JP2016081770A - Gas diffusion layer for fuel battery and fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas diffusion layer for fuel battery capable of improving both of conductivity and durability.SOLUTION: The gas diffusion layer for fuel battery includes: porous layers 22 and 42 which contain at least one conductive material selected from a group including an aluminum carbide (AlC), a titanium nitride (TiN), a zirconium nitride (ZrN), and a foam metal coated with a material having a corrosion resistance property.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fuel cell gas diffusion layer and a fuel cell having a fuel cell gas diffusion layer.

  A fuel cell is a device that generates electrical energy from hydrogen and oxygen, and can achieve high power generation efficiency. The main features of the fuel cell are direct power generation that does not go through the process of thermal energy or kinetic energy as in the conventional power generation method, so high power generation efficiency can be expected even on a small scale, and emissions of nitrogen compounds, etc. There are few, and noise and vibration are also small, and environmental properties are good. In this way, fuel cells can be used effectively for the chemical energy of fuel and have environmentally friendly characteristics, so they are expected as energy supply systems for the 21st century, and are widely used in space, automobiles and portable devices. It is attracting attention as a promising new power generation system that can be used for various applications from scale power generation to small-scale power generation, and technological development is in full swing toward practical use.

  Patent Document 1 discloses a fuel cell in which a catalyst layer, a gas diffusion layer, and a separator are sequentially laminated on both surfaces of a polymer electrolyte membrane. The gas diffusion layer of the fuel cell is made of a conductive carbon sheet, and has a fluid flow path on the surface in contact with the separator.

International Publication No. 11/045889 Pamphlet

  In order to improve the performance of the fuel cell, the gas diffusion layer of the fuel cell is required to have improved conductivity. In addition, there is a demand for improving the durability of the fuel cell, and hence the durability of the gas diffusion layer is also required. In order to improve the electroconductivity of a gas diffusion layer, it is possible to use a metal for a gas diffusion layer, However In this case, there existed a possibility that the durability of a gas diffusion layer might fall.

  The present invention has been made in view of such a situation, and an object thereof is to provide a technique for achieving both improvement in conductivity and improvement in durability in a gas diffusion layer for a fuel cell.

One embodiment of the present invention is a gas diffusion layer for a fuel cell. The fuel cell gas diffusion layer is at least one selected from the group consisting of aluminum carbide (Al ₄ C ₃ ), titanium nitride (TiN), zirconium nitride (ZrN), and foam metal coated with a corrosion-resistant material. A porous layer containing two conductive materials.

  Another embodiment of the present invention is a fuel cell. The fuel cell includes a membrane electrode assembly including an electrolyte membrane, an anode catalyst layer disposed on one surface side of the electrolyte membrane, and a cathode catalyst layer disposed on the other surface side of the electrolyte membrane, and a membrane electrode An anode gas diffusion layer disposed on the anode catalyst layer side of the assembly, and a cathode gas diffusion layer disposed on the cathode catalyst layer side of the membrane electrode assembly. At least one of the anode gas diffusion layer and the cathode gas diffusion layer is constituted by the fuel cell gas diffusion layer of the above aspect.

  ADVANTAGE OF THE INVENTION According to this invention, the technique which aims at coexistence with the improvement of electroconductivity and durability in the gas diffusion layer for fuel cells can be provided.

1 is a perspective view schematically showing the structure of a fuel cell according to an embodiment. It is a schematic sectional drawing along the AA line of FIG. It is a graph which shows the relationship between the lifetime of a gas diffusion layer for fuel cells, and resistivity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

  FIG. 1 is a perspective view schematically showing the structure of a fuel cell according to an embodiment. FIG. 2 is a schematic cross-sectional view along the line AA in FIG. The fuel cell 1 of the present embodiment includes a substantially flat membrane electrode assembly 10 and an anode gas diffusion layer 20 and a cathode gas diffusion layer 40 as gas diffusion layers for a fuel cell. Hereinafter, when the anode gas diffusion layer 20 and the cathode gas diffusion layer 40 are not distinguished, they are collectively referred to as a fuel cell gas diffusion layer. The anode gas diffusion layer 20 and the cathode gas diffusion layer 40 are provided so that their main surfaces face each other with the membrane electrode assembly 10 interposed therebetween. In addition, separators 2 and 4 are provided on the main surface sides of the anode gas diffusion layer 20 and the cathode gas diffusion layer 40 opposite to the membrane electrode assemblies 10. In the present embodiment, a set of membrane electrode assemblies 10, an anode gas diffusion layer 20, and a cathode gas diffusion layer 40 are shown, but a plurality of sets are stacked via separators 2 and 4, thereby forming a fuel cell stack. Also good.

  The membrane electrode assembly 10 includes an electrolyte membrane 12, an anode catalyst layer 14 disposed on one surface side of the electrolyte membrane 12, and a cathode catalyst layer 16 disposed on the other surface side of the electrolyte membrane 12.

  The electrolyte membrane 12 exhibits good ion conductivity in a wet state, and functions as an ion exchange membrane that moves protons between the anode catalyst layer 14 and the cathode catalyst layer 16. The electrolyte membrane 12 is formed of a solid polymer material such as a fluorine-containing polymer or a non-fluorine polymer. As a material of the electrolyte membrane 12, a sulfonic acid type perfluorocarbon polymer, a polysulfone resin, a perfluorocarbon polymer having a phosphonic acid group or a carboxylic acid group, or the like can be used. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (manufactured by DuPont: registered trademark) 112. Examples of the non-fluorine polymer include sulfonated aromatic polyetheretherketone and polysulfone. The thickness of the electrolyte membrane 12 is, for example, not less than 10 μm and not more than 200 μm.

  The anode catalyst layer 14 and the cathode catalyst layer 16 have ion exchange resin and catalyst particles, and optionally carbon particles supporting the catalyst particles. The ion exchange resin included in the anode catalyst layer 14 and the cathode catalyst layer 16 connects the catalyst particles and the electrolyte membrane 12 and plays a role of transmitting protons therebetween. This ion exchange resin can be formed from the same polymer material as the electrolyte membrane 12. Catalyst particles include Sc, Y, Ti, Zr, V, Nb, Fe, Co, Ni, Ru, Rh, Pd, Pt, Os, Ir, alloys selected from lanthanoid elements and actinoid elements, A catalytic metal such as a simple substance can be mentioned. As the carbon particles, acetylene black, ketjen black, carbon nanotubes and the like can be used. The thicknesses of the anode catalyst layer 14 and the cathode catalyst layer 16 are, for example, 10 μm or more and 40 μm or less, respectively.

  The anode gas diffusion layer 20 is disposed on the anode catalyst layer 14 side of the membrane electrode assembly 10. The anode gas diffusion layer 20 has a porous layer 22 and a fluid flow path 24. The thickness of the anode gas diffusion layer 20 is, for example, not less than 50 μm and not more than 500 μm.

The porous layer 22 is at least one conductive selected from the group consisting of aluminum carbide (Al ₄ C ₃ ), titanium nitride (TiN), zirconium nitride (ZrN), and foam metal coated with a corrosion resistant material. Contains material and has a large number of fine pores. The porous layer 22 is preferably a layer mainly composed of the conductive material. The mass of the conductive material described above with respect to the total mass of the porous layer 22 is preferably 50% by mass or more, and more preferably 80% by mass or more.

Al ₄ C ₃ is also called carbon aluminum or aluminum carbide. As the aluminum carbide, for example, a filler or particles can be used. TiN and ZrN can be used in the form of particles, for example. As the foam metal, for example, a surface obtained by subjecting a surface of a foamed urethane sheet to Ni plating treatment or Al plating treatment and then burning urethane by heating can be used. The corrosion-resistant material coated on the surface of the foam metal has corrosion resistance to a substance that contacts the anode gas diffusion layer 20 during operation of the fuel cell 1, such as fuel gas, air, water, etc., and conductivity. It is. For example, carbon, Al ₄ C ₃ , TiN, ZrN, or the like can be used as the corrosion resistant material. The coating of the corrosion resistant material on the surface of the foam metal can be performed by a known method such as immersion of the foam metal in a slurry containing the corrosion resistant material or spray application of the slurry to the foam metal.

  The fluid flow path 24 has a groove shape and is provided on one main surface of the porous layer 22. The fluid flow path 24 is configured by a recess provided on the main surface of the porous layer 22. The fluid flow path 24 is disposed on the separator 2 side and functions as a fuel gas flow path. Fuel gas such as hydrogen gas is distributed to a fluid flow path 24 from a fuel supply manifold (not shown), and passes through the porous layer 22 from the fluid flow path 24 to the anode catalyst layer 14 of the membrane electrode assembly 10. Supplied.

  The dimensions of the fluid channel 24 are, for example, a depth of 30 μm to 450 μm, a width of 100 μm to 1000 μm, and a distance between adjacent fluid channels 24 of 100 μm to 1000 μm. In the present embodiment, five fluid flow paths 24 are provided, but the number is not particularly limited, and may be appropriately set according to the size of the anode gas diffusion layer 20 and the fluid flow path 24. Can do.

  The cathode gas diffusion layer 40 is disposed on the cathode catalyst layer 16 side of the membrane electrode assembly 10. The cathode gas diffusion layer 40 includes a porous layer 42 and a fluid flow path 44. The thickness of the cathode gas diffusion layer 40 is, for example, not less than 50 μm and not more than 500 μm.

The porous layer 42 contains at least one conductive material selected from the group consisting of Al ₄ C ₃ , TiN, ZrN, and foam metal coated with a corrosion-resistant material, and has a large number of fine pores. Have. Since Al ₄ C ₃ , TiN, ZrN, and foam metal contained in the porous layer 42 are the same as those contained in the porous layer 22, detailed description thereof is omitted. The corrosion-resistant material covering the surface of the foam metal used for the porous layer 42 is a substance that contacts the cathode gas diffusion layer 40 during operation of the fuel cell 1, such as an oxidant gas or air (when the air is an oxidant gas). In other words, it has corrosion resistance to water and the like and conductivity. For example, carbon, Al ₄ C ₃ , TiN, ZrN, or the like can be used as the corrosion resistant material. The method of covering the surface of the foam metal with the corrosion resistant material is the same as that for the porous layer 22.

  The fluid flow path 44 has a groove shape and is provided on one main surface of the porous layer 42. The fluid flow path 44 is configured by a recess provided on the main surface of the porous layer 42. The fluid channel 44 is disposed on the separator 4 side and functions as a channel for the oxidant gas. An oxidant gas such as air is distributed from a manifold (not shown) for supplying an oxidant to the fluid flow path 44, passes through the porous layer 42 from the fluid flow path 44, and the cathode catalyst layer 16 of the membrane electrode assembly 10. To be supplied. The fluid flow path 44 also functions as a drainage path for water generated in the cathode catalyst layer 16. The dimensions and the number of installed fluid channels 44 are the same as those of the fluid channel 24 of the anode gas diffusion layer 20.

  A structure in which the anode catalyst layer 14 and the anode gas diffusion layer 20 are stacked may be referred to as an anode, and a structure in which the cathode catalyst layer 16 and the cathode gas diffusion layer 40 are stacked may be referred to as a cathode.

In the polymer electrolyte fuel cell 1 described above, the following reaction occurs. That is, when hydrogen gas as a fuel gas is supplied to the anode catalyst layer 14 through the anode gas diffusion layer 20, a reaction represented by the following formula (1) occurs in the anode catalyst layer 14, and hydrogen is decomposed into protons and electrons. Is done. Protons move through the electrolyte membrane 12 toward the cathode catalyst layer 16 side. The electrons move to the external circuit (not shown) via the anode gas diffusion layer 20 and the separator 2, and flow into the cathode catalyst layer 16 via the separator 4 and the cathode gas diffusion layer 40 from the external circuit. On the other hand, when air as an oxidant gas is supplied to the cathode catalyst layer 16 through the cathode gas diffusion layer 40, a reaction represented by the following formula (2) occurs in the cathode catalyst layer 16, and oxygen in the air is converted into protons and oxygen. It reacts with electrons to become water. As a result, electrons flow from the anode toward the cathode in the external circuit, and electric power can be taken out.
Anode catalyst layer 14: H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode catalyst layer 16: 2H ⁺ + (1/2) O ₂ + 2e ⁻ → H ₂ O (2)

(Manufacturing process of gas diffusion layer for fuel cells)
When the porous layers 22 and 42 are gas diffusion layers for fuel cells containing Al ₄ C ₃ , TiN or ZrN, a mixture of these particles and a binder resin is processed by a known method such as press molding. Thus, a gas diffusion layer for a fuel cell can be manufactured. Binder resins include PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), ETFE (tetrafluoroethylene / ethylene copolymer). Fluorine resin such as (polymer) can be used. When the porous layers 22 and 42 are gas diffusion layers for a fuel cell containing a foam metal, a gas diffusion layer for a fuel cell is manufactured by processing the foam metal sheet by a known method such as press molding. Can do.

As described above, the gas diffusion layer for a fuel cell according to the present embodiment is at least one conductive material selected from the group consisting of Al ₄ C ₃ , TiN, ZrN, and foam metal coated with a corrosion-resistant material. The porous layers 22 and 42 containing the material are provided.

Since the porous layers 22 and 42 contain Al ₄ C ₃ , the conductivity of the fuel cell gas diffusion layer can be improved as compared with a conventionally known carbon gas diffusion layer. Thereby, the resistance overvoltage of the fuel cell 1 can be reduced, and the output of the fuel cell 1 can be improved. Further, the corrosion resistance of the fuel cell gas diffusion layer can be improved as compared with the conventional case. Thereby, the durability of the gas diffusion layer for a fuel cell, and thus the durability of the fuel cell 1 can be improved.

  Further, since the porous layers 22 and 42 contain TiN or ZrN, the conductivity of the gas diffusion layer for a fuel cell can be improved as compared with the conventional case. Thereby, the resistance overvoltage of the fuel cell 1 can be reduced, and the output of the fuel cell 1 can be improved. Further, the corrosion resistance of the fuel cell gas diffusion layer can be improved as compared with the conventional case. Thereby, the durability of the gas diffusion layer for a fuel cell, and thus the durability of the fuel cell 1 can be improved. Furthermore, TiN and ZrN can easily control the particle diameter of each, so that the porosity or air permeability of the fuel cell gas diffusion layer can be increased more reliably. Thereby, the diffusibility of the gas in the gas diffusion layer for fuel cells can be improved, and the gas can be diffused uniformly throughout the gas diffusion layer for fuel cells. For this reason, the diffusion overvoltage of the fuel cell 1 can be reduced.

  Moreover, the electroconductivity of the gas diffusion layer for fuel cells can be improved compared with the past by containing the foam metal by which the porous layers 22 and 42 were coat | covered with the corrosion-resistant material. Thereby, the resistance overvoltage of the fuel cell 1 can be reduced, and the output of the fuel cell 1 can be improved. Further, the corrosion resistance of the fuel cell gas diffusion layer can be improved as compared with the conventional case. Thereby, the durability of the gas diffusion layer for a fuel cell, and thus the durability of the fuel cell 1 can be improved. Further, the foam metal has a large number of voids, and the porosity or air permeability of the fuel cell gas diffusion layer can be easily controlled by selecting urethane materials having different foaming properties. Thereby, the diffusibility of the gas in the gas diffusion layer for fuel cells can be improved, and the gas can be diffused uniformly throughout the gas diffusion layer for fuel cells. For this reason, the diffusion overvoltage of the fuel cell 1 can be reduced. Further, since the metal foam can be easily reduced in thickness by press molding or the like, the fuel cell 1 can be reduced in thickness, whereby the output density of the fuel cell 1 can be improved.

  The gas diffusion layer for a fuel cell according to the present embodiment includes groove-like fluid flow paths 24 and 44 provided on one main surface of the porous layers 22 and 42. By providing the fluid passages 24 and 44 in the porous layers 22 and 42, the fluid passages 24 and 44 having desired dimensions can be easily formed as compared with the case where the fluid passages are formed on the separators 2 and 4 side. be able to. Further, the depth of the fluid flow path can be reduced as compared with the case where the fluid flow path is formed on the separators 2 and 4 side. For this reason, the thickness of the porous layers 22 and 42 and the separators 2 and 4 can be made thin. Therefore, the fuel cell 1 can be thinned and the output density of the fuel cell 1 can be improved. When the porous layers 22 and 42 are made of foam metal, the fluid flow paths 24 and 44 can be easily formed by press molding or the like.

Further, when the fluid flow paths 24 and 44 are formed in the porous layers 22 and 42, the contact area between the fuel cell gas diffusion layer and the separators 2 and 4 decreases. For this reason, it exists in the tendency for the current collection performance in the fuel cell 1 to fall. On the other hand, in the present embodiment, the porous layers 22 and 42 contain at least one of Al ₄ C ₃ , TiN, ZrN, and foam metal, thereby improving the conductivity of the fuel cell gas diffusion layer. Yes. Therefore, the above-described effects due to the formation of the fluid flow paths 24 and 44 can be obtained, and a decrease in the current collection performance of the fuel cell 1 can be suppressed.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. Embodiments to which such modifications are added Can also be included in the scope of the present invention.

In the embodiment described above, the anode gas diffusion layer 20 and the cathode gas diffusion layer 40 are both porous layers 22 and 42 containing at least one of Al ₄ C ₃ , TiN, ZrN, and foam metal, and the fluid flow path. 24, 44. However, it is not particularly limited to this, and only one of the anode gas diffusion layer 20 and the cathode gas diffusion layer 40 may have the above-described configuration. Further, the fluid flow paths 24 and 44 may not be provided. A microporous layer (MPL) may be provided between the membrane electrode assembly 10 and the fuel cell gas diffusion layer.

  EXAMPLES The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

<Evaluation of conductivity and durability of gas diffusion layer for fuel cell>
(Example)
The fuel cell gas diffusion layer according to the example was formed as follows. That is, 35% by mass of acetylene black as a carbon material, 35% by mass of ketjen black, and 20% by mass of a carbon aluminum material and 10% by mass of PTFE as a binder were charged into a predetermined amount of solvent to prepare a solution. Then, the obtained solution was kneaded and dispersed, and formed into a sheet having a thickness of 300 μm by an extrusion molding machine to produce a gas diffusion layer for a fuel cell.

The carbon aluminum material used for the gas diffusion layer can be formed by the following method, for example. That is, first, an aluminum foil is prepared. And the carbon material which consists of acetylene black with an average particle diameter of 0.3 micrometer is apply | coated on this aluminum foil. Subsequently, the aluminum foil coated with the carbon material is rolled in a state of being heated to 300 ° C. or higher to form an Al ₄ C ₃ alloy layer made of aluminum and carbon. In addition, the heating temperature should just be more than an alloying temperature. The thickness of the alloy layer is about 1 μm according to SIMS analysis. Further, the alloy layer of the Al ₄ C ₃ composition has a certain degree of variation from the stoichiometric composition, and this variation becomes more remarkable at the interface between aluminum and Al ₄ C ₃ . Subsequently, the alloy layer having the Al ₄ C ₃ composition thus prepared can be mechanically or chemically peeled and collected to obtain a carbon aluminum material. The carbon aluminum material can be used as a part or all of the material of the gas diffusion layer. Acetylene black is used for the production of the carbon aluminum material, but ketjen black may be used. In this case, since ketjen black is more hydrophilic than acetylene black, the drainage of the cathode gas diffusion layer of the fuel cell can be improved, and the voltage in the high current density region of the fuel cell can be improved. .

(Comparative example)
The fuel cell gas diffusion layer according to the comparative example was formed as follows. That is, 45% by mass of acetylene black as a carbon material and 45% by mass of ketjen black and 10% by mass of PTFE as a binder were charged into a predetermined amount of solvent to prepare a solution. The obtained solution was kneaded and dispersed, and formed into a sheet having a thickness of 300 μm by an extrusion molding machine to prepare a gas diffusion layer for a fuel cell.

(Measurement of resistivity)
And about each gas diffusion layer for fuel cells of an Example and a comparative example, the resistivity was measured as follows and electroconductivity was evaluated. That is, the copper plate which gave gold plating was provided in each of the surface and back surface of each gas diffusion layer for fuel cells of an Example and a comparative example. Then, using this copper plate as a lead electrode, an AC impedance of 1 kHz was measured at a temperature of 25 ° C. Impedance was measured every time a predetermined life time passed. The resistance value of the obtained impedance was normalized by the sheet thickness of each fuel cell gas diffusion layer, and the resistivity of each fuel cell gas diffusion layer was calculated. The obtained results are shown in FIG. FIG. 3 is a graph showing the relationship between the life time and the resistivity of the fuel cell gas diffusion layer.

As shown in FIG. 3, it was confirmed that the fuel cell gas diffusion layer of the example had a lower resistivity at any life time than the fuel cell gas diffusion layer of the comparative example. From this, it was confirmed that the conductivity of the gas diffusion layer for fuel cells is improved by containing Al ₄ C ₃ in the porous layer. Further, it was confirmed that the change in resistivity of the fuel cell gas diffusion layer of the example with the passage of life time was smaller than that of the fuel cell gas diffusion layer of the comparative example. From this, it was confirmed that the durability of the gas diffusion layer for fuel cells is improved by containing Al ₄ C ₃ in the porous layer.

  DESCRIPTION OF SYMBOLS 1 Fuel cell, 10 Membrane electrode assembly, 12 Electrolyte membrane, 14 Anode catalyst layer, 16 Cathode catalyst layer, 20 Anode gas diffusion layer, 22, 42 Porous layer, 24, 44 Fluid flow path, 40 Cathode gas diffusion layer

Claims (3)

Porous containing at least one conductive material selected from the group consisting of aluminum carbide (Al ₄ C ₃ ), titanium nitride (TiN), zirconium nitride (ZrN), and foam metal coated with a corrosion resistant material A gas diffusion layer for a fuel cell comprising a layer.     The gas diffusion layer for a fuel cell according to claim 1, further comprising a groove-like fluid flow path provided on one main surface of the porous layer. A membrane electrode assembly comprising an electrolyte membrane, an anode catalyst layer disposed on one surface side of the electrolyte membrane, and a cathode catalyst layer disposed on the other surface side of the electrolyte membrane;
An anode gas diffusion layer disposed on the anode catalyst layer side of the membrane electrode assembly;
A cathode gas diffusion layer disposed on the cathode catalyst layer side of the membrane electrode assembly,
3. The fuel cell according to claim 1, wherein at least one of the anode gas diffusion layer and the cathode gas diffusion layer is constituted by the gas diffusion layer for a fuel cell according to claim 1.

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