JP2013157279A - Fuel cell stack fastening method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell stack fastening method capable of obtaining a sufficient output and a sufficient anti-shock performance.SOLUTION: In a method for fastening a fuel cell stack 1 having a cell laminate 3 on which plural cells 2 are laminated, end plates 7 arranged outside the cell laminate 3 in a lamination direction, and a tension plate 8 coupling the end plates 7 and giving a fastening load to the cell laminate 3, based on a displacement characteristic to a load of one or more components selected from components of the cells 2, an initial displacement completion time T until initial displacement of the selected components under a maximum fastening load Nmax is found. After the maximum fastening load Nmax is given to the cell laminate 3 during the initial displacement completion time T, the cell laminate 3 is fastened with a fastening load N preset as a design value.

Description

  The present invention relates to a method for fastening a fuel cell stack having a cell stack in which power generation cells are stacked.

  The fuel cell stack includes a joined body (MEA) in which a pair of electrodes are arranged on both sides of an electrolyte membrane, a joined body (MEGA) in which a diffusion layer is placed on both sides of the MEA, and a reactive gas that sandwiches such a joined body. A plurality of cells composed of a pair of separators forming a flow path are stacked. The fuel cell stack is provided with a sealing member such as a gasket in the cell and between the cells in order to prevent leakage of the oxidizing gas and fuel gas supplied into the cell and the cooling water supplied between the cells. Yes.

  The fuel cell stack is assembled in a state where a predetermined fastening load is applied from both ends of the cell stack (see, for example, Patent Document 1). In Patent Document 1, as a technique for suppressing load loss during fuel cell operation due to the sag of the joined body, pressure fluctuation exceeding the load fluctuation during power generation including low temperature fluctuation is pre-applied during assembly of the fuel cell stack. The technology to keep is disclosed.

JP 2010-153174 A

  By the way, in a fuel cell stack having a fixed size structure that is assembled by applying a predetermined fastening load to a cell stack, a rubber gasket (seal member) disposed in and between the cells and the joined body (MEGA) In some cases, initial creep or sag due to aging may occur in a gas diffusion layer (GDL) which is a constituent member.

  In this way, when initial creep or sag occurs in the gasket or gas diffusion layer, the fastening load of the fuel cell stack decreases early, and as a result, it becomes difficult to ensure sufficient surface pressure at the electrode portion, and output ( The power generation voltage) and impact resistance (rigidity) may be reduced. As a countermeasure, the technique of Patent Document 1 has already been proposed. However, even if the maximum load is applied instantaneously as in the technique, there is a possibility that the load omission considering the sag over time cannot be prevented. is there.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for fastening a fuel cell stack capable of obtaining good output and impact resistance.

In order to achieve the above object, a method for fastening a fuel cell stack according to the present invention includes:
A cell stack in which a plurality of cells are stacked, an end plate disposed outside the stack of the cell stack, and a fastening member that connects the end plates and applies a fastening load to the cell stack. A fuel cell stack fastening method comprising:
Based on a displacement characteristic with respect to a load of one or more constituent members selected from among the constituent members of the cell, the selection is performed under a maximum fastening load that can be applied to the cell stack during operation of the fuel cell stack. Obtain the initial displacement completion time until the initial displacement of the constituent members completed,
After the maximum fastening load is applied to the cell laminate during the initial displacement completion time, the cell laminate is fastened with a fastening load preset as a design value.

  In this configuration, the time until the initial displacement of the cell constituent members is completed as the time for applying the maximum fastening load to the cell stack when assembling the fuel cell stack. The initial displacement and the load loss resulting therefrom can be terminated in advance at the time of fastening.

  In the above fastening method, when there are a plurality of selected constituent members, the time for applying the maximum fastening load to the cell stack may be set to the longer initial displacement completion time.

  Further, as a result of earnest research on the fastening method of the fuel cell stack, the inventor of the present invention is a member in which the gasket and the gas diffusion layer are subjected to thermal creep and sag at an early stage among the constituent members of the cell. The knowledge that it is a member which occupies as much as 96% of the contribution to the load loss is obtained.

  Based on this knowledge, the displacement characteristics include initial creep characteristics of a gasket that is provided in the cells and between the cells and seals a fluid flowing in the cells and between the cells, and / or one component of the cells. It is possible to use the load displacement characteristics of the gas diffusion layer.

  According to the method for fastening a fuel cell stack of the present invention, a fuel cell stack capable of obtaining good output and impact resistance can be obtained.

It is a disassembled perspective view which shows the structural example of the fuel cell stack fastened with the fastening method of the fuel cell stack in this embodiment. It is a side view which shows the structural example of a fuel cell stack. It is a graph which shows the fluctuation | variation of the fastening load with time. It is a graph which shows the relationship between the time of a gasket, and creep. It is a graph which shows the relationship between the temperature of a gasket, and the time until completion of initial creep. It is a graph which shows the load displacement characteristic of a gas diffusion layer.

Embodiments of a fuel cell stack according to the present invention will be described below with reference to the drawings.
FIG. 1 is an exploded perspective view showing an example of the structure of a fuel cell stack fastened by the fastening method of the fuel cell stack in the present embodiment, and FIG. 2 is a side view showing an example of the structure of the fuel cell stack.

  As shown in FIGS. 1 and 2, the fuel cell stack 1 has a plurality of cells 2, and the cells 2 are sequentially stacked to form a cell stack 3 (see FIG. 2). Further, in the fuel cell stack 1 composed of the cell stack 3 or the like, for example, a stack member is sandwiched between a pair of end plates 7 and a restraining member including a tension plate 8 is disposed so as to connect the end plates 7 to each other. In this state, a load in the stacking direction is applied and fastened (see FIG. 2).

  Such a fuel cell stack 1 can be used in, for example, an in-vehicle power generation system of a fuel cell vehicle (FCHV; Fuel Cell Hybrid Vehicle). It can also be used in power generation systems mounted on self-propelled devices such as airplanes) and robots, and even stationary power generation systems.

  As an electrolyte contained in the cell 2, a membrane-electrode assembly (MEA) or a membrane-electrode-diffusion layer assembly (MEGA) can be used. For example, in this embodiment, a membrane-electrode-diffusion layer assembly (hereinafter also referred to as MEGA) 30 is used (see FIG. 1 and the like).

  The cell 2 includes a MEGA 30 and a pair of separators 20 (indicated by reference numerals 20a and 20b in FIG. 1 and the like) that sandwich the MEGA 30 (see FIG. 1). The MEGA 30 and the separators 20a and 20b are formed in a substantially rectangular plate shape. The MEGA 30 is formed so that its outer shape is smaller than the outer shapes of the separators 20a and 20b.

  The MEGA 30 includes a polymer electrolyte membrane (hereinafter also simply referred to as an electrolyte membrane) 31 made of a polymer material ion exchange membrane, and a pair of electrodes (an anode side diffusion electrode and a cathode side diffusion electrode) sandwiching the electrolyte membrane 31 from both sides. 32, 33 (see FIG. 1). The electrolyte membrane 31 is formed larger than the electrodes 32 and 33. The electrodes 32 and 33 are joined to the electrolyte membrane 31 by, for example, a hot press method with the peripheral edge 34 left.

  The electrodes 32 and 33 constituting the MEGA 30 are constituted by a gas diffusion layer made of, for example, a porous carbon material carrying a catalyst such as platinum attached to the surface thereof. One electrode (anode) 32 is supplied with hydrogen gas as a fuel gas (reactive gas), and the other electrode (cathode) 33 is supplied with an oxidizing gas (reactive gas) such as air or an oxidizing agent. An electrochemical reaction is generated in the MEGA 30 by the gas, so that an electromotive force of the cell 2 can be obtained.

  The gas diffusion layer is a layer formed to appropriately diffuse the reaction gas supplied to the electrolyte membrane 31. For example, the gas diffusion layer in the present embodiment is formed smaller than the electrolyte membrane 31 (and the electrodes 32 and 33).

  The separator 20 (20a, 20b) is made of a gas impermeable conductive material. Examples of the conductive material include carbon and a hard resin having conductivity, and metals such as aluminum and stainless steel. The base material of the separator 20 (20a, 20b) of the present embodiment is formed of a plate-like metal (metal separator), and a film with excellent corrosion resistance is provided on the surface of the base material on the electrode 32, 33 side. (For example, a film formed by gold plating) is formed.

  Further, a groove-like flow path constituted by a plurality of concave portions is formed on both surfaces of the separators 20a and 20b. These flow paths can be formed by press molding in the case of the separators 20a and 20b of the present embodiment in which the base material is formed of, for example, a plate-like metal. The groove-like flow path formed in this way constitutes a gas flow path 21 for oxidizing gas, a gas flow path 22 for hydrogen gas, or a cooling water flow path 23. More specifically, the gas flow path 22 of hydrogen gas is formed on the inner surface on the electrode 32 side of the separator 20a, and the cooling water flow path 23 is formed on the rear surface (outer surface) ( (See FIG. 1).

  Similarly, a gas flow path 21 for oxidizing gas is formed on the inner surface on the electrode 33 side of the separator 20b, and a cooling water flow path 23 is formed on the back surface (outer surface) (see FIG. 1). . For example, in the case of the present embodiment, regarding the two adjacent cells 2, 2, when the outer surface of the separator 20 a of one cell 2 and the outer surface of the separator 20 b of the cell 2 adjacent to this are combined, The channel 23 is integrated to form a channel having a rectangular or honeycomb cross section.

  Furthermore, as described above, the separators 20a and 20b have a relationship in which at least the uneven shape for forming a fluid flow path is reversed between the front surface and the back surface. More specifically, in the separator 20a, the back surface of the convex shape (convex rib) that forms the gas flow path 22 of hydrogen gas is a concave shape (concave groove) that forms the cooling water flow path 23, and the gas flow path The back surface of the concave shape (concave groove) forming 22 is a convex shape (convex rib) forming the cooling water channel 23.

  Further, in the separator 20b, the back surface of the convex shape (convex rib) that forms the gas flow path 21 of the oxidizing gas has a concave shape (concave groove) that forms the cooling water flow path 23, and the concave that forms the gas flow path 21. The back surface of the shape (concave groove) is a convex shape (convex rib) forming the cooling water channel 23.

  Further, in the vicinity of the longitudinal ends of the separators 20a and 20b (in the case of this embodiment, in the vicinity of one end shown on the left side in FIG. 1), the manifold 21a on the inlet side of the oxidizing gas, hydrogen gas An outlet side manifold 22b and a cooling water inlet side manifold 23a are formed. For example, in the case of this embodiment, these manifolds 21a, 22b, and 23a are formed by substantially rectangular or trapezoidal holes provided in the respective separators 20a and 20b, or long and thin rectangular through holes with semicircular ends (FIG. 1). Etc.).

  Furthermore, a manifold 21b on the outlet side of the oxidizing gas, a manifold 22a on the inlet side of the hydrogen gas, and a manifold 23b on the outlet side of the cooling water are formed at opposite ends of the separators 20a and 20b. In the case of the present embodiment, these manifolds 21b, 22a, and 23b are also formed by a substantially rectangular or trapezoidal shape or a long rectangular through hole having semicircular ends (see FIG. 1).

  Among the manifolds as described above, the inlet side manifold 22a and the outlet side manifold 22b for the hydrogen gas in the separator 20a are connected via an inlet side communication passage 22c and an outlet side communication passage 22d formed in the separator 20a. Each communicates with a gas flow path 22 for hydrogen gas.

  Similarly, the inlet side manifold 21a and the outlet side manifold 21b for the oxidizing gas in the separator 20b are each formed of an oxidizing gas via an inlet side communication passage 21c and an outlet side communication passage 21d formed in the separator 20b. It communicates with the flow path 21 (see FIG. 1).

  Further, the inlet side manifold 23a and the outlet side manifold 23b of the cooling water in each separator 20a, 20b are respectively connected via an inlet side communication passage 23c and an outlet side communication passage 23d formed in each separator 20a, 20b. It communicates with the cooling water passage 23.

With the configuration of the separators 20a and 20b as described above, the cell 2 is supplied with oxidizing gas, hydrogen gas, and cooling water.
As a specific example, when the cells 2 are stacked, for example, hydrogen gas passes from the inlet side manifold 22a of the separator 20a through the communication passage 22c and flows into the gas flow path 22, and is supplied to the MEGA 30 for power generation. After that, it passes through the communication passage 22d and flows out to the outlet side manifold 22b.

  Gaskets 25a and 25b are provided between the separators 20a and 20b (see FIG. 1). These gaskets 25a and 25b are formed of, for example, a plurality of members (for example, four independent small rectangular frames and a large frame for forming a fluid flow path) (see FIG. 1). Among these, the gasket 25a is provided between the MEGA 30 and the separator 20a. More specifically, a part of the gasket 25a is provided around the periphery 34 of the electrolyte membrane 31 and the gas flow path 22 of the separator 20a. It is provided so as to be interposed between the portions.

  The gasket 25b is provided between the MEGA 30 and the separator 20b. More specifically, a part of the gasket 25b is a peripheral portion 34 of the electrolyte membrane 31 and a portion of the separator 20b around the gas flow path 21. Between the two.

  Further, a plurality of members (for example, four independent small rectangular frames and a large frame for forming a fluid flow path) are formed between the separators 20b and 20a of the adjacent cells 2 and 2. A gasket 25c is provided (see FIG. 1). The gasket 25c is a member that is provided so as to be interposed between a portion around the cooling water passage 23 in the separator 20b and a portion around the cooling water passage 23 in the separator 20a, and seals between them.

  Next, the configuration of the fuel cell stack 1 will be briefly described (see FIG. 2). The fuel cell stack 1 according to the present embodiment includes a cell stack 3 formed by stacking a plurality of cells 2, and sequentially outputs the cells (end cells) 2 and 2 located at both ends of the cell stack 3. The terminal plate 5 with the terminal 5a, the insulator (insulating plate) 6, and the end plate 7 are further provided. A predetermined compressive force (fastening force) in the stacking direction is applied to the cell laminate 3 by a tension plate (fastening member) 8 that is bridged so as to connect both end plates 7. The fastening member of the present invention is not limited to the tension plate 8, and for example, a tie rod or the like can be used.

  The terminal plate 5 is a member that functions as a current collecting plate, and is formed in a plate shape from a metal such as iron, stainless steel, copper, or aluminum. The insulator 6 is a member that functions to electrically insulate the terminal plate 5 from the end plate 7 and the like, and is formed in a plate shape from a resin material such as polycarbonate. The end plate 7 is formed in a plate shape with various metals (iron, stainless steel, copper, aluminum, etc.) like the terminal plate 5.

  The tension plate 8 is provided so as to bridge between the end plates 7 and 7 and is disposed so that, for example, a pair is opposed to both sides of the cell stack 3 (see FIG. 2). The tension plate 8 is fixed to the end plates 7 and 7 with bolts or the like, and maintains a state in which a predetermined fastening load is applied in the stacking direction of the single cells 2.

  By the way, in the fuel cell stack 1 having the fixed size structure as described above, initial creep or sag due to aging may occur in the constituent members of the cell stack 3. If initial creep or sag occurs in the constituent members of the cell laminate 3, the fastening load of the fuel cell stack that has been fastened with the initial fastening load may be reduced early and may be below the minimum fastening load, as shown in FIG. There is. As a result, it is difficult to secure a sufficient surface pressure at the electrodes 32 and 33, and the output and impact resistance performance are degraded.

  Such a decrease in the fastening load at an early stage is mainly caused by the initial creep of the gaskets 25a, 25b, and 25c and the sag of the gas diffusion layer that is a constituent member of the electrodes 32 and 33. In the present embodiment, the assembly of the fuel cell stack 1 is performed as follows in order to suppress the decrease in the fastening load.

(Understanding displacement characteristics)
(1) Grasping the initial creep characteristics of the gasket As shown in FIG. 4, assuming the maximum load Nmax that can be applied to the cell stack 3 when the fuel cell stack 1 is actually operated, The thickness change of the gaskets 25a, 25b, and 25c with respect to the elapsed time when the maximum load Nmax is applied is measured. In FIG. 4, as a representative example, changes in the thickness of the gaskets 25a, 25b, and 25c at room temperature and 90 ° C. are shown.

  The gaskets 25a, 25b, and 25c have a thickness that decreases with time, and a change point at which the rate of thickness decrease changes. After this change point, the thickness of the gaskets 25a, 25b, and 25c gradually decreases. Therefore, it is determined that the initial creep is completed at this change point. Such change points are measured at various temperatures. As a result, the relationship between the time until completion of the initial creep and the environmental temperature, that is, the initial creep characteristic of the gasket is represented by an approximate curve as shown in FIG.

(2) Grasping the load displacement characteristics of the gas diffusion layer As shown in FIG. 6, the displacement amount when a load is applied to the gas diffusion layer is measured, and the relationship between the load and the displacement amount is determined. Here, A, B, and C in FIG. 6 are displacement amounts of the gas diffusion layer when the maximum load Nmax is applied and held for a predetermined time, and the holding times Ta, Tb, and Tc at the maximum load Nmax are changed. I am letting. The holding time is Tc>Tb> Ta.

(Calculation of initial displacement completion time)
Based on the initial creep characteristics of the gaskets 25a, 25b, and 25c, that is, the creep completion time T1 until the initial creep at the environmental temperature t when the cell laminate 3 is fastened is determined based on FIG.

  Further, based on the load displacement characteristic of the gas diffusion layer, that is, the load displacement characteristic in which the displacement rate at the fastening load N applied to the cell stack 3 is, for example, 3.5% or less, the characteristic is selected. The load holding time T2 of the maximum load Nmax in the obtained gas diffusion layer is obtained. Here, the fastening load N is a fastening load that is preset as a design value, and is a fastening load that is applied to the cell stack 3 when the fuel cell stack 1 is fastened. Moreover, 3.5% of the displacement rate is an example of a threshold value for determining sag, and is appropriately set according to the specifications of the gas diffusion layer.

  For example, in order to obtain the displacement rate at the fastening load N in the gas diffusion layer A with the holding time Tc, the dimension S1 when the maximum load Nmax is applied (see FIG. 6) and the gas diffusion layer A with the maximum load Nmax applied. The displacement amount ΔS (ΔS = S1−S2) is obtained from the dimension S2 (see FIG. 6) when the load becomes the fastening load N, and the displacement rate is calculated from this ΔS by the following equation. And it is determined whether this displacement rate is 3.5% or less.

Displacement rate = (ΔS / S1) × 100 (%)
Next, the creep completion time T1 and the load holding time T2 are compared, and the longer one is selected, and that time is set as the initial displacement completion time T.

(Give maximum load)
When the initial displacement completion time T is set, the maximum load Nmax is continuously applied to the cell stack 3 until the initial displacement completion time T elapses at the environmental temperature t when the fuel cell stack 1 is fastened.

  When the creep completion time T1 is longer than the load holding time T2, the environmental temperature t at the time when the maximum load Nmax is applied may be increased so that T1 approaches the load holding time T2. In this way, the difference between the creep completion time T1 and the load holding time T2 can be reduced, and the initial displacement completion time T for applying the maximum load Nmax can be shortened as much as possible to suppress the influence on the cell stack 3.

(Applying fastening load)
When the maximum load Nmax is continuously applied to the cell stack 3 until the initial displacement completion time T elapses, the cell stack 3 is fastened with the fastening load N applied.

  As described above, according to the fastening method of the fuel cell stack according to the present embodiment, the time for applying the maximum fastening load Nmax to the cell stack 3 at the time of assembling the fuel cell stack 1 Since the time until the initial displacement is completed is adopted, early initial displacement that may occur during operation of the fuel cell stack 1 can be terminated in advance at the time of fastening.

  Thereby, the initial creep and sag of the structural member in the cell laminated body 3 can be suppressed, and the fall of the output and impact resistance performance by a fastening load falling early can be suppressed. That is, the assembly of the fuel cell stack 1 capable of obtaining good output and impact resistance performance is possible.

  In particular, as in this embodiment, if the fastening load is set based on the displacement characteristics of the gaskets 25a, 25b, 25c having a large initial creep and the gas diffusion layer having a large initial sag, the early reduction of the fastening load is good. Can be suppressed.

1 Fuel cell stack 2 Cell 3 Cell stack 7 End plate 8 Tension plate (fastening member)
25a, 25b, 25c Gasket (component)
32, 33 electrode (gas diffusion layer: component)
N Fastening load Nmax Maximum fastening load T Initial displacement completion time

Claims (3)

A cell stack in which a plurality of cells are stacked, an end plate disposed outside the stack of the cell stack, and a fastening member that connects the end plates and applies a fastening load to the cell stack. A fuel cell stack fastening method comprising:
Based on a displacement characteristic with respect to a load of one or more constituent members selected from among the constituent members of the cell, the selection is performed under a maximum fastening load that can be applied to the cell stack during operation of the fuel cell stack. Obtain the initial displacement completion time until the initial displacement of the constituent members completed,
A method for fastening a fuel cell stack, wherein after applying the maximum fastening load to the cell stack during the initial displacement completion time, the cell stack is fastened with a fastening load preset as a design value.   As the displacement characteristics, the initial creep characteristics of a gasket that is provided in the cells and between the cells and seals the fluid flowing in the cells and between the cells, and / or the gas diffusion layer that is a constituent member of the cells. The method of fastening a fuel cell stack according to claim 1, wherein load displacement characteristics are used.   3. The fuel cell stack according to claim 1, wherein when there are a plurality of selected constituent members, the time for applying the maximum fastening load to the cell stack is set to the longer one of the initial displacement completion times. Fastening method.

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