JP2007123077A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the deterioration of power generation performance caused by the deposition of an oxide of a fuel cell having a metal member on a cathode side. <P>SOLUTION: The fuel cell of a fuel cell system comprises a membrane electrode conjugate having an electrolyte membrane and catalyst layers formed on its both sides, a cathode side current collector provided in contact with one side of the membrane electrode conjugate, and an anode side current collector provided in contact with the other side of the membrane electrode conjugate, and the cathode side current collector includes a metal member. The fuel cell system furthermore comprises a potential setting part to establish the potential of the metal member of the cathode side current collector for the anode side current collector, and the potential setting part has a low potential mode which establishes the potential of the metal member for the anode side current collector at a prescribed low potential mode voltage lower than a maximum output point voltage in which the output power of the fuel cell becomes maximum, when the power generation of the fuel cell is carried out. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an operation control technique for a fuel cell including a metal member on the cathode side.

  A fuel cell is usually configured by stacking a plurality of single cells. When the single cells are stacked, the space between the anode side and the cathode side of the adjacent single cells is separated and the adjacent single cells are electrically connected. Is provided. The separator can be formed of various materials, but may be formed of a metal material in order to improve workability and durability. In general, since a separator of a fuel cell is exposed to oxygen or a high concentration of protons, a material having high corrosion resistance is used as a metal material forming the separator.

JP 2000-353531 A JP 2004-356030 A Japanese Patent Laid-Open No. 11-219715

  However, even if a material with high corrosion resistance is used for the separator, oxidation proceeds by energization for a long time, and the power generation performance of the fuel cell may be reduced due to deposition of the generated oxide. This problem is common to fuel cells that use metal separators and other fuel cells that have a metal member on the cathode side.

  The present invention has been made to solve the above-described conventional problems, and an object thereof is to suppress a decrease in power generation performance due to oxide deposition of a fuel cell having a metal member on the cathode side.

  In order to achieve at least a part of the above object, a fuel cell system according to the present invention includes a membrane electrode assembly having an electrolyte membrane and catalyst layers provided on both surfaces of the electrolyte membrane, and one of the membrane electrode assemblies. A fuel cell comprising: a cathode current collector including a metal member provided in contact with the anode side; and an anode current collector provided in contact with the other side of the membrane electrode assembly; and the anode side current collector. A potential setting unit that sets a potential of the metal member with respect to an electric body, and the potential setting unit has a potential of the metal member with respect to the anode-side current collector when power generation is performed by the fuel cell. Has a low potential mode in which a predetermined low potential mode voltage lower than a maximum output point voltage at which the output power of the fuel cell is maximized is set.

  According to this configuration, the oxide of the metal member can be reduced by executing the low potential mode. As a result, oxide deposition is suppressed, so that a decrease in power generation performance of the fuel cell is suppressed.

  The predetermined low potential mode voltage may be −0.2 V or more.

  According to this configuration, the risk of damage to the fuel cell due to the execution of the low potential mode can be further reduced.

  The potential setting unit may include an output current adjusting unit that sets the potential of the metal member with respect to the anode-side current collector to the low potential mode voltage by adjusting an output current of the fuel cell.

  According to this configuration, since the potential of the metal member can be set by adjusting the output current, it becomes easier to set the potential of the metal member.

  The fuel cell system further includes a series resistance measurement unit that measures a series resistance of the fuel cell, and the potential setting unit is configured such that the series resistance of the fuel cell measured by the series resistance measurement unit is a predetermined limit value. The low potential mode may be executed after exceeding.

  According to this configuration, by appropriately performing the low potential mode, it is possible to more reliably suppress the reduction in power generation performance due to the increase in the series resistance of the fuel cell.

  The potential setting unit may execute the low potential mode when the fuel cell system is stopped or started.

  According to this configuration, since the control of the fuel cell system can be performed by the fuel cell system alone, it is easier to execute the low potential mode.

  The present invention can be realized in various modes. For example, the fuel cell system and the fuel cell system control method, the power generation device using the fuel cell system and the control method, and the fuel cell system are mounted. It can be realized in an aspect such as an electric vehicle.

Next, the best mode for carrying out the present invention will be described in the following order based on examples.
A. Embodiment:
B. Example:
C. Variation:

A. Embodiment:
FIG. 1 is a schematic configuration diagram showing a configuration of a fuel cell system 10 as an embodiment of the present invention. The fuel cell system 10 includes a fuel cell 100 and a fuel cell output control unit 410 connected to the fuel cell 100 via conductors 422 and 424. Normally, the fuel cell is configured as a fuel cell stack in which a plurality of single cells are stacked. However, for convenience of illustration, the fuel cell 100 including one single cell is shown here.

  The fuel cell 100 includes a membrane electrode assembly 110, and a cathode side current collector 200 and an anode side current collector 300 that sandwich the membrane electrode assembly 110 from both sides. The membrane electrode assembly 110 includes an electrolyte membrane 112 and two catalyst layers 120 and 130 that sandwich the electrolyte membrane 112 from both sides. The electrolyte membrane 112 is a proton conductive ion exchange membrane made of a fluorine resin material such as Nafion (trademark of DuPont) and having good conductivity in a wet state. The catalyst layers 120 and 130 are made of carbon powder carrying platinum or an alloy made of platinum and other metals, dispersed in an appropriate organic solvent, and added with an appropriate amount of electrolyte (for example, Nafion) to form a paste. It is formed by screen printing on the electrolyte membrane.

  The cathode side current collector 200 includes a cathode side diffusion layer 210 and a cathode side separator 220. The anode side current collector 300 includes an anode side diffusion layer 310 and an anode side separator 320. The cathode side diffusion layer 210 and the anode side diffusion layer 310 (hereinafter also referred to as “gas diffusion layer”) are conductive porous materials (for example, carbon felt) having a higher porosity than the catalyst layers 120 and 130. ).

  The cathode side separator 220 and the anode side separator 320 (hereinafter also referred to as “separator”) are formed by molding titanium. The separators 220 and 320 are provided with recesses on the sides facing the gas diffusion layers 210 and 310, respectively. An oxidizing gas containing oxygen is supplied to a space (cathode flow path 222) formed by the concave portion provided in the cathode side separator 220 and the cathode side diffusion layer 210. A fuel gas containing hydrogen is supplied to a space (anode channel 322) formed by the recess provided in the anode side separator 320 and the anode side diffusion layer 310. Note that these oxidizing gas and fuel gas are both gases used for the fuel cell reaction, so these gases are also called “reactive gas”.

  In this embodiment, separators 220 and 320 having a recess for forming a reaction gas flow path on the gas diffusion layers 210 and 310 side are used, but on the gas diffusion layers 210 and 310 side. A separator without unevenness can also be used. In this case, the gas diffusion layers 210 and 310 serve as reaction gas flow paths.

  The hydrogen molecules supplied to the anode channel 322 pass through the anode side diffusion layer 310 and reach the catalyst layer 130. In the catalyst layer 130, hydrogen molecules are dissociated into electrons and protons. Protons generated by the dissociation move to the catalyst layer 120 through the electrolyte membrane 112. Electrons generated by the dissociation are supplied to an external conductor via the anode side diffusion layer 310 and the anode side separator 320.

  At this time, since hydrogen is supplied to the catalyst layer 130 containing a catalyst such as platinum, the potential of the catalyst layer 130 and the anode-side diffusion layer 310 and the anode-side separator electrically connected to the catalyst layer 130 Each potential of 320 is almost a standard hydrogen electrode potential.

  Oxygen molecules supplied to the cathode channel 222 pass through the cathode side diffusion layer 210 and reach the catalyst layer 120. In the catalyst layer 120, oxygen molecules supplied through the cathode side diffusion layer 210, protons supplied through the electrolyte membrane 112, and electrons supplied from the external conductor through the cathode side separator 220 and the cathode side diffusion layer 210. Water is produced by the fuel cell reaction.

  The fuel cell output control unit 410 has two operation modes: a normal mode and a low potential mode. In the normal mode, the output of the fuel cell 100 is controlled based on power (required power) required by a load (not shown) of the fuel cell system 10. On the other hand, in the low potential mode, the fuel cell output control unit 410 sets the potential of the cathode separator 220 with respect to the anode separator 320 to be lower than when the normal mode is executed. The output control of the fuel cell 100 in these two operation modes will be described later.

  FIG. 2 is an explanatory diagram showing the power generation characteristics of the fuel cell 100 (FIG. 1). 2A and 2B represent the output current I of the fuel cell 100. The horizontal axis of FIG. 2A represents the potential (cell voltage) V of the cathode side separator 220 with respect to the anode side separator 320 of the fuel cell 100, and the vertical axis in FIG. 2B represents the output power P of the fuel cell 100. Represents. In the present specification, the potential with respect to the anode-side separator 320 is also simply referred to as “voltage”.

As shown in FIG. 2A, when the output current I = 0 where the fuel cell 100 does not output a current, the cell voltage V of the fuel cell 100 is an open circuit voltage (OCV≈1V). As the output current I increases, the cell voltage V decreases. When the output current I becomes the limit current I _lim , the cell voltage V becomes zero.

Since there is a relationship (current-voltage characteristic) shown in FIG. 2A between the output current I and the cell voltage V of the fuel cell 100, the output power of the fuel cell 100 is shown in FIG. P becomes 0 at two points of the output current I being 0 and the limit current I _lim . The output power P of the fuel cell 100 becomes the maximum output power P _XP at the output current I _XP determined by the current-voltage characteristics shown in FIG. In this specification, the output current I (= I _XP ) at which the output power P becomes the maximum output power P _XP is also referred to as the maximum output point current. In addition, the cell voltage V (= V _XP ) associated with the maximum output point current I _XP by the current-voltage characteristic of FIG. 2A is also referred to as the maximum output point voltage.

When the fuel cell output control unit 410 (FIG. 1) operates in the normal mode, the output control of the fuel cell 100 is performed based on the required power P _RQ as described above. Specifically, when the required power P _{RQ of the} load is determined, the target current I _TG is determined based on the relationship shown in FIG. As shown in FIG. 2B, two points of output current I correspond to the required power P _RQ , but the target current I _TG is determined based on the relationship indicated by the solid line in the graph of FIG. Is done. This is because when the same power is output, the maximum output point indicated by the solid line in the graph of FIG. 2B in the region where the current is larger than the maximum output point current I _XP indicated by the dotted line in the graph of FIG. This is because the loss of the fuel cell 100 becomes larger than the region where the current is smaller than the current I _XP .

When the target current I _TG is determined, the fuel cell output control unit 410 sets the cell voltage V of the fuel cell 100 to the target voltage V _TG according to the current-voltage characteristics of FIG. When the cell voltage V of the fuel cell 100 becomes the target voltage V _TG , the output current I of the fuel cell 100 becomes the target current I _TG , and power corresponding to the required power P _RQ is output from the fuel cell 100. The electric power output from the fuel cell 100 is supplied to the load of the fuel cell system 10 via the fuel cell output control unit 410. In this embodiment, the target current I _TG is determined based on the required power P _RQ , and the cell voltage V is set to the target voltage V _TG based on the determined target current I _TG , but the required power The target voltage V _TG may be determined directly from P _RQ, and the cell voltage may be set to the determined target voltage V _TG .

As described above, when the fuel cell output control unit 410 is performing the output control in the normal mode, the cell voltage V is higher than the maximum output point voltage V _{XP as} shown by the solid line in the graph of FIG. Maintained high. In a state where the cell voltage V is high, the surface oxidation reaction of the cathode separator 220 proceeds. Due to the surface oxidation reaction of the cathode separator 220, a titanium oxide (TiO ₂ ) film having low electrical conductivity is formed on the surface of the cathode separator 220, and the thickness of the titanium oxide film increases with time.

  When the titanium oxide film is formed on the surface of the cathode side separator 220, the resistance between the cathode side separator 220 and the cathode side diffusion layer 210 increases. When the resistance between the cathode side separator 220 and the cathode side diffusion layer 210 increases, the loss of the fuel cell 100 increases, and the power generation efficiency of the fuel cell 100 may decrease.

When the fuel cell output control unit 410 operates in the low potential mode, the fuel cell 100 sets the cell voltage V to a predetermined low potential mode voltage V _LV that is lower than the maximum output point voltage V _XP . Specifically, the fuel cell output control unit 410 takes out the low potential mode current I _LV that is associated with the low potential mode voltage V _LV from the fuel cell 100 according to the current-voltage characteristics of FIG. The voltage V is set to the low potential mode voltage _VLV . The fuel cell output control unit 410 sets the cell voltage V to the low potential mode voltage V _LV by adjusting the output current I of the fuel cell, and can also be called an output current adjustment unit.

  Thus, when the fuel cell output control unit 410 is executing the output control in the low potential mode, the cell voltage V becomes low. Therefore, the surface reduction reaction of the cathode side separator 220 proceeds. By this surface reduction reaction, the titanium oxide film formed on the surface of the cathode-side separator 220 is reduced to titanium, and the thickness of the titanium oxide film is reduced.

The predetermined low potential mode voltage V _LV may be a voltage at which the reduction reaction of the titanium oxide film formed on the surface of the cathode separator 220 proceeds. Specifically, the low potential mode voltage V _LV may be a voltage lower than the maximum output point voltage V _XP . Note that the low potential mode voltage V _LV is preferably set to 0.3 V or less so that the reduction reaction of the titanium oxide film proceeds more reliably. The low potential mode voltage V _LV is more preferably 0.2 V or less, and even more preferably 0.1 V or less so that the reduction reaction of the titanium oxide film proceeds faster.

Further, the predetermined low potential mode voltage V _LV can be set to a negative value by using a bipolar current sink as the fuel cell output control unit 410. In this case, a current larger than the limit current I _lim is taken out from the fuel cell 100. Therefore, the amount of heat generated in the fuel cell 100 increases, and the fuel cell 100 may be damaged. The predetermined low potential mode voltage V _LV is preferably set to be equal to or higher than a predetermined lower limit voltage in consideration of such characteristics. The predetermined lower limit voltage can be obtained by experiments or the like, but is preferably set to −0.2 V or more and more preferably −0.1 V or more in order to more reliably suppress damage to the fuel cell 100. It is more preferable to set.

  FIG. 3 is a flowchart showing an output control routine for performing output control of the fuel cell 100 (FIG. 1). This output control routine is repeatedly executed at regular intervals. In the present embodiment, the output control routine is started at regular time intervals. However, this routine only needs to be executed at least once within a predetermined operation time. For example, the output control routine may be executed once every power generation amount. good.

4 is an explanatory diagram showing an example of the state of the fuel cell 100 when the fuel cell output control unit 410 executes the output control routine shown in FIG. The horizontal axis of each graph in FIG. 4 represents time. The vertical axis in FIG. 4A represents the required power P _RQ, and the vertical axis in FIG. 4B represents the operation mode of the fuel cell output control unit 410. The vertical axes of FIG. 4C and FIG. 4D represent the output current I and the cell voltage V of the fuel cell 100, respectively. The vertical axis in FIG. 4E indicates the thickness of the titanium oxide film formed on the surface of the cathode separator 220.

  In step S100 of FIG. 3, the fuel cell output control unit 410 determines whether or not it is necessary to execute the low potential mode. If it is determined that execution of the low potential mode is not necessary, control is transferred to step S200. On the other hand, if it is determined that the low potential mode needs to be executed, the control is moved to step S300.

  The necessity of executing the low potential mode is, for example, estimating the titanium oxide film thickness formed on the surface of the cathode separator 220 (FIG. 1), and the estimated film thickness value is a predetermined film thickness upper limit (for example, 30 nm). It can be determined that the execution of the low potential mode is necessary when the value exceeds. In this case, the estimated value of the film thickness can be calculated based on the relationship between the energization time and power generation amount of the fuel cell 100 and the titanium oxide film thickness experimentally and based on the obtained relationship and the energization time and power generation amount. Is possible.

  Further, whether or not the low potential mode needs to be executed is determined by a series resistance measurement unit (not shown) provided in the fuel cell system 10 (FIG. 1) measuring the series resistance of the fuel cell 100, and the series resistance measurement value is a predetermined value. It can also be determined that execution of the low potential mode is necessary when the upper limit value of the series resistance is exceeded. The series resistance of the fuel cell 100 is determined by measuring the output voltage of the fuel cell 100 when the output current of the fuel cell 100 is set to a predetermined series resistance measurement current during the operation of the fuel cell system 10, for example. Can be measured. The series resistance of the fuel cell 100 can also be obtained by measuring the relationship between the output current and the output voltage of the fuel cell 100 when starting or stopping the fuel cell system 10, and by determining the slope of the graph representing the relationship. it can. In this case, the output current set when determining the series resistance of the fuel cell 100 is preferably set to a value in a region where the current-voltage characteristic graph shown in FIG. .

  In addition, after the series resistance exceeds a predetermined series resistance upper limit value when the cycle in which it is determined that the execution of the low potential mode is necessary is sufficiently long with respect to the operation continuation time between the start and stop of the fuel cell system 10 The low potential mode may be executed when the fuel cell system 10 is started or stopped.

In step S200 of FIG. 3, the fuel cell output control unit 410 performs output control in the normal mode, and then the output control routine ends. In the example of FIG. 4, as shown in FIG. 4B, the normal mode output is performed in the period from time t ₀ to time t ₁ , in the period from time t ₂ to time t ₃ , and in the period after time t _4. Control is performed. In the output control in the normal mode, as shown in FIG. 4C, the target current I _TG is determined based on the requested output P _RQ . Then, as shown in FIG. 4D, the cell voltage V is set to the target voltage V _TG based on the determined target current I _TG and the current-voltage characteristics shown in FIG.

As described above, the surface oxidation reaction of the cathode separator 220 proceeds in a state where the cell voltage V is high due to the execution of the output control in the normal mode. Therefore, as shown in FIG. 4D, the titanium oxide film thickness increases with time in the period from time t ₀ to time t ₁ , in the period from time t ₂ to time t ₃ , and in the period after time t _4. To increase.

  In step S300 of FIG. 3, the fuel cell output control unit 410 performs output control in the low potential mode, and then the control is moved to step S310. In step S310, the output control state in the low potential mode is maintained until a predetermined standby time elapses. The predetermined waiting time is set to a time sufficient for the reduction of the titanium oxide film formed on the cathode separator 220. The predetermined standby time can be determined based on, for example, the estimated titanium oxide film thickness and the titanium oxide reduction rate obtained experimentally. Note that step S310 may be omitted depending on the execution cycle of the fuel cell output control routine shown in FIG. 3, the reduction rate of titanium oxide, and the like.

In the example of FIG. 4, as shown in FIG. 4B, output control in the low potential mode is maintained in the period from time t ₁ to time t _{2 and in} the period from time t ₃ to time t ₄ . In the output control in the low potential mode, as shown in FIG. 4C, the output current I of the fuel cell 100 is set to the low potential mode current _ILV regardless of the value of the required output _PRQ . Then, by extracting the low potential mode current I _LV from the fuel cell 100, the cell voltage V is set to the low potential mode voltage V _{LV as shown} in FIG.

As described above, in the state where the cell voltage V is low due to the execution of output control in the low potential mode, the reduction reaction of titanium oxide formed on the surface of the cathode separator 220 proceeds. Therefore, as shown in FIG. 4D, the titanium oxide film thickness decreases with time in the period from time t ₁ to time t _{2 and in} the period from time t ₃ to time t ₄ .

  Thus, in this embodiment, by performing output control in the low potential mode, titanium oxide formed on the surface of the cathode-side separator 220 is reduced, and the thickness of the titanium oxide decreases with time. Therefore, an increase in resistance of the fuel cell 100 due to the formation of the titanium oxide film is suppressed, and a decrease in power generation efficiency of the fuel cell 100 is suppressed.

B. Example:
[Anode polarization treatment of titanium plate]
FIG. 5 is an explanatory diagram showing the evaluation of the relationship between the potential of the titanium plate relative to the standard hydrogen electrode and the thickness of the titanium oxide film formed on the surface of the titanium plate. In this evaluation, the titanium plate was subjected to an anodic polarization treatment to form a titanium oxide film on the surface of the titanium plate. The titanium plate used for the evaluation corresponds to the cathode side separator 220 (FIG. 1), and the standard hydrogen electrode corresponds to the anode side separator 320 (FIG. 1).

  FIG. 5A shows a configuration of an anodic polarization processing apparatus 500 for anodic polarization processing of a titanium plate. The anodic polarization processing apparatus 500 includes a potentiostat 510, an electrolyte bath 520, and a silver / silver chloride electrode 530.

  A titanium plate 540 was connected to the working electrode (W electrode) of the potentiostat 510, and a platinum electrode 550 was connected to the counter electrode (C electrode). A silver / silver chloride electrode 530 was connected to the reference electrode (R electrode). Then, a titanium plate 540 connected to each electrode of the potentiostat 510, a platinum electrode 550, and a silver / silver chloride electrode 530 were immersed in an electrolytic solution 560 charged into the electrolytic solution tank 520. In addition, the electrolyte solution 560 thrown into the electrolyte solution tank 520 was prepared so that pH might be set to 5.

[Example]
In the embodiment, the potentiostat 510 is controlled, and as shown in FIG. 5B, the potential of the titanium plate 540 with respect to the standard hydrogen electrode (hereinafter referred to as “titanium plate” in the first half of the 1 hour period). The potential of the titanium plate was set to 1.2 V, and the potential of the titanium plate was set to 0.1 V for the latter half of 0.5 hour. And the energization for 100 hours was performed by repeating the setting of the titanium plate potential of this 1 hour period 100 times. As can be seen from this description, the time during which the titanium plate potential was 1.2 V out of 100 hours of the anodic polarization treatment of the titanium plate was 50 hours.

[Comparative example]
In the comparative example, as shown in FIG. 5C, the titanium plate potential was set to 1.2 V for 50 hours continuously.

[Evaluation of contact resistance]
In order to evaluate the thickness of the titanium oxide film formed on the surface of the titanium plate, the contact resistance between the titanium plate subjected to the anodic polarization treatment and the carbon felt used for the diffusion layer (hereinafter simply referred to as “contact”). Also called resistance]).

  Fig.6 (a) is explanatory drawing which shows the mode of a measurement of contact resistance. In the measurement of the contact resistance, the titanium plate 540 subjected to the anodic polarization treatment and the carbon felt 570 were overlapped, and stress was applied perpendicularly to the contact surface between the titanium plate 540 and the carbon felt 570. Then, the resistance between the titanium plate 540 and the carbon felt 570 in a state where stress was applied was measured by a resistance measuring device 580.

  FIG. 6B shows the measurement results of the contact resistance in the example and the comparative example. As shown in FIG. 6B, the contact resistance of the comparative example was about three times the contact resistance of the example. From this, it was found that the thickness of the titanium oxide film on the surface of the titanium plate subjected to the anodic polarization treatment in the comparative example was thicker than the thickness of the titanium oxide film on the surface of the titanium plate subjected to the anodic polarization treatment in the example. .

  As described above, in the anodic polarization treatment of the example and the comparative example, the time when the titanium plate potential is set to 1.2 V is 50 hours. Therefore, the thickness of the titanium oxide film formed on the surface of the titanium plate with the titanium plate potential being 1.2 V is considered to be substantially the same. On the other hand, the thickness of the titanium oxide film on the surface of the titanium plate subjected to the anodic polarization treatment in the example was thinner than the thickness of the titanium oxide film on the surface of the titanium plate subjected to the anodic polarization treatment in the comparative example. From this, it was found that by setting the titanium plate potential to 0.1 V, the titanium oxide film formed on the surface of the titanium plate was reduced, and the thickness of the titanium oxide film was reduced.

C. Variation:
In addition, this invention is not restricted to the said Example and embodiment, It can implement in a various aspect in the range which does not deviate from the summary, For example, the following deformation | transformation is also possible.

C1. Modification 1:
In the above embodiment, the cell voltage V is set to the low potential mode voltage V _LV by taking out the low potential mode current I _LV from the fuel cell 100 (FIG. 1), but the anode side separator 320 (see FIG. It is also possible to set the potential of the cathode separator 220 (FIG. 1) with respect to 1). For example, the potential setting electrode is provided in the membrane electrode assembly 110 (FIG. 1), and the potential of the cathode side separator 220 with respect to the anode side separator 320 is set by flowing an appropriate current between the potential setting electrode and the cathode side separator 220. It may be set.

C2. Modification 2:
In the above embodiment, the present invention is applied to the fuel cell 100 in which the cathode side separator 220 is formed of titanium. However, the present invention is generally applied to a fuel cell in which the cathode side current collector 200 includes a metal member. Can do. The metal member may be formed of any one of a single metal such as titanium and an alloy such as titanium alloy and stainless steel. In addition, the present invention can be applied even when at least one of the cathode side separator 220 and the cathode side diffusion layer 210 is a metal member. In this case, it is only necessary that the potential of the metal member with respect to the anode side current collector 300 can be set to the low potential mode voltage _VLV .

1 is a schematic configuration diagram showing a configuration of a fuel cell system 10 as one embodiment of the present invention. FIG. 3 is an explanatory diagram showing power generation characteristics of the fuel cell. 4 is a flowchart showing an output control routine for performing output control of the fuel cell 100. 4 is an explanatory diagram showing an example of a state of the fuel cell 100 when the fuel cell output control unit 410 executes an output control routine. FIG. Explanatory drawing which shows the mode of evaluation of the relationship between the electric potential of the titanium plate with respect to a standard hydrogen electrode, and the thickness of the titanium oxide film formed on the surface of a titanium plate. Explanatory drawing which shows the evaluation result of the relationship between the electric potential of the titanium plate with respect to a standard hydrogen electrode, and the thickness of the titanium oxide film formed on the surface of a titanium plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 100 ... Fuel cell 110 ... Membrane electrode assembly 112 ... Electrolyte membrane 120, 130 ... Catalyst layer 200 ... Cathode side current collector 210 ... Cathode side diffusion layer 220 ... Cathode side separator 222 ... Cathode flow path 300 ... Anode-side current collector 310 ... Anode-side diffusion layer 320 ... Anode-side separator 322 ... Anode flow path 410 ... Fuel cell output control unit 422, 424 ... Conductor 500 ... Anode polarization treatment device 510 ... Potiostat 520 ... Electrolyte tank 530 ... Silver chloride electrode 540 ... Titanium plate 550 ... Platinum electrode 560 ... Electrolytic solution 570 ... Carbon felt 580 ... Resistance measuring device

Claims (6)

A fuel cell system,
A membrane electrode assembly having an electrolyte membrane and a catalyst layer provided on both surfaces of the electrolyte membrane; a cathode side current collector including a metal member provided in contact with one side of the membrane electrode assembly; and the membrane An anode current collector provided in contact with the other side of the electrode assembly; and a fuel cell comprising:
A potential setting unit for setting a potential of the metal member with respect to the anode-side current collector;
With
The potential setting unit has a predetermined lower potential than the maximum output point voltage at which the output power of the fuel cell is maximized when the electric power is generated by the fuel cell and the potential of the metal member with respect to the anode-side current collector is maximized. A fuel cell system having a low potential mode that is set to a low potential mode voltage. The fuel cell system according to claim 1, wherein
The fuel cell system, wherein the predetermined low potential mode voltage is 0.3 V or less. The fuel cell system according to claim 1 or 2, wherein
The fuel cell system, wherein the predetermined low potential mode voltage is −0.2 V or more. The fuel cell system according to any one of claims 1 to 3,
The potential setting unit includes an output current adjusting unit that sets the potential of the metal member with respect to the anode-side current collector to the low potential mode voltage by adjusting an output current of the fuel cell. The fuel cell system according to any one of claims 1 to 4, further comprising:
A series resistance measuring unit for measuring the series resistance of the fuel cell;
The potential setting unit executes the low potential mode after the series resistance of the fuel cell measured by the series resistance measurement unit exceeds a predetermined limit value. The fuel cell system according to claim 5, wherein
The potential setting unit is configured to execute the low potential mode when the fuel cell system is stopped or started.

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