Patent Application
20050244699
The present invention relates to a fuel cell with a membrane electrode assembly that includes an electrolyte membrane and porous electrodes respectively located on both sides of the electrolyte membrane; the membrane electrode assembly being sandwiched by an anode side separator positioned on one surface thereof and a cathode side separator positioned on the other surface thereof.
Japanese Unexamined Patent Publication No. 2001-319667 discloses a structure of a fuel cell, in which a solid polymer electrolyte membrane of a membrane electrode assembly is formed to have its outer peripheral portion projected out relative to a periphery of the porous electrodes, and a fluid sealant is used to fill a gap between the outer peripheral portion of the solid polymer electrolyte membrane and separators which sandwich the membrane electrode assembly.
Each of Japanese Unexamined Patent Publications 10-50332, 2002-42838, 2002-93434, and 2001-155745 discloses a structure of an outer peripheral separator-sandwiched portion of a solid polymer electrolyte membrane, as well as a seal member and a gasket provided around porous electrodes, for avoiding gas leakage from a peripheral portion of a membrane electrode assembly.
In a fuel cell, a pair of separators are arranged to sandwich a membrane electrode assembly therebetween. Each of the separators is formed to have a gas flow path having a channel-shape in section on its surface opposite to one of porous electrodes of the membrane electrode assembly. The gas flow path is mainly classified into, largely due to the shape thereof, a serpentine flow path that is a continuous flow path having many winding portions, and an interdigitated flow path that includes a main flow path and a plurality of branch flow paths branching from the main flow path. In the serpentine flow path, as a reaction gas supplied thereto flows through the winding portions thereof, the reaction gas seeps out the winding portions, passes through parts of the porous electrode close to the winding portions, and short-circuits between the winding portions of the gas flow path on a reaction surface of the porous electrode. As a result, the reaction gas is not evenly supplied to the entire reaction surface of the porous electrode and the reaction surface thereof cannot be used efficiently. Also in the interdigitated flow path, a reaction gas passes through part of the porous electrode, thereby preventing efficient use of the reaction surface thereof.
The present invention was made in the light of the above problems. An object of the present invention is to provide a fuel cell which evenly supplies a reaction gas to the entire reaction surface of a porous electrode thereof, thus using the reaction surface thereof efficiently.
An aspect of the present invention is a fuel cell comprising: a membrane electrode assembly comprising an electrolyte membrane and a pair of porous electrodes provided on both sides of the electrolyte membrane; and first and second separators sandwiching the membrane electrode assembly, each of the first and second separators being formed to have, on its surface opposite to the membrane electrode assembly, a gas flow path and a rib defining the gas flow path, wherein the rib of at least one of the first and second separators is provided with a projection for pressing the porous electrode.
The invention will now be described with reference to the accompanying drawings wherein:
Embodiments of the present invention will be explained below with reference to the drawings, wherein like members are designated by like reference characters.
As shown in
At the peripheries of the porous electrodes 3, 5, annular gaskets 13, 15 are provided, each being interposed between one of the separators 9, 11 and the solid polymer electrolyte membrane 1, thereby sealing a reaction gas therein such as a fuel gas containing hydrogen, or an oxidant gas containing oxygen.
The solid polymer electrolyte membrane 1 is formed as a proton exchange membrane made of a solid polymer material such as fluorine family resin. Two porous electrodes 3, 5 located on both surfaces of the membrane 1 are constituted of carbon cloth or carbon paper containing a catalyst made of platinum, or platinum and an other metal, and are positioned such that the surfaces thereof containing the catalyst come into contact with the solid polymer electrolyte membrane 1.
Each of the separators 9, 11 is made of dense carbon material or metal material inpenetratable to gas, where an anode side gas flow path 17 for the fuel gas and a cathode side gas flow path 19 for the oxidant gas are respectively formed on the surface of each separator opposite to the membrane electrode assembly 7. As a result of forming the gas flow paths 17, 19 in each of the separators 9, 11, a rib 21 is formed between a pair of gas flow paths 17 and a rib 23 is formed between a pair of gas flow paths 19.
Each of the separators 9, 11 is also formed to have a cooling water flow path, not illustrated, on a surface thereof opposite to the surface where the gas flow path 17, 19 is formed. In the cathode side separator 11, another cooling water path is provided for removing heat generated by cathode reaction in the fuel cell.
The fuel cell mentioned above is used in a stack structure which is formed by stacking a plurality of cells together. Each of cells is constituted of a membrane electrode assembly 7 and a pair of the separators 9, 11 located on both the surfaces thereof. The cooling water flow path mentioned above is not necessarily provided for each cell. However, if more heat needs to be removed from the fuel cell due to an increased output thereof, it is preferable to provide as many cooling water flow paths as possible.
In the fuel cell having the stack structure mentioned above, the fuel gas and the oxidant gas are supplied from respective gas inlets of the fuel cell, distributed to the respective cells thereof, and discharged from respective gas outlets thereof to the outside.
In the first embodiment, as shown in
As described above, since the projection 25 is disposed on the rib 21 of the anode side separator 9, when the membrane electrode assembly 7 is sandwiched by the separators 9, 11, the portion of the porous electrode 3 where the projection 25 comes into contact with, is compressed with an increasing local stress thereupon until it becomes crushed. As a result, resistance for the fuel gas to pass through the compressed portion of the porous electrode 3 increases.
Accordingly, when such a projection 25 is provided on the rib 21 at a location where the fuel gas tends to short-circuit between a pair of the gas flow paths 17 across the rib 21, the fuel gas supplied is guided to flow along the gas flow path 17, whereby the fuel gas is evenly distributed to the reaction surface of the porous electrode 3. Therefore, the reaction surface thereof can be efficiently used, thereby improving performance and fuel economy of the fuel cell.
The provision of the projection 25 on the rib 21 also improves contact condition between the anode side separator 9 and the porous electrode 3, reducing contact resistance therebetween, as well as preventing the relative slide shifting between the anode side separator 9 and the porous electrode 3 in the surface direction thereof.
In the first embodiment mentioned above, the height (h1) of the projection 25 on the rib 21 is set as 0.1 mm, and the width (w1) thereof is set as 0.5 mm. Provision of the projection in such size on the rib, as compared with the related art, effectively reduces gas diffusion inside the porous electrode, thereby reducing an amount of the short-circuited gas.
In the second embodiment, since the projection 27 is disposed on the rib 23 of the cathode side separator 11, when the membrane electrode assembly 7 is sandwiched by the separators 9 and 11, the portion of the porous electrode 5 where the projection 27 on the rib 23 comes into contact with, is compressed with increasing local stress thereupon until it becomes crushed. As a result, it prevents the oxidant gas in a gas flow path 19 from diffusing in the compressed portion of the porous electrode 5, thereby promoting flow of the oxidant gas along the gas flow path 19. Accordingly, the second embodiment can obtain the same effect as in the first embodiment.
In the first and second embodiments, the projection 25 or 27 is disposed on either the rib 21 of the anode side separator 9 or the rib 23 of the cathode side separator 11. However, the projection may be disposed on both of the ribs 21 and 23.
Installation of the projection 25 or 27 on one of the rib 21 of the anode side separator 9 and the rib 23 of the cathode side separator 11, as in the first and second embodiments, enables the selective restraint of diffusion of the fuel gas in the gas flow path 17 and the oxidant gas in the gas flow path 19.
Further, either one of the anode side separator 9 and the cathode side separator 11 can be manufactured in a shape without any projection on the rib, and therefore the manufacturing cost thereof can be reduced in comparison with the structure where the projections are located on the ribs of both the anode side separator 9 and the cathode side separator 11.
In the third embodiment, the plurality of the projections 29 can be located in a spot where a reaction gas flowing in a gas flow path 17 is likely to short-circuit to another neighboring gas flow path 17 across the rib 21. Accordingly, the manufacturing cost can be reduced compared with the first or the second embodiment.
In the third embodiment, the projection 29 applied to the anode side separator 9 is explained, however, the projection 29 may be applied to a cathode side separator 11, or to both the anode side separator 9 and the cathode side separator 11.
In embodiments to be described below, explanations will be made for applications of the projection mainly to the anode side separator 9. However, the projection may be applied to the cathode side separator 11, or to both of the separators 9 and 11, similarly to the third embodiment.
Projections 33 are located on the ribs 21a and 21d that collectively define the gas flow path bundle 31. Crosshatched portions in
In the fifth embodiment, the projections 33 are located on the outermost ribs 21a and 21d defining the gas flow path bundle 31, to thereby avoid leakage of the reaction gas from the gas flow path bundle 31 to the outside, as well as to reduce short-circuiting of the reaction gas from the gas flow path bundle 31 across the ribs 21a and 21d to the neighboring gas flow bundle 31.
And by making the projections 33 on the ribs 21a and 21d as wide and as tall as downstream side of the gas flow path, the short-circuit of the reaction gas between the gas flow path bundles can be reduced more certainly.
In the above-mentioned sixth embodiment, the short-circuiting of the reaction gas between the gas flow paths can be reduced at the bending corners thereof where the reaction gas is more likely to short-circuit.
A rib 45 is located between the gas flow paths 17d and 17e, having a shape that is serpentine in the upward and downward directions in
And projections 55, 57 are located on winding portions of the rib 45 at the ends of the branch flow paths 41, 43. Projections 59, 61 are respectively located on a part of the straight rib 53 at the end of the main flow path 37 downstream thereof, and on a part of the straight rib 51 at the end of the main flow path 39 upstream thereof. Crosshatched portions in
Since the projections 55, 57 are respectively disposed in positions where the reaction gas easily short-circuits from the ends of the branch flow paths 41, 43 to the main flow paths 39, 37, as well as the projections 59, 61 being respectively disposed in positions where the reaction gas easily leaks from the ends of the main flow paths 37, 39 to the outside, an amount of short-circuited reaction gas can be reduced and the leakage of reaction gas to the outside can be prevented.
Thereby, short-circuiting of the reaction gas from the branch flow path 41 for supplying gas to the branch flow path 43 for discharging gas, positioned on the discharge port side (the left side in
In the tenth embodiment, by locating the plurality the projections 25, the portions of a porous electrode 3 where the plurality of the projections 25 are located can be easily compressed and thereby passage of short-circuited gas through the porous electrode 3 can be securely and stably reduced.
In
As described in the eleventh embodiment and the twelfth embodiment, at least one of the height and the width of the plurality of the projections 25a, 25b and the projections 65a, 65b, 65c on the rib 21 is different from the others, thereby enabling a selective adjustment of gas diffusion inside the porous electrode 3. Accordingly, in these embodiments, an amount of short-circuited gas can be more efficiently reduced than in the first embodiment. Herein, an amount of short-circuited gas is reduced further as the projections become taller or wider. And the height and the width of such projections may be changed depending on a gas flow velocity in the gas flow path.
In the thirteenth embodiment and the fourteenth embodiment, a size (at least one of the height and the width) of the projections 67, 69 continuously changes, thereby enabling continuous and selective adjustment of gas diffusion inside the porous electrode 3. Accordingly in these embodiments, an amount of the short-circuited gas can be more efficiently reduced than in the first embodiment.
According to the fifteenth embodiment, the projection 25 of the anode side separator 9 is located opposite to the projection 71 of the cathode side separator 11 and thereby an amount of the short-circuited gas can be reduced in both of the porous electrodes 3, 5.
According to the sixteenth embodiment, an amount of the short-circuited gas can be reduced in both of the porous electrodes 3, 5 similarly to the fifteenth embodiment.
According to the seventeenth embodiment mentioned above, the portions of the porous electrodes 3, 5 corresponding to the above-mentioned projections can be crushed with more certainty, thereby more securely reducing an amount of short-circuited gas.
In the event of selecting the projection 75 having the triangular shape in section, the porous electrode 3 can be stably crushed with a little load, and on the other hand, in the event of selecting the semi-circular projection 77, an excessive concentration of load on the porous electrode 3 can be avoided. Shape and size, for example a radius of curvature, of the projections 75, 77 can be adjusted to be suitable for molding.
According to the twentieth embodiment, it becomes possible to manufacture a separator in a conventional shape without a projection on a rib 21, and thereafter, to form the projection 79 on the rib 21. In this case, it is possible to stably crush the porous electrode 3 by using a projection 79 thereon made of a flexible material.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2003-023712, filed on Jan. 31, 2003, the disclosure of which is expressly incorporated herein by reference in its entirety.
The preferred embodiments described herein are illustrative and not restrictive, and the invention may be practiced Or embodied in other ways without departing from the spirit or essential character thereof. The scope of the invention being indicated by the claims, and all variations which come within the meaning of claims are intended to be embraced herein.
In a fuel cell according to the present invention, at least one of the ribs 21, 23 formed on separators 9, 11 which sandwich a membrane electrode assembly 7 of the fuel cell, is formed to have on its top a projection 25 which compresses and crushes a part of porous electrodes 3, 5 of the membrane electrode assembly 7, when sandwiching the membrane electrode assembly 7 with the separators 9, 11, to thereby restrict gas passage through the crushed part of the porous electrodes 3, 5. Short-circuit of gas between gas flow paths 17, 19 is thus prevented, providing even gas transportation through the entire porous electrodes 3, 5, with the reaction surfaces thereof effectively used. Accordingly, performance and fuel economy of the fuel cell are improved. Therefore, the present invention is useful for an application of a fuel cell.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-023712 | Jan 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/00779 | 1/28/2004 | WO | 1/7/2005 |
