JPWO2000031814A1 - Polymer electrolyte fuel cell stack - Google Patents

Abstract

(57) [Abstract] The separator has a rectangular outer shape, and a cooling medium flow path is formed in the peripheral portion of the fuel gas flow path or oxidant gas flow path formed on the surface of the separator, in a portion substantially parallel to the extension direction of the long side of the separator, so that the cooling medium flows in a direction perpendicular to the separator plane.

Description

Detailed Description of the Invention

[Technical Field] The present invention relates to a polymer electrolyte fuel cell stack using an ion-conductive solid polymer as an electrolyte, and more particularly to a polymer electrolyte fuel cell stack improved to ensure a large reaction area. [Background Art] In recent years, fuel cells have attracted attention as a highly efficient energy conversion device. These fuel cells are broadly classified into low-temperature operating fuel cells, such as alkaline, polymer electrolyte, and phosphoric acid fuel cells, and high-temperature operating fuel cells, such as molten carbonate and solid oxide fuel cells, depending on the type of electrolyte used. Polymer electrolyte fuel cells (hereinafter referred to as PEFCs) using a proton-conductive solid polymer electrolyte membrane as the electrolyte have attracted attention as a power source for space and vehicles because of their compact structure, high power density, and simple system operation. Examples of such polymer electrolyte membranes (hereinafter referred to as polymer membranes) include perfluorocarbon sulfonic acid membranes (e.g., Nafion, a product name manufactured by DuPont). A membrane electrode assembly is constructed by sandwiching such a polymer membrane between a pair of porous electrodes (a fuel electrode and an oxidizer electrode) containing a catalyst such as platinum.
The polymer membrane and porous electrode are both formed in sheet form, with a thickness of approximately 1 mm or less to reduce internal resistance. The polymer membrane and electrode sheets are typically rectangular, with the electrode area determined by the current value required for power generation and the current value per unit area, i.e., current density, and typically set to approximately 100 ^cm2 or more, i.e., 10 cm or more per side. The polymer membrane also serves to prevent mixing of gases supplied to the fuel electrode and oxidizer electrode, so its area is set larger than that of the electrodes. To extract current from the membrane electrode assembly, current collectors are placed on the outside of the fuel electrode and oxidizer electrode. These current collectors have numerous grooves formed parallel to the surfaces of the fuel electrode and oxidizer electrode, which serve as gas channels for supplying the fuel gas and oxidizer gas required for the cell reaction to the fuel electrode and oxidizer electrode. Because the electromotive force generated by a single membrane electrode assembly is small, at less than 1 V, multiple membrane electrode assemblies are stacked and connected in series to form a PEFC stack to increase the electromotive force. In this case, a current collector on the fuel electrode side and a current collector on the oxidizer electrode side are required, so a separator is used in which the current collectors on the fuel electrode side and the current collectors on the oxidizer electrode side of adjacent membrane electrode assemblies are integrated. Heat is generated in membrane electrode assemblies due to the cell reaction. A common cooling method for removing this heat is to insert a cooling plate between multiple membrane electrode assemblies and circulate cooling water through this cooling plate. However, this method requires a separator for supplying cooling water in addition to the separator for supplying gas, which increases the thickness in the stacking direction. To solve this problem, Japanese Patent Laid-Open Publication No. 10-21949 discloses a method for eliminating the need for cooling plates inserted between membrane electrode assemblies by forming cooling water channels surrounding the gas channel on all four sides. Specifically, the technology disclosed in the publication, as shown in FIG. 1 , includes a separator 200 having a groove 201 formed in the center as a gas channel, and four channels 20 for circulating cooling water at the top, bottom, left, and right.
2, and the reaction heat is removed by flowing cooling water through the flow channels 202. However, the above cooling method has the following problems. The first problem is that the reaction area cannot be increased. That is, in the above cooling method, the heat generated in the membrane electrode assembly sandwiched between the separators 200 is transferred to the separators 200, and then transferred in a direction perpendicular to the thickness direction of the separators, and is removed by the cooling water flowing through the flow channels 202. In other words, the temperature of the separator at the center of the reaction section becomes higher than that of the surrounding area. Therefore, if the reaction area is increased, the distance between the center of the reaction section and the cooling flow channels also increases, and the above temperature difference also increases. On the other hand, if the thickness of the separator is increased and the cross-sectional area,
In other words, it is possible to reduce the temperature difference by increasing the heat transfer area, but
This method also increases the thickness of the cell, resulting in a loss of compactness. A second problem is that the temperature distribution within the separator plane is three-dimensional. In other words, with the cooling method described above, the temperature distribution within the separator plane is higher in the center and lower on the four peripheral sides, as described above. As a result, even if the gas flow path is formed in a planar shape, water produced by the reaction condenses around the separator, making it impossible to efficiently recover the water produced by the reaction. A third problem is that the supply and discharge holes for the fuel gas and oxidizer gas cannot be made large. If cooling water flow paths are arranged on all four sides of the gas flow path as shown in Figure 21 , the supply and discharge holes for the fuel gas and oxidizer gas are arranged at the four corners, and the cross-sectional areas of the supply and discharge holes are smaller than the cross-sectional area of the cooling water flow path. This means that if the reaction area is increased and a large amount of fuel gas or oxidizer gas is required, the cross-sectional area of the supply holes, i.e., the gas distribution manifold, becomes smaller, making it impossible to uniformly distribute the fuel gas or oxidizer gas to each unit cell in the stack. [Disclosure of the Invention] An object of the present invention is to provide a polymer electrolyte fuel cell stack that can ensure a large reaction area, ensure smooth gas supply, and achieve miniaturization. To achieve the above object, the present invention provides a polymer electrolyte fuel cell stack including a plurality of unit cells, each having a solid polymer electrolyte membrane sandwiched between an anode and an oxidizer electrode, stacked with separators having at least one of a fuel gas channel for supplying fuel gas to the anode and an oxidizer gas channel for supplying oxidizer gas to the oxidizer electrode, the separators having a rectangular outer shape, and a coolant channel formed in a portion substantially parallel to the long sides of the separator around the fuel gas channel or the oxidizer gas channel, so that the coolant flows perpendicular to the separator plane. According to the present invention having the above configuration, the rectangular outer shape of the separator and the coolant channel formed in a portion substantially parallel to the long sides of the separator reduce the distance between the upper and lower ends of the electrodes and the center of the electrodes, thereby reducing the temperature difference between the electrode ends and the center of the electrodes. Furthermore, because heat generated by the reaction is transferred vertically, the temperature distribution in the horizontal direction is almost constant. Therefore, even if the reaction area is large, the temperature difference within the separator can be kept small. Furthermore, since there is no need to insert a cooling element in the stacking direction of the unit cells, the thickness in the stacking direction can be reduced. Another invention is a solid polymer fuel cell stack formed by stacking a plurality of unit cells, each having a solid polymer electrolyte membrane sandwiched between an anode and an oxidizer electrode, via separators having at least one of a fuel gas channel for supplying fuel gas to the anode and an oxidizer gas channel for supplying oxidizer gas to the oxidizer electrode, wherein the separators have a rectangular outer shape, and a plurality of coolant channels are formed in portions of the separators that are substantially parallel to the extension direction of the opposing long sides, so that the coolant flows perpendicular to the separator plane. According to the invention having the above configuration, since a plurality of coolant channels are formed in portions of the separators that are substantially parallel to the extension direction of the opposing long sides, an even more excellent cooling effect can be achieved in addition to the functions and effects of the invention described above. According to yet another aspect of the present invention, a polymer electrolyte fuel cell stack is provided in which a plurality of unit cells, each having a solid polymer electrolyte membrane sandwiched between an anode and an oxidizer electrode, are stacked via separators each having at least one of a fuel gas channel for supplying fuel gas to the anode and an oxidizer gas channel for supplying oxidizer gas to the oxidizer electrode. The separators have a rectangular outer shape, and a plurality of cooling zones are provided on the surfaces of the separators that contact the anode or the oxidizer electrode. A cooling medium channel is formed in the center of each cooling zone, and the cooling medium flows perpendicular to the separator plane. According to the present invention having the above-described configuration, since the cooling medium channel is formed in the center of each cooling zone, reaction heat generated in each cooling zone is cooled by the cooling medium flowing through the cooling medium channel formed within that zone. In this case, the inner wall of the cooling medium channel serves as a heat transfer surface. Because the channel is located in the center of each cooling zone, the entire surface of the inner wall can be used as a heat transfer surface, enabling efficient cooling. [Best Mode for Carrying Out the Invention] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 2 is a perspective view showing the configuration of a first embodiment of a polymer electrolyte fuel cell stack according to the present invention. Specifically, the fuel cell stack 1 is composed of a cell section 2 and end plates 3. The cell section 2 is composed of a plurality of stacked unit cells 4. The end plates 3 are provided at the front and rear ends of the cell section 2, one at each end, and are arranged to fasten the cell section 2 with fastening jigs such as studs or springs (not shown).
The end plates 3 are also provided with current extraction terminals (not shown) for extracting the electricity generated by the fuel cell stack 1. The front end plate 3a is also fitted with piping for various fluids. Specifically, an oxidant gas inlet 5a is provided at the upper right end of the front end plate 3a, and an oxidant gas outlet 5b is provided at the lower left end of the end plate. A fuel gas inlet 6a is provided at the upper left end of the end plate 3a, and a fuel gas outlet 6b is provided at the lower right end of the end plate 3a. Coolant inlets 7a are provided at the top and bottom of the center of the front end plate 3a. Meanwhile, coolant outlets 7b are provided at the top and bottom of the center of the rear end plate 3b. Figure 3 shows a cross-sectional view of the fuel cell stack 1 shown in Figure 2, cut along a plane including the centerlines of the coolant inlet 7a and coolant outlet 7b. That is, the unit cell 4 is composed of a membrane electrode assembly (MEA) 8, a set of seal packings 9, and a separator 10. The membrane electrode assembly 8 is composed of an electrolyte membrane 8a and two electrodes, namely, a fuel electrode 8b and a digester electrode 8c. The separator 10 has grooves formed on both sides of its central portion through which gas flows. Specifically, a fuel gas flow channel 11 is provided on the surface in contact with the fuel electrode 8b, and an oxidizer gas flow channel 12 is provided on the surface in contact with the oxidizer electrode 8c. The seal packing 9 has portions corresponding to both electrodes, a gas distribution manifold (described later), and a coolant flow channel cut out, and is configured to have approximately the same thickness as the electrodes. Figures 4A and 4B are diagrams showing the configuration of the separator, and Figure 4A shows the separator 1
4A is a front view of the fuel gas flow path side of separator 10, and FIG. 4B is a cross-sectional view taken along the line A-A in FIG. 4A. The outer dimensions of separator 10 are set to 25 cm in length, 7 cm in width, and 2 mm in thickness, and the material may be any material that is conductive and has a dense structure; in this example, a dense carbon material is used. A plurality of through-holes are provided around the periphery of separator 10. Specifically, an oxidant gas supply manifold 13a is provided on the right side of separator 10, and an oxidant gas discharge manifold 13b is provided on the left side. Separator 10 also has a plurality of through-holes.
In the portion substantially parallel to the direction of extension of the long side of separator 10, i.e., the upper portion of separator 10,
A fuel gas supply manifold 14a and eight coolant flow paths 15 are provided, and a fuel gas discharge manifold 14b and eight coolant flow paths 15 are provided at the bottom of the separator 10. Furthermore, a plurality of grooves, each 1 mm wide and 0.5 mm deep, are machined in the center of the surface of the separator 10. These grooves are connected to the fuel gas supply manifold 14a and the fuel gas discharge manifold 14b, and are used to separate the fuel gas flow paths 15.
As shown by the arrows in the figure, the separator 10 is configured such that fuel gas supplied from a fuel gas supply manifold 14a is supplied into the grooves of the separator 10, and unreacted fuel gas is discharged from a fuel gas discharge manifold 14b. A groove similar to that on the front surface is provided in the center of the rear surface of the separator 10,
These grooves are connected to the oxidant gas supply manifold 13a and the oxidant gas discharge manifold 13b to form the oxidant gas flow path 12, and are configured to supply and discharge the oxidant gas. The rectangular dashed lines shown in Figure 4A indicate the size of the fuel electrode 8b and the oxidant electrode 8c, and here, the fuel electrode and the oxidant electrode used were 5 cm long and 20 cm wide. Furthermore, water may be used as the coolant introduced into the coolant flow path 15, but
Considering use in cold climates, antifreeze is more desirable. Here, an ethylene glycol solution was used. The coolant is uniformly introduced into the fuel cell stack 1 through two coolant inlets 7a provided on the front end plate 3a (see FIG. 2). A distribution header (not shown) is provided inside the end plate 3a, which splits the coolant introduced through the coolant inlets 7a into eight upper and eight lower streams. The eight split coolant flows through common coolant channels 15 provided above and below the separator 10, seal packing 9, and electrolyte membrane 8a, perpendicular to the plane of these components. As the coolant flows, it absorbs heat from the walls of the coolant channels 15, thereby cooling the fuel cell. The cooled coolant reaches the rear end plate 3b, where it is combined into two upper and lower streams by a confluence header (not shown) provided inside the end plate 3b and discharged through the coolant outlet 7b. FIG. 5 illustrates the heat flow within the unit cell 4. That is, the heat generated by the cell reaction is conducted through the fuel electrode 8b and the oxidizer electrode 8c, and is transferred from the contact surface with the separator 10 into the separator, and is transferred in a direction perpendicular to the separator plane. The heat is then transferred vertically within the separator, and transferred from the wall surface of the coolant flow channel 15 to the coolant, where it is cooled. The above electrodes (5 cm x 20 cm) and separators (7 cm x 25 cm x 2 m) are
The fuel cell stack of this embodiment is formed by stacking 100 single cells each having a thickness of 1000 μm, and a separator having a size of 10 cm×10 cm and a thickness of 12 cm×12 cm.
A conventional fuel cell stack was fabricated by stacking 100 2 mm thick single cells. _H2 /Air (utilization rate 70%/40%) was supplied as the reactant gas, and an ethylene glycol aqueous solution was supplied as the coolant at an inlet temperature of 50°C and a flow rate of 1.5 kg/sec.
A power generation test was conducted at a current density of 0.5 A/ ^cm² , and the stack voltage, temperature distribution within the separator, and voltage distribution of each cell within the stack were measured. The following results were obtained. Figure 6 shows the voltage distribution characteristics of each unit cell of the fuel cell stack of this embodiment and a conventional fuel cell stack, as verified by the inventors. Cell numbers are assigned in order from the front end plate, i.e., the end where the fuel gas and oxidant gas supply and discharge ports are located. In the fuel cell stack of this embodiment, the voltage of each unit cell was nearly uniform. This is thought to be due to the fact that a sufficient cross-sectional area (1 cm × 5 cm) was ensured by providing an oxidant supply manifold substantially parallel to the extension direction of the short sides of the separator. In contrast, in the conventional fuel cell stack, gas supply/discharge manifolds could only be provided at the four corners of the separator, and their small size of 1 cm × 1 cm prevented uniform supply of oxidant gas to each unit cell, resulting in a ±30% deviation from the average voltage. By providing a fuel gas or oxidant gas supply manifold in a portion substantially parallel to the extension direction of the short side of the separator in this way, the cross-sectional area of the manifold can be made large, and even if a large amount of fuel gas or oxidant gas is required due to a large reaction area, it is possible to distribute it uniformly to each unit cell of the stack. That is, Figure 7 shows the vertical temperature distribution within the separator as verified by the inventors, and Figure 8 shows the horizontal temperature distribution as verified by the inventors. As is clear from the figures, in a conventional fuel cell stack, the electrodes and separators are square and coolant channels are formed on all four sides of the periphery, so the vertical and horizontal temperature distributions are uniform. However, because the distance between the electrode edge and the center of the electrode is 5 cm, the temperature at the center of the electrode rises, and the temperature at the periphery drops by 7 cm.
The temperature rose to 80°C from 0°C, resulting in a temperature difference of 10°C.
The distance between the electrode edge and the center was only 2.5 cm, so the temperature difference between the periphery and the center was small, and was kept to 2°C.
As shown in Figure 8, heat is transferred vertically, so the temperature distribution in the horizontal direction is almost constant, reaching 72°C (see Figure 8). Furthermore, when the stack voltage was examined, it was 40V for the conventional fuel cell stack, while it was 55V for the fuel cell stack of this embodiment. This high stack voltage is thought to be due to the fact that the temperature rise in the center of the electrode can be suppressed, as shown in Figures 7 and 8, thereby preventing the evaporation of moisture that maintains the membrane's conductivity. As described above, by forming a rectangular separator outer shape and a coolant flow path around the separator's gas flow path, substantially parallel to the extension direction of the separator's long sides, so that the coolant flows perpendicular to the separator plane, a structure can be achieved that removes heat generated by the fuel cell reaction, thereby minimizing the temperature difference within the separator even when the reaction area is large. Furthermore, when the reaction area is increased, the electrode shape and the long sides of the rectangular separator can be extended to maintain the distance along the short side for heat transfer, thereby minimizing the temperature difference within the separator as described above. (Second embodiment) This embodiment is a modification of the first embodiment, in which the fuel gas supply manifold and fuel gas discharge manifold are disposed at the sides of the separators. Fig. 9 is a perspective view showing the configuration of a polymer electrolyte fuel cell stack of the second embodiment, and Figs. 10A and 10B are views showing the configuration of the separators, with Fig. 10A being a front view of the fuel gas flow path side of the separator and Fig. 10B being a cross-sectional view taken along the line B-B in Fig. 10A. In this embodiment, the fuel gas supply manifold and fuel gas discharge manifold portions of the fuel cell stack of the first embodiment are used as coolant flow paths, and the oxidant supply manifold and oxidant discharge manifold portions of the first embodiment are respectively disposed at the top and bottom of the separators.
10A and 10B, the fuel gas supply manifold 24a and the oxidant gas discharge manifold 23b are provided on the left side of the separator, which is substantially parallel to the direction of extension of the short side of the separator, around the gas flow path of the separator, and the oxidant gas supply manifold 23a and the fuel gas discharge manifold 24b are provided on the right side. Also, in correspondence with the above configuration, as shown in FIG. 9, an oxidant gas inlet 25a and a fuel gas outlet 26b are provided above and below on the right side of the front end plate 23a, and a fuel gas inlet 26a and an oxidant gas outlet 25b are provided above and below on the left side of the end plate 23a.
The coolant inlet 7a and the coolant outlet 7b are provided at the top and bottom.
10A and 10B, the fuel gas flow channel 11 formed in the center of the separator is connected to the fuel gas supply manifold 24a provided at the top of the left side.
The separator is connected to a fuel gas discharge manifold 24b provided at the bottom of the right side, and is configured to supply and discharge fuel gas to and from the separator as shown by the arrows in the figure. Meanwhile, the coolant flows through nine channels provided at the top and bottom of the separator in a direction perpendicular to the plane of the separator, and is configured to remove reaction heat from the coolant channel wall surface for cooling. In this embodiment, as in the first embodiment, the size of the electrodes is 20 cm in length and 20 cm in width.
The width was 5 cm, and the separator dimensions were 25 cm long, 7 cm wide, and 2 mm thick.
Furthermore, a dense carbon material was used for the separator material. A single cell was fabricated using these components, and 100 of these single cells were stacked together to conduct a power generation test. The test conditions were the same as those of the first embodiment. As a result, the temperature in the peripheral area was 70°C, and in the center was 71.7°C, and the temperature difference in the vertical direction was even smaller than in the first embodiment. This is because the coolant flow path is 1°C above and 1°C below.
The increase in the number of separators and the increased heat transfer area likely resulted in a further reduction in the temperature difference. Furthermore, the stack voltage was 56 V, a higher voltage than that of a conventional fuel cell stack, as in the first embodiment. As described above, by providing fuel gas or oxidant gas supply or discharge manifolds in the separator's gas flow path periphery, substantially parallel to the extension direction of the short sides, the upper and lower portions of the separator's gas flow path periphery can be used as coolant flow paths. This increases the wall area of the coolant flow path, increasing the heat transfer area and enabling a small temperature difference even with a large electrode area. Furthermore, as in the first embodiment, by providing fuel gas and oxidant gas supply manifolds in the separator's short sides parallel to the short sides, the cross-sectional area of the manifolds can be increased, allowing for uniform distribution of large amounts of fuel gas or oxidant gas to each unit cell of the stack, even when the reaction area is large and a large amount of fuel gas or oxidant gas is required. (Third Embodiment) In this embodiment, a separator having a configuration similar to that of the second embodiment is formed from a flexible graphite carbon sheet. This sheet made of flexible graphite carbon is also called expanded graphite material, and is characterized by its softness, ease of molding, and excellent sealing properties. It also has anisotropy in the thickness direction and the plane direction, and for example, its thermal conductivity is about 10 times higher in the plane direction than in the thickness direction, making it an extremely suitable material for the cooling method of the present invention. Here, Nikafilm (trade name) manufactured by Nippon Carbon Co., Ltd. is used as the expanded graphite sheet.
The separators were made in the same shape as in the second embodiment, by press-molding a sheet of 4 mm thick, 0.5 g/ ^cm3 density NiCa film. The electrodes were then 5 cm wide and 20 cm long, and combined with the separator to form a single cell. One hundred of these single cells were stacked to form a fuel cell stack. A power generation test was conducted under the same conditions as in the second embodiment, and the temperature distribution in the separator in the vertical direction was measured. The results showed that the temperature was 70°C in the periphery and 71.5°C in the center.
The temperature difference was kept even smaller than in the second embodiment. Furthermore, the temperature difference between the center of the cathode surface and the center of the separator was measured and found to be approximately 0°C. Although expanded graphite has a low thermal conductivity in the thickness direction, this is not a problem as the heat transfer area is large. In the above example, the temperature difference between the temperature at the center of the separator and the ambient temperature was 1.
5°C, it is desirable to limit the allowable temperature difference between the separator center temperature and the ambient temperature to 5°C or less. Figure 11 is a characteristic diagram showing the relationship between the temperature of the reaction section and the amount of water vapor carried away by the reaction gas, as verified by the inventors.
The values are relative to the amount of water vapor at 0°C, which is set to 1. As the temperature rises, the saturated water vapor pressure rises, and the amount of water vapor carried away by the reaction gas increases. The temperature is higher at the center and edges of the plane perpendicular to the direction of the oxidant gas flow, and the amount of water vapor carried away increases, while it decreases at the edges, resulting in condensation. The amount of water produced in the reaction section is 0.4 in the above relative value, and if the difference in the amount carried away between the center and edges is smaller than this value, it falls within the range of the amount of water produced,
It is desirable to keep the temperature within this range because condensation or evaporation of more than the amount of water produced will not occur. In other words, from FIG. 11, if the temperature at the end is 70°C, the temperature at the center will be 75°C.
It is desirable to keep the temperature below 100°C.
When using this material, the ratio of the long side to the short side of the separator's external dimensions (aspect ratio) and the temperature difference between the center and the end portions are shown.
¹² , if the ratio of the long side to the short side is 3 or more, the temperature difference will be 5°C or less, satisfying the above condition. Figure 13 shows the characteristics of the ratio of the long side to the short side (aspect ratio) of the separator's external dimensions and the temperature difference between the center and the ends when aluminum (thermal conductivity 200 W/mK) is used as the material, as verified by the inventors. The reaction area is 10
¹³ shows that the temperature difference is 5°C or less when the ratio of the long side to the short side is 2.5 or greater, thereby satisfying the above condition. As described above, by constructing the separator from a flexible graphite carbon sheet and setting the ratio of the long side to the short side of the separator's external dimensions to 3 or greater, the temperature difference can be reduced even with a large electrode area. Furthermore, by constructing the separator from a flexible graphite carbon sheet, press molding can be used, enabling the manufacture of a fuel cell stack that is easy to mass-produce and inexpensive. (Fourth Embodiment) In the fourth embodiment, a separator having a configuration similar to that of the second embodiment is constructed from aluminum. Aluminum has extremely high thermal conductivity, making it a material extremely suitable for the cooling method of the present invention. It is also characterized by its softness and ease of molding. Here, a clad aluminum material is used as the aluminum material. The separator shape is the same as that of the second embodiment, and it was manufactured by press-forming a 1.5 mm thick aluminum plate. Furthermore, its surface was coated with a corrosion-resistant and conductive coating. The electrodes were 5 cm wide and 20 cm long, and combined with the separator to form a single cell. 100 of these single cells were stacked to form a fuel cell stack. A power generation test was conducted under the same conditions as in the second embodiment, and the temperature distribution in the separator in the vertical direction was measured. As a result, the temperature was 70°C in the periphery and 71.5°C in the center.
°C, and the temperature difference could be kept small, just like in the third embodiment. At the same time, the thickness of the separator could be made 1.5 mm, which made it possible to make it 0.5 mm thinner than in the first and second embodiments. In the above example, the temperature difference between the temperature at the center of the separator and the ambient temperature was 1.
If the allowable temperature difference between the center of the separator and the ambient temperature is 5°C, the maximum electrode width for aluminum is 66 mm. In this case, the electrode length is 152 mm, and the separator dimensions are preferably 80 mm wide and 200 mm long. In other words, the ratio of the long side to the short side of the separator's external dimensions is 2.
.5 or more. As described above, by constructing the separator from a thin plate of aluminum-based metal and setting the ratio of the long side length to the short side length of the separator's external dimensions to 2.5 or more, it is possible to reduce the temperature difference even with a large electrode area. Furthermore, since the thickness of the separator can be made thin, it is possible to manufacture a compact and cost-effective fuel cell stack. Note that similar effects can be obtained even when other metals with excellent thermal conductivity, such as copper-based metals, are used as separator materials. (Fifth Embodiment) Figures 14A and 14B are diagrams showing the configuration of a separator in a fifth embodiment of the present invention, where Figure 14A is a front view of the separator on the fuel gas flow path side, and Figure 14B is a diagram showing the configuration of a separator in a fifth embodiment of the present invention.
14A. That is, in this embodiment, the separator 30 is provided with a plurality of separators 30a, 30b, 30c, 30d, 30e, 30f ...
A total of 24 cooling medium flow channels are formed in three locations: the top, bottom, and center of the separator, with eight channels in each location. The separator is 13 cm wide and 25 cm long.
The separator was made of aluminum. The electrode was 10 cm wide and 20 cm long, and was divided into upper and lower halves. As shown in Figures 14A and 14B, the separator 3
A fuel gas supply manifold 34a is provided at the upper left of the separator 30, and a fuel gas discharge manifold 34b is provided at the lower right. Furthermore, an oxidant gas supply manifold 33a is provided at the right side of the separator 30, and an oxidant gas discharge manifold 34b is provided at the left side.
3b are provided. A fuel gas flow path is provided on the surface of the separator 30 across two upper and lower sections, and is connected to the fuel gas supply manifold 34a and the fuel gas discharge manifold 34b, respectively, to form the fuel gas flow path 31. The fuel gas supplied from the fuel gas supply manifold 34a is supplied into the grooves of the separator 30 along the flow of the arrows in the figure, and unreacted fuel gas is discharged from the fuel gas discharge manifold 34b. On the other hand, on the back surface (not shown), an oxidant gas flow path is similarly provided across two sections, and is connected to the oxidant gas supply manifolds 33 provided on the left and right sides, respectively.
The separator is connected to the oxidizer gas discharge manifold 33a and the oxidizer gas discharge manifold 33b. A cooling medium is introduced into 24 coolant channels, eight of which are formed in three locations: the top, bottom, and center of the separator. The cooling medium flows perpendicular to the separator plane to remove heat generated by the fuel cell reaction. The separators and electrodes are combined to form a single cell, and 50 of these single cells were stacked and subjected to a power generation test. The conditions were the same as those in the second embodiment. The vertical temperature distribution was the same in the two gas channel sections: 69°C at the top and bottom ends of the separator, 72°C at the center of the gas channel, and 71°C at the center of the separator. In this embodiment, the coolant flowing through the coolant channel in the center of the separator removes the reaction heat from the two upper and lower sections. Therefore, the center of the separator is hotter than the top and bottom ends. However, the temperature difference is smaller than that in conventional fuel cell stacks. 15A and 15B are diagrams showing the configuration of a separator according to a sixth embodiment of the present invention. FIG. 15A is a front view of the separator on the fuel gas flow path side, and FIG. 15B is a diagram showing the configuration of a separator according to a sixth embodiment of the present invention.
15A. That is, in this embodiment, the separator 40 is provided with a plurality of separators 40a, 40b, 40c, 40d, 40e, 40f ...
A total of 27 cooling medium flow channels are formed in three locations: the top, bottom, and center of the separator, with nine in each location. The separator is 13 cm wide and 25 cm long.
The separator was made of aluminum. The electrode was 10 cm wide and 20 cm long, and was divided into upper and lower halves. As shown in Figures 15A and 15B, the separator 4
On the left and right sides of the separator 40, two fuel gas supply manifolds 44a and two fuel gas discharge manifolds 44b, and two oxidant gas supply manifolds 43a and two oxidant gas discharge manifolds 43b are provided, for a total of eight. Furthermore, on the surface of the separator 40, a fuel gas flow path is provided across two upper and lower sections, which are connected to the fuel gas supply manifold 44a and the fuel gas discharge manifold 44b, respectively, to form the fuel gas flow path 41. The fuel gas supplied from the fuel gas supply manifold 44a is supplied into the grooves of the separator 40 along the flow of the arrows in the figure, and unreacted fuel gas is discharged from the fuel gas discharge manifold 44b. On the other hand, on the back surface (not shown), a similar oxidant gas flow path is provided across two sections, and the oxidant gas supply manifolds 43a and the oxidant gas discharge manifolds 43b are connected to the fuel gas supply manifolds 44a and the fuel gas discharge manifolds 44b, respectively, to form the fuel gas flow path 41. The fuel gas supplied from the fuel gas supply manifold 44a is supplied into the grooves of the separator 40, and unreacted fuel gas is discharged from the fuel gas discharge manifold 44b, along the flow of the arrows in the figure. On the other hand, on the back surface (not shown), a similar oxidant gas flow path is provided across two sections, and the oxidant gas supply manifolds 43a and the oxidant gas discharge manifolds 43b are connected to the fuel gas supply manifolds 44a and the fuel gas discharge manifolds 44b.
The separator is connected to the oxidizer gas discharge manifold 43a and the oxidizer gas discharge manifold 43b. A cooling medium is introduced into 27 coolant channels, nine of which are formed in three locations: the top, bottom, and center of the separator. The cooling medium flows perpendicular to the separator plane to remove heat generated by the fuel cell reaction. The separators and electrodes are combined to form a single cell, and 50 of these single cells were stacked and subjected to a power generation test. The conditions were the same as those in the second embodiment. The vertical temperature distribution was the same in the two gas channel sections: 69°C at the top and bottom ends, 72°C at the center of the gas channel, and 71°C at the center of the separator. As in the fifth embodiment, the coolant flowing through the coolant channel in the center of the separator removes the reaction heat from the two upper and lower sections. Therefore, the center of the separator is hotter than the top and bottom ends. However, the temperature difference is smaller than that in conventional fuel cell stacks. 16 is a diagram showing the configuration of a separator according to a seventh embodiment of the present invention, and is a front view of the separator on the fuel gas flow path side. That is, in this embodiment, a plurality of cooling regions 51 are provided in the center of a separator 50, and a coolant flow path 52 for circulating a cooling medium is formed in the center of each cooling region 51. Specifically, the size of the separator is 13 cm wide, 25 cm long, and 2 cm thick.
16, a fuel gas supply manifold 54a and an oxidant gas discharge manifold 53b are provided on the left side of the separator 50, and a fuel gas supply manifold 54b and an oxidant gas discharge manifold 53b are provided on the right side.
A fuel gas exhaust manifold 54b and an oxidant gas supply manifold 53a are provided. A fuel gas flow channel is provided on the surface of the separator to avoid the coolant flow channels 52 and communicate with the left and right supply and exhaust manifolds, respectively. A coolant is introduced into the 21 coolant flow channels 52 and flows perpendicular to the separator plane to remove heat generated by the fuel cell reaction. In this embodiment, each coolant flow channel is configured to remove reaction heat generated in one cooling zone. The inner walls of the coolant flow channels 52 serve as heat transfer surfaces. Because the coolant flow channels 52 are located in the centers of the cooling zones 51, the entire surface of the inner walls can be used as heat transfer surfaces, enabling efficient cooling. (Eighth Embodiment) This embodiment is a modification of the fourth embodiment, in which the shape of the inner surfaces of the coolant flow channels is changed. 17A and 17B are diagrams showing the configuration of the separator in this embodiment, with Fig. 17A being a front view of the separator on the fuel gas flow path side, and Fig. 17B being a cross-sectional view taken along the line E-E in Fig. 17A. Specifically, the separator 60 in this embodiment is made of aluminum, and each coolant flow path 62 has three protrusions 63, each 2 mm wide and 5 mm long, on its inner wall. The remaining configuration is similar to that of the fourth and second embodiments, and therefore a description thereof will be omitted. Furthermore, a coolant is introduced into 18 coolant flow paths 62 provided at the top and bottom of the long sides of the separator, and is configured to remove heat generated by the fuel cell reaction by circulating this coolant in a direction perpendicular to the separator plane.
In this case, the inner walls of the coolant flow channels 62 serve as heat transfer surfaces. In this embodiment, by providing protrusions 63 on the inner walls of each coolant flow channel 62, the length of the inner walls can be increased, thereby increasing the heat transfer area and enabling efficient cooling. (Ninth Embodiment) This embodiment is a modification of the third and eighth embodiments, in which the shape of the inner surfaces of the coolant flow channels is modified. FIGS. 18A and 18B show the configuration of a separator in this embodiment, with FIG. 18A being a front view of the separator on the fuel gas flow channel side, and FIG. 18B being a cross-sectional view taken along the line F-F in FIG. 18A. That is, the separator 70 of this embodiment is made of a flexible graphite carbon sheet, and the central portions of the inner walls of each coolant flow channel 72 are shaped to overhang inward by a width of 2 mm. The overhanging portions 73 are formed by press molding so that the thickness of the overhanging portions is the same as the thickness of the portions where the fuel gas flow channel and the oxidant gas flow channel are provided, i.e., 1 mm. The other configurations are similar to those of the third and second embodiments, and therefore a description thereof will be omitted. The cooling medium is introduced into 18 coolant flow paths 72 provided at the top and bottom of the long sides of the separator, and is configured to circulate this cooling medium perpendicular to the separator plane to remove the heat generated by the fuel cell reaction.
In this case, the inner walls of the coolant flow channels 72 serve as heat transfer surfaces. In this embodiment, the inner walls of each coolant flow channel 72 are provided with protruding portions 73, which increases the heat transfer area and enables efficient cooling. Furthermore, the expanded graphite used in the separators has the advantage that its thermal conductivity increases with decreasing thickness and increasing density. Therefore, by reducing the thickness of the protruding portions to 1 mm, high thermal conductivity can be expected. This enables efficient cooling. (Tenth Embodiment) This embodiment is a modification of the first embodiment, in which two upper and lower rows of coolant flow channels 82 are arranged along the long sides of the separator 80 and are connected in series. Note that FIG. 19 is a perspective view showing the configuration of a polymer electrolyte fuel cell stack according to the tenth embodiment, and FIGS. 20A and 20B are views showing the configuration of a separator. FIG. 20A is a front view of the separator from the fuel gas flow channel side, and FIG. 20B is a cross-sectional view taken along the line G-G of FIG. 20A. That is, in this embodiment, the separator is configured so that the coolant flows in series through eight coolant flow paths 82 provided in each of the upper and lower parts. The other configurations are the same as those of the first embodiment, so a description thereof will be omitted. The outer dimensions of the separator 80 are set to 25 cm in length, 7 cm in width, and 2 mm in thickness, and the material may be any material that is electrically conductive and has a dense structure. In this example,
21A and 21B show the front end plate 83a shown in FIG.
22A and 22B are front views showing the rear end plate 83b. The front end plate 83a and the rear end plate 83b are provided with separators 8
19, the front end plate 83a is provided with a coolant flow path 82b for communicating the two upper and lower rows of coolant flow paths 82 in series. Furthermore, as shown in FIG. 19, piping for each fluid is attached to the front end plate 83a. Specifically, an oxidant gas inlet 85a is provided at the upper right end of the front end plate 83a, and an oxidant gas outlet 85b is provided at the lower left end of the end plate. Furthermore, a fuel gas inlet 86a is provided at the upper left end of the end plate 83a, and a fuel gas outlet 86b is provided at the lower right end.
Furthermore, on the right side of the front end plate 83a, there are coolant inlets 87 at the top and bottom.
On the left side of the front end plate 83a, coolant outlets 87b are provided at the top and bottom. While water may be used as the coolant, antifreeze is preferable for use in cold climates. An ethylene glycol solution was used here. The coolant is introduced through two coolant inlets 87a provided on the front end plate 83a, as shown in FIG. 19, and flows uniformly. Specifically, the coolant flows through the rightmost of the eight common coolant channels provided above and below the separator, seal packing, and electrolyte membrane, perpendicular to the plane of these components. As it flows, it absorbs heat from the channel walls, providing cooling. As shown in FIGS. 19 , 21A , and 21B , the coolant introduced through the two coolant inlets 87 a in the front end plate 83 a reaches the rear end plate 83 b. As shown in FIGS. 22A and 22B , the coolant passes through the communicating coolant channels 82 b in the rear end plate 83 b and is guided to the adjacent coolant channel to the left, where it makes a U-turn and flows to the front end plate 83 a. As shown in FIG. 19 , the coolant then flows serially through the eight coolant channels, absorbing heat from the channel walls and cooling the fuel cell stack. In this embodiment, the coolant inlet is located at the right end and the outlet is located at the left end, so that the coolant flows from right to left. This ensures that the coolant flow is the same as the oxidant gas flow in the separator. As a result, the temperature distribution in the separator can be lower at the right end where the coolant inlet is located and higher at the left end where the coolant outlet is located. In this way, by increasing the temperature of the oxidant gas outlet, it is possible to prevent condensation of water vapor contained in the oxidant outlet, and therefore it is possible to efficiently discharge water produced by the reaction, which is more effective. (Eleventh Embodiment) This embodiment is a modification of the above-mentioned tenth embodiment, in which the flows of the coolant flow channels 92 in two upper and lower rows provided along the long sides of the separator 90 are partially integrated, and the integrated flows are connected in series. Note that Fig. 23 is a perspective view showing the configuration of a polymer electrolyte fuel cell stack of the eleventh embodiment, and Figs. 24A and 24B show the front end plate 93a,
25A and 25B are front views showing the rear end plate 93b. That is, in this embodiment, as shown in FIG. 23, four of the eight coolant channels arranged in two rows at the top and bottom of the separator are configured to flow in the same direction in parallel. To achieve this flow pattern, as shown in FIGS. 24A and 24B, the coolant introduced through two coolant inlets 97a in the front end plate 93a is distributed to four coolant channels from the right end, then flows through the coolant channels, and reaches the rear end plate 93b. As shown in FIGS. 25A and 25B, the coolant that has reached the rear end plate 93b passes through the coolant channels in the rear end plate 93b, is guided to the four coolant channels from the left end, makes a U-turn, and is then guided to the front end plate 93b.
In this way, by dividing the eight coolant flow paths into groups of four and connecting them to each other,
As in the tenth embodiment, the temperature can be lower on the right side of the separator and higher on the left side, so the temperature near the oxidant outlet can be increased, and water produced by the reaction can be efficiently discharged. (Twelfth embodiment) This embodiment is a modification of the tenth embodiment, and is configured so that two rows of coolant flow channels, one above the other, provided along the long sides of the separator are connected in series. Note that Fig. 26 is a perspective view showing the configuration of a polymer electrolyte fuel cell stack of the twelfth embodiment, and Figs. 27A and 27B show the front end plate 10 shown in Fig. 26.
28A and 28B are front views showing the front end plate 100a and the rear end plate 100b.
In the front end plate 100b, two rows of coolant channels 102b, one above the other, are provided in the separator 80 in a portion substantially parallel to the extension direction of the short sides of the separator 80. Coolant introduced through a single coolant inlet provided in the front end plate 100a flows through the rightmost channel of the upper row of coolant channels 102b and reaches the rear end plate 100b. In the rear end plate 100b, upper and lower coolant channels 102b are provided, and the coolant is led to the rightmost channel of the lower row of coolant channels 102b. The coolant introduced into the rightmost channel of the lower row of coolant channels 102b passes through a similar communicating channel in the front end plate 100a and is introduced into the second-from-the-rightmost channel of the upper row of coolant channels 102b. In this way, by alternately flowing the coolant through the upper and lower rows of coolant flow channels 102b from the right end to the left end, the temperature can be lower on the right side of the separator 80 and higher on the left side, as in the tenth embodiment, so that the temperature near the oxidant outlet can be increased and water produced by the reaction can be efficiently discharged. [Industrial Applicability] As described above, according to the present invention, it is possible to maintain a small temperature difference within the separator and reduce the thickness in the stacking direction, thereby providing a solid polymer fuel cell stack that can be made small and ensure a large reaction area.

[Brief explanation of the drawings]

Fig. 1 is a perspective view showing the structure of a separator in a conventional polymer electrolyte fuel cell stack. Fig. 2 is a perspective view showing the structure of a first embodiment of a polymer electrolyte fuel cell stack according to the present invention. Fig. 3 is a cross-sectional view of the fuel cell stack shown in Fig. 2. Figs. 4A and 4B are views showing the structure of the separator in the first embodiment.
4B is a front view of the separator on the fuel gas flow path side, and FIG. 4B is a view taken along the line A-A in FIG. 4A.
FIG. 5 is a cross-sectional view. FIG. 6 is a diagram showing the heat flow within a unit cell of the fuel cell stack of the first embodiment. FIG. 7 is a diagram showing the temperature distribution in the vertical direction of the separator in the first embodiment and a conventional example. FIG. 8 is a diagram showing the temperature distribution in the horizontal direction of the separator in the first embodiment and a conventional example. FIG. 9 is a perspective view showing the configuration of a second embodiment of a polymer electrolyte fuel cell stack according to the present invention. FIGs. 10A and 10B are diagrams showing the configuration of a separator in the second embodiment, where FIG. 10A is a front view of the separator on the fuel gas flow path side, and FIG. 10B is a B-B cross-sectional view of FIG. 10A. FIG. 11 is a diagram showing the relationship between temperature and water vapor amount in the present invention. FIG. 12 is a diagram showing the relationship between the aspect ratio of an expanded graphite separator in the present invention and temperature difference. FIG. 13 is a diagram showing the relationship between the aspect ratio of an aluminum separator in the present invention and temperature difference. Figures 14A and 14B show the configuration of a separator according to a fifth embodiment, with Figure 14A being a front view of the separator on the fuel gas flow path side and Figure 14B being a cross-sectional view taken along C-C in Figure 14A. Figures 15A and 15B show the configuration of a separator according to a sixth embodiment, with Figure 15A being a front view of the separator on the fuel gas flow path side and Figure 15B being a cross-sectional view taken along D-D in Figure 15A. Figure 16 shows the configuration of a separator according to a seventh embodiment, with a front view of the separator on the fuel gas flow path side. Figures 17A and 17B show the configuration of a separator according to an eighth embodiment, with Figure 17A being a front view of the separator on the fuel gas flow path side and Figure 17B being a cross-sectional view taken along E-E in Figure 17A. 18A and 18B are diagrams showing the configuration of a separator of a ninth embodiment, in which Fig. 18A is a front view of the separator on the fuel gas flow channel side, and Fig. 18B is a cross-sectional view taken along the line F-F in Fig. 18A. Fig. 19 is a perspective view showing the configuration of a polymer electrolyte fuel cell stack of a tenth embodiment according to the present invention. Figs. 20A and 20B are diagrams showing the configuration of a separator of the tenth embodiment, in which
Fig. 20A is a front view of the fuel gas flow path side of the separator, and Fig. 20B is a G-G cross-sectional view of Fig. 20A. Figs. 21A and 21B are views showing the configuration of the front end plate shown in Fig. 19, with Fig. 21A being a front view and Fig. 21B being a H-H cross-sectional view of Fig. 21A. Figs. 22A and 22B are views showing the configuration of the rear end plate shown in Fig. 19, with Fig. 22A being a front view and Fig. 22A being a I-I cross-sectional view of Fig. 22A. Fig. 23 is a perspective view showing the configuration of an eleventh embodiment of a polymer electrolyte fuel cell stack according to the present invention. Figs. 24A and 24B are views showing the configuration of the front end plate shown in Fig. 23, with Fig. 24A being a front view and Fig. 24B being a J-J cross-sectional view of Fig. 24A. Figs. 25A and 25B are views showing the configuration of the rear end plate shown in Fig. 23, with Fig. 25A being a front view and Fig. 25B being a K-K cross-sectional view of Fig. 25A. Fig. 26 is a perspective view showing the configuration of a twelfth embodiment of a polymer electrolyte fuel cell stack according to the present invention. Figs. 27A and 27B are views showing the configuration of the front end plate shown in Fig. 26, with Fig. 27A being a front view and Fig. 27B being a cross-sectional view taken along line J-J in Fig. 27A. Figs. 28A and 28B are views showing the configuration of the rear end plate shown in Fig. 26, with Fig. 28A being a front view and Fig. 28B being a cross-sectional view taken along line L-L in Fig. 28A.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (10)

[Claims] [Claim 1] A solid polymer fuel cell stack comprising a plurality of unit cells, each having a solid polymer electrolyte membrane sandwiched between a fuel electrode and an oxidizer electrode, stacked together with a separator having at least one of a fuel gas flow path for supplying fuel gas to the fuel electrode and an oxidizer gas flow path for supplying oxidizer gas to the oxidizer electrode, wherein the separator has a rectangular outer shape, and a cooling medium flow path is formed in the portion of the separator surrounding the fuel gas flow path and the oxidizer gas flow path, which is substantially parallel to the extension direction of the long side of the separator, so that the cooling medium flows in a direction perpendicular to the separator plane. [Claim 2] A polymer electrolyte fuel cell stack in which a plurality of unit cells, each having a solid polymer electrolyte membrane sandwiched between a fuel electrode and an oxidizer electrode, are stacked via a separator having at least one of a fuel gas flow path for supplying fuel gas to the fuel electrode and an oxidizer gas flow path for supplying oxidizer gas to the oxidizer electrode, wherein the separator has a rectangular outer shape, and a plurality of cooling medium flow paths are formed in portions substantially parallel to the extension direction of the opposing long sides of the separator, so as to circulate the cooling medium in a direction perpendicular to the separator plane. [Claim 3] A polymer electrolyte fuel cell stack in which a plurality of unit cells, each having a solid polymer electrolyte membrane sandwiched between a fuel electrode and an oxidizer electrode, are stacked via a separator having at least one of a fuel gas flow path for supplying fuel gas to the fuel electrode and an oxidizer gas flow path for supplying oxidizer gas to the oxidizer electrode, wherein the separator has a rectangular outer shape, and the surface of the separator that contacts the electrode is provided with a plurality of cooling areas, and a cooling medium flow path is formed in the center of each cooling area so as to circulate the cooling medium in a direction perpendicular to the separator plane. 4. A fuel gas supply or discharge manifold for supplying or discharging the fuel gas or the oxidant gas is provided in a portion of the periphery of the fuel gas flow path or the oxidant gas flow path, substantially parallel to the direction of extension of the short sides of the separator.
10. The polymer electrolyte fuel cell stack according to claim 9, wherein the polymer electrolyte fuel cell stack is a polymer electrolyte fuel cell stack according to any one of claims 1 to 9. [Claim 5] A solid polymer fuel cell stack as described in any one of claims 1 to 3, characterized in that the separator is made of a sheet made of flexible graphite carbon, and the ratio of the length of the long side of the separator to the length of the short side is 3 or more. [Claim 6] A solid polymer fuel cell stack as described in any one of claims 1 to 3, characterized in that the separator is made of a thin plate of copper or aluminum-based metal, and the ratio of the length of the long side of the separator to the length of the short side is 2.5 or more. 7. The polymer electrolyte fuel cell stack according to claim 1, wherein a plurality of protrusions are provided on the inner wall of the cooling medium flow path formed in the separator. 8. The polymer electrolyte fuel cell stack according to claim 1, wherein an inner wall of a cooling medium flow path formed in said separator is provided with a protruding portion. 9. The polymer electrolyte fuel cell stack according to claim 1, wherein the plurality of cooling medium flow paths are connected in series. 10. A cooling medium supply passage according to any one of claims 1 to 3, wherein some of the plurality of cooling medium passages are connected in parallel, and the passages connected in parallel are connected in series.
10. The polymer electrolyte fuel cell stack according to claim 9, wherein the polymer electrolyte fuel cell stack is a polymer electrolyte fuel cell stack according to any one of claims 1 to 9.