CA2629627C - Fuel cell system and method for reducing electrode deterioration during start up - Google Patents

Fuel cell system and method for reducing electrode deterioration during start up Download PDF

Info

Publication number
CA2629627C
CA2629627C CA2629627A CA2629627A CA2629627C CA 2629627 C CA2629627 C CA 2629627C CA 2629627 A CA2629627 A CA 2629627A CA 2629627 A CA2629627 A CA 2629627A CA 2629627 C CA2629627 C CA 2629627C
Authority
CA
Canada
Prior art keywords
fuel
gas
hydrogen
air
fuel cell
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA2629627A
Other languages
French (fr)
Other versions
CA2629627A1 (en
Inventor
Shinichi Makino
Masatoshi Iio
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nissan Motor Co Ltd
Original Assignee
Nissan Motor Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nissan Motor Co Ltd filed Critical Nissan Motor Co Ltd
Priority claimed from PCT/IB2006/004310 external-priority patent/WO2008093147A2/en
Publication of CA2629627A1 publication Critical patent/CA2629627A1/en
Application granted granted Critical
Publication of CA2629627C publication Critical patent/CA2629627C/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04097—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with recycling of the reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04223—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells
    • H01M8/04225—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids during start-up or shut-down; Depolarisation or activation, e.g. purging; Means for short-circuiting defective fuel cells during start-up
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/043—Processes for controlling fuel cells or fuel cell systems applied during specific periods
    • H01M8/04302—Processes for controlling fuel cells or fuel cell systems applied during specific periods applied during start-up
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0438—Pressure; Ambient pressure; Flow
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04313—Processes for controlling fuel cells or fuel cell systems characterised by the detection or assessment of variables; characterised by the detection or assessment of failure or abnormal function
    • H01M8/0444—Concentration; Density
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04746—Pressure; Flow
    • H01M8/04753—Pressure; Flow of fuel cell reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2250/00—Fuel cells for particular applications; Specific features of fuel cell system
    • H01M2250/20—Fuel cells in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02T90/40—Application of hydrogen technology to transportation, e.g. using fuel cells

Abstract

A fuel cell system includes a controller that estimates an air replacement state of a fuel electrode and a hydrogen circulation path while the operation of the fuel cell system is stopped. Upon starting the fuel cell system, the controller changes the order in which the operation of a hydrogen circulation pump is started and a hydrogen pressure regulator is opened to start the supply of hydrogen gas on the basis of the estimated air replacement state, thereby preventing deterioration caused by uneven distribution of air and hydrogen in the fuel electrode.

Description

DESCRIPTION
FUEL CELL SYSTEM AND METHOD FOR REDUCING ELECTRODE

DETERIORATION DURING START UP
Technical Field The present invention relates to a proton exchange membrane fuel cell system.

Background Art In general, if hydrogen and oxygen are unevenly distributed in a fuel electrode of a fuel cell-when the fuel cell is started, a local potential is generated in a region where a hydrogen concentration is relatively high and serves to cause a current flow in a direction opposite to that in a normal power-generating state in a region where an oxygen concentration is relatively high. Therefore, an oxidizer electrode, in particular, quickly deteriorates. In order to solve this problem, an invention for discharging oxygen that remains in the fuel electrode and replacing the oxygen with hydrogen gas in a short time is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2004-139984 (see page 12 and Fig. 14). According to this invention, when a fuel cell is started, a control value of a secondary pressure regulator is set to be higher than a supply pressure in a normal power-generating state and hydrogen is supplied to the fuel cell by opening a'hydrogen supply solenoid valve while driving a hydrogen pump.
Disclosure of Invention However, according to the start method disclosed in the above-mentioned publication in which the hydrogen pump is started first, even when the fuel electrode of the fuel cell is filled with air (or hydrogen), if the gas composition in the fuel electrode and a hydrogen circulation path is.uneven, hydrogen (or air) that remains in the hydrogen circulation path flows into the fuel electrode immediately after the operation of the hydrogen pump is started. In addition, it requires a relatively long time for the hydrogen circulation pump to accelerate to a predetermined rotational speed after the hydrogen circulation pump is started. Therefore, it takes a relatively long time to eliminate the uneven distribution of hydrogen and oxygen in the fuel electrode, and accordingly the deterioration of the fuel cell progresses.
In order to solve the above-described problem, a fuel cell system according to one aspect of the present invention includes an air-replacement-state recognizing unit for estimating or detecting a state in which hydrogen and air are unevenly distributed in at least one of a fuel electrode and a fuel-gas circulation path and a start control device that selects an order for operating the fuel-gas circulation pump and supplying the fuel gas upon starting the fuel cell based on the output of the air-replacement-state recognizing means. This system can be used to reduce the period of time in which hydrogen and oxygen are unevenly distributed in the fuel electrode, thereby reducing deterioration.

According to the present invention, the timings of activation of the fuel-gas circulation pump and the supply of fuel gas are changed on the basis of the air replacement state and, as a result, deterioration of the fuel cell caused by uneven distribution of the fuel gas and air in the fuel electrode caused by air infiltration into the fuel chamber (the fuel electrode, the fuel-gas circulation path, and fuel-gas circulating means) is prevented.

The air-replacement-state recognizing means may comprise a timer for estimating the air replacement state, or one or more sensors for detecting the oxygen concentration and/or hydrogen (fuel gas) at a portion of the fuel-gas circulation path where replacement of the hydrogen by air is finished first or last after the fuel cell stops, or any combination thereof.
Thus in one aspect, the present invention provides a fuel cell system comprising: a fuel cell that includes a fuel electrode and an oxidizer electrode and an electrolyte disposed between the fuel electrode and the oxidizer 3a electrode, the fuel cell generating electric power when fuel gas and oxidizing gas are supplied to the fuel electrode and the oxidizer electrode, respectively; a fuel-gas circulation path that connects an inlet of the fuel electrode to an outlet of the fuel electrode, the fuel gas being supplied through the inlet and discharged from the outlet; a fuel-gas circulation pump on the fuel-gas circulation path; air-replacement-state recognizing means that estimates or detects a state in which hydrogen and air are unevenly distributed in at least one of the fuel electrode and the fuel-gas circulation path, wherein the air replacement state recognizing means comprises a timer for estimating the air replacement state, or an oxygen concentration sensor and/or a fuel-gas concentration sensor for detecting the air replacement state and being disposed at a portion of the fuel-gas circulation path where replacement of the fuel gas by air is finished first or last after the fuel cell stops, or any combination thereof; and a controller that detects a desire to start the fuel cell, that samples an output of the air-replacement-state recognizing means after detecting the desire to start the fuel cell and that selects an order for operating the fuel-gas circulation pump and supplying the fuel gas upon starting the fuel cell based on the output of the air-replacement-state recognizing means.

In another aspect, the present invention provides a method for starting up a fuel cell system, wherein the fuel cell system comprises a fuel cell that includes a fuel electrode, an oxidizer electrode and an electrolyte disposed between the fuel electrode and the oxidizer electrode, the fuel cell generating electric power when fuel gas and oxidizing gas are supplied to the fuel electrode and the oxidizer electrode, respectively, a fuel-gas circulation path that connects an inlet of the fuel electrode to an 3b outlet of the fuel electrode, the fuel gas being supplied through the inlet and discharged from the outlet, a fuel-gas circulation pump provided on the fuel-gas circulation path, and air-replacement-state-recognizing means that estimates or detects a state in which hydrogen and air are unevenly distributed in at least one of the fuel electrode and the fuel-gas circulation path, wherein the air replacement state recognizing means comprises a timer for estimating the air replacement state, or an oxygen concentration sensor and/or a fuel-gas concentration sensor for detecting the air replacement state and being disposed at a portion of the fuel-gas circulation path where replacement of the fuel gas by air is finished first or last after the fuel cell stops, or any combination thereof, the method comprising: detecting a desire to start the fuel cell; estimating or detecting a state in which hydrogen and air are unevenly distributed in at least one of the fuel electrode and the fuel-gas circulation path after detecting the desire to start the fuel cell and before starting the fuel cell; and selecting an order for operating the fuel-gas circulation pump and for activating a fuel gas supply upon starting the fuel cell based on whether or not it is estimated or detected that hydrogen and air are unevenly distributed.

In certain embodiments of the above-described fuel cell system, the controller is configured to operate the fuel-gas circulation pump after supplying the fuel gas if the output of the air-replacement-state-recognizing means indicates that hydrogen and air are unevenly distributed, so as to reduce the time period in which hydrogen and oxygen are unevenly distributed in the fuel electrode and reduce deterioration of the fuel cell.
In certain other embodiments, the above-described fuel cell system further comprises a shutoff valve disposed 3c between an outlet of the fuel-gas circulation pump and an inlet of a fuel cell body, and in this type of system, if the output of the air-replacement-state recognizing means indicates that hydrogen and air are unevenly distributed, the controller starts operation of the fuel-gas circulation pump after closing the shutoff valve, and then opens the shutoff valve and starts the supply of the fuel gas when a rotational speed of the fuel-gas circulation pump becomes equal to or more than a predetermined value or when an inner pressure of the fuel electrode becomes equal to or less than a predetermined value.

Brief Description of the Drawings Fig. 1 is a diagram illustrating a fuel cell system.
Fig. 2 is a diagram illustrating a single cell in a fuel cell.
Fig. 3 is a diagram illustrating an inner state (state A) of a fuel chamber.

Fig. 4 is a diagram illustrating another inner state (state B) of the fuel chamber.

Fig. 5 is a diagram illustrating another inner state (state C) of the fuel chamber.

Fig. 6 is a flowchart of a process performed in a fuel cell system according to a first embodiment of the present invention.

Fig. 7 is a diagram illustrating the fuel cell system according to the first embodiment of the present invention.
Fig. 8 is a diagram illustrating a fuel cell system according to a second embodiment of the present invention.
Fig. 9 is a flowchart of a process performed in the fuel cell system according to the second embodiment of the present invention.

Fig. 10 is a diagram illustrating a fuel cell system according to a third embodiment of the present invention.
Fig. 11 is a flowchart of a process performed in the fuel cell system according to the third embodiment of the present invention.

Fig. 12 is a diagram illustrating a fuel cell system according to a fourth embodiment of the present invention.
Fig. 13 is a flowchart of a process performed in the fuel cell system according to the fourth embodiment of the present invention.
Fig. 14 is a diagram illustrating a fuel cell system according to a fifth embodiment of the present invention.
Fig. 15 is a flowchart of a process performed in the fuel cell system according to the fifth embodiment of the present invention.

Fig. 16 is a diagram illustrating a fuel cell system according to a sixth embodiment of the present invention.
Fig. 17 is a flowchart of a process performed in the fuel cell system according to the sixth embodiment of the present invention.

Fig. 18 is a flowchart of a process performed in a fuel cell system according to a seventh embodiment of the present invention.

Reference Numerals 1 fuel cell body la oxidizer electrode lb fuel electrode 11 air compressor 12 air supply path 13 air-system humidifier 14 air discharge path 15 air pressure regulator 16 air pressure gage 17 hydrogen detector 21 high-pressure hydrogen tank 22 hydrogen supply path 23 hydrogen pressure regulator 24 hydrogen circulation pump 25 hydrogen-system humidifier 26 hydrogen circulation path 27 hydrogen discharge path 28 hydrogen discharge valve 29 hydrogen pressure gage 31 cooling water pump 32 cooling water circulation path 33 heat exchanger 34 cooling water thermometer 40 load device 41 voltmeter 42 ammeter 43 controller 50 oxygen concentration meter 51 hydrogen concentration meter 52 oxygen concentration meter 53 hydrogen concentration meter 54 hydrogen-circulation-pump discharge shutoff valve 60 timer =
Detailed Description Next, embodiments of the present invention will be described in detail with reference to the drawings.

First, the overall structure of a fuel cell system to which the present invention may be applied will be described below with reference to Fig. 1, which is a diagram illustrating the fuel cell system and Fig. 2, which is a diagram illustrating a single cell in a fuel cell.

Fuel Cell Body As shown in Fig. 2, a single cell 100 of a fuel cell includes a membrane-electrode assembly (MEA) 101 including a solid polymer electrolyte membrane 102, a fuel-electrode catalyst layer 103 provided on one side of the electrolyte membrane 102, and an oxidizer-electrode catalyst layer 104 provided on the other side of the electrolyte membrane 102;
a fuel-gas diffusion layer 105 provided on one side of the MEA 101; an oxidizing-gas diffusion layer 106 provided on the other side of the MEA 101; and separators 107 and 108.

A fuel-gas path 109 is provided between the separator 107 and the fuel-gas diffusion layer 105 and an oxidizing-gas path 110 is provided between the separator 108 and the oxidizing-gas diffusion layer 106. The fuel cell body includes a plurality of cells similar to the single cell 100.
Fuel gas (hydrogen) and oxidizing gas (air) are externally supplied to the fuel cell body and are caused to flow through the fuel-gas path 109 and the oxidizing-gas path 110, respectively, so that electric power is generated as a result of electrochemical reaction.

A fuel cell system to which the present invention may be applied includes a fuel cell body 1, an air system for supplying air, a hydrogen system for supplying hydrogen, a cooling water system for supplying cooling water, and a load system for extracting the electric power from the fuel cell body 1.

Air System The air system includes an air compressor 11 for sucking in and compressing air, an air-system humidifier 13 for humidifying the air compressed by the air compressor 11 and supplying the humidified air to an oxidizer electrode la, an air pressure gage 16 for detecting the pressure of the air supplied to the oxidizer electrode la, and an air pressure regulator 15 for adjusting the pressure in the oxidizer electrode la by regulating the air discharged from the oxidizer electrode la.

The air compressed by the air compressor 11 is supplied through the air supply path 12 to the air-system humidifier 13, and is humidified. Then, the humidified air is supplied to the oxidizer electrode la of the fuel cell body 1, and is consumed by the electrochemical reaction in the fuel cell body 1. Then, the exhaust air is caused to flow through the air discharge path 14= and is discharged from the system after the pressure adjustment is performed by the air pressure regulator 15. The pressure of the air supplied to the oxidizer electrode la is detected by the air pressure gage 16 disposed at an inlet of the oxidizer electrode la, and the air pressure regulator 15 is controlled such that the detected pressure becomes equal to a desired pressure.
The air-system humidifier 13 may include a water vapor exchange membrane for utilizing moisture included in the exhaust or may use pure water that is externally supplied.

A hydrogen detector 17 for detecting hydrogen included in the exhaust air is disposed downstream of the air pressure regulator 15. Accordingly, hydrogen that enters through the electrolyte membrane 102 from the fuel electrode to the oxidizer electrode and hydrogen that leaks from a sealed portion can be detected.

Hydrogen System The hydrogen system includes a high-pressure hydrogen tank 21 that stores hydrogen gas, a hydrogen pressure regulator 23 for adjusting the pressure of the hydrogen, a hydrogen-system humidifier 25 for humidifying the hydrogen I

-after the pressure thereof is adjusted and supplying the humidified hydrogen to a fuel electrode ib, a hydrogen pressure gage 29 for detecting the pressure of the hydrogen supplied to the fuel electrode ib, a hydrogen circulation pump 24 and a hydrogen circulation path 26 for circulating the hydrogen discharged from an outlet of the fuel electrode lb to an inlet of the fuel electrode lb, and a hydrogen discharge path 27 and a hydrogen discharge valve 28 for discharging impurities accumulated in the fuel electrode lb and the hydrogen circulation path 26 from the system.

The hydrogen supplied from the high-pressure hydrogen tank 21 flows through the hydrogen supply path 22 via the hydrogen pressure regulator 23, where the pressure of the hydrogen is adjusted to a desire pressure, and joins the discharge hydrogen circulated by the hydrogen circulation pump 24. Then, the hydrogen is humidified by the hydrogen system humidifier 25, and is fed to the fuel electrode lb of the fuel-cell body 1. The pressure of the hydrogen supplied to the fuel electrode lb is detected by the hydrogen pressure gage 29 provided at the inlet of the fuel electrode lb, and the hydrogen pressure regulator 23 is controlled such that the detected pressure becomes equal to the desired pressure. After the hydrogen is consumed by the electrochemical reaction in the fuel cell body 1, the excess hydrogen is caused to pass through the hydrogen circulation path 26 by the hydrogen circulation pump 24 and is used for power generation again.

On the other hand, nitrogen that enters from the oxidizer electrode la to the fuel electrode lb during the operation and impurities included in the high-pressure hydrogen tank 21 accumulate in the hydrogen system.
Therefore, these impurities are discharged from the system through the hydrogen discharge path 27 by opening the hydrogen discharge valve 28.

Cooling Water System The cooling water system is provided to maintain the temperature of the fuel cell body 1 at an adequate temperature by removing heat generated as a result of power generation performed by the fuel cell body 1. The cooling water system includes a cooling water pump 31 for circulating the cooling water, a cooling water circulation path 32, a heat exchanger 33 for dissipating heat to the outside of the system, and a cooling water thermometer 34 for detecting the temperature of the cooling water at a position near a cooling-water outlet of the fuel cell body 1.

The cooling water is pressurized by the cooling water .pump 31 so as to flow through the fuel cell body 1, and thereby absorbs heat. Then, the cooling water flows through the cooling water circulation path 32 to the heat exchanger 33, where the.heat is discharged to the outside of the system. Then, the cooling water is caused to flow through the fuel cell body 1 again by the cooling water pump 31.
The temperature of the cooling water is monitored by the cooling water thermometer 34 and is adjusted to a temperature appropriate for the power generation level provided by the fuel cell body by controlling the amount of air flow supplied to the heat exchanger 33 by a blower.
Load System A load device 40 that absorbs the electric power generated by the fuel cell body 1 functions as, for example, an inverter for supplying electric power to a vehicle drive motor in a fuel cell vehicle. A power generation voltage of the fuel cell body 1 is detected by a voltmeter 41 and a .current supplied to the load device 40 from the fuel cell body 1 is detected by an ammeter 42.

Control System A controller 43 operates as a start control device to control the overall operation of the fuel cell system including the fuel cell body 1. The controller 43 includes, for example, a central processing unit (CPU), a read only memory (ROM) that stores control programs and control parameters, a working random access memory (RAM), and a microprocessor including an input/output interface.

The controller 43 outputs control signals to the air compressor 11, the air pressure regulator 15, the hydrogen pressure regulator 23, the hydrogen discharge valve 28, the cooling water pump 31, and the load device 40 on the basis of detected signals obtained from the air pressure gage 16, the hydrogen pressure gage 29, the cooling water thermometer 34, the voltmeter 41, and the ammeter 42 in order to adjust the pressure, temperature, the amount of flow, and the load in the fuel cell body 1.

Next, the state of the fuel chamber (the hydrogen supply path 22, the hydrogen circulation pump 24, the hydrogen-system humidifier 25, the fuel electrode lb, and the hydrogen circulation path 26 that varies in a period from when the fuel cell system stops to when the fuel cell system is restarted will be described with reference to Figs.
3, 4, and 5. In the figures, the hydrogen-system humidifier 25 is omitted.

A. Immediately after stoppage In a period immediately after the stoppage, the fuel chamber is filled with hydrogen provided before the power generation was stopped.

B. After an extended time from stoppage (or when air replacement occurs) After a sufficient time from the stoppage, air leaks or otherwise enters through the MEA 101 from the oxidizer electrode la to the fuel electrode lb and diffuses into the fuel chamber so that the fuel chamber becomes filled with the air. The amount of the original hydrogen that has been replaced by the infiltrated air is referred to herein as the air replacement state. The time required for the air to fill the fuel chamber varies in accordance with the material, the thickness, the temperature, etc., of the MEA, but is generally about several hours.

C. Several minutes to several tens of minutes after stoppage In a relatively short time period after the stoppage, the air diffuses into the fuel electrode lb, whereas other portions (the hydrogen circulation pump 24, the hydrogen-system humidifier 25, and the hydrogen circulation path 26) remain filled with hydrogen provided in the previous operation of power generation. Therefore, different from state B, the air and hydrogen are unevenly distributed in the fuel chamber. The time period and rate in which the hydrogen is replaced with air varies in accordance with the material, the thickness, the temperature, etc., of the MEA, but is generally about several minutes to several tens of minutes. Here, the uneven distribution refers to the state in which hydrogen and oxygen (or gases having different hydrogen densities) exist separately within the fuel chamber.
First Embodiment Next, a fuel cell system according to a first embodiment of the present invention will be described below.
The structure of'the fuel cell system according to the first embodiment is similar to that shown in Fig. 1. However, the controller 43 includes an air-replacement-state estimator for estimating an air replacement state of the fuel electrode lb and the hydrogen circulation path 26 when the fuel cell system is stopped. When the fuel cell system is started, the controller 43 controls the timings at which the operation of the hydrogen circulation pump 24 is started and the hydrogen pressure regulator 23 is opened to start supplying the fuel gas on the basis of the estimated air replacement state.

Start Method for First Embodiment Next, a method for starting the fuel cell system according to the present embodiment will be described below with reference to a flowchart shown in Fig. 6. When, for example, the state of a key switch is changed from Off to On, the controller 43 detects the change and follows the steps of the flowchart of Fig. 6 to start the fuel cell system.

First, in Step 01 ('Step' is hereafter abbreviated as 'S'), it is determined whether or not a time elapsed after the previous stoppage is within a first predetermined time by referring to an air replacement state recognizing means (e.g., a timer 60).

If it is determined that the elapsed time is equal to or less than the first predetermined time in SOl, that is, if the result of the determination of S0l is Yes, it is determined that the fuel chamber is filled with hydrogen provided in the previous operation of power generation (state A). Accordingly, it is determined that hydrogen and oxygen are not unevenly distributed in the fuel electrode lb and the deterioration will not progress during start up.
Therefore, the process proceeds to S06, where the supply of hydrogen is started and the hydrogen circulation pump 24 is activated. Here, the order in which the supply of hydrogen is started and the hydrogen circulation pump 24 is activated is not restricted. Accordingly, the supply of hydrogen may be started and the hydrogen circulation pump 24 may be activated at the same time. Then, the process proceeds to S05, where a normal operation routine is performed. The normal operation routine is a control routine for performing a normal operation. More specifically, in the normal operation, the air system, the hydrogen system, the cooling system, the load system, and the control system are operated in accordance with the load requirement of the system. Here, the uneven distribution refers to the state in which hydrogen and oxygen (or gases having different hydrogen densities) exist separately.

If it is determined that the elapsed time is more than the first predetermined time in S01, that is, if the result of the determination of SO1 is No, the process proceeds to S02, where it is determined whether or not the time elapsed after the previous stoppage is equal to or more than a second predetermined time by referring to the timer.

If it is determined that the elapsed time is equal to or more than.the second predetermined time in S02, that is, if the result of the determination of S02 is Yes, it is determined that the fuel chamber is filled with air from the oxidizer electrode la during the stoppage (state B) and the process proceeds to S03. In S03, first, the hydrogen circulation pump 24 is activated to generate a negative pressure at the outlet of (and gas flow through) the fuel electrode lb, and then the supply of hydrogen gas is started by executing a hydrogen supply start routine. Therefore, the time period in which hydrogen and oxygen are unevenly distributed in the fuel electrode lb is reduced and the deterioration is reduced. Then, the process proceeds to S05, where the normal operation routine is performed.

If it is determined that the elapsed time is less than the second predetermined time in S02, that is, if the result of the determination of S02 is No, it is determined that hydrogen that remains after the previous stoppage of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C), and the process proceeds to S04. In S04, first, the supply of hydrogen gas is started, and then the hydrogen circulation pump 24 is started. Therefore, the uneven distribution of hydrogen and oxygen in the fuel electrode lb, which would otherwise occur under prior art methods immediately after the hydrogen circulation pump is activated, can be avoided and the deterioration can be prevented from progressing. The process then proceeds to S05, where the normal operation routine is performed.

The above-described embodiment provides the following effects:

(1) If it is determined that the fuel electrode lb is filled with hydrogen (state A), then the normal power generating operation can be started immediately. Therefore, the start time can be reduced.

(2) If it is determined that fuel electrode lb is substantially filled with air (state B), then high-pressure hydrogen can be supplied and drawn through the fuel electrode lb in response to a negative pressure generated in the fuel electrode lb by the hydrogen circulation pump 24.
Therefore, the time period during which hydrogen and oxygen are unevenly distributed in the fuel electrode lb can be reduced and the deterioration of the fuel cell can be suppressed.

(3) If it is determined that hydrogen that remains after the previous stoppage of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C), then the hydrogen circulation pump 24 is started after the supply of hydrogen gas is started. Therefore, the uneven distribution of hydrogen and oxygen in the fuel electrode lb, which would otherwise occur using prior art methods immediately after the hydrogen circulation pump is operated, can be avoided and the deterioration of the fuel cell can be prevented from progressing.

Estimation of the air replacement state of the fuel chamber based on the stop period and correction based on temperature Next, the first and second predetermined times for determining the mixed air state of the fuel chamber on'the basis of the time elapsed after the previous stoppage until the restart will be described below. To determine these times, an oxygen concentration sensor or a hydrogen concentration sensor is disposed at a certain position in the fuel chamber of an experimental fuel cell system and a variation with time in the concentration of oxygen or hydrogen after the fuel cell system is stopped is experimentally measured. Then, the first predetermined time is determined as a time period during which the oxygen concentration is equal to or less than a predetermined value (the hydrogen concentration is equal to or more than a predetermined value) and at which the deterioration does not progress even when the normal operation routine is started in the fuel chamber immediately after the fuel cell system is started.

The second predetermined time is based upon temperature and is determined as a time period required for the oxygen concentration to become equal to or more than a predetermined value (for the hydrogen concentration to become equal to or less than a predetermined value) at which the deterioration of the fuel electrode lb does not progress even when the hydrogen circulation pump 24 is operated first in the fuel chamber.

The time rate at which the air enters from the oxidizer electrode la to the fuel electrode lb depends on the temperature of the fuel cell body 1, and the transmission speed is increased as the temperature is increased.
Therefore, an experiment of, for example, varying the fuel cell temperature detected by the cooling water thermometer 34 and measuring the variation with time in gas concentration in the fuel chamber is performed and a correction value (correction coefficient) shown in Fig. 7 is determined and stored in the controller in advance. The first and second predetermined times are multiplied by the correction value so that first and second predetermined times can be used as more accurate determination thresholds.
Second Embodiment A fuel cell system according to a second illustrated embodiment of the present invention will be described below.
Fig. 8 is a system diagram showing the structure according to the second embodiment. The structure according to the second embodiment is similar to that shown in Fig. 1 except an oxygen concentration meter 50 for measuring the oxygen concentration in the hydrogen circulation pump 24 is additionally provided as an air replacement state recognizing means.

Start Method A method for starting the fuel cell system according to the second embodiment will be described below with reference to a flowchart shown in Fig. 9. When, for example, the state of a key switch is changed from Off to On, the controller 43 detects the change and follows the steps of the flowchart of Fig. 9 to start the fuel cell system.
First, in Sil, a detection value of the oxygen concentration meter 50 is read and it is determined whether or not the oxygen concentration in the hydrogen circulation pump 24 is equal to or more than a predetermined value. If it is determined that the oxygen concentration is equal to or more than the predetermined value in S11, that is, if the result of the determination of S11 is Yes, it is determined that the fuel chamber is filled with air transmitted from .
the oxidizer electrode la during the stoppage (state B) and the process proceeds to S12. In S12, first, the hydrogen circulation pump 24 is started to generate a negative pressure at the outlet of (and gas flow through) the fuel electrode lb, and then the supply of fuel gas is started.
Therefore, the time period in which hydrogen and oxygen are unevenly distributed in the fuel electrode lb is reduced and the deterioration is suppressed. The process then proceeds to S14, where the normal operation routine is performed.

If is determined that the oxygen concentration is less than the predetermined value in S11, that is, if the result of the determination of S11 is No, it is determined that hydrogen that remains after the previous stoppage of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C) or =

that the fuel chamber is filled with hydrogen provided before the previous stoppage of power generation (state A), and the process proceeds to S13.

In S13, first, the supply of hydrogen gas is started, and then the operation of the hydrogen circulation pump 24 is started. Therefore, the uneven distribution of hydrogen and oxygen in the fuel electrode lb, which would otherwise occur under prior methods immediately after the hydrogen circulation pump is started, can be avoided and the deterioration of the fuel cell can be prevented from progressing. Then, the process proceeds to S14, where the normal operation routine is performed.

The above-described embodiment provides the following effects:

(1) If it is determined that fuel electrode lb is filled with air (state B), high-pressure hydrogen can be supplied after a negative pressure is generated in, and gas flow resumes, through the fuel electrode lb by operation of the hydrogen circulation pump 24. Therefore, the time period during which hydrogen and oxygen are unevenly distributed in the fuel electrode lb can be reduced and the deterioration of the fuel cell can be suppressed.

(2) If it is determined that hydrogen provided in the previous operation of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C) or that the fuel chamber lb is filled with hydrogen (state A), the operation of the hydrogen circulation pump 24 is started after the supply of hydrogen gas is started. Therefore, the uneven distribution of hydrogen and oxygen in the fuel electrode ib, which would otherwise occur using prior methods immediately after the hydrogen circulation pump is operated, can be avoided and the deterioration of the fuel cell can be prevented from progressing.

State A and state C can be divided from each other on the basis of the time elapsed after the stoppage, as described in the first embodiment. Therefore, the start time may, of course, be reduced by immediately performing the normal operation routine if it is determined that the fuel chamber is in state A.

Predetermined value of oxygen concentration The predetermined value used for the determination performed in Sli is obtained in advance by experiment and is set to an oxygen concentration at which the deterioration of the fuel electrode lb does not progress even when the hydrogen circulation pump 24 is operated first in the fuel chamber.

Reason why the oxygen concentration meter is disposed in the hydrogen circulation pump 24 In the hydrogen circulation pump 24, a gap between a casing and a rotor is set to be sufficiently small so as to prevent an internal leakage from an outlet to an inlet during operation. Therefore, the hydrogen circulation pump 24 cannot be easily filled with air compared to other portions after stopping, and is last to be filled with air in the hydrogen circulation system via diffusion.

Third Embodiment A fuel cell system according to a third illustrated embodiment of the present invention will be described below.
Fig. 10 is a system diagram showing the structure according to the third embodiment. The structure according to the third embodiment is similar to that shown in Fig. 1 except a hydrogen concentration meter 51 for measuring the hydrogen concentration in the hydrogen circulation pump 24 is additionally provided as an air replacement state recognizing means.

Start Method A method for starting the fuel cell system according to the third embodiment will be described below with reference to a flowchart shown in Fig. 11. When, for example, the state of a key switch is changed from Off to On, the controller 43 detects the change and follows the steps of the flowchart of Fig. 11 to start the fuel cell system.

First, in S21, a detection value of the hydrogen concentration meter 51 is read and it is determined whether or not the hydrogen concentration in the hydrogen circulation pump 24 is equal to or less than a predetermined value. If it is determined that the hydrogen concentration is equal to or less than the predetermined value in S21, that is, if the result of the determination of S21 is Yes, it is determined that the fuel chamber is filled with air transmitted from the oxidizer electrode la during the stoppage (state B) and the process proceeds to S22. In S22, first, the hydrogen circulation pump 24 is started to generate a negative pressure at the outlet of the fuel electrode lb (and gas flow through the fuel electrode lb), and then the supply of fuel gas is started. Therefore, the time period in which hydrogen and oxygen are unevenly distributed in the fuel electrode lb is reduced and deterioration is suppressed. Then, the process proceeds to S24, where a normal operation routine is performed.

If is determined that the hydrogen concentration is more than the predetermined value in 521, that is, if the result of the determination of S21 is No, it is determined =

that hydrogen that remains after the previous stoppage of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C) or that the fuel chamber is filled with hydrogen provided before the previous stoppage of power generation (state A), and the process proceeds to S23.

In S23, first, the supply of hydrogen gas is started, and then the hydrogen circulation pump 24 is started.
Therefore, the uneven distribution of hydrogen and oxygen in the fuel electrode lb, which would otherwise occur using prior art methods immediately after the hydrogen circulation pump is operated, can be avoided and the deterioration of the fuel cell is prevented from progressing. Then, the process proceeds to S24, where the normal operation routine is performed.

The above-described embodiment provides the following effects:

(1) If it is determined that fuel electrode lb is filled with air (state B), high-pressure hydrogen is supplied after a negative pressure is generated in the fuel electrode lb (and gas flow resumes through the fuel electrode lb) by operation of the hydrogen circulation pump 24. Therefore, the time period during which hydrogen and oxygen are unevenly distributed in the fuel electrode lb is s reduced and the deterioration of the fuel cell is suppressed.
(2) If it is determined that hydrogen provided in the previous operation of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C) or that the fuel chamber lb is filled with hydrogen (state A), the operation of the hydrogen circulation pump 24 is started after the supply of hydrogen gas is started. Therefore, the uneven distribution of hydrogen and oxygen in the fuel electrode ib, which would otherwise occur using prior art methods immediately after the hydrogen circulation pump is operated, is avoided and the deterioration of the fuel cell is prevented from progressing.

State A and state C can be divided from each other on the basis of the time elapsed after the stoppage, as described in the first embodiment. Therefore, the start time may, of course, be reduced by immediately performing the normal operation routine if it is determined that the fuel chamber is in state A.

Predetermined value of hydrogen concentration The predetermined value used for the determination performed in S21 is obtained in advance by experiment and is set to a hydrogen concentration at which the deterioration of the fuel electrode lb does not progress even when the hydrogen circulation pump 24 is operated first in the fuel chamber.

Reason why the hydrogen concentration meter is disposed in the hydrogen circulation pump 24 In the hydrogen circulation pump 24, a gap between a casing and a rotor is set to be sufficiently small so as to prevent an internal leakage from an outlet to an inlet during the operation. Therefore, the hydrogen circulation pump 24 cannot be easily filled with air compared to other portions after stopping, and is last to be filled with air in the hydrogen circulation system via diffusion.

Fourth Embodiment Next, a fuel cell system according to a fourth illustrated embodiment of the present invention will be described below. Fig. 12 is a system diagram showing the structure according to the fourth embodiment. The structure according to the fourth embodiment is similar to that shown in Fig. 1 except an oxygen concentration meter 52 for measuring the oxygen concentration is additionally provided at the outlet of the fuel electrode lb of the fuel cell body 1 as an air replacement state recognizing means.

Start Method A method for starting the fuel cell system according to the fourth embodiment will be described below with reference to a flowchart shown in Fig. 13. When, for example, the state of a key switch is changed from Off to On, the controller 43 detects the change and follows the step of the flowchart of Fig. 13 to start the fuel cell system.

First, in S31, a detection value of the oxygen concentration meter 52 is read and it is determined whether or not the oxygen concentration at the outlet of the fuel cell body 1 is equal to or less than a predetermined value.
If it is determined that the oxygen concentration is equal to or less than the predetermined value in S31, that is, if the result of the determination of S31 is Yes, then it is determined that the fuel chamber is filled with hydrogen provided before the previous stoppage of power generation (state A). Accordingly, it is determined that hydrogen and oxygen are not unevenly distributed in the fuel electrode lb and the deterioration of the fuel cell will not progress.
Therefore, the process proceeds to S34, where the supply of hydrogen is started and the hydrogen circulation pump 24 is activated. Here, the order in which the supply of hydrogen is started and the hydrogen circulation pump 24 is activated is not restricted. Accordingly, the supply of hydrogen may be started and the hydrogen circulation pump 24 may be activated simultaneously. Then, the process proceeds to S33, where the normal operation routine is performed.

If it is determined that the oxygen concentration is more than the first predetermined time in S31, that is, if the result of the determination at S31 is No, it is determined that the fuel chamber is filled with air transmitted from the oxidizer electrode la during the stoppage (state B) or that hydrogen provided before the previous stoppage of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C), and the process proceeds to S32.
In S32, first, the supply of hydrogen gas is started, and then hydrogen circulation pump 24 is started. Therefore, uneven distribution of hydrogen and oxygen can be avoided and the deterioration of the fuel cell can be prevented from progressing. Then, the process proceeds to S33, where the normal operation routine is performed.

The above-described embodiment provides the following effects:

(1) If it is determined that the fuel electrode lb is filled with hydrogen (state A), the normal power generating operation can be started immediately. Therefore, the start time can be reduced.

(2) If it-is determined that the fuel chamber is filled r with air transmitted from the oxidizer electrode la during the stoppage (state B) or that hydrogen provided in the previous operation of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C), the operation of the hydrogen circulation pump 24 is started after the supply of hydrogen gas is started. Therefore, the uneven distribution of hydrogen and oxygen in the fuel electrode lb, which would otherwise occur using prior art methods immediately after the hydrogen circulation pump is operated, can be avoided and the deterioration of the fuel cell can be prevented from progressing.

State B and state C can be divided from each other on the basis of the time elapsed after the stoppage, as described in the first embodiment. Therefore, the deterioration of the fuel cell can be suppressed by operating the hydrogen circulation pump 24 first when it is determined that the fuel chamber is in state B.
Predetermined value of oxygen concentration The predetermined value used for the determination performed in S31 is obtained in advance by experiment and is set to an oxygen concentration at which the deterioration of the fuel electrode lb does not progress even when the normal operation routine is started in the fuel chamber immediately after the system is started.

Reason why the oxygen concentration meter is disposed at the outlet of the fuel cell body 1 Since the air enters from the oxidizer electrode la into the fuel electrode lb during the stoppage, the air replacement state in the fuel chamber can be detected by placing the oxygen concentration meter at the outlet of the fuel cell body 1. The oxygen concentration meter may, of course, be placed at the inlet of the fuel cell body 1. The outlet and the inlet of the fuel electrode lb of the fuel cell body 1 are first to be filled with air in the hydrogen circulation system except for the inside of the fuel cell, where it is difficult to set the oxygen concentration meter.
Fifth Embodiment Next, a fuel cell system according to a fifth illustrated embodiment of the present invention will be described below. Fig. 14 is a system diagram showing the structure according to the fifth embodiment. The structure according to the fifth embodiment is similar to that shown in Fig. 1 except a hydrogen concentration meter 53 for measuring the hydrogen concentration is additionally provided at an outlet of the fuel electrode lb of the fuel cell body 1 as an air replacement state recognizing means.

s Start Method Next, a method for starting the fuel cell system according to the present embodiment will be described below with reference to a flowchart shown in Fig. 15. When, for example, the state of a key switch is changed from Off to On, the controller 43 detects the change and follows the steps of the flowchart of Fig. 15 to start the fuel cell system.
First, in S41, a detection value of the hydrogen concentration meter 53 is read and it is determined whether or not the hydrogen concentration at the outlet of the fuel cell body 1 is equal to or more than a predetermined value.
If it is determined that the hydrogen concentration is equal to or more than the predetermined value in S41, that is, if the result of the determination of S41 is Yes, it is determined that the fuel chamber is filled with hydrogen provided before the previous stoppage of power generation (state A). Accordingly, it is determined that hydrogen and oxygen are not unevenly distributed in the fuel electrode lb and the deterioration of the fuel cell does not progress.
Therefore, the process proceeds to S44, where the supply of hydrogen is started and the hydrogen circulation pump 24 is activated. Here, the order in which the supply of hydrogen is started and the hydrogen circulation pump 24 is activated is not restricted. Accordingly, the supply of hydrogen may be started and the hydrogen circulation pump 24 may be activated at the same time. Then, the process proceeds to S43, where a normal operation routine is performed.

If it is determined that the hydrogen concentration is less than the first predetermined time in S41, that is, if the result of the determination of S41 is No, then it is determined that*the fuel chamber is filled with air that enters from the oxidizer electrode la during the stoppage (state B) or that hydrogen provided before the previous stoppage of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C), and the process proceeds to S42.

In S42, first, the supply of hydrogen gas is started, and then the operation of the hydrogen circulation pump 24 is started. Therefore, uneven distribution of hydrogen and oxygen can be avoided and the deterioration of the fuel cell can be prevented from progressing. Then, the process proceeds to S43, where the normal operation routine is performed.

The above-described embodiment provides the following effects:

(1) If it is determined that the fuel electrode lb is filled with hydrogen (state A), the normal power generating operation can be started immediately. Therefore, the start time can be reduced.

(2) If it is determined that the fuel chamber is filled with air transmitted from the oxidizer electrode la during the stoppage (state B) or that hydrogen provided in the previous operation of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C), the hydrogen circulation pump 24 is started after the supply of hydrogen gas is started.
Therefore, the uneven distribution of hydrogen and oxygen in the fuel electrode 1b, which would otherwise occur using prior art methods immediately after the hydrogen circulation pump is operated, can be avoided and the deterioration of the fuel cell can be prevented from progressing.

State B and state C can be divided from each other on the basis of the time elapsed after the stoppage, as described in the first embodiment. Therefore, the deterioration of the fuel cell can be suppressed by operating the hydrogen circulation pump 24 first when it is determined that the fuel chamber is in state B.
Predetermined value of hydrogen concentration The predetermined value used for the determination performed in S41 is determined in advance by experiment and is set to a hydrogen concentration at which the deterioration of the fuel electrode lb does not progress even when the normal operation routine is started in the fuel chamber immediately after the system is started.
Reason why hydrogen concentration meter is disposed at the outlet of the fuel cell body 1 Since the air enters from the oxidizer electrode la to the fuel electrode lb during the stoppage, the air replacement state in the fuel chamber can be detected by placing the hydrogen concentration meter at the outlet of the fuel cell body 1. The hydrogen concentration meter may, of course, be placed at the inlet of the fuel cell body 1.
The outlet and the inlet of the fuel electrode lb of the fuel cell body 1 are first to be filled with air in the hydrogen circulation system except for the inside of the fuel cell, where it is difficult to set the hydrogen concentration meter.

Sixth Embodiment A fuel cell system according to a sixth illustrated embodiment of the present invention will be described below.
Fig. 16 is a system diagram showing the structure according to the sixth embodiment. The structure according to the sixth embodiment is similar to that shown in Fig. 1 except a hydrogen-circulation-pump discharge shutoff valve 54 is additionally provided between the outlet of the hydrogen circulation pump 24 and a junction of the hydrogen supply path 22 and the hydrogen circulation path 26.

Start Method Next, a method for starting the fuel cell system according to the present embodiment will be described below with reference to a flowchart shown in Fig. 17. When, for example, the state of a key switch is changed from Off to On, the controller 43 detects the change and follows the steps of the flowchart of Fig. 17 to start the fuel cell system.
First, in S51, the hydrogen-circulation-pump discharge shutoff valve 54 is closed. Then, in S52, the operation of the hydrogen circulation pump 24 is started. Then, in S53, the rotational speed of the hydrogen circulation pump 24 is detected and it is determined whether or not the rotational speed is equal to or more than a predetermined value (e.g., in revolutions per second). If it is determined that the rotational speed is equal to or less than the predetermined value in S53, that is, if the result of the determination of S53 is No, then S53 is repeated until the rotational speed reaches the predetermined value.

If it is determined that the rotational speed is equal to or more than the predetermined value in S53, that is, if the result of the determination of S53 is Yes, then it is determined that a sufficient negative pressure is generated to cause sufficient gas flow through the fuel electrode lb and the process proceeds to S54. The negative pressure in the fuel electrode lb may also be determined on the basis of pressure detected by the hydrogen pressure gage 29, instead of the rotational speed of the hydrogen circulation pump 24.

In S54, the hydrogen-circulation-pump discharge shutoff valve 54 is opened and the process proceeds to S55. In S55, the supply of hydrogen is started to eliminate the uneven distribution of hydrogen and oxygen in the fuel electrode lb, and then the normal operation routine is performed in S56.

According to the above-described sixth illustrated embodiment, the operation of the hydrogen gas circulation pump is started after the shutoff valve 54 provided downstream of the hydrogen circulation pump is closed.
Therefore, if it is determined that hydrogen provided before the previous stoppage of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C), the uneven distribution of hydrogen and oxygen in the fuel electrode lb, which would otherwise occur immediately after the hydrogen circulation pump 24 is activated, can be avoided and the deterioration of the fuel cell can be prevented from progressing.

Seventh Embodiment A fuel cell system according to a seventh embodiment of the present invention will be described below. The structure according to the seventh embodiment is similar to those shown in Figs. 1 and 16 except oxygen concentration meters and hydrogen concentration meters similar to the oxygen concentration meters 50 and 52 and the hydrogen concentration meter 51 and 53, respectively, are additionally provided in the hydrogen circulation pump 24 and at the outlet of the fuel cell body 1, as in the second to fourth embodiments.

Start Method A method for starting the fuel cell system according to the seventh embodiment will be described below with reference to a flowchart shown in Fig. 18. When, for example, the state of a key switch is changed from Off to On, the controller 43 detects the change and follows the steps of the flowchart of Fig. 18 to start the fuel cell system.
First, in S61, it is determined whether or not the fuel chamber is filled with hydrogen that remains after the previous stoppage of power generation. If it is determined that the fuel chamber is filled with hydrogen in S61, that is, if the result of the determination of S62 is Yes, then it is determined that the fuel chamber is filled with hydrogen that remains after the previous stoppage of power generation (state A), that hydrogen and oxygen are not unevenly distributed in the fuel electrode lb and that the deterioration of the fuel cell will not progress. Therefore, the process proceeds to S68 and the normal operation routine is performed.

If it is determined that the fuel chamber is not filled with hydrogen in S61, that is, if the result of the determination of S61 is No, then the process proceeds to S62, where it is determined whether or not the fuel chamber is filled with air that enters from the oxidizer electrode la (state B). If it is determined that the fuel chamber is filled with air in S62, that is, if the result of the determination of S62 is Yes, the uneven distribution of hydrogen and oxygen will not occur in the fuel electrode lb even in the case where the hydrogen-circulation-pump discharge shutoff valve 54 is not closed. Therefore, the routine for closing the hydrogen-circulation-pump discharge shutoff valve 54 (S63) is skipped and the routine for operating the hydrogen circulation pump 24 is performed in S64.

If it is determined that the fuel chamber is not filled with air in S62, that is, if the result of the determination of S62 is No, then it is determined that hydrogen provided in the previous operation of power generation and air that enters from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C). Accordingly, the process proceeds to S63, where the hydrogen-circulation-pump discharge shutoff valve 54 is closed. S63 to S68 are similar to S51 to S56 according to the sixth embodiment, and' explanations thereof are thus omitted.

The above-described embodiment provides the following effects:

(1) If it is determined that the fuel electrode lb is filled with hydrogen (state A), the normal power generating operation can be started immediately. Therefore, the start time can be reduced.

(2) If it is determined that the fuel electrode lb is filled with air (state B), the step of closing the hydrogen-circulation-pump discharge shutoff valve 54 is omitted.
Therefore, the start time can be reduced.

(3) If it is determined that hydrogen provided in the previous operation of power generation and air transmitted from the oxidizer electrode la are unevenly distributed in the fuel chamber (state C), an effect similar to that of the sixth embodiment can be obtained.

Estimation of the air replacement state in the fuel chamber In S61 and S62, the air replacement state in the fuel chamber is estimated on the basis of the time elapsed after the stoppage and the detection results of the oxygen concentration meters 50 and 52 and the hydrogen concentration meters 51 and 53 disposed in the hydrogen circulation pump 24 and at the outlet of the fuel cell body 1, similar to the first, second, third, fourth, and fifth embodiments.

In the above-described embodiments, the case in which the fuel cell system is stopped while the fuel electrode is in the hydrogen state and the air electrode is in the air state. However, the effects of the second to seventh embodiments may also be obtained when the fuel electrode and the air electrode are stopped in inert gas (the case in the fuel chamber is not completely filled with the inert gas and hydrogen remains in the fuel chamber).

A specific embodiment of method and apparatus for providing a fuel cell system has been described for the purpose of illustrating the manner in which the invention is made and used. It should be understood that the invention is not limited by the specific embodiments described.

Claims (23)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A fuel cell system comprising:

a fuel cell that includes a fuel electrode and an oxidizer electrode and an electrolyte disposed between the fuel electrode and the oxidizer electrode, the fuel cell generating electric power when fuel gas and oxidizing gas are supplied to the fuel electrode and the oxidizer electrode, respectively;
a fuel-gas circulation path that connects an inlet of the fuel electrode to an outlet of the fuel electrode, the fuel gas being supplied through the inlet and discharged from the outlet;
a fuel-gas circulation pump on the fuel-gas circulation path;
air-replacement-state recognizing means that estimates or detects a state in which hydrogen and air are unevenly distributed in at least one of the fuel electrode and the fuel-gas circulation path, wherein the air replacement state recognizing means comprises a timer for estimating the air replacement state, or an oxygen concentration sensor and/or a fuel-gas concentration sensor for detecting the air replacement state and being disposed at a portion of the fuel-gas circulation path where replacement of the fuel gas by air is finished first or last after the fuel cell stops, or any combination thereof; and a controller that detects a desire to start the fuel cell, that samples an output of the air-replacement-state recognizing means after detecting the desire to start the fuel cell and that selects an order for operating the fuel-gas circulation pump and supplying the fuel gas upon starting the fuel cell based on the output of the air-replacement-state recognizing means.
2. The fuel system of claim 1, wherein the controller operates the fuel-gas circulation pump after supplying the fuel gas if the output indicates that hydrogen and air are unevenly distributed.
3. The fuel cell system according to claim 2, wherein the air-replacement-state recognizing means includes a timer for measuring the time that elapses after the fuel cell stops;
and wherein hydrogen and air are estimated to be unevenly distributed when the elapsed time is more than a first predetermined time and less than a second predetermined time.
4. The fuel cell system according to claim 3, further comprising:
a thermometer that estimates or detects a temperature in the fuel cell; and wherein the controller corrects the first and second predetermined times such that the first and second predetermined times are reduced as the temperature is increased.
5. The fuel cell system according to claim 3 or 4, wherein the controller starts the supply of the fuel gas after the operation of the fuel-gas circulation pump is started if the elapsed time exceeds the second predetermined time.
6. The fuel cell system according to claim 3 or 4, wherein the controller starts the supply of the fuel gas irrespective of whether or not the fuel-gas circulation pump is operated if the elapsed time is equal to or less than the first predetermined time.
7. The fuel cell system according to claim 2, wherein the air-replacement-state recognizing means includes an oxygen concentration sensor for detecting an oxygen concentration, the oxygen concentration sensor being disposed at a portion of the fuel-gas circulation path where replacement of the fuel gas by air is finished last after the fuel cell stops;
and wherein hydrogen and air are unevenly distributed if the oxygen concentration is less than a predetermined value.
8. The fuel cell system according to claim 1, wherein the air-replacement-state recognizing means includes a fuel-gas concentration sensor for detecting a fuel-gas concentration, the fuel-gas concentration sensor being disposed at a portion of the fuel-gas circulation path where replacement of the fuel gas by air is finished last after the fuel cell stops; and wherein the controller operates the fuel-gas circulation pump after supplying the fuel gas if the output indicates that the fuel-gas concentration is more than a predetermined value.
9. The fuel cell system according to claim 1, wherein the air-replacement-state recognizing means includes an oxygen concentration sensor for detecting an oxygen concentration, the oxygen concentration sensor being disposed at a portion of the fuel-gas circulation path where replacement of the fuel gas by air is finished first after the fuel cell stops;
and wherein the controller starts the supply of the fuel gas irrespective of whether or not the fuel-gas circulation pump is started if the oxygen concentration is equal to or less than a predetermined value.
10. The fuel cell system according to claim 1, wherein the air-replacement-state recognizing means is a fuel-gas concentration sensor for detecting a fuel-gas concentration, the fuel-gas concentration sensor being disposed at a portion of the fuel-gas circulation path where replacement of the fuel gas by air is finished first after the fuel cell stops; and wherein the controller starts the supply of the fuel gas irrespective of whether or not the fuel-gas circulation pump is operated if the fuel-gas concentration is equal to or more than a predetermined value.
11. The fuel cell system according to claim 1, which further comprises a shutoff valve disposed between an outlet of the fuel-gas circulation pump and an inlet of a fuel cell body, wherein, if the output of the air-replacement-state recognizing means indicates that hydrogen and air are unevenly distributed, the controller starts operation of the fuel-gas circulation pump after closing the shutoff valve, and then opens the shutoff valve and starts the supply of the fuel gas when a rotational speed of the fuel-gas circulation pump becomes equal to or more than a predetermined value or when an inner pressure of the fuel electrode becomes equal to or less than a predetermined value.
12. A method for starting up a fuel cell system, wherein the fuel cell system comprisesa fuel cell that includes a fuel electrode, an oxidizer electrode and an electrolyte disposed between the fuel electrode and the oxidizer electrode, the fuel cell generating electric power when fuel gas and oxidizing gas are supplied to the fuel electrode and the oxidizer electrode, respectively, a fuel-gas circulation path that connects an inlet of the fuel electrode to an outlet of the fuel electrode, the fuel gas being supplied through the inlet and discharged from the outlet, a fuel-gas circulation pump provided on the fuel-gas circulation path, and air-replacement-state-recognizing means that estimates or detects a state in which hydrogen and air are unevenly distributed in at least one of the fuel electrode and the fuel-gas circulation path, wherein the air replacement state recognizing means comprises a timer for estimating the air replacement state, or an oxygen concentration sensor and/or a fuel-gas concentration sensor for detecting the air replacement state and being disposed at a portion of the fuel-gas circulation path where replacement of the fuel gas by air is finished first or last after the fuel cell stops, or any combination thereof, the method comprising:
detecting a desire to start the fuel cell;
estimating or detecting a state in which hydrogen and air are unevenly distributed in at least one of the fuel electrode and the fuel-gas circulation path after detecting the desire to start the fuel cell and before starting the fuel cell; and selecting an order for operating the fuel-gas circulation pump and for activating a fuel gas supply upon starting the fuel cell based on whether or not it is estimated or detected that hydrogen and air are unevenly distributed.
13. The method as in claim 12, wherein estimating or detecting the state comprises measuring a time since a previous stoppage of the fuel cell; and the method further comprising:

activating the fuel gas supply before operating the fuel gas circulation pump when the measured time is greater than a first predetermined time but less than a second predetermined time.
14. The method as in claim 13, further comprising:
operating the fuel-gas circulation pump before activating the fuel gas supply when the measured time is equal to or greater than the second predetermined time, the second predetermined time being greater than the first predetermined time.
15. The method as in claim 12, wherein estimating or detecting the state comprises measuring an oxygen level within the fuel-gas circulation pump; and the method further comprising:
operating the fuel-gas circulation pump before activating the fuel gas supply when the measured level is greater than or equal to a predetermined oxygen level.
16. The method as in claim 15, further comprising:
activating the fuel gas supply before operating the fuel-gas circulation pump when the measured level is less than the predetermined oxygen level.
17. The method as in claim 12, wherein estimating or detecting the state comprises measuring a hydrogen level within the fuel-gas circulation pump; and the method further comprising:

operating the fuel gas circulation pump before activating the fuel gas supply when the measured level is equal to or less than a first predetermined hydrogen level.
18. The method as in claim 17, further comprising:
activating the fuel gas supply before operating the fuel-gas circulation pump when the measured level is greater than the predetermined hydrogen level.
19. The method as in claim 12, wherein estimating or detecting the state comprises measuring an oxygen level proximate an outlet of the fuel electrode; and the method further comprising:
operating the fuel-gas circulating pump and activating the fuel gas supply substantially simultaneously when the measured level is equal to or less than a predetermined oxygen level.
20. The method as in claim 19, further comprising:
activating the fuel gas supply before operating the fuel-gas circulation pump when the measured level is more than the predetermined oxygen level.
21. The method as in claim 12, wherein estimating or detecting the state comprises measuring a hydrogen level proximate an outlet of the fuel electrode; and the method further comprising:
operating the fuel-gas circulation pump and activating the fuel gas supply substantially simultaneously when the measured level is equal to or more than a predetermined hydrogen level.
22. The method as in claim 21, further comprising:

activating the fuel gas supply before operating the fuel-gas circulation pump when the measured level is less than the predetermined hydrogen level.
23. The method as in claim 12, wherein the fuel cell system further includes a valve that blocks an outlet of the fuel-gas circulation pump in the fuel-gas circulation path, the method further comprising:

activating the fuel-gas circulation pump;
measuring a rotational speed of the fuel-gas circulation pump; and opening the valve and activating the fuel gas supply when the measured speed is equal to or more than a predetermined speed.
CA2629627A 2005-12-02 2006-12-27 Fuel cell system and method for reducing electrode deterioration during start up Expired - Fee Related CA2629627C (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP2005349703A JP5050342B2 (en) 2005-12-02 2005-12-02 Fuel cell system and starting method thereof
JP2005-349703 2005-12-02
PCT/IB2006/004310 WO2008093147A2 (en) 2006-12-27 2006-12-27 Fuel cell system

Publications (2)

Publication Number Publication Date
CA2629627A1 CA2629627A1 (en) 2007-06-02
CA2629627C true CA2629627C (en) 2012-10-23

Family

ID=38241561

Family Applications (1)

Application Number Title Priority Date Filing Date
CA2629627A Expired - Fee Related CA2629627C (en) 2005-12-02 2006-12-27 Fuel cell system and method for reducing electrode deterioration during start up

Country Status (2)

Country Link
JP (1) JP5050342B2 (en)
CA (1) CA2629627C (en)

Families Citing this family (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5320695B2 (en) * 2007-07-03 2013-10-23 トヨタ自動車株式会社 Fuel cell system
DE102007048317A1 (en) * 2007-10-09 2009-04-16 Daimler Ag Method for operating a fuel cell system
JP4389996B2 (en) * 2007-12-14 2009-12-24 トヨタ自動車株式会社 Fuel cell system
JP5081735B2 (en) * 2008-06-18 2012-11-28 本田技研工業株式会社 Fuel cell system
JP5596744B2 (en) * 2012-05-18 2014-09-24 本田技研工業株式会社 Fuel cell system
JP5555282B2 (en) * 2012-05-25 2014-07-23 本田技研工業株式会社 Fuel cell system
JP6112882B2 (en) * 2013-01-29 2017-04-12 本田技研工業株式会社 Starting method of fuel cell system
JP6489229B2 (en) * 2015-10-08 2019-03-27 日産自動車株式会社 Fuel cell system and control method thereof

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4137796B2 (en) * 2002-01-04 2008-08-20 ユーティーシー パワー コーポレイション Fuel cell system start-up procedure with anode exhaust recirculation loop
JP2005166424A (en) * 2003-12-02 2005-06-23 Nissan Motor Co Ltd Fuel cell system
JP4954443B2 (en) * 2003-12-25 2012-06-13 東芝燃料電池システム株式会社 Starting method of fuel cell system
JP4617675B2 (en) * 2004-01-13 2011-01-26 トヨタ自動車株式会社 Fuel cell system
JP2005203222A (en) * 2004-01-15 2005-07-28 Honda Motor Co Ltd Operation method of fuel cell
JP2005251411A (en) * 2004-03-01 2005-09-15 Toyota Motor Corp Fuel cell system

Also Published As

Publication number Publication date
JP2007157449A (en) 2007-06-21
JP5050342B2 (en) 2012-10-17
CA2629627A1 (en) 2007-06-02

Similar Documents

Publication Publication Date Title
CA2629627C (en) Fuel cell system and method for reducing electrode deterioration during start up
US10522855B2 (en) Method for creating an oxygen depleted gas in a fuel cell system
EP2132819B1 (en) Fuel cell system
US10199666B2 (en) Fuel cell system
WO2010150337A1 (en) Fuel cell system and start timing control method for the fuel cell system
CA2691063C (en) Fuel cell with forced fluid drive
JPWO2007046545A1 (en) Fuel cell system, anode gas generation amount estimation device, and anode gas generation amount estimation method
JP2004342473A (en) Operation control of fuel cell system
US8691460B2 (en) Method of stopping operation of fuel cell system
JP2011228105A (en) Fuel cell system and control method
JP2008041433A (en) Fuel cell system and control method thereof
US9070916B2 (en) Method for controlling fuel cell system
JP2018022571A (en) Fuel cell system
JP6313347B2 (en) Control method of fuel cell system
JP5239201B2 (en) Fuel cell system and impurity discharge method in fuel cell system
JP2018195374A (en) Fuel cell system
JP5186794B2 (en) Fuel cell system and gas pressure adjustment method in fuel cell system
JP5164014B2 (en) Fuel cell system and control method thereof
JP2007157587A (en) Fuel cell system
US8241804B1 (en) Method for controlling fuel cell system
JP5140958B2 (en) Fuel cell system and control method thereof
JP2009129760A (en) Fuel cell system and control method of fuel cell system
JP2007242408A (en) Fuel cell system
JP2006092801A (en) Fuel cell system
JP5581880B2 (en) Fuel cell system

Legal Events

Date Code Title Description
EEER Examination request
MKLA Lapsed

Effective date: 20171227