JP2006202718A - Fuel battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel battery system with high durability through restraint of degradation of an oxidant electrode catalyst layer accompanying a load cycle. <P>SOLUTION: When it is detected that a load state of a fuel battery stack 1 shifts from a high load to a low load below a given value, and a voltage of a unit cell goes beyond a given unit cell voltage, three-way valves 6a to 6d are changed over to a fuel bypass piping 10 and an oxidant bypass piping 11, respectively, to supply fuel gas and oxidant gas not humidified to the fuel battery stack 1. With this, a moisture content of the oxidant electrode catalyst layer can be suppressed below a given value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system.

  In a fuel cell, a fuel gas such as hydrogen gas and an oxidizing gas containing oxygen are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. In particular, a polymer electrolyte fuel cell using a polymer electrolyte has attracted attention as a power source for electric vehicles because of its low operating temperature and easy handling. That is, a fuel cell vehicle is equipped with a hydrogen storage device such as a high-pressure hydrogen tank, a liquid hydrogen tank, or a hydrogen storage alloy tank in the vehicle, and reacts by supplying hydrogen supplied therefrom and air containing oxygen to the fuel cell. This is the ultimate clean vehicle that drives the motor connected to the drive wheels with the electric energy extracted from the fuel cell, and the only exhaust material is water.

  In a polymer electrolyte fuel cell, it is known that when starting and stopping are repeated, the deterioration of the fuel cell is more likely to proceed than when the operation is continued.

In order to suppress such deterioration due to repeated start / stop of the fuel cell, when the fuel cell is stopped, the connection between the fuel cell and the load device is disconnected until a predetermined time elapses. The supply of the oxidant gas and the supply of the fuel gas to the anode are continued. After the supply of the oxidant gas is stopped, the supply of the fuel gas is stopped, so that the voltage of the fuel cell is 0.9 [V] or more. A technique for reducing the time to be within 10 minutes is known (for example, Patent Document 1).
Japanese Patent Laying-Open No. 2004-172106 (page 14, FIG. 6)

  However, the above prior art is a procedure at the time of stopping the operation of the fuel cell system, and does not consider the transient time when the load is made zero, so that the problem that the deterioration of the catalyst layer cannot be sufficiently suppressed. There was a point.

  FIG. 23 is a time chart showing the time variation of each value of (a) load, (b) unit cell voltage, (c) supply gas flow rate, and (d) oxidant electrode catalyst layer water content in a conventional fuel cell system control method. It is a chart. According to the conventional fuel cell system control method, when the load changes from a high load to a low load, the water content of the oxidant electrode catalyst layer gradually decreases due to a decrease in generated water during power generation. This is because the flow rate of the fuel gas or the oxidant gas is decreased at the same time as the load is decreased, so that the water content decrease rate of the oxidant electrode catalyst layer is governed by the spontaneous evaporation rate to the channel residual gas. In addition, since the amount of generated water is small until shifting from a low load to a high load state, the water content of the oxidant electrode catalyst layer is low. For this reason, the water content in the oxidant electrode catalyst layer cannot be sufficiently reduced when the unit cell voltage becomes a high voltage (for example, about 0.95 V) at the time of shifting from a high load to a low load, and the oxidant catalyst layer is deteriorated. Has been promoted.

In addition, not only when the operation is stopped, but also when the duty cycle is repeated, there is a problem that the deterioration of the catalyst layer proceeds more than the constant load operation.

  In order to solve the above problems, the present invention provides a membrane electrode assembly in which a catalyst layer of a fuel electrode and an oxidant electrode and a gas diffusion electrode are disposed on both surfaces of an electrolyte membrane, and the fuel electrode and the oxidant electrode. In a fuel cell system including a fuel cell stack in which a plurality of unit cells each having a membrane electrode assembly sandwiched by separators each having a gas flow path for supplying a fuel gas and an oxidant gas are respectively stacked. When the load state of the fuel cell stack is detected to shift from a high load to a low load of a predetermined value or less, and the voltage of the unit cell of the fuel cell stack becomes equal to or higher than a predetermined unit cell voltage, the oxidant The gist is to control the water content of the electrode catalyst layer to a predetermined value or less.

  The present invention also provides a membrane electrode assembly in which a catalyst layer of a fuel electrode and an oxidant electrode and a gas diffusion electrode are disposed on both surfaces of an electrolyte membrane, and a fuel gas and an oxidant on the fuel electrode and the oxidant electrode, respectively. In a fuel cell system including a fuel cell stack in which a plurality of unit cells each having a membrane electrode assembly sandwiched by separators each having a gas flow path for supplying gas are stacked, the load of the fuel cell stack is When the increase is detected and the voltage of the unit cell of the fuel cell stack is equal to or higher than a predetermined unit cell voltage, the water content of the oxidant electrode catalyst layer is controlled to be a predetermined value or less. And

  According to the experiments of the present inventors, when the constant load operation is performed during fuel cell operation, and when the operation is repeated from high load to low load or no load, and further from low load to high load, the latter load fluctuation It has been clarified that the deterioration of the oxidant electrode catalyst layer further proceeds when the operation involving is performed. This deterioration mechanism includes a decrease in the electrochemical reaction area accompanying aggregation / ionization of catalyst particles, for example, platinum particles in the catalyst layer, and the above phenomenon may be accelerated as the water content of the catalyst layer increases. confirmed. It has been confirmed that the elution of catalytic platinum is remarkable when a duty cycle is applied in a potential range where the electrode potential is high (approximately 0.85 V to 1.1 V). When the battery load fluctuates, there is a large potential fluctuation as compared with the fuel electrode, and the electrode potential is high, so that the above-described deterioration tends to be remarkable.

  According to the experiments conducted by the inventors based on these findings, when the transition from the high load to the low load, the transition from the low load to the high load, and when the voltage exceeds a predetermined unit cell voltage, It has been found that the reduction of the electrochemical reaction area in the oxidant electrode catalyst layer can be suppressed by setting the water content to a predetermined value or less.

  According to the present invention, by setting the water content of the oxidant electrode catalyst layer to a predetermined value or less, the catalyst at the time of transition from a high load to a low load or at the time of transition from a low load to a high load and when the oxidant electrode becomes a high potential. It becomes possible to suppress layer degradation. Therefore, there is an effect that it is possible to provide a highly durable fuel cell by suppressing deterioration of the oxidant electrode catalyst layer accompanying the duty cycle.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. Each embodiment described below is not particularly limited, but is a fuel cell system suitable for a power source of a fuel cell vehicle that repeatedly starts and stops.

  Further, the unit cell voltage in the present invention may be a voltage value of a specific unit cell, or a unit cell voltage is detected for each of a plurality of unit cells inside the fuel cell stack, and a representative value (for example, calculated from these multiple values) The average value obtained by dividing the output voltage value of the fuel cell stack by the number of stacked cells may be used as the unit cell voltage value. The high load of the fuel cell is a load state in which the unit cell voltage is about 0.75 [V] or less.

  FIG. 1 is a system configuration diagram showing the configuration of Embodiment 1 of the fuel cell system according to the present invention. In the figure, a fuel cell system includes a solid polymer electrolyte type fuel cell stack 1 having a catalyst such as platinum, and an anode (fuel electrode) 1 a and a cathode (oxidant electrode) 1 b of the fuel cell stack 1 with conductors 3. The connected load device 2, a fuel gas tank 4 for storing high-pressure hydrogen as a fuel gas, an oxidant blower 5 for supplying air as an oxidant, three-way valves 6a, 6b, 6c and 6d, and humidifying the fuel gas Humidifier 7a, humidifier 7b for humidifying oxidant gas, fuel supply pipe 8, oxidant supply pipe 9, fuel bypass pipe 10 for supplying fuel gas that bypasses humidifier 7a and is not humidified, and humidifier An oxidant bypass pipe 11 that supplies an oxidant gas that bypasses the vessel 7b and does not humidify, a fuel flow rate control device 12 that controls the flow rate of the fuel gas supplied from the fuel gas tank 4, and an acid And an oxidant flow controller 13 for controlling the flow rate of the oxidant gas supplied from the agent blower 5.

  The fuel cell stack 1 includes a membrane electrode assembly in which a catalyst layer of a fuel electrode and an oxidant electrode and a gas diffusion electrode are arranged on both surfaces of an electrolyte membrane, and a fuel gas and an oxidant gas on the fuel electrode and the oxidant electrode, respectively. A plurality of unit cells each having a membrane electrode assembly sandwiched by separators each having a gas flow path for supplying the gas are configured.

  During normal operation, the fuel gas or oxidant gas supplied to the fuel cell stack 1 is humidified to the set relative humidity by passing through the humidifiers 7a and 7b, respectively, but by switching the three-way valves 6a to 6d A feature of this embodiment is that fuel gas and oxidant gas that are not humidified can be supplied to the fuel cell stack 1 via the bypass pipes 10 and 11.

  In this embodiment, both the fuel gas and the oxidant gas have a humidifier, but the basic concept remains the same even if only one of them has.

  Next, the operation of this embodiment will be described with reference to the control flowchart of FIG. 2 and the time chart of FIG. FIG. 3 shows (a) a load when the moisture content of the oxidant electrode catalyst layer is reduced to a predetermined value or lower when the load shifts from a high load to a low load and the unit cell voltage exceeds the criterion. (B) Unit cell voltage, (c) Humidifier passage supply gas flow rate, (d) Bypass pipe passage supply gas flow rate, and (e) Oxidant electrode catalyst layer water content time change are shown.

  In FIG. 2, first, in S10, it is determined whether or not to start the water content control of the oxidant electrode catalyst layer based on the load and cell voltage of the fuel cell. The determination of S10 determines that the moisture content control is started when the load of the fuel cell shifts from a high load to a low load of a predetermined value or less and the unit cell voltage in the fuel cell stack 1 is equal to or higher than the predetermined voltage. Move on to S12. If not, exit without doing anything. In S <b> 12, the three-way valves 6 a to 6 d are switched to the bypass pipes 10 and 11, thereby controlling the fuel gas and the oxidant gas to be supplied to the fuel cell stack 1 without passing through the humidifiers 7 a and 7 b.

  Next, in S14, it is determined whether or not the water content in the oxidizer electrode catalyst layer is equal to or less than a predetermined value. If not less than the predetermined value, the process returns to S12. If it is determined at S14 that the value is equal to or smaller than the predetermined value, the process proceeds to S16, the three-way valves 6a to 6d are switched to the humidifiers 7a and 7b, and the control is terminated.

  Next, with reference to FIG. 4, how to determine the predetermined value of the water content in the oxidant electrode catalyst layer in the present embodiment will be described. FIG. 4 shows changes in the rate of decrease in the electrochemical reaction area of the oxidizer electrode when the load variation of the fuel cell is performed a predetermined number of times using the oxidizer electrode relative humidity during the load fluctuation operation as a parameter. As shown in FIG. 4, when the oxidant electrode relative humidity increases, the oxidant electrode electrochemical reaction area decrease due to the oxidant electrode potential fluctuation accompanying the load fluctuation operation is further accelerated. Here, there is a close relationship between the supply gas relative humidity and the water content of the catalyst layer, but the relationship has an inherent tendency depending on the material (polymer membrane, catalyst, carrier carbon, electrolyte in the catalyst layer). In addition, there is an inherent tendency depending on the amount of electrolyte present in the catalyst layer. Therefore, it is clear that this test result is a result inherent to the combination of the polymer membrane and catalyst used.

  When setting the water content, a test using the relative humidity of the supplied gas as a parameter is performed in advance, and even if the relative humidity of the supplied gas is further reduced, the performance deterioration or electrochemical reaction area decrease greatly changes. Investigate the maximum supply gas relative humidity that would be lost. Next, the desired catalyst layer water content is calculated from the relationship between the above-described material-specific relative humidity of the supply gas and the catalyst layer water content. Here, for example, in order to shift to the desired catalyst layer water content in a short time, the catalyst layer water content can be controlled at a supply gas relative humidity different from the supply gas relative humidity in the relationship.

  Next, referring to FIG. 2 and FIG. 5, in this embodiment, if the unit cell voltage exceeds the criterion when the load is increased, control is performed so that the water content of the oxidant electrode catalyst layer is not more than a predetermined value. The case where it performs is demonstrated. FIG. 5 shows the time of each value of (a) load, (b) unit cell voltage, (c) humidifier passage supply gas flow rate, (d) bypass passage supply gas flow rate, and (e) oxidant electrode catalyst layer water content. Showing change.

  In FIG. 2, first, in S10, it is determined based on the load and cell voltage of the fuel cell whether or not to start the water content control of the oxidant electrode catalyst layer. The determination in S10 is that when the load of the fuel cell is increased from the steady state and the unit cell voltage in the fuel cell stack 1 is equal to or higher than a predetermined value, the control of the water content is started until the predetermined high load is reached. Determine and shift to S12. Otherwise, control is terminated and the stack is generated normally.

  In S12, control is performed so that the fuel gas and the oxidant gas are supplied to the fuel cell stack 1 without passing through the humidifiers 7a and 7b by switching the three-way valves 6a to 6d to the bypass pipes 10 and 11 side.

  Thereafter, the load shifts to a high load equal to or higher than a predetermined value, and at the same time the unit cell voltage in the fuel cell stack 1 becomes equal to or lower than the predetermined value, the process proceeds to S16, and the three-way valves 6a to 6d are switched to the humidifiers 7a and 7b. End control.

  In general, the oxidant electrode catalyst layer immediately after high-load power generation of the fuel cell has a high water content due to the produced water, but the water content of the oxidant electrode catalyst layer can be reduced to a predetermined value or less by the above control.

  According to the present embodiment described above, the moisture content of the oxidant electrode catalyst layer is set to a predetermined value or less, thereby suppressing deterioration of the catalyst layer when shifting from a high load to a low load and when the oxidant electrode is at a high potential. It becomes possible to do. Therefore, there is an effect that it is possible to provide a highly durable fuel cell by suppressing deterioration of the oxidant electrode catalyst layer accompanying the duty cycle.

  Further, according to the present embodiment, the moisture content of the oxidant electrode catalyst layer can be reduced to a predetermined value or less by supplying the low humidified gas. Therefore, there is an effect that it is possible to provide a highly durable fuel cell by suppressing deterioration of the oxidant electrode catalyst layer accompanying the duty cycle.

  FIG. 6 is a system configuration diagram showing the configuration of Embodiment 2 of the fuel cell system according to the present invention. In the figure, a fuel cell system includes a solid polymer electrolyte fuel cell stack 1, and a load device 2 connected to an anode (fuel electrode) 1a and a cathode (oxidant electrode) 1b of the fuel cell stack 1 by a conductor 3. A fuel gas tank 4 that stores high-pressure hydrogen as a fuel gas, an oxidant blower 5 that supplies air as an oxidant, a humidifier 7a that humidifies the fuel gas, a humidifier 7b that humidifies the oxidant gas, Supply pipe 8, oxidant supply pipe 9, fuel flow rate control device 12 that controls the flow rate of fuel gas supplied from the fuel gas tank 4, and oxidant flow rate that controls the flow rate of oxidant gas supplied from the oxidant blower 5 And a control device 13.

  The fuel gas or oxidant gas supplied to the fuel cell stack 1 is humidified to the set relative humidity by passing through the humidifiers 7a and 7b, respectively. In this embodiment, both the fuel gas and the oxidant gas have a humidifier, but even if only one of them has the basic concept, the basic concept remains the same.

  Next, the operation of this embodiment will be described with reference to the control flowchart of FIG. 7 and the time chart of FIG. FIG. 8 shows (a) a load when the moisture content of the oxidant electrode catalyst layer is reduced to a predetermined value or lower when the load shifts from a high load to a low load and the unit cell voltage exceeds the criterion. (B) Unit cell voltage, (c) Humidifier passage supply gas flow rate, (d) Oxidant electrode catalyst layer water content each time change is shown.

  In FIG. 7, first, in S20, it is determined based on the load and cell voltage of the fuel cell whether or not to start the water content control of the oxidant electrode catalyst layer. The determination of S20 determines that the moisture content control is started when the load of the fuel cell shifts from a high load to a low load of a predetermined value or less and the unit cell voltage in the fuel cell stack 1 is equal to or higher than a predetermined voltage. Move on to S22. If not, exit without doing anything. In S22, control is performed such that the flow rate of the supply gas of the fuel gas and / or the oxidant gas is increased by a predetermined amount and supplied to the fuel cell stack 1.

  Next, referring to FIG. 7 and FIG. 9, in this embodiment, if the unit cell voltage exceeds the criterion when the load is increased, control is performed so that the water content of the oxidant electrode catalyst layer is not more than a predetermined value. The case where it performs is demonstrated. FIG. 9 shows changes over time in the values of (a) load, (b) unit cell voltage, (c) flow rate of gas supplied through the humidifier, and (d) oxidant electrode catalyst layer water content.

  The determination of S20 in FIG. 7 is included when the load of the fuel cell shifts from a low load (no load) to a high load equal to or higher than a predetermined value, and the unit cell voltage in the fuel cell stack 1 is equal to or higher than the predetermined voltage. It determines with starting water quantity control, and moves to S22. In S22, the fuel gas and oxidant gas supply gas flow rates are increased by a predetermined amount before being shifted to a high load of a predetermined value or more and while the unit cell voltage is equal to or higher than the predetermined voltage, and supplied to the fuel cell stack 1. Control to do.

  Next, in S24, it is determined whether or not the water content in the oxidant electrode catalyst layer is a predetermined value or less. If not less than the predetermined value, the process returns to S22. If the determination at S24 is less than or equal to the predetermined value, the control is terminated.

  In general, the oxidant electrode catalyst layer immediately after high-load power generation of the fuel cell has a high water content due to the produced water, but the water content of the oxidant electrode catalyst layer can be reduced to a predetermined value or less by the above control.

  According to the present embodiment described above, the moisture content of the oxidant electrode catalyst layer is set to a predetermined value or less, thereby suppressing deterioration of the catalyst layer when shifting from a high load to a low load and when the oxidant electrode is at a high potential. It becomes possible to do. Therefore, there is an effect that it is possible to provide a highly durable fuel cell by suppressing deterioration of the oxidant electrode catalyst layer accompanying the duty cycle.

  Further, according to the present embodiment, the water content of the oxidant electrode catalyst layer can be reduced to a predetermined value or less by increasing the supply gas flow rate at the time of low load. Therefore, it is possible to suppress deterioration of the oxidant electrode catalyst layer accompanying the duty cycle, and there is an effect that a highly durable fuel cell can be provided.

  FIG. 10 is a system configuration diagram showing the configuration of Embodiment 3 of the fuel cell system according to the present invention. In the figure, a fuel cell system includes a solid polymer electrolyte fuel cell stack 1, and a load device 2 connected to an anode (fuel electrode) 1a and a cathode (oxidant electrode) 1b of the fuel cell stack 1 by a conductor 3. A fuel gas tank 4 that stores high-pressure hydrogen as a fuel gas, an oxidant blower 5 that supplies air as an oxidant, a humidifier 7a that humidifies the fuel gas, a humidifier 7b that humidifies the oxidant gas, Supply pipe 8, oxidant supply pipe 9, fuel flow rate control device 12 that controls the flow rate of fuel gas supplied from the fuel gas tank 4, and oxidant flow rate that controls the flow rate of oxidant gas supplied from the oxidant blower 5 A control device 13; a switch 14 for opening and closing the connection between the fuel cell stack 1 and the power storage means 15; a power storage means 15 capable of storing the power generated by the fuel cell stack 1; A detection unit 16, and a switch control means 17 for controlling the opening and closing of the switch 14.

  The switch 14 may be a mechanical relay, but is preferably a semiconductor switch such as a MOS-FET or IGBT in terms of operation speed, durability, and maintainability.

  The fuel cell stack 1 and the power storage means 15 are connected via a switch 14 so that the amount of power generated by the fuel cell stack 1 can be charged to the power storage means 15 via the switch 14 according to the required load detection means 16. The switch control means 17 controls the operation.

  According to the present embodiment, when the required load detecting means 16 detects that the required load has changed from a high load to a low load, and the storage amount of the power storage means 15 is decreasing, the switching signal output means 17 is switched 14 is connected, and the fuel cell stack 1 continuously generates power to store the power storage means 15. When the amount of power stored in the power storage means 15 reaches a predetermined value, the switch control means 17 opens the switch 14 and ends the extraction of current from the fuel cell stack 1. Immediately before this, when it is determined from the required load detected by the required load detection means 16 that the unit cell voltage in the fuel cell stack 1 is equal to or higher than a predetermined value, the water content of the oxidant electrode catalyst layer is set to be equal to or lower than the predetermined value. Control.

  Next, the operation of this embodiment will be described with reference to the control flowchart of FIG. 11 and the time chart of FIG. FIG. 12 shows (a) required load, (b) fuel cell stack load, and (c) unit cell when power is stored in the power storage means with the generated power of the fuel cell stack when the load shifts from high load to low load. It shows the time change of each value of voltage, (d) power storage means storage amount, (e) humidifier passage supply gas flow rate, and (f) oxidant electrode catalyst layer water content.

  In FIG. 11, first, in S30, the required load for the fuel cell is detected by the required load detection means 16. Next, in S32, it is determined whether or not the transition from the high load to the low load and the representative value of the unit cell voltage is greater than or equal to a predetermined value. If the determination in S32 is No, the process ends without doing anything. If the determination in S32 is Yes, the process proceeds to S34, the switch 14 is closed, and the power generated by the fuel cell stack 1 is stored in the power storage means 15.

  Next, in S36, it is determined whether or not the amount of electricity stored in the electricity storage means 15 has become equal to or greater than a predetermined value. If it is determined in S36 that the charged amount is equal to or greater than the predetermined value, the process proceeds to S38, and the required load is detected by the required load detection means 16. Next, in S40, it is determined whether or not the calculated value of the unit cell voltage corresponding to the detected required load is greater than or equal to a predetermined value. If the unit cell voltage is equal to or higher than the predetermined value in S40, the process proceeds to S42, and the control for setting the water content in the oxidizer electrode catalyst layer to the predetermined value or less is started. In S44, the switch 14 is opened to End and end control.

  Next, referring to FIGS. 11 and 13, in this embodiment, the required load increases from a low load to a load below the high load criterion, the unit cell voltage exceeds the criterion, and The operation when the amount of electricity stored in the means 15 is not more than a predetermined value will be described.

  FIG. 13 shows (a) required load, (b) fuel cell stack load, (c) unit cell voltage, (d) power storage means storage amount, (e) humidifier passing supply gas flow rate, (f) oxidant electrode catalyst. The time change of each value of layer water content is shown.

  The demand load detection means 16 detects a demand from a low load (no load) to a high load, the water content of the oxidant electrode catalyst layer is not more than a predetermined value, and the electricity storage amount of the electricity storage means 15 is not more than a predetermined value. In this case, the switching signal output means 17 is connected to the switch 14, and the stack generates power at a predetermined high load regardless of the required load, and stores the power difference from the required load in the power storage means 15. When the amount of electricity stored in the electricity storage means 15 reaches a predetermined value, the switch control means 17 opens the switch 14 and ends the extraction of current from the fuel cell stack. During this time, control is performed to reduce the water content of the oxidant electrode catalyst layer. When the required load exceeds a predetermined high load, the load of the fuel cell stack is set to the same load as the required load, and the fuel cell stack is generated.

  In FIG. 11, the required load for the fuel cell is detected by the required load detecting means in S30. Next, in S32, it is determined whether the load is changed from a low load (no load) to a high load, and the representative value of the unit cell voltage is greater than or equal to a predetermined value. If the determination in S32 is No, the process ends without doing anything. If the determination in S32 is Yes, the process proceeds to S34, the switch 14 is closed, and the power generated by the fuel cell stack 1 is stored in the power storage means 15.

  Next, before shifting to the predetermined high load region, if the amount of power stored in the power storage means 15 is greater than or equal to a predetermined value in the determination in S36, the process proceeds to S38, and the required load detection means 16 detects the required load. Therefore, if the unit cell voltage is equal to or higher than the predetermined value in S40, the process proceeds to S42, and control for setting the water content in the oxidant electrode catalyst layer to be equal to or lower than the predetermined value is started. Power storage is terminated and control is started.

  According to the present embodiment described above, by having the power storage means, the start timing of the control for reducing the water content of the oxidant electrode catalyst layer is determined from the power storage status of the power storage means, and the load request and the power generation amount The difference can be stored. Therefore, there is an effect that it is possible to provide a highly durable fuel cell by suppressing the deterioration of the oxidant electrode catalyst layer accompanying the duty cycle in the control with a high degree of freedom in time.

  FIG. 14 shows (a) load, (b) unit cell voltage, (c) humidifier-passed supply gas flow rate, and (d) oxidant electrode catalyst layer water content during transition from high load to low load in Example 4. It is a time chart which shows the time change of each value of.

  This embodiment can be applied to any configuration of the embodiment 1 in FIG. 1, the embodiment 2 in FIG. 6, and the embodiment 3 in FIG.

  When the load of the fuel cell stack shifts from a high load to a low load, as shown in the hatched portion (from time t1 to t2) in FIG. Control is performed so that the water content in the agent electrode catalyst layer is continuously supplied until the water content becomes a predetermined value or less. In general, the oxidant electrode catalyst layer immediately after high-load power generation of the fuel cell has a high water content due to the produced water, but the water content of the oxidant electrode catalyst layer can be reduced to a predetermined value or less by the above control. It should be noted that both the fuel gas and the oxidant gas may be continued at a high load flow rate, or only one of the electrodes, such as the oxidant gas, may be continued.

  FIG. 15 shows (a) load, (b) unit cell voltage, (c) humidifier passing supply gas flow rate, and (d) oxidant electrode catalyst layer water content at the time of transition from low load to high load in Example 4. It is a time chart which shows the time change of each value of.

  When the load of the fuel cell stack shifts from a low load (no load) to a high load, as shown in the hatched portion (from t1 to t2) in FIG. Control is performed so that the water content of the electrode catalyst layer is continuously supplied until the water content becomes a predetermined value or less. It should be noted that both the fuel gas and the oxidant gas may be continued at a high load flow rate, or only one of the electrodes may be continued, such as only the oxidant gas or only the fuel gas.

  According to the present embodiment, when shifting from a high load to a low load, by continuously supplying at a high load gas flow rate to at least one of the electrodes, a short time and without requiring a special device. It becomes possible to make the water content of the oxidant electrode catalyst layer below a predetermined value. Therefore, the present invention can be applied to a conventional system configuration, and there is an effect that it is possible to provide a highly durable fuel cell by suppressing deterioration of the oxidant electrode catalyst layer accompanying a duty cycle.

  FIG. 16 shows (a) load, (b) unit cell voltage, (c) humidifier passage supply gas flow rate, (d) bypass passage supply gas flow rate, (e) water supply amount, and (f) oxidation in Example 5. It is a time chart which shows the time change of each value of the agent electrode catalyst layer water content.

  In this example, after performing the treatment to reduce the water content of the oxidant electrode catalyst layer of Example 1 or Example 2 to a predetermined value or less, the unit cell voltage is a high voltage (for example, about 0.95 V), and the catalyst layer is If the water content is in a state equal to or lower than the first predetermined value, but this state continues for a predetermined time, the water content in the oxidizer electrode catalyst layer is increased until the water content in the oxidant electrode catalyst layer becomes equal to or higher than the second predetermined value which is greater than the first predetermined value. Supply humidified gas or water to the anode. In addition, the time change of each value shown in FIG. 16 is an example applied to the fuel cell system of Example 1. Further, the highly humidified gas or water may be supplied only to the oxidizer electrode or to both electrodes.

  According to the present embodiment, after the water content reduction treatment of the oxidant electrode catalyst layer, the oxidant electrode catalyst layer has a low water content by increasing the water content of the oxidant electrode catalyst layer to a predetermined value or more. The deterioration of the catalyst layer or the electrolyte membrane caused by continuing the state of becoming is suppressed. Therefore, there is an effect that deterioration of the catalyst layer or the electrolyte membrane can be prevented.

  The configuration of the fuel cell system in the present embodiment is the same as that of the third embodiment shown in FIG. FIG. 17 shows (a) required load, (b) fuel cell stack load, (c) unit cell voltage, (d) power storage amount, (e) humidifier passage supply gas flow rate, and (f) in Example 6. It is a time chart which shows the time change of each value of an oxidizing agent electrode catalyst layer water content.

  According to this example, after controlling the water content of the oxidant electrode catalyst layer to be a predetermined value or less, the unit cell voltage is a high voltage (for example, about 0.95 [V]), and the catalyst layer has a predetermined water content. In the following state, if this state continues for a predetermined time, the fuel cell stack continues power generation below the high load determination standard until the water content becomes a second predetermined value or more greater than the first predetermined value. At this time, the switch 14 is connected by the switch control means 17 and the power storage means 15 is charged.

  According to the present embodiment, after the water content reduction treatment of the oxidant electrode catalyst layer, the oxidant electrode catalyst layer has a low water content by increasing the water content of the oxidant electrode catalyst layer to a predetermined value or more. The deterioration of the catalyst layer or the electrolyte membrane caused by continuing the state of becoming is suppressed. Therefore, there is an effect that deterioration of the catalyst layer or the electrolyte membrane can be prevented.

  The configuration of the fuel cell system in this embodiment shown in FIG. 18 is the same as that of the fuel cell system of Embodiment 2 shown in FIG. 6 except that load transition time detection means 18 is added. Are given the same reference numerals and redundant description is omitted.

  FIG. 19 is a time chart showing changes with time of each value of (a) load, (b) unit cell voltage, (c) humidifier passing supply gas flow rate, and (d) oxidant electrode catalyst layer water content in Example 7. It is. As shown in FIG. 19, the load transition time detection means 18 calculates a time differential value D shown in the following equation (1).

[Equation 1]
D = dL / dt (dL: load reduction allowance, dt: time) (1)
When the D value is less than a predetermined value, that is, when the load drop time is shorter than the predetermined time, or when the unit cell voltage in the fuel cell stack 1 becomes equal to or higher than the predetermined voltage at the time of shifting from a high load to a low load. Control is performed so that the water content of the electrode catalyst layer is not more than a predetermined value.

  As shown in FIG. 20, the load transition time detection means 18 calculates D in the above equation (1). When the value of D is small, that is, when the load increase time is smaller than the predetermined time, or when the load is shifted from the low load to the high load, the unit cell voltage in the fuel cell stack 1 is equal to or higher than the predetermined voltage. In this case, the water content of the oxidant electrode catalyst layer is controlled to be a predetermined value or less. During this transition from low load to high load, if the water content of the oxidizer electrode catalyst layer is greater than the specified value, temporarily supply a gas flow rate higher than the high load at the low load and instantly Reduce the water content of the oxidant electrode catalyst layer.

  According to this example, the shorter the transition time from the high load to the low load, the more the oxidation current value when the oxidant electrode potential becomes a high potential increases. There is an effect that it is possible to control the water content of the oxidant electrode catalyst layer by limiting the conditions to easily proceed.

  The configuration of the fuel cell system shown in FIG. 21 is the same as that of the fuel cell system of Example 2 shown in FIG. 6 except that cell resistance detection means 19 is added. Are given the same reference numerals and redundant description is omitted.

  FIG. 22 shows values of (a) load, (b) unit cell voltage, (c) humidifier passing supply gas flow rate, (d) target cell resistance, and (e) oxidant electrode catalyst layer water content in Example 8. It is a time chart which shows the time change of.

  In this embodiment, the cell resistance value detected by the cell resistance detecting means 19 is obtained from the oxidant electrode catalyst layer by experimentally investigating the correlation between the moisture content change of the oxidant electrode catalyst layer and the cell resistance change in advance. It is used for criteria for determining water content. This cell resistance may be representative of a certain unit cell or may be a cell resistance in a partial stack in the fuel cell stack. The cell resistance detector 19 is an AC ohmmeter that applies an AC voltage between the anode and cathode of a specific cell in the fuel cell stack, and obtains the cell resistance from the AC current flowing between both electrodes and the applied AC voltage. Is known.

  According to the present embodiment, the control time can be determined by controlling the water content of the oxidant electrode catalyst layer based on the cell resistance value detected by the cell resistance detecting means. Therefore, there is an effect that the catalyst layer or the electrolyte membrane can be prevented from being deteriorated by a simple method.

1 is a system configuration diagram showing the configuration of Example 1 of a fuel cell system according to the present invention. 3 is a flowchart for explaining control contents of the first embodiment. (A) Load, (b) Unit cell voltage, (c) Humidifier passage supply gas flow rate, (d) Bypass piping passage supply gas flow rate, (e) Oxidizing agent during transition from high load to low load in Example 1 It is a time chart which shows the time change of each value of a polar catalyst layer water content. It is a figure which shows the relationship between oxidant gas relative humidity at the time of the load fluctuation | variation operation | movement of a fuel cell, and an oxidant electrode electrochemical surface area reduction rate. (A) Load, (b) Unit cell voltage, (c) Humidifier passage supply gas flow rate, (d) Bypass piping passage supply gas flow rate, (e) Oxidizing agent during transition from low load to high load in Example 1 It is a time chart which shows the time change of each value of a polar catalyst layer water content. It is a system block diagram which shows the structure of Example 2 of the fuel cell system which concerns on this invention. 6 is a flowchart for explaining control contents of a second embodiment. Time of each value of (a) load, (b) unit cell voltage, (c) humidifier passing supply gas flow rate, (d) oxidant electrode catalyst layer water content during transition from high load to low load in Example 2 It is a time chart which shows a change. Time of each value of (a) load, (b) unit cell voltage, (c) humidifier passage supply gas flow rate, (d) oxidant electrode catalyst layer water content at the time of transition from low load to high load in Example 2 It is a time chart which shows a change. It is a system block diagram which shows the structure of Example 3 of the fuel cell system which concerns on this invention. 10 is a flowchart for explaining control contents of a third embodiment. (A) Required load at the time of transition from high load to low load in Example 3, (b) Fuel cell stack load, (c) Unit cell voltage, (d) Power storage means storage amount, (e) Humidifier passing supply gas It is a time chart which shows the time change of each value of flow rate and (f) oxidant electrode catalyst layer water content. (A) Required load at the time of transition from low load to high load in Example 3, (b) Fuel cell stack load, (c) Unit cell voltage, (d) Electric storage means storage amount, (e) Humidifier passing supply gas It is a time chart which shows the time change of each value of flow rate and (f) oxidant electrode catalyst layer water content. Time of each value of (a) load, (b) unit cell voltage, (c) humidifier passage supply gas flow rate, (d) oxidant electrode catalyst layer water content at the time of transition from high load to low load in Example 4 It is a time chart which shows a change. Time of each value of (a) load, (b) unit cell voltage, (c) humidifier passage supply gas flow rate, (d) oxidant electrode catalyst layer water content at the time of transition from low load to high load in Example 4 It is a time chart which shows a change. (A) Load, (b) Unit cell voltage, (c) Humidifier passage supply gas flow rate, (d) Bypass passage supply gas flow rate, (e) Water supply amount, (f) Oxidant electrode catalyst layer in Example 5 It is a time chart which shows the time change of each value of moisture content. Example 6 (a) Required load, (b) Fuel cell stack load, (c) Unit cell voltage, (d) Amount of electricity stored in power storage means, (e) Humidifier passing supply gas flow rate, (f) Oxidant electrode catalyst It is a time chart which shows the time change of each value of layer water content. It is a system block diagram which shows the structure of Example 7 of the fuel cell system based on this invention. Time of each value of (a) load, (b) unit cell voltage, (c) humidifier passage supply gas flow rate, (d) oxidant electrode catalyst layer water content at the time of transition from high load to low load in Example 7 It is a time chart which shows a change. Time of each value of (a) load, (b) unit cell voltage, (c) humidifier passage supply gas flow rate, (d) oxidant electrode catalyst layer water content during transition from low load to high load in Example 7 It is a time chart which shows a change. It is a system block diagram which shows the structure of Example 8 of the fuel cell system which concerns on this invention. In Example 8, (a) load, (b) unit cell voltage, (c) humidifier passage supply gas flow rate, (d) target cell resistance, and (e) oxidant electrode catalyst layer water content time change. It is a time chart which shows. It is a time chart which shows the time change of each value of (a) load, (b) unit cell voltage, (c) supply gas flow rate, and (d) oxidant electrode catalyst layer water content in the conventional control method.

Explanation of symbols

1: Fuel cell stack 2: Load device 3: Conductor 4: Fuel gas tank 5: Oxidant blowers 6a-6d: Three-way valves 7a, 7b: Humidifier 8: Fuel supply pipe 9: Oxidant supply pipe 10: Fuel bypass pipe 11 : Oxidant bypass pipe 12: Fuel flow rate control device 13: Oxidant flow rate control device 14: Switch 15: Power storage means 16: Required load detection means 17: Switch control means 18: Load transition time detection means 19: Cell resistance detection means

Claims (13)

A membrane electrode assembly in which a catalyst layer of a fuel electrode and an oxidant electrode and a gas diffusion electrode are respectively disposed on both surfaces of the electrolyte membrane, and a fuel gas and an oxidant gas are supplied to the fuel electrode and the oxidant electrode, respectively. In a fuel cell system including a fuel cell stack in which a plurality of unit cells formed by sandwiching the membrane electrode assembly by a separator having a gas flow path are stacked.
When the load state of the fuel cell stack is detected to shift from a high load to a low load of a predetermined value or less, and the voltage of the unit cell of the fuel cell stack becomes equal to or higher than a predetermined unit cell voltage, the oxidant A fuel cell system, wherein the water content of the electrode catalyst layer is controlled to be a predetermined value or less. A membrane electrode assembly in which a catalyst layer of a fuel electrode and an oxidant electrode and a gas diffusion electrode are respectively disposed on both surfaces of the electrolyte membrane, and a fuel gas and an oxidant gas are supplied to the fuel electrode and the oxidant electrode, respectively. In a fuel cell system including a fuel cell stack in which a plurality of unit cells formed by sandwiching the membrane electrode assembly by a separator having a gas flow path are stacked.
When it is detected that the load of the fuel cell stack increases and the voltage of the unit cell of the fuel cell stack is equal to or higher than a predetermined unit cell voltage, the water content of the oxidant electrode catalyst layer is set to a predetermined value or lower. A fuel cell system characterized by performing control to perform. A power storage means capable of storing the power generated by the fuel cell stack, and a required load detection means for detecting a required load for the fuel cell system,
When the required load detected by the required load detection means changes from a high load to a low load of a predetermined value or less, the fuel cell stack continues to generate power exceeding the low load and stores power in the power storage means, When it is determined that the unit cell voltage in the fuel cell stack is equal to or higher than a predetermined value based on the required load after the storage amount of the storage means reaches a predetermined value, the water content of the oxidant electrode catalyst layer is determined in advance. The fuel cell system according to claim 1, wherein the fuel cell system is shifted to a required load after being less than or equal to the value.   During power storage to the power storage means after the required load has changed from a high load to a low load below a predetermined value, before the amount of power stored in the power storage means reaches a predetermined value and the water content of the oxidant electrode catalyst layer is If the required load increases within the predetermined value or less before the predetermined value or less, control is performed so that the water content of the oxidant electrode catalyst layer is equal to or less than the predetermined value until the charged amount reaches the predetermined value. The fuel cell system according to claim 3, wherein the fuel cell system is continued.   5. The control for reducing the water content of the oxidant electrode catalyst layer to a predetermined value or less by increasing the supply gas flow rate of at least one of the fuel electrode and the oxidant electrode. The fuel cell system according to any one of the above. A control gas flow rate control means for supplying a supply gas flow rate according to the size of the load to the fuel cell stack;
At the time of transition from the high load to the low load, a gas flow rate increased from a gas flow rate corresponding to the magnitude of the load is continuously supplied to at least one of the fuel electrode and the oxidant electrode for a predetermined time. 5. The fuel cell system according to claim 1, wherein the water content of the oxidant electrode catalyst layer is controlled to be a predetermined value or less.   4. The control for reducing the water content of the oxidant electrode catalyst layer to a predetermined value or less by supplying a low humidified gas to at least one of the fuel electrode and the oxidant electrode. The fuel cell system according to any one of the above. A control gas flow rate control means for supplying a supply gas flow rate according to the size of the load to the fuel cell stack;
By continuously supplying a gas flow rate increased from a gas flow rate according to the magnitude of the load to at least one of the fuel electrode and the oxidant electrode when the load increases, an oxidant electrode catalyst is provided. The fuel cell system according to claim 2, wherein the water content of the layer is controlled to be a predetermined value or less.   The fuel cell according to any one of claims 1 to 8, wherein a high load is applied when a representative value of unit cell voltage of the fuel cell stack is about 0.75 [V] or less. system.   When the moisture content of the oxidant electrode catalyst layer is less than or equal to a predetermined value and the state in which the unit cell voltage becomes high voltage has elapsed for a predetermined time, the water content of the oxidant electrode catalyst layer is again set to a second predetermined value greater than the predetermined value. The fuel cell system according to any one of claims 1 to 9, wherein the fuel cell system is equal to or greater than a value.   A load transition time detecting means for detecting a transition time during which a predetermined load amount from a high load to a low load decreases, and when the transition time detected by the load transition time detecting means is a predetermined value or less, 5. The fuel cell system according to claim 1, wherein the water content of the electrode catalyst layer is controlled to be a predetermined value or less.   A load transition time detecting means for detecting a transition time during which a predetermined load amount from a low load to a high load decreases, and the oxidizer is only when the transition time detected by the load transition time detecting means is less than or equal to a predetermined value. The fuel cell system according to claim 2, wherein the water content of the electrode catalyst layer is controlled to be a predetermined value or less. Cell resistance detection means for detecting the resistance value of the unit cell in the fuel cell stack,
13. The control according to claim 1, wherein when the resistance value is equal to or greater than a predetermined value, the control to reduce the water content of the oxidant electrode catalyst layer to a predetermined value or less is stopped. Fuel cell system.

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