JPH07183036A - Phosphoric acid fuel cell - Google Patents

Abstract

PURPOSE:To aim at reducing the differential pressure between the electrodes of a phosphoric acid fuel cell, providing a uniform flow rate within the cell, enhancing the corrosion resistance and various characteristics of the cell, and lowering the highest temperature, while enhancing a quality regarding assembly and the productivity of members. CONSTITUTION:A phosphoric acid fuel cell 1 is of rectangular longitudinal section with the ratio of the lengths of the longer to shorter sides 1.4 3.0. Reduction in the differential pressure between the electrodes of the phosphoric acid fuel cell, a uniform flow rate, enhancement of corrosion resistance and various characteristics of the cell, and lowering of the highest temperature are achieved, and a quality regarding assembly is enhanced. Further, a plurality of composite separators 36 and a plurality of electrodes 2, both of which are members constituting the fuel cell 1 of rectangular longitudinal section, are manufactured in a single operation, thereby enhancing the productivity of the members constituting the cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid type fuel cell using phosphoric acid as an electrolyte, and more particularly to a planar shape of a fuel cell alone when viewed in the stacking direction.

[0002]

2. Description of the Related Art FIG. 17 is a perspective view of a conventional phosphoric acid fuel cell, and FIG. 18 is a plan view thereof. In the figure, reference numeral 1 is a unit cell which is a basic unit of a fuel cell and comprises an electrode 2 and a composite separator 6, and the electrode 2 comprises a matrix 3 holding an electrolyte, a fuel electrode 4 and an oxygen electrode 5. The composite separator 6 is composed of a gas impermeable dense layer 7 and porous layers 8 and 9 formed on both surfaces of the dense layer 7. The groove-shaped fuel channel 1 is formed in each of the porous layers 8 and 9 provided on both surfaces of the composite separator 6.
0 and an oxidant flow channel 11 are provided, and the grooves of the fuel flow channel 10 and the oxidant flow channel 11 are orthogonal to each other. Reference numeral 12 is a cell stack formed by stacking a predetermined number of unit cells 1, 13 is a cooling plate, and a predetermined number of the cell stack 12 and the cooling plate 13 are stacked to form a fuel cell. Generally, the fuel flow path 10 and the oxidant flow path 11 are provided such that the groove directions thereof are orthogonal to each other as described above, and the fuel gas and the oxidant gas are flowed along the grooves.
Such a gas flow method is called cross flow.

Next, the operation will be described. The fuel gas and the oxidant gas are supplied to the fuel channel 10 and the oxidant channel 11 which are orthogonal to each other on both sides of the composite separator 6, and reach the entire surfaces of the fuel electrode 4 and the oxygen electrode 5. At the fuel electrode 4, hydrogen in the fuel gas becomes hydrogen ions and electrons due to the function of the catalyst in the fuel electrode 4. The hydrogen ions move in the electrolyte of the matrix 3 to reach the oxygen electrode 5, and the electrons reach the oxygen electrode of the adjacent unit cell via the composite separator. At the oxygen electrode 5,
Oxygen in the supplied oxidant gas, hydrogen ions moving in the electrolyte, and electrons moving from another unit cell
Again, it reacts under the action of the catalyst in the oxygen electrode 5 to generate water, and at the same time generates heat. Electricity is taken out by circulating electrons from one of the terminals provided at both ends of the fuel cell to the other terminal via an external load.

As shown in FIG. 18, the unit cell in the conventional fuel cell often has an approximately square planar shape (hereinafter simply referred to as planar shape) when viewed in the stacking direction. Japanese Unexamined Patent Publication No. 1-146263 and Actual Fair 3-1
Although the description of a rectangular shape can be seen in Japanese Patent No. 886, etc., the reason therefor is not described at all. Note that Japanese Utility Model Publication No. 5-42618 also describes a fuel cell having a rectangular stacking surface. However, in order to properly tighten the manifold, the ratio of the contact area with the cell stack is set to an appropriate value. Is only mentioned. Further, in the case of a molten carbonate fuel cell, which is regarded as a second-generation fuel cell rather than a phosphoric acid fuel cell, for example, “Ishikawajima Harima Technical Report Vol. 30, No. 1 (January 1990)” Pages 1 to 7, or "Ibid., Vol. 31, No. 2, (March 1991)
Mon) ”, pp. 102-108, and“ Do, 31
Volume 6 (November 1991) "Frontiers and pages 414-
On page 429, it can be seen that the planar shape is rectangular. However, the content is focused on improving the cooling effect by the air-cooling method, which is a cooling method peculiar to molten carbonate fuel cells, and the purpose of facilitating temperature control inside the fuel cell stack is to supply gas. The parallel flow internal manifold system is adopted as the system. Further, a fuel cell having a rectangular planar shape has been developed as a large-capacity stack type, and a small-capacity one has a substantially square shape, and an evaluation test has been performed in such a form. As described above, the description of the above document is limited to the case of the molten carbonate fuel cell based on the air cooling system, and the study result is applied to the phosphoric acid fuel cell based on the water cooling system. I can't.

[0005]

As described above, it is presumed that the conventional phosphoric acid fuel cells often had a substantially square planar shape for the following reason. Full-scale research and development of a phosphoric acid fuel cell as a commercial power supply system began with a pressurized fuel cell that pursues improved power generation efficiency for distributed power generation. In a pressurized fuel cell, the fuel cell main body is housed in a high-pressure container because it is necessary to operate the fuel cell main body under a high pressure atmosphere of about 5 kg / cm ² or higher. Since the high-pressure container generally has to be cylindrical due to its strength requirements, etc., the planar shape of the fuel-cell main unit is designed to efficiently store the fuel-cell main unit inside the cylindrical high-pressure container with less waste of space. Is considered to be almost square. After that, research and development of atmospheric pressure type phosphoric acid type fuel cells for cogeneration as well as fuel cells for distributed power generation began, but the planar shape of the fuel cell body followed the same shape as the high pressure type. There is.

The inventors of the present application have conducted research on phosphoric acid fuel cells, and as a result, found that the conventional fuel cell having a substantially square planar shape has some problems. In particular, it has been concluded that the square planar shape has many disadvantages in a normal-pressure type phosphoric acid fuel cell in which there is no size restriction such as installation inside a high-pressure container. The problems in the plane shape of the square will be described below. The first problem is the problem of the differential pressure distribution between poles. In the phosphoric acid fuel cell, the fuel gas and the oxidant gas face each other with a very thin electrolyte matrix (for example, about 100 μm) interposed therebetween.

This electrolyte matrix plays a role of conducting ions by the electrolyte impregnated inside, preventing mixing of fuel gas and oxidant gas facing each other on both sides, and blocking electron conduction. In the phosphoric acid fuel cell,
The above object is achieved by forming a porous electrolyte matrix with a material having high corrosion resistance and impregnating the pores thereof with phosphoric acid as an electrolyte. However, since a very thin layer is impregnated with phosphoric acid to prevent mixing of the fuel gas and the oxidant gas that face each other on both sides, the pressure difference between the fuel gas and the oxidant gas (this is called the inter-electrode differential pressure). ) Becomes large, it becomes difficult to prevent the mixture of fuel gas and oxidant gas. In order to withstand this electrode-to-electrode differential pressure, the size of the pores (hereinafter simply referred to as the pore size) is reduced by reducing the particle size of the material forming the electrolyte matrix, and the capillary suction force of phosphoric acid. However, this pore size is limited by the particle size of the material used, and there is a certain limit to reducing the pore size. On the other hand, generally, when the pore size is reduced, the porosity of the porous layer (the ratio of the pore volume to the total volume of the porous layer, which is filled with phosphoric acid in the electrolyte matrix) is also reduced. If it is reduced, the resistance to differential pressure is improved, but the resistance associated with ionic conduction is increased, resulting in a problem that battery characteristics are deteriorated. In addition to reducing the pore size, a method of increasing the thickness of the electrolyte matrix is conceivable as a means of increasing the resistance to differential pressure between electrodes.However, as with the above, the resistance associated with ionic conduction increases and the deterioration of battery characteristics is avoided. Absent.

If the resistance function against the inter-electrode differential pressure in the electrolyte matrix (hereinafter referred to as “differential pressure resistance performance”) is low, a gas leak (hereinafter referred to as inter-electrode leak) through the electrolyte matrix between the fuel electrode and the oxygen electrode. ) Is generated, which leads to direct mixed combustion of the fuel gas and the oxidant gas (hereinafter, referred to as crossover), resulting in deterioration of battery characteristics, and
This leads to a state in which the cell is damaged and the fuel cell cannot operate. Thus, the differential pressure resistance performance is an important factor for the fuel cell, but it is necessary to make it a very thin film to improve the cell characteristics as described above, so that the inter-electrode differential pressure during operation can be minimized. It is very important to keep it small from the viewpoint of improving the reliability of the fuel cell.

In a phosphoric acid type fuel cell, generally, a fuel gas obtained by reforming natural gas or the like to increase the content of hydrogen molecules (hydrogen concentration is about 60%) is used as the oxidant gas. Air (oxygen concentration about 21%) is used. The proportion of the supplied gas used for power generation reaction (hereinafter, referred to as utilization rate) is generally 75 to 85% for hydrogen, while it is around 60% for oxygen, which is relatively small compared to hydrogen. . Therefore, the flow rate of gas supplied to the fuel cell is
Oxidant gas is overwhelmingly larger than fuel gas, and if the flow channel structure such as the shape, size, and number of grooves of the fuel gas flow channel and the oxidant gas flow channel is the same, The pressure loss from the inlet to the outlet is overwhelmingly large on the oxidant gas side. Since the pressure loss in the gas flow path is different between the oxidant gas and the fuel gas, the distribution of the fuel gas pressure and the oxidant gas pressure differs in the plane of the unit cell.
As a result, a distribution having a specific gradient in the inter-electrode differential pressure is generated on the matrix plane. FIG. 19 shows an inter-electrode differential pressure distribution in a conventional phosphoric acid fuel cell having a substantially square planar shape.

[0010] Single cell size in this case are those projected area of the planar shape is about 5000 cm ^2, operating conditions are current density: 300 mA / cm ^2, a hydrogen utilization factor: 80
%, Oxygen utilization rate: 60%. As can be seen from this figure, in the conventional fuel cell, even if the adjustment control is performed so that the inter-electrode differential pressure is minimized at the fuel gas outlet and the oxidant gas outlet, There is a problem that the pressure on the oxidant gas side becomes higher than the pressure on the fuel gas side, and there is no choice but to operate in a state where there is always a risk of crossover. Further, in order to eliminate the risk of crossover, even if measures are taken with respect to the structural aspect of the electrolyte matrix, the fuel cell characteristics must be degraded by the means of increasing the thickness and pore size of the electrolyte matrix as described above. There was the problem of not getting.

The second problem is that the flow of fuel gas and oxidant gas is made uniform. As described above, in the case of the phosphoric acid fuel cell, the gas flow rate supplied is predominantly higher than the oxidant gas compared to the fuel gas, and when the fuel gas flow path and the oxidant gas flow path have the same configuration. Also, the flow path pressure loss between the flow path inlet and the flow path outlet is predominantly larger on the oxidant gas side than on the fuel gas side. This indicates that the fuel gas is more likely to have a variation in the flow rate than the oxidant gas for each stacked unit cell or for each gas flow path in the unit cell. Specifically, fuel gas and oxidant gas supplied to each unit cell and each flow path of each unit cell due to the structure of a manifold attached to the cell stack for supplying and discharging gas. Difference due to the difference in flow velocity (dynamic pressure) distribution and the gas composition inside the inlet side manifold and outlet side manifold due to the gas density difference in the flow rate distribution between the cells above and below the stack. As a result, the gas flow rate varies for each cell or for each gas flow path of each cell. FIG. 20 schematically shows the influence of the flow distribution between the unit cells on the upper side of the stack and the unit cells on the lower side of the stack.

In order to suppress these variations in the flow rate as much as possible, the gas pressure loss can be increased by increasing the gas flow rate or increasing the gas flow path resistance. However, increasing the gas flow rate means increasing the gas utilization rate. Also, it cannot be applied because the power generation efficiency will decrease. Therefore, the flow path resistance of the gas is increased to suppress the variation in the flow rate. In order to increase the flow resistance of the gas, make the gas flow narrow or shallow, widen the flow passage interval to reduce the number of flow passages, or attach a throttle mechanism etc. inside the flow passage. For example, the gas flow velocity in the flow path is increased. However, in order to make the flow rate variations of the oxidant gas and the fuel gas to be about the same, it is necessary to reduce the flow passage size on the fuel side considerably or widen the flow passage interval, which impedes uniform gas diffusivity over the entire surface of the electrode. Therefore, it is not preferable in terms of battery characteristics. Further, making the shapes of the oxidant gas flow path and the fuel gas flow path different from each other poses a problem in terms of manufacturing the composite separator and in maintaining the assembly quality of the fuel cell. It goes without saying that the method of attaching a throttling mechanism etc. inside the gas flow path makes it very difficult to manufacture the gas flow path, but it is easy for clogging / blockage due to foreign matter or electrolytes to occur in the throttled part. It is not preferable from the point of view.

As described above, in the case of the conventional phosphoric acid fuel cell having a substantially square planar shape, the flow rate of the fuel gas differs from that of the oxidant gas in the unit cell or in each gas flow path. There was a problem that it was easy to do. Further, various means for suppressing this have been proposed, but none of them has a problem in that they are not satisfactory in terms of battery characteristics, operation reliability, flow path manufacturability, and the like.

The third problem is the problem of the corrosion resistance of the single cell, and particularly the corrosion of the single cell due to the local increase in the hydrogen utilization rate. With the increase in hydrogen utilization,
For the mechanism of corrosion of a single cell, see J. El
microchem. Soc. Vol. 137, p3079-
p3085 (1990). In addition, Japanese Patent Application Laid-Open No. 5-190, which was filed and published earlier by the inventors of the present application, etc.
It is also described in Japanese Patent Publication No. 195.

The summary of this problem is as follows. Corrosion of a cell due to a local increase in the hydrogen utilization rate means that as the absolute amount of hydrogen in the fuel near the outlet of the fuel flow channel becomes insufficient, the hydrogen ions in the electrolyte in that region also become insufficient, causing In the reaction (H2 → 2H + + 2e-) at the same time, the electric potential of the fuel electrode becomes higher as the polarization increases, and at the same time, the potential of the counter electrode, that is, the oxygen electrode in this region is raised, and the constituent materials of the oxygen electrode (carbon, platinum, etc.) When exposed to a potential or higher, a corrosion reaction occurs.

In the phosphoric acid fuel cell, the oxygen utilization rate is 60.
%, The hydrogen utilization rate is high at 75 to 85%.
This is because if the battery characteristics are the same, the smaller the amount of hydrogen consumed (that is, the higher the hydrogen utilization rate), the higher the power generation efficiency. As can be seen from the above, it is desirable for the battery to have a high hydrogen utilization rate in order to increase power generation efficiency, but if the hydrogen utilization rate is increased, the absolute amount of hydrogen in the fuel tends to become insufficient near the outlet of the fuel flow path. , The risk of corrosion of the opposite oxygen electrode will increase. In particular, in the case of a fuel cell having a substantially square planar shape, there is a problem in that this degree of risk becomes significantly higher than in the fuel cell of the present invention described later. In actual power plant operation, the rated hydrogen utilization rate is set at an operating point that avoids such danger, but at light load, when the load changes,
In other transient situations, it may be exposed to hydrogen utilization in the range where corrosion occurs.

Further, even if the average hydrogen utilization rate of the entire battery stack is set to the operating point which avoids the risk of corrosion,
As described above, in the case of a conventional fuel cell in which the planar shape is almost square, the fuel gas flow rate variation easily occurs for each cell or gas flow path. There is a possibility that the local hydrogen utilization rate near the outlet of the flow channel becomes high, and the operation is performed in the hydrogen utilization rate range where corrosion may occur or the boundary point thereof. 21, FIG.
2 is a reference diagram showing a hydrogen utilization rate in the case of a conventional fuel cell having a substantially square planar shape, assuming that the flow rate and the reaction are uniform in the plane, and FIG. 21 shows local hydrogen along the fuel flow path. FIG. 22 schematically shows the change in the utilization rate, which shows the relationship between the average utilization rate and the local hydrogen utilization rate near the outlet of the fuel flow path.

The fourth problem relates to the distribution of the power generation reaction within the cell surface, which also affects the cell characteristics.
FIG. 23 shows the reaction distribution in the plane of the unit cell in the case of a square unit cell. Here, the vertical axis shows the current density at each point in the plane as a percentage with reference to the average current density. Since the current density distribution corresponds to the power generation reaction distribution, it shows how the power generation reaction is distributed in the plane.
For example, if a certain point in the figure is 150, it means that 1.5 times the average current flows at that point. FIG. 23
As shown in Fig. 4, there is a biased current density distribution on the oxidant gas inlet side, which is high in the region where the oxidant partial pressure is high due to the difference in reaction activity mainly depending on the oxidant partial pressure. This is because it becomes active and only low activity is obtained in the region of low oxidant partial pressure on the outlet side. Such a phenomenon is disclosed in Japanese Patent Application Laid-Open No. 4-7 which was filed by the present inventors and published earlier.
9165.

A leveling current flows in the horizontal direction of the unit cell so as to level the plane between the high current density region in the high active region and the low current density region in the low active region. There is an in-plane horizontal electric resistance in the unit cell,
There is a resistance loss due to this leveling current. The larger the resistance loss, the lower the cell characteristics. As described above, in the square cell, there is a problem that the distance between the air inlet and the outlet having a large current density cannot be shortened, the resistance loss due to the leveling current cannot be reduced, and the cell characteristics deteriorate. It was

The fifth problem relates to the maximum temperature in the plane of the unit cell, which also affects the battery life. In a phosphoric acid fuel cell, a cooling plate cooler having a cooler is stacked for each battery stack in which a plurality of unit cells are stacked in order to remove heat generated during a power generation reaction from the battery body. . Basically, the heat generated is transferred in the cell stacking direction,
The heat is taken away by this cooler, but in addition to this, there is also the heat taken away by the fuel gas and the oxidant gas.
In particular, the amount of heat removed by the oxidant gas cannot be ignored, and reaches 10 to 15% of the total amount of heat generated. (Compared to this, the amount of heat removed by the fuel gas is small and can be neglected.) Cooling by the oxidant gas is not possible because the oxidant gas supplied to the battery body is lower than the unit cell temperature. Convective heat transfer from the volatile separator to the oxidant gas. However, since the specific heat of the oxidant gas is small, the temperature of the supplied oxidant gas directly rises, and when the oxidant gas advances to some extent in the flow path, the heat transfer to the oxidant gas hardly occurs.

As described above, the heat removed by the oxidant gas is dominant in the upstream region of the oxidant gas flow path. FIG. 24 shows an in-plane heat transfer pattern in the case of a conventional fuel cell having a substantially square planar shape. From this, it can be seen that in the case of a square fuel cell, the conduction heat transfer distance from the maximum temperature region in the cell surface to the oxidant gas cooling zone is long, and the width dimension of the heat transfer cross section is only the cell cell plane width. . For this reason, the heat conduction thermal resistance in the creeping direction from the maximum temperature region within the cell surface to the oxidant gas cooling region increases, and the maximum temperature of the cell tends to increase. In the case of a conventional fuel cell whose planar shape is almost square,
Since the cooling effect by the sensible heat of the oxidant gas cannot be effectively used, there is a problem that the maximum temperature in the cell surface tends to be high. A high maximum temperature is not desirable from the viewpoint of battery life, because material degradation and phosphoric acid scattering at that portion are likely to occur. In addition, although it is a secondary problem, the square shape is the square with the shortest perimeter and the largest equivalent diameter among the quadrilaterals with the same area. However, there is an inherent problem that the structure is difficult to cool.

The first to fifth problems have been enumerated above. However, the conventional phosphoric acid fuel cell having a substantially square planar shape has the following problems. One of them is a problem in assembling the battery stack. In a fuel cell having a square planar shape, it is difficult to distinguish the fuel gas passage surface and the oxidant gas passage surface at a glance. The same applies to the fuel electrode and the oxygen electrode, and it is difficult to determine if the fuel-side member and the oxidant-side member are mistakenly stacked in reverse. A fuel cell is usually constructed by stacking many unit cells, and the number of stacking operations is very large. Laminating and assembling a large number of confusing parts causes a mistake in the laminating work and a delay in the assembling time, which is a serious problem in the assembling work quality of the fuel cell. Particularly in the case of a fuel cell, since all the stacked cells are electrically connected in series, if one cell is wrong among many stacked cells, the entire cell stack will be defective. Considering this, it can be said to be a very important issue.

The other problem is the productivity of the member. In the case of carbon plates, which are the main material of phosphoric acid fuel cell members, the maximum manufacturable size is 1.
It is up to a square flat plate of about 2 m. Currently, in a fuel cell with a projected area of about 5,000 cm ^{2 in a} planar shape, which is mainly manufactured at present, if the planar shape is a square, each member is
I can only get one. Also, if there is a small defect near the center of the material of a square plate with a side of about 1.2 m,
No member can be obtained from this material. This is
The same applies to the fuel electrode, the matrix, the oxygen electrode, etc., and due to the limited dimensions of these manufacturing facilities, there is a problem that the conventional square-shaped unit cell can complete the entire manufacturing process and obtain only one finished product. there were. FIG. 25 shows a conventional manufacturing process of the fuel electrode, matrix and oxygen electrode. In any case of the carbon plate, the fuel electrode, the matrix, and the oxygen electrode, the productivity becomes extremely poor, which causes an increase in fuel cell member cost and manufacturing cost. In a phosphoric acid fuel cell, which is about to be put into practical use, cost reduction is the most important issue, and improving productivity greatly contributes to cost reduction.

The present invention has been made in order to solve the above problems, and reduces the inter-electrode differential pressure of a phosphoric acid fuel cell, makes the flow rate uniform, improves the corrosion resistance, improves the characteristics, and reduces the maximum temperature. It is intended to improve the quality of assembly work and the productivity of members.

[0025]

The invention according to claim 1 is
Each member constituting the phosphoric acid fuel cell has a rectangular shape as viewed in the stacking direction, and the ratio of the long side to the short side of the rectangle is in the range of 1.4 to 3.0. Is.

According to the second aspect of the present invention, each member constituting the phosphoric acid fuel cell has a rectangular shape as viewed in the stacking direction, and the fuel gas is supplied along the long side of this rectangle and the fuel gas is supplied along the short side thereof. The oxidant gas is made to flow.

According to a third aspect of the present invention, each member constituting the phosphoric acid fuel cell has a rectangular shape as viewed in the stacking direction, and cooling grooves of the cooling plate are formed in the long side direction of the rectangle. is there.

In the invention according to claim 3, the fuel cell is provided in the front stage,
In the serial flow type fuel cell, which is composed of a pair of laminated bodies composed of the latter stage, and which supplies the fuel gas to the former stage laminated body and supplies the exhaust gas to the latter stage laminated body, each member constituting the laminated body The shape viewed from the stacking direction is a rectangle, and the oxidant gas is caused to flow along the long side of this rectangle and the fuel gas is caused to flow along the short side thereof.

[0029]

According to the first aspect of the invention, each member forming the phosphoric acid fuel cell has a rectangular shape when viewed in the stacking direction, and the ratio of the long side to the short side of the rectangle is 1.4. By setting the range to 3.0, the material yield is improved in the production of each member, and since the planar shape is rectangular, the members on the fuel side and the oxidizer side are mistakenly mistaken during assembly of the laminated members. Errors in assembly work such as stacking are reduced.

According to the second aspect of the present invention, each member constituting the phosphoric acid fuel cell has a rectangular shape as viewed in the stacking direction, and the fuel gas is supplied along the long side of the rectangle and the fuel gas is supplied along the short side thereof. Since the oxidant gas is made to flow, even if the fuel gas flow path and the oxidant gas flow path have the same width, depth, pitch dimensions, etc., the pressure loss of the oxidant gas flow path is greatly reduced, It becomes easy to balance the flow path pressure loss and the oxidant gas flow path pressure loss. Further, the pressure difference between the electrodes on the plane of the unit cell during fuel cell operation is made uniform, and the chance of crossover occurring is reduced.

According to the third aspect of the present invention, by forming the cooling groove in the longitudinal direction of the rectangular cooling plate, the number of bends of the cooler embedded in the cooling plate is reduced. Further, the number of cooling grooves for inserting the cooler in the cooling plate is reduced. Further, the amount of phosphoric acid scattered during operation is suppressed.

In the invention according to claim 4, in the serial flow fuel cell, each member constituting the laminated body has a rectangular shape as viewed in the laminating direction, and the oxidant gas is supplied along the long side of the rectangular shape. By causing the fuel gas to flow along the short side, the pressure increase in the reformer and the increase in the inter-electrode differential pressure are reduced.

[0033]

【Example】

Example 1. 1 is an exploded perspective view of a phosphoric acid fuel cell stack according to Embodiment 1 of the present invention, and FIG. 2 is a plan view.
Each reference numeral in the figure is the same as that described in the conventional example. Figure 2
Shows that the phosphoric acid fuel cell itself has a rectangular planar shape, and the ratio of the length of the long side to the length of the short side is about 2.0. ) Fuel gas,
The oxidant gas is flowed in the lateral direction (along the short side). The operation is the same as in the conventional example and will not be described.

The operation of the present invention will be described below.
First, the distribution of differential pressure between poles will be described. FIG. 3 shows a phosphoric acid fuel cell stack having the same operating conditions and the same shape and size (width, depth, and pitch) of the fuel gas flow path and the oxidant gas flow path as in the conventional example shown in FIG. This is the inter-electrode differential pressure in-plane distribution when only the planar shape of the body, that is, the planar shape of the unit cell, is rectangular. Here, the case where the ratio of the length of the long side to the length of the short side is (long side length / short side length) = 2 is shown, and the fuel gas flow path is along the long side and the oxidant gas is The flow path is provided along the short side. In the case of FIG. 3, the length of each side is 1.4 times on the long side and 0.7 times on the short side, as compared with the case where the planar shape of FIG. 19 is square. The passage has a passage length of 1.4 times and the passage width (that is, the number of passages) of 0.7 times, and the oxidant gas passage has a passage length of 0.7 times and the passage width ( That is, the number of channels is 1.4 times. Therefore, regarding each gas flow path, the passing gas flow rate increases 1.4 times on the fuel side, and conversely decreases 0.7 times on the oxidant side. The flow velocity in the gas flow channel of the phosphoric acid fuel cell is very slow, being several meters per second or less, and in a laminar flow state. In this case, the flow path pressure loss is expressed by the following equation. Δp = K × L × v (1) where Δp: flow channel pressure loss, L: flow channel length, v: flow velocity,
K: coefficient, K is a coefficient determined by the type of passing gas, temperature, pressure, flow channel width, and flow channel depth dimension. From equation (1), in FIG. 19, the fuel-side pressure loss is approximately doubled because both the flow passage length and the flow rate (that is, the flow velocity) are 1.4 times larger than in FIG. 3, and the oxidant-side pressure loss is the flow passage length. Since both the flow rate and the flow rate are 0.7 times, they are about half.

In the square shape of FIG. 19, the in-plane distribution of the inter-electrode differential pressure (= fuel side pressure-oxidant side pressure) is -200 mm.
It was Aq to +50 mmAq. On the other hand, in the case of the rectangular shape of FIG. 3, the inter-electrode differential pressure distribution is −100 mmAq to +100 mmAq. In this way, the inter-electrode differential pressure width is reduced. At the same time, the negative maximum value of the differential pressure between the poles is halved. Furthermore, the area in which the inter-electrode differential pressure becomes negative is significantly reduced. As a result, the pressure difference between the fuel gas and the oxidant gas applied to the electrolyte matrix during operation can be kept small, so that even if the electrolyte matrix is thinned to improve its characteristics, reliability against interelectrode leakage etc. It is possible to obtain a high phosphoric acid fuel cell. Further, the low absolute value of the inter-electrode differential pressure means that even if the inter-electrode leak occurs, the amount of the leak decreases in proportion to the inter-electrode differential pressure. The wide high region means that the leak gas flows from the fuel gas side to the oxidant gas side, and it is also difficult for hydrogen gas deficiency to occur in the fuel gas outlet region where the risk of corrosion is high. .
(If a leak occurs from the oxidant gas side to the fuel gas side, the hydrogen gas in the fuel gas flow passage in the downstream region is extremely reduced from the leak location.) By flowing, the pressure loss of the oxidant gas is reduced, the power of the air blower can be reduced, and the effect of improving the power generation efficiency of the fuel cell power plant can be obtained.

Next, the uniformization of the flow rate for each cell or gas flow path will be described. As can be seen from the description of FIG. 3, when the fuel gas is flowed along the long side and the oxidant gas is flowed along the short side in the rectangular shape, the pressure loss of the fuel side flow path and the oxidant side flow path is almost eliminated. Can be equal.
Therefore, compared with the conventional square cell, the pressure loss on the oxidizer side is low and the pressure loss on the fuel side is high, and it was large on the fuel gas side in the past (the shape of the gas caused by the manifold structure, etc. It is possible to make the variation in the flow rate distribution between the cells above and below the stack substantially equal on the fuel gas side and the oxidant gas side. The flow rate variation due to the influence of the flow rate distribution between the upper and lower cell stacks is schematically shown.
Compared with FIG. 20, which is the conventional example already described, the influence of the head difference is reduced, the flow rate variation in the stacking direction is suppressed to half, and the flow rate distribution in the stacking direction is made uniform.

FIGS. 5 and 6 show fuel cell flow paths having the same shape and dimensions (width, depth, pitch) under the same conditions as those of the conventional example described above and shown in FIGS. The relationship between hydrogen utilization rates when the shape is rectangular is shown. Here, the case where the ratio of the length of the long side to the length of the short side is (long side length / short side length) = 2.25 is shown.
A fuel gas channel is provided along the long side and an oxidant gas channel is provided along the short side. The area of the unit cell plane is the same as in FIGS. 21 and 22. FIG. 5 schematically shows changes in the local hydrogen utilization rate along the fuel flow channel, and FIG. 6 schematically shows the relationship between the average utilization rate and the local hydrogen utilization rate near the outlet of the fuel flow channel. Comparing FIG. 21 with FIG. 5 and FIG. 22 with FIG. 6, it can be seen that the rectangular cell has a local utilization rate of about 10% smaller than that of the square cell. When evaluated by the average hydrogen utilization rate at which the local hydrogen utilization rate at the outlet is the same, the rectangular cell has 5 times more than the square cell.
It is possible to operate even with an average hydrogen utilization rate of ~ 7% higher. That is, even if the flow rate of the fuel gas supplied to the fuel cell stack is reduced by about 5 to 7%, it is possible to supply a highly reliable fuel cell having sufficient corrosion resistance of the unit cell. From the viewpoint of the power generation efficiency of the fuel cell, this is in the direction of reducing the amount of raw fuel required and is extremely effective.

FIG. 7 shows the reaction distribution in the plane of the unit cell in the case of the rectangular unit cell. Here, similarly to FIG. 23 which is the conventional example already described, there is a current density distribution that is biased toward the air inlet side. The larger the resistance loss, the lower the unit cell characteristics. Therefore, in order to improve the unit cell characteristics, (1) the electrical resistance in the horizontal direction is reduced as a specific physical property value. (2) Reduce the horizontal distance. (3) The difference in current density between the high current density region and the low current density region is reduced. This is very important. The case of (1) can be realized by applying a low resistance material as the material. In case of (2),
By adopting the rectangular unit cell as in the present invention, it can be realized by reducing the distance between the air inlet and the outlet having a large current density difference. In the case of (3), for example, a low activity catalyst is used for the air inlet and a high activity catalyst is used for the air outlet. However, according to the inventors' study on (3), when such a catalyst distribution is taken, the resistance loss is reduced but the catalyst utilization is lowered, so that the cell characteristics may be lowered. I know.

As a result of reducing the resistance loss due to the leveling current according to the present invention, it was observed that the rectangular cell has a performance improvement of about 2 to 3% as compared with the square cell. Moreover, the maximum current density region (1
When compared as an area ratio of 60 to 180), FIG.
In the conventional square cell shown in Fig. 7 and the rectangular cell of the present invention shown in Fig. 7, the latter is smaller. The difference between the maximum value and the minimum value is 120 for the former and 100 for the latter, and the gradient of the current density is reduced. That is, by adopting the rectangular unit cell, it is possible to equalize the power generation reaction distribution.

FIG. 8 shows the in-plane heat transfer form up to the maximum temperature and the oxidant gas cooling region in the cell surface in the case of the rectangular cell. As can be seen by comparing FIG. 24 with FIG. 8, the ratio of the oxidant gas cooling region to all the planes is almost the same, but the heat transfer distance and the width of the heat transfer cross-section in the creeping direction. Can be greatly changed. as a result,
The heat transfer resistance R ′ in the case of a rectangle can be suppressed to half or less as compared with the heat transfer resistance R in the case of a square. The maximum temperature in the cell surface can be reduced by the amount that the heat transfer resistance can be reduced, which indicates that the cooling effect by the sensible heat of the oxidizing gas is effectively used. If the maximum temperature in the cell surface is kept low in this way, it is effective in preventing deterioration of each member constituting the cell and scattering of phosphoric acid, which is the electrolyte, and is extremely effective from the viewpoint of battery life. large.

Although the first embodiment has been described above, the rectangular cell has the following other characteristics.
One of them is that the laminate plane shape is rectangular,
The fuel gas flow path surface and the oxidant gas flow path surface can be distinguished at a glance. The same applies to the fuel electrode and the oxygen electrode, and it is possible to prevent the fuel side member and the oxidant side member from being mistakenly laminated in reverse. The phosphoric acid fuel cell requires a lot of unit cell stacking and assembling work, which has a great effect on streamlining the stacking and assembling work and improving the quality of the assembling work. The other is to improve the productivity of parts. In the case of carbon plates, which are the main members of phosphoric acid fuel cells, the maximum size that can be manufactured is currently 1.
Although it is up to a flat plate of about 2 m square, the mainstream external area currently 5
A phosphoric acid fuel cell of about 000 cm ² (long side: short side ≒
When manufacturing in a 2: 1) rectangular size, two phosphoric acid fuel cell materials can be cut out from one carbon flat plate. Further, even if there is a small defect near the center of the manufactured 1.2 m square carbon plate, at least one material for a fuel cell can be cut out if it has a rectangular planar shape. That is, productivity is greatly improved,
Cost reduction of phosphoric acid fuel cell members can be realized.

Finally, the inventors examined restrictions on the ratio of the long side length to the short side length. Regarding the above-mentioned uniform distribution of flow rate, reduction of local hydrogen utilization rate, improvement of reaction distribution of single cells, and improvement of in-plane temperature distribution, (long side length / short side length)
The higher the ratio is, the more preferable it is. Therefore, the distribution of the inter-electrode differential pressure in the plane of the unit cell and the productivity of the members will be described here.

FIG. 9 shows the relationship between the ratio of (long side length / short side length) and the differential pressure between electrodes. The projected area is 5000 cm.
^{In the case} of the phosphoric acid fuel cell of No. ^{2 under} the same operating conditions as the conventional example shown in FIG. 19 and using the fuel gas passage and the oxidant gas passage having the same shape and dimensions (width, depth, pitch), It shows how the differential pressure between the electrodes changes by changing the ratio of (length / short side length). The gap between electrodes applied to the matrix during operation is smaller than the gap between electrodes in the case of a square cell (long side length / short side length)
Is in the range of 1 to 4. If a point where the maximum value of the absolute value of the inter-electrode differential pressure is 75% or less of that in the case of a square cell is clearly selected as a point at which a significant difference in the inter-electrode differential pressure is obtained, this ratio is 1.4 to 3. It will be in the range of 0.

FIG. 10 shows a projected area of 5000 cm from a carbon flat plate having a maximum size of 1.2 m square that can be currently manufactured.
^{2 The} number of sheets of carbon material that can be taken out from a fuel cell is expressed by changing the above ratio. From this, when the above ratio is 1.5 or less, a fuel with a projected area of 5000 cm ² is drawn from a 1.2 m square carbon flat plate. Although only one cell carbon material can be taken out, it can be seen that two fuel cell carbon materials having a projected area of 5000 cm ² can be taken out in the range of 1.5 to 2.8. Of course, if the above ratio is 2.8 or more, it is impossible to manufacture a member.

From the above results, it is possible to obtain a projected area of 5 from a carbon flat plate having a maximum size of about 1.2 m square that can be currently manufactured.
The ratio of (long side length / short side length) for producing two pieces of fuel cell carbon material of 000 cm ² is 1.5 to 2.
It can be seen that the range is 8. The region where the fuel gas pressure is higher than the oxidant gas pressure occupies more than half of the entire plane. (Long side length / short side length) ratio 2 to
The range of 2.8 is more desirable.

Example 2. FIG. 11 is a plan view according to the second embodiment, and the gas flow type (serial flow) described in the above-mentioned JP-A-5-190195 is also used.
Is the case. The serial flow is basically the same as the cross-flow type because the fuel gas flow and the oxidant gas flow are orthogonal to each other, but in this case, unlike the first embodiment, the oxidant gas is supplied in the long side direction and the short side direction. Fuel gas is flowing through.
The length ratio in the long side direction and the short side direction is the same as in Example 1, and the ratio of the lengths of the long side and the short side is 1.5 to 3.0.

In the case of the serial flow, the residual fuel gas exhausted after passing through the former unit cell is supplied again to the latter unit cell, so that many problems described in the conventional example have already been solved. . Specifically, uniformization of the fuel gas flow rate, improvement of the outlet hydrogen utilization rate, improvement of the in-plane power generation reaction distribution of the unit cell, etc. have been achieved by the serial flow. On the contrary, in the serial flow, the flow rate of the fuel gas supplied to one unit cell is several times that of the normal cross flow, so that the pressure loss on the fuel gas side becomes large. For this reason, the distribution of the differential pressure between the electrodes also inevitably becomes large. (The pressure on the fuel side becomes higher.) Also, the pressure of the raw fuel gas sent to the reformer located upstream of the fuel cell in the plant also rises accordingly, making it difficult to supply steam to the raw fuel gas by the ejector. become. Therefore, in the case of a phosphoric acid fuel cell that uses a serial flow, oxidant gas is supplied in the long side direction,
Flowing the fuel gas in the direction of the short side has an effect of preventing an increase in the inter-electrode differential pressure. In the second embodiment, serial
Although the description has been limited to the flow, the configuration as described in the second embodiment should be established regardless of the flow of gas, as long as it is a gas flow type in which all or part of the supply gas is supplied to the single cell a plurality of times. Needless to say.

Example 3. FIG. 12 is a plan view according to the third embodiment as seen from the line AA in FIG. In FIG. 12, the cooling groove of the cooling plate 13 is formed in the longitudinal direction. The operation is the same as the above description and is omitted. By thus forming the cooling groove in the longitudinal direction, the number of times of bending the cooler 14 embedded in the cooling plate 13 can be reduced, and the bending cost of the cooler can be reduced. Further, also in the cooling plate 13, since the number of cooling grooves for inserting the cooler is reduced, it is possible to reduce the processing cost for groove processing.

As a cooling method, a pressure cooling method or a boiling cooling method is used. In either case, the cooling water temperature in the inlet region of the cooling water is somewhat low and the cooling effect is large. In this embodiment, as can be seen from FIG. 12, the cooling water inlet region is arranged on the oxidant gas outlet side of the rectangular unit cell. That is, the cooling effect on the outlet side of the oxidant gas can be increased. Usually, in phosphoric acid fuel cells, most of the scattered phosphoric acid is discharged along with the oxidant gas and is discharged to the outside of the fuel cell. However, if the oxidant gas on the outlet side is cooled efficiently, the phosphoric acid saturation in it will occur. Since the vapor pressure is reduced, the amount of scattered phosphoric acid can be greatly suppressed. As described above, by adopting the configuration of Example 3, there is an effect that the amount of scattered phosphoric acid can be suppressed and the life of the fuel cell stack can be extended.

Example 4. FIG. 13 shows an assembly layout in which the rectangular fuel cell group is paired for every two fuel cell stacks in a system using a plurality of phosphoric acid fuel cell groups. The gas flow method is such that each fuel cell stack is a cross flow, but the fuel gas is supplied only to one of the two fuel cell stacks and the exhaust gas is supplied to the other fuel cell stack. , So-called serial flow between stacks. The oxidant gas is supplied and discharged to each fuel cell as in the normal flow, but the oxidant supply and discharge manifold consists of one common manifold for two stacks that make a pair. Has been done. In this way, the rectangular phosphoric acid type fuel cell group is paired for every two fuel cells and assembled so that the long sides thereof face each other, so that the paired two cells form a substantially square shape and lay out compactly. You can

In order to supplement the above description of each embodiment,
A specific example in the case where the present invention is applied will be described with respect to the manufacturing process of each member. FIG. 14 is a manufacturing flow of the rectangular planar matrix 3, the fuel electrode 4, and the oxygen electrode 5. At present, the maximum size that can be manufactured with carbon material is about 1.2 m square, and in the manufacturing flow shown in FIG. 14, a 1.2 m square large area matrix, fuel electrode and oxygen electrode are manufactured, and then a projected area of about 5000 cm ² It is manufactured by dividing the rectangular matrix, the fuel electrode, and the oxygen electrode. By doing so, many steps such as molding, drying, pressure bonding, and firing, which have been performed each time to manufacture a single sheet as shown in FIG. 14, are carried out to manufacture a large-area matrix, fuel electrode, and oxygen electrode. By dividing and collecting a plurality of sheets, the process can be omitted at one time. Thus, the manufacturing process, that is, the manufacturing time can be shortened, and the manufacturing cost can be remarkably reduced. Large area matrix, fuel electrode, oxygen electrode, rectangular matrix,
FIG. 15 shows an example in which the fuel electrode and the oxygen electrode are separated and taken out. Currently, in the production of fuel electrode and oxygen electrode, due to the limitation of the carbon material size, it is possible to produce only two sheets having a size of about 5000 cm ^2, but in matrix production, as shown in the figure, the rolling process is performed continuously. If materials are supplied, two or more matrices can be manufactured collectively, and a plurality of matrices can be manufactured at once.

FIG. 16 is a view showing that a carbon member for a phosphoric acid fuel cell having a rectangular planar shape according to the sixth embodiment is cut from a square large area carbon material. By doing this, the same papermaking, impregnation, molding, firing, and
Only by the graphitization process, it is possible to obtain twice the number of carbon members for fuel cells as in the conventional case. This not only shortens the manufacturing period of the carbon member, but also reduces waste due to improved productivity, and reduces external heat radiation energy during firing and graphitization, thus reducing the cost of the carbon plate member. Further, even if the large-area carbon material has a small defect or the like, it is possible to take out at least one carbon member for a fuel cell from the large-area carbon material by performing plate cutting while avoiding the defective portion.

[0053]

In the invention according to claim 1, each member constituting the phosphoric acid fuel cell has a rectangular shape when viewed in the stacking direction, and the ratio of the long side to the short side of the rectangle is 1. The range of 4 to 3.0 improves the material yield in manufacturing each member, and the planar shape is rectangular, so that the members on the fuel side and the oxidizer side can be separated when the laminated members are assembled. It is possible to obtain an effect such that mistakes in assembling work such as erroneous stacking are reduced.

According to the second aspect of the present invention, each member forming the phosphoric acid fuel cell has a rectangular shape as viewed in the stacking direction, and the fuel gas is supplied along the long side of the rectangle and the fuel gas is supplied along the short side thereof. Since the oxidant gas is made to flow, even if the fuel gas flow path and the oxidant gas flow path have the same width, depth, pitch dimensions, etc., the pressure loss of the oxidant gas flow path is greatly reduced, It becomes easy to balance the flow path pressure loss and the oxidant gas flow path pressure loss. Further, there is an effect that the pressure difference between the electrodes on the flat surface of the unit cell during the fuel cell operation is made uniform, and the chance of occurrence of crossover is reduced.

According to the third aspect of the present invention, by forming the cooling groove in the longitudinal direction of the rectangular cooling plate, the number of bends of the cooler embedded in the cooling plate is reduced, and the cooling plate is inserted into the cooler. Since the number of the cooling grooves is reduced, the cooling plate and the cooler can be manufactured at low cost. further,
Since the oxidant gas is effectively cooled, there is also an effect that the amount of phosphoric acid scattered during operation is suppressed.

In the invention according to claim 4, in the serial flow fuel cell, each member constituting the laminated body has a rectangular shape as viewed in the laminating direction, and the oxidant gas is supplied along the long side of the rectangular shape. Since the fuel gas is caused to flow along the short side, there is an effect that a pressure increase in the reformer, an increase in inter-electrode differential pressure, and the like are reduced.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a phosphoric acid fuel cell stack according to a first embodiment of the present invention.

FIG. 2 is a plan view of a phosphoric acid fuel cell stack of Example 1 according to the present invention.

FIG. 3 is an explanatory diagram showing an inter-electrode differential pressure distribution according to the first embodiment of the present invention.

FIG. 4 is an explanatory view showing a flow rate distribution in the stacking direction of Example 1 according to the present invention.

FIG. 5 is an explanatory diagram showing a local hydrogen utilization rate of Example 1 according to the present invention.

FIG. 6 is an explanatory diagram showing average hydrogen utilization rate-outlet hydrogen utilization rate of Example 1 according to the present invention.

FIG. 7 is an explanatory diagram showing an in-plane power generation reaction distribution of Example 1 according to the present invention.

FIG. 8 is an explanatory diagram showing an in-plane heat transfer pattern diagram of Example 1 according to the present invention.

FIG. 9 is an explanatory diagram showing the relationship between the long side / short side length ratio and the inter-electrode differential pressure.

FIG. 10 is an explanatory diagram showing the relationship between the long side / short side length ratio and the number of boards that can be cut.

FIG. 11 is a plan view of a phosphoric acid fuel cell stack according to a second embodiment of the present invention.

FIG. 12 is a plan view of a phosphoric acid fuel cell stack of Example 3 according to the present invention.

FIG. 13 is an assembly layout diagram of a plurality of rectangular phosphoric acid fuel cell group systems according to a fourth embodiment of the present invention.

FIG. 14 is an explanatory diagram showing a manufacturing flow of a rectangular planar matrix, a fuel electrode, and an oxygen electrode according to the present invention.

FIG. 15 is an explanatory diagram showing a method of taking out a rectangular planar matrix, a fuel electrode, and an oxygen electrode according to the present invention.

FIG. 16 is an explanatory view showing how to cut a carbon member according to the present invention.

FIG. 17 is a perspective view of a conventional square phosphoric acid fuel cell stack.

FIG. 18 is a plan view of a conventional square phosphoric acid fuel cell stack.

FIG. 19 is an explanatory diagram showing an inter-electrode differential pressure distribution of a conventional square fuel cell.

FIG. 20 is an explanatory diagram showing a stacking direction flow rate distribution of a conventional square fuel cell.

FIG. 21 is an explanatory diagram showing a local hydrogen utilization rate of a conventional square fuel cell.

FIG. 22 is an explanatory diagram showing average hydrogen utilization rate-outlet hydrogen utilization rate of a conventional square fuel cell.

FIG. 23 is an explanatory diagram showing an in-plane power generation reaction distribution of a conventional square fuel cell.

FIG. 24 is an explanatory diagram showing an in-plane heat transfer form of a conventional square fuel cell.

FIG. 25 is an explanatory view showing a manufacturing flow of a fuel electrode, a matrix and an oxygen electrode of a conventional square fuel cell.

[Explanation of symbols]

 1 Cell 2 Electrode 3 Matrix 4 Fuel Electrode 5 Oxygen Electrode 6 Composite Separator 7 Dense Layer 8 Porous Layer 9 Porous Layer 10 Fuel Flow Path 11 Oxidant Flow Path 12 Cell Laminate 13 Cooling Plate 14 Cooler

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunio Otani 1-2-2 Wadazakicho, Hyogo-ku, Kobe Sanritsu Electric Co., Ltd. Kobe Works

Claims (4)

[Claims] 1. A fuel cell stack in which a plurality of electrodes consisting of three elements of a fuel electrode, an electrolyte matrix, and an oxygen electrode and a composite separator are alternately stacked, and a heat loss generated in the fuel cell stack is cooled. In a phosphoric acid fuel cell in which a plurality of sets of cooling plates provided with cooling means are alternately laminated, each member constituting the phosphoric acid fuel cell has a rectangular shape when viewed in the laminating direction, A phosphoric acid fuel cell, characterized in that the ratio of the length of the long side of the rectangle to the length of the short side is in the range of 1.4 to 3.0. 2. A fuel cell stack in which a plurality of electrodes consisting of three elements of a fuel electrode, an electrolyte matrix, and an oxygen electrode and a composite separator are alternately stacked, and a heat loss generated in the fuel cell stack is cooled. In a phosphoric acid fuel cell in which a plurality of sets of cooling plates provided with cooling means are alternately laminated, each member constituting the phosphoric acid fuel cell has a rectangular shape when viewed in the laminating direction, A phosphoric acid fuel cell, characterized in that a fuel gas is made to flow along a long side of a rectangle and an oxidant gas is made to flow along a short side thereof. 3. A fuel cell stack in which a plurality of electrodes composed of three elements of a fuel electrode, an electrolyte matrix, and an oxygen electrode and a composite separator are alternately stacked, and a heat loss generated in the fuel cell stack is cooled. In a phosphoric acid fuel cell in which a plurality of sets of cooling plates provided with cooling means are alternately laminated, each member constituting the phosphoric acid fuel cell has a rectangular shape when viewed in the laminating direction, A phosphoric acid fuel cell, characterized in that cooling grooves of a cooling plate are formed in a rectangular long side direction. 4. A fuel cell stack in which a plurality of electrodes composed of three elements of a fuel electrode, an electrolyte matrix, and an oxygen electrode and a composite separator are alternately stacked, and a heat loss generated in the fuel cell stack is cooled. A pair of pre-stage and post-stage laminated bodies configured by alternately laminating a plurality of cooling plates provided with a cooling means are provided, and fuel gas is supplied to the preceding laminated body and the exhaust gas is supplied to the latter laminated body. In the phosphoric acid fuel cell, the shape of each member constituting the stack is rectangular when viewed in the stacking direction, and the oxidant gas is short side along the long side of the rectangle. A phosphoric acid fuel cell, characterized in that a fuel gas is caused to flow along the phosphoric acid fuel cell.