JPH071697B2 - Fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a unit cell having a negative electrode in which a catalyst layer is supported on a grooved porous substrate and a thin porous plate-like positive electrode. The present invention relates to a fuel cell in which a fuel cell and a fuel cell are laminated via a laminated element layer.

(Prior Art) An electrochemical power generation device that reacts a gas that is easily oxidized, such as hydrogen, with a gas that has an oxidizing power, such as oxygen, through an electrochemical reaction process and extracts the released free energy of the cast as DC power. Is usually called a fuel cell and is constituted by stacking a plurality of unitary power generating elements.

By the way, when stacking the unitary power generating elements, it is necessary to secure electrical connection between the unitary power generating elements. At the same time, supply reaction gas to each unit power generation element,
Alternatively, it is necessary to secure a gas passage for removing reaction products. Further, in the fuel cell, it is necessary to have a cell structure in which the electrolyte is constantly supplied to the matrix layer so that the cell can be operated for a long time.

(Problems to be Solved by the Invention) From the viewpoints described above, the problems of the conventional cell structure will be described below.

As shown in FIG. 2, as one method for stacking a plurality of unit cells 25, a high-density grooved conductive separator is used as a stacking element 21.
Is known as an example. That is, both the fuel electrode (negative electrode) 22 and the air electrode (positive electrode) 23 are made of carbon fiber with other binders, and on one side of graphitized thin porous carbon paper, a catalyst layer in which platinum is dispersed on carbon fine powder is formed. Are formed and configured. Both electrodes 22 and 23 are adhered and integrated with each other with the catalyst layer surfaces facing each other through the matrix layer 24 containing the electrolyte. The unit cell 25 configured in this manner is stacked with a plurality of unit cells 25 with the stacking element 21 interposed. Here, the laminated element 21 is a conductive and gas-impermeable carbon plate in which gas circulation grooves for supplying a fuel and an oxidant gas are formed in the upper surface and the lower surface in the respective orthogonal directions. There is.

In such a cell structure, both the positive electrode 23 and the negative electrode 22 are usually 0.3
Since it is composed of a thin porous carbon paper of about 0.5 mm, it has good electric conductivity and good diffusion of the reaction gas, so that high cell performance can be obtained.

However, when the unit cell 25 and the stacking element 21 are alternately stacked to form a power generator, when the stack is compressed and fastened because the electrodes are thin and the compression tolerance is small, the stacking element 21 is very stiff and the unit cell is small. 25 had the drawback of being crushed and possibly broken.

Furthermore, in order to extend the life of the cell, the matrix layer 24
Besides, it is necessary to retain the electrolyte and replenish the electrolyte in the matrix 24, which decreases with the operation of the fuel cell.

In such a cell structure, it is possible to retain the electrolyte in the thin porous portions of the positive electrode 23 and the negative electrode 22 to the extent that the diffusion of the reaction gas into the catalyst layer is not hindered, but since the porous portion is thin, a sufficient amount of Due to the inability to retain the electrolyte, its cell life is at most thousands of hours.

Thirdly, as a structure in which the above-mentioned drawbacks of the cell structure are improved,
A cell structure as shown in the figure has been proposed.

That is, both the fuel electrode (negative electrode) 31 and the air electrode (positive electrode) 32 are 2
Platinum is dispersed on carbon fine powder on one side of a porous carbon sheet of about 3 mm, and a catalyst layer is formed by using a fluororesin such as polytetrafluoroethylene as a binder, and on the opposite side, a reaction gas is flown. Grooved. The gas circulation grooves of the electrodes 31 and 32 are orthogonal to each other, and they are closely adhered and integrated so that the respective catalyst layer surfaces face each other through the matrix layer 33 containing the electrolyte to form the unit cell 34. A plurality of unit cells 34 are stacked while interposing this unit cell 34 with a smooth separator 35 having good airtightness and conductivity.

In such a cell structure, the electrolyte can be retained in the porous portion (reservoir) of the ribbed electrodes 31, 32 several times as much as the matrix layer 33. Therefore, even if the electrolyte in the matrix layer 33 decreases, the electrolyte volume in the matrix layer 33 can be prevented from decreasing by replenishing the electrolyte from the reservoir, so that deterioration of the cell characteristics can be prevented and long-term operation is expected. it can.

However, according to the study results of the present inventors, when the ribbed electrode is used for the positive electrode 32, insufficient diffusion of air into the catalyst layer due to the use of the thick porous sheet occurs, and the cell characteristics deteriorate. There was found. It was also found that the ribbed electrode 32 for the positive electrode cannot practically have the reservoir function of the electrolyte because if the ribbed electrode 32 for the positive electrode contains the electrolyte, the diffusion of air further becomes insufficient.

However, the conventional cell structure described above cannot satisfy the following two conditions at the same time, and thus has a problem that a fuel cell having a long life and high performance cannot be obtained. That is, the retention of the electrolyte for supplying the electrolyte to the matrix. Ensuring the diffusibility of the air in order to promote the air electrode reaction smoothly. Therefore, the present inventors have shown in FIG. 4 (JP-A-58-94768).
As shown in, a fuel cell is proposed in which a plurality of unit cells 45 are laminated. That is, the electrode 41 in which a catalyst layer for promoting an electrode reaction is carried on a porous carbon sheet provided with a gas flow path is used as a fuel electrode (negative electrode). This electrode 41
And an air electrode (positive electrode) 42 in which an electrode catalyst is carried on a thin porous carbon sheet which has been previously subjected to waterproof treatment, and is closely integrated through a matrix layer 43 containing an electrolyte. The unit cell 45 is formed. Then, an electrical connection path between the unit cells 45 is established, and at the same time, a grooved separator 46 made of a gas impermeable carbon plate with a single-sided groove in which a flow path of an oxidant gas (air) is formed is interposed. Then, a plurality of unit cells 45 are stacked to form a fuel cell.

Since this unit cell structure is a structure in which the positive electrode side of FIG. 2 and the negative electrode side of FIG. 3 are mixed, the present inventors named this cell a hybrid cell.
(57th Battery Symposium, Yokohama) This hybrid cell has a ribbed negative electrode 41 that allows electrolyte to be stored in the negative electrode ribs to replenish the matrix layer, and a thin positive electrode with a small air diffusion resistance. Shaped flat plate electrode 42
And a matrix layer 43 for holding the electrolyte and a single-sided grooved separator for facilitating the flow of air
It consists of 46 and.

As described above, in the hybrid cell, by holding the electrolyte in the negative electrode rib 41, it is possible to control the deterioration of the cell characteristics due to the decrease in the electrolyte during long-term operation of the cell, and the thin electrode 42 is used as the positive electrode. By using it, performance deterioration due to insufficient diffusion of the oxidant gas (air) can be suppressed.

The hybrid cell by the present inventors has a cell performance,
Although the cell structure has an excellent cell life, it has been found that there are the following problems in increasing the size of the laminated element having a single-sided groove and in the manufacturing process of the laminated cell. That is, the one-sided grooved separator 46 is a gas impermeable carbon plate or carbon (mainly graphite).
Since it is composed of a resin-bonded carbon plate that is pressure-molded by hot pressing, etc., a mixture made by kneading and a binder such as phenol resin, it is possible to provide an oxidant (air) supply groove on one side of these. As shown in FIG. 5, warpage may occur during processing by die molding or a mechanical method.
In particular, it has been found that the frequency of warpage is high and the degree of warpage is high during the manufacture of large stacked elements.

For example, in a laminated element in which a groove is processed with a thickness of 3 mm, a groove width of 2 mm, and a pitch of 4 mm, there is almost no warpage in a 20 cm square, but a warpage of 2 to 5 mm occurs in about 10% in a 60 cm square. I found out.

When unit cells are stacked by using such a stacking element, as shown in FIG. 6, the unit cell close to the stacking element in which warpage has occurred is locally localized due to uneven pressure when the stack is fastened. It has been found that the electrodes, the electrolyte matrix, and the laminated element itself are collapsed to cause crossing of the reaction gas during operation, which accelerates the deterioration of cell characteristics and the deterioration of cell life.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a fuel cell laminate in which electrodes and an electrolyte matrix are not destroyed during lamination by providing a warpage-free laminated element. To do.

[Structure of the Invention] (Means for Solving Problems) In order to achieve the above object, the present invention provides a laminated element layer incorporated in a fuel cell according to the present invention, which forms a flow path for a positive electrode active material. A first laminated element made of a porous carbon substrate with a single-sided groove for preventing the gas from flowing, and a smooth carbon plate having gas impermeable and good electric conductivity which prevents mixing of the negative electrode active material and the positive electrode active material. It is composed of two laminated elements, and further, the first laminated element and the second laminated element are constituted so as to be joined and integrated by a conductive adhesive.

The unit cell sandwiched between the laminated element layers is configured as follows.

That is, the unit cell is provided with a groove for supplying a negative electrode active material on one surface thereof, and a negative electrode made of a porous substrate carrying a catalyst layer for promoting an electrode reaction on the opposite surface, and is previously subjected to waterproofing treatment. A positive electrode having a catalyst layer supported on one surface of a flat plate-like porous carbon substrate that facilitates diffusion of a positive electrode active material such as air is arranged so that the catalyst layer surfaces face each other through a matrix layer containing an electrolyte. It is the one that is tightly integrated.

(Operation) As the first laminated element composed of the porous carbon substrate having the one-sided groove shown above, a porous carbon substrate for a negative electrode which does not carry a catalyst or a relatively improved electric conductivity or thermal conductivity A dense porous carbon substrate can be used.

These single-sided grooved porous carbon substrates are manufactured by mechanically grooving a smooth porous substrate, or by grooving with a mold in advance when manufacturing the porous substrate. At this time, these porous substrates can be manufactured with almost no warpage even if grooves are provided.

As the second laminated element 2 made of a gas-impermeable electrically conductive smooth carbon plate, a graphite plate or glassy carbon having a thickness of about 0.5 to 1.5 mm can be used. For this smooth carbon plate, a smooth separator made of a carbon plate that does not have a warp and is generally sold can be used as it is.

Further, as the conductive adhesive, it is possible to use an acid resistant conductive material such as carbon powder, tantalum or molybdenum as a conductive species, and a mixture of materials such as an acid resistant phenol resin as an adhesive. Therefore, the laminated element layer includes a first laminated element formed of a porous carbon substrate with a single-sided groove that does not cause warpage and a second laminated element formed of a gas-impermeable smooth carbon plate, which is made of a conductive material. A laminated element layer without warpage can be manufactured by integrally bonding and using an adhesive, and the contact resistance of the first and second laminated elements can be increased by bonding with a conductive adhesive. It can be reduced.

Therefore, it is possible to suppress the deterioration of the cell characteristics and the decrease of the cell life of the laminated body.

(Examples) The present invention will be described below with reference to examples.

The bulk specific gravity is 0.48 to 0.50, the thickness is 2.5 mm, and the size is 60.
1.8 mm wide on 0 mm x 700 mm felt-like porous graphite fiber board
m, depth 1.8 mm, pitch 4 mm, and a catalyst powder (3-5 μ diameter) in which 10% by weight of platinum black was chemically reduced and deposited on fine carbon powder on the surface where no groove was formed. At the same time, a catalyst added and kneaded to 8% by weight of polytetrafluoroethylene suspension was applied to form negative electrode 6.

The bulk specific gravity is 0.42 to 0.45, the thickness is about 0.4 mm, and the size is 60.
320mm x 700mm graphite porous fiber paper is impregnated with 20% polytetrafluoroethylene suspension and dried.
Polytetrafluoroethylene suspension 8 was used together with catalyst powder (3 to 5 μ diameter) obtained by chemically reducing and depositing 10% platinum black on carbon fine powder, which was sintered at 10 ° C for 10 minutes. A positive electrode 9 was formed by applying a mixture obtained by adding and kneading the composition in a weight percentage.

An electrolyte matrix layer 10 formed by impregnating a matrix obtained by mixing and kneading 6% by weight of polytetrafluoroethylene with silicon carbide powder having a particle size of 3 to 5 μm and 95% of phosphoric acid electrolyte is interposed in the middle, The unit cell 11 was constructed by facing the positive electrode 9 and the negative electrode 6 so that the catalyst layer was in contact with the electrolyte matrix 10.

Next, the bulk specific gravity is 0.5 to 0.6, the thickness is 2 mm, and the size is 600 mm.
× 700 mm and a degree of warp of 3 mm or less felt-like porous graphite fiber board with a gas passage of width 2 mm, depth 1.5 mm, pitch 4 mm on one side, gas impermeable at both ends parallel to the gas passage The first laminated element 1 that has been treated with a fluororesin for imparting properties and a smooth carbon plate (product name GC-Composite) of 600 mm x 700 mm in size and 1 mm in thickness manufactured by Kobe Steel, Ltd. Carbon black Vulcan 72R made by Cabot Co., as the laminated element 2
Apply 80 parts by weight and 20 parts by weight of a phenol resin solution to the conductive paste 3 applied on the entire surface of the combined parts of the first and second laminated elements 1 and 2, and join them to sandwich them into a flat heating plate. At 200
Laminated element layer 1 by pressurizing and integrating at ℃ and pressure 2Kg / cm ² for 1 hour 1
Set to 2.

As shown in FIG. 1, the unit cells 11 are sequentially laminated through the laminated element layer 12 of the present invention, and the groove of the first laminated element 1 serves as a flow path for the positive electrode active material (air). As configured.

The flow path of the negative electrode active material gas and the gas flow path of the positive electrode active material were set in directions different from each other by 90 degrees. Even when such a laminated body was tightened at a surface pressure of 5 kg / cm ² , no damage was found in the unit cell 11 and the laminated element layer 12.

On the other hand, the laminated body shown in FIG. 4 was assembled as a comparative example.
Here, a positive electrode active material channel having a width of 2 mm, a depth of 1.5 mm, and a pitch of 4 mm is provided on one surface of a phenol resin-bonded graphite plate as a laminated element, and the degree of warpage is 3 mm or less.
6 was used.

Using this single-sided grooved separator 46, unit cells 45 were sequentially laminated in the same manner as in the present embodiment and tightened with a surface pressure of 5 Kg / cm ² , and one out of 20 single-sided grooved separators 46 was separated. There were streaky cracks along the groove. In addition, the unit cell in the vicinity of the separator with streaky cracks
As a result of observing 45, a cell having a defect such as a crack of the positive electrode or a crack of the electrolyte matrix 43 was found when it abutted on the cracked portion.

That is, in the fuel cell using the laminated element layer 12 according to the present invention, it has been found that the laminated element layer 12 and the unit cell 11 do not have a problem because the distribution of the pressing force during the fastening of the laminated layers is made uniform. .

Further, the fuel cell according to the present invention was subjected to an operation cycle test in which hydrogen was used as a negative electrode active material and air was used as a positive electrode active material at a temperature of 190 ° C. and a current density of 220 mA / cm ² for 100 hours of operation and 50 hours of rest. As a result, the deviation value in the variation with respect to the cell average voltage was 2.5% after 1000 hours of operation and 4% after 5000 hours of operation. As a result of disassembling and investigating the fuel cell operated for 5000 hours, no trouble was found in the laminated element layer 12 and the unit cell 11.

Moreover, since the first and second laminated elements 1 and 2 are pressure-integrated by the conductive adhesive 3, the contact resistance can be reduced, and the conductive adhesive 3 is not used. As compared with the case of stacking, the resistance overvoltage can be reduced by about 5 mV, the thermal conductivity can be improved by integration with the conductive adhesive 3, and the cell average temperature can be lowered by about 3 ° C.

Furthermore, when the fuel cell of the comparative example was operated under the same operating conditions as the fuel cell of the present invention, the deviation value of the variation from the average voltage was 5% after 100 hours of operation and 12% after 5000 hours of operation. Variations in cell characteristics were found in comparison with batteries. Also, when the fuel cell after this 5000-hour operation was similarly disassembled and investigated, it was found that 10
Large and small streak-like cracks were generated along the grooves of the separator at a rate of one per piece.

The frequency of occurrence of such defects and the extent of cracks were greater than at the time of the survey immediately after assembly.

It is speculated that this is due to the fact that the degree of failure has increased due to the distortion of thermal stress during the thermal cycle between operation and suspension.

On the other hand, in the cells close to the defective separator, defects such as cracks in the positive electrode and cracks in the electrolyte matrix occurred, and burns due to high heat were observed in the vicinity of the defects. It is presumed that hydrogen and air directly reacted through the cracks due to the cracks in the separator and the unit cells, and a burn was generated by the reaction heat.
Also, when a direct reaction of hydrogen and air occurs on the electrode catalyst,
Since the normal negative and positive electrode reactions are hindered, cell characteristics deteriorate.

From the above, it is speculated that the variation in the cell characteristics of the comparative example is larger than the cell characteristics of the fuel cell of the present invention because the cell characteristics deteriorate due to the direct reaction of the reaction gas.

[Effects of the Invention] As described above, according to the fuel cell of the present invention, even if a plurality of unit cells are stacked, the electrodes and the electrolyte matrix are not destroyed, and the stability of the cell characteristics is quick. Has the effect of being

[Brief description of drawings]

FIG. 1 is a cell configuration diagram of a fuel cell according to an embodiment of the present invention, FIGS. 2 and 3 are cell configuration diagrams of typical conventional fuel cells, and FIG. 4 is a diagram of a prior art fuel cell. Cell configuration diagram, FIG. 5 is a schematic diagram of a warp of a laminated element (separator with one side groove), and FIG. 6 is a schematic diagram of cell lamination when a laminated element with warpage (separator with one side groove) is used. It is a figure. DESCRIPTION OF SYMBOLS 1 ... 1st laminated element 2 ... 2nd laminated element 3 ... Conductive adhesive 4 ... Grooved porous carbon substrate 5 ... Negative electrode catalyst layer 6 ... Negative electrode 7 ... Smooth porosity Carbon substrate 8 …… Positive electrode catalyst layer 8 …… Positive electrode 10 …… Matrix layer 11 …… Unit cell 12 …… Stacked element layer 21 …… Stacked element 22.31.41 …… Fuel electrode (negative electrode) 23.32.42 …… Air electrode (positive electrode) 24.33.43 …… Matrix layer 25.34.45 …… Unit cell 46 …… Grooved separator

Claims (1)

[Claims] 1. A negative electrode comprising a porous carbon substrate having a groove for a channel through which a negative electrode active material flows on one surface and a catalyst layer for promoting an electrode reaction on the other surface, and a preliminary waterproofing treatment. A unit cell is formed by closely adhering a positive electrode on which a catalyst layer is supported on a flat plate-like porous carbon substrate on which the catalyst layer is supported so that the respective catalyst layer surfaces face each other through a matrix layer containing an electrolytic solution. In addition, a first laminated element composed of a porous carbon substrate with a single-sided groove that secures an electrical connection path between the unit cells and forms a flow path of the positive electrode active material, a negative electrode active material, and a positive electrode active material. The unit cell is formed by interposing a layered element layer in which a second layered element made of a smooth carbon plate that is gas impermeable and electrically conductive to prevent the mixture of A fuel cell characterized by being laminated.