JP2017224575A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of suppressing an oxidation reduction reaction by reducing humidity in hydrogen gas and air using an optimal technique that matches the operating state of a fuel cell, and thus capable of reliably preventing deterioration due to the aggregation/elution of platinum in a catalyst layer.SOLUTION: In each of operating states in which a cell voltage V increases (B), is high (C), and decreases (D) and in which deterioration in a catalyst layer of a fuel electrode 10b and an air electrode 10c occurs, respective moisture reduction techniques b-d are set preliminary such that an optimal control content including control variables is provided to each operating state on the basis of conditions (reduction width of moisture, responsibility, etc.) required to moisture reduction for deterioration prevention. During operation of a fuel cell 10, in each time the operating state is switched, a corresponding moisture reduction technique is selected from among the moisture reduction techniques b-d and performed to achieve moisture reduction so that an oxidation reduction reaction on a catalyst layer is suppressed.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fuel cell system that includes a fuel electrode having a catalyst layer and an air electrode, supplies fuel gas whose humidity is adjusted to the fuel electrode, and supplies air whose humidity is adjusted to the air electrode to generate electricity.

  With the recent increase in environmental awareness, fuel cell systems are attracting attention as one of clean energy power generation that does not rely on fossil fuels. For example, a polymer electrolyte fuel cell is used in a fuel cell system mounted on an automobile, and an MEA is formed by bonding a fuel electrode and an air electrode carrying platinum (Pt) as a catalyst on both sides of a solid polymer film. It is manufactured by stacking a large number of single cells each having a MEA sandwiched between a gas diffusion layer and a separator.

In the fuel cell configured as described above, a power generation reaction is started by supplying the fuel gas whose humidity is adjusted to the fuel electrode and the air whose humidity is adjusted to the air electrode. Since the power generation reaction proceeds in the catalyst layer of the fuel electrode and the air electrode, suppressing the deterioration of the catalyst layer is an important issue for improving the durability of the fuel cell.
As a factor for promoting the deterioration of the catalyst layer, repeated oxidation-reduction reactions occurring on the catalyst layer can be mentioned. For example, when the output power required for the fuel cell fluctuates with the acceleration / deceleration of the vehicle, the operating state of the fuel cell changes between idle operation and power generation operation, and accordingly, the voltage of a single cell (hereinafter referred to as cell voltage). ) Varies between a high voltage range during idle operation and a low voltage range during power generation operation. As the cell voltage increases and decreases, the oxidation-reduction reaction is repeated on the catalyst layer, and in particular, the platinum particles in the catalyst layer on the air electrode side reduce the power generation reaction specific area due to aggregation due to Ostwald growth and platinum elution. However, these phenomena cause the deterioration of the catalyst layer.

  As a countermeasure against such problems, for example, in the technique described in Patent Document 1, the oxidation-reduction reaction that occurs on the catalyst layer when the cell voltage is in a predetermined range (for example, 0.6 to 0.9 V) is a cause of platinum aggregation / elution. When the load fluctuation of the fuel cell is detected, the cell voltage is detected, and when the cell voltage is within the predetermined range, it is supplied to the hydrogen gas or air electrode supplied to the fuel electrode. The humidity of the air to be reduced is reduced to suppress the redox reaction. As a technique for reducing the humidity, for example, the humidity is reduced by suppressing the humidification amount of hydrogen gas or air performed by a humidifier.

JP 2007-179749 A

However, oxidation-reduction reactions that can cause platinum aggregation and elution of the catalyst layer occur in various operating states of the fuel cell. Depending on the operating conditions, for example, the humidity required for suppressing the oxidation-reduction reaction may be reduced. The range of decrease and the response of the decrease in humidity are different, and the optimum method for reducing the humidity is inevitably different.
For this reason, just by applying a single method (such as suppression of the humidification amount by a humidifier) to reduce the humidity on the condition that the cell voltage is within a predetermined range as in the technique of Patent Document 1, the fuel cell It is impossible to achieve an optimal humidity drop that matches the operating conditions. As a result, for example, when the decrease in humidity is insufficient, the oxidation-reduction reaction cannot be sufficiently suppressed, and when the responsiveness of humidity decrease is poor, the oxidation-reduction reaction immediately after occurrence cannot be suppressed quickly. It was difficult to say that the deterioration of the catalyst layer due to platinum aggregation / elution could be reliably prevented.

  The present invention has been made to solve such problems, and the object of the present invention is to reduce the humidity of hydrogen gas and air by an optimal method that matches the operating state of the fuel cell, and to perform the oxidation-reduction reaction. An object of the present invention is to provide a fuel cell system that can be suppressed and that can reliably prevent deterioration due to platinum aggregation / elution of a catalyst layer.

  In order to achieve the above object, a fuel cell system of the present invention includes a fuel electrode having a catalyst layer and an air electrode, and supplies fuel gas to the fuel electrode and supplies air to the air electrode to generate power. In the battery, a voltage detection means for detecting the voltage of the fuel cell that varies according to the output power of the fuel cell, and a plurality selected in accordance with a plurality of voltage states that vary according to the operating state of the fuel cell And a humidity reduction means for performing a humidity reduction by selecting a humidity reduction method corresponding to the current voltage state of the fuel cell.

  According to the fuel cell system configured as described above, there is a humidity reduction method corresponding to the current voltage state from a plurality of humidity reduction methods selected corresponding to a plurality of voltage states that change according to the operating state of the fuel cell. When selected, the humidity reduction is achieved by performing the humidity reduction technique. The optimal control content for humidity reduction differs depending on the voltage state, but the humidity reduction method corresponding to the voltage state is selected, so the optimal control content that matches the voltage (and hence the operating state of the fuel cell) The humidity of the fuel gas or air is lowered, and the oxidation-reduction reaction on the catalyst layer of the fuel electrode or air electrode can be suppressed.

  As another aspect, among the plurality of voltage states, a first state in which the voltage changes in a decreasing direction, a second state in which the voltage becomes a predetermined value or more, and a third state in which the voltage changes in an increasing direction, The humidity reduction method corresponding to each of the two or more states is set in advance, and the humidity reduction means generates any one of the plurality of voltage states. It is preferable to determine that a decrease in humidity is necessary, and select and execute a humidity decrease method corresponding to the generated state.

According to this aspect, it corresponds to at least two states among the first state in which the voltage changes in the decreasing direction, the second state in which the voltage becomes a predetermined value or more, and the third state in which the voltage changes in the increasing direction. When a humidity reduction method is set in advance and any one of the plurality of voltage states occurs, it is determined that the humidity reduction is necessary, and the corresponding humidity reduction method is selected and executed.
As another aspect, the humidity reducing means increases the decrease rate when the voltage changes in the decreasing direction, and approaches the idle equivalent value when the voltage is equal to or greater than a predetermined value. It is preferable to set the target humidity to the lower side as the increase rate increases, and to execute the humidity reduction method based on the target humidity.

According to this aspect, the larger the voltage decrease rate, the closer the voltage approaches the idle operation equivalent value, and the greater the voltage increase rate, the platinum caused by the oxidation-reduction reaction on the catalyst layer. Although the possibility of aggregation / elution increases, the target humidity is set on the lower side accordingly, so that the oxidation-reduction reaction can be more reliably suppressed.
As another aspect, the humidity lowering means sets the humidity during normal control when humidity reduction is not required as the upper limit of the target humidity, and lowers the lower limit of the target humidity when the voltage changes in the decreasing direction. When the voltage changes in the increasing direction, it is preferable that the lower limit of the target humidity is made highest and the target humidity is set between the upper limit and the lower limit.

  According to this aspect, the possibility of platinum aggregation / elution due to the oxidation-reduction reaction on the catalyst layer is the highest when the voltage is changed in the decreasing direction, so the necessity for lowering the humidity is the highest, Accordingly, the lower limit of the target humidity is made the lowest, so that the oxidation-reduction reaction on the catalyst layer is more reliably suppressed by sufficiently reducing the humidity. In addition, the possibility of platinum aggregation / elution is the lowest when the voltage changes in the increasing direction, so the necessity for lowering the humidity is also the lowest, but the lower limit of the target humidity is correspondingly increased accordingly. A reduction in the efficiency of the fuel cell due to a significant decrease in humidity is prevented.

As another aspect, the plurality of humidity reduction methods may be different from each other among cell temperature increase control, non-humidified gas ratio increase control, cell pressure decrease control, and gas flow rate increase control for the purpose of reducing humidity. It is preferable that such control content is set.
According to this aspect, different control contents are set as the plurality of humidity reduction techniques, and the humidity is reduced by the control contents of the humidity reduction technique corresponding to the current voltage.

As another aspect, the plurality of humidity reduction methods may include the same control among cell temperature increase control, non-humidified gas ratio increase control, cell pressure decrease control, and gas flow rate increase control for the purpose of reducing humidity. It is preferable that the content is set and the control amount applied to the set control content is different.
According to this aspect, the same control content is set as a plurality of humidity reduction methods, the control amount applied to the control content is different, and the control content of the humidity reduction method is controlled by the control amount corresponding to the current voltage. When executed, the humidity is lowered.

  According to the fuel cell system of the present invention, it is possible to suppress the oxidation-reduction reaction by reducing the humidity of hydrogen gas or air by an optimal method that matches the operating state of the fuel cell, thereby causing platinum aggregation / elution of the catalyst layer. Deterioration can be reliably prevented.

It is a whole lineblock diagram showing an electric vehicle carrying a fuel cell system of an embodiment. It is a block diagram which shows the fuel cell system of embodiment. It is a time chart which shows the condition where the driving | running state of the fuel cell changed between the idle driving | operation and the electric power generation driving | operation. It is a flowchart which shows the humidity fall routine which FC-ECU performs.

Hereinafter, an embodiment in which the present invention is embodied in a fuel cell system mounted on an electric vehicle will be described.
FIG. 1 is an overall configuration diagram showing an electric vehicle equipped with the fuel cell system of the present embodiment.
The electric vehicle 1 according to the present embodiment is a hybrid fuel cell vehicle including a motor 2 as a driving power source and a secondary battery 3 and a fuel cell system 4 as power sources. As is well known, the secondary battery 3 is a battery capable of charging and discharging DC power by a chemical reaction, and the fuel cell system 4 is a system that generates power by an electrochemical reaction using hydrogen gas in a fuel cell 10 to be described later. is there. Basically, the motor 2 is driven by the power from the secondary battery 3, and the fuel cell system 4 mainly functions as a range extender for charging the secondary battery 3, and its output power is used to drive the motor 2 as an auxiliary. Also used for.

  A secondary battery 3 is connected to the motor 2 via an inverter 5, and the inverter 5 performs a DC / AC conversion function. That is, during power running control of the motor 2, DC power from the secondary battery 3 and the fuel cell system 4 is converted into three-phase AC power by the inverter 5 to drive the motor 2, and during regenerative control of the motor 2, The three-phase AC power is converted to DC power by the inverter 5 and charged to the secondary battery 3.

  An AC-DC converter 7 for charging using an external power source is connected to the secondary battery 3 via a diode 6. When the power plug 8 of the AC-DC converter 7 is connected to an external power source, AC power from the external power source is converted into DC power by the AC-DC converter 7 and charged to the secondary battery 3. A reverse current flow from the side to the AC-DC converter 7 is blocked by the diode 6.

On the other hand, a fuel cell system 4 is connected to the secondary battery 3 and the inverter 5, and its configuration is shown in FIG. 2.
The fuel cell system 4 includes a fuel cell 10, a hydrogen tank 11, an air blower 12, a humidifier 13, a DC-DC converter 14, and the like. The fuel cell 10 of this embodiment is a polymer electrolyte fuel cell, and is formed by stacking a large number of single cells and connecting them in series so that a desired voltage can be obtained. In each single cell, a fuel electrode (negative electrode) 10b and an air electrode (positive electrode) 10c carrying platinum (Pt) as a catalyst are bonded to both sides of a solid polymer membrane 10a (electrolyte), and a MEA (Membrane Electrode Assembly: membrane). / Electrode assembly), and the MEA is sandwiched by a separator having a porous gas diffusion layer and a gas flow path. Since such a configuration follows the configuration of a typical fuel cell 10, the illustration thereof is omitted in FIG.

  A hydrogen supply line 15 that supplies hydrogen gas as a fuel gas is connected to the upstream side of the fuel electrode 10b of the fuel cell 10, and an upstream side of the hydrogen supply line 15 is connected to a hydrogen tank 11 that stores high-pressure hydrogen gas. ing. A main valve 17 for supplying and stopping hydrogen gas is provided in the vicinity of the discharge port of the hydrogen tank 11, and the hydrogen supply line 15 is branched into a humidified hydrogen line 15a and a non-humidified hydrogen line 15b on the downstream side of the main valve 17. Has been. A flow control valve 18 and a humidifier 13 are provided on the humidified hydrogen line 15a, and the hydrogen gas flowing through the humidified hydrogen line 15a is humidified by the humidifier 13 to generate humidified hydrogen gas.

  A flow rate adjusting valve 20 is provided on the non-humidified hydrogen line 15b, and the non-humidified hydrogen line 15b bypasses the humidifier 13 so that the low-humidity hydrogen gas discharged from the hydrogen tank 11 is unhumidified hydrogen gas. It is distributed as. The humidified hydrogen line 15a and the non-humidified hydrogen line 15b join together on the downstream side and are connected to the fuel electrode 10b of the fuel cell 10. For this reason, the gas flow rate of the humidified hydrogen line 15a and the non-humidified hydrogen line 15b changes corresponding to the opening degree of the respective flow control valves 18, 20, and the humidity of the hydrogen gas supplied to the fuel electrode 10b accordingly. Can be arbitrarily adjusted between humidified hydrogen gas and non-humidified hydrogen gas.

  One end of a hydrogen return line 21 is connected to the fuel electrode 10 b of the fuel cell 10, and the other end of the hydrogen return line 21 is connected to the downstream side of the main valve 17 of the hydrogen supply line 15. A back pressure valve 22 and a pump 23 are provided on the hydrogen return line 21, and hydrogen gas is appropriately discharged from the fuel electrode 10 b according to the opening and closing of the back pressure valve 22, so that the fuel electrode 10 b is maintained at a desired pressure. At the same time, the hydrogen gas discharged from the back pressure valve 22 is returned to the hydrogen supply line 15 side by the pump 23 via the hydrogen return line 21.

  On the other hand, an air supply line 25 that supplies air is connected to the upstream side of the air electrode 10c of the fuel cell 10, and an upstream side of the air supply line 25 is connected to an air blower 12 that compresses and supplies the atmosphere. A main valve 27 for supplying and stopping air is provided in the vicinity of the discharge port of the air blower 12, and the air supply line 25 is branched into a humidified air line 25a and a non-humidified air line 25b on the downstream side of the main valve 27. ing. On the humidified air line 25a, the flow rate adjusting valve 28 and the humidifier 13 are provided, and the air flowing through the humidified air line 25a is humidified by the humidifier 13 to generate humidified air.

  A flow control valve 29 is provided on the non-humidified air line 25b, and the non-humidified air line 25b bypasses the humidifier 13 so that low-humidity air discharged from the air blower 12 flows as non-humidified air. doing. The humidified air line 25a and the non-humidified air line 25b join together on the downstream side and are connected to the air electrode 10c of the fuel cell 10. For this reason, the flow rate of the air in the humidified air line 25a and the non-humidified air line 25b changes corresponding to the opening degree of each flow rate adjusting valve 28, 29, and the humidity of the air supplied to the air electrode 10c accordingly. Can be arbitrarily adjusted between humidified air and non-humidified air.

  One end of an air return line 30 is connected to the fuel electrode 10 b of the fuel cell 10, and the other end of the air return line 30 is connected to a suction port of the air blower 12. A back pressure valve 31 is provided on the air return line 30, and air is appropriately discharged from the air electrode 10 c according to opening and closing of the back pressure valve 31, whereby the air electrode 10 c is maintained at a desired pressure, and the back pressure valve The air discharged from 31 is returned to the air blower 12 side through the air return line 30.

Residual hydrogen gas that was not used for power generation at the fuel electrode 10b is discharged to the outside or collected on the hydrogen supply line 15 side, and air that is not used for power generation at the air electrode 10c is also discharged to the outside. Since the configuration is not related to the gist of the present invention, explanation and illustration are omitted.
On the other hand, the fuel cell 10 is connected to a radiator 34 through a pair of cooling lines 32 and 33, and a water pump 35 is interposed in the one cooling line 32. As a result, an annular cooling circuit 36 composed of the fuel cell 10, one cooling line 32, the radiator 34, and the other cooling line 33 is formed, and the cooling water filled therein is circulated by driving the water pump 35.

  A DC-DC converter 14 is connected to the output terminal of the fuel cell 10, and the DC-DC converter 14 is connected to the secondary battery 3 and the inverter 5 via a diode 37. As a result, the output power of the fuel cell 10 is used for charging the secondary battery 3 and driving the motor 2, and at this time, a reverse flow of current from the secondary battery 3 or the motor 2 to the fuel cell 10 is blocked by the diode 37. Is done.

  During operation of the fuel cell 10 configured as described above, the hydrogen supplied to the fuel electrode 10b through the hydrogen supply line 15 is decomposed into hydrogen ions and electrons by the catalytic action, and the hydrogen ions are solid polymer membrane 10a. And reaches the air electrode 10c. Electrons that cannot pass through the solid polymer film 10a reach the air electrode 10c through an external circuit (not shown), and thereby a DC voltage is generated with the fuel electrode 10b minus and the air electrode 10c plus. In the air electrode 10c, water is generated by the reaction of air supplied through the air supply line 25, hydrogen ions that have passed through the solid polymer film 10a, and electrons that have passed through the external circuit.

  For such operation of the fuel cell 10, the FC-ECU 40 controls each device constituting the fuel cell system 4. On the input side of the FC-ECU 40, a voltage sensor 41 (cell voltage detecting means) for detecting the voltage (cell voltage) of a single cell constituting the fuel cell 10, and a hydrogen humidity for detecting the humidity Hh of the hydrogen gas at the fuel electrode 10b. A sensor 42 and an air humidity sensor 43 for detecting the air humidity Ho of the air electrode 10c are connected, and although not shown, a pressure sensor for detecting the pressure of the fuel electrode 10b and the air electrode 10c (hereinafter referred to as cell pressure). Various sensors such as a temperature sensor for detecting the temperature of the fuel electrode 10b and the air electrode 10c (hereinafter referred to as cell temperature) are connected.

Further, on the output side of the FC-ECU 40, the main valves 17, 27 and the flow rate adjusting valves 18, 20, 28, 29 of the hydrogen supply line 15 and the air supply line 25, the air blower 12, the humidifier 13, the hydrogen return line. The back pressure valve 22 and the pump 23, the back pressure valve 31 of the air return line 30, and the devices such as the DC-DC converter 14 are connected.
For example, the FC-ECU 40 opens both the hydrogen tank 11 and the main valves 17 and 27 of the air blower 12 at a predetermined opening, and the hydrogen gas discharged from the hydrogen tank 11 passes through the hydrogen supply line 15 to the fuel electrode 10b. While supplying, the air discharged from the air blower 12 is supplied to the air electrode 10c through the air supply line 25.

  Further, the FC-ECU 40 executes the following control in order to adjust the hydrogen gas supplied to the fuel electrode 10b and the air supplied to the air electrode 10c to a desired humidity. First, the humidity of the humidified hydrogen gas flowing through the humidified hydrogen line 15a is adjusted by the control of the humidifier 13, and similarly, the humidity of the humidified air gas flowing through the humidified air line 25a is adjusted by the control of the humidifier 13. Then, the flow rate adjusting valves 18 and 20 of the humidified hydrogen line 15a and the non-humidified hydrogen line 15b are controlled to open, and the humidified hydrogen gas and the non-humidified hydrogen gas are mixed at a predetermined ratio to be supplied to the fuel electrode 10b. Adjust the hydrogen gas to the desired humidity. Similarly, the air supplied to the air electrode 10c by mixing the humidified air and the non-humidified air at a predetermined ratio by controlling the opening degree of the flow rate adjusting valves 28 and 29 of the humidified air line 25a and the non-humidified air line 25b. Adjust to the desired humidity.

  Further, the FC-ECU 40 appropriately discharges the hydrogen gas of the fuel electrode 10b and the air of the air electrode 10c by controlling the opening of the back pressure valves 22 and 31, thereby maintaining the fuel cell 10 at an intended cell pressure and the hydrogen. Drives the pump 23 and returns it to the hydrogen supply line 15 side through the hydrogen return line 21, and returns the air to the air blower 12 side through the air return line 30 using the pressure difference between the air electrode 10 c and atmospheric pressure.

Further, the FC-ECU 40 drives the water pump 35 to circulate the cooling water in the cooling circuit 36 and releases the heat generated in the fuel cell 10 from the radiator 34 to the atmosphere. Keep at temperature.
On the other hand, a motor ECU 45 is connected to the inverter 5, and drive control and the like of the motor 2 are executed by the motor ECU 45. For example, the motor ECU 45 drives and controls the inverter 5 to drive the motor 2 with output power supplied from the secondary battery 3 or the fuel cell 10, while charging the secondary battery 3 with regenerative power from the motor 2.

The battery ECU 49 is connected to the AC-DC converter 7. When the power plug 8 is connected to an external power source, the battery ECU 49 controls the AC-DC converter 7 to charge the secondary battery 3.
The FC-ECU 40, the motor ECU 45, and the battery ECU 49 described above are connected to a vehicle ECU 46 corresponding to a host unit. Each ECU 40, 45, 46, 49 is an input / output device and a storage device (ROM, RAM, nonvolatile). RAM), a central processing unit (CPU), and the like.

The vehicle ECU 46 is a control unit for performing overall control of the electric vehicle 1, and the operation of the fuel cell system 4 as described above is performed by each of the lower ECUs 40, 45, 49 that have received a command from the vehicle ECU 46. Control, drive control of the motor 2, charge control of the secondary battery 3, etc. are executed.
Therefore, various detection information such as the accelerator opening degree from the accelerator sensor 47 is input to the vehicle ECU 46, and the SOC (charge rate: State Of Charge) of the secondary battery 3 from the battery monitoring unit 48 via the battery ECU 49. And the temperature TBAT are input, the operating state of the fuel cell system 4 is input via the FC-ECU 40, and the operating state of the motor 2 is input via the motor ECU 45.

Then, the vehicle ECU 46 calculates a required output necessary for traveling of the electric vehicle 1 based on the accelerator opening detected by the accelerator sensor 47 and outputs a command signal to the motor ECU 45 so as to achieve the required output. Based on this command signal, the motor 2 is driven by the motor ECU 45 to achieve the required torque.
Further, the vehicle ECU 46 calculates the output power of the fuel cell system 4 based on the SOC of the secondary battery 3 and the required output for vehicle travel, and outputs a command signal to the FC-ECU 40 so as to achieve the output power. For example, when the SOC of the secondary battery 3 decreases to less than a predetermined value and charging is required, or when it is determined that the motor 2 cannot achieve the required output only by supplying power from the secondary battery 3, the vehicle ECU 46 sets the fuel cell The output power of 10 is set on the increasing side.

  On the FC-ECU 40 side, the amount of hydrogen gas to be supplied to the fuel electrode 10b and the amount of air to be supplied to the air electrode 10c to calculate the output power are calculated, and the main valves 17, 27 and the flow rate adjusting valves 18, The supply of hydrogen gas and air is adjusted by opening control of 20, 28, and 29 to achieve the required output power. For example, when the output power is controlled to the increase side as described above, the hydrogen gas amount and the air amount are adjusted to the increase side to increase the output power, and the increase is charged to the secondary battery 3 or the motor 2. It is used for driving. Of course, in response to the control of the output power of the fuel cell 10 as described above, optimal control is performed with respect to the humidity of the hydrogen gas and air, the cell pressure, the cell temperature, and the like.

  By controlling the output power by the FC-ECU 40 as described above, for example, as shown in the time chart of FIG. 3, the operating state of the fuel cell 10 changes between the idle operation and the power generation operation. During idle operation, the fuel cell 10 generates only the power required for its own operation (power consumption of the air blower 12, water pump 35, etc.), and the cell voltage V at this time is relatively high ( 0.9-1.0V). When the output power increases from the idle operation to the power generation operation, the cell voltage V decreases due to the internal resistance of the fuel cell 10 and is switched to the low voltage range (0.5 to 0.8 V).

By the way, as described in [Problems to be Solved by the Invention], a patent document that applies a single method of lowering humidity in order to suppress the oxidation-reduction reaction that may cause the aggregation and elution of platinum in the catalyst layer. In the first technique, there is a problem in that it is impossible to reliably prevent the deterioration of the catalyst layer without realizing an optimum humidity drop that matches the operation state of the fuel cell 10.
In view of such a point, the present inventor previously sets an optimum method (hereinafter referred to as a “humidity reduction method”) for achieving a decrease in humidity for each operation state of the fuel cell 10, and the current operation state of the fuel cell 10. We found a countermeasure to reduce the humidity by selecting the method of reducing the humidity corresponding to the above. Hereinafter, the deterioration prevention of the catalyst layer carried out under this knowledge will be described.

First, in the present embodiment, attention is paid to the following four types of control contents that can be used for the purpose of reducing the humidity. However, it is not limited to these control contents, and may be arbitrarily added or deleted.
The rotational speed of the water pump 35 of the cooling circuit 36 that cools the fuel cell 10 is reduced or stopped, and the flow rate of the cooling water is reduced or the flow rate is zero. As a result, the cell temperature of the fuel cell 10 rises, and the humidity of the hydrogen gas of the fuel electrode 10b and the air of the air electrode 10c decreases (this is cell temperature increase control according to the present invention, hereinafter referred to as control content 1).

  Moreover, the humidity of the hydrogen gas supplied to the fuel electrode 10b or the air supplied to the air electrode 10c is reduced. The target of humidity reduction may be hydrogen gas, air, or both hydrogen gas and air. Specifically, the humidification of the hydrogen gas or air by the humidifier 13 or the opening control of the flow rate adjusting valves 18, 20, 28, 29 is performed to control the mixing ratio of the non-humidified hydrogen gas to the humidified hydrogen gas. The mixing ratio of non-humidified air to air is increased (the control for increasing the ratio of non-humidified gas of the present invention, hereinafter referred to as control content 2).

Further, the back pressure valves 22 and 31 are controlled to the open side to reduce the cell pressure of the fuel cell 10. The humidity of the hydrogen gas of the fuel electrode 10b and the air of the air electrode 10c is reduced with the pressure drop (the cell pressure reduction control of the present invention, hereinafter referred to as control content 3). The target of the pressure drop may be the fuel electrode 10b, the air electrode 10c, or both the fuel electrode 10b and the air electrode 10c.
As for hydrogen gas, the opening amount of the main valve 17 is increased to increase the supply amount of hydrogen gas to the fuel electrode 10b. Regarding air, the rotational speed of the air blower 12 is increased to increase the amount of air supplied to the air electrode 10c. Either of these processes may be performed, or both processes may be executed. Due to the large amount of gas flowing in, the hydrogen gas in the fuel electrode 10b and the air in the air electrode 10c are dried, resulting in a decrease in humidity. In order to cause this phenomenon, the flowing hydrogen gas or air needs to have a certain low humidity (the gas flow rate increase control of the present invention, hereinafter referred to as control content 4).

In the present embodiment, the three types of humidity reduction methods b to d are set in advance by appropriately combining the above control contents 1 to 4 in order to execute the optimum humidity reduction method for each operating state of the fuel cell 10. Prior to the description, classification of the operating state of the fuel cell 10 will be described.
First, as shown in FIG. 3, the operating state of the fuel cell 10 correlates with the cell voltage V, and when the operating state is represented by the cell voltage V, it can be roughly divided into four types of situations. That is, when the fuel cell 10 is in the power generation operation and the cell voltage V is kept in the low voltage range (hereinafter referred to as low voltage A), the cell voltage V increases in the transition from the power generation operation to the idle operation. From a changing situation (hereinafter referred to as “B when voltage increases”), a situation where the cell voltage V is maintained in a high voltage range (idle equivalent value) during idle operation (hereinafter referred to as “C when high voltage”), from idle operation This is a situation in which the cell voltage V is changing in the decreasing direction during the transition to the power generation operation (hereinafter referred to as a voltage drop D).

Therefore, the present inventor considered whether or not the humidity of hydrogen gas or air needs to be reduced in these four kinds of cell voltage V conditions, and the conditions required for the humidity reduction method when humidity reduction is required.
First, Table 1 shows the Pt reaction on the catalyst layer and the deterioration state of the catalyst layer due to the Pt reaction in the situation of each cell voltage V (A to D).

  At a low voltage A of the cell voltage V, a Pt reduction reaction occurs on the catalyst layer, but this reduction reaction does not cause deterioration of the catalyst layer. Therefore, even if the cell voltage V stays in the low voltage range for a long time (meaning continuation of power generation), deterioration of the catalyst layer does not proceed, and it is considered unnecessary to reduce the humidity of hydrogen gas or air to prevent deterioration. A humidity reduction method corresponding to the state of the cell voltage V is not set.

  When the cell voltage V increases (corresponding to the third state of the present invention), the reaction of Pt on the catalyst layer changes from reduction to oxidation, and the change in the reaction state at this time is slight but the catalyst layer. In addition, the degree of influence on the deterioration increases as the increase rate of the cell voltage V increases. Therefore, it is desirable to reduce the humidity of hydrogen gas or air somewhat to prevent deterioration. Further, since the transition from the low voltage A to the voltage increase B occurs, for example, due to the driver's sudden accelerator off, etc., it is necessary to rapidly reduce the humidity with the transition to the voltage increase B. Good response is required for the reduction.

  In view of the conditions required for the humidity lowering method (hereinafter referred to as “b” to distinguish from the others) at the time B when the voltage is increased, as shown in step S9 of FIG. A map for calculating the target humidity from the rate V ′) is set, and based on the map, the target humidity for executing the humidity reduction method b is set. As shown in the figure, the target humidity is set to a lower side as the increase rate of the cell voltage V is larger, with the upper limit Hmax being the humidity during normal control when no humidity reduction is required. It is set to be the highest as compared with the map characteristics of other humidity lowering methods c and d described later. For this reason, the humidity reduction performed by the humidity reduction method b is relatively mild.

  Moreover, in order to implement | achieve favorable responsiveness, all the above-mentioned control contents 1-4 are combined with this humidity reduction method b. As a result, cell temperature increase control, non-humidified gas ratio increase control, cell pressure decrease control, and gas flow rate increase control are performed all at once, and each of these acts in the direction of decreasing humidity to achieve good responsiveness. Is done. In addition, although a rapid decrease in humidity is required in this way, the amount of decrease in target humidity based on the map is small, so that the control amount applied to each control is relatively smaller than, for example, a humidity decrease method d described later. Value is applied.

  At the high voltage C of the cell voltage V (corresponding to the second state of the present invention), an oxidation reaction of Pt occurs on the catalyst layer, and the oxidative deterioration progresses as the idling operation is continued. It also occurs on the low voltage side in the vicinity of the high voltage range, and is most noticeable in the high voltage range. Therefore, lowering the humidity of hydrogen gas or air to prevent deterioration is more strongly required than when the voltage is increased B described above. On the other hand, since the fuel cell 10 at this time is in a steady idle operation, the responsiveness as much as B when the voltage is increased is not required for the humidity reduction. Further, since the gas flow rate is decreased for idle operation, the control content 4 for increasing the gas flow rate is difficult to execute.

  The map is set as shown in step S7 of FIG. 4 in view of the conditions required for the humidity lowering method (hereinafter referred to as c) at the time of high voltage C described above. The target humidity is set to a lower side as the high voltage region is approached in the region of the predetermined value V0 or higher with the humidity during normal control as the upper limit Hmax. Then it is lowered. The predetermined value V0 is a value set in advance as a lower limit cell voltage V at which a catalyst layer deterioration phenomenon that cannot be ignored is generated. For this reason, the humidity reduction performed by the humidity reduction method c is more significant than the humidity reduction method b.

Further, since such responsiveness is not required, the control contents 1 and 2 are combined with this humidity lowering method c, whereby the cell temperature increase control and the non-humidified gas ratio increase control are executed. As the control amount applied to each control, a value larger than the humidity reduction method b is applied since the humidity reduction range based on the map is relatively large.
At the time of voltage drop D of the cell voltage V (corresponding to the first state of the present invention), the reaction of Pt on the catalyst layer changes from oxidation to reduction, and the change in the reaction state at this time is a serious phenomenon that deteriorates the catalyst layer. While becoming a serious factor, the degree of influence on the deterioration increases as the rate of decrease of the cell voltage V increases. Therefore, in order to prevent deterioration, it is most strongly required to significantly reduce the humidity of hydrogen gas or air as compared with other operating conditions. Further, since the transition from the high voltage C to the voltage drop D occurs, for example, when the driver suddenly turns on the accelerator, etc., it is necessary to quickly reduce the humidity with the transition to the voltage drop D. Good response is required for the reduction.

  A map is set as shown in step S5 in FIG. 4 in view of the conditions required for the humidity reduction method (hereinafter, d) at the time of voltage drop D described above. The target humidity is set to the lower side as the decrease rate (change rate | V ′ |) of the cell voltage V is larger, with the humidity during normal control being the upper limit Hmax, but the lower limit Hmin is a decrease in other humidity. It is set to be the lowest compared with the map characteristics of the methods b and c. For this reason, the humidity reduction performed by the humidity reduction method d is the largest compared to the other humidity reduction methods b and c.

In addition, in order to realize good responsiveness, all the control contents 1 to 4 described above are combined with this humidity reduction method d, and a large amount of humidity is reduced based on the map. Control amount is applied.
As is clear from the above description of each of the humidity reduction methods b to d, the humidity reduction method c and the humidity reduction methods b and d are set with different control contents. This corresponds to a relationship between a plurality of humidity reduction methods, and the humidity reduction method b and the humidity reduction method d are set with the same control content and have different control amounts applied to the control content. This corresponds to the relationship among the plurality of humidity lowering methods of claim 6.

Next, humidity reduction processing executed by the FC-ECU 40 based on the various settings as described above will be described. The FC-ECU 40 when executing this humidity reduction process functions as the humidity reduction means of the present invention.
FIG. 4 is a flowchart showing a humidity lowering routine executed by the FC-ECU 40. The FC-ECU 40 executes the routine at predetermined control intervals while the fuel cell 10 is in operation.

First, in step S1, the cell voltage V is detected. The cell voltage V at this time may be a value obtained by averaging the voltages of all the single cells, or may be a voltage of a specific single cell. Next, in step S2, it is determined whether or not the rate of change V ′ per unit time of the cell voltage V is negative, that is, whether or not it is a voltage drop D when the cell voltage V is decreasing.
When the determination in step S2 is No (negative), the process proceeds to step S3, including whether or not the cell voltage V is equal to or higher than a predetermined value V0, that is, the high voltage C when the cell voltage V is maintained in the high voltage range. It is determined whether or not the cell voltage V is high enough to cause a deterioration phenomenon of the catalyst layer. When the determination in step S3 is No, the process proceeds to step S4, and it is determined whether or not the rate of change V ′ of the cell voltage V is positive, that is, whether or not the cell voltage V is B when the voltage is increasing. When NO, the routine is temporarily terminated.

When the determination in step S2 is Yes (positive), the process proceeds to step S5, and the target humidity is calculated from the change rate | V ′ | (decrease rate) of the cell voltage V based on the map shown in the figure. In step S6, the control amount is increased to execute the humidity reduction method d (control contents 1 to 4), and then the routine is terminated.
When the determination in step S3 is Yes, the process proceeds to step S7, and the target humidity is calculated from the cell voltage V based on the illustrated map. In the subsequent step S8, the humidity reduction method c (control contents 1 and 2) is executed with a large control amount.

When the determination in step S4 is Yes, the process proceeds to step S9, and the target humidity is calculated from the rate of change V ′ (increase rate V ′) of the cell voltage V based on the illustrated map. In the subsequent step S10, the humidity reduction method c (control contents 1 to 4) is executed with the control amount being small.
As described above, according to the fuel cell system 4 of the present embodiment, the operating state of the fuel cell 10 in which the catalyst layer may be deteriorated, that is, when the cell voltage V increases, B, when high, and when the voltage decreases. In each operating state of D, considering the conditions (humidity reduction range, responsiveness, etc.) required to reduce the humidity to prevent the catalyst layer from deteriorating, optimally including the control amount in advance for each operating state Each time the humidity reduction methods b to d are set so that the control contents are appropriate, and each time the operation state of the fuel cell 10 is switched, the humidity reduction methods b to d corresponding to the operation state are selected and executed to reduce the humidity. Has achieved.

Therefore, since the humidity of hydrogen gas or air is reduced by the optimum humidity reduction method b to d consistent with the operating state of the fuel cell 10, the oxidation-reduction reaction on the catalyst layer of the fuel electrode 10b or the air electrode 10c is performed. Thus, it is possible to reliably prevent deterioration due to platinum aggregation / elution of the catalyst layer.
Further, when the cell voltage V increases, the target humidity is set to the lower side as the increase rate increases, and at the high voltage C, the target humidity increases as the cell voltage V approaches the high voltage range. Is set to the lower side, and at the time of voltage drop D, the target humidity is set to the lower side as the rate of decrease of the cell voltage V is larger. The higher the cell voltage V decrease rate, the closer the cell voltage V approaches the high voltage range, and the greater the increase rate of the cell voltage V, the more platinum aggregation is caused by the oxidation-reduction reaction on the catalyst layer. -Although the possibility of elution increases, since the target humidity is set on the lower side accordingly, the oxidation-reduction reaction can be more reliably suppressed.

  Furthermore, based on the possibility of platinum aggregation and elution of the catalyst layer in each operating state (B to D), the lower limit of the target humidity is made the lowest at the time of voltage drop D when the necessity of humidity drop is extremely high, and the humidity drop The lower limit of the target humidity is set highest at the time B when the voltage increase is low. At the time of voltage drop D, it is possible to more reliably suppress the oxidation-reduction reaction on the catalyst layer by sufficiently reducing the humidity, and at the time of voltage increase B, the efficiency reduction of the fuel cell 10 due to excessive humidity drop can be prevented in advance. Can do.

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above-described embodiment, the fuel cell system 4 mounted on the electric vehicle 1 is embodied. However, the present invention is not limited to this, and may be applied to, for example, a stationary fuel cell system.

4 Fuel Cell System 10 Fuel Cell 10b Fuel Electrode 10c Air Electrode 41 Voltage Sensor (Cell Voltage Detection Means)
40 FC-ECU (humidity reduction means)

Claims (6)

In a fuel cell comprising a fuel electrode and an air electrode having a catalyst layer, supplying fuel gas to the fuel electrode and supplying air to the air electrode to generate electricity,
Voltage detecting means for detecting the voltage of the fuel cell, which varies according to the output power of the fuel cell;
Humidity reduction is performed by selecting a humidity reduction method corresponding to the current voltage state of the fuel cell from a plurality of humidity reduction methods selected corresponding to a plurality of voltage states that change according to the operating state of the fuel cell. A fuel cell system, comprising: a humidity lowering means. As the plurality of voltage states, at least two or more of a first state in which the voltage changes in a decreasing direction, a second state in which the voltage exceeds a predetermined value, and a third state in which the voltage changes in an increasing direction And the humidity reduction method corresponding to each of the two or more states is preset,
The humidity reduction means determines that a humidity reduction is required when any one of the plurality of voltage states occurs, and selects and executes a humidity reduction method corresponding to the generated state. The fuel cell system according to claim 1. The humidity lowering means changes the voltage in an increasing direction as the rate of decrease increases when the voltage changes in a decreasing direction, and as the voltage approaches a predetermined idle value when the voltage exceeds a predetermined value. 3. The fuel cell system according to claim 2, wherein when the increase rate is larger, the target humidity is set to a lower side, and the humidity reduction method is executed based on the target humidity. The humidity lowering means sets the humidity during normal control when humidity reduction is not required as the upper limit of the target humidity, and when the voltage changes in a decreasing direction, lowers the lower limit of the target humidity and increases the voltage. 4. The fuel cell system according to claim 3, wherein when the direction changes, the lower limit of the target humidity is made highest and the target humidity is set between the upper limit and the lower limit. The plurality of humidity lowering methods have different control contents among cell temperature increase control, non-humidified gas ratio increase control, cell pressure decrease control, and gas flow rate increase control for the purpose of reducing humidity. The fuel cell system according to any one of claims 1 to 4, wherein the fuel cell system is set. In the plurality of humidity reduction methods, the same control contents are set among cell temperature increase control, non-humidified gas ratio increase control, cell pressure decrease control, and gas flow rate increase control for the purpose of reducing humidity. The fuel cell system according to any one of claims 1 to 4, wherein the control amount applied to the set control content is made different.

Images