JP2007059105A - Fuel cell stack equipped with switching means - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell stack preventing voltage drop when the gas flow direction is reversed, or gas flow rate is changed by switching a gas passage, during the operation of the fuel cell stack. <P>SOLUTION: The fuel cell stack is equipped with a first manifold, a second manifold, and each of the first manifold and the second manifold is equipped with a gas supply passage having a switching means and a gas exhaust passage, having a switching means. The fuel cell stack is equipped with the first manifold equipped with the gas supply passage, the second manifold equipped with the gas exhaust passage having the switching means at one end and the gas exhaust passage, equipped with the gas exhaust passage having the switching means at the other end, and a third manifold, equipped with the gas exhaust passage having the switching means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell stack provided with an opening / closing means.

  A fuel cell is a device that generates electric power by supplying a fuel gas such as hydrogen to an anode and an oxidant gas such as air to a cathode to cause an electrochemical reaction. For example, a unit cell of a polymer electrolyte fuel cell (hereinafter referred to as “PEFC”) includes a separator having a membrane / electrode assembly (MEA), a gas diffusion layer, and a gas flow path. Including. In this MEA, electrodes (anode and cathode) are bonded to both surfaces of a solid polymer film.

  When large electric power is generated by the fuel cell, a fuel cell stack in which a plurality of single cells of the fuel cell are stacked in series is used. The fuel cell stack is generally configured by pressing a plurality of single cells from both ends using end plates or the like.

  An example of the electrochemical reaction at each electrode of PEFC using hydrogen as the fuel gas and oxygen as the oxidant gas is shown below.

Anod: H ₂ → 2H ⁺ + 2e ⁻
Cathode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O
Total reaction: H ₂ + 1 / 2O ₂ → H ₂ O
In order to advance such a reaction efficiently, it is necessary to uniformly supply fuel gas and oxidant gas to the anode and cathode of the PEFC. Therefore, a gas flow path for flowing fuel gas or oxidant gas is formed in the separator. The gas channel is a general term for an oxidant gas channel or a fuel gas channel. The gas flow path is generally constituted by a groove formed in the separator.

  The fuel cell stack is provided with a manifold for distributing gas or cooling water to each cell. A separator used in a fuel cell stack has through holes used as a manifold, and these through holes are stacked to form a manifold.

  The manifold of the fuel cell stack includes a gas manifold for use as a reaction gas and a cooling water manifold for use as cooling water. Fuel gas or oxidant gas introduced from the outside is distributed to the gas flow path of each cell through the gas manifold. This gas manifold is called a gas supply manifold. The gas discharged from the gas flow path of each cell is discharged to the outside through another gas manifold. This gas manifold is called a reaction gas discharge manifold. Here, the gas flow path is a path for supplying fuel gas or oxidant gas to the electrode that is a reaction field, and is in contact with the electrode.

  Further, in order to control the temperature of the fuel cell stack and use the generated heat, a cooling water flow path for flowing a coolant such as cooling water is formed between cells or every several cells. This cooling water channel is often formed on the surface opposite to the surface where the gas channel of the separator is located.

  In a polymer electrolyte fuel cell, Patent Documents 1 to 3 disclose techniques for providing on / off valves in a reaction gas passage and an exhaust gas passage.

  In the fuel cell stack of the present application, the cooling water manifold is not an object of the invention and will not be discussed. Therefore, hereinafter, the gas supply manifold and the gas discharge manifold are collectively referred to as a “manifold”.

  Japanese Patent Laid-Open No. 2004-26883 discloses a method of opening and closing the supply of a reaction gas to and from the reaction gas supply system in order to prevent a large pressure difference between both electrodes when the reaction gas is replaced with an inert gas when the fuel cell is stopped. 1 on-off valve, a second on-off valve in an exhaust pipe for releasing excess gas out of the system, and a third on-off valve for opening and closing the supply of inert gas are described. In order to stop the supply of the fuel gas and the oxidant gas to the fuel cell when combustion occurs, it is described that an open / close valve is provided in the oxidant gas supply line and the fuel gas supply line. In order to efficiently use the water collected on the discharge side for humidification of the reaction gas on the supply side, the manifold 1a provided with the three-way valve 21, the manifold 1b provided with the three-way valve 22, the three-way valve 21 and the three-way valve The third three-way valve 20 It is described that comprises a.

  Some fuel cell stacks have a function of reversing the gas flow direction in order to improve performance. Patent Document 4 discloses a fuel cell having a function of reversing the direction of gas flowing in a gas flow path in order to eliminate poisoning of the catalyst by carbon monoxide contained in the reformed gas.

  In the fuel cell power generation system of Patent Document 4, the fuel cell main body is provided with a first fuel gas supply / exhaust port and a second fuel gas supply / exhaust port, outside the first and second fuel gas supply / exhaust ports. There are two electromagnetic on-off valves, and the combination of opening and closing of the electromagnetic on-off valves supplies fuel gas from the first fuel gas supply / exhaust port, and from the second fuel gas supply / exhaust port. Switching between the case of discharging and the case of supplying from the second fuel gas supply / exhaust port and discharging from the first fuel gas supply / exhaust port are performed.

  Further, Patent Document 5 has a function of switching the gas flow path in order to suppress the flooding phenomenon when the gas flow rate generated due to the load fluctuation of the fuel cell stack is small and to reduce the pressure loss when the gas flow rate is high. Proposed fuel cell stacks have been proposed.

  In the fuel cell stack of Patent Document 5, three reaction gas manifolds for supplying or discharging the oxidant gas (air) are provided, the first reaction gas manifold is used as the first external gas supply path, The reaction gas manifold is connected to the first external gas discharge path, and the third reaction gas manifold is connected to the second external gas supply path and the second external gas discharge path, respectively. The external gas supply path and the second external gas discharge path are each provided with opening / closing means, and by opening and closing these opening / closing means, a plurality of gas supply / discharge paths can be conducted in series or in parallel. .

JP 07-272740 A JP 09-147895 A JP 2003-243007 A Japanese Patent Laid-Open No. 08-031442 JP 2004-087457 A

  The on-off valve described in Patent Document 1 closes the first on-off valve, opens the second on-off valve and the third on-off valve when the operation of the fuel cell is stopped, and reacts the reaction gas inside the fuel cell with an inert gas. To replace.

  The on-off valve described in Patent Document 2 has a fuel cell and oxidant gas crossover in the solid polymer electrolyte, and the fuel gas and oxidant gas leak from the gas seal part. When combustion occurs in this case, both the oxidant gas supply line and the on-off valves provided in the fuel gas supply line are closed, and the supply of the fuel gas and the oxidant gas to the fuel cell is stopped.

  In Patent Document 3, by switching three three-way valves, gas flows in the order of three-way valve 20 → three-way valve 21 → manifold 1a → fuel cell → manifold 1b → three-way valve 22, and three-way valve 20 → three-way valve 22 → Switching between the case of flowing gas in the order of manifold 1b → fuel cell → manifold 1a → three-way valve 21 makes efficient use of the water collected on the discharge side for humidification of the reaction gas on the supply side.

  In the polymer electrolyte fuel cells described in Patent Documents 1 to 3, the gas supply pipe and the manifold are provided with the on-off valve and the three-way valve, but one gas supply pipe and the manifold have one on-off valve and the three-way valve. A valve was provided, and it did not reverse the gas flow or change the gas flow rate during operation of the fuel cell.

  During operation of the fixed polymer fuel cell stack using air and reformed gas as the oxidant gas and fuel gas, as described in Patent Document 4, the direction of the gas flowing through the gas flow path is reversed, or As described in Patent Document 5, when an operation of changing the gas flow rate by switching the gas flow path is performed, the exhaust gas of the reaction gas discharge path and the reaction gas discharge manifold temporarily flows back into the gas flow path.

  As a result, on the cathode side, low oxygen concentration air in the oxidant gas manifold used for discharging the oxidant gas is supplied to the gas flow path, and on the anode side, carbon monoxide in the fuel gas manifold used for discharging the fuel gas. It has been found that since the fuel gas having a high concentration is supplied to the gas flow path, a problem that the cell voltage temporarily decreases occurs. In particular, when the utilization rate of the reaction gas is increased, the voltage drop is significant.

  Examples of conventional polymer electrolyte fuel cell stacks (hereinafter referred to as “PEFC stacks”) having a function of switching gas flow paths are shown in FIGS.

  9 to 11 are schematic views showing a cross-sectional structure of a conventional PEFC stack. 9 to 11, the symbol 11a is a first manifold, 11b is a second manifold, 11c is a third manifold, 12a is a gas supply path provided in the first manifold, and 12b is provided in the second manifold. The gas supply path, 13b is the gas discharge path provided in the second manifold, 13c is the gas discharge path provided in the third manifold, 14b is the opening / closing means provided in the gas supply path of the second manifold, and 15b is the first Opening / closing means provided in the gas discharge path of the manifold 2, 15 c is an opening / closing means provided in the gas discharge path of the third manifold, 16 and 17 are gas flow paths, 18 is a membrane / electrode assembly (MEA), 19 is Indicates a separator. When an oxidant gas is allowed to flow through the gas flow path 16, the fuel gas is allowed to flow through the gas flow path 17. When an oxidant gas is allowed to flow through the gas flow path 17, the fuel gas is allowed to flow through the gas flow path 16. . In FIGS. 10 and 11, the direction of gas flow is indicated by arrows.

  In the conventional PEFC stack, as shown in FIG. 9, a gas supply path 12b provided with an opening / closing means 14b and a gas discharge path 13b provided with an opening / closing means 15b are provided at one end of the second manifold 11b. In this PEFC stack, when the opening / closing means 14b, 15b, and 15c are operated to switch the gas flow path from the gas flow direction of FIG. 10 to the gas flow direction of FIG. In the manifold 11b, the exhaust gas existing in the second manifold 11b is mixed with the gas supplied from the gas supply path 12b and flows back to the gas flow path 16, which causes a problem that the cell voltage decreases.

  Accordingly, an object of the present invention is to provide a fuel cell stack in which a voltage drop does not occur when the direction of gas flow is reversed or the gas flow rate is changed by switching the gas flow path during operation of the fuel cell stack. There is.

  The invention of claim 1 relates to a fuel cell stack, comprising a first manifold and a second manifold, each of the first and second manifolds having a gas supply path provided with an opening / closing means at one end. And a gas discharge path provided with an opening / closing means at the other end.

  The invention of claim 2 relates to a fuel cell stack, comprising a first manifold having a gas supply path, a gas supply path having an opening / closing means at one end, and a gas discharge path having an opening / closing means at the other end. A third manifold including a gas discharge path provided with a second manifold and an opening / closing means is provided.

  In the fuel cell stack according to the first aspect of the present invention, when the operation of reversing the direction of the gas flowing through the gas flow path is performed during operation of the fuel cell stack, the gas supply path and the gas provided in the first and second manifolds By opening and closing the discharge passage opening / closing means individually and temporarily opening both the gas supply passage and the gas discharge passage, the gas supplied from the gas supply passage is not passed through the gas passage. Since a discharge path is formed in the discharge path, it is possible to suppress a temporary cell voltage drop caused by the backflow of the exhaust gas.

  Specifically, the gas supply path opening / closing means provided in the first manifold is opened, the gas discharge path opening / closing means is closed, the gas supply path opening / closing means provided in the second manifold is closed, and the gas discharge path opening / closing means is closed. During operation with the opening / closing means open, first, the opening / closing means of the gas supply path provided in the second manifold is opened, then the opening / closing means of the gas supply path provided in the first manifold is closed, The opening / closing means for the gas discharge path provided in the first manifold is opened, and at the same time, the opening / closing means for the gas discharge path provided in the second manifold is closed.

  A fuel cell stack according to a second aspect of the present invention provides a gas supply path and a gas discharge path provided in the second and third manifolds when an operation of switching the gas flow path in accordance with a load change during operation of the fuel cell stack. By opening and closing each of the opening and closing means individually, a path is formed in which the gas temporarily supplied from the gas supply path is discharged to the gas discharge path without passing through the gas flow path. It is possible to suppress a temporary decrease in cell voltage due to the backflow of exhaust gas when operating.

  Specifically, the gas supply path opening / closing means provided in the second manifold is closed, the gas discharge path opening / closing means provided in the second manifold is opened, and the gas discharge path opening / closing means provided in the third manifold. During the operation with the valve closed, first, the opening / closing means provided in the gas supply path of the second manifold is opened, then the opening / closing means of the gas discharge path provided in the second manifold is closed, and at the same time the third The opening / closing means provided in the reaction gas discharge path of the manifold is opened.

  In general, in a fuel cell, when a reformed gas is used for fuel, an electrode catalyst on the discharge side is more likely to be poisoned by carbon monoxide or the like contained in the reformed gas than on the fuel inlet side. Therefore, after the operation for a certain period, the damage can be reduced by reversing the fuel inlet side and the fuel outlet side. In addition, it is necessary to change the flow rate of the reaction gas to be supplied in accordance with the load fluctuation.

  In the following, the present invention will be described by taking “PEFC stack” as an example. However, the present invention is not limited to “solid polymer fuel cell stack”, and other types such as molten carbonate form and phosphoric acid form are used. It can also be applied to a fuel cell stack.

  Here, the PEFC stack having the function of reversing the direction of the gas flowing through the gas flow paths shown in FIGS. 1 to 4 and the PEFC stack having the function of switching the gas flow paths shown in FIGS. 5 to 8 are used. The present invention will now be described.

  1 to 8, reference numeral 1a is a first manifold, 1b is a second manifold, 1c is a third manifold, 2a is a gas supply path provided in the first manifold, and 2b is provided in a second manifold. The gas supply path, 3a is the gas discharge path provided in the first manifold, 3b is the gas discharge path provided in the second manifold, 3c is the gas discharge path provided in the third manifold, and 4a is the first manifold. Opening and closing means provided in the gas supply path of the second manifold, 4b is an opening and closing means provided in the gas supply path of the second manifold, 5a is an opening and closing means provided in the gas discharge path of the first manifold, and 5b is a gas of the second manifold. Opening / closing means provided in the discharge path, 5c indicates opening / closing means provided in the gas discharge path of the third manifold, 6 and 7 indicate gas flow paths, 8 indicates a membrane / electrode assembly (MEA), and 9 indicates a separator. In addition, when the oxidant gas is allowed to flow through the gas flow path 6, the fuel gas is allowed to flow through the gas flow path 7, and when the oxidant gas is flowed through the gas flow path 7, the fuel gas is allowed to flow through the gas flow path 6. .

  First, the operation for reversing the flow direction of the fuel gas in the operating state will be described as an example. FIG. 1 shows an example of a schematic view of a cross section of a PEFC stack of the present invention. As shown in FIG. 1, the PEFC stack includes a first manifold 1 a and a second manifold 1 b, and the two manifolds are connected by a gas flow path 6. One end of the first manifold 1a is connected to the gas supply path 2a and the other end is connected to the gas discharge path 3a. The gas supply path 2a is provided with an opening / closing means 4a, and the gas discharge path 3a is provided with an opening / closing means 5a. The second manifold 1b has one end connected to the gas supply path 2b and the other end connected to the gas discharge path 3b. The gas supply path 2b is provided with an opening / closing means 4b, and the gas discharge path 3b is provided with an opening / closing means 5b. Therefore, the direction of the gas flowing through the gas flow path can be reversed.

  In this example, in FIG. 1, the first manifold 1a and the second manifold 1b are used as a fuel gas manifold, 6 as a fuel gas flow path, and 7 as an oxidant gas flow path. 2 to 4 show gas flows when the direction of the fuel gas flowing through the gas flow path of the PEFC stack shown in FIG.

  FIG. 2 shows a gas flow in a normal operation state, in which the opening / closing means 4a provided in the gas supply path 2a of the first manifold 1a is opened and the opening / closing means provided in the gas discharge path 3a of the first manifold 1a. The means 5a is closed, the opening / closing means 4b provided in the gas supply path 2b of the second manifold 1b is closed, and the opening / closing means 5b provided in the gas discharge path 3b of the second manifold 1b is set to open. As shown by the arrows in FIG. 2, the fuel gas flows in the order of the gas supply path 2a → the first manifold 1a → the gas flow path 6 → the second manifold 1b → the gas discharge path 3b.

  Next, when the flow of the fuel gas is reversed from the gas flow direction shown in FIG. 2 to the state of the gas flow direction shown in FIG. 4, first, as shown in FIG. 3, the gas supply to the second manifold 1b is performed. The opening / closing means 4b provided in the path 2b is opened. In this state, a path is formed in which the fuel gas supplied from the gas supply path 2b is discharged to the gas discharge path 3b without passing through the gas flow path 6, and a part of the exhaust gas is replaced with the supply gas. The

  Subsequently, the opening / closing means 4a in the gas supply path 2a of the first manifold 1a is closed, and at the same time, the opening / closing means 5b provided in the gas discharge path 3b of the second manifold 1b is closed. The opening / closing means 5a in the gas discharge path 3a of the manifold 1a is opened, and the direction of gas flow is set to the state shown in FIG. In FIG. 4, as shown by the arrows, the fuel gas flows in the order of gas supply path 2b → second manifold 1b → gas flow path 6 → first manifold 1a → gas discharge path 3a.

  As described above, when the state shown in FIG. 4 is established, the amount of exhaust gas flowing back to the gas flow path 6 is remarkably reduced, so even when the direction of the gas flowing through the gas flow path 6 is reversed during operation. Thus, it is possible to suppress a temporary decrease in cell voltage due to the backflow of exhaust gas. In addition, in FIG. 3, the effect which suppresses the fall of a cell voltage becomes high as the quantity of the fuel gas supplied from the gas supply path 2b is increased.

  Here, the content of the present invention has been described by taking the flow of the fuel gas as an example, but the same effect can be obtained even when the present invention is applied to the oxidant gas. 1 to 4 exemplify the case where there is one first manifold and two second manifolds, the number of these manifolds may be one, or a plurality of manifolds may be used.

  Next, an operation for switching the operating gas flow path will be described as an example. FIG. 5 shows an example of a schematic cross-sectional view of the PEFC stack of the present invention. As shown in FIG. 5, the PEFC stack is provided with three manifolds, ie, a first manifold 1a, a second manifold 1b, and a third manifold 1c. Are connected to each other. As shown in FIG. 5, in this PEFC stack, one end of the first manifold 1a is connected to the gas supply path 2a, one end of the second manifold 1b is connected to the gas supply path 2b, and the other end is gas. An open / close means 4b is provided in the gas supply path 2b, an open / close means 5b is provided in the gas discharge path 3b, and one end of the third manifold 1c is connected to the gas discharge path 3c. Since the discharge path 3c is provided with the opening / closing means 5c, the connection method of the gas flow paths can be switched according to the gas flow rate.

  In this example, in FIG. 5, the first manifold 1a and the second manifold 1b are used as an oxidant gas manifold, 6 as an oxidant gas flow path, and 7 as a fuel gas flow path. 6 to 8 show the flow of the gas when the direction of the oxidant gas flowing through the gas flow path of the PEFC stack shown in FIG. 5 is switched in accordance with the gas flow rate in the operating state. Each is shown.

  FIG. 6 shows a gas flow in a normal operation state, in which the opening / closing means 4b provided in the gas supply path 2b of the second manifold 1b is closed and the opening / closing means 5b provided in the gas discharge path 3b is open. The opening / closing means 5c provided in the gas discharge path 3c of the third manifold 1c is set to be closed, and the oxidant gas is supplied from the gas supply path 2a → the first manifold 1a → as shown by the arrow in FIG. The gas flows in the order of the gas flow path 6 → the second manifold 1b → the gas discharge path 3b.

  Next, when the connection method of the oxidant gas flow path is switched from the gas flow direction shown in FIG. 6 to the state of the gas flow direction shown in FIG. 8, first, as shown in FIG. The opening / closing means 4b provided in the gas supply path 2b of 1b is opened. In the state shown in FIG. 7, a path is formed in which the oxidant gas supplied from the gas supply path 2 b is discharged to the gas discharge path 3 b without passing through the gas flow path 6, and the exhaust gas having a low oxygen partial pressure. Is replaced with the feed gas.

  Subsequently, the opening / closing means 5b provided in the gas discharge path 3b of the second manifold 1b is closed, and at the same time, the opening / closing means 5c provided in the gas discharge path 3c of the third manifold 1c is opened. Set to the state shown. In FIG. 8, as indicated by arrows, the oxidant gas flows in the order of gas supply path 2a → first manifold 1a → gas flow path 6 → third manifold 1c → gas discharge path 3c, and gas supply path. It flows through two flow paths, that is, a flow path in the order 2b → second manifold 1b → gas flow path 6 → third manifold 1c → gas discharge path 3c.

  Thus, when the state shown in FIG. 7 is established, the amount of exhaust gas flowing back to the gas flow path 6 is remarkably reduced, so even if the connection method of the gas flow path is switched during operation, It is possible to suppress a temporary decrease in the cell voltage due to the backflow. In FIG. 7, as the amount of the oxidant gas supplied from the gas supply path 2b is increased, the effect of suppressing a decrease in the cell voltage becomes higher.

  Here, the content of the present invention has been described by taking the flow of the oxidant gas as an example, but the same effect can be obtained even when the present invention is applied to the fuel gas. 5 to 8, the first manifold, the second manifold, and the third manifold are each illustrated as being one, but the number of these manifolds may be one or plural. Is also possible.

  When reversing the direction of the gas flowing through the gas flow path or switching the gas flow path, a second manifold that reverses the function from the manifold that discharges the reaction gas to the manifold that supplies the reaction gas is provided. The effect of this invention is acquired by providing the gas supply path which provided the opening-and-closing means in one end of this 2nd manifold, and the gas discharge path which provided the opening-and-closing means in the other end.

  That is, unlike the conventional fuel cell stack, the fuel cell stack according to the present invention is different from the gas supply manifold and the gas discharge manifold provided with one opening / closing means at each end. By providing each opening / closing means and simultaneously operating the opening / closing means provided at both ends, it is possible to form a path through which the gas supplied from the gas supply path is discharged to the gas discharge path without passing through the gas flow path. Features.

  The manifold in the present invention is a general term for an oxidant gas manifold, a fuel gas manifold, a gas supply manifold, and a gas discharge manifold. An oxidant gas manifold is a manifold for supplying or discharging an oxidant gas such as air. A fuel gas manifold is a manifold for supplying or discharging a fuel gas such as hydrogen or reformed gas. Is a manifold for supplying oxidant gas or fuel gas, and a gas discharge manifold is a manifold for discharging oxidant gas or fuel gas.

  The gas supply path refers to a pipe for supplying gas from a gas supply source such as a compressor, cylinder, reformer or the like outside the fuel cell stack to the gas supply manifold of the fuel cell stack, and the gas discharge path refers to a fuel cell. The pipe for exhausting gas from the gas exhaust manifold of the stack to the outside.

  Opening and closing means can control the flow rate of gas through the piping at the site where it is installed, and it shuts off the gas flow when it is completely closed and allows the gas to flow sufficiently when it is fully opened. is there. As the opening / closing means, for example, a ball valve, a needle valve, a two-way valve, an electromagnetic valve or the like can be used.

  In the fuel cell system of the present invention, the opening / closing means in the gas supply path provided at one end of the manifold is opened, and then the opening / closing means in the gas discharge path provided at the other end is closed. In this system, the opening / closing means in the gas supply path provided at one end of the manifold and the opening / closing means in the gas discharge path provided at the other end are open at the same time, so the gas in the manifold is replaced. Thus, it is possible to suppress a temporary decrease in cell voltage due to the backflow of exhaust gas.

  In the fuel cell stack of the present invention, the opening / closing means provided in the manifold not only performs an alternative operation of completely closing or opening completely, but also the opening / closing provided in the gas supply path provided at one end of the manifold. It is preferable to control the flow rate to the optimum using the means and the opening / closing means provided in the gas discharge path provided at the other end because more efficient switching operation can be performed.

  The present invention will be described below with reference to preferred embodiments.

[Example 1 and Comparative Example 1]
[Example 1]
A PEFC stack A of Example 1 was manufactured, including five MEAs having an electrode area of 230 cm ² and a platinum loading of 0.5 mg / cm ² . The cross-sectional structure of this PEFC stack is the same as that shown in FIG. That is, three manifolds of a first manifold 1 a, a second manifold 1 b, and a third manifold 1 c are provided, and these three manifolds are connected to each other by a gas flow path 6.

  One end of the first manifold 1a is connected to the gas supply path 2a. The second manifold 1b has one end connected to the gas supply path 2b and the other end connected to the gas discharge path 3b. The gas supply path 2b is provided with an opening / closing means 4b, and the gas discharge path 3b is provided with an opening / closing means 5b. Furthermore, one end of the third manifold 1c is connected to the gas discharge path 3c, and the gas discharge path 3c is provided with an opening / closing means 5c. Therefore, this PEFC stack A can switch the connection method of the gas flow path according to the gas flow rate.

  In this PEFC stack A, the manifolds 1a, 1b and 1c were used as an oxidant gas manifold, the gas flow path 6 as an oxidant gas flow path, and the gas flow path 7 as a fuel gas flow path. Solenoid valves were used for the opening / closing means 4a, 5b and 5c.

For the PEFC stack A, a separator in which 50 grooves having a width of 1.0 mm and a depth of 0.5 mm were used as gas flow paths was used. The cross-sectional area of the manifold of this PEFC stack was 3.5 cm ² and the length was 60 mm.

[Comparative Example 1]
A PEFC stack B of Comparative Example 1 was manufactured, containing 5 MEAs having an electrode area of 230 cm ² and a platinum loading of 0.5 mg / cm ² . The cross-sectional structure of this PEFC stack is the same as that shown in FIG. That is, a first manifold 11 a, a second manifold 11 b, and a third manifold 11 c are provided, and these three manifolds are connected to each other by a gas flow path 16.

  The gas supply path 12b provided in the second manifold 11b is provided with an opening / closing means 14b, and the gas discharge path 13c provided in the third manifold 11c is provided with an opening / closing means 15c. The connection method of the gas flow path can be switched.

  In this PEFC stack B, the manifolds 11a, 11b and 11c were used as an oxidant gas manifold, the gas flow path 16 as an oxidant gas flow path, and the gas flow path 17 as a fuel gas flow path. Solenoid valves were used for the opening / closing means 14b, 15b and 15c.

  In PEFC stack B, the same separator and manifold as those used in PEFC stack A of Example 1 were used.

[Test results]
For the PEFC stack A of Example 1 and PEFC stack B of Comparative Example 1 according to the present invention, air (utilization rate 40%) as the oxidant gas and reformed simulation gas (H ₂ : 80%, CO ₂ 20 as the fuel gas) %, CO 10 ppm, utilization rate 80%), and operation was performed at a current density of 100 mA / cm ² . Subsequently, the switching means was operated to switch the oxidant gas flow path during operation of these PEFC stacks.

  The operation in the case of the PEFC stack A according to the first embodiment will be described with reference to FIGS. In the PEFC stack A, as shown in FIG. 6, the opening / closing means 4b is closed, the opening / closing means 5b is opened, and the opening / closing means 5c is closed during steady operation. Therefore, the oxidant gas flows in the direction indicated by the arrow in FIG. In this state, the manifold 1b is filled with exhaust gas having a low oxygen partial pressure.

  Next, as shown in FIG. 7, first, the opening / closing means 4b was opened, and an oxidant gas was introduced into the manifold 1b. The amount of oxidant gas introduced into the manifold 1b was the same as the amount of oxidant gas introduced into the manifold 1a. In the state of FIG. 7, a path is formed in which the oxidant gas supplied from the gas supply path 2b is discharged to the gas discharge path 3b without passing through the gas flow path 6, and the exhaust gas having a low oxygen partial pressure is the supply gas. As a result, the oxygen concentration in the manifold 1b increases.

  Subsequently, the opening / closing means 5b is closed, and at the same time, the opening / closing means 5c is opened to obtain the state shown in FIG. Thus, the gas flow path is switched, and the oxidant gas flows in the direction indicated by the arrow in FIG.

  The operation in the case of the PEFC stack B of Comparative Example 1 will be described with reference to FIGS. In the PEFC stack B, as shown in FIG. 10, during the steady operation, the opening / closing means 14b is closed, the opening / closing means 15b is open, and the opening / closing means 5c is closed. Therefore, the oxidant gas flows in the direction indicated by the arrow in FIG. In this state, the manifold 1b is filled with exhaust gas having a low oxygen partial pressure.

  Next, the opening / closing means 14b is opened, then the opening / closing means 15c is opened, and at the same time, the opening / closing means 15b is closed to the state shown in FIG. Thus, the gas flow path is switched.

FIG. 12 shows changes in the average cell voltage when the PEFC stack A of Example 1 and the PEFC stack B of Comparative Example 1 are operated at a current density of 100 mA / cm ² and the oxidant gas flow path is switched. The gas channel switching operation was started at a point of 0 second on the horizontal axis. In FIG. 12, the symbol ● represents the result of the PEFC stack A of Example 1, and the symbol ▲ represents the result of the PEFC stack B of Comparative Example 1.

  As shown in FIG. 12, in the PEFC stack A of Example 1, the cell voltage is almost stable, whereas in the PEFC stack B of Comparative Example 1, the cell voltage drops significantly immediately after switching the gas flow path. I found out.

  The PEFC stack A according to the first embodiment of the present invention includes a first manifold having a gas supply path, a gas supply path having an opening / closing means at one end, and a gas discharge path having an opening / closing means at the other end. 2 and a third manifold having a gas discharge path provided with an opening / closing means. Therefore, by temporarily opening both the gas supply path and the gas discharge path, It is possible to suppress a decrease in the cell voltage due to the backflow of the exhaust gas when the operation for switching the path is performed.

[Example 2 and Comparative Example 2]
[Example 2]
A PEFC stack C of Example 2 including 5 MEAs having an electrode area of 230 cm ² and a platinum loading of 0.5 mg / cm ² was manufactured. The cross-sectional structure of this PEFC stack is the same as that shown in FIG. That is, a first manifold 1 a and a second manifold 1 b are provided, and the two manifolds are connected by a gas flow path 6. One end of the first manifold 1a is connected to the gas supply path 2a and the other end is connected to the gas discharge path 3a. The gas supply path 2a is provided with an opening / closing means 4a, and the gas discharge path 3a is provided with an opening / closing means 5a. The second manifold 1b has one end connected to the gas supply path 2b and the other end connected to the gas discharge path 3b. The gas supply path 2b is provided with an opening / closing means 4b, and the gas discharge path 3b is provided with an opening / closing means 5b. Yes. Therefore, this PEFC stack C can reverse the direction of the gas flowing through the gas flow path.

  In this PEFC stack C, the manifolds 1a and 1b were used as a fuel gas manifold, the gas flow path 6 as a fuel gas flow path, and the gas flow path 7 as an oxidant gas flow path. Solenoid valves were used for the opening / closing means 4a, 4b, 5a and 5b.

  In PEFC stack C, the same separator and manifold as those used in PEFC stack A of Example 1 were used.

[Comparative Example 2]
A PEFC stack D of Comparative Example 2 was manufactured, containing five MEAs having an electrode area of 230 cm ² and a platinum loading of 0.5 mg / cm ² . FIG. 13 shows a cross-sectional structure of a PEFC stack having a function of switching a conventional gas flow path. In FIG. 13, symbol 21a is a first manifold, 21b is a second manifold, 22a is a gas supply path provided in the first manifold, 23b is a gas discharge path provided in the second manifold, and 24a is a first manifold. Opening / closing means provided in the gas supply path of the manifold, 25b is an opening / closing means provided in the gas discharge path of the second manifold, 26 and 27 are gas flow paths, 28 is a membrane / electrode assembly (MEA), 29 is a separator. Show.

  In this PEFC stack D, the manifolds 21a and 21b were used as fuel gas manifolds, the gas passage 16 as a fuel gas passage, and the gas passage 17 as an oxidant gas passage. Solenoid valves were used for the opening / closing means 24a and 25b.

  In PEFC stack D, the same separator and manifold as those used in PEFC stack A of Example 1 were used.

[Test results]
For the PEFC stack C of Example 2 and the PEFC stack D of Comparative Example 2 according to the present invention, air (utilization rate 40%) as the oxidant gas and reformed simulated gas (H ₂ : 80%, CO ₂ 20 as the fuel gas) %, CO 10 ppm, utilization rate 80%), and operation was performed at a current density of 100 mA / cm ² . Subsequently, the switching means was operated to switch the oxidant gas flow path during operation of these PEFC stacks.

  The operation in the case of the PEFC stack C according to the second embodiment will be described with reference to FIGS. In the PEFC stack C, as shown in FIG. 2, the opening / closing means 4a is open, the opening / closing means 4b is closed, the opening / closing means 5a is closed, and the opening / closing means 5b is open during steady operation. Therefore, the oxidant gas flows in the direction indicated by the arrow in FIG. In this state, the manifold 1b is filled with exhaust gas having a low oxygen partial pressure.

  Next, as shown in FIG. 3, first, the opening / closing means 4b was opened, and the fuel gas was introduced into the manifold 1b. In the state of FIG. 3, a path is formed in which the fuel gas supplied from the gas supply path 2b is discharged to the gas discharge path 3b without passing through the gas flow path 6, and a part of the exhaust gas is replaced with the supply gas. The fuel concentration in the manifold 1b increases.

  Next, the opening / closing means 4a is closed, the opening / closing means 5b is closed, and at the same time, the opening / closing means 5a is opened. This reverses the gas flow direction, and the fuel gas flows in the direction indicated by the arrow in FIG.

  The operation in the case of the PEFC stack D of Comparative Example 2 will be described with reference to FIG. In the PEFC stack D, during the steady operation, both the opening and closing means 24a and 25b are set to open, and the fuel gas flows in the order of the gas supply path 22a → the manifold 21a → the gas path 26 → the manifold 21b → the gas discharge path 23b.

  Next, the opening / closing means 24a is closed, the opening / closing means 25b is set to open, and the opening / closing means 24a is opened to supply fuel gas from the gas discharge passage 23b. In this case, the fuel gas flows in the order of gas discharge path 23b → manifold 21b → gas flow path 26 → manifold 21a → gas supply path 22a, and the direction of gas flow is reversed.

  As a result of the measurement, the cell voltage is almost stable in the PEFC stack C of Example 2, whereas the cell voltage is significantly decreased immediately after switching the gas flow path in the PEFC stack D of Comparative Example 2. I understood.

  The PEFC stack C according to the second embodiment of the present invention includes a first manifold and a second manifold, and each of the first and second manifolds has a gas supply path having an opening / closing means at one end and the other end. The gas exhaust passage provided with an opening / closing means is provided with a gas supply passage and a gas exhaust passage to temporarily open both of the gas supply passage and the exhaust passage when switching the gas passage. It is possible to suppress a decrease in cell voltage due to backflow.

The schematic diagram which shows the cross-section of the PEFC stack provided with the function to reverse the direction of the gas which flows through the gas flow path of this invention. The schematic diagram which shows the flow of the normal gas of the PEFC stack provided with the function to reverse the direction of the gas which flows through the gas flow path of this invention. The schematic diagram which shows the gas flow at the time of operation which reverses the direction of gas of the PEFC stack provided with the function to reverse the direction of the gas which flows through the gas flow path of this invention. The schematic diagram which shows the flow of the gas after reversing the direction of the gas of the PEFC stack provided with the function which reverses the direction of the gas which flows through the gas flow path of this invention. The schematic diagram which shows the cross-section of the PEFC stack provided with the function which switches the gas flow path of this invention. The schematic diagram which shows the flow of the normal gas of the PEFC stack provided with the function which switches the gas flow path of this invention. The schematic diagram which shows the gas flow at the time of operation which switches a gas flow path of the PEFC stack provided with the function which switches the gas flow path of this invention. The schematic diagram which shows the flow of the gas after switching a gas flow path of the PEFC stack provided with the function which switches the gas flow path of this invention. The schematic diagram which shows the cross-section of the conventional PEFC stack. The schematic diagram which shows the cross-section before switching a gas flow path of the conventional PEFC stack. The schematic diagram which shows the cross-sectional structure after switching a gas flow path of the conventional PEFC stack. The figure which shows the change of the average cell voltage at the time of switching the gas flow path of PEFC stack A and B. FIG. The schematic diagram which shows the cross-section of the PEFC stack provided with the function to switch the conventional gas flow path.

Explanation of symbols

1a, 11a First manifold 1b, 11b Second manifold 1c, 11c Third manifold 2a, 12a Gas supply path 2b, 12b provided in the first manifold Gas supply path 3a first provided in the second manifold Gas exhaust passages 3b, 13b provided in the second manifold Gas exhaust passage 3c, 13c provided in the second manifold Gas exhaust passage 4a provided in the third manifold Opening / closing means 4b provided in the gas supply passage of the first manifold, 14b Opening / closing means provided in the gas supply path of the second manifold 5a Opening / closing means provided in the gas discharge path of the first manifold 5b, 15b Opening / closing means provided in the gas discharge path of the second manifold 5c, 15c Opening / closing means provided in the gas discharge path of the manifold 6, 7, 16, 17 Gas flow path 8, 18 Membrane / electrode assembly ( EA)
9, 19 Separator

Claims (2)

A first manifold and a second manifold are provided, and each of the first and second manifolds includes a gas supply path having an opening / closing means at one end and a gas discharge path having an opening / closing means at the other end. A fuel cell stack characterized by that. A first manifold having a gas supply path; a gas supply path having an opening / closing means at one end; a second manifold having a gas discharge path having an opening / closing means at the other end; and a gas exhaust path having an opening / closing means. A fuel cell stack comprising a third manifold provided.

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