JPH0640493B2 - Fuel cell - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a fuel cell, and in particular, a laminated element having a separated or composite structure of a porous carbon material and a dense carbon, and a porous carbon material having pores formed therein. The present invention relates to a fuel cell configured by impregnating an electrolyte.

[Technical background of the invention and its problems] A gas that is easily oxidized, such as hydrogen, and a gas that has an oxidizing power, such as oxygen, are reacted through an electrochemical reaction process, and the Gibbs free energy release is converted to DC power. A fuel cell for generating power is usually constructed by stacking a plurality of unit cells. In such a fuel cell, when stacking the unit cells, a gas passage for ensuring electrical connection between the unit cells and at the same time supplying a reaction gas to each unit cell and removing a reaction product. Must be secured.

As one of the methods, an example is known in which a high-density, gas-impermeable, grooved conductive carbon plate as shown in FIG. 3 is used as a so-called laminated element.

That is, gas flow grooves in different directions are provided on the upper surface and the lower surface 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 the 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 the positive electrode 2) of the next unit cell to stack a plurality of unit cells one after another and through the grooves of each stacking element 4. Then, the reaction gas is supplied to each unit cell, and the reaction products are removed. Such a unit cell is a porous carbon plate which becomes a positive electrode 2 with an electrolyte layer 3 made of an impregnating material containing an electrolytic solution containing a concentrated phosphoric acid solution and having excellent chemical resistance, heat resistance and oxidation resistance as an intermediate. The porous carbon substrate to be the negative electrode 1 is opposed to and closely adhered to and integrated with each other. Further, in order to smoothly proceed the reaction, a catalyst such as platinum is applied to each of the above-mentioned electrodes, and a waterproof treatment with polytetrafluoroethylene or the like is performed. Such a unit cell has a high electromotive force of about 1 V even if the unit cell has a high electromotive force, and it is necessary to stack a large number of unit cells to construct a practical fuel cell.

In such a cell structure, both the negative electrode 1 and the positive electrode 2 are usually 0.3
Since it is made 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, if the electromotive reaction is continued for a long period of time, the electrolyte solution (phosphoric acid) is discharged to the outside together with the exhaust gas, and the phosphoric acid concentration and amount in the electrolyte layer change, so that the efficiency due to the ohmic loss of the unit cell is reduced. A decline occurs. Furthermore, pores are formed in the electrolyte layer, which causes a leak of the reaction gas through it, resulting in a decrease in performance. Therefore, in such a cell structure, it is possible to retain the electrolyte in the porous portions of the thin electrodes of the negative electrode 1 and the positive electrode 2 to the extent that the diffusion of the reaction gas into the catalyst layer is not hindered, but the porous portions are thin. Since it is not possible to retain a sufficient amount of electrolyte, its cell life is at most several thousand hours.

Therefore, a cell structure as shown in FIG. 4 has been proposed as a structure in which the above-mentioned drawbacks of the cell structure are improved. That is, both the negative electrode 21 and the positive electrode 22 have a porous carbon sheet of about 2 to 3 mm, and platinum is dispersed on fine carbon powder to form a catalyst layer using a fluororesin such as polytetrafluoroethylene as a binder, and A ribbed electrode on the opposite side of which a groove is formed for reaction gas flow is adhered integrally so that the gas flow grooves are orthogonal to each other through the electrolyte layer 3 containing an electrolyte and the respective catalyst layer surfaces face each other. The unit cells thus formed are laminated with a plurality of unit cells being interposed with the air-tight and conductive smooth laminated element 5 interposed.

In such a cell structure, since the electrolyte can be retained in the rib portion 6 of the ribbed electrolysis several times as much as the electrolyte layer 3 (reservoir), evaporation of the electrolyte in the electrolyte layer 3 due to long-term operation is prevented. Also, even if a decrease due to scattering occurs, the volume of the electroactive material in the electrolyte layer 3 can be prevented from decreasing by replenishing the electrolyte from the rib portion 6, so that deterioration of cell characteristics can be prevented and long-term operation can be expected. . However, according to our study results, when the ribbed electrode is used for the positive electrode 22, insufficient diffusion of the oxidant gas (air) into the catalyst layer occurs due to the use of the thick porous sheet, and the porous carbon paper is used. It was found that diffusion failure occurs as compared with. Further, when the ribbed electrode of the positive electrode 22 holds the electrolyte, gas blocking is promoted and further the oxidant gas (air) does not diffuse well. Therefore, the ribbed electrode 22 for the positive electrode practically has the electrolyte reservoir function. It turns out that this is not possible.

In the negative electrode rib electrode 21 for the negative electrode, since diffusion of hydrogen has better diffusivity than diffusion of air, the electrolyte is used in the range of 60% or less of the pore volume of the porous sheet of the rib electrode. In the case of containing hydrogen, the cell characteristics hardly deteriorate due to the poor diffusibility of hydrogen. Therefore, substantially only the ribbed electrode 21 on the negative electrode side can retain the electrolyte, but the negative electrode 21 also has 60% or more of the pore volume of the ribbed electrode porous sheet, which is associated with defective hydrogen diffusion. It cannot be realized because it causes deterioration of the characteristics.

As described above, in order to achieve a long life and high performance in the conventional cell structure, (a) increase the amount of electrolyte retained for replenishing the electrolyte layer with the electrolyte, and to improve handling and yield. Improvement of mechanical strength --- Thickening gas diffusion layer (residual wall) (b) Ensuring gas diffusivity for smoothly proceeding negative and positive electrode reactions --- Thinning residual wall.

There is a problem that the two contradictory matters cannot be satisfied at the same time.

According to the results of studies by the present inventors, as shown in FIGS. 5 (a) and 5 (b), the higher the actual flow velocity of the reaction gas passing through the flow passage of the electrolytic reaction gas, the better the gas diffusivity. It has been confirmed that the cell characteristics are improved.

Therefore, in order to increase the actual gas flow velocity in the above-mentioned cell structure, the ribbed electrode groove portion residual thickness d shown in FIG. 6 should be increased, or the ribbed electrode rib portion a (that is, the ribbed electrode thickness ) Can be achieved.
However, in this case, there is a problem that the following harm occurs.

When (a) d is made thick, gas diffusion resistance occurs in the residual portion of the porous carbon material, gas diffusion becomes poor, and cell characteristics deteriorate.

(B) When d is made thin, mechanical strength becomes small, handling becomes difficult, and the yield decreases.

(C) When a is reduced, the phosphoric acid reservoir portion is reduced, the amount of electrolyte retained is reduced, and the life is shortened.

(D) When a is increased (2.5 mm or more), the height of the stacked pair is increased and the power generation capacity per unit fuel cell is decreased (because the height of the fuel cell is restricted by transportation restrictions). ).

On the other hand, as a solution to some of the problems of the cell structure as described above, Japanese Patent Application No. 56-18805 and Japanese Patent Application Laid-Open No. 58-58805.
A fuel cell having a structure as disclosed in Japanese Patent Publication No. 89780 has been proposed. However, in this system, the amount of phosphoric acid reserved in the porous laminated element is small, and the relationship between the unit cell thickness and the groove depth is not specified.

[Object of the Invention] The present invention has been made in consideration of the above circumstances.
The purpose of this is to allow the laminated element on the negative electrode side to retain the electrolyte without degrading the cell characteristics, and to effectively move the retained electrolyte to the electrolyte layer to achieve a long life, Moreover, it is an object of the present invention to provide a fuel cell capable of increasing the actual flow rate of the reaction gas to improve the diffusion of the reaction gas and improve the cell characteristics.

[Summary of the Invention] In order to achieve the above object, in the present invention, a concentrated acidic solution is used as an electrolyte, a fuel gas containing hydrogen as a main component is used as a negative electrode side active material, and an oxidizing gas is used as a positive electrode side active material. In a fuel cell, a negative electrode having a catalyst layer for promoting an electrode reaction on one surface of a flat plate-like porous carbon substrate on which a hydrophilic portion is selectively formed in a strip shape and a waterproof treatment are previously applied. And a positive electrode having a catalyst layer supported on one surface of a flat plate-shaped porous carbon substrate, which are closely integrated so that the respective catalyst layer surfaces face each other through an electrolyte layer containing an electrolytic solution. A unit cell formed of a porous carbon substrate having a single-sided groove for forming a flow groove for the negative electrode active material between the unit cells, and 40% or more of the pores thereof are impregnated with an electrolyte; Laminated element, the negative electrode active A second laminated element made of a gas-impermeable carbon thin plate for preventing the mixture of the substance and the positive electrode active material, and a porous carbon substrate having a positive electrode active material flow groove formed on the surface in contact with the positive electrode. The third stacking element is superposed so as to sandwich the second stacking element, and the grooves of the first stacking element and the third stacking element are on the outside and are orthogonal to each other. A plurality of laminated elements are arranged so that the groove of the first laminated element to be bonded to the negative electrode is arranged so as to be orthogonal to the strip-shaped hydrophilic portion of the negative electrode. .

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention shown in the drawings will be described below.
FIG. 1 is a vertical cross-sectional perspective view showing a cell configuration example in a fuel cell according to the present invention.

The characteristic feature of the fuel cell according to the present invention resides in the laminated element used for laminating the unit cells and the hydrophilic structure of the negative electrode substrate.
That is, as shown in FIG. 1, the laminated element incorporated in the fuel cell of the present invention has a porous structure having a groove on one side for forming a flow groove for a negative electrode active material, that is, a fuel gas, and impregnated with an electrolyte in the pores. A first laminated element 7 made of a carbon substrate,
A second laminated element 8 made of a gas-impermeable carbon thin plate for preventing the mixture of the negative electrode active material and the positive electrode active material, and a groove for flowing the positive electrode active material, that is, the oxidant gas, is provided on the surface in contact with the positive electrode. The third laminated element 9 is made of a porous carbon substrate in which pores are impregnated with an electrolyte and held. The unit cell sandwiched between these laminated elements 7, 8 and 9 has an electrode reaction on one surface of a flat plate-like porous carbon substrate on which selectively hydrophilic and good electrolyte mobility parts are formed. Negative electrode 1 carrying a catalyst layer for promoting
And a positive electrode 2 in which a catalyst layer is carried on one surface of a flat plate-like porous carbon substrate that has been subjected to a waterproof treatment in advance, and the above-mentioned catalyst layers are opposed to each other via an electrolyte layer 3 impregnated with an electrolytic solution. It is one that is closely attached so that it faces each other.

Next, a specific example thereof will be described. In this example, first, carbon fibers having a thickness of 0.4 mm and a size of 600 mm × 700 mm are formed into a sheet shape, impregnated with a phenolic resin as a binder, and subjected to graphitization and firing treatment to obtain a porosity (void). Porosity of about 70%) Carbon black was added to a polytetrafluoroethylene suspension having a concentration of 8% by weight together with a catalyst powder obtained by chemically reducing and depositing 7% by weight of platinum black on fine carbon powder and kneading. Negative electrode 1 is prepared by applying the above catalyst. Further, here, the carbon paper is masked with a plastic film 13 as shown in FIG. 2 (a), and as shown in FIG. 2 (b), it is latticed with a polytetrafluoroethylene suspension having a concentration of 20% by weight. Selectively water repellent treatment 15
Then, the hydrophilic portion 16 is formed into a band shape.

Also, the thickness is about 0.4 mm, and the size is 600 mm x 700 mm.
The porous carbon paper that has been subjected to the graphitization baking treatment of
A polytetrafluoroethylene suspension having a concentration of 30% by weight was previously impregnated, dried (water repellent treatment), and sintered at 330 ° C. for 15 minutes by using an electrode gas. A positive electrode 2 is produced by applying a catalyst which is obtained by adding and kneading platinum black to a suspension of polytetrafluoroethylene having a concentration of 8% by weight together with a catalyst powder obtained by chemically reducing and depositing platinum black.

Then, an electrolyte layer 3 formed by impregnating 105% phosphoric acid electrolyte into a matrix prepared by mixing and kneading 5% by weight of polytetrafluoroethylene with sillin carbide powder having an average particle size of 0.4 μ is interposed in the middle. The anode 1 and the cathode 2 so that the respective catalyst layer surfaces are in contact with the electrolyte layer 3.
And were arranged so as to face each other to form a unit cell.

Next, the thickness is 2.0mm or less, and the size is 600mm × 700.
mm of carbon fiber and phenolic resin kneaded material is formed into a plate shape, and graphitized and baked on one side of a porous carbon substrate (average density 0.50 g / cm ³ , pore diameter 20 to 150 μ).
A fuel gas flow groove 10 having a groove width of 1.6 mm, a groove depth of 0.9 mm, and a pitch of 3 mm is provided as a first stacking element 7, and the fuel gas flow groove 10 has a negative electrode 1 as shown in FIG. Facing each other, the size is 600mm × 700mm,
A gas-impermeable carbon plate, for example, a vitreous carbon plate having a thickness of 1.0 mm is used as a second laminating element 8 and the first laminating layer opposite to the fuel gas flow groove 10 side as shown in FIG. First laminated element 7 having a size of 600 mm × 700 mm which is bonded to the surface of the element 7 and further has an air circulation groove 11 formed therein.
The same material as in the above but with a thickness of 2.1 mm is used as the third laminated element 9
As shown in FIG. 1, the side of the air circulation groove 11 is joined to the positive electrode 2 and the layers are sequentially laminated.

In this case, 40% or more, preferably 80% or more, of the void volume of the first laminated element 7 before lamination, and 60% or more of the same for the third laminated element 8 are each provided with a phosphoric acid electrolyte. Keep impregnated. Further, the fuel gas flow groove 10 and the air flow groove 11 are in directions different from each other by 90 °, that is, in directions orthogonal to each other. Further, the rib portion 6 of the first laminated element 7 is arranged so as to be orthogonal to the hydrophilicity 16 of the negative electrode 1,
As shown in Figure (c), the phosphate electrolyte transfer part is formed.

In the fuel cell of this example configured as described above, the phosphoric acid electrolyte impregnated and held in the pores of the first stacking element 7 is contained in the electrolyte layer 3 associated with the long-term operation of the fuel cell. When the amount of the phosphoric acid electrolyte is reduced by evaporation and scattering, the phosphoric acid moving part of the negative electrode 1 penetrates through the rib portion 6 of the first stacking element 7 due to gravity and capillary action (surface tension) of the electrolyte itself. It moves and is replenished to the electrolyte layer 3, so that the electrolyte layer 3 is always filled with the phosphoric acid electrolyte and it is possible to prevent the deterioration of the cell characteristics. In this case, unlike the conventional ribbed electrode system, the fuel gas flow surface itself is hardly impregnated with the phosphoric acid electrolyte, so that gas diffusion failure due to blocking against gas diffusion does not occur, and the first lamination The phosphoric acid electrolyte can be impregnated to 60 to 100% of the porosity of the element 7, and the reserve effect of about 2.5 times that of the conventional ribbed electrode can be obtained even with the same laminated element thickness. be able to.

Further, in the conventional ribbed electrode, as described above, the gas diffusion failure, the reduction of the reservoir function, and the like occur, so that the reaction gas flow groove cross-sectional area cannot be reduced.
In this respect, in this embodiment, in order to improve the power generation efficiency of the fuel cell, the operation in which the ratio of the fuel gas and the air involved in the respective electrode reactions is large, that is, the utilization rate of the reaction gas is large. However, by making the groove depths of the fuel gas flow groove 10 of the first stacking element 7 and the air flow groove 11 of the third stacking element 9 shallower, gas diffusion failure in the cell is caused. It can be realized without adverse effects such as the above, and without shortening the life, while maintaining high mechanical strength. As a secondary effect, not only can cell characteristics be improved by increasing the actual flow rate of the reaction gas as shown in FIGS. The pore volume of the element 6 is increased, the negative electrode 1 is thin, and the water repellent portion 15 is not blocked by the phosphoric acid electrolyte and gas diffusion is not hindered, so that more electrolyte can be retained. Becomes This makes it possible to simultaneously improve the cell characteristics and extend the life of the cell.

Furthermore, since the reaction gas flow cross-sectional area can be made smaller than in the conventional case, not only the handleability of the first and third stacking elements 7 and 9 is improved and the yield is improved, but also a large number of unit cells are stacked. In this case, the pressure loss when the reaction gas passes through the flow grooves increases, so that the gas distribution in the stacking direction of the stacked cells can be made uniform, and the battery characteristics in the stacking direction can be made uniform.

The present invention is not limited to the above embodiment, but can be carried out as follows.

(A) In the above embodiment, the groove depths of the first and third laminated elements 7 and 9 are 1.4 mm, and the second laminated element 8 is
Even if the groove depth was 1.5 mm, the same effect was obtained.

(B) In the above example, the same effect was obtained even when a porous carbon material (conventional ribbed electrode material) was used for the first laminated element 7.

(C) In the above embodiment, even if the laminated element in which the fine powder pine (Vulcan XC-72R) is impregnated in the void portion of the first laminated element 7 in advance to 3% of its volume is used,
Similar effects were obtained.

(D) In the above-mentioned example, the negative electrode 1 was coated with a polytetrafluoroethylene suspension having a concentration of 30% by weight in advance and dried to burn the catalyst, and then formed into a lattice with the plastic film 13 as shown in FIG. The same effect as described above was obtained by masking and subjecting the silicon carbide fine powder suspension to print impregnation with a roll coater to form a hydrophilic phosphoric acid transfer portion.

(E) In the above embodiment, the first and third laminated elements 7 and 9 having a porosity of 40 to 70%, preferably about 55 to 65% can be used.

(F) In the above embodiment, the phosphoric acid electrolyte may be impregnated and retained in at least the first laminated element 7 of the first or third laminated elements 7 or 9.

Besides, the present invention can be variously modified and implemented without changing the gist thereof.

As described above, according to the present invention, a concentrated acidic solution is used as an electrolyte, a fuel gas containing hydrogen as a main component is used as a negative electrode side active material, and an oxidizing gas is used as a polar side active material. In the fuel cell, a negative electrode having a catalyst layer for promoting an electrode reaction on one surface of a flat plate-like porous carbon substrate on which a hydrophilic portion is selectively formed in a strip shape and a waterproof treatment are previously performed. A positive electrode having a catalyst layer supported on one surface of a flat plate-shaped porous carbon substrate that has been subjected to, the catalyst layer surface is opposed to each other through an electrolyte layer containing an electrolyte solution, and are integrally integrated. The unit cell thus constructed is composed of a porous carbon substrate having a single-sided groove for forming a flow groove of the negative electrode active material between the unit cells, and 40% or more of the pores are impregnated with an electrolyte. 1 laminated element, the negative electrode active material A second laminated element made of a gas-impermeable carbon thin plate for preventing the mixture of the quality and the positive electrode active material, and a porous carbon substrate provided with a flow groove for the positive electrode active material on the surface in contact with the positive electrode. The third stacking element is formed so as to sandwich the second stacking element, and the grooves of the first stacking element and the third stacking element are located outside and are orthogonal to each other. A plurality of laminated elements are arranged so that the grooves of the first laminated element to be bonded to the negative electrode are arranged so as to be orthogonal to the strip-shaped hydrophilic portion of the negative electrode, with the laminated element to be laminated. The electrolyte can be retained in the laminated element on the negative electrode side without deteriorating the cell characteristics, and the retained electrolyte can be effectively moved to the electrolyte layer to prolong the life, and the actual flow velocity of the reaction gas can be increased. Increase reaction gas diffusion High fuel cell extremely reliable which can favorably improve cell characteristics can be provided.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional perspective view showing an embodiment of the present invention, and FIGS. 2 (a) to (c) are perspective views for explaining a hydrophilic treatment method for a negative electrode in the embodiment, FIG. FIG. 4 shows a typical conventional cell structure, FIGS. 5 (a) and 5 (b) are characteristic diagrams for explaining the function and effect of the present invention, and FIG. 6 shows a conventional typical cell structure. FIG. 1 ... Negative electrode, 2 ... Positive electrode, 3 ... Electrolyte layer, 7 ... First
Laminated element, 8 ... second laminated element, 9 ... third laminated element, 11 ... air circulation groove, 10 ... fuel gas circulation groove, 6 ... rib portion, 12 ... carbon Powder layer, 13 ... Plastic film, 15 ... Water repellent part, 16 ... Hydrophilic part.

Claims (4)

[Claims] 1. In a fuel cell using a concentrated acidic solution as an electrolyte, a fuel gas containing hydrogen as a main component as a negative electrode side active material, and an oxidizing gas as a positive electrode side active material, a band-shaped selective hydrophilic property. One side of the flat plate-like porous carbon substrate on which a part is formed and one side of the negative electrode on which a catalyst layer for promoting an electrode reaction is supported, and one of the flat plate-like porous carbon substrate that has been previously subjected to waterproofing treatment A positive electrode having a catalyst layer supported on its surface, a unit cell constituted by closely integrating the respective catalyst layer surfaces so as to face each other through an electrolyte layer containing an electrolytic solution, between the unit cells. A first laminated element comprising a porous carbon substrate having a single-sided groove for forming a flow groove of the negative electrode active material, and having an electrolyte impregnated into 40% or more of the pores thereof, the negative electrode active material and the positive electrode To prevent mixing of active materials Second consisting scan impermeable carbon thin
And a third stacking element composed of a porous carbon substrate having a positive electrode active material flow groove provided on the surface in contact with the positive electrode so as to sandwich the second stacking element. The first laminated element and the third laminated element have respective grooves on the outer side, and interpose a laminated element formed by overlapping so as to be orthogonal to each other, and further to be orthogonal to the strip-shaped hydrophilic portion of the negative electrode. A fuel cell, wherein a plurality of fuel cells are laminated so that the groove of the first laminated element joined to the negative electrode is arranged. 2. The device according to claim 1, wherein at least one of the first and third laminated elements made of a porous carbon substrate is impregnated with hydrophilic particles. A fuel cell characterized by the above. 3. A fuel cell according to claim (1), characterized in that the negative electrode is impregnated with hydrophilic particles in a strip shape by a roll coater. 4. The fuel cell according to claim (2) or (3), wherein the hydrophilic particles are carbon powder or silicon carbide powder.