Patent Application
20110123888
The present invention relates to a fuel cell stack and a fuel cell using the same. More particularly, it relates to a structure for fastening a fuel cell stack and for controlling a temperature thereof.
Recently, with the rapid widespread of portable and cordless electronic devices, as driving power sources for such devices, small, secondary batteries with lightweight and large energy density 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. In addition, 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 includes a fuel cell stack including a cell stack, a fuel supplying section for supplying fuel to the cell stack, and an oxidizing agent supplying section for supplying an oxidizing agent. 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 an endplate on each of the both end sides in the laminating direction. In the cell stack, it is necessary to laminate the anode electrode, the cathode electrode and the electrolyte membrane onto each other tightly, which is not only for allowing an electrochemical reaction to be carried out uniformly. The end plate and the separator are provided with grooves for running the fuel and oxygen (air) as the oxidizing agent therein. Therefore, the anode electrode, the cathode electrode and the electrolyte membrane are laminated tightly in order to prevent fuel or oxygen from leaking out from a portion between the end plate or the separator and the anode electrode or the cathode electrode. In general, a cell stack is fastened as follows. Backing plates whose contact surface to the cell stack is larger than the cell stack are overlapped onto the both end sides of the laminated stack. Then, the entire periphery of protrusion of both backing plates is tightened by a plurality of pairs of a bolt and a nut. Thus, a cell stack is fastened.
Furthermore, in order to reduce the size of a fuel cell, a structure including a rectangular parallelepiped case with one surface opened into which a cell stack is inserted, and a pressing member for pressing the cell stack from one inner wall surface to the other inner wall surface facing each other has been proposed (see, for example, Patent Document 1).
However, when a cell stack is inserted into a rectangular parallelepiped case with one surface opened as mentioned above, a pressing member increases the size in the laminating direction of the cell stack. Therefore, in particular, it is not suitable for a portable fuel cell to be used in small electronic devices such as a notebook-sized personal computer. Furthermore, heat generated according to the electric generation builds up in the case. As a result, a temperature of the cell stack cannot be controlled easily.
Citation List
Patent Literature
PTL 1: Japanese Patent Unexamined Publication No. 2006-294366
The present invention relates to a fuel cell stack having a small occupied volume, uniformly fastening a membrane electrode assembly, or a membrane electrode assembly, a separator and an end plate, and being capable of sufficiently being cooled, as well as a fuel cell using the fuel cell stack.
The fuel cell stack of the present invention includes a membrane electrode assembly, a pair of end plates, and a first plate spring. The membrane electrode assembly and the end plates form 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 first plate spring tightens the membrane electrode assembly and the end plates in the laminating direction. The first plate spring includes two arm sections configured to press the end plates and a connecting section connecting the two arm sections so as to have a C-shaped cross-section. Space between the connecting section of the first plate spring and, the membrane electrode assembly and the end plates functions as a first cooling air flow passage. In this way, by fastening the unit cell of fuel cell using the first plate spring having a C-shaped cross-section, the fuel cell stack can be reduced in size as compared with the case where the fuel cell stack is fastened with bolts and nuts. Furthermore, the unit cell of fuel cell can be fastened uniformly in the planer direction of the membrane electrode assembly, as well as in the center portion. Furthermore, since the space between the connecting section of the first plate spring, and the membrane electrode assembly and the end plates can be used as a first cooling air flow passage, the unit cell of fuel cell can be cooled.
With this configuration, the occupied volume of the fuel cell stack as a whole can be reduced and the unit cell of fuel cell can be fastened uniformly. Furthermore, a temperature of the unit cell of fuel cell can be easily controlled.
Hereinafter, exemplary embodiments of the present invention are 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 embodiments mentioned below as long as it is based on the basic features described in the description.
The fuel cell includes fuel cell stack 1, fuel tank 4, fuel pump 5, air pump 6, controller 7, storage section 8, DC/DC converter 9, first air blower 10A, and second air blower 10B. Fuel cell stack 1 has an electric generation section, and outputs the generated electric power from positive-electrode terminal 2 and negative-electrode terminal 3. 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 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 supplying section that supplies fuel to anode electrode 31 in fuel cell stack 1. On the other hand, air pump 6 and controller 7 constitute an oxidizing agent supplying section for supplying an oxidizing agent to cathode electrode 32 in fuel cell stack 1.
Furthermore, controller 7 controls the operations of first air blower 10A and second air blower 10B. Note here that although not shown, DC/DC converter 9 supplies electric power to fuel pump 5, air pump 6, first air blower 10A and second air blower 10B. This electric power is generated in fuel cell stack 1 or supplied from storage section 8.
As shown in
As shown in
Anode electrode 31 includes diffusion layer 31A, microporous layer (MPL) 31B and catalyst layer 31C, which are laminated sequentially from the separator 34 side. 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. Positive-electrode terminal 2 is electrically connected to cathode electrode 32, and negative-electrode terminal 3 is electrically connected to anode electrode 31, respectively. Diffusion layers 31A and 32A are made of, for example, carbon paper, carbon felt, carbon cloth, and the like. MPL 31B and 32B are made of, for example, polytetrafluoroethylene, or a tetrafluoroethylene-hexafluoropropylene copolymer, and carbon. Catalyst layers 31C and 32C are formed a carbon, a catalyst such as platinum and ruthenium suitable for each electrode reaction highly diffused onto the surface of the carbon, and a binder. The binder bonds catalyst bodies of the carbon and the catalyst. Electrolyte membrane 33 is formed of an ion-exchange membrane for allowing a hydrogen ion to permeate, for example, a perfluorosulfonic acid-tetrafluoroethylene copolymer. End plates 17 and 18 and separator 34 are made of a carbon material or stainless steel, and are provided with grooves for supplying fuel and/or air to anode electrode 31 and/or cathode electrode 32.
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 the fuel cell. Gases such as nitrogen that do not react in cathode electrode 32 and unreacted oxygen are also exhausted to the outside of the fuel cell. Note here that since not all methanol in the aqueous solution at the anode electrode 31 side react, 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 as a conventional case, a pressing point is provided at the outside of the cell stack. 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.
As shown in
Specifically, when the length in the laminating direction of cell stack 16 is 19.1 mm, and the thickness of backing plates 14 and 15 is 1.5 mm, first plate spring 11 and second plate spring 12 are formed by using a spring steel material having a thickness of 0.5 mm. When the bend elastic modulus thereof is made to be 206,000 MPa, pressing power of 0.21 MPa in average can be applied to MEA 35. Furthermore, variation of pressure in the planer direction of MEA 35 is not more than 4%. In cell stack 16 having such a configuration, it is experimentally shown that when the pressuring power of MEA 35 is not less than 0.15 MPa, electric power generation property is not lowered. Therefore, when such first plate spring 11 and second plate spring 12 are used, a necessary pressing power can be secured.
Note here that as shown in
Furthermore, as shown in
Furthermore, as shown in
Space 20A is provided between connecting section 11C of first plate spring 11 and cell stack 16 including MEAs 35 and end plates 17 and 18. Space 20A can be used as an air passage for cooling cell stack 16. That is to say, space 20A is a first cooling air flow passage provided between connecting section 11C of first plate spring 11, and MEA 35 and end plates 17 and 18. Similarly, space 20B is a second cooling air flow passage provided between a connecting section of second plate spring 12, and MEA 35 and end plates 17 and 18. By using first air blower 10A and second air blower 10B shown in
Note here that as shown in
Furthermore, as shown in
Furthermore, it is preferable that wall parts 14C are provided on backing plates 14 and 15 at the inlet side of space 20A as the first cooling air flow passage. Wall parts 14C are respectively located at outer sides in the vertical direction, namely the laminating direction of cell stack 16, than the upper and lower outsides of arm sections 11B of first plate spring 11. Similarly, it is preferable that wall parts 14C are provided on backing plates 14 and 15 at the inlet side of space 20B as the second cooling air flow passage. Wall parts 14C are respectively located at outer sides in the vertical direction than the upper and lower outsides of the arm sections of second plate spring 12 in the laminating direction of cell stack 16. Thus, cooling air can be allowed to blow preferentially to the surface on which end plates 17 and 18 or separators 34 are exposed.
Note here that in the above description, cell stack 16 is formed by using a plurality of MEAs 35, disposing separators 34 between MAEs 35, disposing end plates 17 and 18 in the both sides in the laminating direction, and further disposing backing plates 14 and 15 on the outside of the end plates 17 and 18. However, the present invention is not necessarily limited to this configuration. A single MEA 35 may be sandwiched between end plates 17 and 18 from the both sides in the laminating direction of MEA 35, and MEA 35 and end plates 17 and 18 may be tightened in the laminating direction only by first plate spring 11. In this case, it is preferable that first plate spring 11 is formed so that it presses the vicinity of the center portion of end plates 17 and 18. Needless to say, in this configuration, second plate spring 12 may be used. Furthermore, in
However, when second plate spring 12 is used in addition to first plate spring 11, a unit cell of fuel cell or a cell stack can be fastened uniformly in the planer direction of MEA 35 reliably without considerably increasing the size of fuel cell stack 1. Furthermore, since space between the connecting section of second plate spring 12, and MEA 35 and end plates 17 and 18 is used as a second cooling air flow passage, the unit cell of fuel cell can be cooled from two surfaces facing each other.
Next, a configuration in which a first plate spring and a second plate spring having different shapes are used is described.
As shown in
With this configuration, sectional areas of space 20A and 20B can be increased when first plate spring 111 and second plate spring 112 are mounted on cell stack 101. At this time, the distance between first plate spring 111 and second plate spring 112 is not different from that between first plate spring 11 and second plate spring 12 in
Note here that, it is preferable that backing plates 14 and 15 are provided and that backing plates 14 and 15 are formed of a material that is different from that of end plates 17 and 18. Thus, backing plates 14 and 15 directly receiving a pressing power of first plate spring 11, and end plates 17 and 18 also functioning as a flow passage of fuel and an oxidizing agent can be optimized. For example, when backing plates 14 and 15 are formed of a material that is more rigid than that of end plates 17 and 18, it is possible to suppress the deformation of backing plates 14 and 15 due to pressing power of first plate spring 11. As a result, the unit cell of fuel cell or the cell stack can be fastened more uniformly in the planer direction of MEA 35. Furthermore, when backing plates 14 and 15 are formed of an electrically-insulating material, it is not necessary to consider the short circuit by arm section 11B of first plate spring 11.
Furthermore, when backing plates 14 and 15 are not used, an electrically-insulating layer is formed at the inner side of the C-shaped cross-section of first plate spring 11 (and second plate spring 12) so that short circuit due to first plate spring 11 does not occur. That is to say, backing plates 14 and 15 are not essential. When backing plates 14 and 15 are not used, it is preferable that end plates 17 and 18 are provide with protrusions corresponding to protrusions 14A and 15A and notch portions corresponding to notch portions 14B and 15B. Furthermore, it is preferable that tips 11A of arm sections 11B of first plate spring 11 (and second plate spring 12) are apart from end plates 17 and 18.
Furthermore, it is preferable that wall parts (corresponding to wall parts 14C) are provided on end plates 17 and 18 at the inlet side of space 20A as the first cooling air flow passage. The wall parts are respectively located at outer sides in the vertical direction, namely the laminating direction of cell stack 16, than the upper and lower outsides of arm sections 11B of first plate spring 11 in. Similarly, it is preferable that wall parts (corresponding to wall parts 14C) are provided on end plates 17 and 18 at the inlet side of space 20B as the second cooling air flow passage. The wall parts are located at outer sides in the vertical direction, namely the laminating direction of cell stack 16, than the upper and lower outsides of the arm sections of second plate spring 12. Thus, cooling air can be sent preferentially to the surface on which end plates 17 and 18 or separators 34 are exposed.
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.
In a fuel cell stack and a fuel cell using the fuel cell stack according to the present invention, a unit cell of fuel cell or a cell stack is fastened by a plate spring. With such a simple configuration, it is possible to form the fuel cell stack compactly, and it is possible to fasten a membrane electrode assembly, or a set of a membrane electrode assembly, a separator and end plates uniformly. Such a fuel cell stack and the fuel cell using the fuel cell stack are particularly useful as a power source of small electronic devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008189300 | Jul 2008 | JP | national |
This application is a 371 application of PCT/JP2009/003005 filed Jun. 30, 2009, which claims priority to JP2008/189300, the entire contents of which are incorporated hereby by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/003005 | 6/30/2009 | WO | 00 | 1/20/2011 |
