JPS628453A - Fuel cell - Google Patents

Abstract

PURPOSE:To lengthen the service life by laminating a first laminating element composed of a porous carbon substrate having grooves in one face and a second laminating element composed of a planar carbon plate while impregnating electrolyte in the void sections of the first laminating element. CONSTITUTION:It is comprising a first laminating element 6 composed of a porous carbon substrate having grooves in one face for forming flow path of negative electrode active material or fuel gas while impregnating electrolyte in the void sections and a second laminating element 7 composed of a conductive smooth carbon plate which is gas impermeable to block mixing of negative electrode active material and positive electrode active material while grooves for passing positive electrode active material or oxidizing agent gas are made in the surface contacting with the positive electrode. The unit cell to be held by said elements 6, 7 has integrated negative electrode 1 composed of porous carbon substrate having one face bearing catalyst layer for promoting electrode reaction and positive electrode 2 where catalyst layer is born on one face of planar porous carbon substrate previously applied with water-proofing.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a fuel cell, and in particular, a stacked element has a structure in which a porous carbon material and a dense carbon are separated, and an electrolyte is provided in the pores of the porous carbon material. The present invention relates to a fuel cell constructed by impregnation.

[Technical background of the invention and its problems] A gas that is easily oxidized such as hydrogen and a gas that has oxidizing power such as oxygen are reacted through an electrochemical reaction process, and a Gibbs free energy release valve is activated by direct current electric power. A fuel cell that generates electricity as a fuel cell is usually constructed by stacking a plurality of unit cells. In such a fuel cell, when stacking each unit cell, it is necessary to ensure electrical connection of each unit cell, and at the same time, to supply a reaction gas to each unit cell and to remove reaction products. It is necessary to ensure that

One known method is to use a high-density, gas-impermeable, grooved conductive carbon plate as a so-called laminated element, as shown in FIG. That is, grooves for gas flow in different directions are provided on the upper and lower surfaces of the conductive carbon plate 4, and the upper surface is brought into contact with the porous carbon plate forming the positive electrode 2 (or negative electrode 1) of one unit cell. , the lower surface is brought into contact with the porous carbon plate forming the negative electrode 1 (or positive electrode 2) of the next unit cell, and a plurality of unit cells are laminated one after another, and the grooves of each laminated element 4 are Reaction gas is supplied to each unit cell via the auxiliary unit, and reaction products are removed. Such a unit cell consists of a porous carbon plate serving as a positive electrode 2 and an electrolyte layer 3 made of an impregnated material with excellent chemical resistance, heat resistance, and oxidation resistance, which contains an electrolyte such as a concentrated phosphoric acid solution. A porous carbon plate serving as the negative electrode 1 is integrated with the electrode in close contact with each other. In addition, each of the above-mentioned electrodes is provided with a catalyst such as platinum in order to smoothly proceed with the reaction, and is also waterproofed with polytetrafluoroethylene or the like. Even if the electromotive force of such a unit cell is high, it is about 1 V, and it is necessary to form a WJ layer from a large number of unit cells to construct a practical fuel cell.

In such a cell structure, the negative electrode 1. For both positive electrodes, usually 0.3
Since it is made of porous carbon vapor with a thickness of about 0.5 #II+, it has good electrical conductivity and good diffusion of reaction gas, so high cell performance can be obtained. However, if the electromotive reaction continues for a long period of time, the electrolyte solution (phosphoric acid) will be carried out with the exhaust gas and the phosphoric acid concentration and tension in the electrolyte layer will change, resulting in a decrease in efficiency due to the ohmic loss of the unit cell. A decrease occurs. Furthermore, pores are formed in the electrolyte layer, causing leakage of reaction scum, resulting in a decrease in performance. Therefore, in such a cell structure, it is possible to have the electrolyte held in the porous part of the thin electrode of the negative electrode 1 and the positive electrode 2 to the extent that it does not inhibit the diffusion of the reaction gas to the catalyst layer, but since the porous part is thin, Because the cells cannot hold sufficient amounts of electrolyte, their cell lifespan is at most several thousand hours.

Therefore, a cell structure as shown in FIG. 3 has been proposed as a structure that improves the drawbacks of the cell structure as described above. That is, the negative electrode 21. For the positive electrode 22, a catalyst layer is formed on one side of a porous carbon sheet of about 2 to 3 #I #I by dispersing platinum on fine carbon powder and using a fluororesin such as polytetrafluoroethylene as a binder, and vice versa. Grooves for reactive gas distribution are applied to the surfaces, and M poles with grooves are closely integrated through the electrolyte layer 3 containing electrolyte, with the gas distribution grooves orthogonal to each other and the surfaces of each catalyst layer facing each other. A plurality of unit cells are stacked with an airtight, electrically conductive and smooth stacked element 5 interposed therebetween.

In such a cell structure, the electrolyte is transferred to the rib portion 12 of the ribbed electrode.
Since the electrolyte layer 3 can be held several times as much as the electrolyte layer 3 (reservoir), even if the electrolyte in the electrolyte layer 3 decreases due to evaporation and scattering due to long-term operation, the electrolyte can be replenished from the rib portion 12. As a result, it is possible to prevent a decrease in the volume of the electrolyte in the electrolyte layer 3, thereby preventing a decrease in cell characteristics.
You can expect to drive for a long time. However, according to our study results, when a ribbed electrode is used for the positive electrode 22, the use of a thick porous sheet causes insufficient diffusion of oxidant gas (air) into the catalyst layer, and the porous carbon paper It was found that poor diffusion occurred compared to the conventional method. Furthermore, if the ribbed electrode of the positive electrode 22 contains an electrolyte, gas blocking will be promoted and oxidant gas (air) will not be diffused properly, so the ribbed positive electrode 22 will effectively have an electrolyte reservoir function. It turned out that it wasn't possible.

In addition, in the negative electrode ribbed electrode 21 on the negative electrode side, the diffusion of hydrogen is better than that of air. Even when hydrogen is contained, deterioration in cell characteristics due to poor hydrogen diffusivity hardly occurs. Therefore, substantially only the ribbed electrode 21 on the negative electrode side is capable of retaining electrolyte, but the ribbed electrode porous sheet for the negative electrode 21 also has electrolyte retention of 60% or more of the pore volume due to poor hydrogen diffusion. This cannot be realized because it would result in a deterioration of the characteristics.

As mentioned above, conventional cell structures have a long lifespan.

In order to achieve high performance, (a) increasing the amount of electrolyte retained to replenish the electrolyte layer, and improving mechanical strength to improve handling and yield - reducing the gas diffusion layer (residue); (b) Ensuring gas diffusivity for smooth negative electrode and positive electrode reactions - thinning the remaining thickness.

There is a problem in that it is not possible to satisfy two distinct requirements at the same time.

According to the study results of the present inventors, as shown in FIGS. 4(a) and 4(b), the higher the actual flow rate of the reaction gas passing through the electrode reaction gas distribution groove, the better the gas diffusivity. It has been confirmed that cell characteristics are improved.

Therefore, in order to increase the actual flow rate of gas in the cell structure described above, the remaining thickness d of the ribbed electrode groove shown in FIG. ) can be achieved by reducing . However, in this case, the following problems arise:

(a) If d is made thicker, gas diffusion resistance occurs in the remaining thickness of the porous carbon material, resulting in poor gas diffusion and deterioration of cell characteristics.

(b) When d is made thinner, the mechanical strength becomes smaller, making handling difficult and reducing the yield.

(C) When a is decreased, a portion of the phosphoric acid reservoir becomes smaller, the amount of electrolyte retained decreases, and the life span is shortened.

(d) When a is increased (2.5s+ or more), the height of the stack increases and the power generation capacity per single fuel cell decreases (because the height of the fuel cell is restricted by transportation restrictions). ).

On the other hand, Japanese Patent Application No. 56-18805 and Japanese Unexamined Patent Application Publication No. 58-1981 have been proposed to solve some of the problems of the cell structure as described above.
A fuel cell having a configuration as disclosed in Japanese Patent No.-89780 has been proposed. However, in this method, the amount of phosphoric acid reserved in the porous laminated element is small, and the relationship between the thickness of the unit cell and the groove depth is not specified.

[Object of the invention] The present invention was made in consideration of the above circumstances, and
The purpose of this is to allow the stacked element on the negative electrode side to retain electrolyte to extend its life without degrading the cell characteristics, and to increase the actual flow rate of the reactant gas to improve diffusion of the reactant gas. The object of the present invention is to provide a fuel cell that can improve cell characteristics.

[Summary of the Invention] In order to achieve the above object, the present invention provides a fuel using a concentrated acidic solution as an electrolyte, a gas mainly composed of hydrogen as a negative electrode active material, and an oxidizing gas as a positive electrode active material. In a battery, a negative electrode consists of a flat porous carbon substrate with a catalyst layer supported on one side to promote electrode reactions, and one side of the flat porous carbon substrate has been previously waterproofed. A unit cell is constructed by closely integrating a positive electrode on which a catalyst layer is supported, with the surfaces of each catalyst layer facing each other via an electrolyte layer containing an electrolytic solution, and an electrical connection is established between the unit cells. A first laminated element consisting of a porous carbon substrate with grooves on one side for securing a connection path and forming a flow path for the negative electrode active material, and preventing mixing of the negative electrode active material and the positive electrode active material. A second laminated element consisting of an electrically conductive flat carbon plate which is gas-impermeable and has grooves for circulation of the positive electrode active material on the surface in contact with the positive electrode is interposed to form a plurality of laminated elements. and an electrolyte is impregnated and held in the pores of the first laminated element.

[Embodiments of the invention] An embodiment of the present invention shown in the drawings will be described below.

FIG. 1 shows an example of a cell configuration in a fuel cell according to the present invention in a vertical cross-sectional perspective view.

The fuel cell according to the present invention is characterized by a stacking element used for stacking unit cells. That is, as shown in FIG. 1, the laminated element incorporated in the fuel cell of the present invention has a porous structure with grooves on one side for forming a flow path for the negative electrode active material, that is, fuel residue, and with the pores impregnated and held with electrolyte. a first laminated element 6 made of a carbon substrate, and a gas-impermeable groove for preventing the mixing of the negative electrode active material and the positive electrode active material and in contact with the positive electrode for the passage of the positive electrode active material, that is, the oxidizing gas. It consists of a second laminated element 7 made of an electrically conductive smooth carbon plate provided with. In this case, the channel for flowing the negative electrode active material provided in the first stacked element 6 is formed smaller than that of the conventional one.

The unit cell sandwiched between these laminated elements 6.7 has a negative electrode 1 made of a porous carbon substrate with a catalyst layer supported on one side for promoting electrode reactions, and a negative electrode 1 that has been waterproofed in advance. A cathode 2 having a catalyst layer supported on one surface of a flat porous carbon substrate is closely integrated with the cathode 2 through an electrolyte layer 3 containing an electrolytic solution so that the surfaces of each catalyst layer face each other. This is what I did.

Next, a specific example will be described. In this example, the thickness is 0.4mm and the size is 600+m x 700ra.
Porous carbon paper is formed by molding carbon m fibers into a sheet shape, impregnating it with phenol resin as a binder, and subjecting it to graphitization firing treatment.Platinum black with an Ill ratio of 7% is chemically applied onto the carbon fine powder. concentration of 8 along with catalyst powder reduced and precipitated.
A negative electrode 1 is prepared by applying a catalyst added and kneaded to a polytetrafluoroethylene suspension of % by weight. In addition, porous carbon paper with a thickness of about 0.4 mtn and a size of 600 s++ x 700 MR subjected to graphitization firing treatment was impregnated in a polytetrafluoroethylene suspension with a concentration of 30%.
The material dried and sintered at 330°C for 10 minutes was used as an electrode base, and catalyst powder prepared by chemically reducing and precipitating 10% platinum black on carbon fine powder and polytetraflu 40 at a concentration of 8% by weight were added to the catalyst powder. A positive electrode 2 is prepared by applying a catalyst added to and kneaded with an ethylene suspension. Then, an electrolyte layer 3 formed by impregnating 105% phosphoric acid electrolyte into a matrix obtained by mixing and kneading 5% by weight of polytetrafluoroethylene with silicon carbide powder having an average particle size of 0.4μ is interposed in the middle. , each catalyst layer surface is the electrolyte layer 3
A unit cell was formed by disposing a negative electrode 1 and a positive electrode 2 facing each other so as to be in contact with each other.

Next, the thickness is 2.561#l or less and the size is 6001n
As the first laminated element 6, a fuel gas distribution groove 8 having a groove width of 1.6s+, a groove depth of 0.81RIR, and a pitch of 3m is provided on one side of a felt-like porous graphite $11ff plate of MX700s+. and the size is 6001NRX700
Grooves with a groove width of 2M are formed on one side of a gas-impermeable carbon plate or a resin-bonded carbon plate made of a binder made by kneading carbon (mainly graphite) and a binder such as a phenolic resin and press-formed by hot pressing or the like. A second laminated element 7 having oxidizing gas circulation grooves with a depth of 1.5 m and a pitch of 4 was used as the second laminated element 7, and the above unit cells were sequentially laminated as shown in FIG.

In this case, 90% of the pores of the first laminated element 6 are impregnated with phosphoric acid electrolyte before lamination. Further, the fuel gas distribution groove 8 and the oxidant gas distribution groove are 99 degrees apart from each other.
The directions are different by 0°, that is, the directions are orthogonal.

In the fuel cell of this embodiment configured as described above, the phosphoric acid electrolyte impregnated and held in the pores of the first stacked element 6 is absorbed into the electrolyte layer 3 during long-term operation of the fuel cell. Lin? i! When the electrolyte decreases due to evaporation and scattering, it is replenished to the negative electrode 1 via the rib portion 9 of the first laminated element 6 due to gravity and electrolyte concentration gradient capillarity, and the phosphoric acid electrolyte in the electrolyte layer 3 It is possible to suppress the volume reduction and prevent the deterioration of cell characteristics. in this case,
Unlike conventional ribbed electrodes, the fuel gas flow surface 10 itself is not impregnated with phosphoric acid electrolyte. By impregnating 90% of the electrode with phosphoric acid electrolyte, it is possible to achieve a reserve effect that is approximately twice that of conventional ribbed electrodes.

In addition, as mentioned earlier, the actual flow velocity of the reactant gas can be increased by reducing the cross-sectional area of the reactant gas flow, which could not be achieved with conventional ribbed electrodes due to poor gas diffusion and reduced reservoir function. In this embodiment, by making the groove depth of the gas flow groove 8 of the first laminated element 6 shallower, this can be realized without adverse effects such as poor gas diffusion on the cell. Furthermore, as a secondary effect, by increasing the actual flow rate of the reactant gas as shown in FIG. Since the volume of 6 also increases, it becomes possible to hold more electrolyte.

This makes it possible to simultaneously improve cell characteristics and extend life.

Furthermore, the cross-sectional area of the reaction gas distribution grooves has been made smaller than before, so when a large number of unit cells are stacked, the pressure when the reaction gas passes through the distribution grooves increases, so the gas distribution of the stacked cells is reduced. There is also an advantage that the battery characteristics can be made uniform in the stacking direction. In addition, since the flow cross-sectional area of the reactant gas has been made smaller than before, even with a laminated element of the same thickness, the remaining thickness of the fuel gas flow groove 11 is thicker and the strength is increased, which reduces breakage during handling. You also get benefits.

It should be noted that the present invention is not limited to the above embodiments, but can also be implemented as follows.

(a) In the above embodiment, the groove depth of the first laminated element 6 is 1.4 m, and the groove depth of the second laminated element 7 is 1.5 m.
A similar effect was obtained even when the paper was closed.

(b) In the above embodiment, when the groove depth of the first laminated element 6 is 2.0s+ or 0.7mm, the number of laminated layers is 50
When it reached the cell height or higher, it was observed that the battery characteristics deteriorated in the height direction, especially at the upper and lower ends. Further, when the groove depth was 0.7 mm, the influence of machining accuracy or blockage was particularly investigated.

(C) In the above embodiment, similar effects were obtained even when a porous carbon material (conventional electrode material with electrodes) was used for the first laminated element 6.

(d) In the above embodiment, the first laminated element 6 may have a porosity of about 40 to 70%, preferably about 55 to 65%.

In addition, the present invention can be implemented with various modifications without changing the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, a fuel is produced in which a concentrated acidic solution is used as an electrolyte, a gas mainly composed of hydrogen is used as an active material on the negative electrode side, and an oxidizing gas is used as an active material on the positive electrode side. In a battery, a negative electrode consisting of a flat porous carbon substrate with a catalyst layer supported on one surface for promoting electrode reaction;
A positive electrode having a catalyst layer supported on one side of a flat porous carbon substrate that has been waterproofed in advance is brought into close contact with the catalyst layer surfaces facing each other through an electrolyte layer containing an electrolyte. A first laminated layer consisting of a porous carbon substrate with one side full for ensuring an electrical connection path between the unit cells integrated and forming a flow path for the negative electrode active material. from an electrically conductive flat carbon plate that is gas-impermeable and has grooves for circulation of the positive electrode active material on the surface in contact with the positive electrode to prevent mixing of the positive electrode active material as the negative electrode active material. The second laminated element is interposed to form a plurality of 8% layers, and the pores of the first laminated element are impregnated and retained with the electrolyte, so that the negative electrode can be formed without deteriorating the cell characteristics. It is an extremely reliable product that can have an electrolyte in the side laminated element to extend its life, and also increases the actual flow rate of the reactant gas to improve the diffusion of the reactant gas and improve the cell characteristics. High-quality fuel cells can be provided.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional perspective view showing one embodiment of the present invention, FIGS. 2 and 3 are typical cell configuration diagrams of a conventional type, and FIG.
FIG. 5 is an enlarged view showing a typical conventional cell configuration. DESCRIPTION OF SYMBOLS 1... Negative electrode, 2... Positive electrode, 3... Electrolyte layer, 6...
...first laminated element, 7...second laminated element, 8
... Fuel gas distribution groove, 9... Rib portion, 1o...
Fuel gas distribution surface, 11...Fuel gas distribution groove remaining thickness. Applicant's agent Patent attorney Takehiko Suzue No. 2 Figure No. 3 Prisoner

Claims (3)

[Claims] (1) To promote electrode reactions on one side in a fuel cell that uses a concentrated acidic solution as an electrolyte, a gas mainly composed of hydrogen as an active material on the negative electrode side, and an oxidizing gas as an active material on the positive electrode side. A negative electrode consisting of a flat porous carbon substrate with a catalyst layer supported on it, and a positive electrode with a catalyst layer supported on one side of a flat porous carbon substrate that has been waterproofed in advance are connected to an electrolytic solution. The unit cells are formed by closely integrating the respective catalyst layer surfaces with each other facing each other via an electrolyte layer containing an electrolyte. a first laminated element consisting of a porous carbon substrate with grooves on one side for forming channels;
and a second plate made of an electrically conductive flat carbon plate, which is gas-impermeable and has grooves for the circulation of the positive electrode active material on its surface in contact with the positive electrode, to prevent mixing of the negative electrode active material and the positive electrode active material. A plurality of laminated layers are formed by interposing a laminated element of
A fuel cell characterized in that the pores of the first laminated element are impregnated and held with an electrolyte. (2) In the product described in claim (1), the groove shape provided in the first laminated element made of a porous carbon substrate has a groove depth of 0.8 to 1.4 mm. A fuel cell characterized by: (3) In the device according to claim (1), the porosity of the first laminated element is 40 to 70%;
A fuel cell characterized in that it is preferably 55-65%.