JP2003115321A - Fuel cell stack assembly method - Google Patents

Abstract

(57) Abstract: Provided is a method of assembling a fuel cell capable of preventing formation of a short circuit between fuel cell members and contamination of a cooling medium. SOLUTION: After applying a sol liquid in advance to a flow path of a cooling medium of each member of a fuel cell, the formed gel is fired,
A fuel cell stack is assembled by forming a dense film by curing by photopolymerization or thermal annealing, and then stacking unit fuel cells via a separator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of assembling a fuel cell stack capable of preventing the formation of a short circuit in the fuel cell stack and preventing the leakage of impurities from the separator.

[0002]

2. Description of the Related Art In order to remove heat generated by a cell reaction of a polymer electrolyte fuel cell, a cooling medium is caused to flow in the fuel cell, and the passage of the cooling medium penetrates a laminated body in which cells and separators are laminated. Is proposed. In this battery, a through hole of the same shape is formed at the same position on the laminated surface of the cell and the separator so as to penetrate in the laminating direction, and the through hole penetrates the laminated body when laminating the cell and the cooling member. To form.

Since a potential difference is generated between the respective members forming the cooling medium passage formed in the contact hole with the electrode on the surface of the separator and the communication hole serving as the passage of the cooling medium in the stacking direction of the fuel cell stack, the cooling member. The cooling member is required to have electrical insulation so as not to form a short circuit therebetween. As the cooling medium, pure water is preferably used from the viewpoint of insulation, but it is common to use an antifreezing liquid such as ethylene glycol as the cooling medium for the fuel cell for automobiles. For this reason,
It is necessary to cover the cooling medium flow path and the communication hole for the cooling medium with an insulating material and to strengthen the coating to ensure electrical insulation. In Japanese Unexamined Patent Publication No. 7-230818, after unit fuel cells are laminated to assemble a laminated body, a film forming material (sol solution obtained by hydrolyzing tetraethoxysilane) is poured into the refrigerant passage and the communication hole to form an inner surface of the passage. There is disclosed a method of forming a coating by depositing a coating forming material on.

However, this method has a drawback that coating unevenness is likely to occur (film thickness distribution occurs), and after assembly, it is impossible to grasp the coating state in the coolant passages and the communication holes formed inside the laminated body. . Also, drying with nitrogen gas cannot be heated at a high temperature, and since the film is dried at a low temperature of 100 to 200 ° C., the film is not sufficiently hardened and the growth (densification) of crystal grains is insufficient. Therefore, when used for a long time,
Due to the difference in the coefficient of thermal expansion between the coating and the separator, there arises a problem that the film is peeled off due to mechanical abrasion or pitting corrosion occurs at the peeled portion in a metal separator or the like.

Further, in the metal separator, corrosion causes the impurity ions to be mixed into the cooling medium, and also in the separator made of a carbon material, the carbon particles are separated and mixed into the cooling medium, thereby contaminating the cooling medium.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method of assembling a fuel cell stack which can prevent the formation of a short circuit between fuel cell members and the contamination of the cooling medium.

[0007]

As a result of earnest research in view of the above object, as a result of applying a sol liquid in advance to the flow path of the cooling medium of each member of the fuel cell, it is densified by curing by firing, photopolymerization or thermal annealing. It was discovered that it is possible to effectively prevent the formation of a short circuit between members and the contamination of the cooling medium by forming such a coating and then assembling the fuel cell stack, and conceived the present invention.

That is, the method of assembling the fuel cell stack of the present invention is the same as the method of assembling a fuel cell stack in which a plurality of unit fuel cells are stacked with a separator in between, and a sol liquid is applied to the flow path of the separator. And let it dry,
It is characterized in that an electrically insulating film is formed in the flow path by one or more of firing, photopolymerization and thermal annealing, and then the unit fuel cells are laminated via the separator.

It is preferable that the flow passage is a communication passage for the refrigerant flow passage and the cooling medium, or further includes a reaction gas passage and a communication hole for the reaction gas in addition to these.

The sol solution preferably contains a polycondensate obtained from a metal alkoxide by a sol-gel method, and the metal alkoxide is preferably tetraethoxysilane.

The firing is preferably carried out by heating at 300 to 600 ° C., and at least one selected from the group consisting of an excimer laser, a high pressure mercury lamp, a metal halide lamp and a CO ₂ laser as a light source for photopolymerization or thermal annealing. It is preferred to use seeds.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A method for assembling a fuel cell stack according to the present invention will be described in detail below.

[1] Construction of Fuel Cell Stack FIGS. 1 and 2 show an example of a fuel cell stack assembled by the method for assembling a fuel cell stack of the present invention, and a unit fuel cell and a separator constituting the fuel cell stack. Fuel cell stack consists of multiple unit fuel cells (membrane / electrode assembly) 12
Are laminated via a separator 11. Unit fuel cell 12
Is composed of a catalyst electrode (12a, 12b) and an electrolyte membrane 12c. The catalyst electrode comprises electrodes (anode and cathode) and a gas diffusion layer supporting each electrode. The gas diffusion layer is formed by coating a slurry of carbon black on a support layer made of carbon paper or the like. Further, on the gas diffusion layer, catalyst particles formed by supporting platinum particles or platinum alloy particles on carbon black are applied to form electrodes. The electrolyte membrane 12c is an ion exchange membrane formed of a fluorine-based polymer membrane such as perfluoroalkylsulfonic acid, a sulfonated non-fluorine-based polymer membrane such as sulfonated polyetheretherketone, and both sides of the electrolyte membrane 12c. A unit fuel cell 12 is constructed by joining a catalyst electrode so that the anode electrode and the cathode electrode face each other.

The separator 11 separates the fuel gas (hydrogen) from the oxidant gas (oxygen or air), secures a flow path for supplying the gas to each electrode, and further generates electricity generated by the fuel cell unit. Takes the role of transmitting to the outside. Therefore, the separator 11 is made of a conductive material such as carbon material, carbon composite material (composite material of carbon and thermosetting resin or thermoplastic resin), metal material, metal composite material (composite material of metal and carbon). Formed from. Further, as shown in FIG. 2, a groove (reaction gas flow path) is formed on the surface of the separator 11 to form a flow path for fuel gas and oxidant gas at the contact portion with the catalyst electrode.
15 is formed, and a groove (refrigerant flow path) 14 that forms a flow path for the cooling medium is formed on the opposite surface. FIG. 3 shows the refrigerant channel 22.
Shows a separator formed with. The separator 11 penetrates to form a fuel gas passage (supply port 24 and discharge port 26), an oxidant gas passage (supply port 25 and discharge port 27), and a cooling medium passage (supply port 21 and discharge port 23). A hole (communication hole) is formed. Through hole (communication hole) provided in the separator
Forms a passage for the reaction gas (fuel gas and oxidant gas) and a cooling medium that penetrates in the stacking direction of the fuel cell stack when the unit fuel cells 12 are stacked via the separator 11.

End plates 8 are attached to both ends of the fuel cell stack, and a manifold 7 serving as a supply / discharge port for the reaction gas and the cooling medium is provided on the end plates.
Here, the cooling medium supplied from the cooling medium inlet 1 travels through the passage (communication hole) formed in the stacking direction of the fuel stack, and from the supply port 21 formed in the separator 11 that sandwiches each unit fuel cell 12, the refrigerant. After exchanging heat with the unit fuel cell 12 through the flow path 22, a passage (communication hole) from the discharge port 23
In the opposite direction and is discharged from the cooling medium outlet 4. Similarly, the fuel gas supplied from the fuel gas inlet 2 and the oxidant gas supplied from the oxidant gas inlet 3 travel through the passages (communication holes) formed in the stacking direction of the fuel stack and pass through each unit fuel cell 12. From the supply ports 24 and 25 formed in the sandwiched separator 11 through the respective reaction gas flow paths 15, the unit battery 12
After supplying the fuel gas and the oxidant gas to the exhaust port 26 and
From 27, they respectively pass through the passages (communication holes) in opposite directions and are discharged from the fuel gas outlet 5 and the oxidant gas outlet 6.

[2] Sol solution (1) Metal alkoxide Sol solution is obtained from metal alkoxide by sol-gel method
It is preferable to contain the obtained polycondensate. Metal alkoki
As the metal used for sid, Al, Ba, Bi, Ca, Cr, Co,
Cu, Fe, La, Mo, Nb, Ni, Pb, P, Si, Sn, Sr, Ti, T
a, V, W, Y, Zr and the like can be mentioned. Also metal alkoxide
Examples of the alkoxy group used for methoxy group, ethoxy group
Group, propoxy group, butoxy and the like. Metal al
As the coxide, aluminum alkoxide (aluminum
(N-butoxide, aluminum ethoxide, etc.), gel
Manium alkoxide (germanium ethoxide, etc.),
Strontium alkoxide (strontium ethoxy
Etc.), titanium alkoxide (titanium butoxide, titanium)
Ethoxide, titanium isopropoxide, titanium methoxide
Sid), zirconium alkoxide (zirconium
Toxide, zirconium ethoxide, zirconium
Toxide, etc., silicon alkoxide (silicon butoki)
Sid, Silicon ethoxide, Silicon propoxide, Si
Reconmethoxide, etc.), vanadyl alkoxide (vanadi)
Ethoxide, etc.) and the like can be preferably used. This
From the viewpoint of handling in these, alkoxysilane (silicon
It is more preferable to use a conalkoxide). concrete
Includes tetrabutoxysilane [Si (OC_FourH₉)_Four], Tetraeth
Xysilane [Si (OC₂H_Five)_Four], Silicon Propoxide [Si (OC
₃H ₇)_Four] And tetramethoxysilane [Si (OCH₃)_Four] Is better
In addition, tetraethoxysilane [Si (OC₂H_Five)_Four] Is even better
Good

(2) Solvent After dissolving the metal alkoxide in a solvent, a sol solution is prepared by a sol-gel method. Preferred solvents for dissolving the metal alkoxide include methyl alcohol, ethyl alcohol, isopropyl alcohol, ethoxyethyl alcohol, allyl alcohol, ethylene glycol, ethylene oxide, triethanolamine, xylene and the like.

(3) Method for Preparing Sol Solution First, a metal alkoxide corresponding to a desired polycondensate (metal oxide) is dissolved in the above alcohol while stirring to prepare a mixed solution. Next, water required for hydrolysis and an acid (or alkali) as a catalyst are added as an alcohol solution to the alcohol solution of the alkoxide to prepare a starting solution. As the acid, hydrochloric acid, sulfuric acid, nitric acid, acetic acid or the like can be used. In addition to the function as a catalyst, the acid has a function of preventing the formation of precipitate and the separation of liquid phase.

The amount of alcohol is preferably 30 to 50 mol, more preferably 38 to 42 mol, per 1 mol of metal alkoxide. The amount of alcohol is appropriately adjusted according to the coating method of the sol liquid (dip coating, spin coating, etc.) so that the viscosity is suitable for each coating method. The amount of water is preferably 1 to 3 mol, more preferably about 2 mol, based on 1 mol of the metal alkoxide. The amount of the acid added as a catalyst is preferably 0.1 to 0.5 mol, based on 1 mol of the metal alkoxide, and is 0.1.
2 to 0.5 mol is more preferable. If it is less than 0.1 mol, the densification of the coating film will be reduced, and the polycondensation reaction will take time.

The prepared starting solution is stirred, for example, at room temperature to 80 ° C. under reflux to carry out polycondensation reaction by hydrolysis and dehydration condensation of alkoxide. As the reaction proceeds, a Me-O network is formed, and metal oxide particles are generated to form a sol solution. A chelating agent such as acetylacetone may be added to the prepared sol solution. By adding acetylacetone or the like, a ring current flows in the molecule and is stabilized, and the storage time of the sol solution can be extended.

[3] Assembling Method In the assembling method of the fuel cell stack of the present invention, the sol liquid is applied to the refrigerant flow path of each separator in advance and dried before assembling, and then baked or photocured (photopolymerization or heat treatment). Annealing) forms an insulative coating on the coolant channel and the like, and then unit fuel cells and separators are alternately laminated.

(1) In order to prevent a short circuit from being formed between the sol liquid coating and cooling members, a coolant channel 22 formed on the separator surface as shown in FIG.
Also, an insulating film is provided on the communication holes 21 and 23 for the cooling medium. The method for assembling a fuel cell stack according to the present invention is characterized in that an insulating film is formed by a sol solution before assembling the fuel cell stack. This makes it possible to prevent coating unevenness from occurring and to increase the strength of the film. When it is desirable to suppress the corrosion of the separator such as a metal separator, it is preferable to provide a coating also on the reaction gas passage and the communication gas communication holes 24 to 27.

FIG. 4 shows the step of applying the sol liquid to the coolant channel. (a) First, prepare a separator provided with a refrigerant channel, (b)
In order to secure electric conductivity, the contact portion (hatched portion) of the separator in the refrigerant flow path is masked in advance. The mask material is not particularly limited, and can be appropriately selected according to the coating method such as a plate, a tape, and a coating film. In the case of also controlling the corrosion, the contact portion of the refrigerant flow passage and the reaction gas flow passage (the convex portion of the separator cross section shown in FIG. 2), the communication hole portion and the portion other than the flow passage of the manifold portion are masked. It is preferable that the metal separator is washed with acetone in advance by boiling.

(C) Next, the separator is heated to about 100 to 200 ° C., and the sol liquid is applied to the refrigerant flow path to cause gelation. Heating is preferably performed using a hot plate or the like. As a coating method, known methods such as spray coating, dip coating, spin coating and roll coating may be used. It is particularly preferable to use spray coating from the viewpoint of suppressing the occurrence of coating spots and improving the solvent removal efficiency in the sol stage. Similarly, the sol liquid is applied to the cooling medium communication hole, the reaction gas communication hole, and the flow path portion of the manifold portion, if necessary.

(2) Drying (d) The gelled separator is kept at about 100 to 200 ° C. for several minutes to be dried and cured (prebaking). In the case of thickening the film, a coating film having a sufficient thickness can be formed by repeating the steps of coating (c) and drying (d). Further, by stacking the thin films, it is possible to reduce stress between the films and suppress the occurrence of cracks. The thickness of the coating film is preferably 10 to 200 μm in order to secure the electric insulation and the strength of the film, 50
˜100 μm is more preferred.

(3) The mask material is removed from the separator on which the cured coating film (metal oxide gel) is formed. Next, as shown in FIG. 4, further firing (e)
And / or the photo-curing (f) is performed to densify the coating film (metal oxide gel). Even if it is used for a long period of time by sufficiently curing the film, it is possible to suppress peeling of the film due to the difference in thermal expansion coefficient.

The firing is performed by further heating the prebaked coating film at 300 to 600 ° C. for 0.5 to 2 hours in an oxidizing atmosphere. The baking can increase the hardness of the film and strengthen the film. Further, by heating in an oxidizing atmosphere in this way, point defects in which oxygen atoms in the crystal escape can be suppressed. If the temperature is lower than 300 ° C, the temperature is low and the hardness of the film cannot be sufficiently increased. If it exceeds 600 ° C, the separator may be deformed or deteriorated. The heating method is not particularly limited, and for example, a commercially available heating furnace or the like can be used. In the case of a gel using alkoxysilane as a metal alkoxide, it is converted into a silica glass film by firing.

The coating may be reinforced by photocuring. Especially when a metal separator is used as the separator, the heat treatment tends to cause warping or compositional deformation. For example, when the member is an austenitic SUS material or the like, embrittlement occurs due to the precipitation of carbides at 500 to 900 ° C. Therefore, when the coating film (metal oxide gel) is formed on the metal separator, it is preferable to cure the film using a photocuring process such as photopolymerization or thermal annealing.

Photopolymerization is carried out by irradiating ultraviolet rays having a strong photochemical action. The ultraviolet irradiation causes the crosslinking reaction of the metal oxide gel to proceed and densify it. As a preferable light source used for ultraviolet irradiation, a high pressure mercury lamp, an ultra high pressure mercury lamp,
Xenon lamp, metal halide lamp, excimer laser [ArF (193nm), KrCl (222nm), KrF (249nm), Xe
Cl (308 nm) or XeF (351, 353 nm)] and the like.
From the viewpoint of ultraviolet efficiency, a high pressure mercury lamp, a metal halide lamp or an excimer laser is more preferable. At the time of irradiation, light having a wavelength unnecessary for curing may be cut by a filter or the like.

Thermal annealing cures the film by instantaneous thermal annealing by pulse transmission using laser light. As the laser light, a CO ₂ laser, an excimer laser or the like can be preferably used.

Photocuring and heating may be used in combination. For example,
The film may be cured by applying heat to the substrate before or after the photocuring or simultaneously with the photocuring. By thus using heating in combination, curing of the film is promoted and the curing time can be shortened. Heating is performed within a range that does not cause deformation or deterioration of the separator.

(4) Assembling A fuel cell stack is assembled by using the separator having the electrically insulating coating formed on the coolant passages and the cooling medium communication holes of the separator as described above. By stacking the unit fuel cells with the separator interposed therebetween, a communication hole covered with an electrically insulating coating is formed, whereby electrical insulation between the cooling members can be secured. Further, when the reaction gas flow path of the separator and the communication gas communication holes are also provided with coatings, a fuel cell stack having electrical insulation and corrosion resistance can be obtained. End plates are attached to both sides of the obtained stack to assemble a fuel cell.

[0033]

The present invention will be described in more detail by the following examples, but the present invention is not limited thereto.

Example 1 (1) Preparation of Molded Separator 70% by weight of artificial graphite powder and 30% by weight of phenolic resin were mixed with each other, and they were sufficiently kneaded by a pressure kneader. The kneaded product was loaded into a mold having the shape of a separator to prepare a plate-shaped separator having a refrigerant channel, a reaction gas channel, and a communication hole.

(2) Preparation of sol solution 0.02 mol of tetraethoxysilane was dissolved in 37 ml of 99.5% ethanol solution in several batches with stirring. Add 0.7 ml of pure water to this ethanol solution and 0.5 ml of 60 as a catalyst.
% Nitric acid was added, and hydrolysis and dehydration condensation reaction were carried out while stirring at 80 ° C. under reflux for 2 hours to prepare a sol liquid. 0.02 mol of acetylacetone was added as a stabilizer to the prepared sol solution.

(3) Application of Sol Solution As shown in FIG. 4, a plate having the same shape as the contact portion was placed on the contact portion (hatched portion) of the molded separator for masking. The masked separator was placed on a hot plate and heated to 150 ° C. Next, the sol liquid was applied to the refrigerant flow path of the separator using air spray. The applied separator was kept at 150 ° C. for 5 minutes to be dried and cured. The steps of applying the sol solution and drying and curing were repeated to form a film having a thickness of 50 μm. Similarly, a film was formed also on the communication hole for the cooling medium of the separator.

(4) The masking plate was removed from the separator on which the fired coating had been formed, placed in a heating furnace and heated at 500 ° C. for 1 hour for firing.

(5) A fuel cell stack was assembled by alternately stacking unit fuel cells and separators using the assembled and fired separators.

In the fuel cell stack thus assembled, no coating spots were formed in the refrigerant flow path of the separator, and neither peeling nor cracking occurred during use.

Example 2 (1) Preparation of Separator Using an austenitic SUS plate, a separator having the same shape as in Example 1 was prepared by press working.

(2) Preparation of sol solution A sol solution was prepared in the same manner as in Example 1.

(3) Application of Sol Solution In the same manner as in Example 1, the sol solution was applied to the refrigerant passages of the separator and the communication holes for the cooling medium. Further, the sol liquid was similarly applied to the reaction gas flow path of the separator and the communication gas communication hole. The masked separator was placed on a hot plate and heated to 150 ° C. The applied separator was kept at 150 ° C. for 5 minutes to be dried and cured. The steps of applying the sol solution and drying and curing were repeated to form a film having a thickness of 50 μm.

(4) The masking plate was removed from the photo-curing separator, and the portion where the coating was formed was irradiated with ultraviolet rays using a high pressure mercury lamp to cure the film.

(5) Assembly A fuel cell stack was assembled in the same manner as in Example 1. The fuel cell stack assembled in this manner did not cause uneven coating in the coolant passage of the separator, and did not cause cracks or corrosion due to use.

Comparative Example 1 A fuel cell stack was assembled by producing a separator in the same manner as in Example 1 and alternately stacking unit fuel cells and separators. After mounting the end plate on the fuel cell stack, a pipe was connected to the cooling medium supply / discharge port of the end plate, and this pipe was also connected to a heat exchanger and a pump to form a circulation channel for the cooling medium. Next, a pipe was connected to the fuel supply / discharge port of the end plate and also connected to the fuel gas supply device to assemble the fuel cell system. Next, the sol liquid prepared in the same manner as in Example 1 was caused to flow in the circulation flow path of the fuel cell system, and then dried and cured by passing nitrogen gas heated to 150 ° C.

When the fuel cell having the film formed thereon was disassembled and examined, unevenness was observed in the film formed in the refrigerant passage.
Further, peeling of the film occurred due to use, and the hardness of the film was not sufficient as compared with Example 1.

[0047]

As described above, in the method for assembling the fuel cell stack of the present invention, the sol liquid is applied in advance to the cooling medium channels of the respective members and then cured by firing, photopolymerization, thermal annealing or the like. Since the densified film is formed and then the fuel cell stack is assembled, the film has no coating unevenness and has excellent film strength. Therefore, it is possible to prevent formation of a short circuit between members, corrosion, and contamination of the cooling medium.

[Brief description of drawings]

FIG. 1 is a side view showing an example of a fuel cell stack assembled by a method for assembling a fuel cell stack of the present invention.

FIG. 2 is a cross-sectional view showing an example of a unit fuel cell and a separator of a fuel cell stack assembled by the fuel cell stack assembling method of the present invention.

FIG. 3 is a plan view showing an example of a fuel cell separator.

FIG. 4 is a diagram showing a step of applying a sol liquid in the method for assembling the fuel cell stack of the present invention.

[Explanation of symbols]

1 ... Cooling medium inlet 2 ... Fuel gas inlet 3 ... Oxidant gas inlet 4 ... Cooling medium outlet 5: Fuel gas outlet 6 ... Oxidant outlet 7: Manifold 8 ... End plate 11 ... Separator 12-Unit fuel cell 12a, 12b ... Catalyst electrodes 12c ... Electrolyte membrane 14, 22 ... Refrigerant flow path 15 ... Reaction gas flow path 21 ... Cooling medium supply port

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshinori Warishi             1-4-1 Chuo 1-4-1 Wako City, Saitama Prefecture             Inside Honda Research Laboratory F-term (reference) 5H026 AA02 BB00 BB01 BB03 BB04                       CC03 CC08 CX04 EE17 HH08

Claims (7)

[Claims] 1. A method of assembling a fuel cell stack comprising a plurality of unit fuel cells stacked with a separator interposed therebetween, wherein a sol liquid is applied to a flow channel formed in the separator, the sol liquid is dried, and then baked. A method of assembling a fuel cell stack, which comprises forming an electrically insulating coating on the flow path by one or more of photopolymerization and thermal annealing, and then stacking the unit fuel cells via the separator. 2. The method for assembling a fuel cell stack according to claim 1, wherein the flow path is a coolant flow path and a communication hole for a cooling medium. 3. The method for assembling a fuel cell stack according to claim 1, wherein the flow path further includes a reaction gas flow path and a communication gas communication hole. Method. 4. The method for assembling a fuel cell stack according to claim 1, wherein the sol liquid contains a polycondensate obtained from a metal alkoxide by a sol-gel method. Method for assembling fuel cell stack. 5. The method for assembling a fuel cell stack according to claim 4, wherein the metal alkoxide is tetraethoxysilane. 6. The method for assembling a fuel cell stack according to claim 1, wherein the firing is performed at 300 to 600 ° C.
A method for assembling a fuel cell stack, which is performed by heating at a temperature of 1. 7. The method for assembling a fuel cell stack according to claim 1, wherein an excimer laser, a high pressure mercury lamp, or a light source for the photopolymerization or thermal annealing is used.
A method for assembling a fuel cell stack, comprising using at least one selected from the group consisting of a metal halide lamp and a CO ₂ laser.