Patent Application
20100143808
The present invention relates to a fuel cell, and in particular to a fuel cell improvement that enables reductions in the size and weight of the fuel cell, and a lower heat capacity.
As shown in
The mechanism for electric power generation by a solid polymer fuel cell generally involves the supply of a fuel gas such as a hydrogen-containing gas to the fuel electrode (the anode side electrode) 50, and supply of an oxidizing gas such as a gas comprising mainly oxygen (O2) or air to the air electrode (the cathode side electrode) 54. The hydrogen-containing gas is supplied to the fuel electrode 50 through fuel gas passages, and the action of the electrode catalyst causes the hydrogen to dissociate into electrons and hydrogen ions (H+). The electrons flow through an external circuit from the fuel electrode 50 to the air electrode 54, thereby generating an electrical current. Meanwhile, the hydrogen ions (H+) pass through the electrolyte membrane 52 to the air electrode 54, and bond with oxygen and the electrons that have passed through the external circuit, thereby generating reaction water (H2O). The heat that is generated at the same time as the bonding reaction between hydrogen (H2), oxygen (O2) and the electrons is recovered using cooling water. Furthermore, the water generated at the air electrode 54 on the cathode side of the assembly (hereafter referred to as “generated water”) is discharged from the cathode side.
Furthermore, in a conventional fuel cell, a single cell and other adjacent cells are partitioned, for example, using separators 60 having a thickness of 100 μm, and this enables the reaction gases to be supplied and diffused individually for each cell, while cooling water is passed through the separators 60 partitioning each of the cells, thereby maintaining the fuel cell at an appropriate temperature and enabling stable electric power generation to be achieved.
For example, Patent Document 1 discloses a fuel cell in which, in order to improve the cooling efficiency, a coolant passage is formed by sandwiching a porous metal material between a pair of plates.
Patent Document 1: JP 2006-286557 A
However, as described above, because conventional separators typically have a thickness of approximately 100 μm, the thickness of a fuel cell prepared by stacking a plurality of cells tends to increase. In contrast, in recent years there have been considerable demands for reductions in the size and weight of fuel cells.
The present invention has been developed in light of the issues described above, and provides a fuel cell that enables reductions in the size and weight of the fuel cell, and a lower heat capacity.
In order to achieve such a fuel cell, the fuel cell of the present invention has the features described below.
(1) A fuel cell comprising a plurality of stacked cells each comprising a membrane electrode assembly having a fuel electrode disposed on one surface of an electrolyte membrane and an air electrode disposed on the other surface, and a pair of metal films that sandwich the membrane electrode assembly therebetween, wherein the fuel cell comprises a porous fuel gas passage comprising a porous metal that is provided between the membrane electrode assembly and one of the metal films and allows passage of a fuel gas, a porous oxidizing gas passage comprising a porous metal that is provided between the membrane electrode assembly and one of the metal films and allows passage of an oxidizing gas, and a porous coolant passage comprising a porous metal that is provided between one cell and another cell, between the metal films, and allows passage of a coolant, and wherein the respective outer dimensions of the porous fuel gas passage and the porous oxidizing gas passage are smaller than the outer dimensions of the metal films.
Because a thin metal film that is thinner than a typical separator is used to partition the reaction gas passages and the coolant passage, the thickness of the cell itself can be reduced, and the weight of the cell can also be lightened. Accordingly, a fuel cell assembled by stacking a plurality of cells can also be reduced in size and weight. Furthermore, by using a metal film that is thinner than a conventional separator, heat conduction and the heat radiating effect are enhanced, meaning a lower heat capacity can be achieved. Moreover, by making the outer dimensions of the reaction gas passages formed from the porous metals smaller than the outer dimensions of the metal films, an appropriate seal width for ensuring gastight sealing of the reaction gas passages can be provided.
(2) The fuel cell disclosed in (1) above, wherein the porous oxidizing gas passage and the porous coolant passage of one cell, and the porous fuel gas passage of another cell are formed as a single integrated assembly with the metal films disposed therebetween.
By forming a three-layer integrated assembly in which the porous oxidizing gas passage and the porous coolant passage of one cell, and the porous fuel gas passage of another cell are integrated into a single assembly with the metal films disposed therebetween, a fuel cell can be subsequently assembled with ease by simply sequentially stacking the three-layer integrated assemblies and the membrane electrode assemblies.
(3) The fuel cell disclosed in (1) or (2) above, wherein the membrane electrode assembly is a seal-integrated type membrane electrode assembly in which a sealing member is molded around the periphery of the membrane electrode assembly as an integral part of the assembly, and the fuel cell is formed by joining the seal-integrated type membrane electrode assembly to an integrated assembly comprising the porous oxidizing gas passage and the porous coolant passage of one cell and the porous fuel gas passage of another cell with the metal films disposed therebetween.
By employing a seal-integrated type membrane electrode assembly, thermocompression bonding or the like can be used to assemble a fuel cell with ease by sequentially stacking the three-layer integrated assemblies and the membrane electrode assemblies.
(4) The fuel cell disclosed in any one of (1) to (3) above, wherein the spacing between contact points between the porous metal of the porous coolant passage and the metal films is not more than 0.5 mm.
By employing the above contact point spacing, the shape of the metal films can be maintained, ensuring favorable strength as a separator.
(5) The fuel cell disclosed in any one of (1) to (3) above, wherein the porous metal is a lath cut metal or an expanded metal.
(6) The fuel cell disclosed in any one of (1) to (5) above, wherein the thickness of the metal films is not less than 10 μm and not more than 50 μm.
Because the thickness of the metal film is one half or less of the thickness of a conventional separator of thickness 100 μm, the thickness of the cell itself can be reduced, and the weight can also be lightened. Accordingly, a fuel cell assembled by stacking a plurality of cells can also be reduced in size and weight.
(7) A fuel cell comprising an anode-side outer frame plate in which is formed a manifold for fluids associated with the fuel cell, a porous fuel gas passage comprising a porous metal that is positioned within the anode-side outer frame plate and allows passage of a fuel gas, an intermediate outer frame plate in which is formed a manifold for fluids associated with the fuel cell, a porous coolant passage comprising a porous metal that is positioned within the intermediate outer frame plate and allows passage of a coolant, a cathode-side outer frame plate in which is formed a manifold for fluids associated with the fuel cell, a porous oxidizing gas passage comprising a porous metal that is positioned within the cathode-side outer frame plate and allows passage of an oxidizing gas, and metal films that partition the porous fuel gas passage from the porous coolant passage and the porous oxidizing gas passage from the porous coolant passage respectively, wherein the respective outer dimensions of the porous fuel gas passage and the porous oxidizing gas passage are smaller than the outer dimensions of the metal films, and the passages and the metal films are formed as a single integrated assembly in a sequence of porous oxidizing gas passage, metal film, porous coolant passage, metal film and porous fuel gas passage, or a sequence of porous fuel gas passage, metal film, porous coolant passage, metal film and porous oxidizing gas passage.
By positioning the porous coolant passage within the electric power generation region of the intermediate outer frame plate, positioning the porous fuel gas passage and the porous oxidizing gas passage within the electric power generation regions of the anode-side outer frame plate and the cathode-side outer frame plate respectively, and making the outer dimensions of the reaction gas passages comprising porous metal smaller than the outer dimensions of the metal films, thereby ensuring an appropriate seal width for ensuring gastight sealing of the reaction gas passages, a three-layer integrated assembly can be formed that has a manifold, and is composed of the porous oxidizing gas passage, the porous coolant passage and the porous fuel gas passage integrated together with the metal films disposed therebetween. Further, because metal films that are considerably thinner than conventional separators are used to partition the reaction gas passages and the coolant passage, the thickness of the cell itself can be reduced, and the weight can also be lightened. Accordingly, a fuel cell assembled by stacking a plurality of cells can also be reduced in size and weight. Furthermore, by using a metal film that is thinner than a conventional separator, heat conduction and the heat radiating effect are enhanced, meaning a lower heat capacity can be achieved.
(8) The fuel cell disclosed in (7) above, formed as an integrated assembly by stacking either the porous oxidizing gas passage, the metal film, the porous coolant passage, the metal film and the porous fuel gas passage in sequence, or the porous fuel gas passage, the metal film, the porous coolant passage, the metal film and the porous oxidizing gas passage in sequence on a membrane electrode assembly having a fuel electrode disposed on one surface of an electrolyte membrane and an air electrode disposed on the other surface.
A five-layer integrated assembly can be formed by integrated stacking of an aforementioned three-layer integrated assembly on each surface of the membrane electrode assembly.
(9) The fuel cell disclosed in (7) or (8) above, wherein the spacing between contact points between the porous metal of the porous coolant passage and the metal films is not more than 0.5 mm.
By employing the above contact point spacing, the shape of the metal films can be maintained, ensuring favorable strength as a separator.
(10) The fuel cell disclosed in any one of (7) to (9) above, wherein the porous metal is a lath cut metal or an expanded metal.
(11) The fuel cell disclosed in any one of (7) to (10) above, wherein the thickness of the metal films is not less than 10 μm and not more than 50 μm.
Because the thickness of the metal film is one half or less of the thickness of a conventional separator of thickness 100 μm, the thickness of the cell itself can be reduced, and the weight can also be lightened. Accordingly, a fuel cell assembled by stacking a plurality of cells can also be reduced in size and weight.
(12) The fuel cell disclosed in any one of (7) to (11) above, wherein the anode-side outer frame plate, the intermediate outer frame plate and the cathode-side outer frame plate are formed from resin, the membrane electrode assembly is a seal-integrated type membrane electrode assembly in which a sealing member is molded around the periphery of the membrane electrode assembly as an integral part of the assembly, and either pressing or heat pressing of the anode-side outer frame plate, the intermediate outer frame plate, the cathode-side outer frame plate and the seal-integrated type membrane electrode assembly is used to prepare an integrated assembly having either a stacked sequence of porous oxidizing gas passage, metal film, porous coolant passage, metal film, porous fuel gas passage, seal-integrated type membrane electrode assembly, porous oxidizing gas passage, metal film, porous coolant passage, metal film and porous fuel gas passage, or a stacked sequence of porous fuel gas passage, metal film, porous coolant passage, metal film, porous oxidizing gas passage, seal-integrated type membrane electrode assembly, porous fuel gas passage, metal film, porous coolant passage, metal film and porous oxidizing gas passage.
By employing a seal-integrated type membrane electrode assembly, thermocompression bonding or the like can be used to assemble a fuel cell with ease by sequentially stacking the aforementioned porous oxidizing gas passage, metal film, porous coolant passage, metal film, porous fuel gas passage and membrane electrode assembly.
(13) The fuel cell disclosed in (12) above, wherein a metal foil is disposed between the seal-integrated type membrane electrode assembly and the anode-side outer frame plate, and between the seal-integrated type membrane electrode assembly and the cathode-side outer frame plate.
In those cases where the anode-side outer frame plate, the intermediate outer frame plate and the cathode-side outer frame plate are formed of resin, there is a difference in the linear coefficients of expansion of the resin plates and the metal films, and therefore when the fuel cell heats up during electric power generation, there is a possibility that warping may occur. However, by inserting a metal foil between the resin plates and the seal-integrated type membrane electrode assembly, heat expansion can be alleviated, enabling warping to be better controlled.
The present invention is able to provide a small and lightweight fuel cell having a low heat capacity.
Embodiments of the present invention are described below with reference to the drawings.
A fuel cell of this embodiment comprises a plurality of stacked cells each comprising a membrane electrode assembly having a fuel electrode disposed on one surface of an electrolyte membrane and an air electrode disposed on the other surface, and a pair of metal films that sandwich the membrane electrode assembly therebetween, wherein the fuel cell comprises a porous fuel gas passage comprising a porous metal that is provided between the membrane electrode assembly and one of the metal films and allows passage of a fuel gas, a porous oxidizing gas passage comprising a porous metal that is provided between the membrane electrode assembly and one of the metal films and allows passage of an oxidizing gas, and a porous coolant passage comprising a porous metal that is provided between one cell and another cell, between the metal films, and allows passage of a coolant, and wherein the respective outer dimensions of the porous fuel gas passage and the porous oxidizing gas passage are smaller than the outer dimensions of the metal films.
In a more detailed description, as shown in
In a fuel cell 100 of this embodiment, in a similar manner to that shown in
Furthermore, in a similar manner to that shown in
Moreover, as shown in
As shown in
The seal width L may be selected appropriately in accordance with the size of the cell, and by ensuring a width of approximately mm, the reaction gas passages can be sealed in a gastight manner, and the three-layer integrated assembly described above can be formed.
Moreover, in this embodiment, a seal-integrated type membrane electrode assembly 38 is used in which the sealing member is molded as an integral part of the assembly around the periphery of a membrane electrode assembly 28 having a fuel electrode disposed on one surface of an electrolyte membrane and an air electrode disposed on the other surface. As a result, by applying pressure via a gasket 39, compression bonding can be used to simply and sequentially assemble the three-layer integrated assembly described above and the membrane electrode assembly.
Further, the metal films 20 described above may be formed of titanium, stainless steel or aluminum or the like, and the metal film surface may be coated with a conductive plating if required. Furthermore, if due consideration is given to the shape retention properties required for favorable function as a separator, then the thickness of the metal films 20 is typically not less than 10 μm and not more than 50 μm, and in terms of achieving both favorable strength for the metal films and a reduction in the weight of the fuel cell, a thickness of 25 μm is preferred.
In the fuel cell 100 of the present embodiment, the spacing between the contact points between the porous metal 30b of the porous coolant passage 26 and the metal films 20 is not more than 0.5 mm. This ensures that the shape of the metal films 20 is retained, thereby providing adequate strength for the films to function as separators.
The porous metals 30a, 30b and 30c may use a lath cut metal or an expanded metal.
In the present embodiment, the term “lath cut metal” describes a flat thin metal sheet in which sequential zigzag cuts have been formed in the sheet, and these cuts have then been pushed and bent so as to form a network of narrow diameter through holes in the metal. The term “expanded metal” describes a flat thin metal sheet in which sequential zigzag cuts have been formed in the sheet, these cuts have then been pushed and bent so as to form a network of narrow diameter through holes in the metal, and the metal sheet has then be rolled to form a substantially flat sheet. Because an expanded metal sheet is molded as a substantially flat sheet, additional process steps for removing unnecessary bends or irregularities in the final molded product need not be conducted, meaning the production costs can be reduced.
The structure of a fuel cell 110 according to a second embodiment is described below with reference to
In the first embodiment, the anode-side outer frame plate 34, the intermediate outer frame plate 10 and the cathode-side outer frame plate 32 may be formed of either metal or resin, but in this embodiment, the anode-side outer frame plate 34, the intermediate outer frame plate 10 and the cathode-side outer frame plate 32 shown in
Further, by forming the above plates from resin, the plates can be made smaller and lighter than those cases where the plates are formed from metal members. Furthermore, by forming the manifold portions from resin, that is, by forming the non-power generation regions from resin, the thermal conductivity can be lowered compared to the case of a metal material. As a result, in the electric power generation region, heat radiation can be proactively promoted by the metal films 20, whereas heat radiation can be suppressed in the non-power generation region, which means that, for example, the rate at which the electrode temperature rises upon startup in sub-zero temperatures can be accelerated.
Examples of resins that may be used for forming the anode-side outer frame plate 34, the intermediate outer frame plate 10 and the cathode-side outer frame plate 32 include thermosetting silicon-based resins and thermoplastic resins.
In the second embodiment, a seal-integrated type membrane electrode assembly 38 similar to the first embodiment may be used in which the sealing member is molded as an integral part of the assembly around the periphery of the membrane electrode assembly 28 having a fuel electrode disposed on one surface of the electrolyte membrane and an air electrode disposed on the other surface. As a result, by applying pressure via the gasket 39 or the like, compression bonding can be used to simply and sequentially assemble the three-layer integrated assembly described above and the membrane electrode assembly. Here, as shown in
The structure of a fuel cell according to a third embodiment of the present invention is also illustrated in the drawings, and differs from the fuel cell of the first embodiment in that the porous metals that form the porous passages are formed so as to partially extend out to the manifold. In other words, in this embodiment, as shown in
Accordingly, as illustrated in
Using the structure shown in
Using the structure shown in
Using the structure shown in
Using the structure shown in
The fuel cells of examples 1 to 3 occupied volumes that were smaller than that of the fuel cell of the comparative example by 35%, 25% and 20% respectively. Furthermore, the weight of the fuel cells was also able to be reduced by 40%, 35% and 35% respectively.
Although a detailed description of the present invention is presented above, the scope of the present invention is not limited by the preceding description.
Furthermore, the detailed description, claims, drawings and abstract for an invention disclosed in Japanese Patent Application No. 2007-158542, filed Jun. 15, 2007, are also incorporated in their entirety within the present application.
The fuel cell of the present invention is effective in any application that requires the use of a fuel cell, and is ideal for vehicle-mounted fuel cell applications.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007 158542 | Jun 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/061172 | 7/12/2008 | WO | 00 | 11/2/2009 |
