JPH0935728A - Phosphoric acid stacked fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably generate power for a long time by effectively recovering phosphoric acid vapor vaporized according to power generation and reducing the scattering amount of phosphoric acid. SOLUTION: A matrix 5 for supporting phosphoric acid is interposed between a fuel electrode 4 and an air electrode 6, and a fuel electrode side reservoir plate 2B (or 2C or 2D) and an air electrode side reservoir plate 7 are arranged on each side of the electrodes 4, 5 to form a unit cell 1. The unit cell 1 and a separator 9 are alternately stacked, then cooling plates 10 are assembled to constitute a fuel cell stacked body, then a manifold is assembled on the side surface of the fuel cell stacked body to form a phosphoric acid fuel cell. Reservoir plates 2B, 2C, 2D are protruded from the side surface of the fuel cell stacked body in the downstream position of a fuel gas, and the protruding length is gradually lengthened as the reservoir plates are apart at the stacking direction distance from the cooling plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid holding structure for a phosphoric acid type laminated fuel cell.

[0002]

2. Description of the Related Art In a phosphoric acid type laminated fuel cell in which fuel gas and air are supplied to generate electric power by an electrochemical reaction, phosphoric acid, which is an electrolyte, evaporates and scatters from a matrix during power generation, and thus phosphoric acid is deficient. Then, the combustion reaction between the fuel gas and the air may occur, resulting in the failure of power generation. In order to avoid this danger and maintain the cell performance, it is necessary to supply phosphoric acid to the fuel cell main body.As a measure for that, a fuel cell structure in which a reservoir plate holding replenishing phosphoric acid is incorporated in advance is used. Are known.

FIG. 3 is a sectional view showing the basic structure of an example of a fuel cell stack conventionally used as this type of phosphoric acid type stacked fuel cell. In this configuration, a flat plate-shaped matrix 5 carrying phosphoric acid as an electrolyte is sandwiched between a flat plate-shaped fuel electrode 4 and an air electrode 6, and a reservoir plate having a fuel gas passage 3 on both main surfaces thereof. Two
And the reservoir plate 7 having the air passage 8 are arranged to form the unit cell 1. The unit cells 1 are alternately laminated with separators 9 for maintaining airtightness, and a cooling plate 1 for removing heat generated by power generation every time a plurality of layers are laminated.
0 is inserted to form a fuel cell stack. In the fuel cell stack, the fuel gas passages 3 and the air passages 8 are orthogonal to each other, and manifolds (not shown) are incorporated in the four side surfaces to supply and discharge fuel gas and air. Each of the reservoir plate 2 and the reservoir plate 7 used in this configuration is made of a material that is hydrophilic to phosphoric acid, and holds in advance phosphoric acid for supply. In this way, if the phosphoric acid for replenishment is held in advance in the fuel cell stack, the phosphoric acid that evaporates and scatters during power generation can be supplemented, and the cell performance can be maintained.

However, in this method, in order to maintain the battery performance for a long period of time, it is necessary to retain a large amount of phosphoric acid, and for that purpose a reservoir plate having a large capacity is required. Further, even if a means for replenishing phosphoric acid from the outside is added, the space is required, which causes a problem that the required size of the fuel cell stack becomes large.

FIG. 4 is a sectional view showing the basic structure of another example of a fuel cell stack conventionally used as this type of phosphoric acid type stacked fuel cell. The difference between the configuration of this figure and the configuration of FIG. 3 is that the reservoir plate 2A on the fuel electrode side is
On the downstream side in the flow direction of the fuel gas, it projects from the side surface of the rectangular fuel cell stack by a predetermined length and extends to the inside of the manifold (not shown).

In this structure, the phosphoric acid evaporated by the power generation reaction in the fuel cell stack is guided to the downstream side of the reservoir plate 2A by the flowing fuel gas,
Eventually, when it reaches a portion protruding from the side surface of the fuel cell stack, since there is no electrochemical reaction in this portion, the temperature is lower than the inside of the fuel cell stack, so the phosphoric acid vapor is condensed,
Further, it is collected into the inside of the fuel cell stack through the reservoir plate 2A by the capillary permeation. in this way,
In this configuration, the phosphoric acid vapor discharged from the fuel cell stack is collected and reused, so that the phosphoric acid retention time becomes longer and the life of the fuel cell can be extended.

[0007]

As described above, if the reservoir plate is formed so as to project from the side surface of the fuel cell stack by a predetermined length on the downstream side of the reaction gas, it will evaporate during power generation. Since the phosphoric acid vapor generated is recovered, the life of the fuel cell is extended. However,
The evaporation amount of phosphoric acid depends on the temperature, and the higher the temperature is, the larger the evaporation amount is. On the other hand, in the fuel cell stack, a cooling plate 10 is inserted and arranged every time a plurality of unit cells 1 are stacked to cool the stack. Reservoir plate 2 included in unit cell 1
The temperature of A varies depending on its installation, and the evaporation amount of phosphoric acid also varies. Therefore, as in the above example, in the phosphoric acid type laminated fuel cell in which the reservoir plate 2A is made to project to the downstream side of the reaction gas by a predetermined length from the side surface of the fuel cell laminated body, the evaporation amount of phosphoric acid is Since the reservoir plate 2A at the highest temperature has the maximum amount, and the amount of phosphoric acid scattered without being condensed and recovered at the protruding portion also has the maximum, the phosphoric acid retention time becomes the minimum at the reservoir plate 2A at the highest temperature part, and the operation It will determine the lifespan. Therefore, in the reservoir plate 2A at a lower temperature, there is a drawback that the function of the protruding portion is not always sufficiently exerted. Further, even if a device for supplying phosphoric acid from the outside is added to the fuel cell stack having the above-mentioned configuration to supply phosphoric acid, the required supply amount will differ for each reservoir plate 2A of each unit cell 1. However, this method is not a good idea because it takes a lot of time and the cost becomes extremely high.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a phosphoric acid type fuel cell stack capable of reducing the amount of phosphoric acid scattered and stably operating for a long period of time. And

[0009]

In order to achieve the above object, in the present invention, a flat plate-like matrix carrying phosphoric acid as an electrolyte is sandwiched between a fuel electrode and an air electrode,
An airtight cell is provided on both main surfaces of which a reservoir plate having a passage for fuel gas and holding replenishing phosphoric acid and a reservoir plate having an air passage for holding replenishing phosphoric acid are arranged. Laminated via a separator to hold
A fuel cell stack is formed by inserting a cooling plate that removes heat generated by an electrochemical reaction, and a manifold for supplying and discharging fuel gas and air is arranged on the side surface of the fuel cell stack. In the phosphoric acid type laminated fuel cell, a protrusion protruding from the side surface of the fuel cell laminate into the manifold is provided on the downstream side of the fuel gas or air flowing through at least one of the two reservoir plates. Among the set of the reservoir plates, the protrusion of the reservoir plate farther from the cooling plate in the stacking direction is longer.

[0010]

A flat plate-shaped matrix carrying electrolyte phosphoric acid is sandwiched between a fuel electrode and an air electrode, and a reservoir plate having a fuel gas passage on both main surfaces thereof for holding replenishing phosphoric acid and air. In a unit cell including a reservoir plate having a passage for holding replenishing phosphoric acid, the vapor pressure of phosphoric acid increases as the temperature rises during power generation. Phosphoric acid which evaporates and is at the same time retained in the reservoir plate is supplied to the matrix by capillary osmosis.

Further, the vaporized phosphoric acid vapor is carried to the downstream side by the fuel gas or air flowing through the passage provided in the reservoir plate. In a reservoir plate provided with a protrusion protruding from the side surface of the fuel cell stack, since the temperature of the protrusion is lower than that of a portion located inside the fuel cell stack, phosphorus carried by fuel gas or air is used. The acid vapor is cooled by this protruding portion, and a part thereof is condensed and is carried by the capillary permeation into the inside of the fuel cell stack through the reservoir plate and is collected.

The longer the length of the protrusion provided on the downstream side of the reservoir plate, the lower the temperature at the end of the protrusion and the lower the average temperature. Further, the contact area of phosphoric acid vapor also increases in proportion to the length. Therefore, a larger amount of phosphoric acid vapor can be condensed and collected in a reservoir plate having a longer protruding portion. On the other hand, since the fuel cell stack has a structure in which it is cooled by a cooling plate inserted every time a plurality of unit cells are stacked, the temperature of the unit cells, and thus the temperature of the matrix, depends on the distance in the stacking direction from the cooling plates. ,
The matrix closer to the cooling plate has a higher temperature and a large amount of phosphoric acid easily evaporates, and the matrix farther from the cooling plate has a lower temperature and the phosphoric acid evaporation amount is smaller.

Therefore, as described above, if the protrusion of the reservoir plate farther from the cooling plate in the stacking direction is made longer, the reservoir plate closer to the matrix where a large amount of phosphoric acid evaporates has a larger amount. This means that phosphoric acid vapor can be condensed and recovered, and by appropriately selecting the protrusion length, the amount of phosphoric acid scattered in each cell can be made approximately the same, and the phosphoric acid retention time can be made almost equal. Thus, the operable time can be effectively lengthened.

If the amount of scattered phosphoric acid in each unit cell is approximately the same, the amount of phosphoric acid supplied to each unit cell may be the same when supplying phosphoric acid from the outside. It is also very easy to supply from.

[0015]

EXAMPLE FIG. 1 is a sectional view showing the basic structure of a fuel cell stack of an embodiment of a phosphoric acid type stacked fuel cell of the present invention.
In the figure, components having the same functions as those of the conventional example shown in FIG. The difference between this embodiment and the conventional example shown in FIG.
It is located at the length of the projecting portion on the fuel gas downstream side of the fuel electrode side reservoir plates 2B, 2C, 2D incorporated in the central and lower three unit cells 1, and is arranged above and below the three unit cells 1. Considering the stacking direction distance from one set of cooling plates 10, the length of the protruding portion of the reservoir plate 2C having the longest distance and the highest temperature is set to be the longest, and the distance is the shortest.
The length of the projecting portion of the reservoir plate 2D having the lowest temperature is set to the shortest, and the length of the projecting portion of the reservoir plate 2B having the distance and the temperature intermediate between these is selected to be an intermediate length between them. Phosphoric acid that evaporates in each cell 1 during power generation operation is recovered, the amount of scattering is reduced and made uniform, the retention time of phosphoric acid is extended, and long-time operation is enabled.

FIG. 2 shows the amount of scattered phosphoric acid in each unit cell of the phosphoric acid type laminated fuel cell of the embodiment shown in FIG. 1 and the unit amount of phosphoric acid type laminated fuel cell of the conventional example shown in FIG. It is shown in comparison with the amount of scattered phosphoric acid. As you can see in the figure,
In the conventional phosphoric acid type laminated fuel cell in which the reservoir plate does not have a protruding portion, the largest amount of phosphoric acid scatters in the central unit cell, and the lower unit cell has the smallest scattering amount.
The greater the distance from the cooling plate, that is, the higher the temperature, the greater the amount of scattering. On the other hand, in the phosphoric acid layered fuel cell of the embodiment of FIG. 1, the amount of phosphoric acid scattered in each unit cell is lower than that in the conventional example, and in particular, in the center part, the amount of scattered phosphoric acid is small. The decrease is remarkable, and it is almost the same as the scattering amount of the upper and lower cells. It can be seen that the protruding portion of the reservoir plate has an effective function of increasing the recovery rate of phosphoric acid and reducing the scattering amount.

In the present embodiment, the phosphoric acid type laminated fuel cell in which the projecting portion is provided for the fuel electrode side reservoir plate and the length thereof is selected in consideration of the distance from the cooling plate has been exemplified. The same effect can be obtained not only by using the reservoir plate on the electrode side but also by using the reservoir plate on the air electrode side. Furthermore, by using it on both the fuel electrode side and the reservoir plate on the air electrode side, it is more effective. is there.

[0018]

As described above, according to the present invention, the flat plate-like matrix carrying the phosphoric acid of the electrolyte is sandwiched between the fuel electrode and the air electrode, and the fuel gas passages are provided on both main surfaces thereof. A single cell comprising a reservoir plate holding replenishing phosphoric acid and a reservoir plate having an air passage and holding replenishing phosphoric acid is laminated via a separator for keeping airtight A fuel cell stack is formed by inserting a cooling plate for removing heat generated by a chemical reaction, and a phosphorus stack is formed by arranging a manifold for supplying and discharging fuel gas and air on the side surface of the fuel cell stack. In the acid-type laminated fuel cell, at least one of the two sets of reservoir plates described above is arranged on the downstream side of the fuel gas or air flowing therethrough, and from the side surface of the fuel cell laminate into the manifold. Since the projecting portion is provided and the projecting portion of the reservoir plate, which is farther from the cooling plate in the stacking direction, of the set of the reservoir plates is made longer, the phosphoric acid vapor evaporated during the power generation operation. Was effectively recovered, the amount of scattered phosphoric acid was reduced, and a phosphoric acid type laminated fuel cell capable of stable power generation operation for a long period of time was obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a basic structure of a fuel cell stack in an embodiment of a phosphoric acid type stacked fuel cell of the present invention.

2 is a phosphoric acid type laminated fuel cell of the embodiment of FIG. 1, and FIG.
Comparison diagram of phosphoric acid scattering amount of each cell of the conventional phosphoric acid type laminated fuel cell

FIG. 3 is a sectional view showing the basic structure of a fuel cell stack in a conventional phosphoric acid type stacked fuel cell.

FIG. 4 is a cross-sectional view showing the basic structure of a fuel cell stack in another conventional phosphoric acid type stacked fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single cell 2 Reservoir plate (fuel electrode side) 2A Reservoir plate (fuel electrode side) 2B Reservoir plate (fuel electrode side) 2C Reservoir plate (fuel electrode side) 2D Reservoir plate (fuel electrode side) 3 Fuel gas passage 4 Fuel electrode 5 Matrix 6 Air electrode 7 Reservoir plate (air electrode side) 8 Air passage 9 Separator 10 Cooling plate 11 Cooling pipe

Claims (1)

[Claims] 1. A reservoir plate for holding a replenishing phosphoric acid having a fuel gas passage on both main surfaces of a flat plate-shaped matrix for supporting phosphoric acid of an electrolyte, which is sandwiched between a fuel electrode and an air electrode. A cooling plate that removes the heat generated by the electrochemical reaction by stacking the unit cells that have a reservoir plate that has an air passage and that holds replenishing phosphoric acid through a separator that holds the airtightness. To form a fuel cell stack, and a manifold for supplying and discharging fuel gas and air is arranged on the side surface of the fuel cell stack to form a phosphoric acid stack fuel cell. At least one of the reservoir plates of the set has a projecting portion projecting from the side surface of the fuel cell stack into the manifold on the downstream side of the flowing fuel gas or air, and Among the reservoir plate, phosphoric acid stacked fuel cell, wherein a distant reservoir plate of the stacking direction distance from the cooling plate is provided with a long projection.