JPH0789491B2 - Molten carbonate fuel cell - Google Patents

Description

The present invention relates to a molten carbonate fuel cell, and more particularly to a fuel having an improved gas seal structure in a laminated body in which a plurality of unit cells are laminated. Regarding batteries.

(Prior Art) In recent years, a molten carbonate fuel cell has been developed as a highly efficient energy conversion device. A molten carbonate fuel cell is one in which an electrolyte composed of an alkali carbonate is melted at a high temperature to cause an electrode reaction, and does not require an expensive precious metal catalyst as compared to other fuel cells such as a phosphoric acid fuel cell. It has major features such as high heat generation efficiency.

By the way, the output of the unit cell of the molten carbonate fuel cell is weak. Therefore, in order to configure a high-output power plant, it is necessary to stack a plurality of unit batteries in series to form a stacked body and obtain the added output of each unit battery.

FIG. 3 shows the main part of a conventionally proposed molten carbonate fuel cell. That is, the longitudinal and lateral dimensions of the electrolyte layer 1 are compared on both sides of an electrolyte layer 1 formed by integrating a carbonate electrolyte such as lithium carbonate and potassium carbonate and a ceramic-based holding material such as lithium aluminate in a flat plate shape. The nickel alloy gas diffusion electrodes 2a and 2b formed so that only one dimension is narrow are applied so as to be orthogonal to each other to form a unit battery 3, and a plurality of the unit batteries 3 are electrically conductive to each other. The laminated body X is formed by laminating the bipolar separator 4 of FIG.

Each bipolar separator 4 has a separator body 5 made of stainless steel, which has vertical and horizontal dimensions equal to those of the electrolyte layer 1, and
The separator plate body 5 is welded or brazed to both parallel sides of one surface of the separator plate 5, and the fuel gas is allowed to flow between them as shown by a thick arrow P in the figure with the one surface as an inner surface of the bottom wall. The stainless steel side wall members 6a and 6b forming the groove-shaped passage A are welded or brazed to the other surface of the separator plate body 5 and to both sides orthogonal to the side wall members 6a and 6b. , A side wall member made of stainless steel that forms a passage B through which the oxidant gas flows, with the other surface being the inner surface of the bottom wall between them.
7a, 7b and a corrugated plate 8 made of stainless steel, which is installed in the passages A, B and divides the gas flow into a plurality of gas flows. Then, locking step portions 9 for locking both side portions of the gas diffusion electrodes 2a, 2b are provided on the inner edge portions of the side wall members 6a, 6b, 7a, 7b.
Are formed respectively. That is, the gas diffusion electrode 2
As shown in FIG. 4, a and 2b are formed to have a thickness substantially equal to the so-called depth of the locking step portion 9, and both sides thereof are locked to the locking step portion so that the passages A and B are formed. Is formed to have a width capable of closing the opening of the. Reference numeral 10 in FIG. 4 denotes a ceramic anticorrosion layer such as alumina or zirconia provided on the surface of the side wall member in order to prevent the portion of the side wall member in contact with the electrolyte layer 1 from being corroded by the electrolyte. ing.

In the molten carbonate fuel cell whose main part is configured as described above, in order to prevent the gas flowing through the passages A and B from leaking to the outside, the side wall members 6a, 6b, 7a, 7b and It is necessary to make a gas seal between the end of the electrolyte layer 1 that contacts the battery, and this seal means is usually used after the laminate X is formed and then at the battery operating temperature (Li ₂ CO ₃ / K ₂ CO ₃ In the case of a two-element electrolyte, a method is generally employed in which the temperature is raised to 650 ° C. and the molten electrolyte is sealed by this temperature rise.
That is, the electrolyte is melted at a eutectic temperature of 488 ° C. during the temperature rise, and this melted material melts the end portion of the electrolyte layer 1 and the side wall members 6a, 6b,
It penetrates into the gap existing between 7a and 7b, and thereby gas sealing is performed.

However, in the conventional molten carbonate fuel cell configured as described above and employing the gas sealing method as described above, the flat surface of the end portion of the electrolyte layer 1 and the side wall member 6a contacting the flat surface are formed. Since the gas is sealed (wet seal) with the molten electrolyte between the flat surfaces of 6a, 6b, 7a and 7b, it is difficult for the electrolyte to enter the gap between the two flat surfaces. However, there is a problem that the seal tends to be insufficient. If the sealing is insufficient in this way, a water generation reaction occurs on the side surface of the laminate, and the effective use of the supply gas is impaired. Further, the above-mentioned sealing structure has a problem that the sealing performance is deteriorated with time due to the escape of the electrolyte or the like accompanying the extension of the operating time. Further, in the above-described wet seal method, the electrolyte wets either the anode side or the cathode side of the side wall member, and therefore the electrolyte layer 1 is cracked due to the difference in the coefficient of thermal expansion between the side wall member and the electrolyte when the temperature is lowered. Was likely to occur, and therefore the heat resistance cycle was insufficient. Further, the above-mentioned sealing structure has a problem that only the defective cell cannot be replaced.

Therefore, in order to eliminate such a problem, the side wall member
It is conceivable to widen the width of 6a, 6b, 7a, 7b and widen the contact area with the electrolyte layer 1. However, in this case, the effective reaction area of the electrolyte layer 1 is reduced and the space utilization rate is reduced.

(Problems to be Solved by the Invention) As described above, the structure of the conventional molten carbonate fuel cell has a problem that essentially good gas sealing performance cannot be expected.

Therefore, the present invention, in a state where the effective reaction area of the electrolyte layer is intended to be enlarged, and yet can perform a reliable and stable gas seal and prevent the occurrence of cracks in the electrolyte layer located in the sarl portion during thermal cycling, and An object of the present invention is to provide a fused carbonate fuel cell in which fusion between the electrolyte layer and the bipolar separator at the seal portion is prevented and only defective cells can be extracted and replaced.

[Structure of the Invention] (Means for Solving the Problems) In the molten carbonate fuel cell according to the present invention, the side wall of the groove-shaped gas passage provided in the bipolar separator directly contacts the end of the electrolyte layer. While providing one or more grooves on the surface, in the groove, the softening temperature is lower than the eutectic temperature of the electrolyte constituting the electrolyte layer boric acid-based glass as a main component and a lithium-containing oxide as a holding material A sealing material composed of a kneaded product of a solvent and a solvent for adjusting viscosity is attached.

(Operation) When the sealing material mounted as described above is heated, not only does the boric acid-based glass, which is the main component, melt and adhere to the electrolyte layer, but also the inside of the groove is sufficiently pressure-free inside the groove. It spreads in the width direction of the groove while accommodating, and eventually exhibits a good sealing function. Therefore, good sealing performance can be achieved without increasing the width of the side wall member.
In addition, since boric acid glass has low compatibility with the electrolyte,
Even when used for a long period of time, there is no migration due to mutual dissolution and the sealing performance can be maintained stably. Therefore, in a state in which the effective reaction area of the electrolyte layer is sufficiently large, and still good,
Delivers highly stable sealing performance. Furthermore, since the boric acid-based glass and the electrolyte have low mutual solubility, fusion does not occur between the electrolyte and the sealing material when the temperature of the battery is lowered. Therefore, the defective cell can be easily extracted without causing deformation or crack in other members.

Also, since the softening point of boric acid glass is lower than that of the electrolyte,
It is possible to suppress the occurrence of cracks at the ends of the electrolyte layer, which are likely to occur due to the difference in coefficient of thermal expansion between the electrolyte layer and the side wall member when the temperature is lowered, and thus it is possible to improve the heat resistance cycle.

(Example) Hereinafter, one example of the present invention will be described.

FIG. 1 shows a bipolar separator 14 incorporated in the main part of the molten carbonate fuel cell according to the present invention, and the same parts are designated by the same reference numerals in FIG. Therefore, the description of the overlapping portions will be omitted.

The bipolar separator 14 in this embodiment is a groove-shaped gas passage.
Grooves having a width of 5 mm and a depth of 1.5 mm, for example, are formed on the surfaces of the side wall portions 6a, 6b, 7a, 7b which are brazed to the separator body 5 to form A and B, which are in direct contact with the ends of the electrolyte layer 1. 15 are formed respectively. Then, as shown in FIG. 2, when the bipolar separators 14 are interposed between the electrolyte layers 1 and stacked, a sealing material 16 containing boric acid glass as a main component is interposed in each groove 15. ing.

Examples of the sealing material 16 include B ₂ O ₃ —P ₂ O ₅ glass (softening point 420 ° C.) powder, lithium aluminate powder (1 part relative to 9 parts of glass) as a holding material, and a viscosity adjusting solvent. A mixture obtained by kneading a mixture obtained by adding silicone oil (4 parts to 10 parts of glass / alumina mixed powder), followed by roll forming and cutting into a string shape is used. Then, as shown in FIG.
After forming a laminated body with the attached, and tightening the laminated body with a tightening bar, etc., it is heated to the battery operating temperature (650 ° C) by external heating, and boric acid, which is the main component of the sealing material 16, is heated by this heating. The system glass is melted near the softening point (420 ° C). As a result, the sealing material 16 finally comes into close contact with the electrolyte layer 1 and is sufficiently conformed to the inner surface of the groove 15. Then, a reaction gas supply manifold is attached to the four side surfaces of this laminated body by a usual method to finally form a fuel cell.

Regarding the fuel cell configured as described above, in order to check the sealing property of the seal portion, each passage A is arranged through the manifold.
The sealing property of the passage A was confirmed by flowing hydrogen gas into the passage A and nitrogen gas into the passage B, respectively, and measuring the hydrogen gas content in the nitrogen gas passing through the passage B with a catalytic combustion hydrogen meter. On the contrary, hydrogen gas was passed through the passage B and nitrogen gas was passed through the passages A, respectively, and the hydrogen gas content in the nitrogen gas passing through the passages A was measured in the same manner to confirm the sealing property of the passage B. In addition, as a reference example, the same measurement was carried out for a product in which the dimensions and the number of steps were set to be the same, and which was sealed without using the groove 15 and the sealing material 16. As a result, the data shown in Table 1 was obtained at the initial stage of battery power generation.

As can be seen from Table 1, if the structure of the present invention is adopted, the gas sealing performance can be greatly improved.

In addition, in the batteries of Examples, the sealing performance was not deteriorated even after about 1000 hours after the start of power generation (after reaching 650 ° C.), but in the reference example, both passages A and B had a hydrogen content of 3 .About.5 times, and the sealing performance was deteriorated. In addition, the laminated battery of this example was cooled to room temperature at a rate of 50 ° C. per hour. At this time, when the number of cracks formed in the electrolyte layer in the portion visible from the side surface of the manifold was confirmed, it was reduced to 1/4 as compared with the case where the above-mentioned sealing material was not used. In addition, the upper end plate to the third cell are removed, the electrode and electrolyte layer of the third cell are new, and the first and second cells are used as they are without the seal and the temperature is raised again to test the power generation. As a result, the deterioration of the V-i characteristics of the first and second cells was 1.05 times that of the cells below the fourth cell.

The present invention is not limited to the above embodiment. That is, if the sealing material 16 mounted in the groove 15 has a sealing material composition that softens below the operating temperature (for example, B ₂ O ₃ —ZnO-based glass), good sealing performance should be exhibited. You can Further, although the groove 15 is provided in one line in the above-described embodiment, a plurality of lines may be formed according to the width of the side wall member to further improve the sealing performance. Further, the holding material is not limited to LiAlO ₂ , and may be lithium zirconate or lithium titanate. When the laminated battery is disassembled after the temperature is lowered and a part of the cells is taken out and replaced, at least either the anode or the cathode and the corrugated plate for forming the current collecting and gas supply channel are fixed to each other, so that the extraction cell is removed. To prevent damage to cells other than
A small amount of BN powder may be applied to the surface of the corrugated plate. further,
The corrugated plate may be provided with some slit-shaped holes.
Further, in order to improve the corrosion resistance of the corrugated plate and the side wall member, NiFe ₂ O ₄ may be formed on the surface located on the cathode side thereof.

[Effects of the Invention] As described above, according to the present invention, one or more grooves are provided in the side wall portion of the bipolar separator, which is in direct contact with the end portion of the electrolyte layer. Since the sealing material is attached, it is possible to provide a molten carbonate fuel cell that not only realizes a strong and reliable seal against heat cycles but also contributes to easy replacement of defective cells.

[Brief description of drawings]

FIG. 1 is a perspective view of a bipolar separator installed in a main part of a molten carbonate fuel cell according to an embodiment of the present invention, and FIG. 2 is a local side view of the main part in which the separator is installed. FIG. 3 is an exploded perspective view of a main part of a conventional molten carbonate fuel cell, and FIG. 4 is a local side view of the main part. 1 ... Electrolyte layer, 2a, 2b ... Gas diffusion electrode, 3 ... Unit battery, 5 ... Separator body, 6a, 6b, 7a, 7b ... With side wall, 1
4 ... Bipolar separator, 15 ... Groove, 16 ... Sealing material, A, B ...
… A groove-shaped gas passage.

Claims (2)

[Claims] 1. A pair of gas diffusion electrodes, in which either one of the dimensions is narrower than the vertical and horizontal dimensions of the electrolyte layer, is applied to both surfaces of a flat molten carbonate electrolyte layer. A plurality of unit cells, each of which has a vertical and horizontal dimension equal to the vertical and horizontal dimensions of the electrolyte layer, and has a groove shape in which openings are closed on both sides by fitting of the gas diffusion electrode. A bipolar separator having a formed fuel gas passage and an oxidant gas passage is laminated with the bipolar separator interposed therebetween, and a sidewall forming the groove-shaped gas passage of the bipolar separator and the electrolyte layer in direct contact with the sidewall. In a molten carbonate fuel cell configured to make a gas seal with the end of the bipolar separator, one line is formed in a portion of the bipolar separator that directly contacts the end of the electrolyte layer on the side wall forming the groove-shaped gas passage. Providing the above groove Both in the groove, the softening temperature is a kneaded product of a boric acid-based glass as a main component lower than the eutectic temperature of the electrolyte constituting the electrolyte layer and a lithium-containing oxide as a holding material and a viscosity adjusting solvent. A molten carbonate fuel cell, characterized in that a molten carbonate fuel cell is mounted. 2. The molten carbonate fuel cell according to claim 1, wherein the lithium-containing oxide contained in the sealing material is LiAlO ₂ .