sputtering while dispersing Au on the surface of the conductive carbon layer was investigated.

  The chamber was evacuated to about 3 to 10 Pa with respect to the gas diffusion layer obtained in Example 1, and then about 5 Pa of argon (Ar) gas was introduced. The temperature of the fuel cell gas diffusion layer (fuel cell GDL) itself was set to 80 ° C. without considering the GDL material.

  During UBMS sputtering, a bias voltage of 140 V was applied to the gas diffusion layer without considering the material of the porous material layer. And 99% or more of Au was used as a target. At that time, the contact resistance of the gas diffusion layer was measured in parallel with Au being sputtered on the surface of the conductive carbon layer. The resulting graph is shown in FIG.

  As in Example 1, a sufficiently small contact resistance can be ensured by disposing a conductive carbon layer in the gas diffusion layer. However, as shown in FIG. 16, it was confirmed that contact resistance can be further reduced by further arranging Au. In addition, the presence of the hydrophilic layer in the gas diffusion layer makes it possible to quickly discharge water from the catalyst layer to the separator side. When the hydrophilic layer is made of a metal oxide, such “hydrophilization” is obtained. On the other hand, when the hydrophilic layer is composed of a non-metal oxide (Au or the like), in addition to the hydrophilic property, the conductivity is extremely excellent, so that an effect of reducing contact resistance can be obtained.

1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to one embodiment of the present invention. It is sectional drawing which shows schematic structure of the part of a gas diffusion layer among FIG. It is the schematic which represented the surface of the porous material layer microscopically. It is the schematic which shows the change of the fiber in each process of manufacture of a PAN-type carbon fiber. It is the photograph (magnification: 400,000 times) which observed the section of the conductive member (conductive member A) which has the conductive carbon layer of R = 1.0-1.2 with the transmission electron microscope (TEM). It is the photograph (magnification: 400,000 times) which observed the section of the conductive member (conductive member B) which has the conductive carbon layer of R = 1.6 by TEM. It is a schematic diagram which shows the 3 times symmetrical pattern of an average peak in the rotational anisotropy measurement of a Raman scattering spectroscopy analysis. It is a schematic diagram which shows the 2 times symmetrical pattern of an average peak in the rotational anisotropy measurement of a Raman scattering spectroscopy analysis. It is a schematic diagram which shows the pattern which does not show the symmetry of an average peak in the rotational anisotropy measurement of a Raman scattering spectroscopy analysis. It is a graph which shows the Raman spectrum when the electrically conductive member B is used as a measurement sample and the rotation angles of the sample are 0 °, 60 ° and 180 °, respectively. 5 is a graph showing an average peak of rotational anisotropy measurement for conductive member B. The Vickers hardness of the conductive carbon layer and the sp3 ratio of the conductive carbon layer in several conductive members in which the Vickers hardness of the conductive carbon layer is made different by changing the bias voltage and the film formation method in the sputtering method. It is a figure which shows the relationship with the value of. It is a graph which shows the result of having measured contact resistance about several electrically-conductive members which have an R value is 1.3 or more, and has the conductive carbon layer from which content of a hydrogen atom differs. It is the schematic which shows the film-forming (lamination | stacking) apparatus of the intermediate | middle layer and conductive carbon layer on or in the surface of the porous material layer using sputtering method. It is a figure which shows the manufacturing process of a general PAN-type carbon fiber, and the manufacturing process of the PAN-type carbon fiber in this invention. It is the schematic of the vehicle carrying the fuel cell stack of one Embodiment of this invention. It is a figure which shows the measuring method of the contact resistance of GDL for fuel cells obtained by the Example and each comparative example, and a separator. It is a graph corresponding to the result regarding the contact resistance of Example 1 shown in Table 1. It is a graph which shows the measurement result of the static contact angle of water with respect to the area ratio of electroconductive carbon and Au computed by the surface mapping and image analysis of AES. It is a graph which shows the resistance reduction effect at the time of carrying out sputtering, disperse | distributing Au on the surface of a conductive carbon layer.

Explanation of symbols

1 polymer electrolyte fuel cell (PEFC),
2 solid polymer electrolyte membrane,
3a anode catalyst layer,
3c cathode catalyst layer,
4a Anode gas diffusion layer,
4c cathode gas diffusion layer,
5a anode separator,
5c cathode separator,
6a Anode gas flow path,
6c cathode gas flow path,
7 Refrigerant flow path,
10 Membrane electrode assembly (MEA),
51, 62 Gas diffusion layer,
52, 72 porous material layer,
53 Carbon fiber (CF),
54 conductive carbon layer,
56 middle class,
58 hydrophilic layer,
60 separator,
61 Fuel cell vehicle,
62 Fuel cell stack,
64 chambers,
66 Gas exhaust port,
68 Atmospheric gas inlet,
70 Target.

Claims (12)

A porous material layer;
A gas diffusion layer for a fuel cell comprising a conductive carbon layer or conductive carbon particles present on or in the surface of the porous material layer,
In the conductive carbon layer or the conductive carbon particles, the intensity ratio R (I _D / I _G ) of _D -band peak intensity I _D and G-band peak intensity I _G measured by Raman scattering spectroscopy is 1.3. A gas diffusion layer for a fuel cell, wherein the average peak measured by rotational anisotropy measurement by Raman scattering spectroscopic analysis of the conductive carbon layer shows a two-fold symmetry pattern. The conductive carbon layer is present on the surface of the porous material layer;
Between the conductive carbon layer and the porous material layer, further comprising an intermediate layer composed of a metal, a fuel cell gas diffusion layer according to 請 Motomeko 1. The conductive carbon layer is present on the surface of the porous material layer;
3. The fuel cell according to claim 1, further comprising a hydrophilic layer formed of at least one selected from the group consisting of metal, metal nitride, metal carbide, and metal oxide on the conductive carbon layer. Gas diffusion layer.   The gas diffusion layer for a fuel cell according to any one of claims 1 to 3, wherein the porous material layer includes one or more selected from the group consisting of carbon fiber, metal fiber, and organic fiber.   The gas diffusion layer for a fuel cell according to claim 4, wherein the carbon fibers are polyacrylonitrile (PAN) -based or pitch-based carbon fibers and are carbonized fibers that do not include graphitized fibers.   The gas diffusion layer for a fuel cell according to claim 4, wherein the porous material layer includes metal fibers, and the conductive carbon layer or the conductive carbon particles cover 50% or more of the surface of the porous material layer.   The said metal has 1 or more types selected from the group which consists of a metal element which comprises a noble metal or a metal separator base material, and the surface treatment of a separator, In any one of Claims 3-6 The gas diffusion layer for fuel cells as described. The method for producing a gas diffusion layer for a fuel cell according to any one of claims 1 to 7, comprising a step of forming a conductive carbon layer or conductive carbon particles on or in the surface of the porous material layer. And
The step (a) of forming the conductive carbon layer or the conductive carbon particles is performed by a sputtering method using conductive carbon as a target, and is a method for manufacturing a gas diffusion layer for a fuel cell. After the step (a), by sputtering using one or more selected from the group consisting of metal, metal nitride, metal carbide and metal oxide, or
After the step (a), by metal plating,
The manufacturing method of the gas diffusion layer for fuel cells of Claim 8 which performs the process (b) of forming a hydrophilization layer.   The method for producing a gas diffusion layer for a fuel cell according to claim 9, wherein the metal used in the plating process is a noble metal or a metal element constituting a metal separator substrate.   The porous material layer includes polyacrylonitrile (PAN) -based or pitch-based carbon fibers, and when the PAN-based or pitch-based carbon fibers are manufactured, the carbonization processing is finished without performing graphitization processing. The manufacturing method of the gas diffusion layer for fuel cells of any one of 10-10. Consisting comprises a gas diffusion layer obtained by the method according to any one of the gas diffusion layer or claim 8-11 according to any one of 請 Motomeko 1-7, a polymer electrolyte fuel battery.