JPH06260192A - Fuel cell - Google Patents

Abstract

PURPOSE:To provide a fuel cell of high reliability which can supply an oxidating gas and a fuel gas to each unit cell in a stabilized state for a long period of time. CONSTITUTION:A fuel cell is embodied as a lamination with separator 10 interposed between unit cells furnished with a channel to form a gas passage in contact with a positive electrode 16 and negative electrode 17 which are installed in contact with the two main surfaces of an electrolyte plate 15 in such a way as pinching it. Adjoining separators 10 for each gas path at the manifold part 12 alternately supplying the oxidating gas and fuel gas to the gas passage are sealded with a sealing element 11 consisting of an insulative ceramic layer 11a and a metal layer 11b having a similar coefficient of thermal expansion relative to the insulative ceramics 11a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell, and more particularly to a fuel cell formed by stacking unit fuel cells.

[0002]

2. Description of the Related Art In a fuel cell that directly converts chemical energy into electric energy, a pair of electrodes (positive electrode, negative electrode) are arranged on both main surfaces of an electrolyte plate (layer), and the positive electrode is
The basic configuration is to obtain an electromotive force by supplying and reacting an oxidant gas and a fuel gas from both electrode sides of the negative electrode. However, since the electromotive force obtained by the unit fuel cell is low, when constructing a high-output power plant, a plurality of unit fuel cells are stacked in series to form a fuel cell stack, and for example, an electromotive force is generated. The unit output is added to each unit battery by keeping the unit temperature at about 650 ℃.

Generally, in the structure of this fuel cell stack,
A separator is disposed between adjacent unit fuel cells, and the fuel gas flow path (or oxidant gas flow path) of one unit fuel cell
And the oxidant gas flow channel (or fuel gas flow channel) of the other unit fuel cell. Therefore, the oxidant gas flow path and the fuel gas flow path are alternately stacked, and the oxidizer gas flow path and the oxidant gas flow path are prevented from leaking to the outside and mixing of the two gases in the manifold supplying each gas. It is necessary to separately form both the fuel gas supply and discharge passages.

FIG. 6 is a perspective view showing a main structure of a conventional fuel cell stack, in which a pair of electrodes (not shown) are respectively provided on both main surfaces and have a thickness of 1 to 1.5 mm. Electrolyte plate 1
And a separator 2 having a thickness of about 3 to 5 mm are alternately laminated to form a stack. Further, at both ends of the laminate, there are oxidant gas / fuel gas supply / discharge channels. Certain manifolds 3 and 4 are arranged and have a role of circulating the above-mentioned gases to the reaction section 5. That is, in general, one surface of the separator 2 is the fuel gas flow path (or oxidant gas flow path) of the one electrolyte plate 1 and the other surface is the oxidant gas flow path of the other electrolyte plate 1 ( Alternatively, it is configured to be divided so as to form a fuel system gas flow path).

This structure will be described with reference to FIG. 7 showing a cross section taken along the line A--A of FIG. 6, and the oxidant-based gas passes through the manifold 3a and flows into the reaction part 5 of the electrolyte plate 1. Manifold 3b is supplied to one side and after power generation
Is discharged via. On the other hand, the fuel-based gas is supplied to the other surface side of the electrolyte plate 1 which is the reaction part 5 via the manifold 4a in the same manner as in the case of the oxidant-based gas, and is discharged via the manifold 4b after the power generation operation. To be done. In the reaction section 5, a unit fuel cell is constituted by a pair of electrodes 6, 7 and a gas channel (not shown) with the electrolyte plate 1 interposed therebetween, and each unit fuel cell is a main body section of the separator 2.
It is divided by 2a. Further, in the area of the manifolds 3 and 4, a seal element including an insulating ring 9a made of alumina or the like and a thin ring 9b made of a sealing alloy integrally disposed on both surfaces of the insulating ring 9a between adjacent separators 2 is formed. 9, the airtightly sealed structure is adopted.
That is, the sealing alloy thin-walled ring 9b of the sealing element 9 is welded to the opposing separators 2 to hermetically seal and integrate them, and the separators 2 are electrically insulated by the insulating ring 9a. ing.

[0006]

By the way, in the above fuel cell stack (stacked fuel cell), the separators 2 of the unit fuel cells adjacent to each other are hermetically sealed and integrated by the sealing element 9. If taken, there is concern about long-term reliability. That is, in this type of stacked fuel cell, it is important that the oxidant gas and the fuel gas are always supplied and discharged in a stable state. However, when the sealing element 9 is manufactured by brazing and joining the insulating ring 9a such as alumina and the sealing alloy, for example, the thin alloy ring 9b made of 42 alloy as described above, the required reliable and airtight sealing Is difficult to achieve.

To further explain this point, when manufacturing the sealing element 9 by brazing, assuming that the strength of the brazing filler metal acts from 700 ° C., the cumulative strain amount between alumina and 42 alloy is shown in FIG. As shown. That is, the brazing joint of the sealing element 9 is generally at a high temperature, for example, about 900 to 1200 ° C. in the case of nickel brazing, and exceeds the bending point corresponding to the Curie point in the 42 alloy. Therefore, there is a problem that the coefficient of linear expansion becomes large and the difference in thermal expansion with alumina becomes 2.9 × 10 ^{−3, which} is too large, and the alumina side, which is brittle, is likely to be damaged. This phenomenon has the same behavior during the power generation process when the temperature is about 650 ° C (however, the difference in expansion coefficient is the opposite sign). In addition, the operating environment of the fuel cell is as high as 650 ° C and the high corrosion environment of the molten carbonate causes the sealing alloy to be damaged due to the corrosive action and the sealing performance is apt to be impaired. There is also.

The present invention has been made in view of the above circumstances, and provides a highly reliable fuel cell capable of stably supplying an oxidant gas and a fuel gas to each unit fuel cell for a long term. To aim.

[0009]

A fuel cell according to the present invention is a unit including a gas channel portion which forms a gas passage in contact with a pair of a positive electrode and a negative electrode which are in contact with and sandwiched between both main surface sides of an electrolyte plate. In a fuel cell formed by stacking separators between cells, an insulating ceramic layer and an insulating ceramics layer are provided between adjacent separators for each gas passage in a manifold portion that alternately supplies an oxidant gas and a fuel gas to the gas passages. It is characterized in that it is hermetically sealed by a sealing element composed of a metal layer having a thermal expansion coefficient relatively close to that of the insulating ceramic.

That is, the present invention particularly relates to a sealing element in which separators which are interposed between unit cells and are involved in forming a gas passage are hermetically sealed and integrated between adjacent separators in a manifold portion, and in particular, , The brazing property, the electrical insulation property, the mechanical strength and the coefficient of thermal expansion are taken into consideration. Here, the insulating ceramics include, for example, magnesia, partially stabilized zirconia, stabilized zirconia, and the like, and as the metal whose thermal expansion coefficient is relatively close to those of the insulating ceramics,
Examples thereof include ferritic stainless steel and ferritic stainless steel-high nickel alloy clad plate. Further, in the case where the sealing element has a structure in which an O-ring having a C-shaped cross section is formed of the metal, and a ceramic flat plate and a metal flat plate are sequentially laminated with the O-ring sandwiched therebetween, the repulsion property against a tightening load in the manifold part, etc. Yes, further airtightness and sealing can be ensured.

[0011]

According to the present invention, the insulating ceramics and the metal forming the sealing element are selected so that their thermal expansion coefficients are relatively close to each other. That is, a ferritic stainless steel having a relatively small coefficient of thermal expansion is used as a metal, and a ceramic such as a partially stabilized zirconia having a relatively large coefficient of thermal expansion and a high strength is combined as a ceramic to reduce the difference in the coefficient of thermal expansion. For example, as shown in Fig. 1, the cumulative amount of strain in the process of constructing the sealing element between the insulating magnesia ring and the clad plate of high nickel alloy plate and ferritic stainless steel plate (plate thickness ratio 2: 1) is shown in Fig. 1. The difference in thermal expansion is at most 0.1 × 10 ^-3 . Further, looking at the cumulative strain amount in the process of forming the clad-type sealing element between the insulating partially stabilized zirconia (or stabilized zirconia) ring and the ferritic stainless steel sheet, as shown in FIG. Is at most 0.8 × 10 ^-3 . Here, assuming brazing, assuming that the strength of the brazing filler metal acts from 700 ° C, we are paying attention to the cumulative amount from 700 ° C.
The vertical axis represents the cumulative strain amount.

As described above, due to the fact that the coefficient of thermal expansion is set relatively close to each other, the process of forming the sealing element, the process of airtightness / sealing between the separators (brazing, etc.), the process of power generation, etc. In a high temperature environment, damage caused by the difference in coefficient of thermal expansion is completely avoided and eliminated, and
On the other hand, since ferritic stainless steel has excellent corrosion resistance, there is no risk of corrosion damage even in a highly corrosive environment, which is the operating environment, and it contributes to maintaining and exhibiting stable functions.

[0013]

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

FIG. 3 is a cross-sectional view showing an example of the structure of the different main parts of the fuel cell stack according to the present invention, in which a seal element 11 seals between adjacent separators 10 made of stainless steel in the manifold part. It is a sealed and integrated structure. In this configuration example, the sealing element 11 is formed of an insulating magnesia ring 11a and a ferritic stainless steel plate 11b having a stress relaxation mechanism 11b '. There is a restricted area. That is, spacers 13 that do not interfere with the flow of gas are provided in each gas flow passage at a plurality of locations on the circumference of the manifold 12 to define an unrestrained area, and to prevent the gas flow passage from being blocked. The deformation in the stacking direction can be easily performed. In other words, it is possible to freely follow the deformation in the stacking direction due to the dimensional accuracy in the assembly stage, the deformation in the stacking direction due to the creep phenomenon of the electromotive part (reaction part) component due to long-term operation, and the like. Here, while there is a gap between the spacer 13 and the edge plate 14 constituting the separator, the unconstrained area is determined by L ₁ , and after the spacer 13 and the edge plate 14 constituting the separator contact each other, there is no constraint. The area will be determined by L ₂ . In FIG. 3, 15 is an electrolyte plate, 16,
Reference numeral 17 is a pair of electrodes (positive electrode, negative electrode).

Furthermore, in the fuel cell stack according to the present invention having the above-mentioned structure, the main structure is shown in cross section in FIG. 4, and in this example, the seal element 11 is provided with corrosion resistance. Therefore, the aluminum diffusion layer 18 is formed and provided on the metal 11b surface and the brazing material surface, for example, by performing an aluminizing treatment. When a nickel-based brazing material formed by adding titanium or the like is used as the brazing material due to the formation of the aluminum diffusion layer 18, in combination with its composition, for example, an alloy layer of nickel, chromium, aluminum, iron, etc. Insulating ceramics 11a and metal 1 of the sealing element 11 are formed.
Corrosion resistance of the brazing material layer 11c connecting with 1b can be improved.

Next, another embodiment of the present invention will be described.

FIG. 5 is a cross-sectional view showing the structure of a main part of a laminated fuel cell according to the present invention. In this embodiment, a sealing element 19 having a C-shaped cross section partially forms a manifold portion. The structure is such that the space between adjacent separators 10 made of stainless steel is hermetically sealed and integrated. That is, here, a metal O-ring having a C-shaped cross section is used.
A ceramic flat plate 19b having an insulating property and a metal flat plate 19b 'that secures rigidity in the plane direction are laminated and integrally arranged on the side facing the separator 10 with the 19a interposed therebetween. In the construction of this sealing element 19,
If necessary, the ceramic flat plate 19b is preferably impregnated with, for example, B ₂ O ₃ —SiO ₂ type glass that melts at the battery operating temperature, and a better sealing property can be expected. Further, instead of the ceramic flat plate 19b, a ceramic layer having an insulating property may be formed and secured on the surface of the metal flat plate 19b 'by thermal spraying or the like. The seal element according to the present invention is not limited to the above-described shape or structure, and may have a cross-sectional shape of, for example, a circle, an ellipse, an ellipse, a quadrangle, a triangle or the like.

[0018]

As described above, according to the present invention, the insulating ceramics and the metal forming the sealing element are selected so that their thermal expansion coefficients are relatively close to each other. Since the coefficient of thermal expansion is set to be relatively similar, the coefficient of thermal expansion is increased in a high temperature environment such as the process of forming the sealing element, the airtightness / sealing process between the separators (brazing, etc.), or the process of power generation. The damage caused by the difference is completely avoided or eliminated, while the ferritic stainless steel has excellent corrosion resistance.
Even in a highly corrosive environment, which is the operating environment, there is no risk of corrosive damage, contributing to maintaining and exhibiting stable functions.

[Brief description of drawings]

FIG. 1 is a curve diagram showing an example of the relationship between temperature and strain amount for ceramics and metals that form a sealing element used in the construction of a fuel cell according to the present invention.

FIG. 2 is a curve diagram showing another example of the relationship between temperature and strain amount for ceramics and metals that form the sealing element used in the construction of the fuel cell according to the present invention.

FIG. 3 is a cross-sectional view showing a configuration example of a main part of a fuel cell according to the present invention.

FIG. 4 is a cross-sectional view showing another configuration example of the main part of the fuel cell according to the present invention.

FIG. 5 is a cross-sectional view showing still another example of the main part configuration of the fuel cell according to the present invention.

FIG. 6 is a perspective view showing a configuration example of a main part of a stacked fuel cell.

7 is a cross-sectional view taken along the line AA of FIG.

FIG. 8 is a curve diagram showing another example of the relationship between temperature and strain amount for ceramics and metals that constitute the sealing element used in the configuration of the conventional fuel cell.

[Explanation of symbols]

1, 15 ... Electrolyte plate (layer) 2, 10 ... Separator 2a
... Separator body 3,3a, 3b ... Oxidizer gas system manifold 4,4a, 4b
… Fuel gas system manifold 5… Reaction part 6, 7,
15, 16 ... Paired electrodes 9, 11, 19 ... Sealing element
9a ... Insulating ring 11a ... Insulating ceramic ring
11b ... Metal ring 11b '... Stress relaxation mechanism 11c
… Brazing material 12… Manifold 13… Spacer 14
・ ・ ・ Edge plate 18 ・ ・ ・ Aluminum diffusion layer 19a ・ ・ ・ C-shaped metal O ring 19b ・ ・ ・ Ceramic plate 19b ・ ・ ・ Metal plate

Claims (1)

[Claims] 1. A separator is interposed between unit cells having a gas channel portion that forms a gas path in contact with a pair of positive and negative electrodes that contact and sandwich both main surface sides of an electrolyte plate. In the fuel cell, the insulating ceramics layer and the thermal expansion coefficient are relatively close to those of the insulating ceramics between the adjacent separators for each gas passage in the manifold portion that alternately supplies the oxidant gas and the fuel gas to the gas passages. A fuel cell characterized in that it is sealed with a sealing element composed of a metal layer.