JP2011003477A - Solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid polymer fuel cell capable of preventing a catalyst and a catalyst carrier from being damaged by preventing a rise of the open circuit voltage when no-load or a light-load is applied.SOLUTION: This fuel cell stack formed by piling a plurality of fuel cells 4 through a separator 1 includes: an external circuit 8 formed by connecting terminals 7 provided in the outer periphery of each separator 1 to each other outside of the fuel cells 4; discharge resistors 6 which give a load onto the external circuit 8; and Zener diodes 5 which make the current on the external circuit 8 flow in the only one direction.

Description

  The present invention is a solid polymer that prevents the occurrence of an excessive open circuit voltage generated at the start and stop of operation and prevents the constituent members from being corroded by a reverse voltage generated by residual gas after the operation is stopped. The present invention relates to a fuel cell.

  Conventionally, a polymer electrolyte fuel cell (PEFC) is a fuel cell that uses a polymer membrane as an electrolyte, and has characteristics such as high output density and long battery life. This polymer electrolyte fuel cell includes a fuel cell stack, a fuel reformer, an air supply device, a cooling device, and the like. The fuel cell stack has a fuel electrode (negative electrode) and an air electrode (positive electrode). By continuously supplying fuel gas to the fuel electrode and air to the air electrode, hydrogen in the fuel gas and oxygen in the air Will react electrochemically to generate electricity. The fuel gas and air supplied to the fuel cell stack are usually set at a flow rate higher than that consumed by the fuel cell stack so as not to extremely reduce the power generation efficiency of the fuel cell stack. The excessively supplied fuel gas and air pass through the battery body and are then combusted by the fuel reformer to become part of the fuel reforming energy.

  FIG. 3 is a cross-sectional view showing an example of a schematic structure of a conventional fuel cell 4 of a polymer electrolyte fuel cell. The fuel cell stack is formed by stacking a plurality of the fuel cells 4. The fuel cell 4 includes a fuel electrode catalyst layer 22 that is in contact with one surface of an electrolyte membrane 21 disposed in the center to be a fuel electrode (negative electrode), and an air electrode (positive electrode) that is in contact with the other surface of the electrolyte membrane 21. An air electrode catalyst layer 23 is provided. The fuel electrode catalyst layer 22 is provided with a fuel electrode diffusion layer 26 for diffusing current collection and fuel gas on the opposite side of the electrolyte membrane 21. Similarly, the air electrode catalyst layer 23 is provided with an air electrode diffusion layer 27 for diffusing air or generated water vapor on the opposite surface side of the electrolyte membrane 21. Further, both sides of the fuel electrode diffusion layer 26 and the air electrode diffusion layer 27 are sandwiched by the separator 1 provided with the gas flow grooves 3 (the fuel electrode side gas flow grooves 3a and the air electrode side gas flow grooves 3b). ing. Further, the periphery of the electrolyte membrane 21 is protected by a protective film 24. The generic name including the electrolyte membrane 21, the fuel electrode catalyst layer 22, the air electrode catalyst layer 23 and the protective film 24 is referred to as a membrane electrode assembly (MEA) 2.

  Hydrogen in the fuel gas supplied to the fuel cell stack is sent to the fuel electrode diffusion layer 26 substantially evenly by the fuel electrode side gas flow groove 3a. In the fuel electrode catalyst layer 22 serving as the fuel electrode (negative electrode), the hydrogen sent from the fuel electrode diffusion layer 26 is separated into electrons by the action of the catalyst to become hydrogen ions. The separated electrons are collected by the fuel electrode diffusion layer 26 and go out to the separator 1. The hydrogen ions that have passed through the electrolyte membrane 21 are oxygen in the air sent to the air electrode catalyst layer 23 serving as the air electrode (positive electrode) on the opposite side, and electrons returned from the separator 1 through an external circuit (not shown). Reacts with water to form water (steam). The oxygen in the air supplied to the fuel cell stack is sent to the air electrode diffusion layer 27 substantially evenly by the air electrode side gas circulation groove 3b. In the air electrode diffusion layer 27, the water vapor generated in the air electrode catalyst layer 23 and the unused air are expelled to the air electrode side gas flow groove 3b and exhausted to the outside of the fuel cell stack. The fuel electrode catalyst layer 22 and the air electrode catalyst layer 23 are generally composed of carbon powder carrying a metal catalyst such as a platinum group. For example, the metal catalyst is mixed with a solution in which a perfluorosulfonic acid polymer is dissolved to form a paste, and is applied to the fuel electrode catalyst layer 22 and the air electrode catalyst layer 23. Moreover, after mixing with a polymer and forming a sheet in advance, it may be integrated with the fuel electrode catalyst layer 22 and the air electrode catalyst layer 23 by hot pressing or the like.

  After the power generation of the fuel cell stack is stopped, an open circuit voltage is generated because hydrogen remains in the fuel electrode side gas circulation groove 3a of the fuel cell 4 and oxygen remains in the air electrode side gas circulation groove 3b. A local battery is formed in the fuel cell 4, corrosion of the catalyst support of the fuel electrode catalyst layer 22 and the air electrode catalyst layer 23 occurs, and deterioration of the catalyst itself is induced, resulting in deterioration of the output voltage of the battery. Generally known. For this reason, it is necessary to always keep the voltage of the fuel battery cell 4 main body, particularly the potential of the air electrode, below the allowable value. For this reason, various countermeasure technologies have been proposed for preventing the occurrence of an excessive open circuit voltage generated when the fuel cell stack is started and stopped. In order to prevent the open circuit voltage of the fuel cell stack from exceeding the allowable value, an external circuit with discharge resistors connected to the terminals at both ends of the fuel cell stack is provided, and current is passed through the external circuit so that the current flows in the fuel cell stack. A method of reducing the open circuit voltage by consuming residual fuel gas remaining in the fuel cell has been proposed.

  Among them, the fuel cell stack is divided into a plurality of blocks, and an external circuit in which discharge resistors, switches, and discharge control devices are connected in units of blocks is provided, and residual fuel gas remaining in the fuel cells in each block is provided. When the fuel cell in the block drops below the specified voltage, the discharge control device is switched off to prevent reverse voltage from being applied to the fuel cell in the block, and to deteriorate the electrode catalyst and catalyst carrier. A technique for preventing it has been proposed (Patent Document 1).

  In addition, an external circuit in which a discharge resistor, a switch, and a voltage measurement device are connected to terminals at both ends of each fuel cell is provided to reduce the open circuit voltage by consuming residual fuel gas remaining for each fuel cell, When the voltage measuring device detects that the voltage has dropped below a predetermined voltage, a technique has been proposed in which the switch is turned off so that no reverse voltage is applied to the fuel cell, thereby preventing deterioration of the electrode catalyst and catalyst carrier (patent) Reference 2).

JP-A-10-223248 JP 2003-115305 A

  However, in Patent Document 1, the amount of residual fuel gas remaining in each fuel battery cell is not necessarily the same and is often non-uniform. Since the external resistance continues to be connected even after consumption, a reverse voltage is applied to the fuel cell, causing damage to the catalyst and the catalyst carrier.

  Patent Document 2 can solve the above-mentioned problem, but it is necessary to provide and control a voltage measuring device for each fuel cell. Therefore, the polymer electrolyte fuel cell device is complicated and enlarged, and the cost is increased. There was a drawback of being connected to.

  Therefore, the present invention has been made in view of the above problems, and prevents an increase in open circuit voltage due to residual fuel gas remaining in the fuel cell, and damages the catalyst and catalyst carrier of the fuel cell. An object of the present invention is to provide a fuel polymer electrolyte fuel cell having a simple fuel cell stack.

  In order to solve the above problems, in a fuel cell stack in which a plurality of fuel cells according to the polymer electrolyte fuel cell of the present invention are stacked via separators, terminals provided on the outer periphery of each separator are connected to each other. An external circuit connected outside the fuel cell, a discharge resistor that applies a load on the external circuit, and a rectifier that allows a current on the external circuit to flow in only one direction are provided.

  According to the above-described invention, in the polymer electrolyte fuel cell comprising a plurality of fuel cells and separators sandwiching both sides of each fuel cell, the discharge resistor and the rectifier are connected between the terminals provided on the outer periphery of each separator. Provided with an external circuit. Therefore, the residual fuel gas existing between the separator and the fuel cell can be consumed by the discharge resistance of the external circuit, and the open circuit voltage generated in each fuel cell can be reduced. In addition, since a rectifier is provided, it is difficult to pass a reverse current. However, when the reverse current is increased, a Zener breakdown or an avalanche breakdown occurs and a current flows rapidly. This is called the breakdown voltage, which is the voltage at which this breakdown phenomenon begins. During this breakdown phenomenon, the voltage change is very small compared to the current change, so that the open circuit voltage can be kept stable at almost the breakdown voltage even if the reverse current is increased. That is, it is possible to prevent the reverse voltage from rising by utilizing the breakdown phenomenon of the rectifier having a breakdown voltage lower than a predetermined value, thereby preventing the catalyst of the fuel cell and the catalyst carrier from being damaged. In addition, since the external circuit has a simple configuration including a rectifier, it is possible to provide a fuel cell stack with reduced cost without damaging the catalyst and catalyst carrier of the fuel cell.

  In the polymer electrolyte fuel cell of the present invention, the external circuit is connected between the terminals of the adjacent separators, and the discharge resistor and the rectifier are provided one for each of the terminals. And

  According to the above-described invention, since the external circuit is provided with one discharge resistor and one rectifier between terminals of adjacent separators, the discharge resistor and rectifier corresponding to one fuel cell are provided. For this reason, the amount of residual fuel gas remaining in each fuel cell is not necessarily the same and is often non-uniform. Therefore, depending on the amount of residual fuel gas in each fuel cell, the discharge resistance of each external circuit The open circuit voltage can be reduced. Moreover, since a rectifier having a breakdown voltage below a predetermined value can be applied to each fuel cell, it is possible to prevent an increase in reverse voltage by utilizing a breakdown phenomenon. Therefore, even if the amount of residual fuel gas in the fuel cell stack is not uniform, the open circuit voltage can be kept low and stable, and damage to the catalyst and catalyst carrier of the fuel cell can be prevented.

  In the polymer electrolyte fuel cell of the present invention, the discharge resistor and the rectifier are connected in series on the external circuit.

  According to the above-described invention, since the discharge resistor and the rectifier are connected in series on the external circuit, power loss due to the discharge resistor can be reduced during the fuel cell stack operation. In addition, when the fuel cell stack is started and stopped, the increase in open circuit voltage that occurs during no load and light load can be effectively reduced by the breakdown phenomenon caused by the rectifier. Therefore, damage to the catalyst and catalyst carrier of the fuel cell can be prevented.

  In the polymer electrolyte fuel cell of the present invention, the rectifier may be configured to maintain the voltage below a predetermined voltage when a voltage is generated in a direction opposite to the one direction in which the current on the external circuit flows. It is a voltage rectifier.

  According to the above-described invention, the constant voltage rectifier is difficult to pass a reverse current, but when the reverse current is increased, a Zener breakdown or an avalanche breakdown occurs and a current flows rapidly. By utilizing this breakdown phenomenon, the open circuit voltage of the fuel cell can be made substantially lower than the breakdown voltage. Therefore, damage to the catalyst and catalyst carrier of the fuel cell can be prevented.

  In the polymer electrolyte fuel cell of the present invention, the constant voltage rectifier has a breakdown voltage of 0.8 V, which is the predetermined voltage held between the separates when the reverse voltage is generated. It is -1.0V.

  In the polymer electrolyte fuel cell of the present invention, the constant voltage rectifier has a breakdown voltage of 0.85 V, which is the predetermined voltage held between the separates when the reverse voltage is generated. It is ˜0.95V.

  In the polymer electrolyte fuel cell of the present invention, the constant voltage rectifier is a Zener diode.

  According to the above-described invention, it is desirable that the constant voltage rectifier has a breakdown voltage of 0.8V to 1.0V, preferably 0.85V to 0.95V. In addition, it is desirable that the Zener diode can design such a small breakdown voltage. Further, there are Zener diodes with high accuracy such that the error of the breakdown voltage is 0.1% or less, for example, and the accuracy of the open circuit voltage that occurs during no load and light load can be increased. Thereby, damage to the catalyst and the catalyst carrier can be prevented without forming a local battery in the fuel cell.

  Further, in a fuel cell stack in which a plurality of fuel cells according to the polymer electrolyte fuel cell of the present invention are stacked via a separator, an external connection circuit having a connection terminal connected to the outer periphery of each separator, and the external A discharge resistor for applying a load on a connection circuit; a switching means for mechanically connecting or disconnecting each of the connection terminals and the corresponding separator; and the switching means when the fuel cell stack is in an unloaded state. And a control means for performing control to mechanically connect each of the connection terminals and the corresponding terminal of each of the separators.

  According to the above-described invention, in the polymer electrolyte fuel cell comprising a plurality of fuel cells and separators sandwiching both sides of each fuel cell, the external connection circuit connected to the discharge resistance is mechanically connected to or disconnected from the separator. And a control means for controlling the switching means so that the external circuit is connected to the separator when there is no load. Therefore, an external connection circuit having a discharge resistance is connected in a no-load state, and the residual fuel gas existing between the separator and the fuel cell is consumed by the discharge resistance, and is generated in each fuel cell. The open circuit voltage can be reduced. Further, since the external connection circuit has a simple configuration, it is possible to provide a fuel cell stack with reduced cost without damaging the catalyst and catalyst carrier of the fuel cell.

  Further, in the polymer electrolyte fuel cell according to the present invention, the control means may be configured such that when the voltage is generated in the direction opposite to the one direction in which the current on the external connection circuit flows, the connection means causes the connection terminals to connect the connection terminals. And the corresponding separators are mechanically cut.

  According to the above-described invention, when the reverse voltage on the external connection circuit is generated, the control means disconnects the external connection circuit from the separator by the switching means and prevents the reverse voltage from being generated in the fuel cell. Can do. Since the residual fuel gas remaining in each fuel battery cell is uneven, the fuel battery cell with a small residual fuel gas generates a potential difference with other fuel battery cells and generates a reverse voltage, but disconnects the external connection circuit. Thus, reverse voltage can be prevented, and damage to the catalyst and catalyst carrier of the fuel cell can be prevented.

  In the polymer electrolyte fuel cell of the present invention, the external connection circuit is connected between the connection terminals corresponding to the adjacent separators, and the discharge resistance is provided for each of the connection terminals. It is characterized by.

  According to the above-mentioned invention, since it consists of the external connection circuit provided with one discharge resistance between each adjacent separator, it has the discharge resistance corresponding to one fuel cell. For this reason, the amount of residual fuel gas remaining in each fuel cell is not necessarily the same and is often non-uniform. Therefore, each discharge resistance of the external connection circuit depends on the amount of residual fuel gas in each fuel cell. Thus, the open circuit voltage can be reduced. Further, by disconnecting the external connection circuit from the fuel cell by the switching means before the reverse voltage is applied, it is possible to prevent the reverse voltage from being generated in the fuel cell. Therefore, even if the amount of residual fuel gas in the fuel cell stack is not uniform, the open circuit voltage can be kept low and stable, and damage to the catalyst and catalyst carrier of the fuel cell can be prevented.

  In the polymer electrolyte fuel cell of the present invention, the switching unit moves the entire external connection circuit under the control of the control unit to connect or disconnect the connection terminals and the corresponding separators. It is characterized by doing.

  In the polymer electrolyte fuel cell of the present invention, the switching means is an electric spring that is movable under the control of the control means.

  According to the above invention, the switching means moves the entire external connection circuit to connect or disconnect the separator terminal and the connection terminal of the external connection circuit. Preferably, the switching means is controlled by the control unit. An electric spring that can be moved by is desirable. Since it is a mechanical switching means, for example, the electric spring main body can be disposed outside the fuel cell stack, and the operating status can be visually confirmed. Further, since the external connection circuit has a simple configuration, it is possible to provide a fuel cell stack with reduced cost without damaging the catalyst and catalyst carrier of the fuel cell.

  Therefore, according to the present invention, when the fuel cell stack is unloaded and lightly loaded, an increase in open circuit voltage due to residual fuel gas remaining in the fuel cell is prevented, and damage to the catalyst and catalyst carrier of the fuel cell is prevented. Therefore, it is possible to provide a solid polymer electrolyte fuel cell having a simple fuel cell stack.

It is explanatory drawing which showed the outline | summary of the polymer electrolyte fuel cell which concerns on Embodiment 1 in this invention. It is explanatory drawing which showed the outline | summary of the polymer electrolyte fuel cell which concerns on Embodiment 2 in this invention. It is sectional drawing which shows an example of schematic structure of the fuel cell of the conventional polymer electrolyte fuel cell

  Hereinafter, two embodiments of the present invention will be described with reference to the accompanying drawings. In addition, this invention is not limited by this Example.

  FIG. 1 is an explanatory diagram showing an overview of a polymer electrolyte fuel cell according to Embodiment 1 of the present invention.

  As shown in FIG. 1, the fuel cell 4 includes a membrane electrode assembly (MEA) 2, a separator 1 that sandwiches the membrane electrode assembly 2, and a gas flow channel groove 3 provided in the separator 1. . The membrane electrode assembly 2 and the gas flow path groove 3 are the same as those in FIG. A fuel cell stack is configured by stacking a plurality of fuel cells 4 via a separator 1. A terminal 7 is provided around each separator 1, and an external circuit 8 connected between the terminals 7 and provided outside the fuel cell stack is provided with a Zener diode 5 and a discharge resistor 6. The Zener diode 5 and the discharge resistor 6 are connected in series on the external circuit 8. Further, here, one Zener diode 5 and one discharge resistor 6 are provided on the external circuit 8 between the terminals 7 of the adjacent separators 1. That is, a Zener diode 5 and a discharge resistor 6 corresponding to each fuel cell 4 are provided.

  The zener diode 5 is a rectifier that allows the current on the external circuit to flow in only one direction. In particular, when a voltage is generated in the reverse direction on the external circuit, the Zener diode 5 is a constant voltage rectifier that maintains an open circuit voltage below a predetermined voltage. is there. The Zener diode 5 has a characteristic of a breakdown voltage of 0.8V to 1.0V, preferably 0.85V to 0.95V. Here, the Zener diode 5 having a breakdown voltage of 0.85 V is connected to the external circuit 8.

  Since the discharge resistor 6 is always connected, the resistance value of the discharge resistor 6 needs to be set to a sufficiently large value so as not to affect the output characteristics of the fuel cell stack. For example, the power consumption by the discharge resistor 6 is set to be 1% or less of the output of the fuel cell stack. Here, a 200Ω discharge resistor 6 was connected to the external circuit 8.

  When the fuel cell stack is shut down, residual fuel gas remaining in the gas flow channel groove 3 causes the hydrogen gas to be electrolyzed on the fuel electrode side even after the stop, resulting in a potential difference between the fuel electrode and the air electrode, The voltage of the fuel cell 4 rises. However, since the external circuit 8 is always connected, electrons immediately flow to the external circuit 8 and the open circuit voltage of the fuel cell 4 can be lowered.

  In addition, when the fuel cell stack is shut down, the amount of residual fuel gas remaining in the gas flow channel groove 3 of each fuel cell 4 is non-uniform. A potential difference with the fuel cell 4 is generated, and a reverse voltage is applied. In this case, when a reverse voltage equal to or higher than the breakdown voltage is applied to the Zener diode 5, a reverse current flows due to a Zener drop, and the voltage of the fuel cell 4 can be lowered. Therefore, it is possible to maintain an open circuit voltage that is substantially the same as the breakdown voltage of the Zener diode 5.

  When the fuel cell stack was stopped, the voltage of the fuel cell 4 was measured and found to be 0.9V. Furthermore, when the voltage of the fuel cell 4 was measured in an open circuit state where there was no load for a while after the operation of the fuel cell stack was stopped, it was similarly 0.9V. Therefore, the breakdown phenomenon of the discharge resistor 6 and the Zener diode 5 due to the external circuit 8 can prevent an increase in the open circuit voltage due to the residual fuel gas remaining in the fuel cell 4, and the catalyst and catalyst carrier of the fuel cell 4 can be prevented. Can be damaged.

  FIG. 2 is an explanatory view showing an outline of a polymer electrolyte fuel cell according to Embodiment 2 of the present invention. FIG. 2 (a) shows an outline of the polymer electrolyte fuel cell in which the operation of the fuel cell stack is stopped, and FIG. 2 (b) is an illustration of the solid height in the open circuit state after the fuel cell stack stops operating. 1 shows an overview of a molecular fuel cell.

  As shown in FIG. 2 (a), the fuel cell 4 includes a membrane electrode assembly (MEA) 2, a separator 1 that sandwiches the membrane electrode assembly 2, and a gas flow channel groove 3 provided in the separator 1. It is configured. As in FIG. 1, a fuel cell stack is configured by stacking a plurality of fuel cells 4 via a separator 1. The external connection circuit 10 includes a discharge resistor 6, a connection terminal 9, and an electric spring 11. The plurality of connection terminals 9 correspond to each separator 1, and are provided in the vicinity of each separator 1. Further, the external connection circuit 10 includes one discharge resistor 6 between the connection terminals 9 corresponding to the adjacent separators 1. That is, one discharge resistor 6 corresponding to each fuel cell 4 is provided. One electric spring 11 is provided in an external connection circuit 10 having a plurality of discharge resistors 6. The electric spring 11 can move the spring portion of the electric spring 11 by a signal line from the control unit 12. The electric spring 11 mentioned here is an example of a switching unit that mechanically connects or disconnects each connection terminal 9 and each corresponding separator 1, and is not limited thereto.

  When the fuel cell stack stops operation, the residual fuel gas remaining in the gas flow channel groove 3 causes the hydrogen gas to be electrolyzed on the fuel electrode side even after the stop, resulting in a potential difference between the fuel electrode and the air electrode, The voltage of the fuel cell 4 rises. However, when the control unit 12 receives the operation stop signal of the fuel cell stack, the control unit 12 transmits a signal for extending the spring portion of the electric spring 11 to the electric spring 11. The electric spring 11 receives the signal from the control unit 12 and extends the spring unit to press the connection terminal of the external circuit 10 against the separator 1 for connection. Therefore, electrons immediately flow to the external connection circuit 10 and the open circuit voltage of the fuel cell 4 can be lowered.

  As shown in FIG. 2 (b), after the fuel cell stack is shut down, the polymer electrolyte fuel when a voltage is generated on the external connection circuit 10 in the direction opposite to the current flowing in FIG. 2 (a). An outline of the battery is shown. When the operation of the fuel cell stack is stopped, the amount of residual fuel gas remaining in the gas flow channel groove 3 of each fuel cell 4 is not uniform. A potential difference from the battery cell 4 is generated, and a reverse voltage is applied. When the control unit 12 receives a signal that detects the reverse voltage, the control unit 12 transmits a signal for compressing the spring portion of the electric spring 11 to the electric spring 11. The electric spring 11 receives a signal from the control unit 12, compresses the spring unit, and separates the connection terminal 9 of the external circuit 10 from the separator 1. Therefore, since the external connection circuit 10 is immediately disconnected, the fluctuation of the open circuit voltage of each fuel cell 4 can be stopped. At this time, the open circuit voltage of each fuel battery cell 4 becomes a predetermined voltage (for example, 1.0 V) or less, and no local battery is formed in the fuel battery cell 4 to prevent deterioration of the electrode catalyst or catalyst carrier. can do.

  Here, when the fuel cell stack is in normal operation, the external connection circuit 10 is connected to the separator 1 as shown in FIG. 2A, but there is no particular limitation. In this case, the resistance value of the discharge resistor 6 needs to be set to a sufficiently large value so as not to affect the output characteristics of the fuel cell stack. For example, the power consumption by the discharge resistor 6 is set to be 1% or less of the output of the fuel cell stack. Here, a 200Ω discharge resistor 6 was connected to the external connection circuit 8.

  When the voltage of the fuel cell 4 was measured in the state of FIG. 2A in which the operation of the fuel cell stack was stopped, it was 0.9V. Furthermore, when the voltage of the fuel cell 4 is measured in the open circuit state of FIG. 2B, which is a time when there is no load for a while after the fuel cell stack is stopped, it is 0.9 V in the same manner. Therefore, the discharge resistance 6, the electric spring 11, and the control unit 12 provided by the external connection circuit 10 can prevent an increase in open circuit voltage due to residual fuel gas remaining in the fuel battery cell 4, and the fuel cell catalyst or The catalyst support can be damaged.

  As described above, in the two embodiments shown in FIGS. 1 and 2, the discharge of the circuit in which the residual fuel gas remaining in the fuel cell 4 is connected outside the fuel cell stack only by adding a simple device. The consumption by the resistor 6 can prevent the open circuit voltage of the fuel battery cell 4 from increasing. In addition, the reverse voltage generated due to the unevenness of the residual fuel gas can be reduced, the open circuit voltage of the fuel cell 4 can be maintained normally, and the catalyst and catalyst support of the fuel cell 4 can be damaged. it can.

  As described above, according to the present embodiment, in the polymer electrolyte fuel cell including the plurality of fuel cells 4 and the separator 1 sandwiching both sides of each fuel cell 4, the fuel cell is provided on the outer periphery of each separator 1. An external circuit 10 having a discharge resistor 6 and a Zener diode (rectifier) 5 connected between terminals 7 is provided. Therefore, the residual fuel gas existing between the separator 1 and the fuel cell 4 can be consumed by the discharge resistance of the external circuit 10, and the open circuit voltage generated in each fuel cell 4 can be reduced. . In addition, since the Zener diode (rectifier) 5 is provided, it is difficult to pass a reverse current, but when the reverse current is increased, a Zener breakdown or an avalanche breakdown occurs and a current flows rapidly. During this breakdown phenomenon, the voltage change is very small compared to the current change, so that the open circuit voltage can be kept stable at almost the breakdown voltage even if the reverse current is increased. That is, the breakdown phenomenon of the Zener diode (rectifier) 5 having a breakdown voltage below a predetermined value can be used to prevent the reverse voltage from increasing, thereby preventing the catalyst of the fuel cell 4 and the catalyst carrier from being damaged. In addition, since the external circuit 8 has a simple configuration including a Zener diode (rectifier) 5, it is possible to provide a fuel cell stack with reduced cost without damaging the catalyst and catalyst carrier of the fuel cell 4.

  Further, according to the present embodiment, since the external circuit is provided with one discharge resistor 6 and one zener diode (rectifier) 5 between the terminals 7 of the adjacent separators 1, the discharge corresponding to one fuel cell 4 is performed. A resistor 6 and a Zener diode (rectifier) 5 are provided. For this reason, the amount of residual fuel gas remaining in each fuel battery cell 4 is not necessarily the same and is often non-uniform, so that each of the external circuits 8 is in accordance with the residual fuel gas amount of each fuel battery cell 4. The open circuit voltage can be reduced by the discharge resistance. In addition, since a Zener diode (rectifier) 5 having a breakdown voltage equal to or lower than a predetermined value can be applied to each fuel cell, it is possible to prevent a reverse voltage from increasing by using a breakdown phenomenon. Therefore, even if the amount of residual fuel gas in the fuel cell stack is not uniform, the open circuit voltage can be kept low and stable, and damage to the catalyst and catalyst carrier of the fuel cell 4 can be prevented.

  In addition, according to the present embodiment, since the discharge resistor 6 and the Zener diode (rectifier) 5 are connected in series on the external circuit 8, it is possible to reduce power loss due to the discharge resistor 6 during the fuel cell stack operation. Can do. In addition, when the fuel cell stack is started and stopped, an increase in open circuit voltage that occurs during no load and light load can be effectively reduced by the breakdown phenomenon caused by the Zener diode (rectifier) 5. For this reason, it is possible to prevent damage to the catalyst and catalyst carrier of the fuel battery cell 4.

  Moreover, according to this embodiment, the Zener diode (rectifier) 5 has a breakdown voltage of 0.85V to 0.95V. Further, there is a Zener diode (rectifier) 5 having a high accuracy such that the error of the breakdown voltage is 0.1% or less, for example, and the accuracy of the open circuit voltage generated at the time of no load and light load can be increased. Thereby, damage to the catalyst and the catalyst carrier can be prevented without forming a local battery in the fuel cell 4.

  Further, according to the present embodiment, in the polymer electrolyte fuel cell including the plurality of fuel cells 4 and the separator 1 sandwiching both sides of each fuel cell 4, the external connection circuit 10 to which the discharge resistor 6 is connected is the separator. An electric spring (switching means) 11 that mechanically switches connection or disconnection to 1 and a control unit 12 that controls the external spring 10 to connect the electric spring (switching means) 11 to the separator 1 when there is no load. It is composed. Therefore, the external connection circuit 10 having the discharge resistance 6 is connected in a no-load state, and the residual fuel gas interposed between the separator 1 and the fuel cell 4 is consumed by the discharge resistance 6, and each fuel is consumed. The open circuit voltage generated in the battery cell 4 can be reduced. Further, since the external connection circuit 10 has a simple configuration, it is possible to provide a fuel cell stack with reduced cost without damaging the catalyst and catalyst carrier of the fuel cell 4.

  Further, according to the present embodiment, the control unit 12 disconnects the external connection circuit 10 from the separator 1 by the electric spring (switching means) 11 when a reverse voltage on the external connection circuit 10 is generated, and the fuel cell unit. 4 can be prevented from generating a reverse voltage. Since the residual fuel gas remaining in each fuel cell 4 is non-uniform, the fuel cell 4 with a small residual fuel gas has a potential difference with other fuel cells 4 and generates a reverse voltage. By cutting 10, reverse voltage can be prevented, and damage to the catalyst and catalyst carrier of the fuel cell 4 can be prevented.

  Moreover, according to this embodiment, since it consists of the external connection circuit 10 provided with one discharge resistance 6 between each adjacent separator 1, the discharge resistance 6 corresponding to one fuel cell 4 is provided. Therefore, since the amount of residual fuel gas remaining in each fuel cell 4 is not necessarily the same and is often non-uniform, each of the external connection circuits 10 depends on the amount of residual fuel gas in each fuel cell 4. The open circuit voltage can be reduced by the discharge resistance. Further, by disconnecting the external connection circuit 8 from the fuel cell 4 by the electric spring (switching means) 11 before the reverse voltage is applied, it is possible to prevent the reverse voltage from being generated in the fuel cell 4. Therefore, even if the amount of residual fuel gas in the fuel cell stack is not uniform, the open circuit voltage can be kept low and stable, and damage to the catalyst and catalyst carrier of the fuel cell 4 can be prevented.

  Further, according to the present embodiment, the electric spring (switching means) 11 can move the entire external connection circuit 10 to connect or disconnect the separator 1 and the connection terminal 9 of the external connection circuit 10. Therefore, the separator 1 and the external connection circuit 10 can be connected or disconnected with a simple configuration, and a fuel cell stack can be provided with reduced costs without damaging the catalyst and catalyst carrier of the fuel cell 4.

  Thus, according to the present invention, when the fuel cell stack is unloaded and lightly loaded, an increase in open circuit voltage due to residual fuel gas remaining in the fuel cell 4 is prevented, and the catalyst of the fuel cell 4 A fuel polymer electrolyte fuel cell having a simple fuel cell stack can be provided without damaging the catalyst carrier.

  In this embodiment, although the electric spring 11 is provided as a switching means, it is not specifically limited. For example, it may be moved by an electric solenoid or an electric motor.

  Moreover, in this embodiment, the detection apparatus which detects a reverse voltage or the electric current of a reverse direction, and transmits to the control part 12 is not specifically limited. Further, the installation position of the detection device may be a location where the reverse voltage or the current in the reverse direction of the fuel cell 1 can be detected. For example, a voltmeter is provided as a detection device on the external connection circuit 10 and the value of the voltmeter is constantly monitored by the control unit 12. When the control unit 12 detects a reverse voltage greater than a predetermined value, the control unit 12 is a switching unit. A signal for controlling the electric spring 11 may be transmitted.

  Further, in the present embodiment, the number of installed switching means is not limited. For example, by providing the discharge resistor 6 and the switching means 11 for each fuel cell 4, it becomes possible to switch the switching means 11 for each fuel cell 4, and the residual fuel gas is uneven in the fuel cell stack. However, since the residual fuel gas can be consumed for each fuel cell 4, the open circuit voltage can be kept low and stable, and damage to the catalyst and catalyst carrier of the fuel cell can be prevented.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications may be made within the scope of the gist of the present invention described in the claims. It can be changed.

1 Separator 2 Membrane / Electrode Assembly (MEA)
DESCRIPTION OF SYMBOLS 3 Gas flow path groove 3a Fuel electrode side gas flow path groove 3b Air electrode side gas flow path groove 4 Fuel cell 5 Zener diode 6 Discharge resistance 7 Terminal 8 External circuit 9 Connection terminal 10 External connection circuit 11 Electric spring 12 Control part 21 Electrolyte membrane 22 Fuel electrode catalyst layer 23 Air electrode catalyst layer 24 Protective film 26 Fuel electrode diffusion layer 27 Air electrode diffusion layer

Claims (12)

In a fuel cell stack in which a plurality of fuel cells are stacked via a separator,
An external circuit in which the terminals provided on the outer periphery of each separator are connected to each other outside the fuel cell; and
A discharge resistor for applying a load on the external circuit;
A solid polymer fuel cell, comprising: a rectifier that allows current on the external circuit to flow in only one direction. The external circuit is connected between the terminals of the separators adjacent to each other,
2. The polymer electrolyte fuel cell according to claim 1, wherein one discharge resistor and one rectifier are provided for each of the terminals. 3. The polymer electrolyte fuel cell according to claim 1, wherein the discharge resistor and the rectifier are connected in series on the external circuit. The rectifier is a constant voltage rectifier that holds the voltage below a predetermined voltage when a voltage is generated in a direction opposite to the one direction in which the current on the external circuit flows. 4. The polymer electrolyte fuel cell according to any one of 3 above. The said constant voltage rectifier has a breakdown voltage of 0.8V to 1.0V, which is the predetermined voltage held between the separates when the reverse voltage is generated. 5. The polymer electrolyte fuel cell according to 4. The constant voltage rectifier has a breakdown voltage of 0.85V to 0.95V, which is the predetermined voltage held between the separates when the reverse voltage is generated. 5. The polymer electrolyte fuel cell according to 4. The polymer electrolyte fuel cell according to claim 4, wherein the constant voltage rectifier is a Zener diode. In a fuel cell stack in which a plurality of fuel cells are stacked via a separator,
An external connection circuit having a connection terminal connected to the outer periphery of each separator;
A discharge resistor for applying a load on the external connection circuit;
Switching means for mechanically connecting or disconnecting each connecting terminal and each corresponding separator;
Control means for controlling the mechanical connection between the connection terminals and the corresponding separators by the switching means when the fuel cell stack is in an unloaded state. Fuel cell. The control means mechanically disconnects the connection terminals and the corresponding separators by the switching means when a voltage is generated in a direction opposite to the one direction in which the current on the external connection circuit flows. 9. The polymer electrolyte fuel cell according to claim 8, wherein control is performed. The external connection circuit is connected between the connection terminals corresponding to the adjacent separators,
10. The polymer electrolyte fuel cell according to claim 8, wherein the discharge resistor is provided for each of the connection terminals. 11. The switch according to claim 8, wherein the switching unit moves the entire external connection circuit under the control of the control unit to connect or disconnect the connection terminals and the corresponding separators. A polymer electrolyte fuel cell according to claim 1. 12. The polymer electrolyte fuel cell according to claim 8, wherein the switching means is an electric spring that is movable under the control of the control means.

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