JP2006179294A - Fuel cell stack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve low temperature startability of a fuel cell stack with a simple configuration.
SOLUTION: A fuel cell stack 1 including a cell stack 3 formed by stacking a plurality of cells 2 that are supplied with a fuel gas and an oxidant gas to generate power, and the contact resistance within the cell 2 and / or between the cells 2 Is provided with a temperature-sensing unit 14 that increases the temperature at the time of low temperature or startup. The temperature sensing unit 14 contracts at the time of low temperature startup to reduce the stack fastening force. Since the amount of heat generated by IR loss increases as the contact resistance increases, the temperature increase rate of the fuel cell stack 1 can be increased, and the low-temperature startability is improved.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell stack, and more particularly to a technique effective for improving low-temperature startability.

A fuel cell (cell) generates electricity by a reaction that generates water from a reaction between hydrogen and oxygen. Since this reaction is an exothermic reaction, there is no problem during operation. However, when the outside air temperature decreases after the operation is stopped, water vapor may condense and become ice. In such a case, gas diffusion in the cell is partially blocked, and power generation cannot be performed or performance may be degraded. In view of this, a technique has been proposed in which the fastening force of the fuel cell stack is temporarily reduced during startup to improve low-temperature startup (warm-up) by increasing contact resistance (see, for example, Patent Document 1).
Japanese Patent Application Laid-Open No. 07-302607

  This technology is equipped with a pressurizing means that pressurizes the fuel cell body in which cells are stacked in the cell stacking direction with gas pressure, and lowers the pressure applied by the pressurizing means at startup to reduce the fastening force of the fuel cell stack It is what However, since the pressurizing means has an air cylinder for supplying and discharging nitrogen gas, there is a problem that the configuration of the fuel cell stack becomes complicated.

  Therefore, an object of the present invention is to improve the low temperature startability of the fuel cell stack with a simple configuration.

  The fuel cell stack of the present invention is a fuel cell stack formed by stacking a plurality of cells that are supplied with fuel gas and oxidant gas to generate electric power, and has a large contact resistance in a cell and / or between cells at a low temperature or at startup. A temperature sensing part is provided.

  When the contact resistance in the cell and / or between the cells increases, the amount of heat generated by IR loss (Joule loss) when the generated current flows through the cell increases as the contact resistance increases. Therefore, according to the above configuration, the temperature increase rate of the fuel cell stack can be increased even at a low temperature or at startup.

  The fuel cell stack of the present invention has a tension member that applies a fastening force to the cell stack by an axial force, and a pair of end plates that are held by the tension member so that the distance from each other is substantially constant, The cell may be provided with a compressive force by a pressing force between the end plates, and the temperature-sensitive portion may be contracted with a decrease in temperature to reduce the compressive force.

  According to such a configuration, since the distance between the tension members is substantially constant, the compressive force in the cell stacking direction acting on the cell as the temperature decreases, in other words, the stack fastening force decreases, / And contact resistance between cells increases. The increase in contact resistance also increases the amount of heat generated by IR loss (Joule loss) when the generated current flows through the cell, so that the temperature rise rate of the fuel cell stack can be increased even at low temperatures or at startup. .

  The temperature sensing unit may be provided between the cells. According to such a configuration, it is possible to suppress variations in contact resistance among cells.

  The temperature sensing unit may be provided on the power generation surface of each cell. According to such a configuration, the contact resistance can be reliably varied in a region where heat is generated by the contact resistance.

  The temperature sensing part may be provided at the top of a rib that defines a cooling passage between the cells. According to such a configuration, since the temperature rise of the coolant flowing through the fuel cell stack is promoted, the cell can be warmed up by the heated coolant.

The temperature sensing part is a component or part of the constituent elements of the fuel cell stack and the part in the constituent element that has a larger amount of expansion and contraction in the cell stacking direction due to temperature change than the others, For example, in the case of metal, iron (linear expansion coefficient: 12 × 10 ⁻⁶ / K) or aluminum (linear expansion coefficient: 23 × 10 ⁻⁶ / K) can be used. In addition to these metals, carbon graphite (linear expansion coefficient: 7 × 10 ⁻⁶ / K) or resin can be used.

Examples of the resin include polyamide PA6 (linear expansion coefficient: 80 × 10 ⁻⁶ / K), polyamide PA66 (linear expansion coefficient: 90 to 100 × 10 ⁻⁶ / K), PE, PP, and PBT (all of It is possible to employ linear expansion coefficient: 110 × 10 ⁻⁶ /), ABS (linear expansion coefficient: 75 × 10 ⁻⁶ / K). These resins are suitable because they have a large linear expansion coefficient with respect to separator constituent members (carbon, metal) and outer dimension fixing members (metal, etc.) such as tension members.

  In addition to the above, it is also possible to use a spring using a bimetal, for example, whose reaction force changes due to temperature change. Moreover, the time of low temperature means the time below 0 degreeC (temperature which product water freezes), for example.

  According to the fuel cell stack of the present invention, the contact resistance within the cell and / or between the cells is increased by utilizing the self-stretching property of the temperature sensitive part accompanying the temperature change, and the IR loss (Joule loss) increases accordingly. The temperature of the fuel cell stack can be raised by the heat generated by the Therefore, it is possible to improve the low-temperature startability (warm-up property) with a simple configuration without causing complication of the configuration of the fuel cell stack.

<First Embodiment>
FIG. 1 is a cross-sectional view of a fuel cell stack according to the first embodiment of the present invention. This fuel cell stack can be applied to, for example, an in-vehicle power generation system or a stationary power generation system for a fuel cell vehicle.

  As shown in the figure, the fuel cell stack 1 has a cell stack 3 in which a large number of cells 2 as basic units are stacked. In the fuel cell stack 1, a cover plate 5, a terminal plate 7 with an output terminal 6, an insulating plate 8, and an end plate 9 are sequentially stacked outside the cells (end cells) 2 positioned at both ends of the cell stack 3. Configured.

  The fuel cell stack 1 has a tension plate (tension member) 11 that is bridged between both end plates 9 and fixed to the end plates 9 with bolts 12. The tension plate 11 applies a fastening force to the cell stack 3 by its axial force. The tension plate 11 holds the pair of end plates 9 so that the distance between them is substantially constant. Thus, a compressive force is applied to the cell 2 by the pressing force between the both end plates 9. In other words, the fuel cell stack 1 is in a state in which a predetermined compression force is applied to the cell 2 in the cell stacking direction by fixing the outer dimensions in the cell stacking direction (configured to be substantially constant). Yes.

  A temperature sensing unit 14 is provided between the end plate 9 on one end side of the cell stack 3 and the insulating plate 8. A pressure plate may be provided between the insulating plate 8 and the temperature sensing unit 14.

The temperature sensing unit 14 is one component of the fuel cell stack 1 and is self-expanding with a change in temperature. Further, the linear expansion coefficient (expansion / contraction amount) in the cell stacking direction caused by such a temperature change is the other component of the fuel cell stack 1, for example, the cell 2 and its respective components, the cover plate 5, the terminal plate 7, and For example, iron (linear expansion coefficient: 12 × 10 ⁻⁶ / K), aluminum (linear expansion coefficient: 23 × 10 ⁻⁶ / K), carbon graphite (linear expansion coefficient). Coefficient: 7 × 10 ⁻⁶ / K), polyamide PA6 (linear expansion coefficient: 80 × 10 ⁻⁶ / K), polyamide PA66 (linear expansion coefficient: 90 to 100 × 10 ⁻⁶ / K), PE, PP, and PBT (all of which have a linear expansion coefficient: 110 × 10 ⁻⁶ /), ABS (linear expansion coefficient: 75 × 10 ⁻⁶ / K), bimetal, or the like can be used.

  The temperature sensing unit 14 self-shrinks in the cell stacking direction due to a temperature drop from the time of assembly of the fuel cell stack (for example, room temperature) at a low temperature of 0 ° C. or less when the generated water freezes or at startup, for example, The fuel cell stack 1 is configured so that the outer dimensions in the cell stacking direction are substantially constant, thereby reducing a predetermined compressive force generated in the cell stack 3, and as a result, within the cell 2 and / or between the cells 2. Increase contact resistance.

  The temperature sensing portion 14 is configured in a truncated cone shape as shown in FIG. 1, for example, and the end surface having the larger surface area is in contact with the insulating plate 8. The shape of the temperature sensing unit 14 is not limited to the illustrated shape, and may be a columnar shape or a prismatic shape. A plurality of temperature sensing units 14 may be provided. Furthermore, as long as the temperature sensing part 14 has conductivity, it is not limited to the case where it is provided outside the cell stack 3, but can also be provided inside the cell stack 3.

  Although not shown in each figure, the cell 2 includes an electrolyte membrane made of an ion exchange membrane and a MEA (Membrane Electrode Assembly) made up of a pair of electrodes sandwiching the electrolyte membrane from both sides, and a pair of separators that hold the MEA from the outside. It is prepared for. Each separator is made of carbon or metal as a base material and has conductivity. Each separator has a fluid flow path for supplying an oxidizing gas (oxygen gas, usually air) or a fuel gas (hydrogen gas) to each electrode.

  With such a configuration, an electrochemical reaction occurs in the MEA of the cell 2 and an electromotive force is obtained. Since this electrochemical reaction is an exothermic reaction, the cooling plate disposed between the separators or cells is provided with a cooling passage through which a coolant for cooling the fuel cell flows.

  Next, with reference to FIG. 2, the operation of the fuel cell stack 1 having the above configuration at the time of low temperature startup will be described. This figure is an explanatory view schematically showing the operation of the temperature sensing unit 14, wherein (a) shows a state during normal power generation and (b) shows a state at a low temperature startup.

  As shown in the figure, the low temperature startup shown in (b) is at a lower temperature than the normal power generation (or assembly of the fuel cell stack) shown in (a). Due to self-shrinkage, the total length of the temperature-sensitive portion 14 along the cell stacking direction is shorter than the total length during normal power generation shown in FIG.

  On the other hand, since the fuel cell stack 1 is configured so that the outer dimensions in the cell stacking direction are substantially constant, if the entire length of the temperature sensing portion 14 is shortened along the cell stacking direction, it acts on the cell stack 3. The compressive force in the cell stacking direction, in other words, the stack fastening force is reduced, and the contact resistance within the cell 2 and / or between the cells 2 is increased. As the contact resistance increases, the amount of heat generated by IR loss (joule loss) when the generated current flows through the cell 2 increases, so that the temperature increase rate of the cell 2 and thus the fuel cell stack 1 increases.

  As described above, according to the fuel cell stack 1 of the present embodiment, the contact resistance in the cell 2 and / or between the cells 2 is increased by utilizing the self-shrinking property of the temperature sensing part 14 due to the temperature decrease. Since it is possible to raise the temperature of the fuel cell stack 1 by heat generation due to the accompanying IR loss (Joule loss), low temperature startability (warm-up) can be achieved with a simple configuration without complicating the fuel cell system 1. Property) can be improved.

  On the other hand, after the transition from the low temperature startup to the normal operation, the length dimension in the cell stacking direction of the temperature sensing unit 14 is restored, so that the contact resistance in the cell 2 and / or between the cells 2 is reduced, and extra heat is generated. Can be suppressed.

Second Embodiment
As shown in FIG. 3, the fuel cell stack 21 according to the second embodiment differs in configuration from the first embodiment in that each cell 22 includes a temperature sensing portion 33. Hereinafter, the difference from the first embodiment will be mainly described.

  The cell 22 includes an MEA 31 and a pair of separators 32 that sandwich the MEA 31 from the outside in the stacking direction. On the outer side in the surface direction of the MEA 31, a plurality of temperature-sensitive portions 33 that self-expand and contract with temperature change are provided in a ring shape or at a predetermined interval over the entire circumference.

  The temperature sensing portion 33 is made of various non-conductive resins used for, for example, adhesives and gaskets, and is assembled as the fuel cell stack 21 shown in FIG. 3, that is, the outer dimension in the cell stacking direction is fixed. In the state fixed (constantly constant) by the means 23, the cell 2 is compressed by a predetermined amount in the cell stacking direction as compared with the state where the cell 2 exists alone.

  Therefore, also in the fuel cell stack 21 of the present embodiment, when starting from a low temperature, the outer dimension along the cell stacking direction of the temperature sensing portion 33 is shorter than that during normal power generation due to self-shrinkage accompanying such temperature decrease. Along with this, the stack fastening force also decreases, and the contact resistance within the cell 22 and / or between the cells 22 increases.

  Therefore, similarly to the first embodiment, it is possible to raise the temperature of the fuel cell stack 21 using the heat generated with the increase in contact resistance. Therefore, the low temperature startability (warm-up property) can be improved with a simple configuration without causing complication of the fuel cell stack 21. In addition, after the transition from the low temperature startup to the normal operation, the outer dimension of the temperature sensing portion 33 in the cell stacking direction is restored, so that the contact resistance in the cell 2 and / or between the cells 2 is reduced, and extra heat is generated. Can be suppressed.

<Third Embodiment>
The fuel cell stack according to the third embodiment is different from the above-described embodiment in that a temperature-sensitive part 53 is provided between the cells as shown in the enlarged cross-sectional view of the main part in FIG. Further, the outer dimensions of the fuel cell stack in the cell stacking direction are not necessarily fixed as in the first and second embodiments. Hereinafter, the difference from the above embodiment will be mainly described.

  FIG. 4 is an enlarged cross-sectional view of the main part showing the contact surface between the separator 51 of one adjacent cell and the separator 52 of the other cell and its peripheral part, where (a) is during normal power generation and (b) is a low temperature. Shows the status at startup. A plurality of ribs 52a are formed at a predetermined interval on the surface of the separator 52 opposite to the MEA side, and the temperature sensing part 53 is accommodated in a recess 52b formed between these ribs 52a. ing.

  The temperature-sensitive part 53 is made of a conductive material having a linear expansion coefficient larger than that of the separators 51 and 52, and the outer dimension in the cell stacking direction is, for example, at a low temperature of 0 ° C. or less when the generated water freezes (FIG. 4B). )) Is not in contact with the separator 51, and is set to contact with the separator 51, for example, during normal operation at 20 to 150 ° C. (see FIG. 4A).

  With this setting, during the normal operation of FIG. 4A, the top surface of the rib 52a formed in the separator 52 and the temperature sensing part 53 accommodated in the recess 52b between the ribs 52a are entirely covered by the separator 51. 4, while the cells are completely in contact with each other, the top surface of the rib 52 a is in contact with the separator 51 at the time of low temperature start in FIG. Since the temperature sensing part 53 is separated from the separator 51 and is not in contact, only part of the cells are in contact.

  Therefore, at the time of low temperature startup shown in FIG. 4B, the contact area between adjacent cells, that is, the contact area between the separator 51 and the separator 52 is larger than that in the normal power generation state shown in FIG. As a result, the contact resistance between cells increases, so the amount of heat generated by IR loss (joule loss) also increases, and the temperature increase rate of the fuel cell stack increases.

  Also in the fuel cell stack of the present embodiment, similarly to the above-described embodiment, the temperature of the fuel cell stack can be raised by using heat generated due to the increase in contact resistance, and the fuel cell stack is simplified without complicating the fuel cell stack. The low temperature startability (warm-up performance) can be improved with a simple configuration, and after the shift to the normal operation, the contact resistance between the cells can be reduced, and excessive heat generation can be suppressed.

  In addition to the above, in the fuel cell stack of the present embodiment, since the temperature sensing part 53 is provided between the cells, it is possible to suppress variations in contact resistance among the cells.

  As a modification of the present embodiment, the temperature sensing part 53 may be made of a conductive material having a smaller linear expansion coefficient than the separators 51 and 52. In such a configuration, the outer dimension of the temperature-sensitive portion 53 in the cell stacking direction is set so as not to contact the separator 51 during the normal operation and to contact the separator 51 during the predetermined low temperature startup. Further, the physical properties and the like of the separators 51 and 52 and the temperature sensing part 53 are set so that the contact resistance between the separators 51 and 52 is smaller than the contact resistance between the separator 51 and the temperature sensing part 53.

  Even with this setting, the temperature of the fuel cell stack can be raised using the heat generated by the increase in contact resistance, and the low temperature start-up (warm-up performance) can be achieved with a simple configuration without incurring the complexity of the fuel cell stack. In addition, after the transition to normal operation, the contact resistance between the cells can be reduced, and excessive heat generation can be suppressed. Moreover, since the temperature sensing part 53 is provided between each cell, it becomes possible to suppress the dispersion | variation in the contact resistance in each cell.

<Fourth embodiment>
The fuel cell stack according to the fourth embodiment is different from the above-described embodiment in that a temperature sensing unit is provided on the power generation surface of each cell. Further, the outer dimensions of the fuel cell stack in the cell stacking direction are not necessarily fixed as in the first and second embodiments. The following description will be made with reference to FIG. 4 with a focus on differences from the above embodiment.

  In the cell of the fuel cell stack according to this embodiment, the member denoted by reference numeral 51 in FIG. 4 is an MEA, and the contact area between the MEA 51 and the separator 52 in the cell is variable between the predetermined low-temperature startup and normal operation. It is comprised so that it may become. The temperature sensing portion 53 is made of a conductive material having a linear expansion coefficient larger than that of the separator 52, and the outer dimension in the cell stacking direction is not in contact with the MEA 51 at the predetermined low temperature startup, and the MEA 51 at the normal operation. Set to contact with.

  According to this setting, at the predetermined low temperature start-up, the contact area between the MEA 51 and the separator 52 decreases, and as a result, the contact resistance in the cell increases and the amount of heat generated by the IR loss increases. On the other hand, during normal operation, the contact area between the MEA 51 and the separator 52 increases. As a result, the contact resistance in the cell decreases, and excessive heat generation is suppressed. In addition, since the temperature sensing portion 53 is provided on the power generation surface of the cell, the contact resistance can be reliably varied in a region where heat is generated by the contact resistance.

  As a modification of the present embodiment, as in the modification of the third embodiment, the temperature sensing part 53 is made of a conductive material having a smaller linear expansion coefficient than that of the separator 52, and the cell stacking direction of the temperature sensing part 53 is as follows. Is set so as not to contact the MEA 51 during the normal operation but to contact with the MEA 51 during the predetermined low temperature start-up, and the contact resistance between the MEA 51 and the separator 52 is determined so that the MEA 51 and the temperature sensing unit 53 Even if the physical properties and the like of the MEA 51, the separator 52, and the temperature sensing part 53 are set so as to be smaller than the contact resistance, the same effect can be obtained.

<Fifth Embodiment>
The fuel cell stack according to the fifth embodiment differs from the above embodiment in that the fuel cell stack includes a temperature sensitive part at the top of the rib that defines the cooling passage between the cells. Further, the outer dimensions of the fuel cell stack in the cell stacking direction are not necessarily fixed as in the first and second embodiments. Hereinafter, the difference from the above embodiment will be mainly described.

  FIG. 5A is an enlarged cross-sectional view of the main part of the fuel cell stack during normal operation, and the cell 81 includes an MEA 61 and a pair of separators 62 and 63 that sandwich the MEA 61 from the outside in the stacking direction. Has been. A plurality of ribs 63a are formed at a predetermined interval on the surface of the separator 63 opposite to the MEA 61, and the recesses formed between the ribs 63a are formed in the cooling passage 71 provided between the cells. Define a part.

  Between the cell 81 and a cell outside the figure, a cooling plate 64 that is separate from these cells is disposed. A plurality of ribs 64a are formed on the surface of the cooling plate 64 on the side in contact with the cells 81 at the same interval as the predetermined interval, and the recesses formed between the ribs 64a are formed in the separator. A cooling passage 71 is defined in cooperation with 63 recesses. A coolant (cooling water) for cooling the fuel cell stack flows through the cooling passage 71.

  At least at the tops of the ribs 63a and 64a of the separator 63 and the cooling plate 64, a material having a linear expansion coefficient larger than that of the base material (for example, carbon or stainless steel) of the separator 63 and the cooling plate 64 and having conductivity ( For example, aluminum, bimetal, etc.) are dispersed or alloyed, and a temperature-sensitive portion (region indicated by hatching in FIG. 5) having a larger linear expansion coefficient than other portions of the separator 63 and the cooling plate 64 is formed. .

  With this configuration, during the normal operation shown in FIG. 5A, the top surface of the rib 63a formed on the separator 63 and the top surface of the rib 64a formed on the cooling plate 64 are in full contact with each other. 5B, at the time of the predetermined low temperature startup, a slight gap 72 of about several μm is formed between the top surface of the rib 63a and the top surface of the rib 64a, and the ribs 63a and 63b are not in contact with each other. Become.

  Therefore, at the predetermined low temperature start-up, the contact area between the separator 63 and the cooling plate 64 decreases, resulting in an increase in contact resistance between cells and an increase in heat generation due to IR loss. During normal operation, the contact area between the separator 63 and the cooling plate 64 increases. As a result, the contact resistance between the cells decreases, and excessive heat generation is suppressed.

  Further, at the predetermined low-temperature start-up, the temperature rise of the coolant flowing through the fuel cell stack through the cooling passage 71 is promoted with the increase in the heat generation amount due to the IR loss. The cell can be warmed up, and the cold startability can be further improved.

  In the present embodiment, the cooling plate 64 has been described as an example of the member that defines the cooling passage 71 in cooperation with the separator 63. However, the present invention is not limited to this configuration, and the separator of another cell adjacent to the cell 81 is used. It may be.

<Other embodiments>
The present invention can be applied with various modifications other than the above embodiment. For example, as a method of fixing (substantially constant) the outer dimensions of the fuel cell stack, a plurality of through holes are formed in the outer edge portions of the end plates 9 disposed at both ends of the fuel cell stack 1, and these through holes are formed. A fastening bolt may be inserted and fastened.

1 is a front view of a fuel cell stack according to a first embodiment of the present invention. Explanatory drawing explaining the effect | action of the temperature sensing part shown in FIG. 1 typically. Sectional drawing of the fuel cell stack which concerns on 2nd Embodiment of this invention. The principal part expanded sectional view of the fuel cell stack which concerns on 3rd Embodiment of this invention. The principal part expanded sectional view of the fuel cell stack which concerns on 4th Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell stack, 2, 22, 81 ... Cell, 3 ... Cell laminated body, 9 ... End plate, 11 ... Tension plate (tension member), 14, 33, 53 ... Temperature sensing part, 71 ... Cooling passage, 63a , 64a ... ribs (temperature sensing part).

Claims (5)

A fuel cell stack formed by stacking a plurality of cells that are supplied with fuel gas and oxidizing gas to generate electricity,
A fuel cell stack provided with a temperature sensing part that increases contact resistance in a cell and / or between cells at a low temperature or at startup. A tension member that applies a fastening force to the cell stack by an axial force; and a pair of end plates that are held by the tension member so that the distance from each other is substantially constant, and the cell is between the end plates. A compressive force is applied by the pressing force,
2. The fuel cell stack according to claim 1, wherein the temperature sensing portion contracts with a decrease in temperature to reduce the compression force.   The fuel cell stack according to claim 1, wherein the temperature sensing unit is provided between the cells.   The fuel cell stack according to claim 1, wherein the temperature sensing unit is provided on a power generation surface of each cell.   The fuel cell stack according to claim 3, wherein the temperature sensing part is provided at a top part of a rib defining a cooling passage between the cells.

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