JP2004139905A - Fuel cell and manufacturing method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a fuel cell for improving the airtightness of a fuel cell stack even if the shapes of separators are not uniform, and improving power generating property by lowering contact resistance. <P>SOLUTION: The manufacturing method of the solid polymer fuel cell is composed of three processes on the whole which are a first process (S1) of forming a separator member of which thermosetting resin is in a half-cured state, a second process (S2) of forming the fuel cell stack (lamination body) by laminating a plurality of unit cells using the separator member in the half-cured state formed at S1, and a third process (S3) of curing the thermosetting resin by heating the stack while pressing the laminated surfaces of the fuel cell stack. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polymer electrolyte fuel cell among fuel cells provided with an electrolyte, and a method for manufacturing the same.
[0002]
[Prior art]
BACKGROUND ART A polymer electrolyte fuel cell has been intensively researched and developed as a power source for an electric vehicle because of its low operating temperature of room temperature to about 100 ° C., short startup time, high power density, and small size and light weight.
[0003]
The operating principle of the polymer electrolyte fuel cell is as follows. Fuel (hydrogen) gas is separated into hydrogen ions (H +, protons) and electrons by a catalytic oxidation reaction at a fuel electrode (anode). Hydrogen ions move from the fuel electrode to the oxidizer electrode (cathode) in the polymer electrolyte with several water molecules around in the hydrated state (H + .xH2O). On the other hand, the electrons move through the electron conductive electrode and move to the cathode via an external load circuit. The electrons that have moved through the external circuit and the hydrogen ions that have moved through the polymer electrolyte undergo a reduction reaction at the cathode with oxygen in the air supplied from the outside to produce water.
[0004]
The solid polymer electrolyte used in the polymer electrolyte fuel cell does not exhibit good hydrogen ion conductivity unless it is in a wet state. In addition, hydrogen ions dissociated at the anode move to the cathode in the electrolyte in a hydrated state.Therefore, there is a shortage of water near the anode surface of the electrolyte membrane, and water is supplied to maintain power generation continuously. There is a need to. Normally, this water is supplied by humidifying the hydrogen gas supplied to the anode. In some cases, the air supplied to the cathode is humidified.
[0005]
This polymer electrolyte fuel cell has a low unit cell voltage of about 1 V at the time of load output. Therefore, when used as a vehicle drive power supply, a stack of several hundred cells is usually stacked (called a fuel cell stack). And an output voltage of several hundred volts by series connection between cells is used.
[0006]
A unit cell of a polymer electrolyte fuel cell includes a membrane-electrode assembly (MEA) in which an anode electrode and a cathode electrode are formed on both surfaces of a hydrogen ion conductive electrolyte membrane, and a hydrogen gas flow disposed outside the anode electrode. A first separator having a passage, and a second separator having an oxidizing gas passage disposed outside the cathode electrode.
[0007]
When a stack is formed by stacking a plurality of unit cells, a plate called an end plate is arranged at both ends of the stack, and the end plates are tightened with a plurality of tie rods or a belt or the like is used. To apply a load to the laminate.
[0008]
As a conventional technique relating to such a fuel cell separator and a method for manufacturing the same, for example, a technique described in Patent Document 1 is known. According to this conventional technique, the first separator and the second separator are each called a half separator, and each half separator is constituted by a gradient carbon plate composed of a porous carbon layer and a dense carbon layer. Then, the MEA of each cell is sandwiched between the first separator and the second separator, and the opposing surfaces of the separators between adjacent cells are coated with a conductive graphite paste and overlapped.
[0009]
When manufacturing a graded carbon plate used for this separator, a thin film of a thermosetting resin is formed on the other surface of the porous carbon plate having a gas flow path formed on one surface, and the porous carbon plate on which the thin film is formed. Was subjected to a heat treatment to transform the thin film into a dense coal bed having a sealing property.
[0010]
[Patent Document 1]
Patent No. 2860209 (paragraph numbers 0039 to 0040, FIG. 4)
[0011]
[Problems to be solved by the invention]
However, in the above-mentioned conventional technology, when a stack is formed by laminating a large number of cells including a separator formed of a graphite powder / resin composite material, the separator or the MEA is excessively large due to warpage of the separator or insufficient thickness accuracy. There is a problem that a high stress is applied and the reliability is reduced.
[0012]
In addition, there is a problem that the local distortion of the separator is retained even after the stack is compressed, and the gas sealing performance of the gasket becomes insufficient.
[0013]
Further, the non-uniformity of the flatness of the separator increases the contact resistance between the separator and the electrode gas diffusion layer of the MEA, resulting in a problem that the power generation performance is reduced.
[0014]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides an electrolyte body, a fuel electrode and an oxidizer electrode disposed on both main surfaces facing the electrolyte body, and an outer side of the electrolyte body and the fuel electrode and the oxidizer electrode. In a fuel cell in which a plurality of unit cells each comprising a first and a second separator provided with a reaction gas flow path are stacked to form a stacked body, when stacking the unit cells, the separator The point is that the degree of curing of the thermosetting resin contained in the composition is in a semi-cured state.
[0015]
【The invention's effect】
According to the present invention, since the separators are laminated before being completely cured, the familiarity between the members constituting each cell and between adjacent cells is improved, and the sealing properties of the cooling water and the reaction gas are improved, and the contact is improved. The fuel cell power generation performance is improved by the reduction in resistance.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an assembly diagram for explaining the structure of a stack (fuel cell stack) in an embodiment of a polymer electrolyte fuel cell according to the present invention.
In the present embodiment, the separators 13 and 14 having dimensions of 300 [mm] × 200 [mm] × 1.8 [mm] are used for lamination as shown in FIG.
[0017]
One unit cell 24 is formed by sandwiching an electrolyte membrane 15 having gas diffusion layers 16 formed on both surfaces thereof together with a gasket 21 between an anode-side separator 13 and a cathode-side separator 14 from above and below. In this embodiment, a fuel cell stack is formed by stacking 50 cells.
[0018]
A cooling water flow path 17 for cooling the fuel cell stack is formed on the upper surface of the anode-side separator 13, and a hydrogen-rich fuel gas (not shown) is flown on the lower surface of the anode separator 13 facing the electrolyte membrane 15. An anode side fuel gas flow path is formed. On the upper surface of the cathode-side separator 14 facing the electrolyte membrane 15, a cathode-side oxidant gas channel 18 for flowing an oxidant gas such as air is formed.
[0019]
At both ends where a plurality of cells are stacked, a current extraction plate 12 is arranged so as to face the anode-side separator 13 and the cathode-side separator 14, respectively, and further, an insulator (heat insulation plate) 11 is arranged outside this. Further, an end plate 10 is arranged from the outside.
[0020]
The upper end plate 10 in the figure is provided with a gas inlet 22 and a cooling water inlet 23, and the lower end plate 10 in the figure is provided with a similar gas outlet and a cooling water outlet. .
[0021]
Each component has a fastening bolt through hole 19, and the end plates 10 at both ends apply a surface pressure to the fuel cell stack by fastening the fastening bolt 20.
[0022]
FIG. 2 is a schematic flowchart illustrating the outline of the method for manufacturing the polymer electrolyte fuel cell shown in FIG.
In FIG. 2, the method for producing a polymer electrolyte fuel cell according to the present invention comprises approximately three steps, a first step (S1) of forming a separator member in which a thermosetting resin is in a semi-cured state; A second step (S2) of stacking a plurality of unit cells by using the semi-cured separator member formed in the above to form a fuel cell stack (stack), and applying a pressure to the stack surface of the fuel cell stack. A third step (S3) of heating the stack to cure the thermosetting resin.
[0023]
Next, the characteristics of the thermosetting resin used for the molding material of the separator will be described. The thermosetting resin is cured by applying heat, but when heated to an extent that it is not completely cured (semi-cured state) when the shape of the product is formed, the temperature is returned to normal temperature and then heated again, and then heated again. At the time, it has the property of softening once (period T1 in FIG. 4C) and hardening again when the heated temperature is maintained.
[0024]
In the present invention, the stack is heated at room temperature using a semi-cured separator by utilizing this property, and then the stack is heated, thereby preventing the deterioration of the sealing property and the contact property caused when the separator is stacked. Things.
[0025]
In the present invention, first, when the separator is heat-formed, the separator is not completely cured as in the related art, but is formed in a semi-cured state, and the fuel cell stack is temporarily assembled using the semi-cured separator.
[0026]
Next, in order to heat the temporarily assembled stack, hot water is supplied to the cooling water flow path of the separator, or the heated gas is supplied to the hydrogen gas flow path or the oxidizing gas flow path (hereinafter, collectively referred to as a gas flow path). Shed. When the separator is softened by this heating, retightening is performed to improve the familiarity between the separators, and the sealing property and the contact property are measured here. In addition, there is an effect that familiarity is improved without necessarily performing retightening.
[0027]
Then, the hot water (heating gas) is continuously flown to completely cure the separator. Thereby, even if the formed separator has warpage or distortion, it is possible to prevent deterioration of the sealing property and the contact property that occur when a plurality of unit cells including the separator are stacked.
[0028]
The separator used in the present embodiment is composed of 19 parts by weight of a novolak type phenol resin, one part of a thermosetting resin, 1 part by weight of hexamine (hexamethylenetetramine) as a curing agent, and 100 parts by weight of graphite powder with respect to 100 parts by weight of graphite powder. A mold mainly composed of 1.2 parts by weight of a mold agent was molded by compression molding for 2 minutes. After molding, post-heating was performed for 30 minutes at the same temperature as during molding to obtain a semi-cured separator member.
[0029]
The thermosetting resin in the present invention is not limited to a phenol resin, but may be an epoxy resin, a silicone resin, a melamine resin, a urea resin, a polyacrylonitrile resin, a polyimide resin, an unsaturated polyester resin, a diallyl phthalate resin, a polyvinyl chloride resin, or a polyvinyl chloride resin. It has at least one or more of the carbodiimide resins in the composition, and includes various additives necessary for curing and accelerating the curing.
[0030]
As the graphite, either natural graphite or artificial graphite can be used, and the shape thereof can be any of a lump, a scale, a needle, and a sphere. As the internal release agent, at least one of known hydrocarbons, aliphatics, aliphatic amides, esters, alcohols, metal soaps, silicones and the like can be used.
[0031]
The degree of curing of the thermosetting resin constituting the separator before lamination can be known by measuring various mechanical properties, electric resistance, and thermophysical properties. The curing reaction speed varies greatly depending on the type of resin used and the temperature and pressure during molding. In addition, since the handleability of the separator after molding is also important, the degree of curing can be appropriately adjusted in consideration of these matters. In the present embodiment, the degree of curing is about the time of complete curing from the degree of the reaction progress of the resin at the temperature at the time of molding and the change in the bending strength of the separator material at room temperature after molding by thermal analysis (differential scanning calorimetry; DSC). 75% was used as a semi-cured separator member in assembling a fuel cell stack. In addition, if the degree of cure of the thermosetting resin is between 30 and 98%, both ease of handling and adhesion of the separator during assembly of the laminate can be achieved.
[0032]
Next, a method for manufacturing a polymer electrolyte fuel cell according to the present invention will be described in detail with reference to a detailed flowchart in FIG. 3 and a time chart in FIG. The time chart of FIG. 4 shows (a) the time change of the surface pressure applied to the stacking surface of the fuel cell stack, (b) the time change of the separator member temperature, and (c) the bending strength of the separator member when 100% is set when completely cured. , Respectively, with time.
[0033]
The correspondence between FIGS. 2 and 3 is that S1 (first step) corresponds to S10 to S14, S2 (second step) corresponds to S20, and S3 (third step) corresponds to S30 to S44. I have.
[0034]
First, in S10 of FIG. 3, graphite powder and a thermosetting resin (novolak-type phenol resin) are kneaded, a hardener (hexamine) and an internal release material are added, and the mixture is heated and kneaded to form a molding material for a separator. obtain. Next, in S12, the molding material is compression-molded with a heated mold and held for 2 minutes.
[0035]
Next, in S14, after releasing, the mold is annealed at the same temperature as the molding temperature of S12 for 30 minutes, and then cooled to room temperature to obtain a separator member in which the thermosetting resin is in a semi-cured state.
[0036]
Next, in S20, the fuel cell stack is assembled as shown in FIG. 1 using the thus obtained semi-cured separator member (temporary assembly).
[0037]
Next, in S30, the end plate is tightened to apply a surface pressure of 0.5 MPa to the stack lamination surface. In this embodiment, the initial tightening is 0.5 MPa, but it is sufficient that the gasket is compressed at a minimum required surface pressure or more.
[0038]
Next, in S32, the fuel cell stack is heated by circulating hot water of 80 ° C. in the cooling water flow path of the fuel cell stack at a flow rate of 10 L / min for 5 minutes. The hot water temperature and the flow rate are not necessarily 80 ° C. and 10 L / min, but may be appropriately determined as needed and circulated at the required flow rate. Due to this heating, the separator member constituting the fuel cell stack is temporarily softened as shown by a period T1 in FIG. 4C.
[0039]
Temporary softening of the separator due to heating of the fuel cell may reduce the tightening of the stack. In this case, when the separator is softened at the heating temperature, the passage for the gasket and the groove for the gasket are excessively deformed at the surface pressure of 0.5 MPa, and the pre-curing adjustment of the separator is necessary in advance so that the surface pressure does not decrease. However, in the present embodiment, the tightening is sequentially adjusted so as to maintain 0.5 MPa with respect to the decrease in the surface pressure with time.
[0040]
Next, in S34, when the temperature of the fuel cell stack reached 80 ° C., a further load was applied with a fastening bolt, and the surface pressure of the stack stacking surface was set to 0.8 MPa. In S36, in addition to the hot water circulation, humidified air at a temperature of 80 ° C. and a humidity of 90% (relative humidity with respect to the stack temperature) was introduced at a flow rate of 3 L / min from the air inlet on the cathode side of the fuel cell and maintained for 10 minutes. This period is indicated by T2 in FIG. Thereby, the curing of the separator member proceeds, and the strength of the separator member increases. The temperature, humidity, and flow rate of air are not limited to these.
[0041]
By introducing the humidified gas into the gas flow path of the fuel cell in S36, the electrolyte membrane of the constituent member can be wetted. In an actual fuel cell operating environment, the electrolyte membrane becomes wet and swells, so that lamination can be performed in consideration of the state of the membrane. In the present embodiment, the humidification gas is supplied in S36, but the supply of the humidification gas may be performed simultaneously with the circulation of the hot water in S32.
[0042]
In S34, the surface pressure of the stacking surface of the stack is set to 0.8 MPa. However, the surface pressure may be determined as needed. In some cases, the surface pressure set in S30 may be continued in S34. .
[0043]
Next, in S38, the tightening bolts are further tightened to apply a surface pressure of 1.2 MPa to the stack lamination surface. Next, in S40, the circulation of the hot water at 80 ° C. and the supply of the humidified gas at a temperature of 80 ° C. and a humidity of 90% were maintained for 15 minutes (T3 in FIG. 4). Thereafter, the circulation of the hot water and the supply of the humidified gas were stopped in S42, and the fuel cell stack was allowed to cool to room temperature in S44.
[0044]
Next, with reference to FIG. 5, a prediction of the output characteristics of the polymer electrolyte fuel cell according to the present embodiment and a comparative example of the polymer electrolyte fuel cell according to the conventional manufacturing method will be shown.
[0045]
In the comparative example, a fuel cell stack was assembled after using a thermosetting resin having the same components as in the embodiment and completely curing the resin by heat treatment at 180 ° C. for 2 hours using a hot press. At the time of assembly, the stack was tightened at a surface pressure of 1.2 MPa without heating.
[0046]
In FIG. 5, the solid line is the characteristic of the embodiment, and the broken line is the characteristic of the comparative example. A performance difference corresponding to the contact resistance occurs between the IV characteristics of both stacks of the embodiment and the comparative example, and the fuel cell according to the present embodiment shows a higher output voltage than the comparative example particularly in a region where the current density is high.
[0047]
According to the present embodiment described above, the fuel cell stack is laminated using the separator member in which the thermosetting resin is in a semi-cured state, and after the lamination, the thermosetting resin is heated to cure the thermosetting resin. In addition, the sealing performance between the separator and the electrolyte membrane can be improved, and the contact resistance can be reduced to improve the fuel cell performance.
[0048]
In the present embodiment, the step of heating and completely curing the fuel cell stack after lamination is also included in the manufacturing process, so that the heating state can be accurately controlled.
[0049]
Next, a modified example of the present embodiment will be described. In the above-described embodiment, the heating temperature after the stack lamination is fixed at 80 ° C., and the curing is completed, but the heating temperature may be changed with time. At this time, the load on the stack lamination surface may be changed according to the heating temperature. Although the fuel cell stack is heated from the inside using the cooling water flow path and the gas flow path, the stack can be heated from the outside using hot air, steam, or the like.
[0050]
In the above embodiment, the example in which the tightening load of the stack is increased stepwise to the target value is shown. However, as a modified example in which the process is simplified, the stack stacked using the semi-cured separator is targeted from the beginning. After tightening with a load (1.2 MPa in the above embodiment), the stack may be heated.
[0051]
In the case of such a modification, the fuel cell system can be heated after the fuel cell system is mounted on the vehicle, without performing the heating step when the fuel cell stack is manufactured. In this heating, the temperature of the fuel cell stack is raised to the operating temperature by causing the fuel cell to actually generate power and performing a test run of the vehicle, and the thermosetting resin in the semi-cured state of the separator is temporarily softened → completely cured. It can also be done. Thereby, it is possible to prevent the deterioration of the sealing property and the contact property that occur when the separators, which are the object of the present invention, are laminated by a simpler method.
[0052]
According to the present invention described above, when forming a fuel cell stack, by setting the degree of curing of the thermosetting resin, which is one of the components constituting the separator, to a semi-cured state, the distance between adjacent cells can be improved. It is said that the adhesion between the separators and between the separator in the cell and the electrolyte membrane is improved, the sealing property of the cooling water flow path and the gas flow path can be improved, and the contact resistance is reduced to obtain a high output voltage and a high power generation efficiency. effective.
[0053]
Further, according to the present invention, after laminating the laminated body using the semi-cured separator, by heating the laminated body, slight deformation or stress relaxation according to the laminated state occurs, and the reliability of the separator is maintained. And at the same time, the separator can be quickly cured.
[0054]
Further, according to the present invention, the degree of cure of the thermosetting resin in the semi-cured state is 30 to 98%, so that both ease of handling of the separator during assembly of the laminate and adhesion of the separator are compatible. Can be done.
[0055]
Further, according to the present invention, after stacking a plurality of unit cells, by increasing the load applied to the stacking surface of the stack in a stepwise manner, it is possible to obtain high adhesion while maintaining the reliability of the separator. .
[0056]
Further, according to the present invention, the heating of the laminated body after laminating a plurality of unit cells includes heating the cooling water flow path of the laminated body, heating the gas flow path of the laminated body, or heating the laminated body from outside. Since the heating is performed by at least one, effective heating of the laminate can be performed.
[0057]
Further, according to the present invention, the heating of the gas flow path at the time of heating the laminate can be performed with the humidified gas, whereby the solid polymer membrane can be cured in the humidified state, and the electrolyte in the operating state of the fuel cell can be cured. The expansion force due to the wetting of the film can be reduced.
[0058]
Further, according to the present invention, at the time of heating the laminate, by changing the load applied to the lamination surface of the laminate according to the heating temperature, it is possible to prevent the separator temporarily softened at the time of heating from being deformed more than necessary. Can be.
[0059]
Further, according to the present invention, by heating the fuel cell stack after the fuel cell is mounted on the vehicle, the fuel cell stack can be completely cured at the same time as the test operation after the fuel cell mounting. Manufacturing process can be reduced.
[Brief description of the drawings]
FIG. 1 is an assembly diagram for explaining a stack structure of a polymer electrolyte fuel cell according to the present invention.
FIG. 2 is a schematic flowchart showing an assembling procedure in an embodiment of a method for manufacturing a polymer electrolyte fuel cell according to the present invention.
FIG. 3 is a detailed flowchart showing an assembling procedure in an embodiment of the method for manufacturing a polymer electrolyte fuel cell according to the present invention.
FIG. 4 is a time chart for explaining a method of manufacturing a polymer electrolyte fuel cell according to the present invention, wherein (a) a time change of a surface pressure, (b) a time change of a temperature, and (c) a time change of a separator strength. Are respectively shown.
FIG. 5 is an IV characteristic diagram illustrating contact resistance characteristics between the embodiment of the polymer electrolyte fuel cell according to the present invention and a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... End plate 11 ... Insulator 12 ... Current extraction plate 13 ... Anode side separator 14 ... Cathode side separator 15 ... Electrolyte membrane 16 ... Gas diffusion layer 17 ... Cooling water channel 18 ... Cathode side oxidant gas channel 19 ... Fastening bolt penetration Hole 20: fastening bolt 21: gasket 22: gas inlet 23: cooling water inlet 24: unit cell

Claims (9)

An electrolyte body, a fuel electrode and an oxidant electrode disposed on both main surfaces of the electrolyte body, and a second electrode disposed outside the electrolyte body and the fuel electrode and the oxidant electrode, and each having a gas flow path. In a fuel cell in which a stacked body is configured by stacking a plurality of unit cells including the first and second separators,
A fuel cell, wherein the thermosetting resin contained in the separator is in a semi-cured state when a plurality of the unit cells are stacked. 2. The fuel cell according to claim 1, wherein after the plurality of unit cells are stacked, the stacked body is heated to further harden the thermosetting resin. 3. The fuel cell according to claim 1, wherein the degree of cure of the thermosetting resin in the semi-cured state is 30 to 98%. 2. The fuel cell according to claim 1, wherein a load applied to a stacking surface of the stack is increased stepwise after stacking a plurality of the unit cells. The heating of the laminate is performed by at least one of heating a cooling water flow path of the laminate, heating a gas flow path of the laminate, or heating the laminate from outside. 2. The fuel cell according to 2. 6. The fuel cell according to claim 5, wherein the fuel cell is a solid polymer type, and the gas flow path is heated by a humidified gas. 3. The fuel cell according to claim 2, wherein a load applied to a stacking surface of the stack is changed according to a heating temperature when the stack is heated. 3. The fuel cell according to claim 2, wherein the heating time of the stack is after the fuel cell is mounted on a vehicle. An electrolyte body, a fuel electrode and an oxidant electrode disposed on both main surfaces of the electrolyte body, and a second electrode disposed outside the electrolyte body and the fuel electrode and the oxidant electrode, and each having a gas flow path. In a method of manufacturing a fuel cell in which a plurality of unit cells each including a first and a second separator are stacked to form a stacked body,
A first step of molding the separator in a semi-cured state of the thermosetting resin included in the separator,
A second step of stacking a plurality of unit cells including the separator formed in the first step to form a laminate,
A third step of heating the laminate while applying pressure to the laminate surface of the laminate to cure the thermosetting resin;
A method for manufacturing a fuel cell, comprising:

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