JPS63245867A - Molten carbonate fuel cell - Google Patents

Abstract

PURPOSE:To aim at effective use of reactive gas by providing grooves along the side edges of a fuel electrode, and installing in the grooves sealant including boric-based glass as the major component which melts when heated to tightly attach to an electrolyte layer. CONSTITUTION:More than one grooves 15 are provided in the side edge parts 11 of a fuel electrode 4, 4a on the surface to be positioned on the side of an electrolyte layer 3 in parallel with fuel gas passage grooves 5. In the grooves 15 is installed sealant 16 including boric-based glass as the major component and lithium-included oxide as an auxiliary component which melts when heated to tightly attach to the electrolyte layer 3 which penetrating into the side edge parts 11. Thus installed sealant 16 not only melts when heated to tightly attach to the electrolyte layer 3 but penetrates sufficiently into the inner surface of the grooves 15, where pressure is not applied, spreading along the width so as to achieve a good sealing function.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to molten carbonate fuel cells, and more particularly to molten carbonate fuel cells.

This invention relates to a molten carbonate fuel cell with an improved seal structure in a laminate in which a plurality of unit cells are stacked.

(Prior art) Molten carbonate fuel cells are made by melting an electrolyte made of alkali carbonates at high temperatures to cause an electrode reaction. It has great features such as high heat generation efficiency without the need for a catalyst.

The output of a unit cell of a molten carbonate fuel cell is weak. Therefore, a large output power generation plant is usually constructed by stacking a plurality of unit batteries in series.

The unit battery has an electrolyte layer made of alkali carbonate.

It consists of a pair of gas diffusion electrodes applied to both sides of this electrolyte layer. When constructing a laminate, a conductive separator plate having reactive gas passages on two surfaces is usually interposed between the unit cells.

By the way, in such a molten carbonate fuel cell, the alkali carbonate contained in each electrolyte layer is...

It tends to decrease over time due to reaction gases taking it outside or leaking out of the battery system. When the electrolyte in the electrolyte layer decreases, the ionic resistance of the electrolyte layer increases, resulting in a gradual decline in battery performance. Therefore, in order to maintain battery performance over a long period of time, it is necessary to increase the amount of electrolyte retained by some means. For this reason, conventionally, we focused on the fact that a pair of gas diffusion electrodes are made of a porous material, and created a molten carbon dioxide solution by forming a thick wall on the fuel electrode side so that the fuel electrode also retains the electrolyte. Salt fuel cells are being considered.

As described above, the laminate X of a molten carbonate fuel cell in which the fuel electrode also holds an electrolyte is usually 1.

It is constructed as shown in FIG. Namely.

This laminate X is made up of a plurality of unit batteries 1 stacked with conductive separators 2 interposed therebetween. The unit cell 1 includes a flat electrolyte layer 3 containing an alkali carbonate, and a fuel electrode formed of a thick porous material and having the same vertical and horizontal dimensions as the electrolyte layer 3, which is applied to one surface of the electrolyte layer 3. (anode) 4, a plurality of gas passage grooves 5 formed in parallel on the surface of the fuel electrode 4 located on the anti-electrolyte layer side and for allowing fuel gas to flow therethrough as shown by thick arrows P in the figure; and an oxidizer electrode (cathode) 6 formed of a porous material 4 and applied to the other surface of the electrolyte layer 3. on the other hand.

The separator 2 is made of a conductive metal material such as stainless steel, and includes a separator main body 7 whose vertical and horizontal dimensions are equal to those of the electrolyte layer 3, and one surface of the separator main body 7 that faces opposite to the separator main body 7. It is comprised of side wall members 9a and 9b which are fixed by brazing, for example, to the two sides and form gas passage grooves 8 for passing the oxidizing gas, as shown by thick arrows Q in the figure. The separator plate 2 is fitted with a conductive corrugated plate 10 that has a function of dividing the oxidant gas into the gas passage groove 8 and a current collecting function, and then the oxidizer electrode 6 is fitted therein. is applied to the other surface of the electrolyte layer 3.

In the stacked body X configured in this manner, the electrolyte is retained even between the gas passage grooves 5 of the fuel electrode 4.

In the molten carbonate fuel cell whose main parts are configured in this way, in order to prevent each gas flowing through the gas passage grooves 5 and 8 from leaking to the outside, (1) the fuel electrode 4 and the side edge portion 11 parallel to the gas passage groove 5 and the electrolyte layer 3
(2) a portion in direct contact with the side edge portion 12 of the fuel electrode 4;
(3) a portion where the side edge portion 11 of the electrolyte layer 3 and the side edge portion of the separator body 7 directly contact; (3) the side edge portion of the electrolyte layer 3 and the side wall member 9a;
, 9b, it is necessary to gas-seal the parts that come into direct contact with the parts. As this sealing means, after forming the laminate X, the battery operating temperature (Li2CO3/K2CO3
In the case of a two-element electrolyte, the temperature is generally raised to 650° C., and the temperature is raised to seal with the molten electrolyte. In other words, the electrolyte is heating up.
It melts at 88° C. and this melt penetrates the gap present in the contact area, thereby creating a gas seal.

However, the conventional molten carbonate fuel cell configured as described above and employing the gas seal method as described above has the following problems.

That is, since the gas seal portion is wet-sealed using the electrolyte, the flat contact portions between the side wall members 9a and 9b and the side edge portions of the electrolyte layer 3 can be well sealed. It was difficult to sufficiently penetrate the electrolyte into the contact area between the side edge portion 11 of the pole 4 and the side edge portion 12 of the electrolyte layer 3. For this reason, the sealing of this contact portion is insufficient, and the effective use of the reactive gas cannot be achieved, resulting in a problem that the battery voltage decreases due to the insufficient supply of the reactive gas. In addition, with such a wet seal method, cracks are likely to occur in the electrolyte layer 3, especially in the side edge portions 12, due to the difference in thermal expansion coefficient between the electrolyte layer 3 and the fuel electrode 4 when the temperature of the battery decreases, resulting in poor thermal cycle resistance. There was also the problem that it was low.

(Problems to be Solved by the Invention) As described above, in the conventional molten carbonate fuel cell that uses a thick-walled fuel electrode and holds electrolyte also in this fuel electrode, the side edge portion of the electrolyte layer and It is difficult to achieve a good gas seal between the fuel electrode and the side edge portion of the fuel electrode, and as a result, it is not only impossible to effectively utilize the two reactive gases, but also a drop in cell voltage is caused.

Moreover, there was a problem that the heat cycle resistance was also poor.

Therefore, an object of the present invention is to provide a molten carbonate fuel cell that can eliminate the above-mentioned problems.

[Structure of the Invention] (Means for Solving the Problems) In the molten carbonate fuel cell according to the present invention, the gas seal portion between the side edge portion of the electrolyte layer and the side edge portion of the fuel electrode is constructed as follows. It is composed of Namely.

At the side edge of the fuel electrode, on the side facing the electrolyte layer.

One or more grooves are provided parallel to the fuel gas passage grooves, and in these grooves, boric acid glass is the main component and lithium-containing oxide is the sub-component, which melts when heated and adheres to the electrolyte layer. At the same time, a sealing material that penetrates into the side edge portion is attached.

(Function) When the sealing material installed as described above is heated, it not only melts and adheres to the electrolyte layer, but also spreads in the width direction of the groove while fully fitting into the inner surface of the groove where no pressure is applied. , exhibits good sealing function. In addition, since the sealing cage mainly composed of boric acid glass has low compatibility with the electrolyte, it exhibits stable sealing performance without movement due to mutual dissolution even after long-term use. Furthermore, since boric acid glass has low mutual solubility with the electrolyte, it suppresses the phenomenon of fusion between the electrolyte layer and the fuel electrode, which tends to occur at the sealing part when the temperature of the battery decreases. Therefore, it is possible to suppress the occurrence of cracks that tend to occur on the electrolyte layer side of the sealing portion due to the difference in thermal expansion between the electrolyte layer and the fuel electrode when the battery temperature is lowered, thereby contributing to improved heat cycle resistance.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

The molten carbonate fuel cell according to the present invention does not differ from the conventional one in appearance, but the elements constituting the unit cell, particularly the thick-walled fuel electrode portion that has the function of retaining the electrolyte, have been improved.

FIG. 1 shows a fuel electrode 4a improved according to the present invention and a separator 2 provided closely on one side of the fuel electrode 4a.
is shown.

The fuel electrode 4a is made of a thick porous material and has dimensions equal to the length and width dimensions of an electrolyte layer (not shown).

A plurality of gas passage grooves 5 are formed on the surface located on the side of the separator 2 to allow fuel gas to flow therethrough.

A side edge portion 11. which is parallel to the gas passage groove 5 on the surface located on the electrolyte layer side. In other words, the parts that contact both side edge parts of the electrolyte layer to form a seal part.

For example, a groove 15 with a width of 5 mm and a depth of 1.5 mm is formed.

On the other hand, the separator 2 has a separator main body 7 similar to the conventional one.
A gas passage groove 8 is fixed to the surface of the separator body 7 located on the side opposite to the fuel electrode, which is perpendicular to the direction in which the gas passage groove 5 extends, to form a gas passage groove 8 for passing the oxidizing gas therethrough. It is composed of side wall members 9a and 9b. All other elements constituting the unit battery are constructed in the same manner as the conventional one shown in FIG.

and 9 in the molten carbonate fuel cell according to the present invention.

A laminate X as shown in FIG. 4 is constructed by stacking unit cells having the fuel electrode 4a constructed as described above as a component in the following manner. That is, in each groove 15 of the fuel electrode 4a, a sealing material mainly composed of boric acid glass, such as B203-ZnO-8iO3 glass (softening point 500'C) powder, and lithium aluminate powder ( A mixture obtained by adding silicone oil (1 part to 9 parts of glass) and silicone oil (4 parts to 10 parts of glass and alumina mixed powder) as a viscosity adjusting solvent was kneaded.

Subsequently, the unit batteries are successively assembled and stacked to form a laminate X with a sealing material 16 formed by roll forming and cutting into a string shape attached thereto.

After this laminate X is tightened with a bar or the like, the temperature is once raised to the battery operating temperature (650'C) by external heating. Due to this heating, the sealing material 16 is melted near its softening point (500'C), and finally comes into close contact with the electrolyte layer and penetrates into the grooves 15 sufficiently.

After raising the temperature in this manner, manifolds for supplying reactive gas were attached to the four sides of the stacked body X in a conventional manner to construct the final fuel cell.

Regarding the fuel cell configured as described above, in order to confirm the sealing performance of the seal portion, hydrogen gas was flowed through the gas passage groove 5 and nitrogen gas was flowed through the gas passage groove 8 through the manifold. The sealing performance of the fuel gas passage was investigated by measuring the hydrogen gas content in the nitrogen gas that passed through No. 8 using a catalytic combustion hydrogen meter. And vice versa.

The sealing performance of the oxidizing gas passage was investigated by flowing hydrogen gas into the gas passage groove 8 and nitrogen gas through the gas passage groove 5, and measuring the hydrogen content in the nitrogen gas that passed through the gas passage groove 5. saw. Further, as a reference example, similar measurements were performed on a case in which each part had the same dimensions and the same number of steps, and was sealed without using the groove 15 or the sealing material 16.

As a result, the sealing performance of the fuel gas passage (hydrogen content ff1vo1% in the oxidant gas passage) was 1.5% in the example, but 10.5% in the reference example. As can be seen from this, it was confirmed that by employing the structure of the present invention, gas sealing performance could be significantly improved.

In addition, when the temperature of the laminated battery of the example was lowered to room temperature at a rate of 50°C/h and the number of cracks formed in the electrolyte layer visible from the side of the manifold was confirmed, it was found that the sealing material 16
It was confirmed that the amount was reduced to 1/3 compared to when not using.

In this way, the sealing material 1 whose main component is boric acid glass
Since the sealing material 16 is installed in the above-mentioned relationship, a good sealing function can be exhibited by the action of the sealing material 16 adapting the molten material to the fuel electrode 4a and adhering to the electrolyte layer. In addition, sealing material 1 whose main component is boric acid glass
Since 6 has low compatibility with the electrolyte, there is no movement due to mutual dissolution even after long-term use. Therefore, stable sealing performance can be exhibited over a long period of time. Furthermore, since boric acid glass has low mutual solubility with the electrolyte, it suppresses the phenomenon of fusion between the electrolyte layer and the fuel electrode, which tends to occur at the sealing part when the temperature of the battery decreases. Therefore, it is possible to suppress the occurrence of cracks that tend to occur on the electrolyte layer side of the sealing portion due to the difference in thermal expansion between the electrolyte layer and the fuel electrode when the battery temperature is lowered, and thereby it is also possible to improve heat cycle resistance.

Note that the present invention is not limited to the embodiments described above. That is, in the embodiment described above, LiA102 is used as a subcomponent of the sealing material 16 installed in the groove 15, but lithium zirconate.

Lithium titanate may also be used. In addition, in the above-mentioned embodiment, a putty-like material made by kneading glass powder with silicone oil is used as the sealing glass, and this is attached to the sealing groove, but the porous material inscribed in the groove A round rod or a square rod fused and impregnated with glass may be installed in the groove. In this case, alumina, a high-porosity metal plated with hot-dip aluminum, or hard glass can be used as the porous rod.

Further, in the above embodiment, one groove for attaching the sealing material is provided on the side edge portion of the fuel electrode, but a plurality of grooves may be provided. In addition, in the embodiment, a groove 15 is provided on the surface of the fuel electrode located on the electrolyte layer side, and a sealing material 16 is attached to this groove 15. As shown in FIG.
A groove] 5 may also be provided on the side surface, and a sealing material 16 may be attached to this groove 15. In this case, the grooves may be arranged so that the grooves on both sides are alternately located in the width direction as shown in Figure 9. When sealing grooves 5 are provided on both sides, shallow striated grooves (depth 0.1 mm) are provided on the surface of the separator body 7 that contacts the sealing material 16.

It is preferable to provide a large number of 0.05 mm wide holes so that the sealing glass can fit into these surfaces. Also, when disassembling a stacked battery and replacing some unit batteries.

In order to prevent cells other than the extracted cells from being damaged due to adhesion between the electrode and the corrugated sheet, BN powder may be applied to the surface of the corrugated sheet. Further, a large number of slit-like holes may be provided in the corrugated plate. Furthermore, in order to improve the corrosion resistance of the corrugated plate and the separator plate, a thin NiFc204 layer may be formed on the surface located on the oxidizing agent electrode side.

[Effects of the Invention] As mentioned above, according to the present invention, it is possible to achieve reliable sealing of the laminate without having the same adverse effect on the electrolyte retention function using the fuel electrode, thereby reducing reactivity. It is possible to provide a molten carbonate fuel cell that not only can effectively utilize gas and prevent a drop in battery voltage, but also can improve heat cycle resistance.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a fuel electrode and a separator incorporated in a molten carbonate fuel cell according to an embodiment of the present invention, and FIG. 2 is a vertical sectional view showing a partially taken out stack of the same fuel cell. , FIG. 3 is a diagram for explaining a modified example of the laminate, and FIG. 4 is an exploded perspective view of the laminate in a conventional molten carbonate fuel cell. X... Laminated body, 1... Unit battery, 2... Separation plate,
3... Electrolyte layer, 4.4a... Fuel electrode, 5... Gas passage groove. 6... Oxidizer electrode, 8... Gas passage groove, 10... Corrugated plate. 11.12...Side edge portion, 15...Groove, 16...
Seal material. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Year 3 Figure 4

Claims (3)

[Claims] (1) A flat electrolyte layer containing carbonate that melts at operating temperature, a fuel electrode made of a porous material and having the same vertical and horizontal dimensions as the electrolyte layer applied to one side of the electrolyte layer, and this fuel A unit cell comprising a plurality of fuel gas passage grooves formed in parallel on a surface of the electrode located on the side opposite to the electrolyte layer, and an oxidizer electrode made of a porous material applied to the other surface of the electrolyte layer, One surface has an oxidizing gas passage groove, and the oxidizing agent electrode is fitted into the gas passage groove, and a plurality of conductive separators are connected to each other through a conductive separator plate applied to the other surface of the electrolyte layer. A molten electrolyte is used to form a portion in which a side edge portion of the fuel electrode parallel to the fuel gas passage groove, a side edge portion of the electrolyte layer, and a side edge portion of the separator plate are in direct contact with each other. In a sealed molten carbonate fuel cell, one or more grooves are provided in the side edge portion of the fuel electrode on the surface located on the electrolyte layer side in parallel with the fuel gas passage groove, and The main component is boric acid glass,
A molten carbonate fuel cell characterized in that it is equipped with a sealing material containing a lithium-containing oxide as a subcomponent, which melts when heated and comes into close contact with the electrolyte layer, and also penetrates into the side edge portions. (2) The composition of the sealing material is set such that it can be melted and sealed.
The molten carbonate fuel cell described in Section 1. (3) The molten carbonate fuel cell according to claim 1, wherein the lithium-containing oxide that is a subcomponent of the sealing material is LiAlO_2.