JP2006164680A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of accelerating the temperature rise of a fuel cell stack in startup. <P>SOLUTION: At the end of the fuel cell stack with a plurality of cells 101 of fuel cells stacked therein, a hollow collector plate 3 with a hollow inside and an end plate 102 are mounted. Side surfaces of the hollow collector plate 3 are so formed as to become recessed surfaces in a state that the internal pressure of the hollow collector plate is low. In normal power generation as shown in fig.(a), the hollow part of the hollow collector plate 3 is filled with a high-pressure fluid 103, the hollow collector plate 3 is swollen, and contact resistance between the hollow collector plate and the cell 101 at the stack end and between the cells 101 is lowered, whereby a resistance loss is reduced. In At a rise in temperature as shown in fig.(b), the hollow part of the hollow collector plate 3 is filled with a low-pressure fluid 104, the hollow collector plate 3 is recessed, the contact resistance is brought into a high state, Joule heat generated by the contact resistance is increased and the temperature of the fuel cell stack can be rapidly raised. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that controls contact resistance of a fuel cell stack.

  In general, a fuel cell is a device that directly converts chemical energy of a fuel into electrical energy by electrochemically reacting a fuel such as hydrogen as a reaction gas with an oxidant such as air. The fuel cells are classified into various types depending on the difference in electrolytes, and one of them is a solid polymer electrolyte fuel cell using a solid polymer electrolyte as an electrolyte.

  The electrode reaction that proceeds at both the fuel electrode and the oxidant electrode of this polymer electrolyte fuel cell is as follows.

Fuel electrode: 2H ₂ → 4H ⁺ + 4e ⁻ (1)
Oxidant electrode: 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2)
When the fuel is supplied to the fuel electrode, the reaction formula (1) proceeds to generate hydrogen ions at the fuel electrode. The generated hydrogen ions permeate (diffuse) through the electrolyte (solid polymer electrolyte membrane in the case of a solid polymer electrolyte fuel cell) in a hydrated state to reach the oxidant electrode, and oxygen-containing gas, For example, when air is supplied, the reaction formula (2) proceeds at the oxidizer electrode. The fuel cell generates an electromotive force when the electrode reactions of the equations (1) and (2) proceed at each electrode.

  For example, in a polymer electrolyte fuel cell that is considered as a driving source for vehicles or the like, freezing of moisture generated by reaction at the time of starting below zero degrades performance. Operation is possible with a low load, but the power that can be extracted is extremely small. Therefore, it is necessary to quickly raise the temperature of the fuel cell stack and shift to a high load.

  However, since the fuel cell has a low load when operated below zero, the amount of heat generated by the reactions (1) and (2) is extremely small, and it is difficult to quickly raise the temperature of the fuel cell stack.

As a conventional example highly relevant to the present invention, a technique described in Patent Document 1 is known. According to this technology, a corrugated conductive heat insulating plate is provided between the end portion of the fuel cell stack and the power extraction terminal plate to enhance the heat insulating effect, thereby increasing the temperature at the time of starting the fuel cell stack below zero. Promotes.
JP 2004-152502 A (page 4, FIG. 1)

  However, in the above conventional example, since the contact area of the member is reduced, the contact resistance increases, so the Joule heat due to the fuel cell current increases, and the temperature rise of the fuel cell stack at the time of starting below zero can be promoted. However, since the contact resistance during normal operation is large, the output performance of the fuel cell stack during normal operation is greatly impaired.

  In order to solve the above problems, the present invention provides a membrane electrode assembly in which a fuel electrode is formed on one surface of a polymer electrolyte membrane and an oxidizer electrode is formed on the other surface, and a fuel is provided in the membrane electrode assembly. And a fuel cell stack comprising a plurality of fuel cells each having a separator formed with a flow path for supplying an oxidant, and an internal portion disposed on at least one of a positive electrode and a negative electrode of the fuel cell stack The gist is provided with a hollow current collector plate and a pressure control mechanism for controlling the pressure of the fluid inside the cavity of the hollow current collector plate.

  According to the present invention, the fuel cell stack includes a hollow current collecting plate disposed inside at least one of the positive electrode and the negative electrode, and a pressure control mechanism for controlling the pressure of the fluid inside the hollow current collecting plate. By changing the pressure of the fluid inside the hollow current collector plate, the hollow current collector plate can be deformed and the contact resistance of the fuel cell stack can be made variable. In some cases, the pressure inside the hollow current collector plate can be reduced to increase the contact resistance of the fuel cell stack, and the Joule heat due to energization can be increased to promote the temperature rise of the fuel cell stack.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. Each embodiment described below is not particularly limited, but is a fuel cell system suitable for a power source of a fuel cell vehicle parked outdoors where the temperature is below zero.

  FIG. 1 is an explanatory diagram of the principle common to the embodiments of the fuel cell system according to the present invention. FIG. 1A shows the time of normal power generation, and FIG. 1B shows the temperature rise of the fuel cell stack.

  In FIG. 1, a hollow current collecting plate 3 and an end plate 102 having a hollow inside are provided at the end of a fuel cell stack in which a plurality of cells 101 that are power generation units of the fuel cell are stacked. The side surface where the hollow current collecting plate 3 is in contact with the cell 101 or the end plate is formed to be a concave surface when the internal pressure of the hollow current collecting plate is low, for example, about 1 atm. The hollow current collecting plate 3 and the end plate 102 may be integrated.

  During normal power generation shown in FIG. 1A, the hollow portion of the hollow current collecting plate 3 is filled with a high-pressure fluid 103 by a pressure control mechanism (not shown). As a result, the hollow current collecting plate 3 swells, the contact resistance between the hollow current collecting plate and the cells 101 at the end of the fuel cell stack, and the cells 101 decreases, and the resistance loss during normal power generation decreases.

  When the temperature of the fuel cell stack shown in FIG. 1B is raised, the hollow portion of the hollow current collecting plate 3 is filled with a low-pressure fluid 104 by a pressure control mechanism (not shown). Thereby, the hollow current collecting plate 3 is recessed, and the contact resistance between the hollow current collecting plate 3 and the cells 101 at the end of the fuel cell stack and between the cells 101 is high. If fuel gas and oxidant gas are supplied to the fuel cell stack in this state and current is taken out, Joule heat due to the contact resistance of the fuel cell increases, and the fuel cell stack can be quickly heated.

  FIG. 2 is a graph showing the relationship between the internal pressure of the hollow current collector plate and the contact resistance of the fuel cell stack. As shown in FIG. 2, the contact resistance decreases as the pressure inside the hollow current collector plate increases.

  FIG. 3 is a schematic configuration diagram illustrating the configuration of the first embodiment of the fuel cell system 1 according to the present invention. The feature of this embodiment is that the internal cavity of the hollow current collector plate is filled with air, and during normal power generation, this air pressure is increased to lower the contact resistance, and at the time of starting the fuel cell from a low temperature, this air pressure is reduced, The object is to increase the contact resistance and increase the Joule heat due to the fuel cell current, thereby speeding up the temperature rise of the fuel cell stack.

  In FIG. 3, the fuel cell system 1 includes a fuel cell stack 2, positive and negative hollow current collecting plates 3 a and 3 b at both ends of the fuel cell stack 2, air supply pipes 4, 8, 9, 10, the inlet side switching valve 5, the compressor 6, the injection side valve 7, the air discharge pipes 11, 14, and 15, the pressure gauge 12 for detecting the pressure of the hollow current collector plate, and the discharge side The valve 13, the outlet side switching valve 16, the hydrogen supply pipe 17, the hydrogen discharge pipe 18, the temperature sensor 19 for detecting the temperature of the fuel cell stack 2, and the hollow portions of the hollow current collecting plates 3a and 3b are connected. A connecting pipe 20 and a control unit 21 are provided.

  The compressor 6 compresses the air sucked through the air supply pipe 4, the inlet side switching valve 5 and the air supply pipe 9, and passes through the injection side valve 7 and the air supply pipe 10 to hollow the hollow current collector plate 3 a. Compressed air can be supplied to the part.

  The hollow portion of the hollow current collecting plate 3a is connected to the hollow portion of the hollow current collecting plate 3b through the connecting pipe 20. Moreover, the hollow part of the hollow current collecting plate 3b communicates with the pressure gauge 12 and the discharge side valve 13, and the pressure in the hollow part is measured by the pressure gauge.

  The discharge side valve 13 is connected to the air discharge pipe 11 via the air discharge pipe 14 and the outlet side switching valve 16 so that high pressure air in the hollow portions of the hollow current collecting plates 3a and 3b can be released. Yes.

  Here, the control unit 21 controls the compressor 6, the inlet side switching valve 5, the injection side valve 7, the discharge side valve 13, and the outlet side switching valve 16 according to the detection value of the temperature sensor 19 when the fuel cell system is started. Control. The control unit 21, the temperature sensor 19, the compressor 6, the inlet side switching valve 5, the injection side valve 7, the discharge side valve 13, and the outlet side switching valve 16 control the pressure inside the hollow current collecting plates 3a and 3b. It constitutes a pressure control mechanism.

  FIG. 4 is a schematic cross-sectional view showing a cell structure of a solid polymer electrolyte fuel cell constituting the fuel cell stack 2. A cell, which is a unit of a fuel cell, includes a polymer electrolyte membrane 110 made of a solid polymer membrane, and a fuel electrode 111 and an oxidizer electrode arranged on both surfaces of the electrolyte membrane so as to sandwich the polymer electrolyte membrane 110. 112, and a fuel electrode diffusion layer 113, an oxidant electrode diffusion layer 114, a fuel gas channel 117, and an oxidant gas channel 118 disposed outside these electrodes.

  The polymer electrolyte membrane 110 is formed as a proton conductive membrane from a solid polymer material such as a fluorine-based resin. The fuel electrode 111 and the oxidant electrode 112 disposed on both surfaces of the polymer electrolyte membrane 110 include platinum or a catalyst layer made of platinum and other metals.

  The fuel gas channel 117 and the oxidant gas channel 118 are formed by a large number of ribs disposed on the fuel electrode separator 115 and the oxidant electrode separator 116 made of a dense carbon material that is impermeable to gas. The fuel gas is supplied from a gas inlet (not shown) and discharged from a gas outlet (not shown).

  Next, with reference to the flowchart of FIG. 5, the control content at the time of starting of the fuel cell system performed by the control unit 21 will be described. In the initial state before this flowchart is started, the pressure inside the hollow current collector plates 3a and 3b is the same as the atmospheric pressure.

  First, in step (hereinafter, step is abbreviated as S) 1, the temperature sensor 19 detects the temperature Tstack of the fuel cell stack 2. Next, in S2, it is determined whether or not Tstack exceeds a predetermined temperature Ts (for example, 70 [° C.]). If it is determined in S2 that Tstack is equal to or lower than the predetermined temperature Ts, the process proceeds to power generation without increasing the pressure inside the hollow current collector plate. As a result, the contact resistance between the cells constituting the fuel cell stack 2 and the contact resistance between the endmost cell of the fuel cell stack 2 and the hollow current collecting plates 3a and 3b remain high, and the fuel cell stack 2 Hydrogen gas and air are supplied to start power generation. As a result, the amount of Joule heat generated by the contact resistance inside and at the end of the fuel cell increases, and the temperature rise of the fuel cell stack 2 can be accelerated. After that, when the stack temperature Tstack detected by the temperature sensor 19 exceeds the predetermined temperature Ts, the operations of S3 to S8 are performed, the pressure inside the hollow current collector plates 3a and 3b is increased, and the contact resistance is reduced. Decreasing operation is performed.

  If it is determined in S2 that Tstack exceeds the predetermined temperature Ts, the process proceeds to S3, the inlet side switching valve 5 is switched to the a direction, the outlet side switching valve 16 is switched to the c direction, and the injection side valve 7 is opened. Next, in S4, the discharge side valve 13 is closed. Next, in S5, the compressor 6 is operated to start injecting air into the hollow current collector plates 3a and 3b. In S6, the detected value of the pressure gauge 12 is read, and it is determined whether or not the air pressure Pa inside the hollow current collector plate exceeds a predetermined pressure Ps. If the air pressure Pa does not exceed the predetermined pressure Ps, S6 is repeated. When the air pressure Pa exceeds the predetermined pressure Ps, the process proceeds to S7, the compressor 6 is stopped and the air injection is stopped, and the inlet side switching valve 5 is switched to the b direction and the outlet side switching valve 16 is switched to the d direction at S8. The injection side valve 7 is closed, and power generation is started after the air pressure inside the hollow current collecting plates 3a and 3b is maintained at a predetermined pressure.

  With such a configuration, as shown in FIG. 2, when the air pressure inside the hollow of the hollow current collector plate is increased, the contact resistance of the fuel cell stack is lowered. Therefore, when Tstack is Ts or less, The power generation can be performed with the contact resistance of the fuel cell stack being high, and the contact resistance of the fuel cell stack can be reduced when Tstack is equal to or higher than Ts. Further, since air is introduced into the hollow current collector plate, the heat conductivity of the air is small, so that heat dissipation from the end of the fuel cell stack can be prevented.

  According to the present embodiment, when power generation is performed in a state where the contact resistance of the fuel cell stack is high, Joule heat increases, so that the temperature rise of the fuel cell stack can be promoted, and the fuel cell stack temperature Tstack is equal to the predetermined temperature Ts. Since the contact resistance of the fuel cell stack is reduced, the power generation performance can be prevented from being lowered.

  In addition, since the air inside the hollow of the hollow current collector plate has a low thermal conductivity, there is an effect that the heat release from the stack end can be suppressed and the temperature rise of the fuel cell stack can be further promoted. Furthermore, since air is introduced into the fuel cell system as an oxidant for the fuel cell, there is no need to newly install a fluid to be injected into the cavity of the hollow current collector plate, and the fuel cell system can be simplified.

  FIG. 6 is a schematic configuration diagram illustrating the configuration of the second embodiment of the fuel cell system 1 according to the present invention. The fuel cell system of the present embodiment is characterized in that a coolant for cooling the fuel cell is introduced as a fluid into the hollow current collector plate, and the pressure control mechanism controls the pressure of the coolant.

  In FIG. 6, the fuel cell system 1 includes a fuel cell stack 2, positive and negative hollow current collecting plates 3 a and 3 b at both ends of the fuel cell stack 2, an air supply pipe 4, an air A discharge pipe 11, a hydrogen supply pipe 16, a hydrogen discharge pipe 17, a temperature sensor 19 for detecting the temperature of the fuel cell stack 2, a connection pipe 20 for connecting the hollow portions of the hollow current collector plates 3a and 3b, and a control Unit 21, coolant tank 30, coolant pump 31, coolant piping 32, 36, 37, 38, 39, 40, 42, inlet side switching valve 33, compressor 35, injection side valve 34, and discharge side A valve 43, a pressure gauge 44, an outlet side switching valve 45, and a radiator 41 are provided.

  The coolant such as antifreeze stored in the coolant tank 30 is pumped by the coolant pump 31 and is supplied to the coolant supply pipe 36 for cooling the fuel cell stack 2 by the inlet side switching valve 33 or the coolant for supplying the coolant to the compressor 35. The supply pipe 37 is selected.

  The coolant supply pipe 37 supplies coolant to the compressor 35, and the compressor 35 can supply the pressurized coolant to the hollow current collector plate 3 a through the injection side valve 34 by pressurizing the coolant. ing.

  The hollow portion of the hollow current collecting plate 3a is connected to the hollow portion of the hollow current collecting plate 3b through the connecting pipe 20. Further, the hollow portion of the hollow current collecting plate 3b communicates with the pressure gauge 44 and the discharge side valve 43 so that the pressure in the hollow portion is measured by the pressure gauge.

  The discharge side valve 43 releases the coolant pressure in the hollow portions of the hollow current collecting plates 3a and 3b to the coolant tank 30 through the coolant pipe 38, the outlet side switching valve 45, the coolant pipe 40, the radiator 41, and the coolant pipe 42. Be able to.

  During normal operation of the fuel cell system, the inlet side switching valve 33 communicates the coolant pipe 32 and the coolant pipe 36, and the outlet side switching valve 45 communicates the coolant pipe 39 and the coolant pipe 40. As a result, during normal operation, the coolant passes through the coolant tank 30, coolant pump 31, coolant pipe 32, coolant pipe 36, fuel cell stack 2, coolant pipe 39, coolant pipe 40, radiator 41, coolant pipe 42, and coolant tank 30. The fuel cell stack 2 can be maintained at an appropriate temperature.

  Here, the control unit 21 controls the compressor 35, the inlet side switching valve 33, the injection side valve 34, the discharge side valve 43, and the outlet side switching valve 45 according to the detection value of the temperature sensor 19 when the fuel cell system is started. Control. The control unit 21, the temperature sensor 19, the compressor 35, the inlet side switching valve 33, the injection side valve 34, the discharge side valve 43, and the outlet side switching valve 45 control the pressure inside the hollow current collecting plates 3a and 3b. It constitutes a pressure control mechanism.

  Since the control in the control unit 21 in the present embodiment is substantially the same as the control in the first embodiment shown in FIG. 5, the description with reference to the flowchart is omitted.

  According to this embodiment, since the coolant is mounted in the fuel cell system as a cooling medium for the fuel cell stack, there is no need to newly install a fluid to be injected into the cavity of the hollow current collector plate. It can be simplified.

  FIG. 7 is a schematic configuration diagram illustrating the configuration of Example 3 of the fuel cell system 1 according to the present invention. The fuel cell system of the present embodiment is characterized in that hydrogen is introduced as a fluid into the hollow current collector plate, and the pressure control mechanism controls the hydrogen pressure.

  In FIG. 7, the fuel cell system 1 includes a fuel cell stack 2, positive and negative hollow current collecting plates 3 a and 3 b at both ends of the fuel cell stack 2, an air supply pipe 4, an air The discharge pipe 11, the hydrogen tank 51, the hydrogen supply pipe 52, the hydrogen pressure adjustment valve 53, the hydrogen supply pipe 16 that supplies hydrogen to the anode of the fuel cell stack 2, and the hydrogen inside the hollow current collector 3 a Injection side valve 54, pressure gauge 55 for detecting the pressure inside the hollow of the current collector plate 3b, discharge side valve 57 for discharging hydrogen from the inside of the hollow of the current collector plate 3b, and hydrogen discharge pipe 17 And a temperature sensor 19 for detecting the temperature of the fuel cell stack 2, a connecting pipe 20 for connecting the hollow portions of the hollow current collecting plates 3a and 3b, and a control unit 21.

  The high-pressure hydrogen stored in the hydrogen tank 51 is reduced to the operating pressure of the fuel cell by the hydrogen pressure adjusting valve 53 and supplied to the anode of the fuel cell stack 2. Hydrogen that is not used at the anode of the fuel cell stack 2 is discharged through the hydrogen discharge pipe 17.

  Further, the hydrogen tank 51 supplies hydrogen to the injection side valve 54 via the hydrogen supply pipe 52, and the injection side valve 54 decompresses the hydrogen to adjust the pressure-adjusted hydrogen to the inside of the hollow current collector plate 3a. Supply is possible. Since the hydrogen stored in the hydrogen tank 51 is high pressure, a desired pressure can be obtained simply by reducing the pressure by the injection side valve 54, and energy is not consumed to increase the pressure inside the hollow of the hollow current collector plate. .

  The hollow portion of the hollow current collecting plate 3a is connected to the hollow portion of the hollow current collecting plate 3b through the connecting pipe 20. Further, the hollow portion of the hollow current collecting plate 3b communicates with the pressure gauge 55 and the discharge side valve 57, and the pressure in the hollow portion is measured by the pressure gauge.

  The discharge side valve 57 can escape the high-pressure hydrogen in the hollow portions of the hollow current collecting plates 3 a and 3 b through the hydrogen discharge pipe 17.

  Here, the control unit 21 controls the injection side valve 54 and the discharge side valve 57 according to the detection value of the temperature sensor 19 when the fuel cell system is activated. The control unit 21, the temperature sensor 19, the injection side valve 54, and the discharge side valve 57 constitute a pressure control mechanism that controls the pressure inside the hollows of the hollow current collector plates 3a and 3b.

  Since the control in the control unit 21 in the present embodiment is substantially the same as the control in the first embodiment shown in FIG. 5, the description with reference to the flowchart is omitted.

  According to this embodiment, in order to control the pressure inside the cavity of the hollow current collector plate using hydrogen used as the fuel of the fuel cell stack, a new fluid to be injected into the cavity of the hollow current collector plate is mounted. This eliminates the need to simplify the fuel cell system and to save energy required to increase the pressure inside the hollow of the hollow current collector plate.

It is principle explanatory drawing of the fuel cell system which concerns on this invention. It is a graph explaining the relationship between the internal pressure of a hollow current collecting plate cavity, and the contact resistance of a fuel cell stack. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram explaining the structure of Example 1 of the fuel cell system based on this invention. It is a schematic cross section explaining the cell of the polymer electrolyte fuel cell used for an Example. 3 is a flowchart illustrating boost control inside a cavity of a hollow current collector in Embodiment 1. It is a schematic block diagram explaining the structure of Example 2 of the fuel cell system which concerns on this invention. It is a schematic block diagram explaining the structure of Example 3 of the fuel cell system which concerns on this invention.

Explanation of symbols

1: Fuel cell system 2: Fuel cell stack 3a, 3b: Hollow current collecting plate 4, 8, 9, 10: Air supply piping 5: Inlet side switching valve 6: Compressor 7: Injection side valve 11, 14, 15: Air Discharge piping 12: Pressure gauge 13: Discharge side valve 16: Outlet side switching valve 17: Hydrogen supply piping 18: Hydrogen discharge piping 19: Temperature sensor 20: Connection piping 21: Control unit

Claims (6)

A membrane electrode assembly in which a fuel electrode is formed on one surface of a polymer electrolyte membrane and an oxidizer electrode is formed on the other surface, and a separator having a flow path for supplying fuel and oxidant to the membrane electrode assembly In a fuel cell system including a fuel cell stack in which a plurality of fuel cells including
A hollow current collector plate having a hollow interior disposed in at least one of a positive electrode and a negative electrode of the fuel cell stack;
A pressure control mechanism for controlling the pressure of the fluid inside the cavity of the hollow current collector plate;
A fuel cell system comprising: Comprising temperature detecting means for detecting the temperature of the fuel cell stack;
When the temperature detected by the temperature detection unit is equal to or lower than a predetermined temperature, the pressure control mechanism sets the pressure of the fluid inside the cavity below a predetermined pressure, and the temperature detected by the temperature detection unit becomes equal to or higher than the predetermined temperature. The fuel cell system according to claim 1, wherein the pressure of the fluid inside the cavity is set to a predetermined pressure.   The fuel cell system according to claim 2, wherein the cavity is filled with a fluid having low thermal conductivity.   The fuel cell system according to claim 3, wherein the cavity is filled with air.   The fuel cell system according to claim 2, wherein the cavity is filled with a coolant for cooling the fuel cell.   The fuel cell system according to claim 2, wherein the cavity is filled with hydrogen.

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