JPH09115532A - Gas seal method for solid electrolytic fuel cell of internal manifold type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple, highly efficient mechanical seal method excellent in the fuel utilization rate by applying an epoch-making idea to a conventional mechanical seal method currently utilized for prevention of cross leak with a fuel gas and oxidizer gas. SOLUTION: This cell is alternately stacked with a flat unit cell 3 in which an air pole 6 and a fuel pole 5 are respectively disposed on both surfaces of a tabular type solid electrolyte layer 4 and a separator 1 which electrically connects adjoining unit cells in series and distributes a fuel and oxidizer gas to each unit cell. In this composition, the cell has a mechanical seal structure in which a metal mesh or a metal felt 7 is disposed between the fuel pole 5 and the fuel gas circulation passage side of the separator 1 and a spacer 2 is placed between the solid electrolyte layer 4 of the unit cell 3 and the separator 1, and regulates a pressure difference between the air and fuel gas by flowing an oxidizer gas and fuel gas as the parallel flow in a stack and by structurally changing a flow resistance in a circulation groove for the air and fuel gas formed in the separator 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sealing method for an internal manifold type solid oxide fuel cell.

[0002]

2. Description of the Related Art Recently, fuel cells which directly convert chemical energy inherent in fuel into electric energy by using, for example, air and hydrogen as oxidizing gas and fuel gas, respectively, have attracted attention from the viewpoint of resource saving and environmental protection. Research and development are progressing because solid electrolyte fuel cells have many advantages such as high power generation efficiency and effective use of waste heat.

In order to supply a fuel gas and an oxidizing gas to a solid electrolyte fuel cell, an external manifold is provided on the outer periphery of the solid electrolyte fuel cell, and a gas supply / exhaust hole for each gas is provided in a separator and a solid electrolyte layer. There is an internal manifold type in which each gas is supplied and exhausted from each hole to each electrode surface of each unit cell through this hole.

FIG. 1 is a cross-sectional view of a flat plate type solid electrolyte fuel cell of the internal manifold type, and FIG. 2 is a perspective view of the composite separator used in FIG.

The flat plate type solid electrolyte fuel cell of the internal manifold type shown in FIGS. 1 and 2 has (La, Sr) on both sides of a flat plate type solid electrolyte layer 4 made of a zirconia sintered body (YSZ) doped with yttria or the like. A flat plate-shaped unit cell 3 in which an air electrode 6 of MnO ₃ and a fuel electrode 5 of Ni / YSZ cermet are arranged, and adjacent unit cells 3 are electrically connected in series to each other. The separators 1 for distributing the fuel gas and the oxidant gas are alternately laminated, the metal mesh 7 is interposed between the fuel electrode 5 and the fuel gas flow passage side of the separator 1, and the solid electrolyte layer 4 of the unit cell 3 is formed. A separator 1 and a separator 2 are interposed between the separators 1 to form a stack, and an electromotive force is generated by bringing a fuel gas and an oxidant gas into contact with the electrode surface of each unit cell 3. That.

The separator 1 separates the fuel gas and the oxidant gas supplied to the fuel electrode 5 and the air electrode 6, respectively, to prevent their cross-leakage, and the cells 3 are electrically connected in series. And the action of connecting. The separator 1 is made of a lanthanum chromite oxide or a heat-resistant metal, or a composite of a lanthanum chromite oxide and a non-conductive oxide.

As shown in FIG. 1, the fuel electrode side surface and the air electrode side surface of the separator have the same shape and dimensions, and the oxidizer for the air electrode 6 side is provided on the air electrode side surface of the separator. A gas distribution structure (such as a groove described later) is formed, and a fuel gas distribution structure to the fuel electrode 5 side is formed on the surface of the separator on the fuel electrode side.

Gas supply / exhaust holes 1a are formed at the four corners of the separator, and the fuel gas and the oxidant gas are evenly distributed to the surfaces of the fuel electrode 5 and the air electrode 6, respectively, and the adjacent unit cells are connected. Electrodes 5 and 6 for connecting 3 in series
A plurality of rows of gas circulation grooves 1c and protrusions 1b are formed on the surface.

When the fuel cell is assembled, the protrusion 1b
Is in contact with the fuel electrode 5 or the air electrode 6 and is electrically conducted to form a current collector. The gas flow groove 1c communicates with a gas supply / exhaust hole 1a formed at a corner in a diagonal direction through a triangular recess 1f formed on the surface of the separator 1 (see FIG. 2). Gas distribution groove 1c and triangular recess 1f
Has a distribution structure for the fuel gas and the oxidant gas. The peripheral edge portion 1d of the surface of the separator 1 serves as a sealing surface that overlaps with the solid electrolyte layer 4 and the spacer 2 of the unit cell 3.

When the fuel gas and the oxidant gas are mixed inside the stack, the fuel utilization rate is lowered, and the efficiency of the fuel cell is lowered. Of course, the mixture of both gases causes combustion and a local temperature rise. Occurs, the thermal stress distribution becomes non-uniform, cracks and strains occur, and the stack life is shortened.

[0011]

Conventionally, in order to prevent the fuel and the oxidant gas from being mixed inside the stack, a method of applying a sealing agent to the sealing surface between the unit cells 3 and the separator 1 or a method of sandwiching the sealing agent has been proposed. However, at present, no suitable material for the sealant is found. For example, when a ceramic adhesive is used as the sealant, the constituent members are completely adhered by the ceramic adhesive, and the bonded portion is distorted due to the difference in thermal expansion between the constituent members, causing cracks in the solid electrolyte layer 4 of the unit cell 3. At the same time, the adhesive deteriorates during the thermal cycle, which causes gas leakage. Further, when silica-based glass is used as the sealant, the silica component in the sealant evaporates during long-term operation and adheres to and deposits on the low temperature part, resulting in deterioration of the electrodes 5 and 6, causing problems in long-term operation. There is. The drawback of such a sealant can be avoided to some extent by adopting a mechanical seal structure.

In this mechanical seal structure, the metal mesh 7 is arranged on the fuel electrode 5, the spacer 2 is arranged around the fuel electrode 5, and a load is applied to the spacer 2 via the upper separator 1 to laminate them. Thus, the airtightness is secured by the surface contact of the separator 1, the spacer 2 and the solid electrolyte layer 4 (see FIG. 1). However, the quality of surface contact depends on the contact pressure between the two surfaces, the contact area, the smoothness of the surfaces, and the like. In FIG. 2, for example, the portion of the shortest distance between the gas flow hole 1a (for example, fuel gas is flowing) and the triangular depression 1f (for example, oxidant gas is flowing) is the most cross leak between the fuel gas and the oxidant gas. It is considered to be an easy place to do. As described above, from the viewpoint of the structure of the constituent members and the processing accuracy, it is impossible to perform a complete seal with the conventional mechanical seal structure, and the fuel cell operates at a high temperature of 1000 ° C. and the unit cell 3 and the separator 1, Alternatively, there is a drawback that the spacers 2 inserted between them are diffusion-bonded and weak against heat cycles.

The present invention has been made in view of the above points, and is a conventional mechanical seal used for preventing cross leak between a fuel gas and an oxidant gas in a flat plate type solid electrolyte fuel cell of an internal manifold type. It is an object of the present invention to provide a high-performance mechanical sealing method that is simple and has a good fuel utilization rate by adding a revolutionary idea to the method.

[0014]

In order to achieve the above-mentioned object, the present invention provides a flat plate-shaped cell in which an air electrode and a fuel electrode are arranged on both sides of a plate-shaped solid electrolyte layer, and adjacent cell cells. In a gas sealing method for an internal manifold type solid electrolyte fuel cell, in which fuel cells and separators for distributing a fuel and an oxidant gas are alternately laminated to each unit to form a stack. And a fuel gas flow passage side of the separator, a metal mesh or a metal felt is interposed between the solid electrolyte layer of the unit cell and the separator, and a mechanical seal structure having a spacer is interposed between the separator and the oxidant gas. The fuel gas is caused to flow as a parallel flow in the stack, and the flow resistance in the air and fuel gas flow grooves formed in the separator is structurally changed so that the pressure of the air and the fuel gas is changed. And adjusting the.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a flat solid electrolyte layer 4
The flat plate-shaped unit cell 3 in which the air electrode 6 and the fuel electrode 5 are arranged on both sides of the unit cell and the adjacent unit cells are electrically connected in series, and the fuel gas and the oxidant gas are connected to each unit cell. The gas sealing method for the solid electrolyte fuel cell of the internal manifold type in which the separators 1 to be distributed are alternately laminated to form a stack is characterized by the following points. (1) The metal mesh 7 is interposed between the fuel electrode 5 and the fuel gas flow passage side of the separator 1 to form the solid electrolyte layer 4 of the unit cell.
The mechanical sealing method in which the spacer 2 is interposed between the separator 1 and the separator 1 is used. (2) Oxidant gas, for example, air and fuel gas are flown as parallel flow in the stack. (3) Structurally adjust the fluid resistance in the air and fuel gas flow grooves 1c formed in the separator.

FIG. 3 is a graph showing the relationship between the pressure difference and the leakage amount when the mechanical sealing method using a metal gasket is performed.

In FIG. 3, the horizontal axis indicates the pressure difference (unit: mmH ₂
O), and the vertical axis shows the amount of helium leakage (unit: sccm / cm)
And the experimental data for the leak rate (unit%) against the actual flow rate. Line A in the figure is the amount of leakage at room temperature, B
The line shows the leak rate at room temperature, the C line shows the leak amount at 1000 ° C., and the D line shows the leak rate at 1000 ° C. From FIG. 3, it is clear that the larger the pressure difference is, the larger the leak amount and hence the leak rate are at both room temperature and 1000 ° C. Therefore, in order to reduce or prevent the cross leak between the fuel gas and the oxidant gas inside the flat type solid oxide fuel cell of the internal manifold type, it is necessary to make the pressure difference between these gases as small as possible. However, the pressure of both gases is designed in consideration of the fact that both gases must be passed in the vertical direction of the stack.

In order to minimize the pressure difference between the two gases inside the flat type solid electrolyte fuel cell of the internal manifold type, it is necessary to make the flows of both gases parallel. That is, it is preferable that the flow of each gas in the gas flow grooves 1c existing on the upper side surface and the lower side surface of the separator 1 that distributes the fuel gas and the oxidant gas to the unit cell 3 be in the same direction. By doing so, the inlet (the gas pressure is high) and the outlet (the gas pressure is low due to the flow resistance in the circulation groove 1c) of each gas to the gas circulation groove 1c are located on the upper side surface and the lower side surface of the separator 1, respectively. Since the positions are almost the same, the pressure difference is small and cross leak is small. On the contrary, when the inlet of the fuel gas and the outlet of the air come to almost the same position on the upper surface and the lower surface of the separator 1 (this is called a counterflow), the pressure difference between the two gases becomes large and the cross leak becomes severe.

As described above, not only the pressure difference is reduced by making the flow directions of the fuel gas and the oxidant gas inside the stack to be parallel flows, but in the sealing method of the present invention, the fuel is The pressure difference between the gas and the oxidant gas is adjusted to be as low as possible.

The flow resistance is increased by processing the width of the gas flow groove 1c on the fuel electrode 5 side to be narrow, the flow rate of the fuel gas is reduced, and the pressure rise of the fuel is adjusted by the degree of the reduction.
The pressure difference with the air electrode 6 side was adjusted to be small. The width of the gas flow groove 1c may be reduced at its inlet or outlet, or in the middle thereof.

The air supplied to the battery has a flow rate larger than that of the fuel because it serves as a cooling gas as well as an oxidizing agent. Therefore, the gas pressure at the inlet of the air electrode (approximately 200 mmH ₂ O) is usually the gas pressure at the inlet of the fuel electrode (approximately several m
mH ₂ O), and this pressure difference causes air to move to the fuel electrode 5
Tends to leak to the side.

Since the metal mesh is interposed between the fuel electrode 5 side and the separator 1, even if the width of the gas flow groove 1c is changed, the effect on the current collecting effect is small. A method of adjusting the width of the circulation groove 1c is convenient. However, since the width of the gas flow groove 1c on the side of the air electrode 6 affects the current collecting effect, when changing this to adjust the pressure difference,
This needs to be taken into consideration.

In the above embodiment, the pressure difference is adjusted by adjusting the width of the gas flow groove 1c, but the gas flow groove 1c is adjusted.
By changing the number and height of c, in essence, the gas distribution groove 1c
The total cross-sectional area may be structurally adjusted to throttle the fuel gas.

In the above embodiment, the fluid resistance in the flow groove of the fuel gas is structurally adjusted. However, by adjusting the fluid resistance in the flow groove of the oxidant gas structurally, It is also possible to carry out the method of the invention.

[0025]

INDUSTRIAL APPLICABILITY The present invention relates to a gas sealing method for an internal manifold type solid electrolyte fuel cell, in which a metal mesh is interposed between the fuel electrode and the fuel gas flow passage side of the separator, and the solid electrolyte layer of the unit cell and the separator are separated. Using a mechanical sealing method with a spacer in between, an oxidant gas such as air and fuel gas is flowed as a parallel flow in the stack,
Since it is configured to structurally adjust the fluid resistance in the air and fuel gas flow grooves formed in the separator, it is possible to implement a high performance mechanical seal that is simple and has a good fuel utilization rate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a flat solid electrolyte fuel cell of an internal manifold type.

2 is a perspective view of the composite separator used in FIG. 1. FIG.

FIG. 3 is a graph showing a relationship between a pressure difference and a leak amount when a mechanical sealing method using a metal gasket is performed.

[Explanation of symbols]

 1 Separator 1A Heat Resistant Metal Plate 1B Conductive Oxide Plate 1b Protrusion 1c Groove 1d Peripheral Edge 1f Triangle Dimple 2 Spacer 3 Flat Single Cell 5 Fuel Electrode 6 Air Electrode 7 Metal Mesh or Metal Felt

Claims (6)

[Claims] 1. A flat plate type single cell having an air electrode and a fuel electrode arranged on both sides of a flat plate type solid electrolyte layer, and adjacent single cells are electrically connected in series, and a fuel is supplied to each single cell. In a gas sealing method for an internal manifold type solid electrolyte fuel cell in which a separator that distributes a gas and an oxidant gas are alternately stacked to form a stack, a metal mesh is provided between the fuel electrode and the fuel gas flow passage side of the separator. Or, having a mechanical seal structure in which a metal felt is interposed and a spacer is interposed between the solid electrolyte layer of the unit cell and the separator, the oxidant gas and the fuel gas are caused to flow in parallel in the stack, Internal manifold system characterized by adjusting the pressure difference between air and fuel gas by structurally changing the flow resistance in the air and fuel gas flow grooves formed in the separator Gas sealing method for solid electrolyte fuel cell of. 2. The gas sealing method for an internal manifold type solid electrolyte fuel cell according to claim 1, wherein the separator is a conductive oxide. 3. The gas sealing method for an internal manifold type solid electrolyte fuel cell according to claim 1, wherein the separator is made of a heat resistant metal. 4. The gas sealing method for a solid electrolyte fuel cell of the internal manifold type according to claim 1, wherein the separator is a composite separator of a conductive oxide and a non-conductive oxide. 5. The gas sealing method for a solid oxide fuel cell of the internal manifold type according to claim 1, wherein the separator is a composite separator of a conductive oxide and a heat resistant metal. 6. The pressure difference between the air and the fuel gas is 50 mm.
The gas sealing method for an internal manifold type solid electrolyte fuel cell according to claim 1, wherein the gas sealing method is H ₂ O or less.