JP3448550B2 - Polymer electrolyte fuel cell stack - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte fuel cell stack, and more particularly to a polymer electrolyte fuel cell stack capable of preventing deterioration of cell performance of single cells located at both ends of the stack.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell uses a solid polymer electrolyte membrane as an electrolyte layer, and an anode and a cathode are provided on both sides of the solid polymer electrolyte membrane, and a fuel gas containing hydrogen (hydrogen rich gas) and oxygen. An oxidant gas (air) containing is supplied to obtain an electromotive force by an electrochemical reaction. As shown in FIG. 1, the basic cell structure of this solid polymer electrolyte fuel cell has a cell unit 4 in which an anode 2 and a cathode 3 are joined to both main surfaces of a solid polymer electrolyte membrane 1. The unit cells 7 are formed by disposing the separators 5 and 6 on both sides of the cell unit 4.

The solid polymer electrolyte membrane 1 comprises, for example, a polystyrene cation exchange membrane having a sulfonic acid group as a cation conductive membrane, a mixed membrane of fluorocarbon sulfonic acid and polyvinylidene fluoride, and a fluorocarbon matrix with trifluorocarbon. A grafted product of ethylene, a perfluorocarbon sulfonic acid film (Nafion film manufactured by DuPont), and the like are known. These solid polymer electrolyte membranes 1 have a proton exchange group in the molecule and have a specific resistance of 20 Ωcm ^{2 at} room temperature when the water content is saturated.
Below, it functions as a proton conductive electrolyte.

The anode 2 is an anode catalyst layer 2a.
And a gas diffusion layer 2b and a mixture layer 2c interposed therebetween, and the cathode 3 is a cathode catalyst layer 3a.
, A gas diffusion layer 3b, and a mixture layer 3c interposed therebetween. This anode 2 and cathode 3
Are arranged on both main surfaces of the solid polymer electrolyte membrane 1,
By hot pressing, the cell unit 4 which is an electrode / polymer membrane assembly is formed.

The separators 5, 6 of the unit cell 7 have gas passages 5a, 6a on the inner surface side and a cooling water passage 5 on the outer surface side.
b and 6b are provided respectively, and the gas flow path 5a of the separator 5 on the anode 2 side contains a fuel gas containing hydrogen (hydrogen rich gas), and the gas flow path 6a of the separator 6 on the cathode side 3 contains oxygen. Oxidant gas (air) is supplied respectively.

When the gas is supplied in this way, an anode reaction for decomposing hydrogen molecules into hydrogen ions and electrons is carried out at the anode 2, and an electrochemical reaction for producing water from oxygen, hydrogen ions and electrons is carried out at the cathode 3. I am the anode 2
The electrons moving in the external circuit from the cathode to the cathode 3 generate electromotive force, and water is generated on the cathode 3 side. That is, the following electrochemical reaction is performed. Anode: H ₂ → 2H ⁺ + 2e ⁻ (anode reaction) Cathode: 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (cathode reaction) Whole: H ₂ + 1 / 2O ₂ → H ₂ O

Since the solid polymer electrolyte membrane 1 properly exhibits conductivity by being kept in the water-containing state as described above, the fuel gas and / or the oxidant gas is humidified to contain a certain amount of water. It is supplied later and is moistened by this humidified water. Moreover, in order to reduce the specific resistance of the solid polymer electrolyte membrane 1 and maintain high power generation efficiency, it is usually required to
It is operated at 0 to 100 ° C., but cooling water is supplied to the cooling water passages 5 b and 6 b of the separators 5 and 6 so that the temperature does not rise due to the heat generated by the electrochemical reaction. Trying to hold.

Since the electromotive force of the unit cell 7 is small,
As shown in FIG. 2, a plurality of unit cells 7 are stacked in series, current collector plates 8 and 9 are arranged on both sides, and electric insulating plates 10 and 11 are arranged outside them, and further tightened on the outside. Board 1
2 and 13 are arranged, and the fastening plates 12 and 13 are fastened and fixed by the bolts 14 and the nuts 15 to form the stack 16. Reference numeral 17 is a disc spring that gives the stack 16 an appropriate tightening force.

[0009]

In the solid polymer electrolyte fuel cell stack having the above structure, the unit cells 7A and 7B located at both ends of the stack 16 have current collector plates 8 and 9 at one end face.
Since it is held in a state of being in contact with, the ratio of heat radiated by heat conduction from the side surface is larger than that of the unit cell 7 located at the other portion where the unit cells are arranged on both sides and stacked. Therefore, the temperatures of the unit cells 7A and 7B located at both ends of the stack 16 tend to be lower than the temperatures of the unit cells 7 located in other parts.

FIG. 4 shows a structure in which ten unit cells 7 are laminated 1
It is a graph which measured the cell temperature distribution in a 0 cell stack, and in this case, cell numbers 1 and 10 are unit cells located at both ends of the stack, and both are higher in temperature than unit cells 7 located in other parts. Was low.

When the temperatures of the unit cells 7A and 7B located at both ends of the stack 16 are lowered as described above, the vapor pressures of the electrode reaction product water and the transfer water from the anode 2 are lowered at the cathode 3 of these cells, Condensed water stays in the cathode side catalyst layer 3a or the gas diffusion layer 3b, which causes a problem that the battery performance is deteriorated.

To solve the above problem, there is a technique disclosed in, for example, Japanese Patent Laid-Open No. 10-308229.
In this conventional technique, a cooling water flow path is provided in the electrical insulating plate of the stack, and the cooling water that has passed through the stack and has received the heat of the battery reaction to raise the temperature is flowed through this cooling water flow path to dissipate heat from both ends of the stack. To suppress the temperature drop of the unit cells located at both ends.

However, according to this conventional technique, it is necessary to provide a dedicated passage for the cooling water in the electric insulating plate, which complicates the battery module structure. Further, when the reaction gas is supplied to each cell through the internal manifold, the reaction gas is usually supplied from the side of the clamping plates located at both ends of the stack. When the reaction gas is air, the supply amount is much larger than that of the fuel, so that the air flow velocity in the internal manifold is increased, and as a result, the cells located near the tightening plate (the parts corresponding to 7A and 7B)
In some cases, the supply amount may be smaller than that in other cells. In such a case, even if a means for suppressing heat radiation from both ends of the stack is provided, the battery performance may be deteriorated due to the water condensation as described above.

As another solution, for example, a means for preventing heat radiation from the side of the unit cell by attaching a heat insulating member to the side of the unit cell located at both ends of the stack is conceivable. There are problems such as an increase in the number of constituent members, an increase in cost, and an increase in the size of the stack.

Therefore, according to the present invention, it is possible to prevent the deterioration of the battery performance of the unit cells located at the both ends of the stack while allowing the temperature decrease of the unit cells located at the both ends of the stack without changing the constituent members of the stack. An object of the present invention is to provide a polymer electrolyte fuel cell stack having the above structure.

[0016]

In order to achieve the above object, the present invention provides, as a first means, a cell unit in which a cathode and an anode are bonded to both surfaces of a solid polymer electrolyte membrane, and a cell unit is disposed on both surfaces of the cell unit. is, a polymer electrolyte fuel cell stack formed by stacking a plurality of configured single cell and a separator having a gas flow path for flowing the oxidant gas or fuel gas, positioned at both ends of the stack In a single cell to form the gas diffusion layer of the cathode
It is characterized in that the specific surface area of the carbon material is made larger than that of the unit cells located in other portions .

According to the first means of the present invention, the stack
The gas diffusion layers of the single cell cathodes located at both ends of the
By increasing the specific surface area of the constituent carbon materials,
Due to the capillary force of the pores formed by the carbon material
The water absorption capacity is increased, and as a result, reaction product water and transfer water are
It becomes easier to move in the diffusion layer and is released into the oxidant gas.
Are easily discharged. As a result, in the cathode catalyst layer
Water does not stay excessively and the gas diffusivity becomes good.

Further, in addition to the first means, as a second means, the solid polymer fuel cell stack has
The single cell cathodes located at the ends of this stack
The pressure loss of the side gas flow path should be
Make it smaller than that.

According to the second means, both ends of the stack are
The pressure loss of the gas flow path on the cathode side of the single cell
By making it smaller, the flow rate of the oxidant gas flowing through the gas flow path
Is increased, and the reaction product water and the transfer water are easily discharged.
As a result, excessive water is retained in the cathode catalyst layer.
Therefore, the gas diffusivity is improved.

As a third means, a solid polymer electrolyte is used.
Cell unit with cathode and anode bonded to both sides of the electrolyte membrane
And the oxidizer gas on both sides of this cell unit.
Alternatively, a separator having a gas flow path for flowing fuel gas
The solid height formed by stacking multiple unit cells composed of
A molecular fuel cell stack, the ends of which are
In the single cell located at
The water repellency of the layer is better than that of the unit cells located in other parts.
The pressure loss in the gas passage on the cathode side as well as
Was made smaller than that of the single cell located in the other part
It is characterized by

According to the third means, both ends of the stack are
The water repellency of the cathode side gas diffusion layer of the single cell
By lowering the reaction product water at the cathode and the anode
Transfer water from the gas diffusion layer side easily becomes
Because the contact area with the gas increases, it is
The gas is easily discharged through the gas flow path. This allows you to
Excessive water does not stay in the sword catalyst layer and gas diffusion
It will be good.

Further , the single cells located at both ends of the stack
By reducing the pressure loss of the cathode gas flow path of
The flow rate of the oxidant gas flowing through the gas flow path increases and reaction is generated.
Water and mobile water are easily discharged. This will allow you to
Excessive amount of water does not stay in the catalyst layer and gas diffusion is good
Becomes

[0023]

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described. The basic structure of the polymer electrolyte fuel cell stack is the same as that of the stack 16 shown in FIG. 2, and is formed as described above. However, the number of stacked single cells 7 is 10,
The cell units 4 of single cells (denoted by cell numbers 1 and 10) located at both ends of the stack 16 are manufactured as in the following embodiments.

Example 1 A carbon paper (TGP-H060 manufactured by Toray Industries, Inc.) used as the gas diffusion layer 3b of the cathode 3 is cut into a predetermined size. The cut carbon paper is immersed in an FEP (tetrafluoroethylene-hexafluoropropylene copolymer) dispersion whose specific gravity is adjusted by mixing with water. At this time, the FEP content was adjusted to 10% by weight for the single cell gas diffusion layers located at both ends of the stack 16, and the FEP content was adjusted to 20% by weight for the other single cell gas diffusion layers. Then, it is dried and heat-treated at 380 ° C. for about 1 hour. A catalyst layer 3a made of platinum-supporting carbon and a solid polymer is formed on the carbon paper which has been heat-treated to complete the cathode 3. The cathode 3 completed with the anode 2 prepared by the existing method is used as a solid polymer electrolyte membrane 1 (made by DuPont: Na
The cell unit 4 is obtained by arranging on both sides of the fion 112) and hot pressing. Among the cell units 4 produced by the methods (1) to (4), the cell unit having a small FEP amount of the gas diffusion layer 3b, that is, the cell unit having a low water repellency is used as a single cell unit located at both ends of the stack, and a cell having a large FEP amount is used. The unit was used as a cell unit of a single cell located in the other part, and lamination was performed to prepare a 10-cell stack.

In the first embodiment, the water repellency of the cathode gas diffusion layers 3b of the single cells located at both ends of the stack 16 is
It is configured to have a lower water repellency than the cathode gas diffusion layer of the single cell located in the other portion.

Example 2 Carbon paper used as the gas diffusion layer 3b of the cathode 3 (manufactured by Toray Industries, Inc .: TGP-H060, thickness of about 0.2).
mm, thickness of about 0.3 mm with TGP-H090). These carbon papers are immersed in FEP dispersion liquid whose specific gravity is adjusted by mixing with water. At this time, the FEP amount was set to 20% by weight in any thickness of carbon paper. Then, it is dried and heat-treated at 380 ° C. for about 1 hour. A catalyst layer 3a made of platinum-supporting carbon and a solid polymer is formed on the carbon paper which has been heat-treated to complete the cathode 3. The cathode 3 completed with the anode 2 prepared by the existing method is used as a solid polymer electrolyte membrane 1 (made by DuPont: Na
The cell unit 4 is obtained by arranging on both sides of the fion 112) and hot pressing. Among the cell units 4 produced by the methods 1 to 3, the cell unit having a small thickness of the carbon paper of the cathode gas diffusion layer 3b, that is, a cell unit having a high gas permeability,
Used as a cell unit of a single cell located at both ends of
A cell unit having a large thickness of carbon paper is used as a cell unit of a single cell located in another portion to perform stacking to form a 10 cell stack.

In the second embodiment, the gas permeability of the single cell cathode gas diffusion layers 3b located at both ends of the stack 16 is higher than the gas permeability of the single cell cathode gas diffusion layers located in other portions. It is constructed high.

Example 3 Carbon paper (TGP-H060 manufactured by Toray Industries, Inc.) used as the gas diffusion layer 3b of the cathode 3 is cut into a predetermined size. The carbon paper is immersed in the FEP dispersion liquid whose specific gravity is adjusted by mixing with water, then dried and heat-treated (380 ° C., 1 hour). Carbon black (surface area 700-800 m ² /
g) 10 g of powder and 16.7 g of 60 wt% PTFE (polytetrafluoroethylene) dispersion are mixed with terpineol to which several cc of a surfactant has been added as a dispersant to prepare a paste. In addition, carbon black (surface area 200 to 300 m ²
/ G) 10 g powder and 60 wt% PTFE dispersion 16.7
g is mixed with terpineol to which several cc of a surfactant has been added as a dispersant to prepare a paste. The paste obtained in step (1) is applied onto the carbon paper obtained in step (3). The paste obtained in (1) is used for the cell units of the single cells located at both ends of the stack 16, and the paste obtained in (1) is used for the cell units of the single cells located in other portions. After drying the carbon paper coated with paste, 3
Heat treatment is performed at 60 ° C. for 1 hour to complete the gas diffusion layer 3b. Platinum-supporting carbon (supported carbon specific surface area of 200 to 300 m ² /
g), the catalyst layer 3a made of a solid polymer is formed to complete the cathode 3. The cathode 3 completed with the anode 2 prepared by the existing method is used as the solid polymer electrolyte membrane 1 (Na
The cell unit 4 is obtained by arranging on both sides of the fion 112) and hot pressing. Among the cell units prepared by the methods (1) to (4), those having a large carbon specific surface area of the paste added to the cathode gas diffusion layer 3b are used as single cell cell units located at both ends of the stack 16 and have a small carbon specific surface area. The thing is used as a cell unit of a single cell located in the other part to create a 10 cell stack.

In Example 3, the specific surface area of the carbon material in the mixture layer 3c in the cathodes 3 of the unit cells located at both ends of the stack was determined to be different from the specific surface area of the unit cells located at both ends of the stack. It is larger than the single cell.

(Example 4) In Example 1, when a 10-cell stack was prepared using the cell units 4 used for the unit cells other than the both ends of the stack, the cathodes 3 of the unit cells located at the both ends were confronted. Gas flow path 6a of the separator 6
A 10-cell stack is prepared by using the groove depth of which is increased by 10% as compared with the gas flow path of the single cell located in the other portion.

In the fourth embodiment, the gas flow paths 6 of the cathode side separators 6 of the single cells located at both ends of the stack 16 are arranged.
The pressure loss of a is smaller than the pressure loss of the gas passage of the cathode side separator of the single cell located in the other part.

(Comparative Example) In order to compare with these Examples 1 to 4, the same method as in Example 1 was adopted except that the unit cells at both ends of the stack 16 were formed to have the same specifications as the unit cells of the other portions. Then, a 10-cell stack was prepared.

Next, a cell voltage distribution test was performed on the 10 cell stack formed in Examples 1 to 4 and the 10 cell stack formed in the comparative example. The test results are shown in FIG. According to this test result, in Examples 1 to 4, almost the same distribution tendency as a whole was exhibited, and the cell voltages of cell numbers 2 to 9 were 6
Values within the range of 85-695 mV were obtained, with cell number 1 672-680 mV and cell number 10 675-68 mV.
Values in the range of 0 mV were obtained, with the unit cells located at the ends of the stack 16 being only slightly lower than the unit cells located in the other parts. On the other hand, in the comparative example, the cell voltages of the cell numbers 2 to 9 are the cell numbers 2 to 9 in the examples 1 to 4.
Although a value within the substantially same range as 9 was obtained, the cell number 1 was 656 mV, which was much lower than the cell number 1 in Examples 1 to 4, and the cell number 10 was 662 mV. It was much lower than the cell number 10 in Examples 1 to 4.

Therefore, in Examples 1 to 4, although the cell performance of the single cells located at both ends of the 10 cell stack is slightly inferior to that of the single cells located in other portions, the 10 cells in the comparative example are not. It turned out to be much better than the single cells located at the ends of the stack.

In the first embodiment, as described above, the single cell cathode gas diffusion layers 3 located at both ends of the 10 cell stack.
Since the water repellency of b is configured to be lower than that of the unit cells located in other parts, the reaction product water at the cathode 3 and the anode 2
The moving water from the water easily permeates to the gas diffusion layer 3b side and the contact area with the oxidant gas increases, so that it easily discharges together with the oxidant gas through the gas flow path 6a. It is considered that, as a result, excess water did not stay in the catalyst layer 3a of the cathode 3 and the gas diffusibility was improved.

In the second embodiment, as described above, the single cell cathode gas diffusion layers 3 located at both ends of the 10 cell stack.
Since the gas permeability of b is higher than that of the unit cells located in other parts, the permeation amount of the oxidant gas is increased, and the reaction product water at the cathode 3 and the water transferred from the anode 2 side are oxidant gas. It is considered that the gas is easily moved together with the gas and is easily discharged to the gas flow path 6a of the separator 6, whereby excessive water does not stay in the cathode catalyst layer 3a and the gas diffusibility is improved.

In the third embodiment, as described above, the specific surface area of the carbon material in the mixture layer 3c in the cathode 3 of the unit cells located at both ends of the 10-cell stack is set larger than that of the unit cells located in other portions. Therefore, the water absorption capacity due to the capillary force of the pores formed by the carbon material particles is increased, and the reaction product water at the cathode 3 and the moving water from the anode 2 side easily move in the mixture layer 3c, and the oxidation is performed. It is considered that the gas diffuses easily into the agent gas and is easily discharged, and as a result, excessive water does not stay in the cathode catalyst layer 3a, and the gas diffusibility is improved.

In Example 4, as described above, the groove depth of the gas passage 6a of the separator 6 facing the cathodes 3 of the single cells located at both ends of the 10-cell stack was set to be different from that of the single cells located in other parts. Of the oxidant gas flowing through the gas flow path 6a is increased by making the pressure loss of the gas flow path 6a smaller than that of the reaction product water at the cathode 3 and the anode 2 side. It is considered that the moving water was easily discharged, so that excessive water did not stay in the cathode catalyst layer 3a and the gas diffusibility was improved.

As described above, in the present invention, the stack 1
While accepting the temperature drop of the single cells located at both ends of 6,
By any of the above means, the battery performance of the single cells located at both ends can be improved as compared with the conventional one, and thereby stable operation is possible, and the stack 16 having good output characteristics is formed. be able to.

[0041]

As described above, the present invention provides a polymer electrolyte fuel cell stack comprising: (1) a single cell cathode located at both ends of the stack .
The specific surface area of the carbon material that constitutes the gas diffusion layer
Constitute greater than the single cell located at the portion, the cathode side of the single cells located at both ends of the (2) Stack
Compares the pressure loss in the gas flow path with the unit cells located in other parts.
Base to constitute small, Kasodoga single cells located at both ends of the (3) Stack
The water repellency of the diffusion layer is better than that of single cells located in other areas.
It is designed to be low and located at both ends of the stack.
Pressure loss in the cathode gas flow path of the
By adopting any one of such means, which is smaller than the unit cell, the reaction product water at the cathode and the transfer water from the anode side in the unit cells located at both ends of the stack are easily discharged, This has the effect of preventing deterioration of battery performance.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a configuration example of a single cell of a polymer electrolyte fuel cell.

FIG. 2 is an explanatory diagram showing a configuration example of a polymer electrolyte fuel cell stack.

FIG. 3 is a graph showing a test result of cell voltage distribution in a 10-cell stack.

FIG. 4 is a graph showing the measurement result of cell temperature distribution in a 10-cell stack.

[Explanation of symbols]

1 ... Solid polymer electrolyte membrane 2 ... Anode 3 ... Cathode 3a ... Catalyst layer 3b ... Gas diffusion layer 3c ... mixture layer 4 ... Cell unit 5, 6 ... Separator 5a, 6a ... Gas flow path 5b, 6b ... Cooling water flow path 7 ... Single cell 8, 9 ... Current collector 10, 11 ... Electrical insulation board 12, 13 ... Tightening plate 14 ... Bolt 15 ... Nut 16 ... Stack 17 ... Disc spring

Continuation of the front page (56) Reference JP-A-9-283153 (JP, A) JP-A-2001-57218 (JP, A) JP-A-2001-135326 (JP, A) JP-A-2001-118587 (JP, A) JP-A-2001-15145 (JP, A) JP-A-5-251086 (JP, A) JP-A-58-163173 (JP, A) JP-A-8-167424 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) H01M 4/86-4/98 H01M 8/00-8/24

Claims (3)

(57) [Claims] 1. A cell unit in which a cathode and an anode are joined to both sides of a solid polymer electrolyte membrane, and a separator which is arranged on both sides of the cell unit and has a gas flow path for passing an oxidant gas or a fuel gas. polymer electrolyte fuel cell stack der formed by stacking a plurality of a single cell further including a
I, the single cells located at both ends of the stack, the ratio of carbon material constituting the cathode gas diffusion layer
The surface area is larger than that of single cells located in other parts.
Ku and a polymer electrolyte fuel cell stack, characterized in that the. 2. A polymer electrolyte fuel cell stack according to claim 1.
, The cathode side gas of the single cells located at the ends of this stack.
The pressure loss of the flow passage is that of a single cell located in another part.
A polymer electrolyte fuel cell stack characterized by being made smaller . 3. A cathode and an anode on both sides of the solid polymer electrolyte membrane.
The cell unit that joins the node and this cell unit
It is placed on both sides to pass the oxidant gas or fuel gas.
Unit cell composed of a separator having a gas flow path
A polymer electrolyte fuel cell stack formed by stacking a plurality of
I, the single cells located at both ends of the stack, the water repellency of the cathode side gas diffusion layer, located on other parts
Lower than that of the unit cell, and the pressure loss of the cathode side gas flow path is
The polymer electrolyte fuel cell stack is characterized by being made smaller than that of the single cell .