JP4954362B2 - Method for producing polymer electrolyte fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a polymer electrolyte fuel cells, particularly a method for forming a catalyst layer.
[0002]
[Prior art]
As the electrode of the polymer electrolyte fuel cell, generally used is one in which a catalyst layer containing a noble metal such as platinum or ruthenium as a catalyst component is formed on a porous conductive substrate. Normally, these catalyst layers are formed by mixing fine carbon powder carrying a noble metal, a solution of a hydrogen ion conductive polymer electrolyte, and an organic solvent such as isopropyl alcohol into an ink, and screen printing this ink. In general, it is formed on carbon paper as a base material using a spraying method or a spraying method. The electrode thus produced is joined by hot pressing through the electrolyte membrane to produce an electrode electrolyte membrane assembly. In addition, a method has also been proposed in which a catalyst layer is formed on a chemically inert polymer film and then transferred to an electrolyte membrane.
[0003]
[Problems to be solved by the invention]
The performance of the polymer electrolyte fuel cell deteriorates when carbon monoxide is mixed in the fuel gas. This is because platinum in the catalyst layer is poisoned with carbon monoxide.
[0004]
Further, the catalyst layer formed on a porous electrode substrate such as carbon paper is generally basically a single layer, and it is difficult to make it multilayer. For example, although it is possible as a manufacturing method to make a catalyst layer multilayer by techniques, such as screen printing, in the coating of the 2nd layer, there exists a danger that the catalyst layer formed previously may be destroyed by printing pressure. . Even if the coating can be performed, an intermediate layer in which the two layers are mixed is inevitably generated at the interface, and the boundary at which the two catalyst layers are switched becomes ambiguous. As a result, the effect of the multilayer catalyst layer is reduced. Moreover, the manufacturing method in which two or more catalyst layers are formed on such a porous conductive base material is not suitable for mass production because the process becomes complicated.
[0005]
In addition, when an electrode is formed on a porous electrode substrate, the catalyst layer enters the porous electrode substrate and the catalyst utilization rate decreases, and the catalyst layer depends on the surface shape of the substrate, and the uniform thickness Formation of the catalyst layer becomes difficult. Moreover, since the porous electrode base material also plays the role of a gas diffusion layer, the gas diffusibility is also inhibited when the catalyst layer enters, so that the electrode structure is not ideal.
[0006]
Moreover, regarding the method of forming the catalyst layer on the polymer film, it is necessary to increase the viscosity of the electrode ink. For this purpose, it is common to add a high boiling point alcohol or a viscosity modifier. In this case, there is a need for sufficient drying and baking after the electrode ink coating process. In addition, when these treatments are insufficient, there are problems such as deterioration of battery characteristics. Furthermore, when the viscosity of the electrode ink is low, it is necessary to gently dry the drying process over time. Moreover, a crack may arise in a coating film and the uniformity of a coating film may be impaired.
[0007]
[Means for Solving the Problems]
In order to solve this problem, the method for producing a polymer electrolyte fuel cell according to the present invention applies an electrode ink containing catalyst particles and a hydrogen ion conductive polymer electrolyte on a chemically inert porous sheet. Forming a semi-dried coating film and drying it , then repeating the process of transferring the coating film to both sides of the hydrogen ion conductive polymer electrolyte membrane a plurality of times, or chemically inert Two or more types of electrode inks containing catalyst particles and a hydrogen ion conductive polymer electrolyte are sequentially applied on the porous sheet to form a semi-dry coating film, and after drying , the coating film It has the process of transcribe | transferring to the both sides of a hydrogen ion conductive polymer electrolyte membrane .
[0008]
At this time, the electrode of the polymer electrolyte fuel cell obtained by the production method of the present invention includes a first catalyst layer in contact with the hydrogen ion conductive polymer electrolyte membrane and a second catalyst formed on the first catalyst layer. The catalyst component constituting the first catalyst layer is platinum, the catalyst component constituting the second catalyst layer is platinum, and in addition to this, ruthenium, palladium, rhodium, nickel, iridium, iron It is effective to have at least one metal selected from the group consisting of:
[0011]
At this time , it is useful that the chemically inert porous sheet has been subjected to water repellent treatment.
[0012]
In addition, it is useful that a chemically inert porous sheet is formed by laminating two or more kinds of sheets having different gas permeability.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the polymer electrolyte fuel cell obtained by the production method of the present invention , the catalyst layer is composed of two discontinuous layers, so that the two layers of catalyst are not mixed at the interface between the catalyst layers. Therefore, the original effect of multilayering the catalyst layer appears more remarkably. In addition, when reformed gas is used as the fuel gas, it is known that CO in the reformed gas poisons the platinum electrode. In this case, if a catalyst layer using a multi-component catalyst such as platinum, ruthenium, and palladium is used as the anode for the second catalyst layer that is not in contact with the polymer electrolyte membrane, the second layer uses CO in the reformed gas. Oxidation and the original electrode reaction can be performed in the first layer, so that the battery characteristics are remarkably improved.
[0014]
Also, the method for producing a polymer electrolyte fuel cell of the present invention comprises applying a polymer electrolyte membrane by sequentially applying two or more types of electrode inks onto a porous sheet substrate, and then transferring the ink to a polymer electrolyte membrane. Since a type fuel cell can be manufactured, a multilayer catalyst layer can be formed continuously. In this case, by employing a coater coating or the like, after the catalyst layer is applied and dried, the next catalyst layer can be applied in layers. If this method is used, the next catalyst layer can be formed without destroying the catalyst layer on the substrate, and the mixing at the boundary interface such as screen printing is relatively reduced.
[0015]
In addition, by transferring the catalyst layer to the polymer electrolyte membrane twice or more, for example, after the first catalyst layer is transferred, another catalyst layer can be transferred thereon. Thereby, a multilayer catalyst layer can be formed. Furthermore, this catalyst layer has been multilayered by transfer, and each catalyst layer is formed in two layers while maintaining the shape, so that the two layers are formed independently without intermingling the catalyst at the interface. Has been.
[0016]
Furthermore, in the method for producing a solid polymer electrolyte fuel cell according to the present invention, an electrode catalyst layer is formed on a porous sheet base material having an appropriate gas permeability, so that the solvent component in the electrode catalyst ink is applied after coating. The porous sheet can be quickly impregnated to form a semi-dried coating film. This eliminates the need to use high boiling alcohols and viscosity modifiers that were conventionally used for viscosity adjustment. Thereby, the fall of battery performance can also be avoided. In addition, a catalyst layer can be formed even with low viscosity ink, and the selection range of the solvent is expanded. In addition, since the coating film is already in a semi-dry state after coating, the uniformity of the coating film can be maintained and the occurrence of cracks during drying can be reduced. Further, by subjecting the porous sheet to a water repellent treatment, the penetration of the catalyst component into the substrate can be reduced, and the releasability at the time of transfer is improved. Furthermore, by using a bonded product of porous sheets having different gas permeability, it is possible to minimize the entry of the catalyst into the substrate.
[0017]
【Example】
Hereinafter, an electrolyte fuel cell and a manufacturing method thereof according to the present invention will be described with reference to the drawings.
[0018]
( Reference Example 1)
First, two types of ink for electrodes were produced. An electrode ink A was prepared by adding 5% by weight of Nafion solution (manufactured by Aldrich), 2-propanol (IPA) and terpineol as solvents to a carbon powder supporting 25% by weight of platinum, and mixing them by a ball mill method. . Further, 5% by weight of Nafion solution, 2-propanol and terpineol were added to carbon powder supporting 50% by weight of platinum, and mixed in the same manner as above to prepare electrode ink B.
[0019]
A catalyst layer was formed on the substrate of these inks using the coater coating apparatus shown in FIG. In FIG. 1, a polyester film (thickness 50 μm, width 250 mm) was used as the substrate. After putting the electrode ink B into the paint tank 3, the polyester film 2 was sent from the unwinding part 1 of the coater device, and coating was performed. The coating is applied on the film from the paint tank through a slit nozzle. At this time, the gap between the nozzle and the film was set to 50 to 250 μm, and the feeding speed was set to 1 m / min. The catalyst B layer 5 was formed on the film by sending the film coated with the catalyst layer to the drying chamber 4 set at a temperature of 100 ° C. and an air volume of 10 m ³ .
[0020]
Next, the paint was applied onto the catalyst B layer from the paint tank 6 filled with the electrode ink A through a nozzle on the slit. Thereafter, the catalyst A layer 8 was formed by drying in the drying chamber 7 set to the same conditions as above. The film with the catalyst layer thus produced was collected by the winding unit 9 of the coater device. The film with the catalyst layer prepared by the above steps was designated as film A.
[0021]
In addition to this, with the same device as above, using a coater device without the second coating unit 6 and the drying chamber 7, only the electrode ink B is applied on the film, dried, wound up, A film with a catalyst layer was produced. This film was designated as film B.
[0022]
Moreover, only the electrode ink A was applied, dried, and wound up to prepare a film with a catalyst layer. This film was designated as film C.
[0023]
Generation | occurrence | production of the crack etc. was not recognized on the surface of the catalyst layer of the film produced at the above process. As a result of observing the state of the cross section of the film A, the thickness of the catalyst layer A1 + catalyst layer B2 was about 15 μm, and the thickness of the catalyst layer B1 to the catalyst layer A1 was about 8 μm. From this, it was found that the catalyst layer A1 and the catalyst layer B1 are basically composed of two discontinuous separated layers although a slightly mixed portion is seen.
[0024]
Next, the film A and the film B were joined using a hot roller with a polymer electrolyte membrane (Nafion 112, manufactured by DuPont) interposed therebetween, and an electrode electrolyte assembly was produced. The joining temperature was 100 ° C. and the joining pressure was 3 × 10 ⁷ Pa. The electrode electrolyte assembly A was prepared in this step.
[0025]
Moreover, after preparing two films 2 with a catalyst layer and carrying out transfer using a hot roller in the same manner as before with a polymer electrolyte membrane sandwiched, a film with a catalyst layer is arranged on one side and again hot The catalyst layer A1 was formed on the catalyst layer B1 using a roller, and the electrode electrolyte assembly B was produced. FIG. 5 shows a cross-sectional observation of the electrode electrolyte assembly B. From this, it was found that the boundary between the catalyst layer B1 and the catalyst layer A1 is composed of two discontinuous layers with no catalyst mixing. The solid content of the catalyst layer was not observed on the polyester film after bonding, and both transfers were good.
[0026]
Further, for comparison, electrode ink B and electrode ink A were applied on the electrode base material by screen printing to produce an electrode electrolyte assembly C. First, carbon paper of a predetermined size was set in a printing machine, and the electrode ink B was applied. At this time, a stainless steel 200 mesh screen was used. This was dried in a drier set at 80 ° C. to form catalyst layer B2 on carbon paper. This was set again on a screen printer, and the electrode ink A was applied in the same manner and dried to form the catalyst layer A2 on the catalyst layer B2. Thus, an electrode substrate 1 with a catalyst layer was produced. Separately from this, an electrode substrate 2 with a catalyst layer in which only the catalyst layer A2 was formed on carbon paper was also produced using the same apparatus as above. FIG. 6 shows a cross section of the electrode substrate 1 with a catalyst layer. From this, it was found that a mixed layer in which the layers were mixed was formed at the interface between the catalyst layer A2 and the catalyst layer B2. This electrode base material 1 with a catalyst layer and the electrode base material 2 with a catalyst layer were joined by hot press through the membrane, and the electrode electrolyte assembly C was produced.
[0027]
Next, the electrode electrolyte assemblies A and B are punched out to a predetermined size, and sandwiched between carbon paper and a gasket. The electrode-electrolyte assembly C has gaskets on both sides, and each of the multilayered catalyst layers has a fuel electrode. Then, it was set in a single cell test apparatus and the battery characteristics were examined. In the fabricated unit cell, a reforming simulation gas (carbon dioxide 25%, carbon monoxide 50 ppm, hydrogen balance gas) is flowed to the fuel electrode, air is flowed to the air electrode, the cell temperature is 80 ° C., and the fuel utilization rate is 80 %, The air utilization rate was 40%, and the humidification was adjusted so that the dew point of the reforming simulation gas was 75 ° C and the air was 60 ° C.
[0028]
FIG. 7 shows a comparison of current-voltage characteristics of the batteries. From this, it was found that the characteristics of the battery using the electrode electrolyte assembly B were the most excellent. The performance using the electrode electrolyte assembly C was the lowest. This is because carbon monoxide should be efficiently oxidized and removed by the catalyst layer B2 that is not in contact with the membrane on the fuel electrode side of the assembly C, but the boundary between the catalyst layer B2 and the catalyst layer A2 is mixed. Therefore, the effect was considered to have decreased. On the other hand, since the joined body B is not mixed at the interface between the catalyst layer B1 and the catalyst layer A1 on the fuel electrode side, the carbon monoxide is efficiently removed by the catalyst layer B1, It was thought that the impact was made as low as possible. In addition, the characteristics of the joined body A were slightly inferior to those using the joined body B, but the mixing of the catalyst layers was much smaller than that of the joined body C, and the characteristics were better than those using the joined body C. It was. Although not shown here, platinum ruthenium is supported even when carbon powder supporting platinum palladium, platinum rhodium, platinum nickel, platinum iridium, or platinum iron is used instead of the carbon powder supporting platinum ruthenium of electrode ink B. It showed the same characteristics as carbon.
[0029]
If this method is used, multilayering of the catalyst layer of the electrode electrolyte assembly can be realized. In addition, it is possible to produce a polymer electrolyte fuel cell having higher characteristics than the conventionally proposed multilayering method.
[0030]
(Example 1 )
First, carbon powder carrying 25% by weight of platinum, 5% by weight of Nafion solution (manufactured by Aldrich), 2-propanol (IPA) and butyl acetate are added as solvents, and they are mixed by the ball mill method to produce ink C for electrodes. did. The viscosity of this ink was lower than that of the electrode inks A and B used in Reference Example 1, and was 10 (mPa · s) at a shear rate of 100 (1 / sec).
[0031]
First, the electrode catalyst layer was formed on the porous sheet using the coating apparatus 2 used in Reference Example 1. As the porous sheet, a polyester fiber woven fabric having a thickness of 50 denier, two types obtained by subjecting the woven fabric to a water repellent treatment, and a normal polyester film used in Reference Example 1 were used. The thickness of the woven fabric is about 0.1 mm. The electrode ink C is put into the paint tank 6, the operation speed of the coating apparatus is set to 5 m / min, a catalyst layer is formed on the polyester woven fabric without water repellent treatment, and then dried in a drying room at 100 ° C. Rolled up. The drying time was 1.5 times that of Reference Example 1. Immediately after coating, the solvent component in the electrode ink quickly permeated the polyester woven fabric. At this time, it was confirmed that the catalyst component slightly permeated the back side of the woven fabric. The coating film after drying, the generation of cracks was not observed, et al.
[0032]
Further, when the polyester woven fabric subjected to the water repellent treatment was used, the catalyst component permeated less than the non-treated fabric, and the surface shape of the coating film was improved. Further, the film thickness of the formed catalyst layer was about 10 μm. On the other hand, when applied to the polyester film in the same way, the solvent component in the electrode ink remains on the film, so the coating film is unstable and difficult to stick, and the catalyst layer coating film after drying There was uneven coating. This was thought to be because the coating film after coating could not maintain its shape because the viscosity of the coating material was low, and the coating film had a shape during drying.
[0033]
Two electrode sheets thus prepared were prepared and joined to both sides of the electrolyte membrane (Nafion 112) using the hot roller used in Reference Example 1, and the electrode-electrolyte assembly D (water-repellent woven fabric) Use), an electrode electrolyte assembly E (using a water-repellent woven fabric), and an electrode-electrolyte assembly F (using a film). The joining conditions were the same as in Reference Example 1. The water-repellent treated polyester woven fabric after joining showed a slight residual catalyst ink solids, but the water-repellent treated one showed almost no residual catalyst ink solids. It was found that the transfer was performed better. Further, when the polyester film was used, the bonding could be performed well, but the unevenness at the time of forming the coating film was directly transferred to the electrolyte membrane side.
[0034]
Next, coating was performed using a composite sheet in which a porous Teflon sheet having an air permeability of 35 sec and a polyester woven fabric having an air permeability of 5 sec or less were laminated as the porous sheet. The air permeability was shown as an average number of seconds required for 100 ml of air to pass through a sample having an area of 645.16 mm 2 by a JIS standard air permeability test (JIS P8117). In other words, the higher this value, the worse the gas permeability, which is rather dense. The electrode ink, coating apparatus, coating conditions, etc. were the same as when using the polyester woven fabric shown above. The coated surface was the polyester woven fabric side. Immediately after coating, the solvent component in the electrode ink quickly permeated into the front polyester woven fabric, but the catalyst component permeated into the back surface as seen when using the previous polyester woven fabric was not seen at all. There wasn't. This was presumed that the porous Teflon sheet on the back side had a low air permeability and the material was dense, so that the catalyst component was in the shape of the target. Moreover, generation | occurrence | production of the crack etc. was not recognized in the coating film after drying.
[0035]
The electrode sheet thus produced was joined using a hot roller in the same manner as described above, and an electrode electrolyte joined body G was produced. No residual catalyst ink solid was observed on the polyester woven fabric of the composite sheet after bonding.
[0036]
Next, the electrode-electrolyte assemblies D, E, F, and G were punched out to a predetermined size, sandwiched between carbon paper and a gasket, set in a single cell test apparatus, and battery characteristics were examined. In the produced unit cell, hydrogen gas is flowed to the fuel electrode, air is flowed to the air electrode, the cell temperature is 80 ° C., the fuel utilization rate is 80%, the air utilization rate is 40%, and humidification is performed using 75 reformed simulation gas. The air was adjusted to a dew point of 60 ° C. FIG. 8 shows a comparison of current-voltage characteristics of the batteries. From this, it was found that the characteristics of the battery using the electrode-electrolyte assembly G were the most excellent.
[0037]
It was also found that the battery characteristics were improved in the order of good transferability.
[0038]
If this method is used, in order to form an electrode catalyst layer on a porous sheet substrate having an appropriate gas permeability, the solvent component in the electrode catalyst ink is impregnated into the porous sheet immediately after coating, and is semi-dried. A coating film in which the state does not move can be formed. This eliminates the need to use a viscosity modifier such as terpineol that has been used for viscosity adjustment in the past. Thereby, the fall of battery performance can also be avoided. In addition, a catalyst layer can be formed even with low viscosity ink, and the selection range of the solvent is expanded. Further, by using a bonded product of porous sheets having different gas permeability, the catalyst does not enter the substrate.
[0039]
【Effect of the invention】
As described above, the characteristics could be improved by making the catalyst layer of the fuel cell into two layers. Furthermore, since the present invention can produce a polymer electrolyte fuel cell by sequentially applying two or more types of electrode inks onto a porous sheet substrate, and then transferring the ink to a polymer electrolyte membrane. Thus, a multi-layered catalyst layer can be formed. In this case, by employing a coater coating or the like, after the catalyst layer is applied and dried, the next catalyst layer can be applied in layers. By using this method, the next catalyst layer can be formed without destroying the catalyst layer on the substrate, and the mixing at the boundary interface such as screen printing is relatively reduced.
[0040]
In addition, by transferring the catalyst layer to the polymer electrolyte membrane twice or more, for example, after the first catalyst layer is transferred, another catalyst layer can be transferred thereon. Thereby, a multilayer catalyst layer can be formed. Furthermore, this catalyst layer has been multilayered by transfer, and each catalyst layer is formed in two layers while maintaining its shape, so that the catalyst is formed without mixing at the interface.
[0041]
Further, in order to form an electrode catalyst layer on a porous sheet substrate having an appropriate gas permeability, the solvent component in the electrode catalyst ink is impregnated into the porous sheet immediately after coating, and the coating film in a semi-dry state Can be formed. This eliminates the need to use high boiling alcohols and viscosity modifiers that were conventionally used for viscosity adjustment. Thereby, the fall of battery performance can also be avoided. In addition, a catalyst layer can be formed even with low viscosity ink, and the selection range of the solvent is expanded. Moreover, since the coating film has already been fixed in a semi-dry state after coating, the uniformity of the coating film can be maintained and the occurrence of cracks during drying can be reduced. Further, by using a bonded product of porous sheets having different gas permeability, the catalyst enters the base material to a minimum.
[Brief description of the drawings]
[1] in the reference example of the present drawing showing a second manufacturing apparatus used in Reference Example of Figure 2 shows the present invention showing a first manufacturing apparatus used in Reference Example of the Invention [3] The present invention third view Figure 5 showing a manufacturing device is a component of the reference example is the electrode electrolyte junction of the present invention used in reference example of FIG. 4 shows the present invention showing a cross section of the catalyst layer with a film which is a component characteristics of the polymer electrolyte fuel cell is a reference example in FIG. 7 the invention showing a cross section of the catalyst layer with the electrode substrate which is a component of the reference example of FIG. 6 the invention showing a body section FIG. 8 is a diagram showing characteristics of a polymer electrolyte fuel cell that is an embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1,9 Unwinding part of coater 2 Polyester film 3,6 Fuel tank 4,7 Drying chamber 5 Catalyst B layer 8 Catalyst A layer 9 Winding part of coater 10 Polymer electrolyte membrane 11 Hot roller −
12 Electrode electrolyte assembly A1 Catalyst layer A1
B1 Catalyst layer B1

Claims (3)

On the chemically inert porous sheet, an electrode ink containing catalyst particles and a hydrogen ion conductive polymer electrolyte is applied to form a semi-dry coating film, and after drying , the coating film A step of repeating the process of transferring the hydrogen ion conductive polymer electrolyte membrane on both sides of the hydrogen ion conductive polymer membrane multiple times, or containing catalyst particles and a hydrogen ion conductive polymer electrolyte on a chemically inert porous sheet It comprises the steps of applying two or more kinds of electrode inks in sequence, forming a semi-dried coating film , drying, and then transferring the coating film to both sides of the hydrogen ion conductive polymer electrolyte membrane. A method for producing a polymer electrolyte fuel cell.   2. The method for producing a polymer electrolyte fuel cell according to claim 1, wherein the chemically inert porous sheet is subjected to water repellent treatment.   The method for producing a polymer electrolyte fuel cell according to claim 1 or 2, wherein the chemically inert porous sheet comprises two or more kinds of sheets having different gas permeability.

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