JP2004111118A - Fuel cell stack - Google Patents

Abstract

With a simple configuration, it is possible to effectively prevent heat transfer from an electrolyte / electrode structure of an end unit cell to an end separator, and to improve power generation performance of the end unit cell.
A fuel cell stack includes a plurality of stacked unit cells, and end unit cells disposed at ends of the unit cells. The contact area between the first and second end separators 60, 62 constituting the end unit cells 12a, 12b and the electrolyte membrane / electrode structure 22 is determined by the first and second separators 24, 26 constituting the unit cell 12. It is configured to be smaller than the contact area between the electrode and the electrolyte membrane / electrode structure 22.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a fuel comprising: an electrolyte / electrode structure in which a pair of electrodes are provided on both sides of an electrolyte; and a stack in which a plurality of unit cells in which the electrolyte / electrode structure is sandwiched via a separator are stacked. Related to a battery stack.
[0002]
[Prior art]
In general, a polymer electrolyte fuel cell has an electrolyte membrane / electrode structure in which an anode electrode and a cathode electrode are provided on both sides of an electrolyte membrane composed of a polymer ion exchange membrane (cation exchange membrane). , And a separator. This type of fuel cell is generally used as a fuel cell stack by alternately stacking a predetermined number of electrolyte membrane / electrode structures and separators.
[0003]
In this fuel cell, a fuel gas supplied to the anode electrode, for example, a gas mainly containing hydrogen (hereinafter, also referred to as a hydrogen-containing gas) is obtained by ionizing hydrogen on the electrode catalyst and passing through the electrolyte to the cathode side. Move to the electrode side. The electrons generated during that time are taken out to an external circuit and used as DC electric energy. Since an oxidant gas, for example, a gas mainly containing oxygen or air (hereinafter also referred to as an oxygen-containing gas) is supplied to the cathode side electrode, hydrogen ions, electrons, And oxygen react to produce water.
[0004]
By the way, in a fuel cell stack, there is a unit cell in which a temperature drop is more likely to be caused by heat radiation to the outside than in other unit cells. For example, a unit cell (hereinafter, also referred to as an end unit cell) disposed at an end in the stacking direction includes, for example, a power extraction terminal (a current collecting plate) for collecting electric charges generated by each unit cell, and a stacked unit cell. A large amount of heat is dissipated by an end plate or the like provided to hold the unit cells, and the above-described temperature drop is remarkable. It has been pointed out that due to this temperature drop, dew condensation is more likely to occur in the end unit cells than in the central part of the fuel cell stack, and the generated water is less discharged, resulting in lower power generation performance.
[0005]
Therefore, for example, as disclosed in Patent Document 1, a groove for cooling fluid flow is not formed in an outer separator constituting an end unit cell, and the separator is cooled by a cooling fluid. There is known a solid polymer electrolyte fuel cell having a simple structure. This prevents the end unit cells from being overcooled.
[0006]
In the stacked fuel cell disclosed in Patent Document 2, gas connect plates are disposed at both ends of the cell stack, and a vacuum layer and an air layer are formed on the gas connect plates. For this reason, the heat radiation to the outside of the cell stack is prevented under the heat insulating effect of the vacuum layer and the air layer.
[0007]
[Patent Document 1]
JP-A-8-130028 (FIG. 1)
[Patent Document 2]
JP-A-7-326379 (FIG. 1)
[0008]
[Problems to be solved by the invention]
In this case, Patent Document 1 described above relates to a structure for preventing dew condensation in the end unit cells by preventing the end unit cells from being excessively cooled by the cooling fluid. On the other hand, Patent Literature 2 described above relates to a structure in which heat dissipation to the outside of the cell stack is prevented under the heat insulating action of the vacuum layer and the air layer, thereby preventing dew condensation in the cell stack.
[0009]
As described above, Patent Literatures 1 and 2 basically provide a heat insulating structure for stabilizing the power generation function of an end unit cell or a cell stack when the ambient temperature is about room temperature. However, when starting below the freezing point, the cell temperature must be raised all at once to a temperature at which the generated water does not freeze, and there is a problem that the above Patent Documents 1 and 2 cannot cope.
[0010]
That is, at the time of starting below the freezing point, the blockage of the reaction gas channel due to the freezing of the generated water easily occurs in the diffusion layer constituting the electrolyte membrane / electrode structure. For this reason, the diffusion layer on the gas flow path side needs to be rapidly heated to 0 ° C. or higher. However, according to Patent Documents 1 and 2, the diffusion layer cannot be maintained at 0 ° C. or higher.
[0011]
The present invention is intended to solve this kind of problem, and with a simple configuration, effectively prevents the transfer of heat from the electrolyte / electrode structure of the end unit cell to the end separator. It is an object of the present invention to provide a fuel cell stack capable of improving power generation performance.
[0012]
[Means for Solving the Problems]
In the fuel cell stack according to claim 1 of the present invention, the contact area between the separator and the electrolyte / electrode structure constituting at least one end unit cell arranged at the end in the stacking direction of the stack is smaller than that of the end. The contact area is set to be smaller than the contact area between the separator and the electrolyte / electrode structure constituting the unit cell disposed inside the unit cell.
[0013]
For this reason, in the end unit cells, the heat transfer coefficient between the electrolyte / electrode structure and the separator is lower than that of the unit cell side, and the electrolyte / electrode structure can be directly insulated. Therefore, particularly when starting at a temperature below the freezing point, transfer of heat from the electrolyte / electrode structure to the separator is prevented, and it is possible to effectively prevent freezing of generated water due to a decrease in the temperature of the electrolyte / electrode structure. Become.
[0014]
In addition, the contact resistance at the contact portion between the electrolyte / electrode structure and the separator increases. As a result, heat is generated in the contact portion, whereby the temperature of the electrolyte / electrode structure can be quickly raised, and freezing in the electrolyte / electrode structure can be reliably prevented.
[0015]
Further, in the fuel cell stack according to claim 2 of the present invention, the unit cell is opened to face the electrolyte / electrode structure, and a reaction gas flow channel for supplying a reaction gas to the electrode is provided. The unit cell includes an end reaction gas flow channel groove having a flow channel groove width larger than that of the reaction gas flow channel groove. Therefore, with a simple configuration, the heat transfer coefficient between the electrolyte / electrode structure and the separator can be effectively reduced as compared with the unit cell side.
[0016]
Further, in the fuel cell stack according to claim 3 of the present invention, the unit cell is opened to face the electrolyte / electrode structure, and a reaction gas flow channel for supplying a reaction gas to the electrode is provided. The unit cell includes an end reaction gas flow channel having a larger flow channel cross-sectional area than the reaction gas flow channel. For this reason, a larger amount of reaction gas can be supplied to the end reaction gas flow channel than the reaction gas flow channel, and it is possible to improve drainage satisfactorily and to improve power generation performance. It is planned.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic sectional view of a fuel cell stack 10 according to an embodiment of the present invention.
[0018]
In the fuel cell stack 10, a plurality of unit cells 12 are stacked in the direction of arrow A, and end unit cells 12a and 12b are arranged at both ends of the unit cells 12 in the stacking direction to form a stacked body 13. Outside the laminate 13, a positive terminal plate 14a and a negative terminal plate 14b, insulating plates 16a and 16b, and end plates 18a and 18b are sequentially arranged. The fuel cell stack 10 is configured by fastening the end plates 18a and 18b with a tie rod or the like (not shown).
[0019]
As shown in FIG. 2, the unit cell 12 includes an electrolyte membrane / electrode structure 22, and first and second separators 24 and 26 sandwiching the electrolyte membrane / electrode structure 22. A seal member 28 such as a gasket is interposed between the electrolyte membrane / electrode structure 22 and the first and second separators 24 and 26 so as to cover a periphery of a communication hole described later and an outer periphery of an electrode surface (power generation surface). Is equipped.
[0020]
One end edge of the unit cell 12 in the direction of arrow B communicates with each other in the direction of arrow A, which is the laminating direction, to form an oxidant gas supply passage 30a for supplying an oxidant gas, for example, an oxygen-containing gas. A cooling medium discharge communication hole 32b for discharging the medium and a fuel gas discharge communication hole 34b for discharging a fuel gas, for example, a hydrogen-containing gas, are provided in an arrow C direction (vertical direction).
[0021]
The other end edges of the unit cells 12 in the direction of arrow B are connected to each other in the direction of arrow A to provide a fuel gas supply communication hole 34a for supplying a fuel gas and a cooling medium supply communication hole for supplying a cooling medium. 32a and an oxidizing gas discharge communication hole 30b for discharging the oxidizing gas are arranged in the arrow C direction.
[0022]
The electrolyte membrane / electrode structure 22 includes, for example, a solid polymer electrolyte membrane 36 formed by impregnating a perfluorosulfonic acid thin film with water, an anode electrode 38 and a cathode electrode sandwiching the solid polymer electrolyte membrane 36. 40 (see FIGS. 1 and 2).
[0023]
The anode electrode 38 and the cathode electrode 40 include a gas diffusion layer made of carbon paper or the like, and an electrode catalyst layer in which porous carbon particles having a platinum alloy supported on the surface are uniformly applied on the surface of the gas diffusion layer. Respectively. The electrode catalyst layers are joined to both surfaces of the solid polymer electrolyte membrane 36 so as to face each other with the solid polymer electrolyte membrane 36 interposed therebetween. An opening 44 is formed at the center of the seal member 28 so as to correspond to the anode 38 and the cathode 40.
[0024]
An oxidizing gas flow path 46 communicating with the oxidizing gas supply communication hole 30a and the oxidizing gas discharge communication hole 30b is provided on the surface 24a of the first separator 24 on the side of the electrolyte membrane / electrode structure 22. As shown in FIG. 2, the oxidizing gas channel 46 is formed, for example, between a plurality of grooves (serpentine grooves) 48 extending in the direction of arrow C while meandering in the direction of arrow B and the cathode-side electrode 40. A flat surface 50 that contacts the cathode electrode 40 is provided between the grooves 48 (see FIG. 1).
[0025]
As shown in FIG. 3, a fuel gas flow path 52 communicating with the fuel gas supply passage 34a and the fuel gas discharge passage 34b is formed on the surface 26a of the second separator 26 on the side of the electrolyte membrane / electrode structure 22. Is done. The fuel gas flow path 52 is formed, for example, between a plurality of grooves (serpentine grooves) 54 extending in the direction of arrow C while meandering in the direction of arrow B, and the anode-side electrode 38. A flat surface 56 that contacts the anode electrode 38 is provided between them (see FIG. 1).
[0026]
As shown in FIG. 2, a cooling medium flow path 58 communicating with the cooling medium supply communication hole 32a and the cooling medium discharge communication hole 32b is formed on the surface 26b opposite to the surface 26a of the second separator 26. The cooling medium flow path 58 is constituted by, for example, a plurality of linear flow grooves extending in the direction of arrow B.
[0027]
The end unit cells 12a and 12b have the same configuration. Hereinafter, the end unit cell 12a will be described in detail, and the detailed description of the end unit cell 12b will be omitted.
[0028]
As shown in FIG. 1, the end unit cell 12 a includes an electrolyte membrane / electrode structure 22, and first and second end separators 60 and 62 that sandwich the electrolyte membrane / electrode structure 22. , Are basically configured in the same manner as the unit cell 12. The first and second end separators 60 and 62 have an oxidizing gas flow path 64 and a fuel gas flow path 66 on surfaces 60a and 62a facing the electrolyte membrane / electrode structure 22, respectively.
[0029]
As shown in FIGS. 1 and 4, the oxidizing gas flow path 64 is formed between a plurality of meandering grooves (serpentine grooves) 68 and the cathode-side electrode 40. A flat surface 70 that contacts the cathode electrode 40 is provided. The fuel gas flow path 66 is formed between a plurality of meandering grooves (serpentine grooves) 74 and the anode-side electrode 38, and a flat surface 76 contacting the anode-side electrode 38 is provided between the grooves 74. Is provided (see FIG. 1).
[0030]
In the unit cell 12, as shown in FIGS. 1 and 3, the flow channel width H1 of the grooves 48 and 54 is set, while in the end unit cells 12a and 12b, as shown in FIGS. The flow channel groove width H2 of the groove portions 68 and 74 is set. The flow channel groove width H2 is selected to be larger than the flow channel groove width H1, and has, for example, a relationship of flow channel groove width H2 = 2 × flow channel groove width H1. In other words, the contact area of the flat surfaces 70, 76 where the first and second end separators 60, 62 contact the electrolyte membrane / electrode structure 22 is such that the first and second separators 24, 26 have the electrolyte membrane / electrode. It is considerably smaller than the contact area of the flat surfaces 50, 56 that contact the structure 22.
[0031]
The operation of the fuel cell stack 10 configured as described above will be described below.
[0032]
As shown in FIG. 1, in the fuel cell stack 10, a fuel gas such as a hydrogen-containing gas, an oxidizing gas such as an oxygen-containing gas such as air, and a unit cell 12 and end unit cells 12a and 12b are provided. A cooling medium such as pure water, ethylene glycol or oil is supplied.
[0033]
For this reason, as shown in FIG. 2, in the unit cell 12, the oxidizing gas is introduced into the oxidizing gas passage 46 of the first separator 24 from the oxidizing gas supply communication hole 30 a, and the oxidizing gas is It moves along the cathode electrode 40 constituting the electrode structure 22. The fuel gas is introduced from the fuel gas supply passage 34 a into the fuel gas flow channel 52 of the second separator 26, and moves along the anode 38 forming the electrolyte membrane / electrode structure 22.
[0034]
Therefore, in the electrolyte membrane / electrode structure 22, the oxidizing gas supplied to the cathode electrode 40 and the fuel gas supplied to the anode electrode 38 are consumed by the electrochemical reaction in the electrode catalyst layer, and the power is generated. Is performed.
[0035]
Next, the fuel gas supplied to the anode 38 and consumed is discharged in the direction of arrow A along the fuel gas discharge communication hole 34b. Similarly, the oxidant gas supplied to and consumed by the cathode electrode 40 is discharged in the direction of arrow A along the oxidant gas discharge communication hole 30b.
[0036]
Further, the cooling medium supplied to the cooling medium supply passage 32a is introduced into the cooling medium flow path 58 of the second separator 26, and then flows in the direction of arrow B. This cooling medium is discharged from the cooling medium discharge communication hole 32b after cooling the electrolyte membrane / electrode structure 22.
[0037]
On the other hand, in the end unit cells 12a and 12b, the oxidizing gas supplied to the oxidizing gas flow path 64 of the first end separator 60 flows along the cathode electrode 40 constituting the electrolyte membrane / electrode structure 22. As the fuel gas moves, the fuel gas supplied to the fuel gas flow path 66 of the second end separator 62 moves along the anode 38 constituting the electrolyte membrane / electrode structure 22. Thus, power is generated in the end unit cells 12a and 12b.
[0038]
In this case, in the present embodiment, in the unit cell 12 and the end unit cells 12a and 12b, the first and second end separators 60 and 62 have the flat surfaces 70 and 76 in contact with the electrolyte membrane / electrode structure 22. The contact area is considerably smaller than the contact area of the flat surfaces 50, 56 where the first and second separators 24, 26 contact the electrolyte membrane / electrode structure 22.
[0039]
Therefore, in the end unit cells 12a and 12b, the heat transfer coefficient between the electrolyte membrane / electrode structure 22 and the first and second end separators 60 and 62 is lower than the heat transfer coefficient on the unit cell 12 side. Thus, the electrolyte membrane / electrode structure 22 can be directly insulated. Therefore, particularly when starting at a temperature below freezing, transfer of heat from the electrolyte membrane / electrode structure 22 to the first and second end separators 60 and 62 is prevented, and the temperature of the electrolyte membrane / electrode structure 22 is reduced. This makes it possible to effectively prevent freezing of generated water due to the above.
[0040]
Moreover, in the end unit cells 12a, 12b, the contact resistance at the contact portions between the electrolyte membrane / electrode structure 22 and the first and second end separators 60, 62 increases. As a result, heat is generated in the contact portion, so that the temperature of the electrolyte membrane / electrode structure 22 can be quickly raised, and freezing in the electrolyte membrane / electrode structure 22 can be reliably prevented. .
[0041]
Furthermore, the flow channel width H2 of the grooves 68, 74 provided in the end unit cells 12a, 12b is selected to be larger than the flow channel width H1 of the grooves 48, 54 provided in the unit cell 12, for example, It has a relationship of channel groove width H2 = 2 × channel groove width H1. Therefore, a larger amount of oxidizing gas and fuel gas (reactive gas) can be supplied to the grooves 68 and 74 which are the end reaction gas flow grooves than the grooves 48 and 54 which are the reaction gas flow grooves. In addition, it is possible to improve the drainage property, and to improve the power generation performance.
[0042]
In order to secure a stoichiometric ratio (the ratio between the amount of reactant gas supplied and the amount of reactant gas actually consumed), the end unit cells 12a and 12b have a flow rate of the reactant gas which is about twice that of the unit cell 12. Need to supply. However, the number of stacked unit cells 12 is usually about several hundreds, and an increase in the total flow rate of the reaction gas is hardly a problem. Alternatively, the unit cells 12 may be arranged in place of the end unit cells 12b, and only a single end unit cell 12a may be used.
[0043]
【The invention's effect】
In the fuel cell according to the present invention, the heat transfer coefficient between the separator and the electrolyte / electrode structure constituting at least one end unit cell disposed at the stacking direction end of the stack is higher than the heat transfer coefficient on the unit cell side. , And the electrolyte / electrode structure can be directly insulated. Therefore, particularly when starting at a temperature below the freezing point, transfer of heat from the electrolyte / electrode structure to the separator is prevented, and it is possible to effectively prevent freezing of generated water due to a decrease in the temperature of the electrolyte / electrode structure. Become.
[0044]
In addition, the contact loss at the contact portion between the electrolyte / electrode structure and the separator increases. As a result, heat is generated in the contact portion, whereby the temperature of the electrolyte / electrode structure can be quickly raised, and freezing in the electrolyte / electrode structure can be reliably prevented.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a fuel cell stack according to an embodiment of the present invention.
FIG. 2 is a partially exploded perspective view of the fuel cell stack 10. FIG.
FIG. 3 is an explanatory front view of a second separator constituting a unit cell.
FIG. 4 is an explanatory front view of a first end separator constituting the end unit cell.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Fuel cell stack 12 ... Unit cell 12a, 12b ... End unit cell 13 ... Stack 14a, 14b ... Terminal plate 16a, 16 ... Insulating plate 18a, 18b ... End plate 22 ... Electrolyte membrane and electrode structure 24, 26 ... Separator 30a ... Oxidizing gas supply communication hole 30b ... Oxidizing gas discharge communication hole 32a ... Cooling medium supply communication hole 32b ... Cooling medium discharge communication hole 34a ... Fuel gas supply communication hole 34b ... Fuel gas discharge communication hole 36 ... Solid height Molecular electrolyte membrane 38 Anode side electrode 40 Cathode side electrode 46, 64 Oxidant gas flow path 48, 54, 68, 74 Groove 50, 56, 70, 76 Flat surface 52, 66 Fuel gas flow path 58 ... Cooling medium channel 60,62 ... End separator

Claims (3)

A fuel cell stack comprising: an electrolyte / electrode structure provided with a pair of electrodes on both sides of an electrolyte; and a stack of a plurality of unit cells in which the electrolyte / electrode structure is sandwiched via a separator. hand,
The contact area between the separator and the electrolyte / electrode structure constituting at least one end unit cell arranged at the stacking direction end of the laminate, the unit cell arranged inside the end unit cell. A fuel cell stack having a small contact area with a constituent separator and an electrolyte / electrode structure. 2. The fuel cell stack according to claim 1, wherein the unit cell disposed inward is opened to face the electrolyte / electrode structure, and has a reaction gas flow channel for supplying a reaction gas to the electrode. 3. Along with
The fuel cell stack according to claim 1, wherein the end unit cell includes an end reaction gas passage groove having a larger passage groove width than the reaction gas passage groove. 3. The fuel cell stack according to claim 1, wherein the unit cell disposed inward is opened to face the electrolyte / electrode structure, and a reaction gas flow path for supplying a reaction gas to the electrode. 4. With a groove,
The fuel cell stack according to claim 1, wherein the end unit cell includes an end reaction gas passage groove having a larger passage groove cross-sectional area than the reaction gas passage groove.

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