JP2001236967A - Separator for solid polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a solid polymer electrolyte having high electric conductivity and high corrosion resistance. SOLUTION: In a fuel cell, a unit holding a solid polymer electrolyte layer and a catalyst electrode layer arranged on either side of the solid polymer electrolyte layer between a gas dispersing electrode and a separator on either external side thereof is used as a single cell, and a plurality of such cells are laminated to form a laminated body for a fuel cell. The separator consists of a coated layer and a metal base substance. The coated surface layer has a multi-layer construction consisting of two or more metal nitrided membrane layers of different types.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid polymer electrolyte fuel cell separator having good corrosion resistance and conductivity and low internal resistance.

[0002]

2. Description of the Related Art A fuel cell is known as a device for directly converting energy of fuel into electricity. Among them, a fuel cell using a solid polymer electrolyte is composed of a fuel gas containing hydrogen and an oxidizing gas containing oxygen such as air.
It is supplied to a pair of electrodes and generates an electromotive force and heat simultaneously by an electrochemical reaction occurring at both electrodes.

The structure of a single cell of the present fuel cell is, for example,
On both surfaces of the polymer electrolyte membrane that selectively transports hydrogen ions, a catalytic reaction layer mainly composed of a carbon powder carrying a platinum-based metal catalyst, and then on both outer surfaces of the catalytic reaction layer,
Two types of diffusion layers having both gas permeability and oxidant gas permeability and electronic conductivity, and the diffusion layer and the catalytic reaction layer are combined to form electrodes, each of which has a fuel electrode (anode) and an air electrode (cathode). being called. Further, a separator is provided on both sides of the separator via a gasket, and a flow path for an oxidizing gas such as a fuel gas or oxygen is formed on a surface on the electrode side of the separator. These fuel cells and the separator form a single fuel cell unit. However, the fuel cell has a low electromotive force per single cell, and therefore is usually used as a stack of a plurality of units.

In the operation principle of such a fuel cell,
The separator must have good conductivity in order to electrically connect the cells. Further, the temperature of the fuel gas and the oxidizing gas is in a high temperature state of 80 to 90 ° C., and since the separator is exposed to each gas, high corrosion resistance and oxidation resistance are required. Therefore, it is generally considered to use carbon material for the separator (TOYO
TA Technical Review Vol. 47, No. 2, Nov. 1997, p. 70-
75, and JP-A-7-272731).

[0005]

However, the solid polymer electrolyte fuel cell separator provided with the conventional battery stack as described above has the following problems.

[0006] First, in a solid polymer electrolyte fuel cell having a separator provided with a carbon plate, the carbon material is poor in toughness, so that it is mounted on a vehicle, for example, under conditions where stresses other than mechanical shock, vibration and compression exist. In such a case, it has been considered that the separator is damaged by vibration. Therefore,
In order to maintain the strength as a separator, it is necessary to use a separator made of a relatively thick carbon plate,
In order to make the battery stack compact, it is important to reduce the thickness of the unit cell. When a separator made of a carbon plate is used as described above, there is a problem that it is difficult to reduce the size of the separator because there is a limit in reducing the thickness.

[0007] Further, since machining of a carbon plate is difficult, there is a problem that machining cost of a separator using a carbon material is high, and it is difficult to reduce the cost.
Furthermore, since the carbon plate has a poorer thermal conductivity than a metal plate of aluminum, stainless steel, copper, etc., there is a problem that a cooling plate for cooling each unit cell becomes large. There was a problem that it was difficult.

[0008] Therefore, a method of using a metal plate having good electrical conductivity and current collecting performance and having high thermal conductivity has been studied. However, since the separator is exposed to a potential of about 1 V due to the electrode reaction and to a gas at about 80 ° C. containing supplied air and hydrogen and water vapor, the environmental conditions are severe, and the metal having the required corrosion resistance is required. Alternatively, many alloy materials are expensive. Relatively inexpensive stainless steel and aluminum alloys have insufficient corrosion resistance, so if they are used for a long period of time, the metal plate is likely to corrode and melt. Gradually rise. As a result, Joule heat is generated, and the power generation efficiency of the fuel cell stack in which a large number of cells are stacked gradually decreases, and the temperature of the battery stack tends to increase.

To solve this problem, see, for example, JP-A-10-3
According to Japanese Patent Application Laid-Open No. 08226, the solid substrate is characterized in that the separator substrate is made of aluminum, iron, stainless steel, or the like, and a carbon-containing film is attached to at least a surface of the surface that contacts the gas diffusion electrode. Molecular electrolyte fuel cells have been proposed. However, since such a carbon film has low mechanical strength, that is, low film hardness, there is a problem that the carbon film is damaged by vibrations during mounting on a vehicle and the corrosion resistance is impaired.

Also, for example, JP-A-10-12246, JP-A-10-162842, and JP-A-11-162.
JP-A-162478 and JP-A-11-162479 disclose a solid polymer electrolyte fuel cell characterized by being coated with a metal nitride film or the like.
However, a single-layer film of various nitrides has a large internal residual stress in the film, and tends to cause film defects such as film cracking, peeling or pinholes generated during film formation, and it is difficult to maintain corrosion resistance for long-term use. There was a problem.

The present invention has been made in view of the above prior art, and has as its object to provide a solid polymer electrolyte fuel cell separator having excellent corrosion resistance and low internal resistance.

[0012]

According to the present invention, there is provided a separator for a solid polymer electrolyte fuel cell, comprising: a solid polymer electrolyte layer;
A unit in which the catalyst electrode layers disposed on both surfaces are sandwiched between the gas diffusion electrodes and the separator from both outer surfaces is a single cell, and the unit is used in a fuel cell having a structure in which a plurality of such single cells are stacked to form a fuel cell stack. The separator is characterized in that the separator has a multilayer structure including a coating layer and a metal substrate, and the surface coating layer includes two or more layers of different types of metal nitride films. Moreover,
It is preferable that at least the outermost surface layer of the surface coating layer is a conductive metal nitride film.

According to the present invention, since an arbitrary metal separator substrate is coated with a conductive metal nitride film having excellent corrosion resistance, an increase in contact resistance on the separator surface due to corrosion can be prevented.

Further, in the present invention, the separator substrate may be a metal having sufficient mechanical strength as a fuel cell for a vehicle, and further having good workability, electrical conductivity, thermal conductivity, and the like. Not something. Further, the shape is not particularly limited, but a shape having a structure having sufficient strength as a vehicle-mounted fuel cell is desirable.

[0015]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a schematic longitudinal sectional view of one embodiment of a single cell of a solid polymer electrolyte fuel cell using the separator of the present invention. In FIG. 1, reference numeral 1 denotes a solid polymer electrolyte membrane, which is composed of a proton-conductive ion-exchange membrane exhibiting good electric conductivity in a wet state, and a plurality of which includes carbon particles carrying a catalyst such as platinum on both sides thereof. One cell (single cell) is formed by the gas diffusion electrodes 4, 5, which are further provided outside, and the separators 6, 7, which are further provided outside thereof. Be composed.

In such a cell, the base 10 is formed into a required shape as a separator by mechanical processing such as press forming, punching or the like. One side of the separator is provided between the gas diffusion electrode 4 and the fuel gas path 8. The other surface is formed between the gas diffusion electrode 5 and the oxidant gas path 9.
Are formed. Gas diffusion electrode 4 through gas passage 8
When a fuel gas containing hydrogen flows through the gas flow path 9 and an oxidizing gas containing oxygen flows into the gas diffusion electrode 5 through the gas flow path 9, the electrochemical reaction occurs via the catalyst electrode layers 2 and 3 and the solid polymer electrolyte, respectively. Proceeds to generate electrons. By extracting these electrons from the catalyst electrode layer to a gas diffusion electrode and from the gas diffusion electrode to a separator through an external circuit, electric energy is generated. Further, the voltage that can be generated in a single cell is around 1 volt, and in actual use, the cell is used as a fuel cell stack in which a plurality of single cells are stacked.

It is preferable that at least the outermost surface layer of the separator surface coating layer 11 in contact with the gas diffusion electrode is a conductive metal nitride film. This is because the metal nitride film itself has extremely excellent corrosion resistance and does not produce a high-resistance substance such as a passive film on the surface.

Further, a single-layer film formed of a low-resistance metal nitride film alone among the metal nitride films as the surface coating layer 11 is preferable, and a high-resistance metal nitride film is not suitable for this application. . The resistivity (electrical resistivity) is preferably 10 Ωcm or less in order to suppress the resistance of the entire fuel cell and extract energy efficiently. 10Ωc
If it exceeds m, it is not preferable because the contact resistance increases.
The resistivity is a value measured by coating the surface of an insulating base material (for example, silica glass) with a film to be measured and measuring it by a measuring method called a four-terminal method.

In addition, even if a high-resistance metal nitride film is combined with a low-resistance metal nitride film, at least the outermost surface layer in contact with the gas diffusion electrode is formed of a low-resistance metal nitride film. The resistivity of the surface coating layer can be set to 10 Ωcm or less, and a multilayer structure film of such a metal nitride film may be used.

Further, since the metal nitride film of the present invention has excellent adhesion strength and high film hardness, and scars are less likely to occur due to vibrations during vehicle mounting, a highly reliable separator is produced. be able to. As for the hardness of the metal nitride film of the surface coating layer, it is preferable that the micro Vickers hardness or the Knoop hardness is 8 GPa or more. By using such a high-hardness film, durability against vibrations and the like in a vehicle can be obtained. The micro-Vickers hardness is a hardness measured using a Vickers indenter at a pressing load of 50 g or less, and the Knoop hardness is a hardness measured using a Knoop indenter at a pressing load of 50 g or less.

Further, the surface coating layer has a multilayer structure of two or more kinds of metal nitride films, and further has a total film thickness of 5 μm.
m, and preferably IVa, V in the periodic table.
It is preferable to contain any one or more of the a and VIa group metals.

TiN and CrN are typical materials for the metal nitride film. These films can be made of a single layer having sufficient hardness depending on the manufacturing method. For example, a multilayer structure of TiN and CrN can further improve the film hardness. In the case of a single-layer film, the thickness is 10 to 1
If the thickness is not more than 5 μm, a coating film with few pinholes cannot be produced.
With a thin film thickness of less than m, a coating film having almost no pinholes can be produced, which leads to cost reduction.

The method of coating the metal nitride film may be a sputtering method using a solid metal as a raw material, a cathode arc ion plating method, an ionization vapor deposition method, or a plasma CVD method using an organic metal gas as a raw material. preferable. By using these methods, it is possible to simultaneously provide excellent adhesion strength.

The surface coating layer may cover the entire surface or a part of the surface of the substrate, and at least cover the surface in contact with the electrode. The thickness may be uniform or non-uniform.

Example 1 A separator (150 mm × 150 mm × thickness) in which a plurality of parallel corrugated grooves were previously formed on the front and back by press molding using SUS304 as a separator for a solid polymer electrolyte fuel cell. 0.3 mm) One surface of the substrate was coated with a surface coating layer having a film material and a film structure shown in Table 1 by using various methods. For comparison, only a separator substrate made of SUS304 (without coating), and T
One coated with iN at 1.0 μm, one coated with gold at 5.0 μm, and one coated with lead-carbon composite plating were also prepared. Furthermore, before actually assembling the fuel cell, the separator coated with the surface coating layer and the gas diffusion electrode were rubbed lightly to simulate the damage to the surface coating layer due to vibration during mounting on a vehicle. A gas diffusion electrode (porous graphite plate using polytetrafluoroethylene as a binder) prepared separately from these separators, a Pt catalyst on the positive electrode side, and a Pt catalyst on the negative electrode side
FIG. 1 shows a 100 μm-thick solid polymer electrolyte membrane coated with a Ru catalyst (a trade name “Nafion membrane: Nafion 115”, which is a proton conductive ion exchange membrane formed of a fluororesin manufactured by DuPont). A single cell was assembled by making contact so as to form a structure, and power was actually generated using hydrogen and oxygen.

During power generation, a continuous power generation test was performed under the conditions of a current density of 0.1 A / cm ² . With respect to the change with time of the internal resistance value between the separator and the gas diffusion electrode, before and after power generation for a predetermined time, the resistance value between 2 and 6 in FIG. Was evaluated. Table 2 shows the results.

[0028]

[Table 1]

[0029]

[Table 2]

As is evident from Table 1, the product of the present invention shows a small increase in the internal resistance value after 100 hours, and exhibits long-term stability in a long-term power generation operation.
On the other hand, in the comparative example, as can be seen from Table 2, the change in the internal resistance value is large due to the long-term power generation operation, and the performance required for use as a fuel cell separator is not satisfied.

Example 2 In the same manner as in Example 1, as a separator for a solid polymer electrolyte fuel cell, a plurality of parallel wavy grooves were previously formed on the front and back by press molding.
Aluminum alloy with alloy number A5052 specified by IS-H4000 (aluminum alloy content of 96% by weight or more)
Separator substrate consisting of (length 150 mm x width 150 mm
x thickness 0.5 mm) was coated with a surface coating layer having a film material and a film structure shown in Table 3 using various methods. For comparison, only a separator substrate made of SUS304 (without coating), and T
One coated with iN at 1.0 μm, one coated with gold at 5.0 μm, and one coated with lead-carbon composite plating were also prepared. Furthermore, before actually assembling the fuel cell, the separator coated with the surface coating layer and the gas diffusion electrode were rubbed lightly to simulate the damage to the surface coating layer due to vibration during mounting on a vehicle. Separately prepared separators, gas diffusion electrodes (porous graphite plates using polytetrafluoroethylene as a binder), solid polymer electrolytes (Pt
A single cell was assembled by contacting the catalyst and the Pt-Ru catalyst coated on the negative electrode side so that the structure shown in FIG. 1 was obtained, and power was actually generated using hydrogen and oxygen.

During power generation, a continuous power generation test was performed under the conditions of a current density of 0.1 A / cm ² . The change with time of the internal resistance value between the separator and the gas diffusion electrode was evaluated in the same manner as in Example 1. In addition, before actually assembling the fuel cell, an operation of lightly rubbing the separator and the gas diffusion electrode was performed on all of the products of the present invention and the comparative examples, thereby simulating damage to the surface coating layer due to vibration during vehicle mounting. Table 4 shows the results.

[0033]

[Table 3]

[0034]

[Table 4]

As is clear from Tables 3 and 4, it was found that the product of the present invention showed a small increase in the internal resistance after a long period of power generation operation, especially after 100 hours, and exhibited long-term stability. On the other hand, in the comparative example, as can be seen from Table 4, the change in the internal resistance was large due to the long-term power generation operation, and did not satisfy the required performance for use as a fuel cell separator.

Although specific embodiments of the present invention have been described above, it is needless to say that the present invention is not limited to these embodiments.

[0037]

According to the present invention, a solid polymer electrolyte fuel cell separator having high reliability over a long period of time can be obtained and is useful.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing a configuration example of a single cell of a solid polymer electrolyte fuel cell incorporating a separator of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 solid polymer electrolyte membrane 2, 3 catalyst electrode layer 4, 5 gas diffusion electrode 6, 7 separator 8 fuel gas flow path 9 oxidizing gas flow path 10 substrate 11 surface coating layer

Continuation of the front page (72) Inventor Hisanori Ohara 1-1-1 Kunyokita, Itami-shi, Hyogo F-term (reference) in Itami Works, Sumitomo Electric Industries, Ltd. 5H026 AA06 BB04 EE02 EE08 EE11 HH00

Claims (4)

[Claims] 1. A unit in which a solid polymer electrolyte layer and a catalyst electrode layer disposed on both surfaces thereof are sandwiched between a gas diffusion electrode and a separator are formed as a single cell, and a plurality of the single cells are stacked to form a fuel cell stack. Wherein the separator used in the fuel cell having the above-mentioned structure has a surface coating layer and a metal substrate, and the surface coating layer has a multilayer structure comprising two or more layers of different types of metal nitride films. Solid polymer electrolyte fuel cell separator. 2. The solid polymer electrolyte type fuel according to claim 1, wherein at least the outermost surface layer of the surface coating layer in contact with the gas diffusion electrode is a conductive metal nitride film. Battery separator. 3. The method according to claim 1, wherein the surface coating layer is selected from the group consisting of:
2. The separator for a solid polymer electrolyte fuel cell according to claim 1, wherein the separator contains one or more of Va and VIa group elements. 4. The solid polymer electrolyte fuel cell separator according to claim 1, wherein the surface coating layer has a hardness of 8 GPa or more in micro Vickers hardness or Knoop hardness.