JP2006318678A - Fuel cell system and operation method of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system and an operation method of the same, advantageous to improvement of durability of a fuel cell. <P>SOLUTION: The system is provided with a switching means 8 (valves 81 to 84) capable of switching a relation of a fuel flow channel and an oxidant flow channel between a parallel flow mode and an opposite flow mode. The switching means 8 switches over to operate in the opposite flow mode at a high power generation area with a relatively high power generation volume and in the parallel flow mode at a low power generation area with a power generation volume relatively lower than the high power generation area. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system advantageous for improving the durability of a fuel cell and a method for operating the fuel cell system.

The fuel cell includes a membrane electrode assembly (hereinafter also referred to as MEA) having a fuel electrode and an oxidant electrode sandwiching an electrolyte, an oxidant flow path for flowing an oxidant gas to the oxidant electrode, and a fuel flow to the fuel electrode. And a fuel flow path. Patent Document 1 focuses on the fact that the phosphoric acid component constituting the electrolyte membrane scatters and disappears with the passage of the operating time of the fuel cell and the performance of the fuel cell is reduced, and the phosphoric acid component is generated as waste, A technique is disclosed in which the operating time of a fuel cell is measured by a measuring means, and the flow of the fuel flow path and the oxidant flow path is switched when the operating time reaches a predetermined value. According to this, it is described that the disappearance of the phosphoric acid component that is scattered and disappeared is made uniform in the gas flow direction. Patent Document 2 discloses a technique for detecting whether or not a flooding phenomenon in which water narrows the flow path is generated in the fuel cell, and switching the gas flow direction when the flooding phenomenon occurs.
Japanese Patent Laid-Open No. 06-089729 JP 2003-249247 A

  There is a demand in the industry to improve the durability of fuel cells. Further, according to the above-described technique, the direction of gas flow is not switched between a high power generation region where the power generation amount is relatively large and a low power generation region where the power generation amount is relatively small.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a fuel cell system and a fuel cell system operating method that are advantageous in improving the durability of the fuel cell.

  (1) The present inventor has been diligently researching the fuel cell system for many years based on the above-described problems. The present inventor discovered the following items (a) and (b) through research, and completed the present invention based on the findings. When adopting a counter flow configuration in which the basic direction of the fuel flow and the basic direction of the oxidant are opposed, there is an advantage that the uniformity of the power generation distribution in the fuel cell is improved. The reason is presumed as follows. According to the counterflow configuration (see FIG. 1), the upstream region of the oxidant flowing through the oxidant flow path (region where the oxidant concentration is high) and the downstream region of the fuel flowing through the fuel flow channel (region where the fuel concentration is low) Are opposed to each other through the electrolyte membrane, and the downstream area of the oxidant flowing through the oxidant flow path (the area where the oxidant concentration is low) and the upstream area of the fuel flowing through the fuel flow path (the area where the fuel concentration is high) are the electrolyte. Opposing through the membrane. For this reason, the region where the oxidant concentration is high and the region where the fuel concentration is high are opposed to each other through the electrolyte membrane, and the region where the oxidant concentration is low and the region where the fuel concentration is low are opposed to each other via the electrolyte membrane. Thus, when the counterflow mode is adopted, there is an advantage that the uniformity of the power generation distribution in the flow direction is improved.

  (A) By the way, in the power generation operation of the fuel cell, in general, the water generated by the power generation reaction is transferred to the downstream region of the oxidant flow path together with the oxidant gas flowing through the oxidant flow path. Water often narrows the gas flow path in the downstream area of the flow path. For this reason, the power generation reaction is easily restricted in the downstream region of the oxidant flow path. For this reason, the power generation reaction is unlikely to occur in the upstream region of the fuel flow channel facing the downstream region of the oxidant flow channel via the electrolyte membrane. As a result, when the above-described counterflow mode is employed, fuel consumption is reduced and fuel concentration (fuel partial pressure) is increased in the upstream region of the fuel flow path. Therefore, a fuel component having a high concentration existing in the upstream region of the fuel flow path (in a gaseous state when the fuel is in a gaseous state) may permeate the electrolyte membrane and move to the oxidant electrode side.

  (B) Further, the present inventor has found that the amount of transition (fuel is gas) that the fuel on the fuel electrode side moves to the oxidant electrode side through the electrolyte membrane as shown by the characteristic line W1 in FIG. The amount of gas state transition is small in the high power generation region where the power generation amount is relatively large (region where the current density is relatively high), but low in the power generation region where the power generation amount is relatively small (current). Recently, it has been newly discovered that there is a tendency to increase in areas where the density is relatively low. The high power generation region and the low power generation region are regions that are distinguished by the magnitude of the current density in the current density-output characteristics (IV characteristics) of the fuel cell.

  Therefore, a counter flow mode is adopted in a region where the power generation amount is relatively large to improve the uniformity of power generation distribution in the gas flow direction, while a parallel flow mode is used in a low power generation region where the power generation amount is relatively small (see FIG. 2). ) Was adopted. That is, the parallel flow mode is the same direction as the basic direction of the fuel flow and the basic direction of the oxidant. According to the parallel flow mode, as can be understood from FIG. 2, the upstream region of the oxidant flowing through the oxidant flow channel (region where the oxidant concentration is high) and the upstream region of fuel flowing through the fuel flow channel (the fuel concentration is high). Region) through the electrolyte membrane, the downstream region of the oxidant flowing through the oxidant flow path (region where the oxidant concentration is low), and the downstream region of fuel flowing through the fuel flow channel (region where the fuel concentration is low) Are opposed to each other through the electrolyte membrane. According to such a parallel flow mode, the fuel is favorably consumed in the power generation reaction in the upstream region of the fuel flow path, so that the fuel in the upstream region of the fuel flow path moves to the oxidant electrode side through the electrolyte membrane. It is suppressed. In this way, if the fuel on the fuel electrode side is suppressed from moving to the oxidant electrode side through the electrolyte membrane, the properties of the electrolyte membrane may change even when the fuel cell is used over a long period of time. It is suppressed well, and the lifetime of the electrolyte membrane can be improved and the durability can be improved. The present invention has been developed based on such findings.

(2) That is, a fuel cell system according to the present invention includes a membrane electrode assembly having a fuel electrode and an oxidant electrode sandwiching an electrolyte membrane, an oxidant flow path for flowing an oxidant to the oxidant electrode, and fuel as fuel. In the fuel cell system including a fuel cell having a fuel flow channel that flows to the pole, the relationship between the flow direction of the fuel that flows through the fuel flow channel and the oxidant that flows through the oxidant flow channel is the first mode and the second mode. In the first embodiment, the switching means opposes the upstream area of the oxidant flowing through the oxidant flow path and the upstream area of the fuel flowing through the fuel flow path through the electrolyte membrane. And making the downstream area of the oxidant flowing through the oxidant flow path and the downstream area of the fuel flowing through the fuel flow path face each other through the electrolyte membrane,
In the second embodiment, the upstream region of the oxidant flowing through the oxidant flow channel and the downstream region of the fuel flowing through the fuel flow channel are opposed to each other through the electrolyte membrane, and the downstream region of the oxidant flowing through the oxidant flow channel and the fuel The upstream portion of the fuel flowing through the flow path is opposed to the fuel through the electrolyte membrane, and the switching unit operates in the second form in the high power generation region where the power generation amount is relatively large, and the power generation amount is higher than that in the high power generation region. In a relatively small low power generation region, switching is performed so as to operate in the first mode.

(3) A method of operating a fuel cell system according to the present invention comprises a membrane electrode assembly having a fuel electrode and an oxidant electrode sandwiching an electrolyte membrane, an oxidant channel for flowing an oxidant to the oxidant electrode, and a fuel Preparing a fuel cell having a fuel flow path that flows to the fuel electrode, and preparing a switching means that can switch a relationship between a fuel flow in the fuel flow path and an oxidant flow in the oxidant flow path;
The upstream area of the oxidant flowing through the oxidant flow path is opposed to the downstream area of the fuel flowing through the fuel flow path, and the downstream area of the oxidant flowing through the oxidant flow path and the upstream area of the fuel flowing through the fuel flow path are In the operation method of the fuel cell system for carrying out the step of performing the power generation operation in the form of facing,
When the power generation amount changes to a low power generation region that is relatively smaller than the high power generation region, the upstream region of the oxidant that flows through the oxidant flow channel and the upstream region of the fuel that flows through the fuel flow channel face each other. The power generation operation is switched in such a manner that the downstream region of the oxidant flowing through the passage and the downstream region of the fuel flowing through the fuel flow channel are opposed to each other.

  (4) According to the present invention, in the high power generation region where the power generation amount is relatively large, the switching unit switches the relationship between the flow direction of the fuel and the oxidant to the second mode. According to the second form (corresponding to the counter flow form), the upstream area of the oxidant flowing through the oxidant flow path and the downstream area of the fuel flowing through the fuel flow path are opposed to each other, and the oxidant flowing through the oxidant flow path And the upstream region of the fuel flowing through the fuel flow path are opposed to each other. For this reason, in the high power generation region where the power generation amount is relatively large, the uniformity of the power generation distribution in the flow direction is improved as described above. In contrast, in the low power generation region where the power generation amount is relatively smaller than the high power generation region, the switching unit switches the flow of the fuel and the oxidant to the first mode (corresponding to the parallel flow mode). According to the first aspect, the upstream region of the oxidant flowing through the oxidant flow channel is opposed to the upstream region of the fuel flowing through the fuel flow channel, and the downstream region of the oxidant flowing through the oxidant flow channel and the fuel flow channel are It faces the downstream area of the flowing fuel. As a result, the fuel is favorably consumed for the power generation reaction in the upstream region of the fuel flow path. Therefore, the amount of transition of the fuel in the upstream region of the fuel flow path to the oxidant electrode side through the electrolyte membrane is suppressed. Thereby, the change in the properties of the electrolyte membrane can be suppressed, and the lifetime of the electrolyte membrane can be extended and the durability can be improved.

  According to the present invention, it is possible to provide a fuel cell system and an operation method of the fuel cell system that are advantageous for extending the life and durability of the fuel cell.

  According to the present invention, the switching means is switched to the second form in the high power generation region where the power generation amount is relatively large, and is switched to the first form in the low power generation region where the power generation amount is relatively smaller than the high power generation region. . According to the present invention, a parallel flow configuration in which the basic flow direction of the fuel and the basic flow direction of the oxidant are in the same direction can be adopted as the first mode. As the second mode, a counter flow mode in which the basic flow direction of the fuel and the basic flow direction of the oxidant are opposite to each other can be adopted. The amount of power generation in the high power generation region and the amount of power generation in the low power generation region are relative. Therefore, the high power generation region means a region where the power generation amount (current density) per unit area of the power generation area is relatively larger than that of the low power generation region. The high power generation region is generally a region where the power load operated by the fuel cell is large. The high power generation region can include a medium power generation region. The low power generation region means a region where the power generation amount (current density) per unit area of the power generation area is relatively smaller than that of the high power generation region. Therefore, the low power generation region is generally a region where the power load operated by the fuel cell is small.

  According to the present invention, in the first mode (corresponding to the parallel flow mode), the ratio of the basic flow direction of the oxidant and the basic flow direction of the fuel is the same in the power generation area of the fuel cell. It means a form higher than two forms (corresponding to the counterflow form). In the second mode (corresponding to the counter flow mode), the ratio of the basic flow direction of the oxidant and the basic flow direction of the fuel in the power generation area of the fuel cell is the first mode (parallel flow mode). Higher form). Therefore, the first form (corresponding to the parallel flow form) is a power generation area in which the basic flow direction of the oxidant and the basic flow direction of the fuel are in the same direction by the area ratio when the power generation region is 100%. Can account for 55% or more or 60% or more (or 70% or more). Further, in the second mode (corresponding to the counter flow mode), when the power generation area of the fuel cell is 100%, the basic flow direction of the oxidant and the basic flow direction of the fuel are opposite in the area ratio. It is possible to occupy 55% or more or 60% or more (or 70% or more).

  According to the present invention, the switching means switches the direction of the flow of the fuel flowing through the fuel flow path while maintaining the direction of the flow of the oxidant flowing through the oxidant flow path. The form which can switch a form can be illustrated. The basic direction of the oxidant flow that flows through the oxidant flow path is preferably maintained downward. This is because water is generated by a power generation reaction at the oxidant electrode, and thus water in the oxidant flow path is discharged using gravity. According to the present invention, the fuel flow path includes a first fuel opening that can be switched to one of an inlet through which fuel is supplied and an outlet through which fuel off fluid is discharged, and the inlet through which fuel is supplied and the fuel off. The form which is provided with the 2nd opening for fuel which can be switched to the other of the outlets from which fluid is discharged can be illustrated. In this case, the switching means preferably has a first supply valve for supplying fuel connected to the first opening for fuel and a first discharge valve for discharging fuel off fluid, and a first supply valve for supplying fuel connected to the second opening for fuel. 2 supply valves and a second discharge valve for discharging the fuel-off fluid. Each of the above-described valves may be an on-off type on-off valve, a variable opening area on-off valve, a three-way valve, or a known valve.

  Further, according to the present invention, the oxidant flow path includes a first oxidant opening that can be switched to one of an inlet through which the oxidant is supplied and an outlet through which the oxidant-off fluid is discharged. The form which is provided with the 2nd opening for oxidizers which can be switched to the other of the entrance which is discharged, and the outlet from which oxidant off fluid is discharged can be illustrated. In this case, the switching means preferably has a first supply valve for supplying oxidant connected to the first opening for oxidant, a first discharge valve for discharging oxidant-off fluid, and an oxidation connected to the second opening for oxidant. A second supply valve for supplying the agent and a second discharge valve for discharging the oxidant-off fluid.

According to the present invention, as a boundary value for partitioning the high power generation region and the low power generation region, that is, a boundary for switching between the first form (corresponding to the parallel flow form) and the second form (corresponding to the counter flow form). Values include the type of fuel cell system, the use of the fuel cell system (for example, stationary, vehicle, portable, electrical equipment, electronic equipment, etc.), maximum power output value, fuel type, oxidizer type, etc. It depends on the factors. Since this boundary value is a relative value that partitions the high power generation region and the low power generation region, it cannot be uniquely determined. Assuming that the current density of the fuel cell during rated operation is Imax, this boundary value is within the range of 3% to 80% of Imax (for example, 3%, 10%, 20%, 40%, 50%, 60%). 80%) within the range of 5% to 70%, and within the range of 10% to 60%. In general, the current density during rated operation corresponds to the maximum current density. Depending on the specifications of the fuel cell, a maximum current density larger than the current density during rated operation may be set. In this case, Imax may be the maximum current density. As the boundary value, when the fuel cell system is stationary, for example, within the range of 0.01 to 0.5 ampere / cm ² (for example, 0.01 ampere / cm ² , 0.1 ampere / cm ^2). , 0.2 ampere / cm ² , 0.3 ampere / cm ² , 0.4 ampere / cm ² , 0.5 ampere / cm ² ), but not limited thereto. . Further, when the fuel cell system is used for a vehicle, for example, the fuel cell system can be appropriately selected within the range of 0.02 to 1.5 amperes / cm ² , but is not limited thereto. Further, when the fuel cell system is for an electronic device or an electric device, it can be appropriately selected within a range of 0.005 to 2.5 amperes / cm ² , for example, but is not limited thereto. Absent.

  Embodiments of the present invention will be described below with reference to FIGS. FIG. 4 shows the concept of the fuel cell. As shown in FIG. 4, the membrane electrode assembly 1 of the fuel cell includes a fuel electrode 11 and an oxidant electrode 12 that sandwich a polymer electrolyte membrane 10 that is an ion conductor (proton conductor). The fuel cell includes an oxidant flow path 32 for flowing an oxidant gas (generally air or oxygen gas) to the oxidant electrode 12, and a gaseous fuel (generally hydrogen gas or hydrogen-containing gas) as a fuel electrode. 11 and a fuel flow path 42 that flows into the fuel cell 11. The oxidant channel 32 and the fuel channel 42 are formed by the flow distribution plate 2. The fuel electrode 11 has a gas diffusion layer 11e formed of a carbon-based porous body (for example, an aggregate of carbon fibers) so as to have current collecting properties and gas diffusibility. The oxidant electrode 12 has a gas diffusion layer 12e formed of a carbon-based porous body (for example, an aggregate of carbon fibers) so as to have current collecting properties and gas diffusibility. As shown in FIG. 4, the fuel electrode 11 includes a gas diffusion layer 11e and a fuel catalyst layer 13 for promoting a power generation reaction. The oxidant electrode 12 has a gas diffusion layer 12e and an oxidant catalyst layer 14 for promoting a power generation reaction.

  As shown in FIG. 5, the oxidant flow path 32 of the fuel cell discharges the oxidant first opening 171 serving as an inlet to which the oxidant gas before the power generation reaction is supplied and the oxidant off-gas after the power generation reaction. And an oxidant second opening 172 serving as an outlet. The first oxidant opening 171 is connected to the oxidant supply main channel 191. An oxidant supply valve 181 and a humidifier 183 are provided in the oxidant supply main channel 191. The second oxidant opening 172 is connected to the oxidant discharge main flow path 192. An oxidant discharge valve 182 is provided in the oxidant discharge main flow path 192. As shown in FIG. 5, the fuel flow path 42 of the fuel cell includes a first fuel opening 71 and a second fuel opening 72. The first fuel opening 71 is one of an inlet through which fuel before power generation reaction is supplied and an outlet through which fuel off-gas after power generation reaction is discharged. The second fuel opening 72 is the other of the inlet through which fuel before power generation reaction is supplied and the outlet through which fuel off-gas after power generation reaction is discharged.

  The switching means 8 shown in FIG. 5 makes it possible to switch the gas flow relationship between the fuel flow path 42 and the oxidant flow path 32 in the fuel cell between a parallel flow mode and a counter flow mode. In this embodiment, the direction of the flow of the fuel inside the fuel cell is changed upward or downward while the direction of the flow of the oxidant gas inside the fuel cell is maintained downward. As shown in FIG. 5, the switching means 8 includes a first supply valve 81 for supplying fuel connected to the first opening 71 for fuel, and a first discharge valve 83 for discharging fuel off-gas connected to the first opening 71 for fuel. The second supply valve 82 for supplying fuel connected to the second opening 72 for fuel and the second discharge valve 84 for discharging fuel off-gas connected to the second opening 72 for fuel are provided. The first supply valve 81 and the second supply valve 82 are connected to the fuel source 95 via the fuel supply main channel 91. The first discharge valve 83 and the second discharge valve 84 are connected to the fuel discharge portion via the fuel off-gas discharge main flow path 92. According to the present embodiment, in the high power generation region where the power load is large and the power generation amount is relatively large, the control device 200 switches the switching unit 8 so as to operate the fuel cell in the counterflow mode. In the low power generation region where the power load is small and the power generation amount is relatively smaller than the high power generation region, the control device 200 switches the switching means 8 so as to operate the fuel cell in a parallel flow mode. Further explanation will be given below.

  During the power generation operation of the fuel cell, the valves 181 and 182 are opened, so that the oxidant gas humidified by the humidifier 183 is supplied from the first oxidant opening 171 of the fuel cell to the oxidant flow path 32 of the fuel cell. The oxidant channel 32 flows downward and is used for power generation reaction. The oxidant off-gas after undergoing a power generation reaction inside the fuel cell is discharged to the oxidant discharge main channel 192 from the second oxidant opening 172 serving as an outlet. At the time of power generation operation of the fuel cell, in a high power generation region where the power generation amount is relatively large (including a middle power generation region where the power generation amount is relatively intermediate), the control device 200 performs the fuel and oxidant in the fuel cell. The switching means 8 is controlled so that the gas flow is operated in a counterflow mode in which the countercurrent flow is a counterflow. According to such a counter flow mode, as schematically shown in FIG. 1, the upstream region of the oxidant flowing through the oxidant flow channel 32 and the downstream region of the fuel flowing through the fuel flow channel 42 are opposed to each other, and oxidation is performed. The downstream area of the oxidant flowing through the agent flow path 32 and the upstream area of the fuel flowing through the fuel flow path 42 are opposed to each other.

  Specifically, according to this counterflow mode, in FIG. 5, the first supply valve 81 is opened and the first discharge valve 83 is closed. Further, the second discharge valve 84 is opened and the second supply valve 82 is closed. As a result, the gaseous fuel passes through the fuel supply main flow path 91 → the first supply valve 81 → the first branching part 101 → the first opening for fuel 71 → the fuel flow path 42 inside the fuel cell in the direction of arrow Y2 (upward). Flow → Second opening for fuel 72 → Second exhaust valve 84 → Fuel off-gas exhaust main flow path 92 is discharged.

  On the other hand, in the low power generation region where the power generation amount is relatively small, the control device 200 is operated in a parallel flow mode in which the flow relationship between the fuel and the oxidant in the fuel cell is a parallel flow. The switching means 8 is controlled. According to such a parallel flow mode, as schematically shown in FIG. 2, the upstream region of the oxidant flowing through the oxidant flow path 32 of the fuel cell and the upstream region of the fuel flowing through the fuel flow path 42 of the fuel cell And the downstream region of the oxidant flowing through the oxidant flow path 32 of the fuel cell and the downstream region of the fuel flowing through the fuel flow path 42 of the fuel cell through the electrolyte membrane 10. . Specifically, according to this parallel flow mode, the second supply valve 82 is opened and the second discharge valve 84 is closed in FIG. Further, the first discharge valve 83 is opened and the first supply valve 81 is closed. As a result, the gaseous fuel flows in the direction of arrow Y1 in the fuel supply main flow path 91 → second supply valve 82 → second branching section 102 → second fuel opening 72 → fuel flow path 42 in the fuel cell → fuel The first opening 71 → the first branch portion 101 → the first discharge valve 83 → the fuel off-gas discharge main flow path 92 is discharged.

  As described above, according to the present embodiment, in the high power generation region where the power generation amount is relatively large, the control device 200 switches the switching unit 8 so as to operate in the counterflow mode. As a result, the power generation distribution in the fuel cell can be made uniform while securing a high power generation amount. On the other hand, in the low power generation region where the power generation amount is relatively smaller than the high power generation region, the control device 200 switches the switching unit 8 so as to operate in a parallel flow mode. As a result, in the low power generation region, the fuel on the fuel electrode 11 side of the fuel cell is suppressed from transferring to the oxidant electrode 12 of the fuel cell. As a result, the change in the properties of the electrolyte membrane 10 is suppressed, the life of the electrolyte membrane 10 can be extended and the durability can be improved, which is advantageous in improving the durability of the fuel cell.

  FIG. 6 shows a second embodiment. The present embodiment basically has the same configuration and operational effects as the first embodiment. However, the flow direction of the oxidant gas is changed downward or upward while maintaining the flow direction of the fuel upward. As shown in FIG. 6, the fuel flow path 42 of the fuel cell includes a first fuel opening 171x connected to the fuel supply valve 181x and a second fuel opening 172x connected to the fuel discharge valve 182x. The oxidant flow path 32 of the fuel cell includes a first oxidant opening 71x and a second oxidant opening 72x. The first oxidant opening 71x is one of an inlet through which oxidant gas before power generation reaction is supplied and an outlet through which oxidant off-gas after power generation reaction is discharged. Further, the second oxidant opening 72x is the other of the inlet for supplying the oxidant gas before the power generation reaction and the outlet for discharging the oxidant off-gas after the power generation reaction.

  As shown in FIG. 6, the switching means 8x includes a first supply valve 81x for supplying an oxidant connected to the first opening for oxidant 71x and a first oxidant off-gas discharge connected to the first opening for oxidant 71x. A discharge valve 83x, a second supply valve 82x for supplying oxidant connected to the second opening 72x for oxidant, and a second discharge valve 84x for discharging oxidant off-gas connected to the second opening 72x for oxidant are provided. Yes. The first supply valve 81x and the second supply valve 82x are connected to an oxidant transport source 95x (for example, a blower or a fan) via the oxidant supply main flow path 91x and the humidifier 183. The first discharge valve 83x and the second discharge valve 84x are connected to an oxidant discharge part (outside air or the like) via an oxidant off-gas discharge main flow path 92x. Also in the present embodiment, in the high power generation region where the power load is large and the power generation amount is relatively large, the switching means 8x is switched so as to operate the fuel cell in the counterflow mode. In the low power generation region where the power load is small and the power generation amount is relatively smaller than the high power generation region, the switching means 8x is switched so as to operate the fuel cell in a parallel flow mode.

  Further explanation will be given below. During the power generation operation, the fuel supply valve 181x and the fuel discharge valve 182x are opened. Then, the fuel in the fuel supply main channel 91 is supplied to the fuel channel 42 of the fuel cell from the fuel first opening 171x of the fuel cell, flows upward through the fuel channel 42, and is used for the power generation reaction. The fuel off-gas after undergoing a power generation reaction inside the fuel cell is discharged to the fuel off-gas discharge main flow path 92 from the fuel second opening 172x serving as an outlet.

  Now, in the high power generation region where the power generation amount is relatively large, the control device 200 controls the switching unit 8x so that the flow relationship between the fuel and the oxidant gas is operated in a counterflow configuration in which the countercurrent flow is counterflowing. Specifically, in FIG. 6, the second supply valve 82x is opened and the second discharge valve 84x is closed. Further, the first discharge valve 83x is opened and the first supply valve 81x is closed. Therefore, the oxidant gas flows through the oxidant supply main flow path 91x → the second supply valve 82x → the second branch portion 102 → the second oxidant opening 72x → the oxidant flow path 32 inside the fuel cell in the direction of arrow Y1 (downward). ) → first oxidant opening 71 x → first branch portion 101 → first discharge valve 83 x → oxidant off-gas discharge main flow path 92 x is discharged. On the other hand, in the low power generation region where the power generation amount is relatively small, the control device 200 sets the switching unit 8x so that the flow relationship between the fuel and the oxidant gas is operated in a parallel flow mode in which the flow is parallel. Control. According to such a parallel flow mode, specifically, in FIG. 6, the first supply valve 81x is opened and the first discharge valve 83x is closed. Further, the second discharge valve 84x is opened and the second supply valve 82x is closed. As a result, the oxidant gas flows through the oxidant supply main flow path 91x → the first supply valve 81x → the first branch portion 101 → the first opening for oxidant 71x → the oxidant flow path 32 inside the fuel cell in the direction of arrow Y2 (upward). ) → second oxidant opening 72 x → second discharge valve 84 x → oxidant off-gas discharge main flow path 92 x is discharged.

  As described above, according to the present embodiment, in the high power generation region where the power generation amount is relatively large, the control device 200 switches the switching unit 8x so as to operate in the counterflow mode. As a result, the power generation distribution in the fuel cell can be made uniform while securing a high power generation amount. On the other hand, in the low power generation region where the power generation amount is relatively smaller than the high power generation region, the control device 200 switches the switching unit 8x so as to operate in a parallel flow mode. As a result, in the low power generation region, the fuel on the fuel electrode 11 side of the fuel cell is suppressed from transferring to the oxidant electrode 12 of the fuel cell. As a result, the life of the electrolyte membrane 10 can be extended and the durability can be improved, which is advantageous for improving the durability of the fuel cell.

  The third embodiment is an application of the first embodiment of the present invention. This example will be described with reference to FIGS. The distribution plate 2 is made of a conductive material, for example, a carbon material or a metal material having good corrosion resistance, and is also called a separator. The distribution plate 2 has an oxidant channel 32 on one side and a fuel channel 42 on the other side. As shown in FIG. 7, the flow distribution plate 2 has a vertically long rectangular shape, and includes an upper side portion 20 and a lower side portion 21 that face each other, and two side portions 22 and 23 that face each other. The distribution plate 2 has protrusions 27. The protrusions 27 of the flow distribution plate 2 are in contact with the fuel electrode 11 and the oxidant electrode 12 to ensure electron conductivity, and conduct electrons generated by the power generation reaction between the flow distribution plate 2 and the oxidant electrode 12. be able to.

  As shown in FIG. 7, the oxidant inlet 30 allows an oxidant gas (generally air or oxygen gas) to flow, and is provided in a horizontally long shape on the upper side 20 side of the flow distribution plate 2. The oxidant outlet 31 (oxidant outlet) is provided in a horizontally long shape on the lower side 21 side of the flow distribution plate 2. The oxidant flow path 32 has a straight shape formed by a large number of partitioning protrusions 27 that extend intermittently from the oxidant inlet 30 to the oxidant outlet 31. Accordingly, in the flow distribution plate 2, the oxidant gas flows downward (in the direction of arrow Y <b> 1) from top to bottom in the order of the oxidant inlet 30, the oxidant flow path 32, and the oxidant outlet 31. Therefore, the oxidant gas flowing through the flow distribution plate 2 flows downward from the top to the bottom on the one surface side of the flow distribution plate 2.

  In addition, as described above, the oxidant flow path 32 extends straight, and the oxidant outlet 31 is provided on the lower side 21 side of the flow distribution plate 2, so that the generated water flows in the oxidant flow path 32. Even when there is water, it is possible to enhance the discharge property of discharging the generated water downward using gravity. As shown in FIG. 7, the protrusions 27 are intermittent in the length direction via the notches 28 and are arranged in the vertical direction. Since the cutout portion 28 is formed, even if the generated water is clogged in the oxidant flow path 32, the oxidant gas is generated through the cutout portion 28 so as to avoid the clogged portion of the generated water. The water clogging portion can be bypassed, and the flowability of the oxidant gas is ensured.

  Next, the fuel flow will be described. As shown in FIG. 8, one fuel inlet / outlet port 40 flows fuel (generally, hydrogen gas, hydrogen gas) and is provided vertically below one side portion 22 of the flow distribution plate 2. Yes. The other fuel inlet / outlet port 41 is provided vertically above the other side portion 22 of the flow distribution plate 2. The fuel flow path 42 is provided on the other surface side of the flow distribution plate 2 so as to face the oxidant flow path 32 so as to have a front-back relationship with the oxidant flow path 32. A plurality of fuel flow paths 42 are extended in parallel from the fuel inlet / outlet 40 toward the fuel inlet / outlet 41.

  According to the above-described counter flow configuration, the fuel flow is opposite to the flow direction of the oxidant gas, and is basically upward (in the direction of arrow Y2). The existing generated water can be conveyed upward and transferred to the upper part (downstream) of the fuel flow path 42. Since the generated water passes through the electrolyte membrane 10 and travels between the oxidant electrode 12 and the fuel electrode 11, the oxidant electrode 12 and the fuel electrode 11 constituting the fuel cell are between the upper part and the lower part. The moisture unevenness is reduced, and as a result, the power generation unevenness between the upper part and the lower part of the flow distribution plate 2 is easily reduced. Thus, in order to reduce power generation unevenness, it is preferable to set the length of the vertical flow path (second flow path 42b described later) along the vertical direction of the fuel flow path 42 to be long. As will be described below, the present embodiment is set to such a structure.

  As shown in FIG. 8, the fuel flow path 42 includes a first flow path 42 a extending from the fuel inlet / outlet port 40 along the lateral direction (that is, along the lower side portion 21), and an end portion of the first flow path 42 a. And the second flow path 42b extending along the vertical direction (that is, along the side portions 22 and 23) and the upper part of the second flow path 42b and along the horizontal direction (that is, A third flow path 42c extending along the upper side 20). As shown in FIG. 8, the first flow path 42a and the second flow path 42b are L-shaped. The second flow path 42b and the third flow path 42c are L-shaped. The first flow path 42a, the second flow path 42b, and the third flow path 42c are extended by protrusions 27x. Here, according to the counterflow mode, in the flow distribution plate 2, the fuel flows upward in the order of the fuel inlet / outlet port 40, the first channel 42a, the second channel 42b, the third channel 42c, and the fuel inlet / outlet 41 (in the direction of arrow Y2). ). As shown in FIG. 8, each of the second flow paths 42 b is branched into a plurality of branch walls 47 that can also function as protrusions that ensure electron conductivity. The straight branch wall 47 has an upper end 47u and a lower end 47d.

  Looking at the plurality of branch walls 47, the lower end 47 d of the branch wall 47 gradually inclines along a virtual inclination line R 1 that inclines so as to descend from the fuel inlet / outlet port 40, as shown in FIG. Further, the upper end 47u of the branch wall 47 is gradually inclined to rise along a virtual inclination line R2 that is inclined to rise as the distance from the fuel inlet / outlet 41 increases. As shown in FIG. 8, the virtual tilt line R1 and the virtual tilt line R2 can be parallel to each other or almost parallel to each other. Note that a region defined by the virtual inclination line R1 and the virtual inclination line R2 is a parallelogram or a substantially parallelogram.

  As shown in FIG. 8, the fuel flow path 42 through which the fuel flows is bent at the connection portion between the first flow path 42a and the second flow path 42b and at the connection section between the second flow path 42b and the third flow path 42c. A bent channel 49 (49d, 49u) is formed. That is, portions corresponding to the virtual inclination line R1 and the virtual inclination line R2 constitute a bent flow path 49 in which the fuel flow path 42 through which the fuel flows is bent. Thus, the fuel flow path 42 has the bent flow path 49. As shown in FIG. 8, the channel width of one first channel 42a is D1, the channel width of one second channel 42b is D2, and the channel width of one third channel 42c. Is denoted as D3. The relationship is D1> D2, D3> D2, and D1≈D3 (D1 = D3). However, it is not limited to this.

  As shown in FIG. 8, the overall width of the first flow path group formed by the first flow paths 42a constituting each fuel flow path 42 (the overall width in the direction crossing the gas flow) is LA, and each fuel flow When the overall width of the second flow path group formed by the second flow paths 42b constituting the path 42 (the overall width in the direction crossing the gas flow) is LB, the relationship of LA <LB is set. Further, when the overall width of the third flow path group formed by the third flow paths 42c constituting each fuel flow path 42 is LC, the relationship LC <LB is set. Here, LA = LC and LA≈LC. According to this example as described above, the lengths M1 and M2 (see FIG. 8) of the second flow path 42b extending in the vertical direction in the fuel flow path 42 can be increased. As a result, the area of the area SA occupied by the second flow path 42b of the fuel flow path 42 can be increased. As a result, the area of the counter flow form in which the oxidant gas and the fuel flow in opposite directions can be increased. For this reason, it is advantageous to take advantage of the counter flow configuration. As shown in FIGS. 7 and 8, the distribution plate 2 is formed with a cooling water inlet 50 through which cooling water for cooling the fuel cell is introduced, and a cooling water outlet 51 through which the cooling water flows out. Is formed. A cooling water flow path communicating with the cooling water inlet 50 and the cooling water outlet 51 is formed in a flow distribution plate (not shown). According to this embodiment shown in FIGS. 7 and 8, in the high power generation region, if the lower fuel inlet / outlet 40 is used for fuel supply and the upper fuel inlet / outlet 41 is used for fuel discharge, the fuel flow path Since the basic flow of the fuel at 42 is upward (in the direction of arrow Y2), it can be switched to the counterflow mode. On the other hand, in the low power generation region, if the lower fuel inlet / outlet 40 is used for fuel discharge and the upper fuel inlet / outlet 41 is used for fuel supply, the basic fuel in the fuel flow path 42 is obtained. Since the target flow is downward (the direction opposite to the arrow Y2 direction), it can be switched to the parallel flow mode.

(Other)
7 and 8 show only an example of the oxidant flow path 32 and the fuel flow path 42, and the shape of the oxidant flow path 32 is not limited to the structure shown in FIG. 7, and can be changed as appropriate. Thus, the shape of the fuel flow path 42 is not limited to the structure shown in FIG. 8, but can be changed as appropriate. According to the above-described embodiment, the switching is performed by the valves 83 and 84 and the valves 83x and 84x. However, the switching may be performed by providing a switching valve (for example, a three-way valve) at the branch points 101 and 102. The present invention is not limited to the embodiments described above and shown in the drawings, and can be implemented with appropriate modifications without departing from the scope of the invention.

  The present invention can be used in, for example, fuel cell power generation systems for stationary use, vehicle use, portable use, electrical equipment use, electronic equipment use, and the like.

It is a conceptual diagram when the flow of the fuel which flows through the fuel flow path of the fuel cell and the flow of the oxidant gas which flows through the oxidant flow path are in a counterflow form. It is a conceptual diagram when the flow of the fuel flowing through the fuel flow path of the fuel cell and the flow of the oxidant gas flowing through the oxidant flow path are in a parallel flow form. It is a graph which shows typically the relationship between the transfer amount of the fuel which transfers from a fuel electrode to an oxidant electrode, and current density. It is a conceptual diagram which shows the inside of a fuel cell. FIG. 4 is a layout diagram related to Example 1 and having a valve connected to a fuel cell. FIG. 6 is a layout diagram related to Example 2 and having a valve connected to a fuel cell. It is a front view which shows typically the oxidizing agent flow path side of a flow distributor. It is a front view which shows typically the fuel flow path side of a distribution plate.

Explanation of symbols

  In the figure, 1 is a membrane electrode assembly, 10 is an electrolyte membrane, 11 is a fuel electrode, 12 is an oxidant electrode, 32 is an oxidant channel, 42 is a fuel channel, 71 is a first opening, and 72 is a second opening. , 8 is a switching means, 81 is a first supply valve, 82 is a second supply valve, 83 is a first discharge valve, and 84 is a second discharge valve.

Claims (5)

A fuel cell having a membrane electrode assembly having a fuel electrode and an oxidant electrode sandwiching an electrolyte membrane, an oxidant flow path for flowing an oxidant to the oxidant electrode, and a fuel flow path for flowing fuel to the fuel electrode In the fuel cell system provided,
Comprising a switching means for switching the flow direction relationship between the fuel flowing through the fuel flow path and the oxidant flow path between the first form and the second form;
The switching means is
In the first embodiment, the upstream region of the oxidant flowing through the oxidant flow channel and the upstream region of the fuel flowing through the fuel flow channel are opposed to each other through the electrolyte membrane, and the oxidant flowing through the oxidant flow channel The downstream region of the fuel and the downstream region of the fuel flowing through the fuel flow path through the electrolyte membrane,
In the second embodiment, the upstream region of the oxidant flowing through the oxidant flow channel and the downstream region of the fuel flowing through the fuel flow channel are opposed to each other through the electrolyte membrane, and the oxidant flowing through the oxidant flow channel The downstream region of the fuel and the upstream region of the fuel flowing through the fuel flow path through the electrolyte membrane, and
The switching means switches to operate in the second mode in the high power generation region where the power generation amount is relatively large, and to operate in the first mode in the low power generation region where the power generation amount is relatively smaller than the high power generation region. A fuel cell system.   2. The first mode according to claim 1, wherein the switching unit switches the flow direction of the fuel flowing through the fuel flow path in reverse while maintaining the flow direction of the oxidant flowing through the oxidant flow path. And the second mode can be switched. 3. The fuel flow path according to claim 1, wherein the fuel flow path includes a first fuel opening that can be switched to one of an inlet through which fuel is supplied and an outlet through which fuel off fluid is discharged, an inlet through which fuel is supplied, and A second opening for fuel that can be switched to the other of the outlets from which the fuel-off fluid is discharged,
The switching means includes a first supply valve for supplying fuel connected to the first opening for fuel and a first discharge valve for discharging fuel off fluid, and a second supply valve for supplying fuel connected to the second opening for fuel. And a second discharge valve for discharging the fuel-off fluid. 3. The oxidant flow path according to claim 1, wherein the oxidant flow path includes a first oxidant opening that can be switched to one of an inlet through which an oxidant is supplied and an outlet through which an oxidant-off fluid is discharged. A second opening for oxidant that can be switched to the other of the supplied inlet and the outlet from which the oxidant-off fluid is discharged;
The switching means includes a first supply valve for supplying an oxidant connected to the first opening for oxidant, a first discharge valve for discharging an oxidant-off fluid, and an oxidant supply connected to the second opening for oxidant. And a second discharge valve for discharging the oxidant-off fluid. A fuel cell having a membrane electrode assembly having a fuel electrode and an oxidant electrode sandwiching an electrolyte membrane, an oxidant flow path for flowing an oxidant to the oxidant electrode, and a fuel flow path for flowing fuel to the fuel electrode Preparing a switching means that can switch a relationship between a fuel flow in the fuel flow channel and an oxidant flow in the oxidant flow channel; and
The upstream area of the oxidant flowing through the oxidant flow path faces the downstream area of the fuel flowing through the fuel flow path, and the downstream area of the oxidant flowing through the oxidant flow path and the fuel flowing through the fuel flow path In the operation method of the fuel cell system for performing the power generation operation in a form facing the upstream region,
When the power generation amount changes to a low power generation region that is relatively smaller than the high power generation region, the upstream region of the oxidant that flows through the oxidant flow channel and the upstream region of the fuel that flows through the fuel flow channel face each other, and A method for operating a fuel cell system, wherein the power generation operation is switched in such a manner that a downstream region of an oxidant flowing through an oxidant channel and a downstream region of fuel flowing through the fuel channel are opposed to each other.

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