JPH084009B2 - Fuel cell - Google Patents

Description

The present invention relates to a fuel cell, and more particularly to a fuel cell having a gas seal structure at an electrode end portion of a cell stack of a phosphoric acid fuel cell. .

(Prior Art) Conventionally, a fuel cell has been used as a device for directly converting the energy of fuel into electrical energy. In this fuel cell, a pair of porous electrodes are usually arranged with a matrix impregnated with an electrolyte, a fluid fuel such as hydrogen is brought into contact with the back of one electrode, and a fluid oxidizer such as oxygen is placed on the back of the other electrode. It is configured to contact the agent and take out the electric energy between the two electrodes by utilizing the electrochemical reaction that occurs at this time. As long as the fuel and the oxidant are supplied, high conversion efficiency is obtained. Can extract electrical energy.

FIG. 3 is a longitudinal sectional perspective view of a fuel cell constituting a fuel cell stack by stacking a plurality of unit cells of a fuel cell using phosphoric acid as an electrolyte. That is, as shown in FIG. 3, a unit cell is a pair of ribbed electrodes 2 formed of a porous body on both sides of a matrix 1 impregnated with phosphoric acid as an electrolyte and having a catalyst added thereto.
(Usually made of carbon material), and this pair of ribbed electrodes 2 is opposite to the catalyst-added surface, that is, the anti-matrix 1.
Each of the surfaces has a flow passage for a fluid fuel and a fluid oxidant, and a plurality of the unit cells are alternately stacked via a gas separation plate 3 to constitute a fuel cell stack.

By the way, in this type of fuel cell, as shown in the sectional view of FIG.
In order to prevent leakage of fuel gas or oxidant gas, a fluororesin film 4 is adhered to the end portion of the ribbed electrode 2, and a fluorogrease, a fluororubber sheet or a fluororesin tape 6 is further arranged thereon. I try to seal it. However, since the conventional seal lacks heat resistance, electrolyte resistance, compactness and elasticity, the adhesion between the ribbed electrode 2 and the gas separation plate 3 is poor, resulting in gas leakage from these parts. Mixing of the fuel gas and the oxidant gas occurred, which burned on the catalyst and caused local heat generation, increasing the scattering of the electrode quality. Moreover, this causes a crossover between the electrodes, which has been a problem of significantly shortening the life of the fuel cell.

(Problems to be Solved by the Invention) The present invention has been made to solve the above problems, and its purpose is to provide elasticity between each electrode end portion and a gas separation plate adjacent thereto. Another object of the present invention is to provide a fuel cell capable of improving the adhesion and reliably preventing gas leakage from this gap, and extending the life of the fuel cell.

[Structure of Invention]

(Means for Solving Problems) In order to achieve the above object, the present invention arranges a pair of electrodes with ribs in which a flow passage for a liquid fuel and a fluid oxidant is formed with an electrolyte-impregnated matrix sandwiched therebetween. And then
In a fuel cell configured by stacking a plurality of unit cells that output electric energy under the condition that a fuel and an oxidant are flowing in each of the flow passages, the unit cell facing the gas separating plate Kneading in which a fluororesin tape is placed at the end of the ribbed electrode, and 30-60 wt% of scale-like graphite powder and 70-40 wt% of phosphoric acid are kneaded on the surface of the gas separating plate facing the fluororesin tape. The graphite powder has a particle size range of 20 to 100.
The feature is that the average particle size is 20 to 30 μm.

(Operation) First, the feature of the present invention lies in that a kneaded material obtained by kneading heat-resistant and electrolyte-resistant scale-like graphite powder and an appropriate amount of two components of phosphoric acid is combined with a porous fluororesin tape. The point is that it is used as a sealing material.

In this case, as the graphite powder, a high-purity scale-like material or the like is used, and preferably the particle size range is 20 to 100 μ and the average particle size is 20.
-30μ is preferable. That is, if there are many fine powders or ultrafine powders less than this, it is necessary to remarkably increase the amount of phosphoric acid in the mixing ratio when kneading with phosphoric acid to form a slurry having an appropriate viscosity. In this case, the sealing property can be initially maintained, but if phosphoric acid volatilizes due to long-term operation, gas leakage from the gap between the ribbed electrode end and the gas separation plate will increase. This is because it has drawbacks. The proper mixing ratio of the two components of phosphoric acid and graphite powder was examined. That is, as an example, a scale-like graphite powder and an orthophosphoric acid conversion concentration of 100 wt% phosphoric acid were used to determine an appropriate blending range of the two components. That is, when the amount of scaly graphite powder is increased, it tends to gradually harden and lack in extensibility, and when the amount of graphite powder is further increased, it becomes powdery and the effect as a sealing material cannot be expected. Further, when the amount of phosphoric acid is increased, it becomes less viscous and approaches a liquid state, the fluidity becomes extremely large, and the sealing property is lost.

From the above qualitative results, in more detail, the kneaded mixture of the two components was sandwiched between the fluororesin film and the gas separation plate, the grease spread under a predetermined load, and the thickness and sealing property were observed. Is as shown in Table 1.

By the way, if the kneaded product is used as it is, many air bubbles remain inside and the sealing performance will deteriorate.
When the mixture is heated at 200 ° C. for about 1 hour and then degassed under reduced pressure, air bubbles in the interior are almost eliminated and a smooth slurry-like kneaded product is obtained, which facilitates the coating treatment on the end portion of the electrode.

Next, the second example of kneading mixture preparation with a specific mixing ratio
The table will be described.

First, the concentration (orthophosphoric acid equivalent) 100w in the container (content 11)
t% Phosphoric acid (650 g) is added, the scale-like graphite (350 g) is added, and the mixture is stirred until it becomes a slurry. Next, the whole container is placed in a constant temperature bath at 200 ° C., heated for about 1 hour and then depressurized to remove air present in the kneaded product.
At this time, the phenomenon of being degassed is observed when the mixture rises in a Calmey-like state in the initial stage. Mixing, heating and degassing are repeated again to obtain a smooth kneaded product.

The kneaded product of graphite and phosphoric acid according to the present invention is also well compatible with the gas separation plate and the ribbed electrode made of a carbon material, and even if used alone as a sealing material, good sealing properties can be obtained. Do you get it.

By the way, although the example shows the case of 100 wt% phosphoric acid, the same effect can be obtained by using phosphoric acid having an orthophosphoric acid equivalent concentration of 50 wt% to 130 wt%, but phosphoric acid in the range of 80 wt% to 110 wt% is used. It has been found that a better effect can be obtained by using.

However, by adopting a structure in which the coating layer of the kneaded material and the porous fluororesin tape are arranged to face each other, the kneaded material is added to the porous portion of the fluororesin tape by stacking and pressurizing the gas separation plate. A part of is mixed in, and a flexible and durable sealing layer is formed. Therefore, even if an abnormal differential pressure of the gas is generated, the kneaded material is not extruded from the predetermined position by the gas pressure, and the sealing property of the laminated surface is completely maintained,
It has been found that a long-life fuel cell can be obtained. The appropriate thickness of the fluororesin tape was around 0.1 mm from the viewpoint of sealability and usability.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an example of a structure between an electrode end portion of a laminate and a gas separation plate in a phosphoric acid fuel cell to which the sealing material of the present invention is applied.

As shown in the figure, in the present embodiment, the heat-resistant and electrolyte-resistant flaky graphite powder described above is provided between the end portion of the ribbed electrode 2 and the gas separation plate 3 in the fuel cell stack having the above-described structure. A kneaded material 5 obtained by kneading 30 to 60 wt% and phosphoric acid 70 to 40 wt% and a porous fluororesin tape 6, for example, a polytetrafluoroethylene tape are provided as a sealing material.

The phosphoric acid fuel cell stack is configured by stacking electrodes with ribs, gas separation plates, cooling plates, etc. in multiple stages. Therefore, it is efficient to apply the kneaded material to the end of the gas separation plate in advance.

Further, as a result of disassembling after operating at 200 ° C., it was observed that the fluororesin tape 6 and the mixture 5 were entangled with each other to form a flexible and dense sealing layer according to the gap value.

The proper amount of the kneaded material 5 is preferably such that a small amount of the kneaded material 5 is pushed out of the laminate when the gas separation plate 3 or the like is pressed.

As described above, in this embodiment, the matrix 1 impregnated with phosphoric acid having an electrolyte is sandwiched between the pair of ribbed electrodes 2 in which the flow passages for the fluid fuel and the fluid oxidant are formed. In a phosphoric acid fuel cell configured by stacking a plurality of unit cells that output electric energy under the condition that fuel and an oxidant are flowing in the flow passage, with the gas separating plate 3 interposed therebetween, the fluororesin film 4 is Between the bonded ends of the ribbed electrode 2 and the gas separating plate 3, 30 to 60 wt% of heat-resistant and electrolyte-resistant flake graphite powder and phosphoric acid
The coating layer of the kneaded material obtained by kneading 70 to 40 wt% and the porous fluororesin tape 6 are arranged so as to face each other and provided as a sealing material.

Therefore, the stepping force between the end portion of each electrode 2 with ribs to which the fluororesin film 4 is adhered and the gas separation plate 3 adjacent thereto is
It is possible to improve the adhesiveness, reliably prevent gas leakage from the gap between them, and prolong the service life, and it is possible to obtain a highly reliable fuel cell.

In addition, although the case where the present invention is applied to the phosphoric acid type fuel cell has been described in the above-mentioned embodiments, the present invention can be similarly applied to a fuel cell using other substances as an electrolyte.

〔The invention's effect〕

As described above, according to the fuel cell of the present invention, the coating layer of the heat-resistant and electrolyte-resistant kneaded material and the fluororesin tape are disposed so as to face each other between the ribbed electrode end and the gas separation plate. Since it is configured as a material, the elasticity and adhesion of each electrode end portion to which the fluororesin film is adhered and the gas separation plate adjacent to this are improved, and gas leakage from this gap is reliably prevented, The excellent effect of being able to provide an extremely reliable fuel cell capable of extending the life is exhibited.

[Brief description of drawings]

FIG. 1 is a sectional view of a unit cell according to the present invention, FIG. 2 is a longitudinal sectional perspective view of a phosphoric acid fuel cell stack to which the present invention is applied, and FIG. 3 is a sectional view of a sealing portion of a conventional fuel cell. It is a figure. 1 ... Matrix, 2 ... Ribbed electrode 3 ... Gas separation plate, 4 ... Fluororesin film 5 ... Kneaded material, 6 ... Fluororesin tape

Claims (2)

[Claims] 1. A sandwich of a matrix impregnated with an electrolyte,
A unit cell that outputs electric energy under the condition that the fuel and the oxidant are flowing in each of the flow passages is formed by arranging a pair of electrodes with ribs in which the flow passages of the liquid fuel and the fluid oxidant are formed. In a fuel cell constituted by stacking a plurality of separator plates, a fluororesin tape is placed at the end of the ribbed electrode facing the gas separator plate, and the gas separator plate surface facing the fluororesin tape is placed. Is provided with a coating layer of a kneaded material obtained by kneading 30 to 60 wt% of graphite powder on scales and 70 to 40 wt% of phosphoric acid. The graphite powder has a particle size range of 20 to 100 μm and an average particle size of 20 to 30 μm. A fuel cell characterized by using one of the following. 2. The fuel cell according to claim 1, wherein the fluororesin tape is a polytetrafluoroethylene tape.