JP2008300138A - Structure and method for sealing gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas-seal structure capable of further improving the performance of a fuel battery. <P>SOLUTION: The fuel battery has cells with MEAs 16 sandwiched by a pair of metallic separators 14. A seal member is provided along the periphery of the separator 14 to prevent outflow of gas supplied to the MEA 16. The seal member has hollow elastic bodies 28, 30 for preventing the outflow of the gas supplied to the MEA 16 by adhering to the separator 14. A liquid supplying apparatus 36 makes the thickness of the elastic bodies 28, 30 variable based on an instruction from a control part 38 so as to set a gas-seal pressure as a predetermined reference seal pressure, by varying a liquid volume to be supplied inside the elastic bodies 28, 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell in which an MEA having an electrolyte membrane sandwiched between a pair of electrode members is further sandwiched between a pair of metal separators, and a gas seal structure that prevents the gas supplied to the MEA from flowing out of the separator. And a gas sealing method.

  A fuel cell mounted on a vehicle or the like comprises a membrane / electrode assembly (MEA) in which an electrolyte membrane is sandwiched between a pair of electrodes, and is further sandwiched between a pair of separators to form a cell. Formed. The separator is formed with a gas flow path for supplying fuel gas (hydrogen gas) or oxidizing gas to the MEA. In order to prevent the gas supplied to the MEA from flowing out of the cell, a seal member is usually disposed on the periphery of the separator.

JP 2006-172960 A

  Here, in order to reliably prevent external leakage of the gas supplied to the MEA, it is desirable to increase the seal pressure of the seal member, in other words, the contact pressure between the seal member and the separator. However, when the sealing pressure is increased, there is a problem that the contact resistance between the electrode and the current collector increases. That is, in order to reduce the contact resistance between the electrode and the current collector, it is necessary to apply a large load (fastening load) to the cell so that the separator and the MEA are brought into close contact with each other. However, when the sealing pressure increases, the separator receives a force in a direction away from the MEA. In this case, the contact resistance between the electrode and the current collector increases, and as a result, the battery performance decreases. Conversely, when the seal pressure of the seal member is lowered so that the separator and the MEA are in close contact with each other, the contact resistance is improved, but the gas sealability is lowered, and the battery performance is adversely affected. In other words, in the conventional gas seal technology, the two problems of maintaining the gas seal performance and reducing the contact resistance between the electrode and the current collector are contradictory problems, and it has been difficult to solve them at the same time.

  Further, factors that complicate this problem include changes in the environment inside the cell, that is, changes in temperature, humidity, pressure, and the like. As is well known, as the fuel cell is driven, the temperature, humidity, and pressure inside the cell change greatly. Due to the environmental change inside the cell, the expansion and contraction of the MEA, the seal member, and the like, and consequently the change in the distance between the pair of separators that sandwich them. As a result, the separator-to-separator distance increases relative to the seal member thickness and gas sealing performance decreases, and conversely, the separator-to-separator distance increases relative to the thickness of the MEA. In some cases, the contact resistance increases. That is, in the prior art, it has been difficult to maintain an appropriate gas sealing property while reducing the contact resistance. Patent Document 1 discloses a technique in which a water-absorbent resin whose volume increases by absorbing moisture inside the cell is used as a seal member. However, this technique aims to maintain the drainage performance of the cell in a desired state, and does not achieve both the above-described sealing performance maintenance and contact resistance reduction. That is, conventionally, there has been no technology for effectively improving the cell performance of the fuel cell by reducing the contact resistance while maintaining the sealing performance.

  Accordingly, an object of the present invention is to provide a gas seal structure and a gas seal method that can further improve battery performance.

  The gas seal structure of the present invention prevents a gas supplied to the MEA from flowing out of the separator in a fuel cell in which an MEA sandwiched between a pair of electrode members is further sandwiched between a pair of metal separators. An elastic member having a hollow structure disposed on the periphery of the separator, wherein the elastic member prevents the gas supplied to the MEA from flowing out to the outside by being in close contact with the separator, and the elastic member A fluid supply means for supplying fluid to the inside of the elastic member, and by varying the amount of fluid supplied to the hollow interior of the elastic member, the thickness of the elastic member is set so that at least the gas seal pressure becomes a predetermined reference seal pressure. And a fluid supply means for changing.

  In a preferred aspect, the fluid supply means changes the thickness of the elastic member so that the gas seal pressure is a predetermined reference seal pressure and the electrode-current collector contact resistance is a predetermined reference resistance value.

  In another preferred aspect, the elastic member includes an inner elastic member disposed between the pair of separators, and an outer elastic member disposed on the opposite side of the inner elastic member with the separator interposed therebetween. In this case, it is desirable that the fluid supply means adjusts the amount of fluid supplied to the inner elastic member and the amount of fluid supplied to the outer elastic member independently of each other.

  In another preferred aspect, the fluid supply means includes a manifold formed on a peripheral edge of the separator and communicated with the elastic body, and a pump provided outside the cell and communicated with the manifold.

  Another gas sealing method according to the present invention is a gas sealing method for a fuel cell, in which an MEA in which an electrolyte membrane is sandwiched between a pair of electrode members is further sandwiched between a pair of metal separators. The thickness of the elastic member is changed as much as possible so that at least the gas seal pressure becomes a predetermined reference seal pressure by changing the amount of fluid supplied to the inside of the elastic member having a hollow structure disposed on the periphery of the elastic member.

  According to the present invention, by changing the amount of fluid supplied to the elastic body, the thickness of the elastic body can be changed so that at least the gas seal pressure becomes the predetermined reference seal pressure. Therefore, an appropriate gas seal can be maintained regardless of changes in the cell internal environment. In addition, since the gas seal pressure is prevented from becoming excessive, an increase in contact resistance can also be prevented. As a result, the battery performance can be further improved.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a cell 12 constituting a fuel cell 10 according to an embodiment of the present invention. The fuel cell 10 is configured by stacking one or more cells 12 as shown in FIG.

  Each cell 12 includes a membrane / electrode assembly 16 (hereinafter referred to as “MEA 16”) in which an electrolyte membrane 18 is sandwiched between a pair of electrodes 20 and is further sandwiched between a pair of separators 14. The electrolyte membrane 18 constituting the MEA 16 is a membrane body made of a polymer material having ion conductivity and functions as an ion exchange membrane. A pair of electrodes 20, that is, a fuel electrode (anode side electrode 20 a) and an oxygen electrode (cathode side electrode 20 b) are provided on both sides of the electrolyte membrane 18. Each electrode 20 includes a diffusion layer that diffuses a gas supplied via the separator 14 and a catalyst layer that includes a catalyst material. The diffusion layer is made of a sub-carbon material such as carbon cloth or carbon paper. The catalyst layer is formed by applying carbon powder (electrode catalyst material) carrying a catalyst noble metal (for example, Pt or the like) to both surfaces of the electrolyte membrane 18 or one surface of the diffusion layer.

  The separator 14 is a plate material made of a metal material having conductivity, and functions as a partition member that partitions cells. In addition, a large number of irregularities are formed on the surface of the separator 14, and these irregularities function as a gas flow path 22 supplied to the MEA 16. Furthermore, the separator 14 also functions to electrically connect each cell 12 by contacting the separator 14 of the adjacent cell 12.

The power generation mechanism in the fuel cell 10 is as follows. Fuel gas (for example, hydrogen-containing gas) is supplied to the fuel electrode 20a through the flow path 22 formed in the separator 14, and oxidant gas (for example, air) is supplied to the air electrode 20b. The fuel gas is decomposed into electrons and hydrogen ions (H +) by the action of the catalyst of the electrode 20a. The electrons pass through the external circuit and move from the fuel electrode 20a to the air electrode 20b to generate an electric current. On the other hand, hydrogen ions (H +) pass through the electrolyte membrane 18 and reach the air electrode 20b, combine with oxygen and electrons that have passed through the external circuit, and become reaction water (H ₂ O). Heat generated simultaneously with the bonding reaction of hydrogen (H ₂ ), oxygen (O ₂ ), and electrons is recovered by cooling water. Further, water generated on the cathode side having the air electrode 20b (hereinafter referred to as “reaction water”) is discharged from the cathode side. The generated electricity is transmitted to another adjacent cell 12 through the separator 14 or the like that functions as a current collector. In other words, the plurality of cells 12 are connected in series through a current collector such as the separator 14. With this series connection, the fuel cell 10 as a whole can generate a large amount of current.

  Here, in order to efficiently and appropriately generate power in the fuel cell 10, it is necessary to reduce the contact resistance between the electrode and the current collector. When the contact area between the electrode and the current collector is small and the contact resistance is large, the power generation efficiency is reduced. Therefore, conventionally, the cells 12 are fastened with a large force so as to increase the MEA clamping force of the separator 14.

  Moreover, in order to generate electric power appropriately, it is necessary to ensure gas sealing performance reliably. That is, if the gas supplied to the MEA 16 leaks to the outside of the cell or the oxidizing gas and the hydrogen gas are mixed, appropriate power generation cannot be performed. Therefore, conventionally, a sealing member has been provided on the periphery of the separator 14 to ensure gas sealing performance. However, the configuration of the conventional seal member only considers the gas sealing property, and the consideration about the contact resistance between the electrode and the current collector is poor. In addition, due to poor consideration of changes in the environment (temperature, humidity, etc.) inside the cell, there are cases where appropriate gas sealing properties cannot be obtained.

  Therefore, in this embodiment, the sealing member has a special configuration, so that an appropriate gas sealing property is always ensured regardless of the environmental change inside the cell, and an increase in contact resistance between the electrode and the current collector is prevented. is doing. Hereinafter, this seal member will be described in detail.

  First, a conventional seal member will be briefly described. FIG. 5 is a diagram showing a schematic configuration of the seal member 42 provided in the conventional cell 40. The conventional seal member 42 is configured by adhering a pair of resin plates 32 that sandwich the end of the MEA 16 with an adhesive 34. Each sealing member 42 has a thickness corresponding to the thickness of the MEA 16, and ensures gas sealing performance by being in close contact with the separator 14. At this time, the degree of adhesion between the seal member 42 and the separator 14 is high. In other words, the higher the gas seal pressure, the higher the gas seal performance. However, when the gas seal pressure is excessively high, a force in a direction away from the MEA 16 is applied to the separator 14, and the separator 14 and the like, which are current collectors, are separated from the electrode 20 and the contact resistance is increased. Therefore, it is desirable that the seal member 42 has a thickness that can provide a minimum required gas seal pressure.

  However, since the thickness of the seal member 42 for achieving both gas sealing performance and reduction in contact resistance changes as the fuel cell 10 is driven, the conventional seal member 42 has these two characteristics. It has always been difficult to achieve both. That is, the internal environment (temperature, humidity, internal pressure, etc.) of each cell 40 greatly changes during the power generation process, and the MEA 16 and the seal member 42 are expanded and contracted with the change of the internal environment. At this time, it is extremely difficult to cause the expansion / contraction amount of the seal member 42 made of different materials and having different thicknesses to follow the expansion / contraction amount of the MEA 16, resulting in a decrease in gas sealability and an increase in contact resistance. .

  For example, when the expansion amount of the MEA 16 is larger than the expansion amount of the seal member 42, the separator 14 is separated from the seal member 42 by being pressed by the expanded MEA 16 as illustrated in FIG. To do. As a result, a gap is generated between the sealing member 42 and the separator 14, and gas sealing performance may not be ensured. Conversely, when the expansion amount of the seal member 42 is larger than the expansion amount of the MEA 16, as shown in FIG. 5C, the separator 14 is separated from the MEA 16 by the expanded seal member 42. It will be pushed in the direction to do. As a result, the separator 14 functioning as a current collector is separated from the electrode 20 and the contact resistance between the electrode and the current collector is increased.

  In order to solve such a problem, it is also conceivable to use an expandable material, specifically, a separator made of carbon. In the case of a carbon separator, instead of providing a seal member provided with a resin frame, the peripheral portion of the carbon separator is formed thick, and this thick portion is used as a seal member. That is, gas sealing is achieved by bonding the peripheral edges (thick portions) of the carbon separators facing each other with an adhesive. In this case, since there is no separate member such as a resin frame, the thickness fluctuation at the cell periphery (gas seal portion) is reduced, and the above-mentioned problem can be improved to some extent. However, carbon separators tend to be expensive as compared to metal separators, and there is a problem that processing is difficult. Furthermore, since carbon has a lower rigidity than metal, it tends to be thick, and there is a problem that it is difficult to reduce the thickness of the cell.

  Therefore, in this embodiment, by using a seal member whose thickness changes so as to keep the gas seal pressure constant, even when the metal separator 14 is used, it is possible to achieve both ensuring of gas seal properties and reduction of contact resistance. It is possible. Hereinafter, the configuration of the seal member of the present embodiment will be described in detail.

  As shown in FIG. 1, the seal member of this embodiment includes a partition member 26, an inner elastic body 28, and an outer elastic body 30. The partition member 26 is a member that partitions a gap formed at the periphery of the separator 14 into an anode side and a cathode side, and is configured by adhering a pair of resin plates 32 that sandwich the end of the MEA 16 with an adhesive 34. The However, unlike the conventional seal member 42 (see FIG. 5), the partition member 26 has a thickness sufficiently smaller than the height of the gap portion.

  The inner elastic body 28 is made of an elastic material such as rubber and is a member disposed between the partition member 26 and the separator 14 and is a so-called O-ring. In the present embodiment, this inner elastic body 28 is brought into close contact with the separator 14 and the partition material 26 to ensure gas sealing performance. However, the inner elastic body 28 is different from a normal O-ring, and the inner elastic body 28 is hollow inside. In other words, the inner elastic body 28 can also be said to be a substantially tubular body disposed on the periphery of the separator 14. A fluid (for example, water) is supplied into the inside elastic body 28 which is a substantially tubular body by a fluid supply device 36 which will be described later. And the thickness (height) of the inner side elastic body 28 is changed by changing this fluid quantity supplied. That is, when the inside of the inner elastic body 28 is filled with a fluid, the inner elastic body 28 is not crushed by the pressure received from the fluid and is initially, that is, in a state where no external force is applied. Maintain thickness (height). On the other hand, when the fluid inside the inner elastic body 28 is sucked, a negative pressure acts on the inner elastic body 28. And, by the action of this negative pressure, the inner elastic body 28 is crushed (closed) and its thickness (height) is reduced. As shown in FIG. 1, in the present embodiment, two inner elastic bodies 28 are provided on the cathode side and the cathode side, respectively, a total of four. It can be changed.

  Similarly to the inner elastic body 28, the outer elastic body 30 is an O-ring made of an elastic material, and is a substantially tubular body having a hollow inside. The fluid is also supplied into the outer elastic body 30 by the fluid supply device 36. The thickness of the outer elastic body 30 is changed according to the amount of fluid supplied to the inside. Here, the outer elastic body 30 is disposed on the outer surface of the separator 14, in other words, on the outer side of the cell 12. In order to form a space for accommodating the outer elastic body 30 disposed outside the cell 12, the separator 14 is provided with a step corresponding to the height of the outer elastic body 30.

  A fluid supply device 36 and a control unit 38 are provided outside the cell 12. Each cell 12 is provided with an environmental sensor 39 for detecting the environment (temperature, humidity, internal pressure, etc.) inside the cell, and the detection knowledge of the environmental sensor 39 is input to the control unit 38. Yes.

  The fluid supply device 36 includes a known pump or the like, and supplies fluid into the elastic bodies 28 and 30 in response to an instruction from the control unit 38. The fluid supply device 36 can control the amount of fluid supplied to the inner elastic body 28 and the amount of fluid supplied to the outer elastic body 30 independently of each other. In other words, the amount of fluid supplied to the inner elastic body 28 and the amount of fluid supplied to the outer elastic body 30 can be made different. Therefore, for example, a large amount of fluid can be supplied to the inner elastic body 28 and the amount of fluid supplied to the outer elastic body 30 can be reduced.

  The environmental sensor 39 is a sensor that detects the internal environment of each cell 12, specifically, the temperature and humidity, as well as the internal pressure as necessary. The detection value detected by the environmental sensor 39 is output to the control unit 38 and used for various drive controls of the fuel cell 10.

  The control unit 38 controls the drive of the fuel cell 10 and controls the supply operation of the fuel gas and the oxidizing gas in accordance with a command from the host control unit, and also controls the drive of the fluid supply device 36. The drive control of the fluid supply device 36 is performed so that the gas seal pressure becomes a predetermined reference seal pressure. That is, if the thickness of the MEA 16 changes with changes in the internal environment of the cell, the thickness of the elastic bodies 28 and 30 required to maintain the reference seal pressure, and hence the amount of fluid supplied to the elastic bodies 28 and 30 also changes. To do. Based on the output value from the environment sensor 39, the control unit 38 calculates the amount of fluid necessary for maintaining the reference seal pressure, and instructs the fluid supply device 36.

  Here, the reference seal pressure is a value that is arbitrarily set in advance, but is desirably a minimum value necessary for reliably preventing gas leakage. This is because when the reference seal pressure is excessively large, the contact resistance between the electrode and the current collector is increased.

  Various methods can be employed as a method for calculating the amount of fluid required for maintaining the reference seal pressure. For example, the amount of fluid may be calculated based on the relationship between the thickness of the elastic body necessary for maintaining the reference seal pressure and the internal environment, which is measured in advance by experiments. That is, based on the experimental results, a matrix indicating the relationship between the optimum fluid amount and the internal environment as shown in FIG. 2 is stored in the control unit 38 in advance, and this matrix and the detection result by the environmental sensor 39 The fluid supply amount may be calculated with reference to the above. Further, the supply fluid amount may be stored not by a matrix but by a mathematical expression having temperature and humidity as variables. Furthermore, a sensor capable of directly measuring the gas seal pressure may be provided, and the fluid amount may be calculated based on the detection result of the sensor.

  FIG. 3 is a diagram showing a state of gas sealing in the present embodiment. FIG. 3A shows a state where the MEA 16 expands as the temperature and humidity inside the cell increase. FIG. 3B shows a state where the MEA 16 is reduced as the temperature and humidity inside the cell are reduced.

  As illustrated in FIG. 3A, when the temperature and humidity rise and the MEA 16 expands, the distance between the pair of separators 14 that sandwich the MEA 16 also increases. In this case, the control unit 38 instructs the fluid supply device 36 to change the amount of fluid supplied to the elastic bodies 28 and 30 based on the detection value of the environment sensor 39. Specifically, in this case, the control unit 38 instructs to increase the amount of fluid supplied to the inner elastic body 28 and supplies the fluid amount to the outer elastic body 30 disposed on the opposite side of the inner elastic body 28. Instruct to reduce As a result, even when the interval between the separators 14 is widened, the adhesion between the inner elastic body 28 and the separator 14 is maintained, and an appropriate gas seal pressure is obtained.

  On the other hand, as illustrated in FIG. 3B, when the temperature and humidity are reduced and the MEA 16 is reduced, the interval between the pair of separators 14 that sandwich the MEA 16 is also reduced. At this time, if the thickness of the inner elastic body 28 is unchanged, the gas sealing property can be ensured, but the contact resistance between the electrode and the current collector increases. Therefore, in this case, the control unit 38 instructs to reduce the amount of fluid supplied to the inner elastic body 28 and increases the amount of fluid supplied to the outer elastic body 30 disposed on the opposite side of the inner elastic body 28. Instruct. As a result, it is possible to prevent the gas seal pressure from becoming excessive, and consequently to prevent an increase in contact resistance between the electrode and the current collector.

  That is, according to this embodiment, since the thickness of the sealing member changes according to the environmental change inside the cell, the contact resistance between the electrode and the current collector is always increased while maintaining a certain gas sealing property. Can be prevented. As a result, more efficient power generation becomes possible.

  In the above embodiment, the amount of fluid supplied to the elastic bodies 28 and 30 is controlled based on the gas seal pressure. However, the amount of fluid is controlled in consideration of the contact resistance between the electrode and the current collector. Also good. That is, it is known that the contact resistance between the electrode and the current collector varies with the supply of fuel gas or oxidizing gas into the cell even when the gas seal pressure is constant. This is presumably because the gas pressure (internal pressure) generated inside the cell acts as a force for peeling off the MEA 16 and the current collector (separator 14 or the like). In order to prevent an increase in the contact resistance between the electrode and the current collector due to such gas pressure action, the contact resistance between the electrode and the current collector is supplied to the elastic bodies 28 and 30 so as to have a predetermined reference resistance value. The amount of fluid may be controlled. For example, when the contact resistance between the electrode and the current collector increases as the gas pressure (cell 12 internal pressure) increases, the amount of fluid supplied to the outer elastic body 30 is greatly increased. The contact resistance may be reduced by pressing the separator 14. In this case, the contact resistance between the electrode and the current collector may be calculated from the value detected by the environmental sensor 39, that is, temperature, humidity, internal pressure, etc., or a sensor for detecting contact resistance is dedicated. May be provided. The relationship between the contact resistance value and the amount of fluid supplied to the elastic bodies 28 and 30 is stored in advance in the control unit as a matrix as shown in FIG. May be.

  Normally, the separator 14 is formed with a through-hole through which an oxidizing gas or a fuel gas flows as a manifold. However, an elastic body adjusting manifold may be further formed. That is, as shown in FIG. 4, in addition to the oxidant gas and fuel gas manifold 50, the separator 14 has an elastic body adjusting manifold 52 communicated with elastic bodies 28 and 30 disposed on the periphery of the separator 14. May be formed. A fluid (for example, air) supplied to the elastic bodies 28 and 30 is allowed to flow through the elastic body adjusting manifold 52, and the elastic body adjusting manifold 52 and the elastic bodies 28 and 30 are communicated with each other. Thereby, it is not necessary to provide a tube for connecting to the fluid supply device 36 for each of the elastic bodies 28 and 30, and the gas seal structure can be simplified.

It is a schematic block diagram of the cell used for the fuel cell which is embodiment of this invention. It is an example of the matrix which shows the relationship between the environment memorize | stored in a control part, and the amount of supply fluids. It is a figure which shows the mode of a gas seal. It is a schematic top view of the separator in which the manifold for elastic body adjustment was formed. It is a schematic structure figure of the conventional cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Fuel cell, 12, 40 cells, 14 Separator, 16 Membrane electrode assembly (MEA), 18 Electrolyte membrane, 20 Electrode, 22 Flow path, 26 Partition material, 28 Inner elastic body, 30 Outer elastic body, 32 Resin plate, 34 Adhesive, 36 Fluid supply device, 38 Control unit, 39 Environmental sensor, 42 Seal member, 50 Manifold, 52 Manifold for adjusting elastic body.

Claims (6)

In a fuel cell in which an MEA sandwiched between a pair of electrode members is further sandwiched between a pair of metal separators, a gas seal structure that prevents the gas supplied to the MEA from flowing out of the separator,
An elastic member having a hollow structure disposed on the periphery of the separator, the elastic member preventing the outflow of gas supplied to the MEA by being in close contact with the separator;
Fluid supply means for supplying fluid to the inside of the elastic member, and by varying the amount of fluid supplied to the hollow inside of the elastic member, at least the gas seal pressure of the elastic member should be a predetermined reference seal pressure. Fluid supply means for changing the thickness;
A gas seal structure comprising: The gas seal structure according to claim 1,
The fluid supply means changes the thickness of the elastic member so that the gas seal pressure is a predetermined reference seal pressure and the electrode-current collector contact resistance is a predetermined reference resistance value. . The gas seal structure according to claim 1 or 2,
The gas sealing structure, wherein the elastic member includes an inner elastic member disposed between a pair of separators, and an outer elastic member disposed on the opposite side of the inner elastic member with the separator interposed therebetween. The gas seal structure according to claim 3,
The gas seal structure, wherein the fluid supply means adjusts the amount of fluid supplied to the inner elastic member and the amount of fluid supplied to the outer elastic member independently of each other. The gas seal structure according to any one of claims 1 to 4,
The fluid supply means includes
A manifold formed on the periphery of the separator and communicated with the elastic body;
A pump provided outside the cell and communicated with the manifold;
A gas seal structure comprising: A fuel cell gas sealing method in which an MEA having an electrolyte membrane sandwiched between a pair of electrode members is further sandwiched between a pair of metal separators,
The thickness of the elastic member is changed so that at least the gas seal pressure becomes a predetermined reference seal pressure by changing the amount of fluid supplied to the inside of the elastic member having a hollow structure disposed on the periphery of the separator. Gas sealing method.

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