JP2006086034A - Solid polymer type fuel cell method, fuel cell system, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stop a solid polymer type fuel cell without causing deterioration of a cell due to a stop operation and without using an inert gas. <P>SOLUTION: This is an operating method of the solid polymer type fuel cell which has a fuel cell having a solid polymer type electrolyte film to separate a fuel gas and an oxidizer gas, a short-circuit device, an inverter connected in parallel to the fuel cell and the short-circuit device, and a control device to control a fuel cell system, and which includes a step to control so that at least an anode potential at the time of an open circuit will exist between the lowest potential (LP) and the highest potential (HP) of a prescribed anode potential and cathode potential by connecting the short-circuit device and the fuel cell and by making the external short-circuit current flow in stopping of the fuel cell, or to control so that a crossing point of the anode potential and the cathode potential at the time of the open circuit will exist between the lowest potential (LP) and the highest potential (HP) of the prescribed anode potential and cathode potential. A recording medium in which a fuel cell system and a control program of the fuel cell system capable of computer reading are recorded is also disclosed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid polymer fuel cell operating method, a fuel cell system, and a computer-readable recording medium capable of operating a battery system without causing a performance degradation of the fuel cell.

  The polymer electrolyte fuel cell has advantages such as high output, long life, little deterioration due to start / stop, low operating temperature (about 70-80 ° C), and easy start / stop. Have. For this reason, a wide range of uses such as power sources for electric vehicles, distributed power sources for business use and home use are expected.

  Among these applications, a distributed power source (for example, a cogeneration power generation system) equipped with a polymer electrolyte fuel cell takes out electricity from the polymer electrolyte fuel cell, and at the same time, generates heat from the battery during power generation with hot water. It is a system that tries to make effective use of energy by collecting as Such a distributed power source is required to have a service life of 50,000 hours or more as a period of use, and improvements in membrane-electrode assemblies, cell configurations, power generation conditions, and the like are being promoted. Further, regarding the entire power generation system equipped with a fuel cell, it is desired by the user that the output and the decrease in power generation efficiency due to repeated start-stop are as small as possible. In particular, it is known that when the system is stopped, it is necessary to remove the fuel gas (combustible gas) from the inside of the fuel cell in order to prevent the output voltage from decreasing (Patent Document 3). As this related technology, in the past, a stop technology (Patent Documents 1 and 2) using an inert gas purge in a phosphoric acid fuel cell system is known. In addition, in order to save space in the power generation system and downsize equipment, a stopping method that does not use an inert gas is desired, and a stopping method of a polymer electrolyte fuel cell by an external short-circuit method using a resistor is also known. (Patent Document 3).

  When the power generation system equipped with the polymer electrolyte fuel cell is stopped, the output may decrease depending on the conditions due to repeated start-stop of the system, that is, start-stop of the polymer electrolyte fuel cell. In particular, when the fuel cell is stopped, there are fuel gas and oxidizing gas contained in the cell, and in the plane of the membrane-electrode assembly, local cells are formed and the platinum catalyst fine particles in the electrode aggregate, It is estimated that the output voltage will drop. In order to suppress this, it is necessary to remove the fuel gas. Conventionally, a method of purging by supplying an inert gas to the battery has been adopted (Patent Document 3).

  As another method, first, the fuel gas and the oxidizing gas are reacted by an external short circuit through a resistor provided outside the battery in a state where the supply of the fuel gas is stopped and the valve of the fuel gas outlet is also closed. There is.

  When a stop operation is adopted in which the cell voltage is short-circuited through a resistor and the cell voltage is lowered while the cell voltage is monitored, the anode and cathode potentials are in a potential region where a degradation reaction occurs at the end of the operation. Cell degradation can occur. Whether the cell voltage is in a potential state where a deterioration reaction can occur even if only the cell voltage is monitored when the potential of one of the electrodes fluctuates and the other potential moves following the cell voltage. It cannot be determined whether or not.

JP-A-7-183039 Japanese Patent Laid-Open No. 10-144334 Japanese Patent Publication No. 7-93147 Electrochemistry, Vol. 71, No. 9, 898-899, 2003

  An object of the present invention is an operation method of a fuel cell, a fuel cell system, and an operation of the fuel cell system that can stop the fuel cell without causing an inert gas supply device or the like without causing a decrease in the performance of the fuel cell. It is to provide a recording medium in which the driving information is recorded.

  The present invention includes a fuel cell having a solid polymer electrolyte membrane that separates fuel gas and oxidant gas, an inverter connected in parallel to the fuel cell, and a short-circuit device, and when the fuel cell is stopped, The short-circuit device and the fuel cell are connected to cause an external short-circuit current to flow, and at least the final potential of the anode immediately before stopping the current is between a predetermined lower limit potential (LP) and an upper limit potential (HP). The end potential of the anode and the cathode when the current does not flow when the potentials of the anode and the cathode coincide with each other and the cell voltage becomes zero is set to the predetermined lower limit potential (LP) and the upper limit potential (HP). The present invention provides a method for operating a polymer electrolyte fuel cell, comprising the step of controlling the fuel cell to exist between the two.

  The present invention also provides a fuel cell having a solid polymer electrolyte membrane that separates a fuel gas and an oxidant gas, a fuel manufacturing apparatus that supplies a fuel degas to the fuel cell, and an oxidant gas supplied to the fuel cell. A supply device, an inverter for converting the output of the fuel cell, a short circuit device connected in parallel to the fuel cell and the inverter, and a control device for controlling the operation of the fuel cell, the control device comprising: Based on the stop signal of the fuel cell, the supply of fuel gas to the fuel cell is stopped, the short-circuit device and the fuel cell are connected, an external short-circuit current is passed, and the end potential of the anode immediately before stopping the current is The current is controlled by at least a predetermined lower limit potential (LP) and an upper limit potential (HP) being present, or when the anode and cathode potentials coincide with each other and the cell voltage becomes zero. A solid polymer fuel characterized by controlling the end potential of the anode and cathode when no longer flows between a predetermined anode potential and a lower limit potential (LP) and an upper limit potential (HP) of the cathode potential A battery system is provided.

  Furthermore, the present invention provides a fuel cell system operation program and a fuel cell system start / stop program, and a lower limit potential (LP) and an upper limit potential (HP) of an anode potential and a cathode potential at the time of an open circuit. It is an object of the present invention to provide a recording medium in which data obtained in advance as operating characteristics is recorded on a computer-readable medium.

  By the operation method of the present invention, an inert gas purge facility can be omitted.

  A specific configuration example of the present invention includes a polymer electrolyte fuel cell having a polymer electrolyte membrane that separates a fuel gas and an oxidant gas, a short circuit device, an inverter, the inverter for the fuel cell, and the short circuit. The switch for switching the connection of the apparatus, the fuel cell has a supply pipe and a discharge pipe for the fuel gas and the oxidant gas, and a supply valve and a discharge valve connected to the supply pipe and the discharge pipe. The short-circuit device may include a fixed resistor, a variable resistor, and the like.

  According to the present invention, when the fuel cell is stopped, the fuel gas supply valve is closed, and at the end of the flow of the current that is short-circuited through the short-circuit device, at least the anode potential is lower than the potential in the open circuit by a predetermined lower limit. The step of stopping the fuel cell is performed while maintaining the potential (LP) to be equal to or higher than the upper limit potential (HP) and avoiding adverse effects on the anode and a decrease in battery performance.

  By controlling the potentials of the anode and cathode within the potential range defined in the present invention, the oxidation reaction on the catalyst layer of the anode or cathode can be performed even in the case of multi-stacked cells (so-called cell stacks), even if some cells are reversed. Or it can prevent deteriorating by a reductive reaction. For example, when the voltage is positive in the entire cell stack and an external short-circuit current is allowed to flow, if the anode potential of each cell is within the range of LP and HP, the anode potential of some cells is the cathode. Even if it becomes higher than the potential (so-called inversion), if it is within this range, only the oxidation reaction to the extent that an oxide film is formed on the Pt catalyst proceeds, and the catalyst layer is greatly damaged. Can be avoided. Also, in the cathode, if the potential is higher than LP, deterioration due to the generation of hydrogen peroxide can be avoided even if the potential becomes lower than that of the anode (that is, even if the polarity is reversed).

  The control device includes a control circuit that operates a program for operating the valve and the changeover switch. Furthermore, an opening / closing device for supplying fuel gas and oxidant gas to the fuel cell can be provided.

  The control device controls a switching device that supplies fuel gas and oxidant gas to the fuel cell. Further, the control device performs control so that the intersection between the anode potential and the cathode potential is within the range of LP and HP. As another control method, immediately before stopping the external short-circuit current due to the short-circuiting device, at least the end potential of the anode is in the range of LP and HP, and in the open circuit state after stopping the external short-circuit current, If the circuit does not return to the open circuit voltage before the stop operation, it may be omitted to continue the external short circuit to the intersection. It is preferable to include a step of delaying the supply of the fuel gas and / or the oxidant gas as necessary.

  The control device can control the cathode supply valve to be closed after a predetermined time has elapsed after the external short-circuit current starts flowing through the short-circuit device in a state where the fuel gas supply valve is closed. The LP is preferably set to 0.2 V to 0.8 V, the HP is set to 0.2 V to 0.8 V, and LP <HP. In addition, since the starting potentials of hydrogen adsorption-desorption and oxygen adsorption-desorption on Pt occur in the vicinity of 0.4 V and 0.7 V, respectively, LP can be set to 0.4 to 0 if more precise control can be performed. It is desirable that the range of .5V and HP be 0.6 to 0.7V. Thereby, the lifetime improvement of a cell can be achieved more effectively.

  The control device can control the supply of the fuel gas and / or the oxidant gas to be delayed so that the intersection or the end potential exists in the range of the LP and HP. The control device also includes an operation program for the fuel cell system, a start / stop program for the fuel cell system, and a lower limit potential (LP) and an upper limit potential (HP) of the anode potential and the cathode potential at the time of the open circuit. It is desirable to store data obtained in advance as operation characteristics as a database. The database can be recorded on a computer-readable recording medium. As the recording medium, an arbitrary medium such as a magnetic disk, a magnetic tape, a flexible magnetic disk, an IC card, or a compact disk can be used.

  The data may include a program for controlling the intersection of the anode potential and the cathode potential to be within the range of the LP and HP. The data may include a program that delays the supply of fuel gas and / or oxidant gas.

  As a specific configuration example of the fuel cell system of the present invention, a fuel cell system including a reformer that supplies fuel gas to a stack and a control device for closing a supply valve for supplying fuel gas or air to the fuel cell There is. As another specific configuration example, before the supply valve and the discharge valve for hydrogen gas are closed, the polymer electrolyte fuel cell and the short-circuit device are connected, the external current flowing through the short-circuit device is taken out, and the hydrogen in the fuel gas is removed. There are power generation systems that include a controller that controls the resistor to oxidize. The fuel cell system may include a control device for closing a discharge valve for discharging fuel gas or air from the fuel cell.

  Hereinafter, the concept and characteristics of the present invention for stopping the power generation system will be described. First, FIGS. 1 to 10 will be described using reference numerals.

  FIG. 1 is a conceptual diagram showing a relationship between an open circuit voltage of an anode and a cathode for explaining a stop operation process of a fuel cell system in an embodiment of the present invention. 1a is a power generation state immediately before the stop operation, 1b is 1c is an operation for closing the fuel gas supply / discharge valve and turning on the resistor, and 1c is an operation for closing the oxidant gas supply / discharge valve and keeping the resistor on.

  FIG. 2 is a conceptual diagram when the relationship between the open circuit voltage of the anode and the cathode in the fuel cell stop operation process is inappropriate. 2a closes the fuel gas supply / discharge valve and turns on the resistor. The operation 2b is an operation for closing the supply / discharge valve of the fuel gas and the oxidant gas and turning on the resistor.

  FIG. 3 is a conceptual diagram of another example in the case where the relationship between the open circuit voltage of the anode and the cathode is inappropriate in the fuel cell stop operation process. The operation to turn on, 3b closes the fuel gas supply / discharge valve, and the resistor turns on, 3c delays the time to close the oxidant gas supply / discharge valve than 1b in FIG. This is an operation to keep the resistor on.

  FIG. 4 is a conceptual diagram for explaining a method of measuring an anode potential in an open circuit. 4a is a power generation state immediately before a stop operation, 4b is a fuel gas supply / discharge valve closed, and air is supplied to the cathode side. This is an operation to turn on the resistor.

  FIG. 5 is a conceptual diagram for explaining a method of determining the anode potential from the end state Q. 5a is a power generation state immediately before the stop operation, 5b is a state in which the fuel gas supply / discharge valve is closed and air is supplied to the cathode side. 5c is an operation of turning on the resistor and turning off the resistor, opening the fuel gas supply / discharge valve, and supplying the fuel gas to the anode side.

  FIG. 6 is a conceptual diagram for explaining a cathode potential measurement method in an open circuit, 6a is a power generation state immediately before a stop operation, 6b is a oxidant gas supply / discharge valve closed, and fuel gas is connected to the anode side. This is an operation to keep the resistor on.

  FIG. 7 is a conceptual diagram for explaining a method of determining the cathode potential from the end state R. 7a is a power generation state immediately before the stop operation, 7b is a state where the oxidant gas supply / discharge valve is closed and the anode side is closed. An operation of continuing the supply of the fuel gas and turning on the resistor, and 7c is an operation of turning off the resistor, opening the oxidant gas supply / discharge valve, and supplying air to the cathode side.

  FIG. 8 is a conceptual diagram for explaining a method for adjusting a termination condition in an embodiment of the present invention, where 9a is a power generation state immediately before the stop operation, and 9b is a supply / discharge valve for fuel gas and oxidant gas. This is an operation to close and turn on the resistor.

  FIG. 9 is a conceptual diagram for explaining another adjustment method of the termination condition in the embodiment of the present invention. 10a is a power generation state immediately before the stop operation, 10b is an oxidant gas supply than 1b in FIG. An operation for delaying the time for closing the discharge valve and keeping the resistor on, 10c is an operation for closing the oxidant gas supply / discharge valve and keeping the resistor on.

  When switching to the stop mode of the power generation system, it is normal that the power generation state has been reached by then. As shown in FIG. 1 (1a), the potential of each electrode at this time is such that the anode is higher than the OCV (anode) and the cathode is lower than the OCV (cathode). Become a voltage. Note that OCV is an abbreviation for open circuit voltage.

  Next, in order to shift from the power generation state to the stop state, the first step of the stop mode is to allow the current supplied from the fuel cell stack to the inverter to flow through the resistor by the changeover switch. In this way, gas shortage power generation can be avoided. At this time, as shown in (1b) of FIG. 1, since the current flowing through the resistor is smaller than the current in the power generation state, the potential may fluctuate slightly.

  When stopping the supply of the fuel gas, the fuel gas supply valve and the discharge valve at the front and rear of the stack are closed. The gas supplied until immediately before the valve closing operation may be a fuel gas containing hydrogen gas at a concentration required for normal power generation, or a fuel gas having a lower hydrogen concentration than during normal power generation. May be.

  A current flows through the resistor that short-circuits the external terminal of the stack, and the potential of the anode in the open circuit (zero in FIG. 1) gradually increases due to the oxidation of hydrogen, as shown in FIG. 1 (1c). .

  In the case of the oxidant gas, a constant potential is shown in a normal power generation state (FIG. 1 (1a)), and the same as the anode. Thereafter, the cell is short-circuited by the resistor after the condition shown in FIG. In FIG. 1, as a representative example, the supply of air to the cathode side is continued immediately before the state shown in FIG. 1 (1c).

  Immediately after the operation shown in FIG. 1 (1c), an operation of closing the cathode supply side and discharge side valves is performed. Since the oxygen concentration inside the stack decreases by closing the valve, the cathode potential decreases. When the intersection of the cathode potential and the anode potential is P, the potential of both electrodes is between LP and HP when the cell voltage is zero. If the deterioration reaction is unlikely to occur in each electrode in the potential region divided by LP and HP, cell deterioration due to the stop operation can be suppressed. FIG. 2 shows a case where the cathode valve closing time is set simultaneously with the anode valve closing time, and the cathode potential is smaller than LP. In this case, oxygen present in the cathode flow path of the stack partitioned by the valve is insufficient, and the cathode potential becomes too low, so hydrogen peroxide is likely to be generated. Oxidative degradation occurs.

  FIG. 3 shows a case where the cathode valve closing time is set later than that in FIG. 1 and the cathode potential becomes higher than HP. In this case, contrary to FIG. 2, there is a shortage of hydrogen present in the anode flow path of the stack partitioned by the valve, and the anode potential becomes too high, so an electrode catalyst (platinum, ruthenium, etc.) There is a possibility that metal dissolution, dissolution of conductive material (carbon), catalyst deterioration due to oxidation, and oxidation of separator material may occur.

  Next, a specific procedure for determining the termination condition for the stop operation of the present invention will be described. In the state where the stack is assembled in the power generation system, it is assumed that there is a valve for each of the fuel gas and oxidant gas of the stack on the supply side and the discharge side. When the valve is closed, the fuel gas and the oxidant gas can be confined in a space (hereinafter referred to as gas occupied volume) closed by the valves at both ends. The space includes a gas pipe, a pipe connector, a manifold and a channel in the stack.

  First, the power generation state immediately before the stop operation is determined. Here, the gas flow rate and load current are determined in consideration of the system operation method. Next, the resistance value of the resistor is determined. The resistance value of the resistor used in the present invention is determined according to the following conditions depending on the number of stacked cells. Assuming that the lower limit value of the resistance distributed per cell is 0.5Ω or more, the voltage at the time of open circuit is about 1 V, the electrode area is 100 cm2, and the short-circuit current density per cell is larger than 20 mA / cm2. It is possible to avoid current, and it is possible to prevent inversion of some cells in the stack.

  Depending on the type of stack (that is, the cell structure, the characteristics of the membrane-electrode assembly, etc.), when the current density per cell is large, some cells in the stack may be inverted. In order to prevent this, it is desirable to set the current per cell to be 0.1 mA / cm 2 or less. That is, the resistance value per cell under this condition corresponds to 1Ω or more.

  On the other hand, if a resistor with a very large resistance is used, the short-circuit current becomes too small and it takes time until the end of the stop, or the cell voltage decreases when the cell voltage is high for a long time. Occurs. For this reason, the upper limit value of the resistance needs to be 50Ω (current density is 0.2 mA / cm 2) or less. For example, when the occupied volume of the above-described fuel gas is 600 cc (based on 0 ° C.) and the hydrogen concentration is 70%, the number of moles of hydrogen contained in the occupied volume is 0.019 mol. Assuming that this hydrogen is completely oxidized at a constant current, in order to make the external short circuit time of the stack within 10 minutes, the short circuit current needs to be 1.2 mA / cm 2 or more with 50 stacked cells and an electrode area of 100 cm 2. is there. Therefore, the resistance value is about 850Ω (when the voltage between terminals is 1V).

Therefore, in the present invention, the upper limit resistance value HR is obtained by the following equation.
HR = n.V.C.F / (N.S.t) (Equation 1)
Where n is the number of oxidized electrons (2 for hydrogen), V is the fuel gas occupied volume, C is the hydrogen concentration, N is the number of cells in the stack, S is the electrode area per cell, and t is the time limit for external short circuit It is.

  The resistance value of the resistor used in the present invention is variable, or a plurality of resistors having different resistance values are prepared, and at the initial stage of a short circuit, an excessive current is passed to prevent the cell voltage of the stack from being inverted. It is possible to shorten the short circuit time by increasing the resistance value because the cell voltage decreases at the end of the short circuit and the cell voltage decreases at the end of the short circuit.

  Next, a method for determining supply / stop conditions for the oxidant gas will be described. As will be described later, the procedure for determining this stop condition is as follows: (1) Evaluation of the behavior of the anode potential, (2) Evaluation of the behavior of the cathode potential, (3) Supplying the oxidant gas based on these data It consists of three processes: determining the closing timing of the discharge valve.

  First, the test method (1) will be described with reference to FIG. In the state where the stack is actually incorporated in the power generation system, first, the oxidant gas is supplied at the gas flow rate immediately before the stop operation, and is continuously supplied to the stack while the short-circuit current by the resistor is flowing. Under this condition, only the fuel gas supply is shut off by closing the fuel gas supply valve after the resistor is connected. The valve on the anode discharge side is also closed. Thereafter, only the potential of the anode is increased, so that the cell voltage is decreased.

  The anode potential can be measured by bringing a reference electrode into contact with the electrolyte membrane (Non-Patent Document 1).

  In many cases, it is difficult to attach a stack mounted on an actual power generation system. Therefore, in the present invention, the anode potential can be determined by a simple method described below (FIG. 5). In the state at the time of termination Q in FIG. 5, the gas discharge valve and the supply valve on the anode side are opened, and the gas corresponding to the normal power generation is supplied again to the anode side. Simultaneously with the start of supply, the cell voltage increases and an open circuit voltage (OCV) is obtained. The voltage change ΔVa changed at this time is measured. At the same time as the cell voltage rises, the anode potential drops from the Q position and returns to the potential at the open circuit (FIG. 5). Since the cell voltage change before and after the gas supply to the anode side coincides with the anode potential change ΔVa, the anode potential at the end time Q can be obtained.

  Next, the test method (2) will be described with reference to FIG. In a state where the stack is actually incorporated in the power generation system, first, the fuel gas is continuously supplied to the stack at the gas flow rate immediately before the stop operation while the short-circuit current by the resistor is flowing. Under this condition, only the supply of the oxidant gas is shut off by closing the oxidant gas supply valve after the resistor is connected. The valve on the cathode discharge side is also closed. Thereafter, only the potential of the cathode is lowered, so that the cell voltage is lowered.

  The cathode potential can also be determined by the same method described in FIG. 5 (FIG. 7). In the state of R at the end of FIG. 7, the gas discharge valve and the supply valve on the cathode side are opened, and air corresponding to normal power generation is supplied again to the cathode side. Simultaneously with the start of supply, the cell voltage increases and an open circuit voltage (OCV) is obtained. The voltage change ΔVc changed at this time is measured. At the same time as the cell voltage rises, the cathode potential drops from the R position and returns to the potential at the time of the open circuit (FIG. 7). Since the cell voltage change before and after the gas supply to the cathode side coincides with the cathode potential change ΔVc, the cathode potential at the end time R can be obtained.

  When the two graphs of FIGS. 4 and 6 are overlaid, FIG. 1 is obtained. Here, LP is defined as the lower limit potential, and HP is defined as the upper limit potential. It is desirable that LP be at a potential in a state where adsorbed hydrogen on the anode platinum catalyst is desorbed. That is, it becomes about 0.4V with respect to the anode potential at the time of OCV. However, even if a small amount of adsorbed hydrogen remains, the cell does not deteriorate immediately, and there is no problem even if it is set in the range of 0 to 0.4 V in consideration of the useful life of the stack.

  On the other hand, HP is set to a potential at which an oxidation reaction starts on the anode electrode. Since an ordinary Pt catalyst has a voltage of 0.7 to 0.8 V, the HP is desirably 0.8 V or less. Considering the cathode potential, since the reduction reaction from oxygen to hydrogen peroxide is about 0.7 V, if the potential of P is too low, the electrolyte membrane may be deteriorated by hydrogen peroxide. Therefore, it is advantageous that the P point is as close as possible to the HP because cell deterioration can be prevented.

  The case of FIG. 1 is an example in which the intersection point P is between LP and HP, and even if the anode and cathode valves are closed almost at the same time, the potential of the anode and cathode is in a potential range where cell deterioration reaction is unlikely to occur. You can stop the stack.

  If the P point exceeds HP, the anode may deteriorate, so the time for closing the oxidant gas valve is delayed from the time for closing the anode supply valve, and the potential of P is shifted to the low potential side. Can be made. The idea is shown in FIG.

  On the other hand, when the P point is lower than LP, the oxygen at the cathode is insufficient, so that the hydrogen at the anode cannot be oxidized sufficiently. In this case, conversely, the potential of P can be made higher than LP by closing the cathode supply valve first and delaying the time for closing the fuel gas supply valve from the closing time of the cathode supply valve. The idea is shown in FIG.

  As described above, by controlling the closing timing of the anode and cathode supply valves, the potential of the anode and cathode at the time of termination can be controlled so as to be in a potential region where the cell deterioration reaction hardly occurs. In the present embodiment, the end point of the stop operation (the timing at which the external short-circuit current becomes zero) is the state of intersection in FIG. 1, but it is also possible to stop in the state before that. What is necessary is just to make it so that the end potential of the anode immediately before turning off the short-circuiting device is between LP and HP, and the cathode becomes more than LP. In this way, hydrogen is oxidized and removed on the anode side, and generation of hydrogen peroxide can be suppressed at the cathode, so that a decrease in cell voltage can be avoided.

  To open and close the resistor changeover switch and the valve, a controller having a calculation function mounted on the power generation system can be used, and the operation of the changeover switch and the like can be controlled from the controller via the signal cable. The controller can record the operation conditions in advance, thereby enabling repeated operations. It is also possible to predict the potential change of the anode and the cathode due to deterioration of the stack and change the valve opening / closing operation according to the operation time.

  12 (a), (b), and (c) each show three stopping methods, FIG. 12a is a flowchart of the first stop step, FIG. 12b is a flowchart of the second stop step, and FIG. A flow chart of the steps is shown, and the stop step in the operation method of the fuel cell system of the present invention is simplified and shown. A database as shown in the upper right of FIG. 12a is prepared on a computer-readable recording medium, and the fuel cell system is operated by the control device based on this data. Of particular importance is the acquisition of LP and HP data determined as described above, and further comparison of anode potential, cathode potential with LP and HP, stopping of fuel gas and oxidant gas, etc. It is also necessary to prepare a database. The procedure in FIG. 12 can be easily understood from the following description.

The stop control database of the present invention has the following data.
(1) Lower limit potential (LP)
(2) Upper limit potential (HP)
(3) Profile program of anode potential and cathode potential (4) Cell voltage or cell stack voltage calculation program (5) Comparison program of anode potential, cathode potential and LP, HP (6) Stop supply of fuel gas and oxidant gas Program (7) Short-circuit device control program.

  This database is also used in the stop second step and stop third step. LP can be set in the range of 0.2V to 0.8V, and HP can be set in the range of 0.2V to 0.8V. However, LP <HP. The profile program of anode potential and cathode potential (hereinafter referred to as potential profile program) of (3) is data as shown in FIG. 4 and FIG.・ It is necessary to create a program.

  In the cell voltage or cell stack voltage calculation program of (4), the anode potential and the cathode potential are calculated based on the data of the previous potential profile program based on the relationship between the data such as the cell voltage and the current and time passed through the short-circuit device. The purpose is to calculate. The comparison program of (5) compares the calculated value of this potential with LP or HP. The fuel gas / oxidant gas supply stop program of (6) is a program for operating the valves of the gas supply system and the exhaust system. The short-circuit device control program of (7) is for operating on / off of the short-circuit device and the current value in order to consume the hydrogen present in the cell by the external short-circuit current.

  Next, the control sequence of the present invention will be described. The control of the present invention is roughly divided into three parts. Hereinafter, a specific example will be described with reference to FIG. The first stop step is a portion for starting a stop operation after the controller receives a stop signal. After receiving the stop signal, an operation of disconnecting from an external load such as an inverter is performed (the right end of 9 (a) in FIG. 9). That is, the switch with the external load is turned off. Next, the fuel gas supply from the reformer and the hydrogen cylinder is stopped. This stop operation may be omitted because the subsequent operation of the anode gas switch is scheduled. Next, a short-circuit device is connected so that an external short-circuit current flows from the cell stack. Next, the gas supply stop program (6) is operated to stop the supply of fuel gas (9 (b) in FIG. 9).

  In the second stop step, the cathode gas supply stop timing is determined, and the cathode gas supply is stopped. First, anode and cathode potential calculation processing is performed. At this time, as information from the cell stack, voltage of the entire stack or cell voltage data is measured. Since this voltage is the difference between the anode potential and the cathode potential, the respective potentials cannot be simply obtained. Therefore, in the present invention, the potential profile program of (3) is used to calculate from the relationship between the external short-circuit current and time, and predict the potential of the anode and the cathode. That is, the potential of the anode and the cathode can be obtained by calculating which potential on the potential profile is based on the integral value (electric quantity) of the short-circuit current.

  From this result, the timing for stopping the cathode supply is calculated. For example, when the method (a) of FIG. 12 is applied to the stop operation of FIG. 9, the supply of the cathode gas is continued until the cell voltage reaches a certain set voltage. In FIG. 9, the cell voltage is represented by the difference between the anode potential and the cathode potential. While the cathode gas is supplied (9b in FIG. 9), when the cell voltage reaches the set value (the left end of 9c in FIG. 9), the cathode gas switch is driven to stop the supply of the cathode gas.

  Similarly, there is also a method of managing the supply of cathode gas by time (method FIG. 12B). In this case, the supply of the cathode gas is continued with the short-circuit current flowing until a certain set time (standby time) elapses (9b in FIG. 9). When the set time is reached (the left end of 9c in FIG. 9), the cathode gas switch is driven to stop the supply of the cathode gas.

  In the second stop step, * 1; the cathode gas switch drive timing (set voltage) is calculated based on the anode and cathode potential profile program. When the cell stack voltage or the cell voltage does not reach the set voltage, the process returns to the previous step. When the set voltage is reached, proceed to the next step.

  * 2: Calculate the cathode gas switch drive timing (standby time) based on the anode and cathode potential profile program. When the elapsed time from the drive time of the anode gas switch does not reach the standby time, the process returns to the previous step. When the waiting time is reached, the process proceeds to the next step.

  In the third stop step (FIG. 12C), the anode and cathode potentials are calculated from the cell voltage or the stack voltage with the supply of the anode and cathode gases closed. In the calculation, the potential profile program and the current and time data that have been passed through the short-circuit device are used. The magnitude relationship between the anode or cathode potential and HP and LP is compared.

  In the third stop step, * 3; the anode and cathode potentials are predicted (calculated) based on the anode and cathode potential profile program. When both the anode potential and the cathode potential are in the range of LP and HP, the process proceeds to the next step. When the anode potential is lower than LP or the cathode potential is higher than HP (provided that the condition is not * 4), the process returns to the previous step.

  * 4: When the anode potential is higher than HP and the cathode potential is lower than LP, the process of * 4 is performed as a failure process, and finally an alarm is displayed.

  Next, the magnitude relationship between the obtained potential and LP or HP is evaluated. When the anode potential and cathode potential are both in the range of LP and HP, proceed to the next step, disconnect the short-circuit measure (set the external short-circuit current to zero), drive the switchgear, and stop the fuel cell. This operation ends.

  Note that the opening / closing device is driven in such a manner that air is naturally sucked to the cathode side, the cathode pressure inside the stack is returned to atmospheric pressure, and the restart after the stop is facilitated. Further, if hydrogen on the anode side is removed, air can be supplied also to the anode side, and both the anode and the cathode can be stored at atmospheric pressure. This may be advantageous in that it can avoid problems such as poor sealing due to the pressure difference between the anode and the cathode. However, in the present invention, the driving of the switchgear may be omitted depending on the type of system.

  When the cathode potential is higher than HP in the state of 9 (c) in FIG. 9, the process returns to the anode / cathode potential calculation step. When both the anode potential and the cathode potential are in the range of LP and HP, the process proceeds to the step of disconnecting the short circuit device.

  If the anode potential is higher than HP but the cathode potential is higher than HP due to some trouble, if the anode potential exceeds HP and the cathode potential falls below LP, both the anode potential and cathode potential become lower than LP. In an abnormal state such as a case, the sequence proceeds to a warning display sequence. In these cases, after the short-circuit device is disconnected and the switchgear is driven, this operation is terminated by displaying an alarm.

  Although this operation has been described with reference to FIG. 9, when it is necessary to delay the time for closing the anode gas supply valve, the cathode gas supply continues and the anode gas switch is closed at the end of the second step. Drive.

The contents of the present invention will be described below with reference to examples. In addition, this invention is not limited to the Example described below.
Example 1
A conventional battery configuration is shown in FIGS. FIG. 10A is a cross-sectional view showing an outline of the fuel cell system of the present invention, and FIG. 10B is an enlarged view of a portion indicated by a dotted circle in FIG.

  The power generation unit is a single cell, and DC power is taken out from the fuel cell by a multi-layered cell of usually several tens of cells or more. In this embodiment, the number of cells is 80. This single cell is composed of a membrane-electrode assembly (a membrane consisting of 102 and 103 in FIG. 10B) having electrode layers on both sides of a solid polymer electrolyte membrane and two separators 104 sandwiching the membrane-electrode assembly. A gasket 105 was inserted between the separators 104. An enlarged view of the periphery of this membrane-electrode assembly is shown in FIG. On one side of the separator 104, a groove through which the fuel gas flows is processed. The other separator 104 has a groove through which an oxidant gas, usually air, flows. These are laminated, and the positive electrode current collector plate 113 and the negative electrode current collector plate 114 are disposed at the ends. Pressure is applied from the outside of the current collecting plates 113 and 114 by the end plate 109 through the insulating plate 107. Components that fix the end plate 109 are a bolt 116, a disc spring 117, and a nut 116. Fuel gas, oxidant gas, and cooling water are supplied from connectors 110, 111, and 112 provided on the end plate, and discharged from the connector provided on the other end plate. DC power (output) can be obtained from the positive current collector 113 and the negative current collector 114.

  The stopping method according to the present invention is performed by the changeover switch 120 and the resistor 121 in the middle of the load cable 123 connected to the current collector plates 113 and 114 of the stack. During normal power generation, the switch 120 is connected to the inverter 122 side, and DC power is supplied from the stack to the inverter 122. When the stop mode is entered, an external short-circuit current can be passed by switching the switch 120 toward the resistor 121.

  FIG. 11 is a block diagram of the polymer electrolyte fuel cell system of the present invention. The reformed gas is supplied using city gas or the like as a raw material gas, and is supplied to the reformer 1003 through the prefilter 1013. Air and water necessary for generating the reformed gas are supplied by pumps 1008 and 1019. The hydrogen concentration contained in the reformed gas was 70% (dry base). The fuel gas supplied to the stack 1005 is manufactured by the reformer 1003 and supplied from a supply pipe having a fuel gas supply valve 1015.

  The oxidant gas is supplied to the stack through a pipe having an oxidant gas supply valve 1017 by driving an air supply pump (blower) 1009. After power is generated in the stack, the fuel gas is returned to the reformer 1003 via a pipe having a discharge valve 1016, and is used to keep the reforming catalyst warm. Air is discharged to the atmosphere through a pipe having an oxidant gas discharge valve 1018. In order to remove the heat from the stack and recover the heat, pure water is supplied from the pump 1010 to the stack. The water discharged from the stack is transferred to the water stored in the hot water storage tank 1007 by the heat exchanger 1011 and is circulated to the stack by the pump 1010. Water in the hot water tank is circulated by a pump 1010.

  In the present invention, the microcomputer 1012 has a mechanism for opening and closing the fuel gas supply valve 1015, the discharge valve 1016, the oxidant gas supply valve 1017, and the discharge valve 1018.

  From the rated power generation state of the stack, the operation shifted to the stop operation mode and the stack was stopped. First, a command is issued from the microcomputer 1012 to connect the open / close switch 1020 to the resistor 1021 side, and the current flowing through the inverter 1022 is set to zero. Next, the fuel gas supply valve 1015 is stopped, and the supply of hydrogen to the stack 1005 is shut off. Next, the anode discharge valve 1016 is also closed to shut off the fuel gas inside the stack.

  The supply of the oxidant gas was continued until the time Tmin given by using the equation (10), and immediately after that, the blower-1009 was stopped, the supply valve 1017 was closed, and then the valve 1018 was closed.

  The resistor 1021 is preferably a variable resistor, and the initial resistance value is such that a current corresponding to 1 A flows with respect to the open circuit voltage (Vo) of the stack. That is, in this example, Vo was 79-80 V, so the initial value (Ro) of the resistor was 80Ω. The stack voltage decreases with time due to an external short circuit due to the resistor, but when the voltage of the open circuit voltage Vo reaches 50% (40 V), the voltage of the current collector plates 113 and 114 can hold 40 BV. Increased resistance. The external short circuit time by the resistor was 15 minutes. After that time, the main switch of the system was turned off after the changeover switch 120 was not connected to either the inverter side or the resistor side.

  In addition, the external short circuit by a resistor may take the method of opening the circuit between a battery and a resistor after the lapse of a predetermined time as time control. Further, after the operation of the external short circuit is completed in this way, air may be supplied to the stack from the cathode pipe, and the gas pressure on the cathode side may be returned to the atmospheric pressure. In this way, when the next activation starts after a relatively short time, an effect of simplifying the activation operation can be obtained. After the hydrogen is consumed, air is supplied to the anode and the cathode, and the pressure applied between the MEAs in the cell is made approximately equal, which is desirable in order to avoid tensile breakage of the MEA due to differential pressure and poor airtightness. In this example, after the main power supply was turned off, air was slowly supplied to the anode and the cathode until atmospheric pressure was reached.

  After the operation due to the external short-circuit is completed, an operation to lower the temperature of the cooling water supplied to the stack may be added, or the cooling water supply may be continued for natural cooling, or the supply may be stopped. Also good. In this embodiment, as described above, since the main power supply of the system is turned off, the supply of cooling water is stopped. However, the main power supply is turned off as a timer setting, and the circulation of the cooling water is stopped after a predetermined time has elapsed. Also good.

  These series of valve operations were performed under the control of the microcomputer 1012. As a result of conducting the experiments of FIGS. 4 to 6 described in the detailed description of the invention for the power generation system manufactured in Example 1, the potential of P is LP and LP even when the fuel gas and the oxidant gas are supplied simultaneously. It was confirmed that it was between HP. Here, LP was 0.4V and HP was 0.8V.

Subsequently, the power generation system of the present invention was started, a power generation test under rated conditions was performed, and a stop mode operation was performed under the same conditions. As a result of repeating this start-stop operation 100 times, the output voltage of the stack input to the inverter 1022 was 59.9 V after the 100-times repeated test with respect to the initial 50 V under rated conditions.
(Example 2)
The delay time of the anode discharge valve and the cathode discharge valve was set to 1 second, 30 seconds, 60 seconds, and 5 minutes by changing the parameters of the microcomputer, and 100 start-stop tests were performed for each time. As a result, when the delay time was 1 second, the voltage measured when the power generation test was performed after 100 start-stop operations with respect to the initial voltage of 60 V was 59.7 to 59.9 V. It was confirmed that the stack voltage did not substantially decrease. When the delay time was 3 conditions of 30 seconds or more, the voltage after the test dropped to 58.2-59.3V. In particular, when the delay time was 5 minutes, the minimum value was 58.2 V after the test.

The conceptual diagram which shows the relationship of the open circuit voltage of an anode for demonstrating the stop operation process of the fuel cell system in the Example of this invention. The conceptual diagram in case the relationship between the open circuit voltage of an anode and a cathode in a fuel cell stop operation process is improper. The conceptual diagram of the other example in case the relationship between the open circuit voltage of an anode and a cathode in a fuel cell stop operation process is improper. The conceptual diagram for demonstrating how to measure the anode potential in an open circuit. The conceptual diagram for demonstrating the method to determine an anode electric potential from the final state Q. FIG. The conceptual diagram for demonstrating the measuring method of the cathode potential in an open circuit. The conceptual diagram for demonstrating the method of determining a cathode potential from the final state R. FIG. The conceptual diagram for demonstrating the adjustment method of the termination condition in the Example of this invention. The conceptual diagram for demonstrating the other adjustment method of the termination conditions in the Example of this invention. 1 is a schematic cross-sectional view showing an internal configuration of a polymer electrolyte fuel cell system to which the present invention is applied. The diagram which shows the structure of the electric power generation system carrying the polymer electrolyte fuel cell by the Example of this invention. It is a flowchart which shows the procedure of the operation | movement stop 1st step in the fuel cell operation method of this invention. It is a flowchart which shows the procedure of the operation | movement stop 2nd step in the fuel cell operation method of this invention. It is a flowchart which shows the procedure of the operation | movement stop 3rd step in the fuel cell operation method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Single cell, 102 ... Solid polymer electrolyte membrane, 103 ... Catalyst layer, 104 ... Single cell separator, 105 ... Gasket, 106 ... Gas diffusion layer, 107 ... Insulating plate, 108 ... Cooling water separator, 109 ... End 110, ... connector for fuel gas piping, 111 ... connector for cooling water piping, 112 ... connector for oxidant gas piping, 113 ... current collecting plate, 114 ... current collecting plate, 116 ... bolt, 117 ... disc spring, 118 ... Nut, 120 ... changeover switch, 121 ... resistor, 122 ... inverter, 123 ... load cable, 1003 ... reformer, 1005 ... fuel cell laminate, 1007 ... hot water tank, 1008 ... air supply pump, 1009 ... oxidant Gas pump, 1010 ... circulating water pump, 1011 ... heat exchanger, 1013 ... pre-filter, 1014 ... fuel gas return Pipe, 1015 ... Fuel gas supply valve, 1016 ... Fuel gas discharge valve, 1017 ... Oxidant gas supply valve, 1018 ... Oxidant gas discharge valve, 1019 ... Water supply pump, 1020 ... Switch, 1021 ... Resistor, 1022 ... Inverter.

Claims (15)

  A fuel cell having a solid polymer electrolyte membrane for separating fuel gas and oxidant gas, a short-circuit device, an inverter connected in parallel to the fuel cell and the short-circuit device, and a control device for controlling the fuel cell system When the fuel cell is stopped, the short-circuit device and the fuel cell are connected to cause an external short-circuit current to flow, and the final potential of the anode immediately before stopping the current is a predetermined lower limit potential (LP) and an upper limit potential (HP) A method for operating a polymer electrolyte fuel cell, comprising the step of controlling so as to exist during HP.   2. The method for operating a polymer electrolyte fuel cell according to claim 1, wherein the control device controls a switching device for supplying fuel gas and oxidant gas to the fuel cell.   The solid polymer form according to claim 1, further comprising a step of delaying the supply of the fuel gas and / or the oxidant gas so that the end potential is within the range of the LP and HP. How to operate a fuel cell.   2. The solid polymer according to claim 1, further comprising a step of closing the cathode supply valve after a predetermined time has elapsed after an external short-circuit current starts flowing through the short-circuit device in a state where the fuel gas supply valve is closed. Fuel cell operation method.   2. The method for operating a polymer electrolyte fuel cell according to claim 1, wherein LP is set to 0.2 V to 0.8 V, HP is set to 0.2 V to 0.8 V, and LP <HP.   A fuel cell having a solid polymer electrolyte membrane for separating fuel gas and oxidant gas, a short-circuit device, an inverter connected in parallel to the fuel cell and the short-circuit device, and a control device for controlling the fuel cell system When the fuel cell is stopped, the short-circuit device and the fuel cell are connected to cause an external short-circuit current to flow, and at least the anode potential in the open circuit is a predetermined anode potential and a lower limit potential (LP) of the cathode potential. And an upper limit potential (HP).   A fuel cell having a solid polymer electrolyte membrane that separates fuel gas and oxidant gas; a fuel manufacturing device that supplies fuel gas to the fuel cell; a device that supplies oxidant gas to the fuel cell; An inverter for converting the output of the fuel cell, a short circuit device connected in parallel to the fuel cell and the inverter, and a control device for controlling the operation of the fuel cell, wherein the control device stops the fuel cell Based on the signal, the supply of fuel gas to the fuel cell is stopped, and the short-circuit device and the fuel cell are connected to cause an external short-circuit current to flow. The final potential of the anode immediately before stopping the current is a predetermined lower limit potential ( LP) and an upper limit potential (HP).   8. The polymer electrolyte fuel cell system according to claim 7, further comprising an opening / closing device for supplying fuel gas and oxidant gas to the fuel cell.   The control device delays the supply of the fuel gas and / or the oxidant gas so that the intersection of the predetermined lower limit potential (LP) and the upper limit potential (HP) exists within the range of the LP and HP. The polymer electrolyte fuel cell system according to claim 7 or 8, wherein   The control device includes an operation program for the fuel cell system, a start / stop program for the fuel cell system, a lower limit potential (LP) and an upper limit potential (HP) of the anode potential and the cathode potential in the open circuit, and the operation of the fuel cell. 10. The polymer electrolyte fuel cell power generation system according to claim 7, wherein data obtained in advance as characteristics is held as a database.   11. The polymer electrolyte fuel cell power generation system according to claim 10, wherein the database is recorded on a computer-readable recording medium.   A fuel cell having a solid polymer electrolyte membrane that separates a fuel gas and an oxidant gas; a fuel manufacturing device that supplies a fuel gas to the fuel cell; a device that supplies an oxidant gas to the fuel cell; An inverter for converting the output of the fuel cell, a short circuit device connected in parallel to the fuel cell and the inverter, and a control device for controlling the operation of the fuel cell, wherein the control device stops the fuel cell Based on the signal, the supply of fuel gas to the fuel cell is stopped, and the short-circuit device and the fuel cell are connected to cause an external short-circuit current to flow. The final potential of the anode immediately before stopping the current is a predetermined lower limit potential ( LP) and an upper limit potential (HP).   The computer uses the fuel cell system operation program and the fuel cell system start / stop program, and the data obtained in advance as the fuel cell operating characteristics of the anode potential and cathode potential lower limit potential (LP) and upper limit potential (HP). A recording medium recorded on a readable medium.   12. The recording medium according to claim 11, wherein the data includes a program for controlling the intersection of the anode potential and the cathode potential to be within the range of LP and HP. The recording medium according to claim 11 or 12, wherein the data includes a program for delaying the supply of fuel gas and / or oxidant gas.

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