JP2006114434A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of effectively restraining deterioration of an oxidant electrode at start. <P>SOLUTION: A small amount of hydrogen taken out from a hydrogen tank 31 is led into an oxidant gas flow passage 17 through a piping 41 at the start of the system. By the above, fuel gas is led into a fuel gas flow passage 18 from the fuel tank 31 through a piping 33 with an oxidizing electrode 2 lowered in potential. By introducing the fuel gas into the fuel gas flow passage 18 with the potential of the oxidant electrode 2 in a state lowered in advance, cell voltage is restrained to restrain corrosion reaction of a catalyst. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell system. In particular, the present invention relates to a configuration related to activation of a fuel cell system.

In a fuel cell system, when starting the system from a state where air is mixed in both the fuel electrode and the oxidant electrode, in the initial stage when hydrogen is supplied to the gas flow channel on the fuel electrode side, A region where hydrogen exists and a region where hydrogen does not exist are formed. In a region where hydrogen is supplied to the fuel electrode, a reaction similar to that in a normal operation state occurs, and a potential of 0.8 V or more is generated on the oxidant electrode side. On the other hand, in the region where hydrogen does not exist in the fuel electrode,
C + 2H ₂ O → CO ₂ + 4H ⁺ + 4e ⁻ (1)
This reaction occurs. As a result, the carbon carrier carrying the catalyst such as Pt is corroded, the electrode catalyst of the oxidant electrode is greatly deteriorated, and the performance of the subsequent fuel cell is lowered. At this time, in the region where the air on the fuel electrode side exists,
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (2)
Reaction occurs and water is generated.

In the conventional fuel cell system, in order to prevent the deterioration of the oxidizer electrode due to this phenomenon, the boundary between the region where the hydrogen exists in the fuel electrode and the region where the hydrogen does not exist (hereinafter referred to as hydrogen) in a short time (1 second or less). Has been proposed to supply hydrogen so that it passes through the fuel gas passage (see, for example, Patent Document 1).
US Patent Application Publication No. 2002/0076582

  However, in the above conventional fuel cell system, the pressure difference between the inlet and the outlet of the fuel gas flow path must be increased, and it is difficult to control the pressure difference between the two electrodes of the electrolyte membrane. There was a limit to shortening the stay time.

  In order to pass the hydrogen / air front in a short time, depending on the design of the flow path of the fuel cell, an additional device such as a compressor is placed in the middle of the piping flow path for supplying hydrogen to the fuel gas flow path. In other words, a measure for reducing the cross-sectional area of the fuel gas channel and increasing the flow velocity in the fuel gas channel is required. In the former, an additional device is required, which increases costs and causes a problem that the fuel cell system becomes large, and if the pressure adjustment between the fuel electrode and the oxidant electrode is not successful, the polymer electrolyte membrane is broken due to the differential pressure. May cause problems. The latter has a problem that the pressure loss during normal operation increases.

  In order to prevent the formation of a hydrogen / air front, a technique of purging with an inert gas such as nitrogen is known. In this case, an inert gas storage device such as a nitrogen cylinder is required in the system. In other words, it is necessary to provide an oxygen consuming device such as a fuel device in the system, which causes a problem that the system becomes complicated and large.

  Therefore, an object of the present invention is to provide a fuel cell system that can effectively suppress deterioration of an oxidizer electrode at the time of startup.

  The present invention includes an electrolyte membrane, an oxidant electrode and a fuel electrode that sandwich the electrolyte membrane, an oxidant gas passage that supplies an oxidant gas to the oxidant electrode, and at least hydrogen in the fuel electrode. A fuel cell stack having a fuel cell including a fuel gas flow path for supplying fuel gas. A first oxidant gas supply means for introducing an oxidant gas into the oxidant gas flow path; a first fuel gas supply means for introducing a fuel gas into the fuel gas flow path; and the oxidant gas flow path. And a second fuel gas supply means for introducing a fuel-containing gas containing at least hydrogen. At the time of system start-up, the fuel-containing gas is introduced into the oxidant gas flow path, and then the fuel gas is introduced into the fuel gas flow path. The introduction of the fuel-containing gas to the road is terminated.

  By introducing a fuel-containing gas containing at least hydrogen into the oxidant gas flow path when the system is activated, the potential of the oxidant electrode can be lowered. For this reason, when the fuel gas is introduced into the fuel gas flow path, the potential difference between the fuel electrode and the oxidant electrode can be reduced even if the potential of the fuel electrode decreases, and the deterioration reaction of the oxidant electrode can be suppressed. Can do.

  A first embodiment will be described. An outline of the fuel cell system is shown in FIG.

  A fuel cell stack 1 that generates power using fuel gas and oxidant gas is provided. The fuel cell stack 1 is configured by stacking one or a plurality of unit cells 1a. FIG. 1 shows a cross section of one unit cell 1a as the fuel cell stack 1 for convenience.

  The unit cell 1a includes a proton-conducting polymer electrolyte membrane (hereinafter referred to as an electrolyte membrane) 10 and an oxidant electrode catalyst layer 11 formed by supporting a catalyst such as Pt on a carbon support that sandwiches the polymer electrolyte membrane. A fuel electrode catalyst layer 12 is provided. The unit cell 1a further includes an oxidant gas diffusion layer 13 and a fuel gas diffusion layer 14 formed of carbon paper or the like on the outside thereof. A membrane electrode assembly (MEA) is constituted by the electrolyte membrane 10, the catalyst layers 11 and 12, and the gas diffusion layers 13 and 14. The oxidant electrode catalyst layer 11 and the oxidant gas diffusion layer 13 constitute the oxidant electrode 2, and the fuel electrode catalyst layer 12 and the fuel gas diffusion layer 14 constitute the fuel electrode 3.

  Furthermore, an oxidant gas separator 15 and a fuel gas separator 16 are provided on the outside thereof. Between the oxidant gas diffusion layer 13 and the oxidant gas separator 15, there is provided an oxidant gas flow path 17 including a groove provided on the surface of the oxidant gas separator 15. Further, a fuel gas flow path 18 formed of a groove provided on the surface of the fuel gas separator 16 is provided between the fuel gas diffusion layer 14 and the fuel gas separator 16.

  Further, the fuel cell system includes an oxidant supply system 20 that supplies an oxidant gas to the fuel cell stack 1, in FIG. 1, the oxidant gas flow path 17 of the unit cell 1 a. Here, air is used as the oxidant gas.

  The oxidant supply system 20 includes an air filter 21 for purifying the atmosphere, and an air blower 22 that sucks external air through the air filter 21. A compressor or the like may be used instead of the air blower 22. Moreover, the valve | bulb 23 which selectively interrupts | blocks between the exterior and the oxidizing agent electrode 2 side is provided. Furthermore, a pipe 24 for supplying air introduced by the air blower 22 through the air filter 21 to the fuel cell stack 1 through the valve 23 is provided. The air introduced into the fuel cell stack 1 flows through the oxidant gas flow path 17, reaches the oxidant electrode catalyst layer 11 through the oxidant gas diffusion layer 13, and is used for the power generation reaction.

  In addition, a pipe 25 that circulates the oxidant exhaust gas discharged from the fuel cell stack 1 and a valve 26 that is provided in the pipe 25 and adjusts the air pressure in the fuel cell stack 1 are provided. Furthermore, a combustion catalyst device 51 that performs combustion treatment of fuel exhaust gas, which will be described later, using the oxidant exhaust gas supplied from the pipe 25 is provided.

  The fuel cell system also includes a fuel supply system 30 that supplies fuel gas to the fuel cell stack 1, in FIG. 1, the fuel gas flow path 18 of the unit cell 1 a. Here, hydrogen is used as the fuel gas. Note that a fuel reforming system may be provided instead of the hydrogen tank 31 described later, and a hydrogen-rich reformed gas may be used as the fuel gas.

  The fuel supply system 30 includes a hydrogen tank 31 that stores hydrogen gas in a high-pressure state. The hydrogen tank 31 is provided with a pressure reducing valve and a flow rate adjusting device so that the pressure and flow rate of hydrogen gas taken out from the hydrogen tank 31 can be adjusted. Further, a valve 32 for selectively blocking between the take-out port of the hydrogen tank 31 and the fuel electrode 3 and a pipe 33 for introducing hydrogen taken out from the hydrogen tank 31 into the fuel cell stack 1 through the valve 32 are provided. . Hydrogen introduced into the fuel cell stack 1 from the pipe 33 flows through the fuel gas flow path 18, reaches the fuel electrode catalyst layer 12 through the fuel gas diffusion layer 14, and is used for power generation reaction. Further, a pipe 34 that circulates the fuel exhaust gas discharged from the fuel cell stack 1 and a valve 35 that is provided in the pipe 34 and adjusts the hydrogen gas pressure in the fuel cell stack 1 are provided. The fuel exhaust gas discharged from the fuel cell stack 1 is supplied to the combustion catalyst device 51 through the pipe 34, subjected to combustion treatment, and then discharged outside the system.

  When the fuel cell stack 1 is formed by stacking a plurality of unit cells 1a, the pipes 24 and 25 are connected to an oxidant gas manifold that communicates with the oxidant gas flow path 17 of each unit cell 1a. The pipes 33 and 34 are connected to a fuel gas manifold communicating with the fuel gas flow path 18 of each unit cell 1a.

  Further, a pipe 41 is provided for connecting between the pipe 24 of the oxidant supply system 20 and the pipe 33 for introducing hydrogen of the fuel supply system 30. One end of the pipe 41 is connected between the valve 23 of the pipe 24 and the fuel cell stack 1, and the other end is connected between the hydrogen tank 31 and the valve 32 of the pipe 33. Further, the pipe 41 is provided with a valve 42 for selectively blocking the pipe 41. When the valve 42 is opened, the hydrogen taken out from the hydrogen tank 31 is introduced to the pipe 24 side through the pipe 41 and supplied to the oxidant gas flow path 17 of the fuel cell stack 1.

Furthermore, the unit cell 1a includes a voltage sensor 52 that detects a cell voltage. In the case where the fuel cell stack 1 is formed by stacking a plurality of unit cells 1a, the voltage sensor 52 may be provided for each unit cell 1a, but the unit comprising a plurality of unit cells 1a or the fuel cell stack 1 The voltage may be configured to be detectable. In this case, the output is converted into a cell voltage, or a reference value (V _a , V _b ) described later is converted into a value obtained by multiplying the reference value of the unit cell 1a by the number of cells to be detected.

  In such a fuel cell system, during normal operation, air is supplied to the oxidant gas flow path 17 and hydrogen is supplied to the fuel gas flow path 18 so that the following electrochemical reaction occurs.

Fuel electrode side: H ₂ → 2H ⁺ + 2e ⁻ (3)
Oxidant electrode side: 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (4)
In the fuel electrode catalyst layer 12, as shown in the equation (3), hydrogen as a fuel is separated into protons and electrons. Protons diffuse inside the electrolyte membrane 10 and reach the oxidant electrode catalyst layer 11 side, and electrons flow through an external circuit (not shown) and are taken out as an output. On the other hand, in the oxidant electrode catalyst layer 11, the equation (4) is formed on the three-phase interface formed by protons that have diffused in the electrolyte membrane 10, electrons that have moved through an external circuit (not shown), and oxygen in the air. The following reaction occurs.

  When such a fuel cell stack 1 is utilized as a power source for a moving body, for example, an automobile, start / stop is frequently repeated. While the fuel cell stack 1 is stopped, the fuel cell stack 1 is left in a state where the supply of hydrogen and air is stopped. Alternatively, it is left in a state filled with an inert gas. If the storage is continued for a long time, air may enter from the outside and air may exist in the fuel gas flow path 14.

  When the system is started from a state in which air is mixed in the fuel electrode 3, the fuel cell stack 1 is in the following state at the initial start-up.

  The oxidant gas flow path 17 is filled with air. Immediately after the supply of hydrogen is started, a region A in which hydrogen is present and a region B in which air is present are formed in the fuel gas flow path 18. In the region A, a reaction similar to the normal operation occurs, and a potential of 0.8 V or higher is established on the oxidant electrode 2 side. A hydrogen / air front that is an interface between hydrogen and air is formed in the fuel gas flow path 18. On the other hand, in the region B where air exists in the fuel gas flow path 18 with this hydrogen / air front as a boundary, the reaction shown in the above-described formula (1) on the oxidant electrode 2 side is performed on the fuel electrode 3 side. (2) Reaction like Formula arises. That is, corrosion of the carbon carrier carrying a catalyst such as Pt occurs on the side of the oxidant electrode 2 having a high potential. As a result, the oxidant electrode catalyst layer 11 is greatly deteriorated, causing the performance of the unit cell 1a to deteriorate.

Here, when the cell voltage is changed by an external voltage in a state where air is present at both electrodes of the unit cell 1a, the amount of CO ₂ released along with the carbon oxidation generated on the high potential side and the cell voltage. FIG. 2 shows the relationship.

  As can be seen from FIG. 2, when there is a local area where air is present in both electrodes during the starting process, the higher the cell voltage, the greater the amount of oxidation of carbon. In other words, the amount of carbon oxidation can be suppressed by lowering the cell voltage during the startup process.

  Therefore, here, control is performed to suppress the cell voltage during the startup process. A control routine during the startup process will be described with reference to the flowchart of FIG.

  When the starting process is started, in step S1, the valve 42 is opened with the valves 23 and 32 closed. Thereby, hydrogen gas is introduced only into the oxidant gas flow path 17 of the unit cell 1a. At this time, the flow rate of hydrogen gas introduced into the oxidant gas passage 17 is set to a sufficiently small amount as compared with the flow rate introduced into the fuel gas passage 18 during normal operation. For example, the hydrogen gas flow rate is set so that the ratio of H 2 introduced to oxygen in the air in the oxidant gas flow channel 17 is 0.5 or less.

Next, in step S2, detects the output of the voltage sensor 52, and determines whether or not the cell voltage in step S3 drops below the first reference value V _a. Here, set, for example, the first reference value V _a to -0.2V. Cell voltage continues the supply of hydrogen gas to only the oxidizing gas channel 17 until the following first reference value V _a. After lowering the cell voltage to a first reference value V _a, in step S4, by opening the valve 32, it starts the introduction of hydrogen gas into the fuel gas flow path 18.

Next, in step S5, the output of the voltage sensor 52 is detected again, and in step S6, it is determined whether or not the cell voltage is equal to or higher than the second reference value _Vb . The supply of hydrogen gas to the oxidant gas passage 17 and the fuel gas passage 18 is continued until the cell voltage reaches the second reference value _Vb . As hydrogen spreads through the fuel gas channel 18, the cell voltage increases. The second reference value V _b is a reference value for determining whether or not hydrogen gas has spread to the fuel gas flow path 18 and is obtained in advance through experiments or the like. Here, for example, the second reference value _{Vb is set} to 0.5V.

When the cell voltage reaches the second reference value _Vb , the valve 42 is closed in step S7, and the introduction of hydrogen gas into the oxidant gas flow path 17 is terminated. Next, in step S8, the valve 23 is opened, and the introduction of air into the oxidant gas flow path 17 is started. As a result, the start-up process is terminated and the normal operation is started.

  Thus, in the present embodiment, as a means for lowering the cell voltage during the start-up process, a small amount of fuel gas is supplied to the oxidant electrode 2 side before supplying hydrogen to the fuel electrode 3 side. As a result, a region where air is present on the oxidant electrode 2 side and a region where hydrogen gas is present are mixed to generate a mixed potential.

  Here, the concept of the mixed potential will be described with reference to FIG.

  During the start-up process, the potential of the oxidant electrode 2 becomes a hybrid potential in which the hydrogen oxidation current and the oxygen reduction current are balanced as shown in FIG. Since the hydrogen oxidation reaction proceeds more easily than the oxygen reduction reaction, even if only a small amount of hydrogen is introduced, the hybrid potential is biased toward the hydrogen oxidation standard potential side. Therefore, by introducing air into the oxidant electrode 2, the mixed potential of the oxidant electrode 2 becomes much smaller than the oxygen reduction standard potential that is the potential when air is present alone in the oxidant electrode 2. Therefore, the carbon corrosion reaction is suppressed by introducing a small amount of hydrogen gas into the oxidant gas flow path 17 at the time of startup and lowering the potential on the oxidant electrode 2 side.

  Next, FIG. 5 shows the change in the hybrid potential when the hydrogen mole fraction in the air is changed.

  As the molar fraction of hydrogen in the air increases, that is, as more hydrogen is introduced into the air, the hybrid potential approaches the hydrogen oxidation standard potential and decreases.

At the start of starting the fuel cell stack 1, since the oxidant electrode 2 and the fuel electrode 3 are filled with air, the molar fraction of hydrogen is close to 0 and the hybrid potential is E ₁ . At this time, since the mixed potential of the oxidizer electrode 2 and the fuel electrode 3 is equal, the cell voltage is 0V.

Next, when the introduction of hydrogen gas to the fuel electrode 3 side is started as in the conventional starting method, the mixed potential of the fuel electrode 3 is lowered to E ₃ . At this time, the cell voltage is ΔV ₁ + ΔV ₂ in FIG. That is, the potential of the oxidant electrode 2 becomes higher than the fuel electrode 3, and a carbon corrosion reaction occurs.

In contrast, in the present embodiment, after the start of activation, by introducing a small amount of hydrogen gas (S1) to the oxidizer electrode 2, lowering the mixed potential of the oxidant electrode 2 to E _2. At this time, the potential of the oxidizer electrode 2 becomes smaller than the fuel electrode 3 by ΔV ₁ (= E ₁ −E ₂ ). In other words, the cell voltage is −ΔV ₁ .

Next, supply of fuel gas to the fuel gas channel 18 is started (S4). When hydrogen gas is introduced into the fuel gas channel 18, the mixed potential of the fuel electrode 3 is reduced to E _3. At this time, since more hydrogen gas is introduced into the fuel gas channel 18 than when introduced into the oxidant gas channel 17, the mixed potential of the fuel electrode 3 is higher than the mixed potential of the oxidant electrode 2. Get higher. As shown in FIG. 6, in the state where hydrogen has spread to the fuel gas flow path 18, the oxidant electrode 2 has a potential higher by ΔV ₂ (= E ₁ −E ₃ ) than the fuel electrode 3.

As described above, when hydrogen is introduced into the fuel gas flow path 18, the cell voltage can be suppressed to ΔV ₂ , so that the catalyst deterioration reaction of the oxidant electrode 2 can be suppressed. When hydrogen reaches the fuel gas flow path 18, the supply of hydrogen to the oxidant gas flow path 17 is stopped (S7), and air is introduced (S8) to shift to normal operation.

That is, the hydrogen flow rate introduced into the oxidant gas flow path 17 is such that ΔV ₁ is in a range in which the deterioration reaction of the fuel electrode 3 does not occur and ΔV ₂ is in a range in which the deterioration reaction of the oxidant electrode 2 does not occur. It is preferable to set so that At this time, −ΔV ₁ is a first reference value V _a, and ΔV ₂ is a second reference value V _b . Here, the first reference value V _{a is set} to −0.2V, and the second reference value V _{b is set} to 0.5V.

  Here, hydrogen gas is introduced into the oxidant gas flow path 17, but this is not restrictive, and hydrogen-containing gas may be used.

  Next, the effect of this embodiment will be described.

  Electrolyte membrane 10, oxidant electrode 2 and fuel electrode 3 sandwiching electrolyte membrane 10, oxidant gas flow path 17 for supplying oxidant gas to oxidant electrode 2, and fuel electrode 3 contain at least hydrogen. A fuel cell stack 1 having a unit cell 1a having a fuel gas flow path 18 for supplying fuel gas. Further, an oxidant supply system 20 for introducing an oxidant gas into the oxidant gas flow path 17 and a fuel supply system 30 for introducing a fuel gas into the fuel gas flow path 18 are provided. The oxidant gas flow path 17 is further provided with second fuel gas supply means for selectively introducing a fuel-containing gas containing at least hydrogen. Here, the second fuel gas supply means is constituted by a pipe 41 and a valve 42 branched from the fuel supply system 30. When the system is started, the fuel-containing gas is introduced into the oxidant gas flow path 17, the fuel gas is introduced into the fuel gas flow path 18, and the fuel gas reaches the fuel gas flow path 18. The introduction of the fuel-containing gas to 17 is terminated. In this way, by introducing the fuel-containing gas into the oxidant gas flow path 17, the fuel gas is supplied to the fuel gas flow path 18 with the potential of the oxidant electrode 2 lowered, so that the cell voltage is suppressed. The catalyst deterioration reaction of the oxidizer electrode 2 can be suppressed.

  Further, as a fuel-containing gas, a gas containing hydrogen is introduced within a range in which the fuel electrode 3 is not deteriorated. Thus, by introducing a gas containing hydrogen in a range that does not degrade the fuel electrode 3 into the oxidant gas flow path 17, the potential of the oxidant electrode 2 can be lowered by introducing the fuel-containing gas. At the same time, it is possible to avoid the potential difference from the fuel electrode 3 occurring at that time from causing deterioration of the fuel electrode 3.

  Here, a fuel gas having a flow rate in a range that does not deteriorate the fuel electrode 3 is introduced as the fuel-containing gas. As described above, by using the existing fuel gas as the fuel-containing gas, the configuration for introducing the fuel-containing gas into the oxidant gas flow path 17 can be easily configured with the pipe 41 and the valve 42.

Further, a voltage sensor 52 for detecting the voltage value of the unit cell 1a or the fuel cell stack 1 is provided, and after the fuel-containing gas is introduced into the oxidant gas flow path 17, the output of the voltage sensor 52 is the first reference value V _a. When it becomes below, introduction of the fuel gas to the fuel gas flow path 18 is started. Thus, since the supply of hydrogen to the fuel gas passage 18 is started after the voltage sensor 52 confirms that the potential of the oxidant electrode 2 has decreased, the deterioration reaction of the oxidant electrode 2 can be performed more reliably. Can be suppressed.

  It is determined from the output of the voltage sensor 52 whether or not the fuel gas has spread to the fuel gas passage 18. Thus, since the voltage sensor 52 can detect whether or not the fuel gas has spread to the fuel gas flow path 18, the fuel-containing gas to the oxidant gas flow path 17 can be detected without using other sensors. It is possible to appropriately determine the supply stop.

  Next, a second embodiment will be described. FIG. 7 shows an outline of the fuel cell system used in this embodiment. Hereinafter, a description will be given centering on portions different from the first embodiment.

  An MFC (Main Fuel Control) 27 that controls the flow rate of the oxidant gas supplied to the oxidant gas flow path 17 is disposed between the air blower 22 and the valve 23. Further, an MFC 43 that controls the flow rate of the fuel gas introduced into the oxidant gas flow path 17 is disposed between the valve 42 and the connection portion of the pipe 41 to the pipe 24. Thus, the oxidant gas and fuel gas flow rates introduced into the oxidant gas flow path 17 can be accurately controlled.

  Next, referring to FIG. 8, the control routine of the activation process will be described.

  In step S 11, the valve 23 is opened while the valves 32 and 42 are closed, and air is introduced into the oxidant gas flow path 17. The air flow rate at this time is adjusted by the MFC 27. In step S 12, the MFC 43 is adjusted so that the molar ratio of hydrogen to oxygen is 0.5 or less, the valve 42 is opened, and a mixed gas of hydrogen and air is supplied to the oxidant gas channel 17. As a result, the potential on the oxidant electrode 2 side is lowered.

In step S13, it detects a cell voltage, compares the cell voltage and the first reference value V _a detected in step S14. Here, the first reference value V _{a is set} to −0.2V. When the cell voltage decreases to −0.2 V or less, the valve 32 is opened and hydrogen is introduced into the fuel gas passage 18 in step S15. As a result, hydrogen is supplied to the fuel electrode 3 and the hybrid potential is lowered. At this time, the amount of hydrogen introduced into the fuel gas channel 18 is set larger than the amount of hydrogen introduced into the oxidant gas channel 17, so that the potential of the fuel electrode 3 is lower than that of the oxidant electrode 2.

In step S16, the cell voltage is detected again. In step S17, the detected cell voltage is compared with the second reference value _Vb . Here, the second reference value V _{b is set} to 0.5V. When the cell voltage rises to the second reference value V _b, it is determined that hydrogen has spread to the fuel gas flow path 18, the valve 42 is closed in step S 18, and the introduction of hydrogen into the oxidant gas flow path 17 is finished. Transition to normal operation.

  Thus, in this embodiment, at the time of start-up, a fuel-containing gas in which oxygen and hydrogen are mixed at a predetermined ratio is supplied to the oxidizer electrode 2 to lower the potential, and then hydrogen is introduced into the fuel electrode 3. .

  Next, the effect of this embodiment will be described. Only the effects different from those of the first embodiment will be described below.

As a fuel-containing gas, a mixed gas of an oxidant gas and a fuel gas is used. At the time of starting the system, the supply of the oxidant gas to the oxidant gas flow path 17 is started and then the supply of the fuel gas is started. A fuel-containing gas is introduced into the agent gas flow path 17. As a result, the volume of the fuel-containing gas can be increased. Therefore, when the fuel-containing gas is introduced into the oxidant gas flow path 17, the time during which the hydrogen / air front is formed can be shortened. The catalyst deterioration reaction on the pole 3 side can be suppressed. Moreover, since the supplied hydrogen reacts in a wide range, it is possible to suppress a local increase in the catalyst temperature due to the reaction between hydrogen and oxygen. Here, as the fuel-containing gas, a mixed gas in which a fuel gas and an oxidant gas are mixed so that the ratio of H ₂ to O ₂ is 0.5 or less is used.

  Next, a third embodiment will be described. Hereinafter, a description will be given centering on differences from the second embodiment.

  The configuration of the fuel cell system will be described with reference to FIG.

  A pipe 28 branched from the pipe 24 and connected to the pipe 25 downstream of the oxidant gas flow path 17 is provided. The pipe 28 connects between the MFC 27 and the valve 23 and between the fuel cell stack 1 and the valve 26.

  Further, instead of the pipe 41, the valve 42, and the MFC 43, a pipe 44, a valve 45, and an MFC 46 are provided. The pipe 44 branches from the pipe 33 and is connected to the pipe 25 downstream of the oxidant gas flow path 17 of the fuel cell stack 1. The pipe 44 connects between the hydrogen tank 31 and the valve 32 and between the fuel cell stack 1 and the valve 26. The valve 45 is configured so that the pipe 44 can be selectively cut off, and the MFC 46 is configured so that the flow rate of the fuel gas introduced from the outlet side into the oxidant gas flow path 17 can be adjusted.

  Furthermore, a pipe 61 branched from between the valve 23 of the pipe 24 and the fuel cell stack 1 and connected to the combustion catalyst device 51 and a valve 62 for selectively blocking the pipe 61 are provided. The fuel gas or oxidant gas that has circulated in the oxidant gas channel 17 from the outlet toward the inlet is introduced into the combustion catalyst device 51 through the pipe 61 and subjected to combustion treatment, and then discharged to the outside of the system. .

  Further, here, during normal operation, the flow direction of air and hydrogen in each unit cell 1a is configured to be parallel. On the other hand, during start-up operation, control is performed so that air is supplied via the pipe 28 and fuel gas is supplied via the pipe 44 so that the fuel-containing gas flows in the oxidant gas flow path 17 from the outlet side toward the inlet side. To do. Further, fuel gas is introduced into the fuel gas channel 18 from the inlet side, and at the time of startup, the fuel-containing gas in the oxidant gas channel 17 and the fuel gas in the fuel gas channel 18 face each other. Control.

  Next, referring to FIG. 8, the control routine of the activation process will be described.

In step S21, the valves 29, 62 are opened while the valves 23, 26, 32, 45 are closed. Thereby, air is circulated through the oxidant gas flow path 17 from the outlet toward the inlet. In step S22, the MFC 46 is adjusted so that the molar ratio of H ₂ to O ₂ in the mixed gas is 0.5 or less, the valve 45 is opened, and the fuel gas is introduced from the outlet side of the oxidant gas flow path 17. As a result, in the oxidant gas flow path 17, a mixed gas of air and fuel gas flows from the outlet toward the inlet.

In step S23, it detects the cell voltage, in step S24, compares the detected cell voltage and the first reference value V _a. Here, the first reference value V _a and -0.2V, and waits until the cell voltage drops to -0.2V, Once dropped to -0.2V, in step S25, the fuel gas flow by opening the valve 32 Fuel gas is supplied to the passage 18.

In step S26, the cell voltage is detected again, and the cell voltage detected in step S27 is compared with the second reference value V _b , here 0.5V. This state is maintained until the cell voltage reaches 0.5V. When 0.5V is reached, it is determined that hydrogen has spread throughout the fuel gas flow path 18, and the valve 45 is closed in step S28. Next, in step S29, the valves 23 and 26 are opened, and the valves 62 and 29 are closed. As a result, air flows from the inlet side to the outlet side of the oxidant gas flow path 17.

  In the present embodiment, the fuel gas and the oxidant gas in the unit cell 1a are in parallel flow during normal operation, but may be in counterflow. In this case, the control in step S29 is omitted.

  Next, the effect of this embodiment will be described. Hereinafter, a description will be given centering on differences from the second embodiment.

  When the system is started, the flow of the fuel-containing gas that flows through the oxidant gas flow path 17 and the flow of the fuel gas that flows through the fuel gas flow path 18 are opposed to each other. As a result, when the fuel gas is introduced into the fuel gas channel 18 before the fuel-containing gas reaches the entire oxidant gas channel 17, only air exists in both the oxidant electrode 2 and the fuel electrode 3. Generation of the region can be further suppressed.

  Next, a fourth embodiment will be described. Hereinafter, a description will be given centering on differences from the second embodiment.

  The configuration of the fuel cell system will be described with reference to FIG.

  A pipe 47 that connects between the MFC 27 and the valve 23, between the valve 32 and the fuel cell stack 1, and a valve 48 that selectively blocks a cross section of the pipe 47 are provided. That is, by opening the valve 48, the oxidant gas can be selectively introduced into the fuel gas flow path 18. The resistance meter 53 for detecting the resistance value of the fuel cell stack 1 is also provided.

  Furthermore, a humidifier 63 that selectively humidifies the air introduced through the air filter 21 and a humidifier 36 that selectively humidifies the hydrogen taken out from the hydrogen tank 31 are provided.

  The startup process of such a fuel cell system will be described using the control routine of FIG.

  In step S31, the valves 23, 48, 26, and 35 are opened with the valves 32 and 42 closed. As a result, dry air is introduced into the oxidant gas flow path 17 and the fuel gas flow path 18 to dry the electrolyte membrane 10 and lower the ionic conductivity.

  In step S32, the cell resistance is detected, and it is determined whether or not the cell resistance detected in step S33 is a specified value or more. Drying of the electrolyte membrane 10 is continued until the specified value or more is reached. When the cell resistance becomes equal to or more than the specified value, the valve 48 is closed in step S34. Thereby, the supply of the dry air to the fuel gas channel 18 is finished.

  Steps S35 to S41 are the same as steps S12 to S18. In step S41, when the control shifts to supplying air to the oxidant gas flow path 17 and fuel gas to the fuel gas flow path 18, in step S42, the operation of the humidifier 63 is started, and the oxidant gas is supplied. If necessary, humidify and introduce into the oxidant gas flow path 17, start operation of the humidifier 36, humidify the hydrogen as necessary, and introduce it into the fuel gas flow path 18 to complete the startup process. .

  Next, the effect of this embodiment will be described. Hereinafter, only effects different from those of the second embodiment will be described.

  Dry gas flow means for flowing dry gas through at least one of the oxidant gas flow path 17 and the fuel gas flow path 18 is provided. Here, the dry gas flow means is constituted by the oxidant supply system 20, the pipe 47 and the valve 48. When the system is activated, the fuel-containing gas is introduced into the oxidant gas flow path 17 after circulating the dry gas. Thus, since the MEA drying operation is performed before the fuel-containing gas is supplied to the fuel cell, the ionic conductivity of the electrolyte membrane 10 is lowered and the electrochemical reaction can be delayed. can do.

  The configurations of the oxidant supply system 20 and the fuel supply system 30 are not limited to the above configurations. The second fuel supply means is not limited to the above configuration, and may be any configuration that can supply a gas containing hydrogen to the oxidant gas flow path 17.

  Thus, the present invention is not limited to the best mode for carrying out the invention, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

  The present invention can be applied to a fuel cell system. In particular, an appropriate effect can be obtained by applying to a moving body such as a vehicle having a high start / stop switching frequency.

1 is a schematic configuration diagram of a fuel cell system according to a first embodiment. It is a figure which shows the relationship between the cell voltage in a Air / Air state, and a carbon oxidation current. It is a flowchart which shows the control routine of the starting process by 1st Embodiment. It is a figure explaining the concept of a hybrid potential. It is a figure which shows the change of the hybrid potential with respect to the molar fraction of hydrogen. It is a figure which shows the gas main in a bipolar gas flow path during a starting process, and a cell voltage change. It is a schematic block diagram of the fuel cell system by 2nd Embodiment. It is a flowchart which shows the control routine of the starting process by 2nd Embodiment. It is a schematic block diagram of the fuel cell system by 3rd Embodiment. It is a flowchart which shows the control routine of the starting process by 3rd Embodiment. It is a schematic block diagram of the fuel cell system by 4th Embodiment. It is a flowchart which shows the control routine of the starting process by 4th Embodiment.

Explanation of symbols

1 Fuel cell stack 1a Unit cell (fuel cell)
2 Oxidant electrode 3 Fuel electrode 20 Oxidant supply system (first oxidant gas supply means)
30 Fuel supply system (first fuel gas supply means)
41, 44 Piping (second fuel gas supply means)
42, 45 Valve (second fuel gas supply means)
47 Piping (Dry gas distribution means)
48 valve (dry gas distribution means)
52 Voltage sensor

Claims (9)

An electrolyte membrane;
An oxidant electrode and a fuel electrode that sandwich the electrolyte membrane;
An oxidant gas flow path for supplying an oxidant gas to the oxidant electrode;
A fuel cell stack having a fuel cell comprising: a fuel gas flow path for supplying a fuel gas containing at least hydrogen to the fuel electrode; and
First oxidant gas supply means for introducing an oxidant gas into the oxidant gas flow path;
First fuel gas supply means for introducing fuel gas into the fuel gas flow path;
A second fuel gas supply means for selectively introducing a fuel-containing gas containing at least hydrogen into the oxidant gas flow path;
At the time of starting the system, after introducing the fuel-containing gas into the oxidant gas flow path, the fuel gas is introduced into the fuel gas flow path,
The fuel cell system is characterized in that the introduction of the fuel-containing gas into the oxidant gas flow channel is terminated when the fuel gas is distributed to the fuel gas flow channel.   The fuel cell system according to claim 1, wherein a gas containing hydrogen is introduced as the fuel-containing gas in a range that does not deteriorate the fuel electrode.   The fuel cell system according to claim 2, wherein a fuel gas having a flow rate in a range that does not deteriorate the fuel electrode is introduced as the fuel-containing gas. As the fuel-containing gas, a mixed gas of oxidant gas and fuel gas is used,
3. The fuel-containing gas is introduced into the oxidant gas flow path by starting the supply of the fuel gas after starting the supply of the oxidant gas to the oxidant gas flow path at the time of starting the system. The fuel cell system described in 1. 5. The fuel cell system according to claim 4, wherein the fuel-containing gas is a mixed gas in which the fuel gas and an oxidant gas are mixed so that a ratio of H ₂ to O ₂ is 0.5 or less.   The fuel cell system according to claim 1 or 2, wherein the flow of the fuel-containing gas flowing through the oxidant gas flow path and the flow of the fuel gas flowing through the fuel gas flow path are opposed to each other when the system is started. A dry gas flow means for flowing a dry gas in at least one of the oxidant gas flow path and the fuel gas flow path;
3. The fuel cell system according to claim 1, wherein when the system is started, the fuel-containing gas is introduced into the oxidant gas flow path after the dry gas is circulated. A voltage sensor for detecting a voltage value of the fuel cell or the fuel cell stack;
The fuel gas introduction into the fuel gas passage is started when the output of the voltage sensor becomes a predetermined value or less after the fuel-containing gas is introduced into the oxidant gas passage. The fuel cell system according to any one of the above. A voltage sensor for detecting a voltage value of the fuel cell or the fuel cell stack;
The fuel cell system according to any one of claims 1 to 7, wherein it is determined from an output of the voltage sensor whether or not fuel gas has spread to the fuel gas flow path.

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