JP2007053020A - Method of controlling fuel cell, its control device, and vehicle loaded with its control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover activity of catalyst metal by conducting reduction treatment. <P>SOLUTION: A method of controlling a fuel cell using the catalyst metal as an electrode catalyst contains a stage S1 starting the starting treatment of the fuel cell, stages S2, S3 supplying anode gas to an anode of the fuel cell, stages S4, S5 passing reduction current of the catalyst metal between the anode and a cathode of the fuel cell, and a stage S6 finishing the starting treatment of the fuel cell when voltage across the anode and the cathode reaches reference voltage or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control method for a fuel cell, a control device therefor, and a vehicle equipped with the control device.

In recent years, fuel cells have attracted attention as vehicle drive sources and stationary power sources in response to social demands and trends against the background of energy and environmental problems. Fuel cells are classified into various types depending on the type of electrolyte, the type of electrode, and the like, and representative types include alkaline type, phosphoric acid type, molten carbonate type, solid electrolyte type, and solid polymer type. Among them, as a low-pollution power source for automobiles, a polymer electrolyte fuel cell (PEFC) that can operate without raising the temperature (usually below 100 ° C) is attracting attention, and development is proceeding toward practical application. It has been. In order for PEFC to be put into practical use as a low-pollution power source for automobiles, it is an essential condition to have durability over a long period of time.

  The PEFC generally has a structure in which a membrane-electrode assembly (hereinafter also referred to as “MEA”) is sandwiched between separators. The MEA generally has a structure in which a gas diffusion layer, a cathode catalyst layer, a solid polymer electrolyte membrane, an anode catalyst layer, and a gas diffusion layer are laminated. The cell reaction proceeds in a catalyst layer comprising a catalyst, a carrier supporting the catalyst, and an ionomer (ion conductive polymer). For this reason, preventing deterioration of the catalyst layer is an important issue in enhancing the durability of PEFC.

  However, when the PEFC is continuously operated for a long period of time or is frequently started and stopped, the three-phase structure composed of the catalyst, the support, and the ionomer causes carbon corrosion and ionomer decomposition degradation, and the electrode structure changes. When the electrode structure is changed, gas diffusibility and generated water discharge properties are lowered, and power generation performance is lowered. In addition, changes in the electrode structure may cause a decrease in battery durability. In particular, since an oxidation-reduction reaction occurs near the interface between the solid polymer electrolyte membrane and the cathode catalyst layer, carbon corrosion and elution of catalyst metal (for example, platinum) to the solid polymer electrolyte membrane are likely to occur. It causes a decrease in power generation characteristics and a decrease in PEFC durability. Therefore, development of a technique for preventing the deterioration of the catalyst layer is eagerly desired.

  Even if the catalytic metal is maintained at a constant potential even at a high potential, the elution of the catalytic metal to the solid polymer electrolyte membrane is slight, but during a violent potential change that involves oxidation and reduction of the catalytic metal. The elution of the catalytic metal becomes significant. It has been found that elution of catalytic metals, particularly platinum, is promoted by repeated oxidation and reduction of platinum metal and platinum oxide. During actual PEFC operation, platinum is oxidized because the cathode potential rises when it is stopped or when OCV (open circuit voltage) is maintained, and platinum is in a reduced state during power generation. It is thought to promote the elution of platinum.

For this reason, as a technique for improving the durability of the catalyst layer, for example, as described in Patent Document 1 below, when the fuel cell is started, the output voltage per cell is forcibly set to 0 V or more and 0.3 V or less. In order to recover the activity of the catalytic metal by lowering it for 1 to 10 seconds, it has been proposed.
Japanese Patent No. 3460793 Specification

  However, in such a conventional technology, since the PEFC is started at a lower voltage (high current density) than necessary from the state where the PEFC is not generating power (stopped state), local current concentration on the catalyst metal And local catalyst deterioration may occur.

  In addition, even though the recovery conditions (temperature, voltage, time) of the catalyst metal are different due to differences in PEFC usage history and storage environment, the activity is to be recovered under uniform conditions, so a uniform recovery is desired. Cannot be achieved, resulting in uneven recovery.

  The present invention has been made in view of the above-described problems of the prior art, and can reduce the catalytic metal before starting the power generation of the PEFC, and can recover the activity of the catalytic metal. It is an object of the present invention to provide a control method, a control device thereof, and a vehicle equipped with the control device.

  In order to achieve the above object, a control method for a fuel cell according to the present invention is a control method for a fuel cell in which a catalytic metal is used as an electrode catalyst, the step of starting the fuel cell startup process, Supplying anode gas to the anode of the fuel cell; passing a reduction current of the catalytic metal between the anode and cathode of the fuel cell; and a voltage between the anode and the cathode is equal to or lower than a reference voltage. And a step of ending the fuel cell start-up process.

  A fuel cell control device according to the present invention for achieving the above object is a fuel cell control device using a catalytic metal as an electrode catalyst, and supplies an anode gas to the anode of the fuel cell. An anode gas supply means, a cell voltage detection means for detecting a cell voltage between the anode and cathode of the fuel cell, a load means for flowing a reduction current of the catalytic metal between the anode and cathode, and the fuel When the battery activation signal is input, the anode gas supply means is operated to supply anode gas, and the load means reduces the cell voltage detected by the cell voltage detection means until the cell voltage is lower than a reference voltage. And a control means for flowing current.

  Furthermore, a vehicle according to the present invention for achieving the above object is characterized in that the fuel cell control device according to any one of claims 11 to 15 is mounted.

  According to the control method of the fuel cell according to the present invention configured as described above, the oxidized catalytic metal on the cathode side can be completely reduced during the stop before the start of power generation, and due to load fluctuation during operation. The elution of the catalytic metal can be significantly reduced.

  Further, according to the fuel cell control device according to the present invention configured as described above, the oxidized catalytic metal on the cathode side during the stop before the start of power generation can be completely reduced, and the load during operation can be reduced. The elution of catalyst metal due to fluctuations can be significantly reduced.

  Furthermore, according to the vehicle equipped with the fuel cell control device according to the present invention, a vehicle that exhibits stable performance over a long period of time can be obtained.

Hereinafter, a fuel cell control method, a control device thereof, and a vehicle equipped with the control device according to the present invention will be described in detail with reference to the drawings, divided into a first embodiment to a third embodiment.

Before describing these embodiments, the overall configuration of the fuel cell stack will be briefly described in order to facilitate understanding of the present invention. FIG. 1 is a perspective view showing the overall configuration of the fuel cell stack, and FIG. 2 is an enlarged cross-sectional view of the main part showing the cell structure of the fuel cell stack.

  As shown in FIG. 1, the fuel cell stack 1 is a laminated body 3 in which a predetermined number of cells 2 as unit cells that generate electromotive force by the reaction of anode gas and cathode gas are laminated. The current collecting plate 4, the insulating plate 5 and the end plate 6 are arranged, and a tie rod 7 is passed through a through hole (not shown) penetrating the laminated body 3, and a nut (illustrated) is connected to the end of the tie rod 7. Are omitted).

  In this fuel cell stack 1, an anode gas inlet 8 for allowing anode gas, cathode gas and cooling water to flow through flow channel grooves formed in separators (not shown) of each cell 2, anode gas exhaust, respectively. An outlet 9, a cathode gas inlet 10, a cathode gas outlet 11, a cooling water inlet 12 and a cooling water outlet 13 are formed in one end plate 6.

  The anode gas is introduced from the anode gas introduction port 8, flows through the anode gas supply channel groove formed in the separator, and is discharged from the anode gas discharge port 9. The cathode gas is introduced from the cathode gas introduction port 10, flows through the cathode gas supply channel groove formed in the separator, and is discharged from the cathode gas discharge port 11. The cooling water is introduced from the cooling water introduction port 12, flows through the cooling water supply channel groove formed in the separator, and is discharged from the cooling water discharge port 13.

  As shown in FIG. 2, the cell 2 is composed of a membrane electrode assembly (hereinafter also referred to as MEA (membrane electrode assembly)) 14 and separators 15 disposed on both surfaces of the MEA 14. Hereinafter, the separator 15 disposed on the anode side of the MEA 14 is referred to as an anode separator 15A, and the separator 15 disposed on the cathode side is referred to as a cathode separator 15B.

  The MEA 14 includes, for example, a solid polymer electrolyte membrane 141 that is a polymer electrolyte membrane that allows hydrogen ions to pass through, an anode electrode 144A that is an anode composed of an anode catalyst layer 142A and a gas diffusion layer 143A, and a cathode that is a catalyst metal that is an electrode catalyst. It consists of a cathode electrode 144B as a cathode comprising a catalyst layer 142B and a gas diffusion layer 143B. The MEA 14 has a laminated structure in which a solid polymer electrolyte membrane 141 is sandwiched from both sides by an anode electrode 144A and a cathode electrode 144B.

  The separator 15 is formed by forming a thin metal plate into a predetermined shape using a mold. As shown in the figure, the separator 15 has an uneven shape (so-called corrugated shape) in which convex portions 16 and concave portions 17 are alternately formed in an active region that contributes to power generation (region of the central portion in contact with the MEA 14). is doing.

The convex portion 16A and the concave portion 17A of the anode separator 15A arranged in contact with the anode electrode 144A side of the MEA 14 serve as a channel groove for flowing an anode gas (hydrogen; H ₂ ) between the MEA 14 and an anode gas channel (anode ) 18) is formed. On the other hand, the convex portion 16B and the concave portion 17B of the cathode separator 15B disposed in contact with the cathode electrode 144B side of the MEA 14 serve as a channel groove for flowing a cathode gas (oxygen; O ₂ ) between the MEA 14 and the cathode gas channel. (Cathode channel) 19 is formed. When hydrogen is passed through the anode gas flow path 18 and oxygen is passed through the cathode gas flow path 19, the hydrogen is turned into hydrogen ions by the catalytic action of the anode catalyst layer 142A and discharges electrons. The hydrogen ions that have released the electrons pass through the solid polymer electrolyte membrane 141. In the cathode catalyst layer 142B, hydrogen that has passed through the solid polymer electrolyte membrane 141 and electrons that have passed through an external circuit (not shown) react with oxygen to generate water. By this action, the anode electrode 144A becomes negative and the cathode electrode 144B becomes positive, and a DC voltage is generated between the anode electrode 144A and the cathode electrode 144B as shown in FIG.

In this specification, a voltage appearing between the anode electrode 144A and the cathode electrode 144B is referred to as a cell voltage, and the cell voltage is detected by the cell voltmeter 20 functioning as a cell voltage detection means. The cell voltage may be detected from all cells constituting the fuel cell stack 1 or may be detected only from a plurality of representative cells among the cells constituting the fuel cell stack 1. In the present invention, before starting the operation of the fuel cell, a reduction current for reducing platinum, which is a catalytic metal, flows between the anode electrode 144A and the cathode electrode 144B, but electrons are supplied from the anode electrode 144A. It flows toward the cathode electrode 144B. Since the activity of platinum is restored when an appropriate amount of reducing current is applied, the cell voltage is adjusted when the fuel cell is started by supplying an appropriate amount of reducing current.

In the fuel cell control method and control apparatus according to the present invention, the catalyst metal, specifically platinum, carried on the cathode catalyst layer 142B is reduced before the fuel cell is operated by adjusting the cell voltage at the time of startup. The platinum oxide (PtO or PtO ₂ ) generated on the cathode catalyst layer 142B is completely removed before power generation can be performed. Further, even during power generation, the fuel cell is operated so that platinum oxide is not generated as much as possible in the cathode catalyst layer 142B.

Hereinafter, the fuel cell control method and the control device according to the present invention will be described in detail from the first embodiment to the third embodiment.
[First Embodiment]
FIGS. 3 and 4 are diagrams for explaining the control method and the control device of the fuel cell according to the first embodiment of the present invention. FIG. 3 is a schematic block diagram of the control apparatus for the fuel cell according to the present embodiment, and FIG. 4 is an operation flowchart of the control unit shown in FIG. 3, which is a control method for the fuel cell according to the present embodiment. It is also equivalent to this procedure.

  As shown in FIG. 3, the fuel cell control device according to the present embodiment includes a fuel cell stack 1 that generates power by supplying anode gas (hydrogen) and cathode gas (oxygen), and all the fuel cell stacks 1 that constitute the fuel cell stack 1. A cell voltmeter 20 that detects the cell voltage of the cell, a loader 21 that adjusts the magnitude of the reduction current to each cell from the start to the end of the fuel cell startup process, and the cathode gas flow rate adjustment The flow rate regulator 22 for controlling the flow rate of the anode gas, the flow rate regulator 23 for adjusting the flow rate of the anode gas, and the control unit 24 for controlling the intermittent operation of the loader 21 and the operation of the flow rate regulators 22 and 23 based on the detection voltage of the cell voltmeter 20 It has.

  The fuel cell stack 1 uses a catalytic metal as an electrode catalyst. Specifically, platinum is used for the cathode catalyst layer 142B (see FIG. 2) of the cathode electrode 144B.

  The cell voltmeter 20 functions as cell voltage detection means for detecting cell voltages between all the anode electrodes 144A and the cathode electrodes 144B constituting the fuel cell stack 1.

  The loader 21 functions as a load means for flowing a reduction current of platinum as a catalyst metal between the anode electrode 144A and the cathode electrode 144B.

  The flow rate regulator 23 functions as anode gas supply means for supplying anode gas to the anode of the fuel cell stack 1. The flow regulator 23 has a function of measuring the supply amount of the anode gas.

  When the start signal of the fuel cell is input, the control unit 24 opens the flow rate regulator 23 to supply the anode gas to the fuel cell stack 1, and the cell voltage detected by the cell voltmeter 20 is equal to or lower than the reference voltage. Until this time, the loader 21 functions as a control means for causing a reduction current to flow between the anode electrode 144A and the cathode electrode 144B.

In the present embodiment, using the fuel cell control apparatus configured as described above, the reduction treatment of platinum of the cathode electrode 144B is performed for the following reason.

When the fuel cell is stopped, oxygen remains in the cathode gas flow path 19 of the fuel cell stack 1, and since it is at a high potential, a part of platinum of the cathode electrode 144B is oxidized, and platinum oxide (PtO or PtO) PtO ₂ ) is generated. The elution of platinum oxide is promoted in response to potential changes during the subsequent operation of the fuel cell. The elution of platinum not only lowers the power generation performance of the fuel cell, but also has a significant effect on the life of the fuel cell.

  For this reason, in the present embodiment, the platinum oxide generated at the cathode electrode 144B when the fuel cell is stopped is reduced and completely removed before the start of operation, and the operation is performed under the condition that platinum oxide is not generated even during the subsequent operation. Is continued (to prevent the occurrence of platinum-platinum oxide oxidation-reduction cycle) to prevent the elution of platinum as much as possible, to maintain the power generation performance of the fuel cell, and to improve the life, perform the reduction process at the start-up ing.

  With reference to FIG. 4, the procedure of the reduction process of the present embodiment will be described in detail. First, when the control unit 24 inputs a fuel cell activation signal for starting the operation of the fuel cell from an external device (not shown), the control unit 24 starts the activation process of the fuel cell (S1). The control unit 24 opens the flow rate regulator 23 and starts supplying anode gas (hydrogen) to the fuel cell stack 1. At this time, in order to suppress consumption of the anode gas, the flow rate regulator 22 is closed and the cathode gas (oxygen) is not supplied (S2).

  The control unit 24 determines whether or not the anode gas flow path 18 (see FIG. 2) is filled with the anode gas, that is, whether or not the anode gas purge is completed. Whether or not the anode gas purge is completed is determined by the amount of the anode gas that has passed through the flow rate regulator 23. That is, the determination is made based on whether or not the amount of the anode gas that has passed through the flow rate regulator 23 exceeds the total volume of the anode gas flow path 18 of the fuel cell stack 1. Alternatively, a hydrogen sensor is provided in the anode gas passage 18 or at the outlet side, and an oxygen sensor is provided in the cathode gas passage 19 or at the outlet side, so that the detected hydrogen concentration exceeds 99% and the oxygen concentration is When it is 0.2% or less, it may be determined that the anode gas purge is completed (S3).

  If the anode gas purge is not completed (S3: NO), the supply of the anode gas is continued. On the other hand, if the anode gas purge is completed (S3: YES), the control unit 24 closes the flow rate regulator 23 to shut off the supply of the anode gas, and loads all the cells 2 (see FIG. 1) to the loaders 21, As an example, resistors are individually connected, and a reduction current for reducing oxidized platinum flows from the cathode electrode 144B to the anode electrode 144A. That is, the reduction current application process is started (S4).

  The control unit 24 individually detects the voltage of each cell 2 with the cell voltmeter 20 and determines whether or not the cell voltage has become 0.5 V or less, which is the reference voltage. The cell voltage is the potential of the cathode electrode 144B with respect to the anode electrode 144A. When the reduction current application process is started, the cell voltage decreases from the open circuit voltage (OCV) with time as shown in FIG. The control unit 24 monitors this voltage and determines whether or not it is lower than the reference voltage, 0.5 volts.

The reason why the reference voltage is 0.5 volts or less is that when platinum is oxidized to platinum oxide (PtO), it can be sufficiently reduced even at about 0.76 volts (the divalent PtO is 0. 0). If it is reduced to 76 volts or less), but it has become platinum oxide (PtO ₂ ), it cannot be reduced at about 0.76 volts, and the voltage must be reduced to about 0.5 volts. (Because tetravalent PtO ₂ is reduced at 0.5 volts or less).

  For this reason, although the reference voltage is set to 0.5 volts in the present embodiment, the reference voltage can be set to 0.76 volts or less. In order to completely remove platinum oxide, it is conceivable to set the reference voltage to 0.5 volts or less (for example, 0.35 volts). However, if the reference voltage is set too low, a good reduction action can be obtained. There is a concern that the metal catalyst may be damaged by the rapid reduction action. If the set voltage is too low, the value of the reduction current becomes too large and the current concentrates and flows only in specific parts of the metal catalyst, creating hot spots, which can damage the metal catalyst. Yes (S5).

  If the voltage of each cell 2 is not lower than 0.5 volts (S5: NO), the control unit 24 has platinum oxide that has not been reduced yet. Keep flowing. On the other hand, if the voltage of each cell 2 is 0.5 volts or less (S5: YES), the control unit 24 removes the loaders 21 from all the cells 2 because platinum oxide is no longer present. To cut off the reduction current. That is, the reduction current application process is terminated. Upon completion of the reduction current application process, the fuel cell activation process is completed (S6).

  In the above example, the reduction current is cut off when the cell voltage of all cells becomes lower than the reference voltage. However, instead of all the cell voltages, an achievement ratio is provided, and an arbitrary number of cells can be set. When the voltage becomes lower than the reference voltage, it may be determined that the cell voltage has become lower than the reference voltage, and the reduction current may be cut off. Further, the cell voltage may not be detected for all cells, but only for an arbitrary cell.

  When the starting process of the fuel cell is completed, the control unit 24 opens the flow rate regulators 22 and 23 and starts supplying the anode gas (hydrogen) to the fuel cell stack 1 and also starts supplying the cathode gas (oxygen-containing gas). Then, the fuel cell is operated and power generation is started. While the fuel cell is in operation, the voltage between the anode electrode 144A and the cathode electrode 144B is controlled to 0.8 volts or less by connecting an auxiliary device mounted on the vehicle according to the load fluctuation. .

  The reason why the cell voltage is controlled to 0.8 volts or less is to prevent platinum oxide from being generated on the catalyst metal during power generation. Platinum oxide is produced at 0.8 volts and above. A typical polymer electrolyte fuel cell has an open circuit voltage of 0.9 to 1.0 volts. For this reason, it is considered that platinum is oxidized by this voltage at the cathode electrode 144B. Since oxidation and reduction of platinum promotes elution of platinum, it is not preferable to cause oxidation of platinum during power generation.

  Therefore, it is desirable that the power generation state be established in order to reduce the voltage to 0.8 volts or less even when idling (when large power is not supplied to the load). Therefore, when surplus power is generated, the auxiliary device is moved by this surplus power, or used for charging a secondary battery mounted on the vehicle. In this way, since the amount of platinum oxide generated during power generation is suppressed, it is possible to considerably reduce the reduction current application processing time performed at the start of startup (S7).

As described above, in the present embodiment, the metal catalyst is completely reduced before the fuel cell is operated. When power generation with a large load change is performed in a state where the metal catalyst is oxidized, the metal catalyst is easily eluted. For this reason, a reduction current application process is performed at the start of the fuel cell, and the cell voltage is lowered below the reference voltage to completely remove the metal catalyst that has been oxidized before the operation of the fuel cell. In order to prevent the catalyst from being oxidized, the power generation performance of the fuel cell is prevented from being deteriorated and the durability is improved by setting a target voltage and continuing the power generation.
[Second Embodiment]
FIGS. 5 and 6 are diagrams for explaining a control method and a control apparatus for a fuel cell according to the second embodiment of the present invention. FIG. 5 is a schematic block diagram of the fuel cell control device according to the present embodiment, and FIG. 6 is an operation flowchart of the control unit shown in FIG. 5. This flowchart is a control method for the fuel cell of the present embodiment. It is also equivalent to this procedure.

  The first embodiment is different from the second embodiment only in that a shutoff valve 25 as a shutoff means for shutting off the supply of the cathode gas is provided in the cathode gas exhaust path in FIG. The other constituent elements are exactly the same as those in FIG. 3, so that the description of those constituent elements is omitted.

The shut-off valve 25 is provided to completely shut off the cathode gas that diffuses and flows in from the outlet side of the cathode gas exhaust path. When performing the reduction current application process as described above, if oxygen remains in the cathode gas flow path 19, a reduction reaction of the oxygen also occurs. Therefore, when a large amount of oxygen is present, residual oxygen The cell voltage does not decrease until is reduced. If the volume of the cathode gas channel 19 is small, it is considered that the reduction current is applied and at the same time the residual oxygen is reduced and immediately becomes water, so that the reduction current application processing time is not greatly affected. If the cathode gas passage 19 is forcibly shut off by the shut-off valve 25 as in the present embodiment, oxygen is prevented from flowing in from the outlet side of the cathode gas exhaust path even during the reduction current application process. Therefore, the time required for the reduction current application process can be shortened.

The procedure of the reduction process of the present embodiment will be described in detail according to FIG. Note that the flowchart of FIG. 6 differs from the flowchart of FIG. 4 only in the process of S14, and therefore, the description of the same steps as the flowchart of FIG. 4 will be simplified. First, when the control unit 24 inputs a fuel cell activation signal, the control unit 24 starts a fuel cell activation process (S11). The control unit 24 opens the flow rate regulator 23 and starts supplying anode gas (hydrogen) to the fuel cell stack 1. At this time, no cathode gas (oxygen) is supplied to suppress consumption of the anode gas (S12). The control unit 24 determines whether or not the anode gas flow path 18 (see FIG. 2) is filled with the anode gas, that is, whether or not the anode gas purge is completed (S13). If the anode gas purge is not completed (S13: NO), the supply of the anode gas is continued.

  On the other hand, if the anode gas purge is completed (S13: YES), the control unit 24 closes the flow rate regulator 23 to shut off the supply of the anode gas, and simultaneously closes the shutoff valve 25 to exit the cathode gas exhaust path. Oxygen does not flow in from the side (S14), loaders 21 are individually connected to all the cells 2 (see FIG. 1), and the oxidized platinum is directed from the cathode electrode 144B toward the anode electrode 144A. A reduction current for reduction is applied. That is, the reduction current application process is started (S15). The control unit 24 individually detects the voltage of each cell 2 with the cell voltmeter 20 and determines whether or not the cell voltage is equal to or lower than the reference voltage of 0.5 volts (S16).

  If the voltage of each cell 2 is not less than or equal to 0.5 volts (S16: NO), the control unit 24 has platinum oxide that has not yet been reduced. Keep flowing. On the other hand, if the voltage of each cell 2 is 0.5 volts or less (S16: YES), the control unit 24 removes the loaders 21 from all the cells 2 because platinum oxide no longer exists. To cut off the reduction current. That is, the reduction current application process is terminated. When the reduction current application process ends, the fuel cell startup process ends (S17).

  When the starting process of the fuel cell is completed, the control unit 24 opens the flow rate regulators 22 and 23 and starts supplying the anode gas (hydrogen) to the fuel cell stack 1 and also starts supplying the cathode gas (oxygen). Operate the fuel cell and start power generation. While the fuel cell is in operation, the voltage between the anode electrode 144A and the cathode electrode 144B is controlled to 0.8 volts or less by connecting an auxiliary device mounted on the vehicle according to the load fluctuation. (S18).

As described above, in this embodiment, the cathode gas supply is shut off so that the cathode gas does not flow into the cathode, and the cathode gas supply is shut off until the cell voltage becomes equal to or lower than the reference voltage. Before the fuel cell is operated by supplying a reduction current, the metal catalyst is completely reduced.
[Third Embodiment]
7 and 8 are diagrams for explaining a control method and a control device for a fuel cell according to a third embodiment of the present invention. FIG. 7 is a schematic block diagram of the fuel cell control device according to the present embodiment, and FIG. 8 is an operation flowchart of the control unit shown in FIG. 7. This flowchart is a control method for the fuel cell of the present embodiment. It is also equivalent to this procedure.

  In the second embodiment and the third embodiment, in FIG. 7, only an inert gas supply unit 26 as an inert gas supply means for positively injecting an inert gas into the cathode gas inflow path is provided. Is different. The other components are exactly the same as those in FIG. 5, and thus description of those components is omitted.

  The inert gas supply unit 26 supplies an inert gas generally used for the cathode gas flow path 19 of the fuel cell stack 1 and completely removes oxygen remaining in the cathode gas flow path 19 from the cathode gas flow path. It is provided to drive out of the road 19. The inert gas supply unit 26 is connected to the inlet side (upstream side) of the cathode gas supply path so that a predetermined amount of inert gas can be supplied into the cathode gas channel 19 at a predetermined flow rate. The operation of the inert gas supply unit 26 is controlled by the control unit 24. The inert gas is stored in a known manner in a storage means such as a high-pressure gas cylinder. The inert gas may be nitrogen or a rare gas main component gas having a lower oxygen content than the atmosphere. In addition to pure nitrogen gas and pure rare gas, the inert gas was discharged from the cathode gas passage 19 during power generation. Gas can be stored and used.

  When performing the reduction current application process, if oxygen remains in the cathode gas flow path 19, the cell voltage does not decrease until the residual oxygen is reduced as described above. However, the reduction current is applied. If the cathode gas channel 19 is previously purged with an inert gas or supplied while supplying an inert gas, the influence of residual oxygen is completely removed, so that the time required for the reduction current application process is further shortened. be able to.

If the cathode gas passage 19 is forcibly shut off by the shut-off valve 25 after the inert gas purge, oxygen can be prevented from flowing in from the outlet side of the cathode gas exhaust path even during the reduction current application process. The time required for the current application process can be shortened.

The procedure of the reduction process of the present embodiment will be described in detail according to FIG. Note that the flowchart of FIG. 8 differs from the flowchart of FIG. 6 only in the processing of S22 and S23, and therefore, the description of the same steps as the flowchart of FIG. 6 will be simplified. First, when the control unit 24 inputs a fuel cell activation signal, the control unit 24 starts a fuel cell activation process (S21). The control unit 24 opens the flow rate regulator 23 and starts supplying anode gas (hydrogen) to the fuel cell stack 1. At the same time, the control unit 24 closes the flow rate regulator 22, completely stops the supply of the cathode gas, and starts supplying the inert gas from the inert gas supply unit 26 into the cathode gas flow path 19. As a result, the oxygen remaining in the cathode gas channel 19 is replaced with the inert gas (S22).

  The control unit 24 determines whether the anode gas flow path 18 (see FIG. 2) is filled with the anode gas, that is, whether the anode gas purge is completed, and whether the cathode gas flow path 19 is filled with the inert gas. That is, it is determined whether or not the cathode gas purge is completed (S23). If the anode gas purge and the cathode gas purge are not completed (S23: NO), the supply of the anode gas and the inert gas is continued. Whether the entire cathode gas channel 19 is filled with the inert gas and replaced with the inert gas depends on the flow rate of the inert gas supplied to the cathode or the concentration of the inert gas present in the cathode channel. to decide.

  On the other hand, if the anode gas purge and the cathode gas purge are completed (S23: YES), the control unit 24 closes the flow rate regulator 23 to shut off the supply of the anode gas, and simultaneously closes the shut-off valve 25 to remove the inert gas. Oxygen does not flow in from the outlet side of the exhaust path (S24), and loaders 21 are individually connected to all the cells 2 (see FIG. 1), from the cathode electrode 144B toward the anode electrode 144A, A reduction current for reducing oxidized platinum is passed. That is, the reduction current application process is started (S25). The control unit 24 individually detects the voltage of each cell 2 with the cell voltmeter 20 and determines whether or not the cell voltage is equal to or lower than the reference voltage of 0.5 volts (S26).

  If the voltage of each cell 2 is not less than 0.5 volts (S26: NO), the control unit 24 has platinum oxide that has not yet been reduced. Keep flowing. On the other hand, if the voltage of each cell 2 is 0.5 volts or less (S26: YES), the control unit 24 removes the loaders 21 from all the cells 2 because platinum oxide no longer exists. To cut off the reduction current. That is, the reduction current application process is terminated. When the reduction current application process ends, the fuel cell startup process ends (S27).

  When the starting process of the fuel cell is completed, the control unit 24 closes the inert gas supply unit 26, opens the flow rate regulators 22 and 23, and starts supplying anode gas (hydrogen) to the fuel cell stack 1 and cathode gas. (Oxygen) supply is also started, the fuel cell is operated, and power generation is started. While the fuel cell is in operation, the voltage between the anode electrode 144A and the cathode electrode 144B is controlled to 0.8 volts or less by connecting an auxiliary device mounted on the vehicle according to the load fluctuation. (S28).

  As described above, in this embodiment, before flowing the reduction current, the inert gas is supplied to the cathode until the entire cathode flow path is replaced with the inert gas, and the cathode gas is prevented from flowing into the cathode. With the gas supply shut off and the cathode gas supply shut off, the anode gas is allowed to flow, and a reduction current is allowed to flow through the load until the cell voltage falls below the reference voltage. Is completely reduced. For this reason, the time required for the reduction current application process can be shortened.

  The fuel cell control device shown as the first to third embodiments can be mounted on a vehicle. If the fuel cell control device of the present invention is mounted on a vehicle, a vehicle that exhibits stable performance over a long period of time can be obtained.

  In the above-described embodiment, the magnitude of the reduction current is changed according to the cell voltage, but the magnitude of the reduction current is changed with time (wave shape, pulse shape) according to the cell voltage. Is also possible.

Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. Further, in this example, the display of% represents a mass percentage unless otherwise specified.
(Creation of electrode catalyst layer)
The electrode catalyst layer was prepared as follows. After adding 5 times the amount of purified water to the weight of Pt-supported carbon powder (Pt-supported amount: 48.1%, Pt average particle size: 3.2 nm, carbon support: Vulcan XC-72), 0.5 times An amount of isopropyl alcohol was added, and a Nafion solution (containing 5 wt.% Nafion manufactured by Aldrich) was added so that the weight of Nafion was 0.8 times. A catalyst ink was prepared by dispersing the mixed slurry well with an ultrasonic homogenizer followed by a vacuum degassing operation. A predetermined amount of catalyst ink is printed on one side of carbon paper (Toray TGP-H-060 manufactured by Toray Industries, Inc.), which is a gas diffusion layer (GDL), and dried at 60 ° C. for 24 hours to create an electrode layer. did.
(Production of MEA)
Regarding the preparation of MEA (membrane-electrode assembly), MEA was prepared by hot pressing at 120 ° C. and 1.2 MPa for 10 minutes with the surface on which the catalyst was applied aligned with the electrolyte membrane. The MEA of the reference example used the reference example electrode layer as the cathode (air electrode), and the example MEA used the example electrode layer as the cathode. In both Reference Examples and Examples, the MEA used was 0.3 mg for the anode and 0.5 mg for the cathode per 1 cm ^{2 of the} apparent electrode area, and the electrode area was 25 cm ² . Further, Nafion 112 (thickness: about 50 μm) was used as the electrolyte membrane.
(Example cell evaluation)
A fuel cell was constructed using the prepared MEA, and the cell voltage and the cathode Pt effective electrode area change with respect to the number of start / stop operations with different start methods were evaluated by the following method.

Hydrogen was supplied as fuel to the anode side of the fuel cell, and air was supplied to the cathode side. When operating at a constant current density of 0.2 A / cm ² with both gas supply pressures set to atmospheric pressure, fuel cell body temperature set to 70 ° C., hydrogen utilization rate of 67%, air utilization rate of 40% Changes in cell voltage were examined. When stopping, no air was supplied to the cathode, and the outlet side was opened to the atmosphere.

When starting after stopping for 10 minutes, hydrogen is first supplied to the anode, and after the purge of the fuel gas is completed, the cathode gas is not supplied, and the cathode gas shut-off valve is closed and the reduction current is reduced to 0. When 1 A / cm ² was passed and the cell voltage became 0.5 volts or less, the reduction current application process was terminated, the cathode gas outlet shut-off valve was opened, the cathode gas supply was started, and the power generation operation was started. To do. The change in the metal catalyst performance was examined from the change in the cell voltage when the current density was operated at a constant 0.2 A / cm ² . Furthermore, the Pt effective electrode area of the cathode was also compared by cyclic voltammetry.
(Reference example cell evaluation)
Similarly, the change in the performance of the metal catalyst was examined from the change in the cell voltage when the current density was operated at a constant 0.2 A / cm ² except that the start-up operation after the stop was performed in the same manner as the normal start-up operation. . Furthermore, the change in the Pt effective electrode area of the cathode was also examined by cyclic voltammetry.

  FIG. 10 is a diagram illustrating a change state of the cell voltage with respect to the number of times of starting and stopping when the reduction current application process is performed (Example) and when the reduction current application process is not performed (Reference Example).

  As is apparent from this figure, it can be seen that the degree of decrease in the cell voltage with respect to the number of start / stops is smaller in the example than in the reference example. That is, since the reduction current application process is performed in the embodiment, the oxidation of platinum is not observed, and the power generation performance as a fuel cell is not significantly reduced. However, in the case of the reference example, the amount of platinum oxide increases and the elution of platinum occurs as the number of start / stop operations increases, so that the cell voltage decreases, and the power generation performance as a fuel cell is significantly reduced. It is done.

  Table 1 shows a comparison of the cathode Pt effective electrode area determined by cyclic voltammetry before the start / stop test and after the 2000 cycle test. It can be seen that the amount of decrease in the Pt effective electrode area is considerably small. This result is consistent with the result of FIG. The ECA in Table 1 indicates the Pt effective electrode area per unit weight of Pt used, and is an index for determining the degree of elution of Pt.

  From the above, it can be considered that the Pt elution during operation can be suppressed and the decrease in the effective catalyst surface area can be suppressed by completely reducing Pt of the cathode at the time of startup.

  The present invention can remarkably reduce the elution of the catalyst metal, and can be useful for improving the life of the fuel cell in the future.

It is a perspective view which shows the whole structure of a fuel cell stack. It is a principal part expanded sectional view which shows the cell structure of a fuel cell stack. It is a schematic block diagram of a fuel cell control device according to the first embodiment. It is an operation | movement flowchart of the control part shown in FIG. It is a schematic block diagram of a fuel cell control device according to a second embodiment. 6 is an operation flowchart of the control unit shown in FIG. 5. It is a schematic block diagram of the control apparatus of the fuel cell which concerns on 3rd Embodiment. It is an operation | movement flowchart of the control part shown in FIG. It is a figure which shows the fall condition of the cell voltage during a reduction current application process. It is a figure which shows the change state of the cell voltage with respect to the frequency | count of a start / stop with the case where a reduction current application process is performed (Example) and when it is not performed (reference example).

Explanation of symbols

1 Fuel cell stack,
2 cells,
3 laminates,
4 current collector,
5 Insulating plate,
6 End plate,
7 Tie rods
8 Anode gas inlet,
9 Anode gas outlet,
10 Cathode gas inlet,
11 Cathode gas outlet,
12 Cooling water inlet,
13 Cooling water outlet,
15 separator,
15A anode separator,
15B cathode separator,
16 ridges,
16A convex part,
16B convex part,
17 Concave part,
17A recess,
17B recess, 18 anode gas flow path,
19 Cathode gas flow path,
20 cell voltmeter,
21 loader,
22 Flow regulator,
23 Flow regulator
24 control unit,
25 shutoff valve,
26 inert gas supply section,
141 solid polymer electrolyte membrane,
142A anode catalyst layer,
142B cathode catalyst layer,

143A gas diffusion layer,
143B gas diffusion layer, 144A anode electrode,
144B Cathode electrode.

Claims (16)

A method for controlling a fuel cell in which a catalytic metal is used as an electrode catalyst,
Starting the fuel cell startup process;
Supplying an anode gas to the anode of the fuel cell;
Passing a reduction current of the catalytic metal between an anode and a cathode of the fuel cell;
Ending the fuel cell start-up process when the voltage between the anode and the cathode falls below a reference voltage;
A control method for a fuel cell comprising: Before passing the reduction current,
The method of claim 1, further comprising shutting off the supply of the cathode gas so that the cathode gas does not flow into the cathode. Before passing the reduction current,
The method of claim 1, further comprising supplying an inert gas to the cathode. Supplying the anode gas comprises:
The fuel cell control method according to any one of claims 1 to 3, wherein the entire anode flow path is continued until the anode gas is filled with the anode gas. Supplying the inert gas comprises:
4. The method for controlling a fuel cell according to claim 1, wherein the entire flow path of the cathode is continued until it is replaced with an inert gas.   Whether or not the entire anode flow path is filled with the anode gas is determined by a flow rate of the anode gas supplied to the anode or a concentration of the anode gas existing in the anode flow path. The method for controlling a fuel cell according to claim 4.   Whether or not the entire cathode flow path has been replaced with an inert gas is determined by the flow rate of the inert gas supplied to the cathode or the concentration of the inert gas present in the cathode flow path. The fuel cell control method according to claim 5, wherein: After the stage of completing the startup process,
The method of claim 1, further comprising operating a fuel cell by supplying an anode gas to the anode and supplying a cathode gas to the cathode.   2. The fuel cell control method according to claim 1, wherein the reference voltage is preferably 0.76 volts, and most preferably 0.5 volts.   2. The fuel cell control method according to claim 1, wherein the voltage between the anode and the cathode is controlled to 0.8 volts or less while the fuel cell is operated. A fuel cell control device in which a catalytic metal is used as an electrode catalyst,
An anode gas supply means for supplying an anode gas to the anode of the fuel cell;
Cell voltage detecting means for detecting a cell voltage between an anode and a cathode of the fuel cell;
Load means for flowing a reduction current of the catalytic metal between the anode and the cathode;
When the start signal of the fuel cell is input, the anode gas supply means is operated to supply anode gas, and the load means causes the cell voltage detected by the cell voltage detection means to become a reference voltage or less. Control means for flowing the reduction current;
A fuel cell control device comprising: And further has a blocking means for blocking the supply of the cathode gas so that the cathode gas does not flow into the cathode,
When the fuel cell activation signal is input, the control means operates the anode gas supply means to supply the anode gas, and further shuts off the supply of the cathode gas by the shut-off means. 12. The fuel cell control device according to claim 11, wherein the reduction current is caused to flow by the load means until a cell voltage detected by the cell voltage detection means becomes equal to or lower than a reference voltage. An inert gas supply means for supplying an inert gas to the cathode;
When the start signal of the fuel cell is input, the control means operates the anode gas supply means to supply anode gas, further activates the inert gas supply means, and deactivates the cathode gas of the cathode. 12. The control of a fuel cell according to claim 11, wherein the reducing current is caused to flow by the load means until the cell voltage detected by the cell voltage detecting means becomes equal to or lower than a reference voltage in a state where the active gas is replaced. apparatus.   14. The fuel cell control device according to claim 11, wherein the reference voltage is preferably 0.76 volts, and most preferably 0.5 volts. The cell voltage is either to detect the cell voltage of all cells composed of the anode and the cathode, or to detect the cell voltage of an arbitrary number of cells,
The control means determines that the cell voltage has become equal to or less than the reference voltage when all the cell voltages have become equal to or less than the reference voltage, or when any number of cell voltages have become equal to or less than the reference voltage. The fuel cell control device according to any one of claims 11 to 13.   A vehicle comprising the fuel cell control device according to claim 11.

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