JPH0793146B2 - Molten carbonate fuel cell stack - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a molten carbonate fuel cell stack, and more particularly to a fuel cell stack capable of improving reaction gas sealing performance.

[Technical background of the invention and its problems]

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 brought into a molten state at a high temperature to cause an electrode reaction, and an electrode reaction easily occurs as compared with other fuel cells such as phosphoric acid type and solid electrolyte type. It has major features such as no need for expensive noble metal catalysts and high heat generation efficiency.

By the way, in order to construct a high-output power plant with a molten carbonate fuel cell, since the output of the unit cell is weak, a plurality of unit cells are laminated in series to form a laminated body,
It is necessary to obtain the added output of each unit battery. For this reason, conventionally, the molten carbonate fuel cell has a laminated structure as shown in FIG.

That is, each unit battery 1 is composed of a pair of porous electrodes 2a and 2b and an electrolyte layer 3 made of carbonate interposed therebetween. These unit batteries 1 are stacked via a conductive separator 4 having both an electrical connection function between the unit batteries 1 and a function of forming a passage of a reaction gas to each electrode plate. That is, the separator 4 includes a conductive separator plate body 5, a side wall member 6a made of stainless steel brazed and fixed to two opposite sides of one surface of the separator plate body 5, and the separator plate body. On the other surface of 5, the side wall member 6b made of stainless steel, for example, is brazed and fixed to two opposite side portions in the direction orthogonal to the side wall member 6a.
And the passage of the reaction gas formed by these side wall members 6a, 6b
It is composed of corrugated plates 7a and 7b which are fitted to A and B to divide the reaction gas.

A manifold (not shown) having a function of distributing and recovering the reaction gas is applied to the four side surfaces of the fuel cell stack X thus configured. Then, the oxidant gas P was supplied to one of these manifolds, and the fuel gas Q was supplied to the adjacent manifold, and both gases contributed to the electrode reaction inside the fuel cell stack X to obtain a DC output. After that, the gas can be discharged from each of the facing manifolds.

In the fuel cell configured in this way, the side wall members 6a, 6b
A wet seal portion is formed between the electrolyte layer 3 and the electrolyte layer 3, and both reaction gases P and Q leak to an unintended side inside the fuel cell,
Prevents mixture. A wet seal is also formed between each side face of the fuel cell stack X and each manifold by impregnating a molten felt with, for example, a ceramic felt.

However, in the case where the wet seal portion is formed by interposing a ceramic felt or the like between the fuel cell stack X and the manifold, between the side wall members 6a and 6b made of stainless steel and the felt. In addition to the poor familiarity, there is a problem that the sealing performance between the laminate X and the manifold is deteriorated with time due to the corrosion loss of the side wall members 6a and 6b due to the molten carbonate.

Further, the welded or brazed portion of the side wall members 6a, 6b and the separator plate body 5 is affected by the carbonate or the like moving on the surface of the side wall members 6a, 6b, so that the side wall members 6a, 6b and the separator plate body 5 are There will be a gap between and. There is a problem that such a gap causes the reaction gas to leak or mix, resulting in a decrease in power generation efficiency.

In addition, when manufacturing the separator 4, it includes a step of brazing or welding the side wall members 6a and 6b to the end of the separator plate body 5, and further, the processing accuracy of the surface of the side wall members 6a and 6b that is in contact with the manifold flange is improved. There is a problem in that it is necessary to sufficiently finish the gas in terms of airtightness, resulting in complicated production and a reduction in yield.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and is capable of reliably sealing the periphery of the unit cell and the stack and the manifold, and is a manufacturable and easy molten carbonate fuel. An object is to provide a battery stack.

[Outline of Invention]

The present invention, while a plurality of unit batteries formed by arranging a pair of porous electrode plates on both sides of the carbonate electrolyte layer are laminated via a conductive separator plate, the peripheral portion of the electrolyte layer and the periphery of the separator plate. In the molten carbonate fuel cell stack provided in a sidewall member forming a gas passage for guiding a reaction gas in a direction orthogonal to the stacking direction of the unit cells, the sidewall member, It is characterized by being formed of a mixed material of alumina fibers and glass exhibiting plasticity at the operating temperature of the fuel cell.

〔The invention's effect〕

According to the present invention, the leakage of the reaction gas disposed between the peripheral edge of the electrolyte layer and the peripheral edge of the separator plate, a sidewall corrugated material for preventing mixing, a glass exhibiting plasticity at the operating temperature of the fuel cell, Since it is made of a mixed material composed of alumina fibers as a holding material for holding the glass, the plasticity of the glass in this side wall member effectively acts, and the familiarity with the manifold can be held well. Moreover, since the side wall member having the above composition has sufficient corrosion resistance against carbonates, the gas seal can be surely performed after all.
Furthermore, when the temperature of the fuel cell stack is raised, the thermal strain generated in the fuel cell stack can be absorbed by the plasticity of the glass in the side wall member, so the soundness of the fuel cell stack can be maintained, Further, since the side wall member does not contain carbonate, it is not necessary to perform corrosion resistance treatment on the portion of the separator that comes into contact with the side wall member.

Further, according to the present invention, the separator plate may be a simple plate-like member, there is no need to braze or weld the side wall member as in the conventional case, and the side wall member is not required to have high surface accuracy.
For this reason, the manufacturability is improved, and the problem that a gap is generated due to corrosion at the portion due to the elimination of the welded portion and the brazed portion is solved.

Example of Invention

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

<Example> A fuel cell stack Y as shown in FIG. 1 was constructed.

A plurality of unit batteries 11 are stacked with a separator plate 12 in between. As shown in FIG. 2, the unit battery 11 has side wall members 21a, 21a arranged in parallel on two opposite side portions of one surface of an electrolyte layer 13 formed in a step described later.
The anode 14a and the corrugated plate 15a are arranged between the a and 21a in the above order, and the side wall member 21b is provided on the other surface of the electrolyte layer 13 at two sides orthogonal to the side where the side wall members 21a and 21a are disposed. , 21b are arranged in parallel, and the cathode 14b and the corrugated plate 15b are arranged between the side wall members 21b, 21b in the above order. Electrolyte layer 13
Is filled with mixed powder of lithium aluminate / lithium carbonate / potassium carbonate = 40: 28: 32 (w%) in a mold and hot-pressed by a press at a pressure of about 300 Kg / cm ² and a temperature of 460 ° C. Obtained. The thickness of the electrolysis chamber layer 13 is 2 mm.

On the other hand, the side wall members 21a and 21b are made of a mixed material composed of glass showing plasticity at the operating temperature of the fuel cell such as boric acid glass or phosphoric acid glass, and alumina fiber as a holding material for holding the glass. It has a thickness of 6 mm, and is fixed to the electrolysis chamber layer 13 during assembly by a small amount of an organic adhesive that can be vaporized when the temperature of the fuel cell is raised.

The anode 14a is formed of a nickel alloy porous body and is mounted in the groove C formed by the side wall members 21a, 21a. The cathode 14b is also formed of a nickel alloy porous body and is mounted in the groove D formed by the side wall members 21b and 21b. Also,
Two corrugated plates 15a and 15b for gas distribution, which are respectively provided on the anode 14a and the cathode 14b, are made of stainless steel. Further, the separator plate 12 interposed between the unit batteries 11 is formed of a stainless steel (SUS316) plate having a thickness of 0.2 mm and having the same vertical and horizontal dimensions as the electrolyte layer 13.

The fuel cell stack Y having the above-mentioned structure was applied with a conductive end plate (not shown) from above and below and tightened by a usual method, and then a manifold (not shown) for guiding a reaction gas was pressed against each side surface. In addition, as in the conventional case, a zirconia felt impregnated with a molten carbonate having the same composition as the electrolyte composition was interposed in the peripheral flange portion of each manifold, and this was used as a sealing material.

A fuel cell constructed in this way is
The temperature is raised to 0 ° C., carbon dioxide gas is made to flow as the oxidant gas Q, and hydrogen gas is made to flow as the fuel gas P, and the difference ΔF (= F ₁ −F ₀ ) between the supply gas amount F ₀ and the exhaust gas amount F ₁ The ratio (reduction amount ΔF / F ₀ ) to the supply gas amount F ₀ was measured. At the same time, in order to see the contribution of the mixing of the gases on the oxidant gas side and the fuel side, the gas composition of the exhaust gas was examined, and the gas of the other electrode was not detected from any of the electrode sides. Therefore, it was decided to consider the amount of decrease as the amount of leakage from the manifold seal.

As a comparative example, the leakage amount from the manifold seal was similarly measured using the conventional fuel cell stack X shown in FIG. The results are shown in the table below.

As is clear from the above results, the leak amount of the reaction gas from the manifold was reduced in the example, and it was confirmed that the battery structure in the example was effective.

Further, after both fuel cells of the above-mentioned example and the comparative example were operated for 200 hours, the temperature was lowered and disassembled. In the comparative example, a gap due to corrosion of the welded portion between the side wall members 6a, 6b and the separator plate body 5 was obtained. There were 3 cells per 10 cells, and the current-voltage characteristics of the three unit cells having these gaps were 0.2 to 0.3 V lower than those of the other unit cells immediately before cooling. On the other hand, in the fuel cell stack Y according to this example, no gas leakage path due to such corrosion was observed, and the variation in the current-voltage characteristics among the unit cells 11 was within ± 5%. Was there.

Further, in the present embodiment, the separator plate 12 is formed of only a metal flat plate, and the conventional side wall members for sealing 6a, 6
Since the welding of b was not necessary, the productivity was extremely good.

As described above, according to the molten carbonate fuel cell stack Y of this example, the sealing property and the manufacturability are good, and the deterioration of the performance over time can be sufficiently suppressed.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the composition of the electrolyte layer is lithium aluminate / lithium carbonate / potassium carbonate = 40.
Although it was set to / 28/32 (w%), lithiated alumina fiber or lithium zirconate fiber may be mixed in the electrolyte layer for reinforcement / reduction of cracks. Further, a small amount of an organic binder or a plasticizer may be mixed to impart flexibility to the electrolyte layer to enhance manufacturability, and the organic binder or the plasticizer may be volatilized while the fuel cell stack is being heated. .

Further, in the above-described embodiment, the plane size of the separator plate 12 and the plane size of the electrolyte layer 13 are the same, but as shown in FIG. 3, the separator plate 12 may be slightly smaller than the electrolyte layer 13. Further, as shown in FIG. 4, a porous metal plate 26 having a high porosity may be used instead of the corrugated plate.

Note that, in the present invention, as shown in FIGS. 5 and 6, the fuel gas P and the oxidant gas Q are arranged to intersect each other inside the fuel cell stack Z in a direction orthogonal to the stacking direction and in a diagonal direction. It can also be applied to products that are distributed in the market.

That is, the sidewalls 32a and 32b, which are L-shaped and made of a mixed material composed of glass and alumina fibers, are added to the peripheral portions of both sides of the electrolyte layer 31 in the same manner as in the above-mentioned embodiment, and the fuel gas P and the oxidizer are added. Crank-shaped grooves are formed so that the gas Q intersects with the electrolyte layer 31, and the anode 33a and the cathode 33b are arranged so as to fit into these grooves. Porous metal plates 34a, 34b having an electric function are arranged. Unit battery 3 configured in this way
The fuel cell stack Z is formed by stacking a plurality of layers 5 through the conductive separator plate 36.

In the thus constructed fuel cell stack Z, the fuel gas supply / discharge manifolds 37a, 37b are arranged on one side of two opposing side surfaces, and the oxidant gas supply / discharge is provided on the other side.
A fuel cell is constructed by arranging the exhaust manifolds 38a, 38b.

It goes without saying that the effects of the present invention can be obtained even with a fuel cell having such a configuration.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of a molten carbonate fuel cell stack according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view showing an electrolyte layer in the same fuel cell stack, FIG. 3 and FIG. 4 are exploded side views showing a constitutional example of a unit cell in a fuel cell stack according to different embodiments, and FIG. 5 shows a constitution of a fuel cell stack in another embodiment of the present invention. FIG. 6 is an exploded perspective view of a fuel cell using the fuel cell stack, and FIG. 7 is an exploded perspective view of a conventional molten carbonate fuel cell stack. 1 , 11 , 35 …… Unit battery, 2a, 2b …… Porous electrode plate, 3,1
3, 31 ... Electrolyte layer, 4 ... Separator, 5 ... Separator plate body, 6a, 6b, 21a, 21b, 32a, 32b ... Side wall member, 7a, 7
b, 15a, 15b …… Corrugated plate, 12,36 …… Separator plate, 14a, 33a
…… Anode, 14b, 33b …… Cathode, 26, 34a, 34b ……
Porous metal plate, 37a, 37b, 38a, 38b ... Manifold, A
~ D ... Groove, P ... Fuel gas, Q ... Oxidizer gas.

Claims (1)

[Claims] 1. A unit battery comprising a pair of porous electrode plates arranged on both sides of a carbonate electrolyte layer is laminated with a conductive separator plate in between, and a peripheral portion of the electrolyte layer and the separator plate are formed. In the molten carbonate fuel cell stack including a sidewall member that is interposed between the sidewall and a gas passage that guides a reaction gas in a direction orthogonal to the stacking direction of the unit cells, the sidewall member is A molten carbonate fuel cell laminate, which is formed of a mixed material of alumina fiber and glass that exhibits plasticity at the operating temperature of the fuel cell.