JP2002270187A - High polymer electrolyte type fuel cell and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high polymer electrolyte type fuel cell having higher performance than a conventional fuel cell by improving inplane structure of a catalyst layer and a manufacturing method for realizing this fuel cell. SOLUTION: A cavity for increasing gas diffusion performance is provided in a catalyst layer face. This cavity occupies 0.1 to 15% of volume in the catalyst layer face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a catalyst layer for a polymer electrolyte fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art Generally, an electrode of a polymer electrolyte fuel cell has a catalyst layer formed on a porous substrate. These catalyst layers are formed by inking a solution of a fine carbon powder supporting a noble metal and a polymer electrolyte having hydrogen ion conductivity using a solvent such as water or isopropyl alcohol, and then printing the catalyst ink by a screen printing method. It is common to apply it on carbon paper or carbon cloth as an electrode substrate by using a spraying method or a spray method, and then dry or fire it. The electrode fabricated in this way is
Joining is performed by hot pressing via the electrolyte membrane, and this is used as an electrolyte membrane-electrode assembly.

As another method, a method has been considered in which a catalyst ink is applied to a polymer film by gravure printing or a coater method, dried to form a catalyst layer, and then transferred to an electrolyte membrane. .

As described above, the catalyst layer used in the fuel cell is
In general, the catalyst is manufactured as densely as possible in order to increase the utilization of the catalyst, and is manufactured so that voids such as cracks are not formed in the plane of the catalyst layer. For this purpose, a surfactant or the like is added to the catalyst layer ink to suppress aggregation of carbon particles,
The dispersibility of the carbon particles carrying the catalyst is increased, the particle size of the carbon particles is reduced as much as possible, or the particle size of the carbon particles is reduced by using a grinding device such as a planetary ball mill capable of obtaining a strong grinding force. Methods such as reducing the size are taken. In addition, cracks are suppressed by a method such as drying the applied catalyst layer ink at a temperature as low as possible and gently over time.

On the other hand, in order for the electrode reaction to proceed smoothly in the catalyst layer, the reaction gas must be efficiently supplied into the catalyst layer. As a technique for this, a countermeasure has been taken such that a pore former is added to the catalyst layer ink in advance, applied, and then fired to make microscopic pores exist in the electrode.

[0006]

The catalyst layer can be formed by reducing the particle diameter of the carbon particles carrying the catalyst particles by a method of adding a surfactant to the catalyst ink or a method of increasing the dispersibility of the ink. It is effective to manufacture the catalyst only densely from the viewpoint of the utilization rate of the catalyst itself. However, a densely formed catalyst layer is particularly poor in gas diffusion in the thickness direction. When a polymer electrolyte fuel cell is operated at a high current density, a large amount of water, which is a reaction product, is generated and stays. For this reason, there is a problem that diffusion of the reaction gas into the catalyst layer is hindered and sufficient battery performance cannot be obtained.

In the case of adding a surfactant, it is necessary to bake after applying the catalyst layer ink, and the number of steps is increased, and the process is complicated. In addition, it is necessary to reduce the particle size of the carbon particles by a method such as a planetary ball mill, but if it is too small, the catalyst layer becomes too dense as described above, and the battery performance is reduced.

[0008] A pore-forming agent or the like is put in the catalyst layer ink in advance,
Although there is a method for improving gas diffusivity, it is necessary to apply and dry the catalyst layer and then to bake it, which increases the number of steps and complicates the process, which is not preferable. In addition, when a pore-forming agent is added, there is a problem that the thickness of the catalyst layer is increased.

It is not preferable to dry the applied catalyst layer ink at a temperature as low as possible for as long as possible, because the size of the drying equipment becomes large, the cost is reduced, and the process is reduced in size.

[0010] In view of the above, there is a need for a production method capable of maintaining gas diffusivity without lowering the catalyst utilization in the catalyst layer as much as possible.

[0011]

In order to solve the above problems, a polymer electrolyte fuel cell according to the present invention comprises a hydrogen ion conductive polymer electrolyte membrane and two sides of the hydrogen ion conductive polymer electrolyte membrane. A single cell including a pair of electrodes arranged, a pair of electrodes having a gas supply groove for supplying and discharging a fuel gas containing hydrogen to one of the electrodes and supplying and discharging an oxidizing gas to the other of the electrodes. In a polymer electrolyte fuel cell sandwiched between conductive separators, the electrode has a catalyst layer in contact with the hydrogen ion conductive polymer electrolyte membrane, and a gas diffusion layer in contact with the catalyst layer and the conductive separator. The catalyst layer has a gas circulation gap through which the fuel gas or the oxidizing gas flows from a surface in contact with the gas diffusion layer toward the inside of the catalyst layer.

Here, the proportion of the voids in the plane of the catalyst layer is preferably 0.1% to 30% of the geometric area in the plane direction of the catalyst layer.

[0013] In the method for producing the catalyst layer, the catalyst layer may be formed by applying a catalyst ink containing at least carbon particles carrying catalyst particles, a hydrogen ion conductive polymer electrolyte and a solvent; A drying step of drying the passed catalyst ink, wherein the drying step includes at least two or more drying steps having different heating temperatures.

At this time, the median diameter of the carbon particles supporting the catalyst particles in the catalyst ink is 0.1 μm or more and 10 μm or more.
m or less is effective.

Further, in the method for manufacturing a polymer electrolyte fuel cell according to the present invention, the catalyst layer is formed by applying a catalyst layer ink containing at least carbon particles carrying catalyst particles, a polymer electrolyte, and a solvent component. The method is characterized by being obtained from the second step of drying the applied catalyst layer ink.

Here, the median diameter of the carbon particles supporting the catalyst particles in the catalyst layer ink in the first step of applying the catalyst layer ink is preferably 0.1 to 10 μm.

In the second step of drying the applied catalyst layer ink, it is preferable to dry the catalyst layer ink in at least two or more steps having different drying temperatures. Further, it is preferable that the subsequent drying temperature is the same as or higher than the preceding drying temperature.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In the fuel cell of the present invention, a void is provided in the plane of the catalyst layer for enhancing the gas diffusing ability.
Battery performance is improved as compared to a battery using a densely formed catalyst layer. In particular, the performance improvement when operating at a high current density becomes remarkable. Further, the inventors have found that when the ratio of the voids is 0.1 to 30%, the utilization rate of the catalyst does not significantly decrease. This gap can be created by controlling the drying conditions of the catalyst ink applied to the base material, and does not require any special device to create the gap. Also, the median diameter of the carbon particles carrying the catalyst particles is
When the thickness was 0.1 to 10 μm, the carbon particles did not become extremely small or large, and a catalyst layer having stable voids could be produced.

Further, by setting the drying temperature to two or more stages, voids could be formed in the catalyst layer surface without adding a pore-forming agent or the like.

Hereinafter, the fuel cell of the present invention and a method of manufacturing the same will be described with reference to the drawings. First, FIG. 1 shows a schematic conceptual diagram of a catalyst layer formed according to the present invention and a conventional catalyst layer. In FIG. 1, it can be seen that the catalyst layer of the conventional example has no voids in the surface of the catalyst layer and has a very dense coating film. On the other hand, in the catalyst layer of the present invention, it can be seen that voids are randomly present in the surface of the catalyst layer and penetrate in the thickness direction of the catalyst layer. Thereby, the diffusion of the gas in the catalyst layer thickness direction is promoted as compared with the conventional example. The shape of the gap is not limited to that shown in FIG. 1 and may be a crack shape or a circular shape. Hereinafter, the embodiment will be described in detail.

Example 1 First, a catalyst layer ink was prepared. 50% by weight of platinum-supported carbon powder and 5% by weight of Na
Fion solution (manufactured by Aldrich) and water were mixed at a predetermined ratio to prepare a catalyst layer ink. This catalyst layer ink was divided into five parts, and a bead mill disperser (GETZMA, Germany)
NN: Dispermat SL-C12Z), the median diameter of the platinum-supported carbon powder is 0.05,
Five kinds of inks of 0.1, 5, 10, and 20 μm were prepared, and these were designated as catalyst inks A, B, C, D, and E.

These inks were applied on the substrate 4 using the coating apparatus 1 shown in FIG. The base material is a polyethylene terephthalate (PET) film (thickness 50μ).
m, width 250 mm). First, after the catalyst layer ink 6 is put into the tank 2, P
The ET film was fed and applied. The coating is performed on the film from a tank through a slit-shaped nozzle 7. At this time, the gap between the nozzle and the film is 50 to 25.
0 μm and the feed speed were set to 1 m / min. The PET layer coated with the catalyst layer was sent to a drying chamber 8 set at a temperature of 60 ° C. to form a catalyst layer on the film.

Next, a catalyst layer A prepared using the catalyst layer ink A (hereinafter similarly referred to as a catalyst layer B, a catalyst layer C, a catalyst layer D,
The in-plane porosity of the catalyst layer E) was measured. The porosity is determined by image processing (binarization processing, measurement range about 30 mm2, Imag
e Analyzer V10: Toyobo Co., Ltd.). Table 1 shows the porosity of the catalyst layers A to E.

[0024]

[Table 1]

These catalyst layers A to D were joined by a hot press with a polymer electrolyte membrane (Nafion 112, manufactured by Dupont) interposed therebetween, to produce electrode-electrolyte assemblies A to E. Next, these electrode-electrolyte assemblies were sandwiched between carbon paper (manufactured by Toray; TGP-H-120) via a gasket, thereby producing cells A to E. These were set in a unit cell test apparatus, and the characteristics of each battery were examined. In the fabricated cell, a reforming simulated gas (carbon dioxide 2
5%, carbon monoxide 50 ppm, hydrogen balance gas)
Air was passed through the air electrode, and the cell temperature was adjusted to 80 ° C, the fuel utilization rate to 80%, the air utilization rate to 40%, and the humidification was adjusted so that the reforming simulation gas was 75 ° C and the air was 60 ° C. .

FIG. 3 shows the current-voltage characteristics of the respective batteries in comparison. Catalyst layer A having the lowest porosity than this
It has been found that the performance of the unit cell A using the battery has a lower characteristic in the high current density region than the other cells. In addition, it was found that the performance of the single cell E using the catalyst layer E having the highest porosity was deteriorated in battery characteristics as a whole. FIG.
FIG. 4 shows the relationship between the battery voltage of each battery when the current density was 0.7 A / cm ² and the porosity of the catalyst layer used in each battery. From this, it was found that the battery performance was deteriorated when the in-plane porosity of the catalyst layer was too low or too high. Thus, the in-plane porosity of the catalyst layer is 0.1 to 15%.
It can be seen that a high-performance battery can be provided at a low level.

Next, using the catalyst layer ink C, the drying temperature was set at 40 ° C., 60 ° C., and 80 ° C.
1, C2 and C3 were prepared, and the porosity was measured. As a result, the porosity, which was 4% at 60 ° C., changed to a drying temperature of 40 ° C.
It was found that C1 was 2% and C3 at a drying temperature of 80 ° C. was 6%. When the cell performance of the electrode-electrolyte assembly manufactured using these catalyst layers was examined, the same performance as that of the cell C was shown.

As described above, when the catalyst layer having a small porosity is operated at a high current density, the generated water stays in the catalyst layer and inhibits the diffusion of the reaction gas, thereby deteriorating the battery characteristics. it is conceivable that. In addition, it is considered that the catalyst layer having a high porosity has a large overall thickness of the catalyst layer, a shortage of catalyst near the polymer electrolyte, and a reduction in the reaction area.

In the catalyst layer having an intermediate porosity, an appropriate porosity (0.1 to 15%) is maintained. It is considered that the generated water was quickly discharged from the gap to the carbon paper as the gas diffusion layer, and did not hinder the diffusion of the reaction gas.

According to this method, a high-performance battery can be obtained without changing the catalyst utilization rate by changing the median diameter of the catalyst layer ink and controlling the in-plane porosity of the catalyst layer. In addition, the porosity can be changed by controlling the drying temperature. Further, by controlling the porosity, it becomes possible to design the fuel cell in accordance with the intended use. In this embodiment, the PET film is used as the base material, but the present invention is not limited to this. Alternatively, it can be produced by directly coating the catalyst layer ink on the carbon paper to be the gas diffusion layer. Further, the composition of the catalyst, the composition of the electrode ink, the drying conditions, and the like are not limited to those in the present embodiment, but may be any as long as the present invention can be applied.

(Embodiment 2) First, the drying chamber attached to the coating apparatus 1 used in Embodiment 1 was redesigned so as to be divided into two stages, a former stage and a latter stage, so that the drying temperature could be controlled respectively. . Next, using the catalyst layer ink B used in Example 1 and applying the other conditions in the same manner as in Example 1, coating was performed using the coating apparatus 1 whose design was changed. At this time, the catalyst layers B1 to B4 were prepared under different drying conditions, and the porosity in the catalyst layer plane was measured in the same manner as in Example 1. Table 2 shows the relationship between the drying temperature and the porosity in the catalyst layer surface at this time.

[0032]

[Table 2]

Thus, it was found that, even when the same catalyst layer ink was used, the in-plane porosity of the catalyst layer could be controlled by controlling the drying temperature. This is presumably because, by changing the drying conditions, the cohesion between the polymer electrolyte and the catalyst-supporting carbon particles in the catalyst layer changes, and crack-like voids in the catalyst layer surface change.

Using these catalyst layers B1 to B4, an electrode-electrolyte assembly was prepared in the same manner as in Example 1, and these were used as single cells B1 to B4, and the battery characteristics were examined. The test conditions for the battery were the same as in Example 1. FIG. 5 shows the current-voltage battery characteristics of these cells.

As a result, it has been found that, in the unit cell B1 using the catalyst layer B1 having a small porosity in the plane of the catalyst layer, the characteristics in the high current density region are reduced. In the case of the catalyst layer B1, since the drying temperature in the former stage is low, there is an advantage that a catalyst layer having a low porosity is formed. Since gas diffusion is hindered, the performance of the battery is reduced.

Conversely, in the case of the catalyst layer B4, since the drying temperature in the former stage is higher than that in the latter stage, rapid solvent volatilization occurs in the former stage, and the porosity in the catalyst layer surface increases. As a result, the porosity is increased, but the thickness of the catalyst layer is increased as a whole, the catalyst is insufficient in the vicinity of the polymer electrolyte, and the reaction area is reduced. For this reason, it is considered that the battery performance decreases.

The catalyst layers B2, B3 having an intermediate porosity
In, the drying temperature of the former stage is set lower than that of the latter stage,
Since a catalyst layer having an appropriate porosity is obtained, and the water generated by the battery reaction is quickly discharged from the voids to the carbon paper serving as the gas diffusion layer, the diffusion of the reaction gas is not hindered. It is considered that the battery exhibited high battery characteristics.

By using this method, a catalyst layer having an appropriate porosity can be obtained by controlling the drying temperature after coating the catalyst layer ink. As a result, a battery with higher performance than before can be provided.

[0039]

As described above, the fuel cell of the present invention is provided with a void in the surface of the catalyst layer for enhancing the gas diffusivity. In comparison, the battery performance is improved. In particular, the performance improvement in the high current density operation range becomes remarkable. Further, the battery performance can be improved without lowering the utilization rate of the catalyst.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic concept of a catalyst layer which is a component of the fuel cell of the present invention.

FIG. 2 is a diagram showing a manufacturing apparatus used in the first embodiment of the present invention.

FIG. 3 is a diagram showing first characteristics of the fuel cell according to the first embodiment of the present invention;

FIG. 4 is a diagram showing a second characteristic of the fuel cell according to the first embodiment of the present invention.

FIG. 5 is a diagram showing first characteristics of a fuel cell according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coating apparatus 2 Tank 3 Unwinding part 4 Substrate 5 Coating roll 6 Catalyst layer ink 7 Nozzle 8 Drying chamber 9 Guide roll 10 Winding part

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Makoto Uchida 1006 Kadoma Kadoma, Kazuma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. 72) Inventor Yasushi Sugawara 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. AS03 BB06 BB08 BB12 CC06 DD08 EE03 EE05 EE17 EE18 HH01 5H026 AA06 BB03 BB04 CC01 CC03 CX04 EE02 EE05 EE18 HH01 HH08

Claims (3)

[Claims] 1. A cell comprising a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes disposed on both sides of the hydrogen ion conductive polymer electrolyte membrane, a fuel gas containing hydrogen on one of the electrodes. And a polymer electrolyte fuel cell sandwiched between a pair of conductive separators formed with a gas supply groove for supplying and discharging an oxidizing gas to the other of the electrodes, wherein the electrode has a high hydrogen ion conductivity. A catalyst layer in contact with the molecular electrolyte membrane, and a gas diffusion layer in contact with the catalyst layer and the conductive separator, wherein the catalyst layer is from the surface in contact with the gas diffusion layer toward the inside of the catalyst layer. A polymer electrolyte fuel cell having a gas circulation gap through which the fuel gas or the oxidizing gas flows. 2. A method for forming a catalyst layer, comprising: applying a catalyst ink containing at least carbon particles carrying catalyst particles, a hydrogen ion conductive polymer electrolyte, and a solvent; 2. The method for producing a polymer electrolyte fuel cell according to claim 1, further comprising a drying step of drying, wherein the drying step includes at least two or more drying steps having different heating temperatures. 3. The method for producing a polymer electrolyte fuel cell according to claim 3, wherein the median diameter of the carbon particles carrying the catalyst particles in the catalyst ink is 0.1 μm or more and 10 μm or less. .