JP2007026808A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deterioration of an MEA (Membrane Electrode Assembly) due to high potential after power generation stop without causing complication and efficiency deterioration of a system in a polymer electrolyte fuel cell system. <P>SOLUTION: The partial pressure of oxygen at a cathode 1c is controlled under a generation halt state where a load device 2 is separated from a fuel cell 1 and a state where fuel gas is filled in an anode 1a so that cell potential becomes target potential by adjusting amount of cathode capacity in a cathode gas path 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system, and more particularly to cell potential control after power generation is stopped in a polymer electrolyte fuel cell system.

  A polymer electrolyte fuel cell is configured as a fuel cell stack by sandwiching unit fuel cells each composed of a proton conductive solid polymer membrane and an anode and a cathode respectively disposed on both sides thereof by a separator. The anode and the cathode have a catalyst layer composed of a mixture of a catalyst body obtained by supporting a platinum (Pt) -based metal catalyst on carbon powder and a proton conductive polymer electrolyte.

  In a state close to an open circuit, such as when power generation is stopped, the fuel cell may have a high voltage exceeding 0.9V. As described above, it is known that when the cathode is in a high potential state, problems such as elution of the Pt catalyst at the cathode and reduction in the reaction area of the Pt catalyst due to sintering (Pt particle expansion) occur.

  It is also known that when the fuel cell holds a high voltage close to an open circuit state, the problem that the polymer electrolyte decomposes also occurs. This is thought to be due to the following reasons. That is, the open circuit voltage of a fuel cell using hydrogen and oxygen as reactive species is theoretically 1.23V. However, the actual open circuit voltage depends on the mixed potential of impurities and adsorbed species at the anode and cathode electrodes, and is about 0.93 V to 1.1 V. In addition, the open circuit voltage is lower than the theoretical value because hydrogen and oxygen are slightly diffused in the polymer electrolyte membrane.

  If there is no dissolution of impurities such as extreme metal species, the potential of the anode is greatly influenced by the adsorbed species of the cathode, and as described in Non-Patent Document 1, reaction equation (1) to reaction equation (5) It is considered that the mixed potential of the chemical reaction as shown in FIG. The voltage shown corresponding to the reaction formula indicates the standard electrode potential with respect to SHE (Standard Hydrogen Electrode) when the reaction indicated by the reaction formula occurs.

In this case the anode potential is higher, radical hydroxide (OH ·), superoxide (O ₂ ^- ·), and hydrogen radical (H ·) is a state that occurs in a high concentration, these radicals polyelectrolyte It is considered that the highly reactive part of the polymer is attacked to decompose the polymer electrolyte.
(Reaction Formula 1) O ₂ + 4H ⁺ + 4e ⁻ = 2H ₂ O 1.23V
(Reaction Formula 2) PtO ₂ + 2H ⁺ + 2e ⁻ = Pt (OH) ₂ 1.11V
(Reaction Formula 3) Pt (OH) ₂ + 2H ⁺ + 2e ⁻ = Pt + 2H ₂ O 0.98V
(Reaction Formula 4) PtO + 2H ⁺ + 2e ⁻ = Pt + H ₂ O 0.88V
(Scheme 5) O ₂ + 2H ⁺ + 2e ⁻ = H ₂ O ₂ 0.68V
In order to avoid the problems caused by the fuel cell having an open circuit voltage as described above, several methods for operating the fuel cell system have been proposed. For example, Patent Document 1 discloses a method for stopping and storing a fuel cell system in which a discharge means for suppressing an open circuit voltage is provided in the fuel cell system to avoid the fuel cell from becoming an open circuit voltage. Is disclosed. Further, in Patent Document 2, by applying a predetermined voltage between the anode and the cathode using an external power source, the cathode potential is set within a range of 0.6 to 0.8 V with respect to the standard hydrogen electrode. It has been proposed to control.
H. Wroblowa, et al., J. Electroanal. Chem., 15, p139-150 (1967), "Adosorption and Kinetics at Platinum Electrodes in The Presence of Oxygen at Zero Net Current" JP 2002-93448 A JP 2004-172105 A

  However, when the cell is generated with the supply of the oxidant gas stopped, and the anode is purged with the inert gas after the supply of the oxidant gas is stopped, as in the case of Patent Document 1, the anode is purged with an inert gas. Since the cathode potential is not uniform and the activation state of the cathode is different each time the power generation of the fuel cell is stopped, there is a problem that the battery voltage at the start-up varies. In addition, in order to apply the control method proposed in Patent Document 2, an external power source and electrical wiring are required for the number of cells, which causes a problem that the device is complicated and energy efficiency is reduced.

  The present invention has been made by paying attention to such conventional problems, and does not cause complication or deterioration in efficiency of the fuel cell system, and the MEA (Membrane Electrode Assembly: membrane) caused by the high potential after power generation is stopped. The purpose is to suppress deterioration of the electrode assembly), that is, reduction of the reaction area of the catalyst due to elution and sintering of the Pt catalyst at the cathode and decomposition of the polymer electrolyte by radicals.

  In the polymer electrolyte fuel cell system, the cathode potential or cell potential (hereinafter simply referred to as “cell potential”) with respect to the standard hydrogen electrode in the fuel cell after power generation is stopped is strong against the oxygen partial pressure of the cathode. That is, the gist of the present invention is that, in a polymer electrolyte fuel cell, the cell potential is reduced under the condition that the load is disconnected and the fuel gas is present in the anode. The purpose is to control the oxygen partial pressure of the cathode so as to obtain the target potential.

  The target potential is usually set in the range of 0.6 to 0.8 V in the case of a fixed polymer fuel cell. As the control means for controlling the oxygen partial pressure so that the cell potential becomes the target potential, various configurations can be applied as will be described later in detail as embodiments, but basically the oxygen amount relative to the cathode is controlled. Since it is control, it is possible to perform control using only devices that are inherently equipped in the fuel cell system, such as supply and discharge of cathode gas.

  According to the present invention, since the cell potential is controlled by manipulating the oxygen partial pressure as described above, an external power source and electrical wiring are not required, and power consumption due to these is not generated. The deterioration of the MEA after the stoppage of power generation can be suppressed without incurring complexity and efficiency deterioration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows the overall configuration of a fuel cell system to which the present invention is applicable.

  In the figure, reference numeral 1 denotes a main body of a polymer electrolyte fuel cell, and 1a and 1c denote an anode (fuel electrode) and a cathode (oxygen electrode), respectively. Reference numeral 2 denotes a load device that uses the fuel cell as a power source, for example, an electric motor or a secondary battery. Reference numeral 3 denotes an anode gas path for supplying an anode gas from an anode gas supply source (not shown) to the anode 1a, and a flow rate control valve 5 is interposed upstream of the anode 1a. Reference numeral 4 denotes a cathode gas path for supplying cathode gas to the cathode 1c. Flow control valves 6 and 7 are interposed on the upstream side and the downstream side of the cathode 1c, respectively. 8 is an oxygen sensor as oxygen partial pressure detection means, 9 is a voltmeter that detects the cell potential, and 10 is a temperature sensor that detects the stack temperature of the fuel cell 1. The cell potential is the potential of a specific cell of the fuel cell 1 or the potential of the entire stack.

  Reference numeral 11 denotes a control unit that functions as the control means of the present invention, and is constituted by a microcomputer comprising a CPU and its peripheral devices. The control unit 11 is supplied with the oxygen concentration Po from the oxygen sensor 8, the cell potential Vc from the voltmeter 9, and the stack temperature TI from the temperature sensor 10, and the control unit 11 is based on these signals. After the power generation is stopped after disconnecting the load device 2, the gas amount of the cathode 1c is mainly controlled so that the cell potential Vc becomes the target potential. Details of this control will be described later.

  This fuel cell system includes a humidification adjusting device for adjusting the humidification amount of the anode gas. The humidification adjustment device has as its main elements a humidification path 12 provided so as to bypass the anode gas path 3 on the downstream side of the flow control valve 5 and a regulator 13 interposed in the middle thereof. . The adjuster 13 includes a humidifier or a water remover, and the anode gas humidity can be increased or decreased by passing the anode gas in the anode gas passage 3 through the adjuster 13 as necessary. Va, Vb, and Vc are for selectively connecting the regulator 13 to the anode gas path 3. When the humidity is not adjusted, the valve Va is opened and the anode gas is closed by closing Vb and Vc. It supplies to the anode 1a, without letting the regulator 13 pass. When adjusting the humidity, the valve Va is closed and Vb and Vc are opened, so that the anode gas is passed through the regulator 13 and then supplied to the anode 1a. Opening and closing of the valves Va to Vc is controlled by the control unit 11.

  Next, cell potential control after stopping power generation of the fuel cell system under the above configuration will be described with reference to the flowchart shown in FIG. In the following description and flowcharts, the numbers indicated by the reference sign S represent processing step numbers. In addition, a program corresponding to the processing routine shown in each flowchart is periodically executed by the control unit 11 about every 10 ms, for example.

  FIG. 2 shows a first embodiment of the voltage control (corresponding to claims 1, 3, 4, 10, and 11). In this control, first, a process for stopping the fuel cell is performed in S1. Specifically, the load device 2 is disconnected and the flow rate control valves 6 and 7 in the cathode gas path 4 are closed to stop the supply of the cathode gas to the cathode 1c. However, anode gas is supplied to the anode 1a so that a predetermined amount of anode gas exists. This is for maintaining the anode 1a exposed to the anode gas during this control. For example, the flow rate control valve 5 of the anode gas path 3 is opened to keep a small amount of anode gas flowing through the anode 1a. . Alternatively, the anode gas path 3 may be sealed with the anode 1a filled with a required amount of anode gas.

  In S2, the fuel cell temperature TI is detected based on a signal from the temperature sensor 10, and then in S3, the temperature TI of the fuel cell is determined by comparing the temperature TI with a reference value Ts. Since the deterioration does not occur if the fuel cell temperature is sufficiently low, when the actual temperature TI is lower than the temperature reference value Ts predetermined according to the characteristics and specifications of the fuel cell, the following cell potential control process is bypassed, The process proceeds to S8 and a control end process is performed. In the control termination process, if the anode gas is supplied, this is stopped, and the current cell potential control is terminated. When the fuel cell temperature TI is equal to or higher than the reference value Ts, there is a possibility that the fuel cell temperature TI is deteriorated, so that the process proceeds to cell potential control after S4.

  In S4, the oxygen partial pressure is detected. It is assumed that the oxygen partial pressure detects the oxygen concentration from the oxygen sensor 8 as the correlation amount. Since the relationship between the oxygen concentration of the cathode 1c and the cell potential is determined by the fuel cell, the cell potential can be indirectly known by detecting the oxygen concentration.

  In S5, the potential value Po corresponding to the oxygen concentration is compared with the target potential. In this case, the target potential is set in a band with a lower limit of 0.6V and an upper limit of 0.8V. In the comparison process of S5, if Po> 0.8V, an operation for stopping the oxygen supply to the cathode 1c is performed in S6 in order to lower the cell potential, and then the process returns to S2. On the other hand, if Po <0.6 V, the operation returns to S2 after the operation of supplying oxygen to the cathode 1c in S7 in order to increase the cell potential. If 0.6V ≦ Po ≦ 0.8V, the cell potential is within the target potential range, so the process returns to S2 without doing anything.

  When the supply of the cathode gas is stopped, the anode gas is present in the anode 1a at this time, and immediately after that, power is generated by the residual oxygen of the cathode 1c, and a certain cell potential is generated. Eventually, the cell potential decreases due to the consumption of oxygen at the cathode 1c. In the present invention, the cell potential is maintained in the target potential region by performing the oxygen supply control in the process of changing the cell potential. If the fuel cell temperature falls below the reference value Ts during the cell potential control process, the control is terminated in S8.

  By the above control, the cell potential of the fuel cell 1 is maintained within an appropriate range from when the power generation is stopped until the temperature is sufficiently lowered, so that the MEA is prevented from deteriorating due to the high potential after the power generation is stopped. be able to. In addition, the supply or stop of oxygen to the cathode 1c can be realized without requiring an additional device such as an external power source by controlling the supply of cathode gas by the flow rate control valves 6 and 7 under the configuration of FIG. Therefore, the system is not complicated and the efficiency is not deteriorated.

  In the configuration of the above embodiment, the oxygen sensor 8 having an oxygen pump function may be provided on the cathode 1c or upstream of the cathode 1c. Oxygen supply or oxygen supply stop can be controlled by operating the oxygen sensor 8 as an oxygen pump. Since the amount of oxygen supplied by the oxygen pump function can be accurately controlled according to the amount of current supplied to the oxygen sensor 8, high control accuracy can be expected for the cell potential.

  In this embodiment, the characteristic of the present invention focusing on the fact that the oxygen partial pressure of the cathode affects the cell potential is well represented. By detecting the oxygen concentration on the cathode side, which strongly correlates with the oxygen partial pressure, the cell potential is determined. A configuration for feedback control is shown. The control method in the present invention is not limited to the method for detecting the oxygen concentration as described above, and more specifically, another embodiment will be described later. For example, the cell potential is determined by a signal from the voltmeter 9 in FIG. It is also possible to adopt a configuration in which oxygen supply to the cathode is controlled by direct detection.

  FIG. 3 shows a routine that is additionally executed before the oxygen partial pressure detection process (S4 in FIG. 2) in the cell potential control. A local oxygen supply shortage is caused by the influence of liquid water in the gas supply path. In this case, the cell potential is controlled after removing the liquid water (corresponding to claims 6 and 7). First, in S1, the oxygen partial pressure (oxygen concentration) Po from the oxygen sensor 8 and the cell potential Vc from the voltmeter 8 are sampled, and then in S2, for example, the respective change rates from the difference between a predetermined period or before and after the control cycle. ΔPo and ΔVc are calculated.

  In S3, the influence of liquid water is determined from the ratio between the change rates ΔPo and ΔVc. When the oxygen supply is insufficient due to liquid water, the cell potential decreases rapidly after power generation is stopped, and the rate of change ΔVc becomes larger in the negative direction than in the normal state. By comparing [Delta] Vc / [Delta] Po) with that at normal time, it is possible to determine the presence or absence of the influence of liquid water. Although the influence of liquid water can be determined to some extent only by the cell potential change rate ΔVc, since the oxygen partial pressure also affects the decrease in the cell potential, based on the ratio to the oxygen partial pressure as described above. Higher determination accuracy can be obtained by determination.

  When ΔVc / ΔPo is in the normal range, it is assumed that there is no influence of liquid water, and the process proceeds to cell potential control after S4 in FIG. On the other hand, when ΔVc / ΔPo is large, that is, when the decrease rate of the cell potential Vc is larger than that in the normal state, the liquid water removal process on the anode side is performed in S4. The liquid water can be removed by various methods. As an example, under the configuration of the fuel cell system shown in FIG. 1, the humidification adjustment device (adjuster 13) stops the humidification or removes the water, or controls it. By opening the valve 5 and increasing the anode gas supply amount, liquid water is discharged from the anode 1a to the outside. Such liquid water removal processing is performed until ΔVc / ΔPo falls within the normal range, that is, until the cell potential decrease rate decreases, and then the cell potential control shown in FIG. 2 is performed. As a result, the cell potential can be controlled more accurately by eliminating the influence of liquid water.

  FIG. 4 shows a second embodiment of cell potential control according to the present invention. This improves the control accuracy of the cell potential by calculating the amount of oxygen supplied to the cathode based on the rate of change of the oxygen concentration when the cell potential drops below the target potential (corresponding to claim 2). ). Hereinafter, differences from FIG. 2 will be mainly described.

  In the figure, the processes (S1 to S3, S8) related to the temperature determination from the fuel cell stop process are the same as those in FIG. In this control, when starting the cell potential control as a result of the temperature determination, first, in S4, the oxygen concentration and the cell potential are detected in the same manner as S1 to S2 in FIG. 3, and the respective change rates ΔPo, ΔVc are detected. Ask for. Next, in S5, it is determined whether or not the change rates ΔPo and ΔVc are both less than zero, that is, whether both the oxygen concentration and the cell potential tend to decrease. If any of them is greater than or equal to zero, that is, not decreasing, the process returns to S2.

  If the oxygen concentration and cell potential change rates ΔPo and ΔVc are both decreasing, then the cell potential is determined based on the oxygen concentration Po in S6. Here, the target potential is set to 0.8 V, and when Po> 0.8 V, the oxygen supply is stopped in S7 and the process returns to S2. If Po = 0.8V, do nothing and return to S2. On the other hand, when Po <0.8v, the oxygen consumption amount Qo at the cathode 1c is calculated based on the oxygen concentration change rate ΔPo at that time. This calculation is obtained by making a table of the relationship between the oxygen consumption amount Qo and the oxygen concentration reduction rate ΔPo in advance and referring to this table. Next, in S10, an amount of oxygen corresponding to the oxygen consumption amount Qo thus obtained is supplied to the cathode 1c. The supply oxygen amount is controlled by controlling the flow rate of the cathode gas by the flow rate control valves 6 and 7 or by controlling the oxygen sensor having the oxygen pump function described above.

  FIGS. 5 and 6 respectively show a fuel cell system according to a third embodiment of the present invention and a flowchart of its cell potential control (corresponding to claims 8 and 9). In FIG. 5, a different part from FIG. 1 will be described. In this fuel cell system, a humidifier and a water removing device are provided in the middle of the cathode gas path 4.

  The humidifier includes a humidifying passage 20 branched in a bypass shape from a portion downstream of the flow rate control valve 6 in the cathode gas passage 4 and a humidifying container 21 interposed in the middle thereof as main components. The cathode gas can be humidified by passing the cathode gas in the cathode gas passage 4 through a humidification container 21 in which water is stored. Va, Vb, and Vc are for selectively connecting the humidification container 21 to the cathode gas path 4, and when humidification is not performed, the valve Va is opened and the cathode gas is humidified by closing Vb and Vc. 21 is supplied to the anode 1a without passing through. When humidifying, the valve Va is closed and Vb and Vc are opened, so that the cathode gas passes through the humidifying vessel 21 and then supplied to the anode 1a. Opening and closing of the valves Va to Vc is controlled by the control unit 11.

  As a water amount adjusting means for adjusting the amount of water stored in the humidifying container 21, a humidifying water supply valve 25, a pressure buffer container 22, and a flow meter 23 are provided in the middle of the humidifying water supply path 19 connected to the upper portion of the humidifying container 21. Provided. The humidifying container 21 is provided with a liquid level gauge 24 for measuring the amount of water inside and a humidified water drain valve 26 for discharging water to the outside. When the humidified water supply valve 25 is opened, pressurized water from a water supply source (not shown) is injected from the humidified water supply path 19 into the humidified container 21 via the pressure buffer container 22. The control unit 11 supplies the supply valve so that the amount of water injected or discharged from the humidifying container 21 is basically a predetermined water amount or liquid level position based on a signal from the flow meter 23 or the liquid level meter 24. 25 or the discharge valve 26 is opened and closed for control.

  On the other hand, the water removal device includes a water separation path 28 branched in a bypass shape from a portion of the cathode gas path 4 downstream of the humidification device, and a water separation device 29 interposed in the middle thereof as main components. To do. By passing the cathode gas in the cathode gas path 4 through the water separator 29, moisture in the cathode gas can be removed. Vd, Ve, and Vf are for selectively connecting the water separation device 29 to the cathode gas path 4. When water removal is not performed, the valve Vd is opened and the cathode gas is closed by closing Ve and Vf. The water separation device 29 is supplied to the anode 1a without passing through. When removing water, the valve Vc is closed and Ve and Vf are opened, so that the cathode gas passes through the water separator 29 and is then supplied to the anode 1a. Opening and closing of the valves Vd to Vf is controlled by the control unit 11. The water separation device 29 includes a liquid level sensor 31 that detects that the amount of separated water has reached the storage limit, and a water discharge valve 30 that opens when the limit water level is detected and discharges internal water. With. This water discharge control is also performed by the controller 11.

  FIG. 6 shows a flowchart relating to cell potential control under the above-described configuration. In this control, while the fuel cell temperature detected by the thermometer 10 is equal to or higher than a predetermined value, the amount of water in the humidifying vessel 21 is increased or decreased while the cell potential is monitored by the voltmeter 9, so that the oxygen in the cathode gas path 4 is increased. The contained gas is moved to control the amount of oxygen in the cathode 1 c, and this control is periodically executed by the controller 11.

  In FIG. 6, the processes (S1 to S3, S12) related to the temperature determination from the stop process of the fuel cell are the same as those in FIG. In this control, when the cell potential control is started as a result of the temperature determination, the cell potential Vc is first detected in S4, and then it is determined in S5 whether or not the cell potential Vc satisfies the target potential. The target potential is set in a band with a lower limit value of 0.6V and an upper limit value of 0.8V. If Vc> 0.8 V in the comparison process of S5, the process proceeds to S10 after executing the process of reducing the cell potential in S6. If Vc <0.6 V in the comparison process of S5, the process proceeds to S10 after executing the process of increasing the cell potential of S7 to S9. In the comparison process of S5, if 0.6V ≦ Vc ≦ 0.8V, the cell potential is within the target potential range, so the process proceeds to S10 without doing anything.

  As a process in S6 for lowering the cell potential Vc, the water discharge valve with the flow rate control valves 6 and 7 in the cathode gas path 4 and the humidified water supply valve 25 in the humidified water supply path in FIG. 26 is opened and the water in the humidification container 21 is discharged outside. As a result, the water level in the humidifying container 21 decreases, and the gas in the cathode 1c is sucked toward the container 21 as the spatial volume in the container 21 increases, so that the oxygen partial pressure at the cathode 1c decreases. Therefore, the cell potential Vc decreases. Thereby, when the cell potential Vc becomes 0.8 V or less, the discharge valve 26 is closed to stop the discharge of water from the humidification container 21. The water separation device 29 may be connected to the cathode path 4 in the process of control, but in order to reflect the change in volume in the humidification vessel 21 to the change in oxygen partial pressure in the cathode 1c with good response. It is desirable that the water separation device 29 is not connected, that is, the valve Vd is opened and the valves Ve and Vf are closed.

  On the other hand, as a process for increasing the cell potential Vc, first, in S7, the flow rate control valve 6 of the cathode gas path 4 is closed, the flow rate control valve 7 is opened, and the humidified water discharge valve 26 is closed. In the state, the humidified water supply valve 25 is opened, and water is introduced into the humidified container 21. When the water level in the humidifying container 21 rises by this operation, the cathode gas accumulated in the space in the humidifying container 21 and the cathode gas path 4 downstream thereof flows into the cathode 1c, thereby raising the cell potential Vc. At the time of this water supply control, the pressure fluctuation accompanying the opening and closing of the humidification water supply valve 25 occurs in the humidification container 21. In this embodiment, the pressure buffer container 4 is provided at a position higher than the highest water level of the humidification container 21. By utilizing the pressure due to the difference in water level, the pressure fluctuation is reduced and the stability of the supply flow rate is improved.

  Further, during the water supply control, the water separation device 29 may be disconnected. However, when the valve Vd is closed and the valves Ve and Vf are opened, the cathode 1c is removed from the humidifying vessel 21. It is more desirable to remove moisture in the cathode gas supplied to the battery. This is because when a humidified cathode gas enters the fuel cell at the time of stoppage, a highly reactive metal such as platinum in the cathode catalyst reacts with water contained in the cathode gas to oxidize the metal and lower the catalytic activity. This is because there is a possibility that the phenomenon will occur. If the amount of water in the water separation device 29 reaches the upper limit value during the water separation process, this is detected in S10, and the discharge valve 26 is opened for a certain time in S11 to discharge the water inside the device to the outside. After that, the process returns to S2.

  When the cell potential Vc becomes 0.6 V or more in the process of S7, the supply of water to the humidification container 21 with the humidification water supply valve 25 closed is stopped, and then the process returns to S2. However, in S8, the water level in the humidifying container 21 is measured by the liquid level gauge 24, and when the water level reaches the upper limit in the process of supplying water to the humidifying container 21, the humidifying water supply valve 25 is closed. The discharge valve 26 is opened, and water is discharged from the humidification container 21. As a result, the gas in the cathode gas path 4 is sucked back into the humidification container 21, and the external air flows back to the cathode 1c through the flow rate control valve 7 accordingly, so that the oxygen content in the cathode 1c is reduced. The cell potential can be increased while maintaining the pressure high.

  By repeating the above control, the cell potential Vc can be maintained at the target potential until the fuel cell temperature falls below a predetermined reference value Ts, and deterioration of the fuel cell can be prevented. As described above, this control can be realized basically by operating the humidifier installed in the fuel cell system, so that it is not necessary to provide additional complicated equipment and the energy consumption is small.

1 is a schematic configuration diagram of a fuel cell system to which the present invention is applicable. The flowchart showing 1st Embodiment of the control which concerns on this invention. The flowchart showing the control additionally performed in the process of FIG. The flowchart showing 2nd Embodiment of the control which concerns on this invention. The schematic block diagram of the other fuel cell system which can apply this invention. The flowchart showing 3rd Embodiment of the control which concerns on this invention.

Explanation of symbols

1 Fuel cell (main unit)
DESCRIPTION OF SYMBOLS 1a Anode 1c Cathode 2 Load apparatus 3 Anode gas path 4 Cathode gas path 5, 6, 7 Flow control valve 8 Oxygen sensor (oxygen partial pressure detection means)
9 Voltmeter 10 Temperature sensor 11 Control unit (control means)
20 Humidification path 21 Humidification container 24 Level gauge 25 Humidification water supply valve 26 Humidification water discharge valve 28 Water separation path 29 Water separation device 30 Drain valve 31 Liquid level sensor

Claims (11)

In polymer electrolyte fuel cells,
Oxygen partial pressure detecting means for detecting the oxygen partial pressure of the cathode of the fuel cell;
And a control means for controlling the oxygen partial pressure so that the cell potential becomes a target potential in a power generation stop state with the load disconnected and in a state where fuel gas is present in the anode. Battery system. In claim 1,
The control means is configured to calculate a rate of decrease in oxygen partial pressure and to supply, to the cathode, an oxygen amount corresponding to an oxygen consumption determined from the rate of decrease when the cell potential is less than the target potential. Fuel cell system. In claim 1 or claim 2,
The oxygen partial pressure detecting means is a fuel cell system that detects the oxygen concentration in the cathode gas path as a correlation amount of the oxygen partial pressure. In claim 1 or claim 2,
The oxygen partial pressure detecting means is a fuel cell system that detects a cell potential of the fuel cell as a correlation amount of oxygen partial pressure. In claim 1 or claim 2,
The oxygen partial pressure detecting means includes an oxygen sensor having an oxygen pump function,
A fuel cell system in which the control means operates the oxygen sensor as an oxygen pump when supplying oxygen to the cathode. In claim 1,
A fuel cell system configured to calculate a rate of decrease in oxygen partial pressure, and to perform a liquid water removal process for the anode when the rate of decrease is greater than a predetermined reference value. In claim 6,
A fuel cell system that performs control to increase the supply amount of the anode gas and / or control to decrease the water content of the anode gas as the liquid water removal process. In claim 1,
A water amount adjusting means for providing a humidification path selectively connected to the gas path and interposing a humidification container in the middle of the cathode gas path upstream of the fuel cell, and supplying or discharging water to the humidification container Provided,
The control means;
Under the power generation stop state where the load is disconnected, the supply of the cathode gas from the upstream side of the humidification path is cut off and the humidification path is connected to the cathode gas path,
When the cell potential is lower than the target potential, the water amount control means changes the water level in the humidifying vessel to circulate oxygen-containing gas inside and outside the cathode gas path to the cathode, and when the cell potential rises above the target potential A fuel cell system configured to lower the water level in the humidifying container by the water amount control means in a state where the inflow of gas from the outside is blocked, and to extract the gas in the cathode to the humidifying container side. In claim 8,
A fuel cell system comprising a water removal device selectively connected to the cathode gas path in the middle of the cathode gas path between the humidification container and the cathode. In polymer electrolyte fuel cells,
Under the condition that power generation is stopped with the load disconnected and fuel gas is present in the anode,
A fuel cell system, wherein an oxygen partial pressure of a cathode is controlled so that a cathode potential with respect to a standard hydrogen electrode becomes a target potential. In claim 1 or claim 11,
The fuel cell system, wherein the target potential is set within a range of 0.6 to 0.8V.

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