Patent Application
20110177418
The present invention relates to a fuel cell stack and a fuel cell system using the same. More particularly, it relates to a structure for supplying fuel and an oxidizing agent to a fuel cell stack.
Recently, with the rapid widespread of portable and cordless electronic devices, as driving power sources for such devices, small, lightweight and large energy density secondary batteries have been increasingly demanded. Furthermore, technology development has been accelerated in not only secondary batteries used for small consumer goods but also large secondary batteries for electric power storages and electric vehicles, which require long-time durability and safety. Furthermore, much attention has been paid to fuel cells enabling long-time continuous use with fuel supplied, rather than secondary batteries that need charging.
A fuel cell system includes a fuel cell stack including a cell stack, a fuel supply section for supplying fuel to the cell stack, and an oxidizing agent supply section for supplying an oxidizing agent to the cell stack. The cell stack is formed by laminating a membrane electrode assembly that includes an anode electrode, a cathode electrode, and an electrolyte membrane interposed between the anode and cathode electrodes, and a separator onto each other, and disposing end plates on the both end sides in the laminating direction.
In general, end plates and separators have holes penetrating in the thickness direction. When a cell stack is formed, the holes coincide with each other to form flow passages for fuel and an oxidizing agent. Then, the flow passages are connected to a fuel supply port and an oxidizing agent supply port provided on backing plates disposed outside the end plates (for example, Patent Document 1).
However, in this structure, in order to form flow passages for fuel and an oxidizing agent, it is necessary to laminate the end plates, the separators and the backing plates precisely. Furthermore, since it is necessary to increase the size of the end plate and separator by the size of the flow passage, the size of the cell stack is increased.
Meanwhile, a fuel cell stack, in which fuel and an oxidizing agent are supplied from a side surface parallel to the laminating direction, is proposed (for example, Patent Document 2). This fuel cell stack is formed by combining two unit cells to form a module and electrically connecting the modules. In each unit cell, a fuel supply port is provided on the side surface of the end plate at the anode side, and a through hole penetrating from the fuel supply port to a flow passage groove formed on the surface facing the anode electrode is provided. Thus, fuel can be supplied from the side surface parallel to the laminating direction, thus reducing the size of the fuel cell stack in the planer direction.
However, Patent Document 2 does not disclose a seal structure of a connection portion between a fuel supply port and a device such as a pump for supplying fuel to the fuel cell stack in detail. Since fuel such as methanol has toxicity, tight sealing is required. However, when the end plate is made to be thin, the size of the fuel supply port is also reduced. Therefore, it is difficult to carry out connection while a fuel leakage is prevented.
Furthermore, according to Patent Document 2, fuel supply ports of unit cells in the module are joined into one port, to which a fuel is supplied uniformly. However, in cells, there is variation in electromotive force or a pressure loss of the flow passage, it is preferable that a flow rate is controlled for every unit cell. On the contrary, it is not possible to control the fuel flow rate for every unit cell in the above-mentioned fuel supply method.
The present invention provides a fuel cell stack having a structure capable of being connected to a fuel pump reliably even in the case where a thin end plate and a separator are used and fuel is supplied from the side surface parallel to the laminating direction.
The fuel cell stack of the present invention includes a membrane electrode assembly, and a pair of end plates. The membrane electrode assembly and the end plates constitute a unit cell of fuel cell. The membrane electrode assembly is formed by laminating an anode electrode, a cathode electrode, and an electrolyte membrane interposed between the anode and cathode electrodes. The end plates are disposed so as to sandwich the membrane electrode assembly from both sides in the laminating direction of the membrane electrode assembly. The fuel cell stack has a first side surface and a second side surface which are parallel to the laminating direction. An anode side end plate has a first plane portion on the first side surface. The dimension in the laminating direction of the first plane portion is made to be larger than a thickness of the anode side end plate in a portion where the membrane electrode assembly is sandwiched. The first plane portion is provided with a first fuel inlet port for taking in fuel from the outside. The cathode side end plate has a first gas inlet port on the second side surface. The first gas inlet port is configured to take in a gas containing an oxidizing agent from the outside
In this fuel cell stack, the first fuel inlet port is provided on the first plane portion. Thereby, even in the case where thin end plates are used, the fuel cell stack can be connected to the fuel supply section (fuel pump) by carrying out reliable sealing with the use of the first plane portion. Thus, it is possible to prevent fuel from leaking. In this way, it is possible to secure the sealing in a connection portion that supplies fuel from the fuel supply section to the fuel cell stack.
Hereinafter, an exemplary embodiment of the present invention is described with reference to drawings in which a direct methanol fuel cell (DMFC) is taken as an example. Note here that the present invention is not limited to the embodiment mentioned below as long as it is based on the basic features described in the description.
The fuel cell system includes fuel cell stack 1, fuel tank 4, fuel pump 5, air pump 6, controller 7, storage section 8, and DC/DC converter 9. Fuel cell stack 1 has an electricity generation section. The generated electric power is output from anode terminal 3 of the negative electrode and cathode terminal 2 of the positive electrode. The output electric power is input into DC/DC converter 9. Fuel pump 5 supplies fuel in fuel tank 4 to anode electrode 31 of fuel cell stack 1. Air pump 6 supplies air as an oxidizing agent to cathode electrode 32 of fuel cell stack 1. Controller 7 controls the driving of fuel pump 5 and air pump 6, and controls DC/DC converter 9 so as to control the output to the outside and the charge and discharge to storage section 8. Fuel tank 4, fuel pump 5 and controller 7 constitute a fuel supply section that supplies fuel to anode electrode 31 in fuel cell stack 1. On the other hand, air pump 6 and controller 7 constitute a gas supply section that supplies a gas containing oxygen as an oxidizing agent to cathode electrode 32 in fuel cell stack 1.
As shown in
As shown in
Anode electrode 31 includes diffusion layer 31A, microporous layer (MPL) 31B and catalyst layer 31C, which are laminated from the separator 34 side in this order. Cathode electrode 32 also includes diffusion layer 32A, microporous layer (MPL) 32B and catalyst layer 32C, which are laminated sequentially from the separator 34 side. Anode terminal 3 is electrically connected to anode electrode 31 and cathode terminal 2 is electrically connected to cathode electrode 32, respectively. Diffusion layers 31A and 32A are made of, for example, carbon paper, carbon felt, carbon cloth, and the like. MPLs 31B and 32B are made of, for example, polytetrafluoroethylene or a tetrafluoroethylene-hexafluoropropylene copolymer, and carbon. Catalyst layers 31C and 32C are formed by highly diffusing a catalyst such as platinum and ruthenium suitable for each electrode reaction onto a carbon surface and by binding those catalysts with a binder. Electrolyte membrane 33 is formed of an ion-exchange membrane which allows a hydrogen ion to permeate itself, for example, a perfluorosulfonic acid-tetrafluoroethylene copolymer.
End plates 17 and 18 and separator 34 are made of a carbon material or stainless steel. As shown in
As shown in
Note here that the opposite side to fuel inlet port 341 of fuel flow passage groove 34B communicates with fuel outlet port (second fuel outlet port) 342 for exhausting at least any of reaction product of the fuel and reaction residue of the fuel as shown in
Note here that fuel flow passage groove 17B is also provided on anode side end plate 17 facing anode electrode 31, and air flow passage groove 18D for feeding air is also provided at the cathode side end plate 18 facing cathode electrode 32. Fuel flow passage groove 17B is formed in the same shape as that of fuel flow passage groove 34B, and air flow passage groove 18D is formed in the same shape as that of air flow passage groove 34D. Furthermore, plane portion (first plane portion) 17A provided with fuel inlet port (first fuel inlet port) 171 is formed on end plate 17, and fuel flow passage groove 17B communicates with fuel inlet port 171 via through hole 17C. Gas inlet port (first gas inlet port) 181 for taking in air from the outside is provided on the second side surface parallel to the laminating direction of cell stack 16.
Backing plate 14 is disposed at the anode electrode 31 side in cell stack 16, and backing plate 15 is disposed at the cathode electrode 32 side. Backing plates 14 and 15 are made of insulating resin, ceramic, resin containing a glass fiber, a metal plate coated with an electrically-insulating membrane, or the like.
First plate spring 11 and second plate spring 12 tighten cell stack 16 with the spring elastic force thereof via backing plates 14 and 15. Second plate spring 12 is disposed so as to face first plate spring 11. First plate spring 11 and second plate spring 12 are made of, for example, a spring steel material.
Next, an operation in fuel cell stack 1 is briefly described. As shown in
On the other hand, oxygen contained in the air supplied to cathode electrode 32 is diffused in diffusion layer 32A to the entire surface of MPL 32B. The oxygen further passes through MPL 32B and reaches catalyst layer 32C. Methanol that reaches catalyst layer 31C reacts as in formula (1), and oxygen that reaches catalyst layer 32C reacts as in formula (2).
CH3OH+H2O→CO2+6H++6e− (1)
3/2O2+6H++6e−→3H2O (2)
As a result, electric power is generated, as well as carbon dioxide is generated at the anode electrode 31 side and water is generated at the cathode electrode 32 side as reaction products, respectively. Carbon dioxide is exhausted to the outside of fuel cell stack 1. Gases such as nitrogen that do not react in cathode electrode 32 and unreacted oxygen are also exhausted to the outside of fuel cell stack 1. Note here that since not all methanol in the aqueous solution react at the anode electrode 31 side, the exhausted aqueous solution is generally allowed to return to fuel pump 5 as shown in
In the exemplary embodiment, cell stack 16 is fastened by first plate spring 11 and second plate spring 12 via backing plates 14 and 15. First plate spring 11 and second plate spring 12 fasten cell stack 16 extremely compactly along the outer shape of cell stack 16 as shown in
Furthermore, in a case in which a cell stack is fastened by using bolts and nuts, a pressing point is provided at the outside (in the vicinity of the outer periphery) of cell stack 16. However, first plate spring 11 and second plate spring 12 have a pressing point in a relatively central portion in cell stack 16. Therefore, pressing power is operated in cell stack 16 uniformly in the planar direction of backing plates 14 and 15. With such a pressing power, entire cell stack 16 can be fastened uniformly. Thus, the electrochemical reactions expressed by the formulae (1) and (2) proceed uniformly in the planar direction of MEA 35. As a result, current-voltage characteristics of fuel cell stack 1 are improved.
Next, the connection between fuel cell stack 1 and fuel pump 5 is described with reference to
As shown in
With this structure, even if thin end plate 17 and separator 34 are used, the fuel cell stack can be connected to fuel pump 5 with securely sealing by the use of plane portions 17A and 34A. This makes it possible to prevent fuel from leaking at the connection portion.
Note here that as shown in
In
Furthermore, it is further preferable that plane portion 17A and plane portion 34A or plane portions 34A are provided on the same plane. By providing plane portion 17A and plane portion 34A on the same plane in which they are displaced from each other in the direction perpendicular to the laminating direction, fuel discharging sections 51A and 51B may be provided on the same plane. Thus, in fuel pump 5, when fuel discharging sections 51A and 51B are formed on the same plane, they can be sealed with respect to plane portions 17A and 34A, reliably.
Furthermore, it is preferable that fuel pump 5 is capable of individually controlling the flow rates of fuel discharged from fuel discharging sections 51A and 51B, respectively. By using such a fuel pump 5, it is possible to supply fuel at an optimum flow rate to each unit cell. In a unit cell, since there is a variation in the electromotive force and/or the pressure loss of flow passage, it is preferable that the flow rate of the fuel is controlled for each unit cell.
Next, the connection between fuel cell stack 1 and air pump 6 is described with reference to
Air pump 6 constituting a gas supply section has gas discharging section 6A as shown in
On the other hand, seal member (third seal member) 62 is attached to the second side surface provided with gas inlet ports 181 and 343 and fuel outlet ports 172 and 342 of cell stack 16 as shown in
Integrated member 61 is attached to fuel cell stack 1 with seal member 62 sandwiched therebetween by screwing screws 65 into screw holes 67 provided on backing plates 14 and 15. In this state, seal member 62 separates gas inlet ports 181 and 343 from fuel outlet ports 172 and 342. Furthermore, seal member 62 connects gas discharging section 73 with gas inlet ports 181 and 343. Therefore, air sent from air pump 6 is supplied to gas inlet ports 181 and 343. Furthermore, seal member 62 connects receiver section 74 with fuel outlet ports 172 and 342.
By using integrated member 61 and seal member 62 in this way, an air introducing passage and a fuel side exhaust passage can be formed in compact in size on the second side surface. As a result, a fuel cell system can be miniaturized.
In the above description, a configuration in which fuel inlet ports 171 and 341 are provided on the first side surface of fuel cell stack 1 and gas inlet ports 181 and 343 are provided on the second side surface is described. However, the present invention is not limited to this configuration. Fuel inlet ports 171 and 341 and gas inlet ports 181 and 343 may be formed on the same side surface. For example, in the case where an elongated fuel cell stack is used, fuel inlet ports 171 and 341 and gas inlet ports 181 and 343 can be provided on one surface. Also in this case, when plane portions 17A and 34A are provided, fuel can be prevented from leaking.
Furthermore, a configuration is described in which a plurality of MEAs 35 are laminated with separator 34 disposed between MEAs 35, end plates 17 and 18 are disposed on both sides in the laminating direction so as to form cell stack 16, and backing plates 14 and 15 are further disposed on the outside end plates 17 and 18. However, the present invention is not limited to this configuration. A single MEA 35 may be sandwiched by end plates 17 and 18 from the both sides in the laminating direction, and MEA 35 and end plates 17 and 18 may be fastened in the laminating direction by only first plate spring 11. In this case, it is preferable that first plate spring 11 is arranged so as to press the vicinity of the center part of end plates 17 and 18. Needless to say, in this configuration, second plate spring 12 may further be used. Furthermore, in
Furthermore, without using backing plates 14 and 15, end plates 17 and 18 may be directly sandwiched by first plate spring 11 (and second plate spring 12). In this case, an insulating film is formed inside the C-shaped cross section of first plate spring 11 (and second plate spring 12) so that first plate spring 11 does not cause short circuit. Furthermore, fastening section (for example, screw hole 67) to fuel pump 5 and integrated member 61 are provided on end plates 17 and 18. That is to say, backing plates 14 and 15 are not essential.
However, it is preferable that backing plates 14 and 15 are provided and that backing plates 14 and 15 are formed of different materials from those of end plates 17 and 18. Thus, it is possible to optimize backing plates 14 and 15 that directly receive a pressing force of first plate spring 11 and end plates 17 and 18 that also function as flow passages of fuels and air. For example, by adding backing plates 14 and 15 to end plates 17 and 18, it is possible to suppress the deformation of backing plates 14 and 15 due to the pressing force of first plate spring 11. As a result, a unit cell of fuel cell or a cell stack can be fastened more uniformly in the planner direction of MEA 35. Furthermore, since backing plates 14 and 15 are formed of an insulating material, it is not necessary to consider short circuit due to arm sections of first plate spring 11.
Note here that in this exemplary embodiment, cell stack 16 is fastened by using first plate spring 11 and second plate spring 12, and fuel and air are supplied from the side surfaces that are opposite each other and are not fastened by first plate spring 11 and second plate spring 12. However, the present invention is not limited to this configuration. When second plate spring 12 is not used, a side surface, which is covered with second plate spring 12 in this exemplary embodiment, may be used for supplying fuel and air. Furthermore, when a pair of backing plates are fastened by, for example, a bolt, without using first plate spring 11 and second plate spring 12, any side surfaces may be used for supplying fuel and air.
In the exemplary embodiment, DMFC is described as an example. However, the configuration of the present invention can be applied to any fuel cells using a power generation element that is the same as cell stack 16. For example, it may be applied to a so-called polymer solid electrolyte fuel cell and a methanol modified fuel cell, which use hydrogen as fuel.
A fuel cell stack of the present invention is provided with plane portions on end plates and separators and these plane portions are disposed on the stack side surface. Furthermore, a fuel inlet port is provided on each of the plane portions. Then, in a fuel cell system of the present invention, a fuel discharging section of a fuel pump and a fuel inlet port are connected water-tightly to each other by using the plane portions. Thus, fuel can be prevented from leaking. Such a fuel cell stack and the fuel cell system using the fuel cell stack are particularly useful as a power source of small electronic devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-203982 | Aug 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/003735 | 8/5/2009 | WO | 00 | 2/4/2011 |
