JPH0782866B2 - Molten carbonate fuel cell - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a molten carbonate fuel cell constituted by stacking a plurality of unit cells.

[Technical background of the invention and its problems]

Conventionally, a fuel cell has been widely known as a highly efficient energy conversion device. Fuel cells are classified into phosphoric acid type, molten carbonate type, and solid electrolyte type depending on the electrolyte layer used.

Among such fuel cells, a molten carbonate fuel cell having particularly high heat generation efficiency is usually a fuel cell main body X and a fuel gas and an oxidant gas in the fuel cell main body X as shown in FIG. And a manifold (not shown) that guides the.

Since the output of each unit cell 1 is weak, the fuel cell main body X is usually formed by stacking a plurality of unit cells 1 with a conductive separator 2 interposed therebetween.

Each unit cell 1 is configured by providing a pair of porous electrode plates, that is, an electrolyte layer 4 composed of an electrolyte of alkali carbonate and a holding material for holding the electrolyte between the fuel electrode 3a and the oxidizer electrode 3b. It Each of the electrode plates 3a and 3b is formed of a rectangular plate-shaped body and is arranged so that the longitudinal directions thereof are orthogonal to each other. The electrolyte layer 4 is composed of a plate-shaped body whose longitudinal and lateral dimensions are the longitudinal lengths of these electrode plates.

The separator 2 has large grooves 7a, 7b extending in directions orthogonal to each other while leaving flange surfaces 6a, 6b of predetermined widths at both ends on both surfaces of a plate-shaped body made of a conductive material.
A plurality of grooves 8a and 8b extending in the same direction as the large grooves are provided on the bottom surfaces of the large grooves 7a and 7b, respectively. The large grooves 7a and 7b have a depth and a width so that the fuel electrode 3a and the oxidant electrode 3b are exactly fitted to each other. Therefore,
In the fuel cell main body X, when the unit cells 1 and the separators 2 are alternately laminated, one surface of the electrolyte layer 4 and the flange surfaces 6a and 6b facing this surface are polymerized, and the other surface of the electrolyte layer 4 is formed. The flange surfaces 6c and 6d facing this surface overlap.

When the temperature of such a fuel cell is raised to 500 to 750 ° C., the carbonate of the electrolyte layer 4 becomes in a molten state and slightly penetrates the porous fuel electrode 3a and the oxidant electrode 3b. In this state, when the fuel gas P is introduced into the gas passage formed by the groove 8b and the oxidant gas Q is introduced in the gas passage formed by the groove 8a, each gas is diffused to each electrode plate and the electrode, It is subjected to a reaction at a three-phase interface consisting of gas and molten carbonate. At this time, the fuel gas P
And the oxidant gas Q are the above-mentioned electrolyte layer 4 and the flange surface.
6a to 6d are separated by a wet seal part formed of molten carbonate exuded in the polymerization part.

In such a conventional molten carbonate fuel cell, the self-weight of the laminate and the tightening force are directly applied to the electrolyte layer 4. Therefore, the electrolyte layer 4 needs to have a compressive strength that can withstand these loads.

Various proposals have been made for increasing the compressive strength of the electrolyte layer 4, but the most effective one is to increase the content of the holding material in the electrolyte layer 4.

However, when the content of the holding material in the electrolyte layer is increased, there is a problem that the ionic conductivity of the electrolyte layer is lowered and the battery performance is deteriorated. Further, when the content of the holding material is increased in this way, the decrease in the specific surface area due to the grain growth reaction of the holding material during the operation of the battery cannot be ignored, and even if the compressive strength is sufficient at the beginning of the operation, the strength over time is increased. There was also the problem of causing a decline.

Therefore, for example, as proposed in USP 3723186, the content of the holding material in the peripheral portion of the electrolyte layer forming the wet seal portion is increased more than that in the central portion, and the compressive strength is reduced without lowering the battery performance. One way to increase it is.

However, when the holding material contents of the peripheral portion and the central portion of the electrolyte layer are made to differ in this way, the degree of thermal expansion between the peripheral portion and the central portion can be different, and therefore the electrolyte layer is affected by thermal stress due to the temperature cycle. There was a problem that through-cracking occurred in the resin and cross-mixing of the reaction gases occurred.

Further, in any of the fuel cells described above, since the wet seal is formed of molten carbonate which is the electrolyte, the electrolyte migrates and dissipates through the wet seal portion, and the seal performance and the cell performance over time. There was also a problem that the value would decrease.

[Object of the Invention]

The present invention has been made based on such circumstances, and an object of the present invention is to ensure a sufficient compressive strength of a laminate without lowering battery performance at all, and further It is intended to provide a molten carbonate fuel cell excellent in stability over time.

[Outline of Invention]

The present invention relates to a molten carbonate fuel cell including a fuel cell main body formed by alternately laminating a unit cell formed by arranging a pair of porous electrodes on both surfaces of a molten carbonate electrolyte layer and a conductive separator. Formed of an oxide ceramic that is chemically stable with respect to carbonates and non-electroconductive, and is formed so as to surround the unit battery between the peripheral portions of the separators adjacent in the stacking direction. A spacer for suppressing a load applied to the molten carbonate electrolyte layer; and a sealing material made of a material different from carbonate that is interposed between the spacer and the separator and seals between the spacer and the separator. It has a feature.

〔The invention's effect〕

According to the present invention, since a spacer formed of an oxide ceramic that is chemically stable with respect to carbonate and is non-electroconductive is provided between the separators, it has been conventionally added to the electrolyte layer. The existing pressure can be received by the spacer. Therefore, since it is not necessary to give the electrolyte layer a high compressive strength as in the conventional case, the content of the holding material in the electrolyte layer is the minimum necessary amount capable of holding the electrolyte. Therefore, it is possible to increase the size of the unit cell and increase the output by increasing the number of stacked layers without causing various problems such as a decrease in ionic conductivity and occurrence of penetration cracking due to temperature cycling.

Further, in the present invention, since the sealing material interposed between the separator and the spacer is made of a material other than carbonate, the electrolyte can be completely sealed and the airtightness due to the evaporation loss of the electrolyte or the like can be achieved. There is no decrease in sex over time.

Example of Invention

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

FIG. 1 is a diagram showing an embodiment, and the points that are particularly different from the conventional ones are that a unit battery 11 is surrounded by an annular spacer 12, and sealing means is provided at a contact portion between the spacer and the separator 13. That is, the wet seal portion between the peripheral portion of the separator 13 and the spacer is formed with the glass interposed.

That is, the fuel electrode 14a and the oxidizer electrode 1 that form the unit cell 11
4b are arranged such that their long sides substantially match the vertical and horizontal dimensions of the electrolyte layer 16 and their longitudinal directions are orthogonal to each other.

The separator 13 has a function of forming a flow path of a reaction gas and an electrical connection function between the unit batteries 11, and has a flange of a predetermined width at both ends on both sides of a plate-like body made of a conductive material. A plurality of grooves 18a, 18b extending in the directions orthogonal to each other are provided while leaving the surfaces 17a, 17b and 17c, 17d, and the flange surfaces 17a to 17d are provided with ridges 19a, respectively, leaving the peripheral portions of the flange surfaces 17a to 17d. , 19b, 19c, 19d are provided.

The spacer 12 is formed by forming dense alumina, which is chemically stable with respect to carbonate and is non-electron conductive, into a square ring shape. The spacer 12 has a vertical and horizontal dimension of its outer shape,
The dimensions of the separator 13 are substantially equal to each other, and the vertical and horizontal dimensions of the inner shape are formed to be slightly larger than the dimensions of the electrolyte layer 16, and the thickness thereof is greater than the thickness of the unit battery 11 immediately after assembly as described later. It is formed to be slightly thinner.

When the unit cell 11, the spacer 12 and the separator 13 are stacked and assembled, the fuel electrode 1 is formed between the protrusions 19c and 19d of the separator 13.
4a, the oxidant electrode 14b is fitted between the protrusions 19a, 19b, respectively, the electrolyte layer 16 is disposed between the protrusions 19a, 19c and between the protrusions 19b, 19d, further the flange surface 17a of the separator 13, 17b
The spacer 12 is disposed between the fuel cell body 17 and the fuel cell body 17c. In this state, the thickness of the spacer 12 is slightly smaller than the thickness of the unit battery 11, so that a small gap of 0.1 to 0.15 mm is formed between the spacer 12 and the separator 13. The gap is filled with powdery glass which is a sealing body. In this state, the temperature of the fuel cell body Y is raised, and a part of the melted electrolyte layer moves to the electrode side, whereby the electrolyte layer 16
When the conformity with each electrode plate is improved, the above-mentioned gap is reduced, and the spacer 12 and the separator 13 are almost in close contact with each other as shown in FIG. On the other hand, the powdery glass filled between the spacer 12 and the separator 13 becomes in a molten state as the temperature of the fuel cell main body Y rises, and as shown in FIG. The seal portion W is formed. Therefore, the molten carbonate is completely sealed via the wet seal portion W, and the migration of carbonate can be suppressed. Further, since the load in the stacking direction is received by the separator 13 and the spacer 12 having high mechanical strength, no pressure is applied to the electrolyte layer 16.

In this embodiment, an external manifold is attached to the side surface of the fuel cell main body Y. In this type, the airtight portion between the peripheral surface of the laminate and the manifold is plastic at the cell operating temperature. It is composed of a plastically deformable material that deforms, a holding layer of this material, and an electrical insulating layer. However, conventionally, since the plastically deformable material is in direct contact with the electrolyte layer exposed along the peripheral surface of the laminate, only the plastically deformable material having the same composition as the electrolyte can be used. For this reason, the electrical insulating layer formed of zirconia, alumina, etc. is gradually affected by the strong corrosive force of the molten carbonate, causing a leakage current to flow between adjacent unit cells or pulling the electrolyte into this corroded part. The resistance value of the electrolyte layer was sometimes increased.

However, in this embodiment, since the periphery of the unit battery 11 is surrounded by the spacer 12 and the wet seal between the spacer 12 and the separator 13 is glass, the carbonate is not directly exposed on the laminated end surface. That is, since the plastically deformable material in the airtight portion does not come into direct contact with the electrolyte layer, a material different from the electrolyte, such as glass, can be used as the plastically deformable material. Therefore, it is possible to solve the problems such as the leakage current and the pulling of the electrolyte into the corroded portion.

The present invention is not limited to the above embodiment.

For example, although a dense spacer is used as the spacer in the above embodiment, a porous alumina material (for example, an average pore diameter of 1 μm,
The porosity of 50%) may be treated in molten lithium carbonate to convert the surface into lithium aluminate, which may be melt impregnated with borate glass to form a spacer having a sealing means. In addition, ZrO ₂ can be used as the spacer instead of Al ₂ O ₃ .

Although powdery glass was used as the sealing material in the above-mentioned embodiment, a plate-like body mixed with ZrO ₂ , Al ₂ O ₃ powder or Al ₂ O ₃ fiber may be used.

Further, the sealing means is not limited to the wet sealing made of glass or the like, and for example, as shown in FIG. 3, a flexible metal pipe 20 is attached to the groove 22 of the spacer 21 so as to have a sealing function. It is also possible. Metal pipe 20
It is not necessary to use a hollow pipe as long as it has high temperature creep strength and flexibility. Further, in order to improve the wettability with the sealing material, the metal pipe may be subjected to surface treatment such as formation of an alumina layer.

In addition, the shapes and types of the separator and the sealing means are not limited to those specifically exemplified. For example, a groove may be cut parallel to the side at the end of the separator as the sealing material, or the internal manifold type. The present invention can be applied to the above fuel cell. Further, in the above-mentioned embodiment, as the separator, the ones in which the gas flow passages are formed by machining so that they are orthogonal to each other on the front and back sides are used, but a combination of a corrugated thin plate and a flat thin plate may be used.

In short, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a main structure of a molten carbonate fuel cell according to an embodiment of the present invention, and FIG. 2 is a sectional view of the fuel cell cut along the line AA in FIG. FIG. 3 is a partial sectional view showing another embodiment of the present invention,
FIG. 4 is an exploded perspective view showing a main part of a conventional molten carbonate fuel cell. 1,11 …… Unit battery, 2,13,21 …… Separator, 3a, 14a…
… Fuel electrode, 3b, 14b …… Oxidizer electrode, 4, 16 …… Electrolyte layer, 12
…… Spacer, 20 …… Metal pipe, P …… Fuel gas, Q
...... Oxidizer gas, W ・ ・ ・ Wet seal part of glass.

Claims (3)

[Claims] 1. A molten carbonate fuel cell comprising a fuel cell body in which unit cells having a pair of porous electrodes arranged on both surfaces of a molten carbonate electrolyte layer and conductive separators are alternately laminated. In the above, a ring is formed of an oxide ceramic that is chemically stable with respect to carbonate and is non-electroconductive, and is inserted so as to surround the unit battery between the peripheral portions of the separators that are adjacent in the stacking direction. A spacer for suppressing a load applied to the molten carbonate electrolyte layer; and a sealing material made of a material different from carbonate that is interposed between the spacer and the separator and seals between the spacer and the separator. Characterized molten carbonate fuel cell. 2. The molten carbonate fuel cell according to claim 1, wherein the sealing material is made of glass that melts at an operating temperature of the cell. 3. The molten carbonate fuel cell according to claim 1, wherein the sealing material is made of a heat-resistant metal material having flexibility.