Fuel cell with cooling medium circulation arrangement and method

[0002] The present invention relates to a fuel cell having an electrolyte membrane sandwiched between an anode electrode and a cathode electrode.

[0003] Solid polymer electrolyte fuel cells comprise a plurality of stacked fuel cell structural bodies (unit cells) each comprising an electrolyte membrane in the form of an ion exchange membrane and a catalytic electrode and a porous carbon electrode which are disposed one on each side of the electrolyte membrane, and a plurality of separators sandwiching the structural bodies.

[0004] Hydrogen supplied to the anode of the fuel cell is converted into hydrogen ions on the catalytic electrode, which move through the electrolyte membrane that has been humidified to an appropriate extent toward the cathode of the fuel cell. Electrons generated while the hydrogen ions are moving are transferred to an external circuit for use as direct-current electric energy. An oxygen containing gas such as an oxygen gas or air is supplied to the cathode electrode to generate water through a reaction between the hydrogen ions, the electrons, and the oxygen on the cathode electrode.

[0005] For such a fuel cell, there has been known a structure which, as shown in FIG. 11 of the accompanying drawings, comprises fuel cell structural bodies 2 and separators 4 which are alternately stacked together, each of the fuel cell structural bodies 2 having an electric generation section (electrode) 2awhich is supplied with cooling water in a direction parallel to the flow of a fuel gas, e.g., a hydrogen gas and an oxygen containing gas, e.g., an oxygen gas.

[0006] Since the cooling water flows vertically in the electric generation section 2a, a relatively large temperature difference is developed between central and opposite side regions of the electric generation section 2adue to thermal diffusion. Because of a drop in the temperature, moisture is condensed in the opposite side regions of the electric generation section 2a, creating inoperative regions in the electric generation section 2a. In addition, the electric generation section 2atends to have low-performance regions on account of the low temperature. As a result, the electric generation section 2ahas its effective operative area and performance greatly lowered.

[0007] It is an object of the present invention to provide a fuel cell which will solve the above problems and has a simple structure for preventing partial temperature differences from being developed in fuel cell structural bodies thereby to maintain an effective operative area and performance.

[0008] According to the present invention, a cooling medium, which has been used to cool an electric generation section of a fuel cell structural body, is then circulated along outer sides of the electric generation section. Therefore, the cooling medium whose temperature has been increased by a heat exchange in the electric generation section flows outside of the electric generation section. Consequently, any temperature difference between a central region of the electric generation section and outer edges thereof is minimized, thereby preventing moisture condensation and increasing an effective operative area and the performance of the electric generation section.

[0009] FIG. 1 is a fragmentary perspective view of a fuel cell according to the present invention;

[0010] FIG. 2 is an exploded perspective view of the fuel cell;

[0011] FIG. 3 is a front elevational view of an electric generation section of the fuel cell;

[0012] FIG. 4 is a front elevational view of a gasket of the fuel cell;

[0013] FIG. 5 is a front elevational view of a first manifold plate of the fuel cell;

[0014] FIG. 6 is a front elevational view of a second manifold plate of the fuel cell;

[0015] FIG. 7 is a front elevational view of a surface pressure generating plate of the fuel cell;

[0016] FIG. 8 is a front elevational view of a separator body of the fuel cell;

[0017] FIG. 9 is a diagram illustrative of a lateral temperature distribution in the electric generation section of the fuel cell;

[0018] FIG. 10 is a fragmentary perspective view of a fuel cell, showing another arrangement of circulatory passages; and

[0019] FIG. 11 is a diagram illustrative of a lateral temperature distribution in an electric generation section of a conventional fuel cell.

[0020] As shown in FIGS. 1 and 2, a fuel cell according to the present invention basically comprises a horizontal stack of fuel cells (fuel cell structural bodies) 20. Each of the fuel cells 20 includes an electric generation section 28 which comprises an anode electrode 26 and a cathode electrode 24 which sandwich a solid polymer electrolyte membrane 22 therebetween. The electric generation section 28 is described in detail in International laid-open publication WO94-15377, U.S. patent application Ser. No. 07/996,258 which is incorporated herein by reference. In FIG. 2, the solid polymer electrolyte membrane 22, the anode electrode 26, and the cathode electrode 24 are separate from each other. However, they may be of an integral structure.

[0021] As shown in FIG. 3, the solid polymer electrolyte membrane 22 has an oblong hole 22afor passing a fuel gas such as a hydrogen gas or the like in one direction, a hole 22bfor passing cooling water, and a hole 22cfor passing an oxygen containing gas, e.g., an oxygen gas, with the holes 22a, 22b, 22cbeing defined in an upper portion of the solid polymer electrolyte membrane 22. The solid polymer electrolyte membrane 22 also has a hole 22dfor passing the fuel gas, a hole 22efor passing the cooling water, and a hole 22ffor passing the oxygen containing gas, with the holes 22d, 22e, 22fbeing defined in a lower portion of the solid polymer electrolyte membrane 22. The solid polymer electrolyte membrane 22 further has holes 23a-23c, 23d-23fdefined in opposite side regions thereof and providing circulatory passages 29a, 29bfor circulating the cooling water (cooling medium) which has been used to cool the electric generation section 28 along outer edges of the electric generation section 28.

[0022] A first gasket 30 and a second gasket 32 are disposed one on each side of the electric generation section 28. As shown in FIG. 4, the first gasket 30 has a large opening 34 for accommodating the cathode electrode 24 therein, and the second gasket 32 has an opening 36 for accommodating the anode electrode 26. As with the solid polymer electrolyte membrane 22, the first gasket 30 has holes 30a, 30dfor passing the fuel gas, holes 30b, 30efor passing the cooling water, and holes 30c, 30ffor passing the oxygen containing gas, these holes being defined respectively in upper and lower end portions of the first gasket 30. The first gasket 30 also has holes 31a-31c, 31d-31fdefined in opposite side regions thereof and serving as the circulatory passages 29a, 29b. The second gasket 32 is of the same structure as the first gasket 30.

[0023] The fuel cell 20 is sandwiched by separators 40. As shown in FIG. 2, each of the separators 40 comprises a first manifold plate 42, a first surface pressure generating plate 44 held against the first manifold plate 42, a second surface pressure generating plate 46, a separator body 48 sandwiched between the first surface pressure generating plate 44 and the second surface pressure generating plate 46 and, a second manifold plate 50 held against the second surface pressure generating plate 46.

[0024] As shown in FIG. 5, the first manifold plate 42 comprises a rectangular flat plate, and has a fuel gas supply recess 42adefined in an upper right corner thereof for supplying the fuel gas, and a cooling water discharge hole 42bdefined therein adjacent to the fuel gas supply recess 42afor discharging the cooling water. The first manifold plate 42 also has an oxygen containing gas supply hole 42cdefined in an upper left corner thereof for supplying the oxygen containing gas, and a fuel gas discharge recess 42ddefined in a lower left corner thereof for discharging the fuel gas. The first manifold plate 42 further has a cooling water supply hole 42eand an oxygen containing gas discharge hole 42fdefined therein and spaced successively from the fuel gas discharge recess 42dtoward a lower right corner thereof. The fuel gas supply recess 42aand the fuel gas discharge recess 42dare held in communication with each other through an opening 45 which accommodates a fuel gas flow rectifying plate 80, described later on. The first manifold plate 42 also has holes 43a-43c, 43d-43fdefined in opposite side regions thereof and serving as the circulatory passages 29a, 29b.

[0025] As shown in FIG. 6, the first manifold plate 42 and the second manifold plate 50 are basically of a symmetrical and near-image structure. Therefore, details of the second manifold plate 50 will not be described in detail below. The second manifold plate 50 has a fuel gas supply hole 50a, a cooling water discharge hole 50b, and an oxygen containing gas supply recess 50c, which are defined in an upper portion thereof, and a fuel gas discharge hole 50d, a cooling water supply hole 50e, and an oxygen containing gas discharge recess 50f, which are defined in a lower portion thereof. The oxygen containing gas supply recess 50cand the oxygen containing gas discharge recess 50fare held in communication with each other through an opening 52 which accommodates an oxygen containing gas flow rectifying plate 82, described later on. The second manifold plate 50 also has holes 51a-51c, 51d-51fdefined in opposite side regions thereof and serving as the circulatory passages 29a, 29b.

[0026] As shown in FIG. 7, the first surface pressure generating plate 44 that is held against the first manifold plate 42 comprises a flat plate made of an electrically conductive material or is formed integral with or made of the same material as the fuel gas flow rectifying plate 80, described later on. The first surface pressure generating plate 44 has a fuel gas supply communication hole 44aheld in communication with the fuel gas supply recess 42ain the first manifold plate 42, a cooling water discharge communication hole 44bheld in communication with the cooling water discharge hole 42b, and a communication hole 44cheld in communication with the oxygen containing gas supply hole 42c, with the holes 44a, 44b, 44cbeing defined in an upper portion of the first surface pressure generating plate 44. The first surface pressure generating plate 44 further has a communication hole 44dheld in communication with the fuel gas discharge recess 42din the first manifold plate 42, a communication hole 44eheld in communication with the cooling water supply hole 42e, and a communication hole 44fheld in communication with the oxygen containing gas discharge hole 42f. The first surface pressure generating plate 44 also has holes 57a-57c, 57d-57fdefined in opposite side regions thereof and held in communication with the holes 43a-43c, 43d-43fin the first manifold plate 42. The second surface pressure generating plate 46 is of essentially the same structure as the first surface pressure generating plate 44, and will not be described in detail below.

[0027] The separator body 48, as a third manifold plate, serves to supply cooling water upwardly to cool the electric generation section 28. As shown in FIG. 8, the separator body 48, which is relatively thick, is made of an electrically conductive dense material (solid). The separator body 48 has a fuel gas supply hole 48adefined in an upper right corner thereof and held in communication with the recess 42ain the first manifold plate 42 and the communication hole 44ain the first surface pressure generating plate 44, for supplying the fuel gas. The separator body 48 also has a cooling water discharge recess 48bdefined in a substantially central upper portion thereof adjacent to the fuel gas supply hole 48aand held in communication with the cooling water discharge hole 42bin the first manifold plate 42 and the communication hole 44bin the first surface pressure generating plate 44. The separator body 48 further has an oxygen containing gas supply hole 48cdefined in an upper left corner thereof and held in communication with the oxygen containing gas supply hole 42cin the first manifold plate 42 and the communication hole 44cin the first surface pressure generating plate 44.

[0028] The separator body 48 also has a hole 48ddefined in a lower left corner thereof and held in communication with the fuel gas discharge recess 42din the first manifold plate 42 and the communication hole 44din the first surface pressure generating plate 44, and a cooling water supply recess 48edirectly below the cooling water discharge recess 48b. The separator body 48 also has an oxygen containing gas discharge hole 48fdefined in a lower right corner thereof. The recesses 48b, 48ecommunicate with each other through a large opening 62. The separator body 48 further has holes 49a-49c, 49d-49fdefined in opposite side regions thereof and held in communication with the holes 43a-43c, 43d-43fin the first manifold plate 42 and the holes 57a-57c, 57d-57fin the first surface pressure generating plate 44.

[0029] Cooling water flow rectifying plates 70, 72 are fitted and fixed in the opening 62 in the separator body 48. The combined thickness of the cooling water flow rectifying plates 70, 72 is essentially the same as the thickness of the separator body 48. The cooling water flow rectifying plate 70 has a plurality of parallel grooves 70aextending vertically in FIG. 2. Likewise, the cooling water flow rectifying plate 72 has a plurality of parallel grooves 72a. When the cooling water flow rectifying plates 70, 72 are combined with each other, the grooves 70a, 72ajointly define large cooling water flow rectifying passages (cooling passages) which are held in communication with the cooling water discharge recess 48band the cooling water supply recess 48e, respectively.

[0030] As shown in FIG. 2, the fuel gas flow rectifying plate 80 is fitted in the opening 45 in the first manifold plate 42. The fuel gas flow rectifying plate 80 has a flat surface and an opposite surface having a plurality of parallel grooves 80adefined therein and extending vertically. The parallel grooves 80aprovide communication between the fuel gas supply recess 42aand the fuel gas discharge recess 42d.

[0031] The oxygen containing gas flow rectifying plate 82 is fitted in the opening 52 in the second manifold plate 50. The oxygen containing gas flow rectifying plate 82 has a flat surface and an opposite surface having a plurality of parallel grooves 82adefined therein and extending vertically. The parallel grooves 82aprovides communication between the oxygen containing gas supply recess 50cand the oxygen containing gas discharge recess 50f. The thickness of the first manifold plate 42 and the fuel gas flow rectifying plate 80, and the thickness of the second manifold plate 50 and the oxygen containing gas flow rectifying plate 82 are essentially the same as each other.

[0032] The separator body 48 thus constructed is sandwiched by the first surface pressure generating plate 44 and the second surface pressure generating plate 46, which are in turn sandwiched by the first manifold plate 42 and the second manifold plate 50. The second gasket 32 is held against the first manifold plate 42, and the first gasket 30 is held against the second manifold plate 50, with the electric generation section 28 sandwiched between the gaskets 30, 32, thus making up the fuel cell 20.

[0033] Many fuel cells 20, each comprising the first manifold plate 42 with the flow rectifying plate 80 assembled therein, the second gasket 32, the anode electrode 26, the solid polymer electrolyte membrane 22, the cathode electrode 24, the first gasket 30, the second manifold plate 50 with the flow rectifying plate 82 assembled therein, the second surface pressure generating plate 46, the separator body 48 with the flow rectifying plates 70, 72 assembled therein, and the first surface pressure generating plate 44, which are arranged in the direction indicated by the arrow in FIG. 2, are stacked together. One end of the stack is held against a first end plate 84, and the other end of the stack is held against a second end plate 86. The first and second end plates 84, 86 are fastened to each other by stud bolts 87 (see FIG. 1).

[0034] The first end plate 84 has a groove 84adefined therein for dividing the cooling water into left and right flows, the groove 84afacing the cooling water discharge hole 42bin the first manifold plate 42. The groove 84ahas opposite ends facing the holes 43a, 43din the first manifold plate 42. The first end plate 84 has grooves 84b, 84cdefined in respective opposite regions thereof and providing communication between the holes 43b, 43cin the first manifold plate 42 and also between the holes 43e, 43ftherein. The first end plate 84 further has a through hole 84ddefined therein for introducing the oxygen containing gas and a through hole 84edefined therein for discharging the oxygen containing gas.

[0035] The second end plate 86 has a through hole 86adefined therein and held in communication with the fuel gas supply hole 50ain the second manifold plat 50, for supplying the fuel gas, a through hole 86bdefined therein and held in communication with the cooling water supply hole 50e, a through hole 86cdefined therein and held in communication with the fuel gas discharge hole 50d, and through holes 86d, 86edefined therein and held in communication with the holes 51c, 51f(see FIG. 2). The second end plate 86 also has grooves 88a, 88bdefined in an inner surface thereof which faces the second manifold plate 50 and providing communication between the holes 51a, 51bin the second manifold plate 50 and also between the holes 51d, 51etherein.

[0036] Operation of the fuel cell 10 thus constructed will be described below.

[0037] Plural fuel cells 20 are sandwiched between separators 40, stacked such that their communication holes, other holes, and recesses are held in communication with each other, and fixed by the first and second end plates 84, 86.

[0038] When the fuel gas (hydrogen gas) is supplied from the through hole 86ain the second end plate 86 into the fuel cell 10, the fuel gas is supplied from the fuel gas supply hole 50ain the second manifold plate 50 into the fuel gas supply recess 42ain the first manifold plate 42, and then supplied through the grooves 80ain the fuel gas flow rectifying plate 80 disposed in the opening 45 held in communication with the fuel gas supply recess 42a, to the anode electrode 26 of the electric generation section 28.

[0039] The oxygen containing gas (air) is supplied from the through hole 84din the first end plate 84 into the fuel cell 10, and flows through the oxygen containing gas supply hole 42cin the first manifold plate 42 and the oxygen containing gas supply hole 48cin the separator body 48 into the oxygen containing gas supply recess 50cin the second manifold plate 50. The oxygen containing gas passes from the oxygen containing gas supply recess 50cthrough the grooves 82ain the oxygen containing gas flow rectifying plate 82 to the cathode electrode 24.

[0040] The unused fuel gas is discharged through the fuel gas discharge recess 42din the first manifold plate 42 out of the fuel cell 10 from the through hole 86cin the second end plate 86. The unused oxygen containing gas is discharged through the oxygen containing gas discharge recess 50fin the second manifold plate 50 out of the fuel cell 10 from the through hole 84ein the first end plate 84.

[0041] The cooling water is supplied from the through hole 86bin the second end plate 86 into the fuel cell 10, and flows through the cooling water supply hole 50ein the second manifold plate 50 into the cooling water supply recess 48ein the separator body 48. The cooling water then flows upwardly along the cooling water flow rectifying passages defined between the cooling water flow rectifying plate 70, 72 fixedly fitted in the opening 62 in the separator body 48, absorbs heat generated by the electric generation section 28, thereby cooling the electric generation section 28, and thereafter flows from the cooling water discharge recess 48bin the separator body 48 toward the first end plate 84.

[0042] The cooling water which has been used to remove the heat from the electric generation section 28 flows from the groove 84ain the first end plate 84 through the circulatory passages 29a, 29b, and is discharged out of the fuel cell 10 from the through holes 86d, 86ein the second end plate 86. Therefore, the cooling water introduced in the groove 84ain the first end plate 84 is supplied to the holes 43a, 43din the first manifold plate 42 which serve as the circulatory passages 29a, 29b.

[0043] The cooling water supplied into the hole 43ain the first manifold plate 42 flows through the hole 49ain the separator body 48 and the hole 51ain the second manifold plate 50 into the groove 88ain the second end plate 86. The cooling water is then introduced through the hole 51bin the second manifold plate 50 which is held in communication with the groove 88a, the hole 49bin the separator body 48, and the hole 43bin the first manifold plate 42 into the groove 84bin the first end plate 84. Then the cooling water flows from the groove 84bthrough the hole 43cin the first manifold plate 42, the hole 49cin the separator body 48, and the hole 51cin the second manifold plate 50, and is discharged out of the fuel cell 10 from the through hole 86din the second end plate 86.

[0044] The cooling water which has been supplied from the groove 84ain the first end plate 84 into the circulatory passage 29bflows through the hole 43din the first manifold plate 42, the hole 49din the separator body 48, and the hole 51din the second manifold plate 50 into the groove 88bin the second end plate 86, and thereafter returns through the holes 51e, 49e, 43einto the groove 84cin the first end plate 84.

[0045] The cooling water is discharged through the holes 43f, 49f, 51fwhich are held in communication with the groove 84cout of the fuel cell 10 from the through hole 86ein the second end plate 86.

[0046] In this embodiment, as described above, the cooling water which has been supplied to the fuel cell 10 and removed the heat from the electric generation section 28 circulates along the circulatory passages 29a, 29bon the opposite sides of the electric generation section 28. Consequently, on the opposite sides of the electric generation section 28, the cooling water whose temperature has been increased by a heat exchange in the electric generation section 28 flows along the circulatory passages 29a, 29bfor thereby preventing the electric generation section 28 in the vicinity of its opposite edges from being lowered in temperature (see FIG. 9).

[0047] As a consequence, any temperature difference between a central region of the electric generation section 28 and opposite edges thereof is minimized, thereby preventing moisture condensation on the opposite edges of the electric generation section 28 due to a temperature drop. Therefore, the electric generation section 28 is free of inoperative regions which would otherwise be caused by moisture condensation, and any low-performance regions of the electric generation section 28 due to low temperatures are reduced. Thus, the effective operative area and performance of the electric generation section 28 are effectively increased.

[0048] According to this embodiment, furthermore, the fuel cell 10 is only required to have the circulatory passages 29a, 29btherein for circulating the cooling water which has absorbed heat through a heat exchange along the opposite outer sides of the electric generation section 28. The fuel cell 10 is not complicated in overall structure, and can easily and economically be constructed.

[0049] In the present embodiment, the circulatory passages 29a, 29bpass three times on the opposite sides of the electric generation section 28 (one and a half reciprocating cycle on each side). However, the fuel cell 10 may have circulatory passages 90a, 90bshown in FIG. 10. The circulatory passages 90a, 90bare provided by oblong holes 92a, 92bdefined as vertically elongate holes in respective opposite sides of the second manifold plate 50. The first manifold plate 42, the second gasket 32, the solid polymer electrolyte membrane 22, the first gasket 30, the second surface pressure generating plate 46, the separator body 48, and the first surface pressure generating plate 44 also have vertically elongate oblong holes (not shown) defined in opposite sides thereof and held in communication with each other.

[0050] The circulatory passages 90a, 90bcirculate cooling water, which has been used to remove heat from the electric generation section 28 and sent to the first end plate 84, through the vertically elongate oblong holes 92a, 92b, and then discharge the cooling water out of the fuel cell 10. Therefore, the circulatory passages 90a, 90bare capable of regulating the temperatures of the opposite sides of the electric generation section 28 together in the vertical direction, and also offer the same advantages as those of the circulatory passages 29a, 29b.

[0051] In the fuel cell according to the present invention, a cooling medium whose temperature is relatively high due to a heat exchange at an electric generation section is circulated along the outer sides of the electric generation section to prevent a partial temperature difference from being developed in the electric generation section. Therefore, moisture condensation is prevented, and the effective operative area and performance of the electric generation section are increased.