WO2011152112A1

WO2011152112A1 - Catalyst layer for fuel cell

Info

Publication number: WO2011152112A1
Application number: PCT/JP2011/057896
Authority: WO
Inventors: 山本　泰三
Original assignee: 株式会社エクォス・リサーチ
Priority date: 2010-05-31
Filing date: 2011-03-29
Publication date: 2011-12-08
Also published as: JP2012015089A

Abstract

The purpose of the present invention is to provide a fuel cell capable of stably delivering higher output under conditions of low or no humidification. The present catalyst layer for a fuel cell contains: an innumerable number of catalysts (1) joined to a surface of an electrolyte layer and comprising catalytic metal particulate (1b) that is supported by a support (1a), the catalytic metal particulate (1b) comprising platinum and the support (1a) comprising carbon black; and a polyelctrolyte (2). Hydrophilic functional groups of the side-chain (101) of the polyelectrolyte (2) are oriented toward the catalyst (1) in a manner such that a hydrophilic layer (3) is formed on the catalyst (1). In addition, the catalyst layer for a fuel cell does not contain holes having a width that exceeds 1μm.

Description

Fuel cell catalyst layer

The present invention relates to a catalyst layer for a fuel cell.

A fuel cell includes an electrolyte layer, a cathode electrode joined to one surface of the electrolyte layer and supplied with air, and an anode electrode joined to the other surface of the electrolyte layer and supplied with fuel. The cathode electrode and the anode electrode have a catalyst layer. The catalyst layer contains innumerable catalysts in which catalytic metal fine particles such as platinum are supported on a conductive carrier such as carbon black, and a polymer electrolyte.

As a conventional method for producing a catalyst layer, for example, Patent Document 1 discloses an invention of a production method by the inventors of the present invention. In this production method, first, a countless catalyst after pulverization is mixed with water to obtain a pre-paste. During this time, by adopting a centrifugal stirring method using a large amount of water, bubbles that may exist between the respective catalysts are suitably removed. Next, the pre-paste is mixed with the polymer electrolyte solution to form a catalyst paste. And a catalyst layer is obtained with a catalyst paste. For example, the catalyst paste is printed on a substrate having gas permeability such as carbon cloth, and the catalyst paste is dried together with the substrate. Thereby, the electrode used as the cathode electrode or anode electrode in which the catalyst layer was formed on the base material is obtained.

In the catalyst layer thus obtained, the hydrophilic functional group of the polymer electrolyte is oriented to each catalyst side, and a continuous hydrophilic layer is formed between each catalyst and the polymer electrolyte. This catalyst layer is referred to as having a PFF (Proton Film Flow) structure. If an electrode having a catalyst layer of this PFF structure is used as a cathode electrode and an anode electrode and these are provided on both surfaces of the electrolyte layer, a membrane electrode assembly (MEA: Membrane Electrode Assembly) is obtained. According to the test results of the inventor, in the fuel cell using this membrane electrode assembly as a cell, protons move favorably, and high output is obtained while being lightly humidified or non-humidified.

Japanese Patent Laid-Open No. 2006-140062

However, there is a demand for a fuel cell that can stably exhibit higher output under light or no humidification.

That is, in “Carbon” (Kim Kinoshita; John Wiley & ９９Sons 1988), page 199 and Japanese Patent Application Laid-Open No. 7-134995, a treated catalyst is obtained by boiling a support or a catalyst with an aqueous acid solution such as an aqueous nitric acid solution. Is disclosed. This treated catalyst has a hydroxyl group on the surface and is considered to improve hydrophilicity. For this reason, if a catalyst layer is manufactured with this treated catalyst, protons are likely to move in the obtained catalyst layer, and high output can be obtained.

However, according to the inventor's test, if the support or catalyst is boiled with an aqueous acid solution, the catalyst or support is oxidized and deteriorated. For this reason, high activity cannot be stably expected with this treated catalyst.

On the other hand, some existing catalysts contain nitrate groups. According to the inventor's test, when the catalyst contains a nitrate group or the like, the nitrate group or the like plays an important role in forming the PFF structure of the catalyst layer.

Furthermore, in the catalyst layer of the conventional fuel cell, the generated water is released, so that the output is higher when the pores having a certain size or more are scattered. However, since the electrical resistance increases if the pores are large, it is preferable that the catalyst layer has no large pores with a diameter exceeding 1 μm as much as possible.

The present invention has been made in view of the above-described conventional situation, and an object to be solved is to provide a fuel cell that can stably exhibit higher output under light humidification or no humidification.

The catalyst layer for a fuel cell of the present invention is a catalyst layer for a fuel cell that contains a polymer electrolyte and a myriad of catalysts that are bonded to one surface of an electrolyte layer and on which a catalyst metal fine particle is supported.
A structure in which hydrophilic functional groups of side chains of the polymer electrolyte are oriented to the catalyst so that a hydrophilic layer is formed on the catalyst;
In addition, it has only pores having a width of 1 μm or less (claim 1).

In the catalyst layer for a fuel cell of the present invention, a hydrophilic layer is formed between each catalyst and the polymer electrolyte. The catalyst layer is formed on the side of the polymer electrolyte so that the hydrophilic layer is formed on the catalyst. The hydrophilic functional group of the chain is oriented to the catalyst (PFF structure). Further, the catalyst layer of the present invention does not have pores having a width exceeding 1 μm according to the test results of the inventors. Such a catalyst layer having no pores does not have a useless space for blocking the movement of electrons and protons, and the resistance value of the catalyst layer is reduced, so that the fuel cell exhibits high output.

Therefore, if the catalyst layer of the present invention is employed in a fuel cell, the fuel cell can stably exhibit higher output under light or no humidification.

The catalyst metal fine particles are preferably modified with a hydrophilic modifying group (Claim 2). According to the knowledge of the inventors, the modifying group may be at least one selected from a nitric acid group, an amino group, a sulfonic acid group, a hydroxyl group and a halogen group (Claim 3). It is considered that the hydrophilic layer is formed not only by the ion exchange group of the polymer electrolyte but also by a hydrophilic group generated on the surface of each catalyst.

The catalyst layer of the present invention is obtained by a production method including a modification process, a water immersion process, a wet pulverization process, a catalyst paste preparation process, and a final process.

That is, the catalyst layer of the present invention is a modification step of preparing a precious metal complex solution containing a modifying group and obtaining a treated catalyst that is a catalyst modified with the modifying group by bringing the catalyst into contact with the noble metal complex solution;
A water immersion step of immersing the treated catalyst in water;
A pre-paste preparation step for performing a wet pulverization treatment on the treated catalyst in water to make a pre-paste,
A catalyst paste preparation step in which a pre-paste is mixed with a polymer electrolyte solution to form a catalyst paste;
It is also characterized by being manufactured by a final process of obtaining a fuel cell catalyst layer with a catalyst paste.

In the modification step, a precious metal complex solution containing a modifying group is prepared, and a treated catalyst that is a catalyst modified with the modifying group is obtained by bringing the catalyst into contact with the precious metal complex solution. At this time, since the catalyst has already supported catalyst metal fine particles, the modifying group of the noble metal complex solution modifies the catalyst.

Thereby, a treated catalyst which is a catalyst modified with a modifying group is obtained. Since this treated catalyst is not a product obtained by boiling the support or catalyst with an aqueous acid solution, the catalyst or support is not oxidized and does not deteriorate.

According to the inventor's knowledge, as the noble metal complex solution, dinitrodiamine platinum (II) nitric acid solution (cis- [Pt (NH ₃ ) ₂ (NO ₂ ) ₂ ] / HNO ₃ sol.), Hexahydroxo platinum (IV An acid nitric acid solution ((H ₂ Pt (OH) ₆ ) / HNO ₃ sol.) Or the like can be employed.

In the water immersion process, the treated catalyst is immersed in water. At this time, since the treated catalyst is modified with a modifying group, the surface of each treated catalyst is more reliably covered with water. Further, by adopting a centrifugal stirring method using a large amount of water, bubbles that may exist between the respective catalysts are suitably removed.

In the wet pulverization process, wet pulverization is performed on the treated catalyst in water, for example, pulverization with an ultrasonic homogenizer or a wet jet mill to obtain a pre-paste. As a result, the order or size of the catalyst particles is reduced, so that useless spaces (pores) cannot be formed in the catalyst layer, and the resistance value of the catalyst layer is reduced, so that the fuel cell exhibits high output.

In the catalyst paste preparation step, the pre-paste is mixed with the polymer electrolyte solution to form a catalyst paste. At this time, since each treated catalyst has wettability to water, the polymer electrolyte orients the hydrophilic functional group of the polymer electrolyte on each treated catalyst side. Thus, a catalyst paste is obtained in which hydrophilic layers that are continuous with each other are formed with water between the treated catalyst and the polymer electrolyte that are in contact with each other.

In the final step, a fuel cell catalyst layer is obtained from the catalyst paste. For this reason, if a catalyst layer is manufactured using this catalyst paste, the catalyst layer has a PFF structure more reliably.

For this reason, in the fuel cell having this catalyst layer, the hydrophilic layer is continuously formed in the catalyst layer, so that the protons easily move along this. Moreover, since the polymer electrolyte orients the hydrophilic functional group of the polymer electrolyte on the hydrophilic layer side, the hydrophilic layer is effectively used for proton transfer. For this reason, the amount of water necessary for the movement of protons is retained in the water channel and moves well in the water channel. Excess water is not necessary.

It is a flowchart which shows the manufacturing method of the catalyst layer for fuel cells of an Example. It is a graph which shows the relationship between the cell temperature, voltage, and resistance in the fuel cell of Example 1 and Comparative Examples 1 and 2 in connection with Test 1. It is a schematic cross section which shows a part of catalyst layer for fuel cells of an Example. It is a graph which shows the relationship between the cell temperature, the voltage, and resistance in the fuel cell of Example 2 and Comparative Examples 1 and 2 in connection with Test 2. It is a graph which concerns on the test 3 and shows the XPS analysis result in the process supernatant catalyst of Example 2 under the superimposition of N1s. 4 is a photomicrograph at 5000 times showing a cross section of an electrode of Example 3 according to Test 4. 4 is a photomicrograph at 5000 times showing a cross section of an electrode of Comparative Example 3 according to Test 4. 6 is a graph showing pore distributions of Example 3, a catalyst layer, and a catalyst layer of Comparative Example 3 according to Test 4. 6 is a graph showing a relationship between current density and voltage in fuel cells of Example 4 and Comparative Example 4 according to Test 5. 6 is a graph showing the relationship between current density and voltage in fuel cells of Examples 5-1 and 5-2 and Comparative Example 5 in connection with Test 5.

(Test 1)
First, an assembly consisting of a myriad of catalysts was purchased. The catalyst support type is Ketjen Black EC600JD and the catalyst type is Pt / Co. Each catalyst has platinum and cobalt supported on a carrier made of carbon black at a loading amount of 60% by mass. Then, as shown in FIG. 1, in step S1, the aggregate was pulverized using a blade mill.

Next, in step S2, a modification process using a noble metal complex solution was performed. That is, a platinum complex solution was prepared, and the pulverized catalyst was added to the platinum complex solution.

Specifically, dinitrodiamineplatinum (II) nitric acid solution (cis- [Pt (NH ₃ ) ₂ (NO ₂ ) ₂ ] / HNO ₃ sol.) (Pt 0.05 g / 150 mL, nitric acid concentration 0.07% (0 .01M)) was used as the platinum complex solution.

The catalyst was added to the platinum complex solution and stirred with a stirrer for 5 hours. Thereby, it is considered that the modifying group present around the dinitrodiamine platinum modifies the platinum of the catalyst. The platinum complex solution after the treatment was filtered, the residue was dried at 60 ° C. for 2 hours, and heat-treated at 150 ° C. for 2 hours in nitrogen gas. The reason why the treated catalyst is heat-treated is to remove impurities on the surface of each treated catalyst as much as possible. Thus, 1.012 g (Pt yield 84.3%) of the treated catalyst was obtained from 1 g of the catalyst. A treated catalyst is a catalyst modified with a modifying group.

Thereafter, in step S3, the treated catalyst was subjected to a pre-paste preparation process. First, in step S31, 100 mL of water was added to 1 g of the treated catalyst, and water immersion was performed.

Next, in step S32, an ultrasonic homogenizer was inserted into the water in which the treated catalyst was immersed, and ultrasonic waves with a frequency of 20 kHz were added for 10 minutes to perform wet pulverization.

Further, in Step S33, a rotation / revolution centrifugal stirrer (manufactured by Keyence Corporation, trade name “Hybrid Mixer HM-500”) was prepared, and the centrifugal stirring method was executed. At this time, the treated catalyst and water reduced to 8 times the amount of the treated catalyst were accommodated in the chamber of the stirrer. Thereafter, while applying centrifugal force to the mixture by revolving the chamber, the mixture was stirred by its own weight by rotating the chamber to obtain a pre-paste. During this time, since the modifying group is modified on the treated catalyst, the surface of each treated catalyst is more reliably covered with water.

Next, in step S4, a catalyst paste preparation step was performed. At this time, the pre-paste and the polymer electrolyte solution were accommodated in a chamber of the same kind of stirrer, and the centrifugal stirring method was executed. During this time, since each treated catalyst has wettability to water, the polymer electrolyte orients the sulfone group of the polymer electrolyte on each treated catalyst side. A hydrophilic layer that is continuous with water is formed between the treated catalyst and the polymer electrolyte that are in contact with each other.

Thereafter, as a final process of step S5, a catalyst layer is obtained with a catalyst paste. First, carbon cloth was prepared as a base material having gas permeability. A diffusion layer having a carbon cloth as a base material and a water repellent layer made of a mixture of carbon black and PTFE on both sides was prepared. Thereafter, in step S51, screen printing of the cathode catalyst layer and the anode catalyst layer was performed using the catalyst paste.

In step S52, the substrate after printing was rapidly dried to obtain a cathode electrode and an anode electrode. These were provided on both surfaces of the electrolyte layer to obtain a membrane electrode assembly. Using this membrane electrode assembly as a cell, the fuel cell of Example 1 was assembled. The catalyst layer of the fuel cell of Example 1 has Pt of 0.1 mg / cm ² .

As Comparative Example 1, a catalyst paste was obtained by a conventional manufacturing method in which the modification step S2 and the wet pulverization treatment S32 were not performed, and a similar fuel cell was assembled with this catalyst paste. The catalyst layer of the fuel cell of Comparative Example 1 has a Pt of 0.1 mg / cm ² .

Further, as in Comparative Example 1, the fuel cell of Comparative Example 2 was assembled. The catalyst layer of the fuel cell of Comparative Example 2 has Pt of 0.4 mg / cm ² .

In these fuel cells, the humidification temperature is 60 ° C., the supply amount of H ₂ is 0.8 L / min (0.1 MPa-G), the supply amount of air is 3.0 L / min (0.1 MPa-G), conditions of electrode area 45mm × 45mm (20.25cm ^2), the cell temperature (° C), were determined and voltage (V), and the relationship between the resistance (Ω · cm ^2). The results are shown in FIG.

FIG. 2 shows that the fuel cell of Example 1 can stably exhibit higher output under light humidification than the fuel cell of Comparative Example 1. The performance of the fuel cell of Example 1 is the same as that of Comparative Example 2 in which the amount of platinum is four times. For this reason, in the fuel cell of Example 1, even if it reduces platinum amount, it turns out that a high output can be exhibited stably under light humidification. As shown in FIG. 3, the catalyst layer of the fuel cell of Example 1 contains innumerable catalyst 1 in which catalyst metal fine particles 1b are supported on a carrier 1a, and a polymer electrolyte 2. In this catalyst layer, The hydrophilic functional group of the side chain 101 of the polymer electrolyte 2 is oriented to the catalyst 1 (PFF structure) so that the hydrophilic layer 3 is formed on the catalyst 1. Thereby, the continuous hydrophilic layer 3 is reliably formed between each catalyst 1 and the polymer electrolyte 2.

(Test 2)
The platinum complex solution was a hexahydroxoplatinum (IV) acid nitric acid solution ((H ₂ Pt (OH) ₆ ) / HNO ₃ sol.), And the fuel cell of Example 2 was assembled. Other conditions are the same as in the first embodiment. The catalyst layer of the fuel cell of Example 2 has Pt of 0.1 mg / cm ² .

In the fuel cells of Example 2 and Comparative Examples 1 and ² , the relationship between the cell temperature (° C.), the voltage (V), and the resistance (Ω · cm ² ) was obtained under the same conditions as in Test 1. The results are shown in FIG.

FIG. 4 shows that, similarly to Example 1, the fuel cell of Example 2 can stably exhibit high output under light humidification.

(Test 3)
XPS analysis of the treated catalyst of Example 2 was performed. FIG. 5 shows the result of superimposing N1s.

As shown in FIG. 5, the catalyst of the treatment supernatant of Example 2 has a NO component. For this reason, it turns out that the catalyst is modified with NO ₃ ⁻ .

(Test 4)
A cross section of the electrode of Example 3 manufactured in the same manner as in Example 1 is shown in FIG. 6, and a cross section of the electrode of Comparative Example 3 manufactured in the same manner as in Comparative Example 1 is shown in FIG. The catalyst layers of the electrodes of Example 3 and Comparative Example 3 were screen-printed under the same conditions. The catalyst layers of Example 3 and Comparative Example 3 have Pt of 0.11 mg / cm ² . 6 and 7 are photomicrographs of each electrode magnified 5000 times.

Further, the pore distribution between the catalyst layer of Example 3 and the catalyst layer of Comparative Example 3 was determined. The results are shown in FIG. As shown in FIG. 8, the pores of about 0.04 to 0.1 μm are not so different between the catalyst layer of Example 3 and the catalyst layer of Comparative Example 3. For this reason, it turns out that a wet grinding process does not affect the pore distribution of a catalyst layer.

However, as shown in FIGS. 6 and 7, the electrode of Example 3 has a catalyst layer thickness of about 2 μm, the catalyst layer is dense, and no pores are present in the catalyst layer. The electrode of Example 3 has a catalyst layer thickness of about 5 μm, and pores are conspicuous in the catalyst layer. This difference occurs depending on whether or not wet pulverization is performed on the treated catalyst in water by ultrasonic waves in the pre-paste preparation process.

As in the electrode of Example 3, it is preferable that the catalyst layer is thin, because even if generated water is generated at a position close to the electrolyte layer under high-temperature and low-humidification conditions, the generated water is preferably easily removed. In addition, the absence of pores in the catalyst layer as in the electrode of Example 3 indicates that the resistance value is low, which is also preferable.

Therefore, in the present invention, in the pre-paste preparation step, it is preferable to perform wet pulverization treatment with ultrasonic waves on the treated catalyst in water.

(Test 5)
Manufactured in the same manner as in Example 1 and the fuel cell of Example 4 using a treated catalyst containing only 2 μg / g of the modifying group, and the same production as in Comparative Example 1 and containing only 2 μg / g of the modifying group. For the fuel cell of Comparative Example 4 using a catalyst, the relationship between current density (A / cm ² ) and voltage (V) under conditions of 50 ° C., normal pressure, and full humidification was determined. The results are shown in FIG.

On the other hand, the fuel cell of Example 5 using the treated catalyst containing 4700 μg / g of the modifying group produced in the same manner as in Example 1 and the catalyst containing 4700 μg / g of the modifying group produced in the same manner as Comparative Example 1 were prepared. With respect to the fuel cell of Comparative Example 5 used, the relationship between current density (A / cm ² ) and voltage (V) under the same conditions was determined. The results were obtained for two types of treated catalyst in Example 5 (Example 5-1 and Example 5-2). The results are shown in FIG.

As shown in FIG. 9, the effect of the wet pulverization treatment does not appear with the treated catalyst having a small number of modifying groups. However, as shown in FIG. 10, the effect of the wet pulverization treatment is remarkable in the treated catalyst with many modifying groups.

In the above, the present invention has been described with reference to the first to fifth embodiments. However, the present invention is not limited to the first to fifth embodiments, and can be appropriately modified and applied without departing from the spirit of the present invention. Needless to say.

The present invention can be used for a moving power source for an electric vehicle or the like, or a stationary power source.

1a ... support 1b ... platinum (catalyst metal fine particles)
DESCRIPTION OF SYMBOLS 1 ... Catalyst 2 ... Polymer electrolyte 2 ... Hydrophilic layer S2 ... Modification process S3 ... Pre paste process S4 ... Catalyst paste preparation process S5 ... Final process S32 ... Wet grinding process

Claims

In a fuel cell catalyst layer containing a myriad of catalysts bonded to one surface of an electrolyte layer and supported by catalytic metal fine particles on a carrier, and a polymer electrolyte,
A structure in which hydrophilic functional groups of side chains of the polymer electrolyte are oriented to the catalyst so that a hydrophilic layer is formed on the catalyst;
And a catalyst layer for a fuel cell having only pores having a width of 1 μm or less.
The catalyst layer for a fuel cell according to claim 1, wherein the catalytic metal fine particles are modified with a modifying group having hydrophilicity.
The fuel cell catalyst layer according to claim 2, wherein the modifying group is at least one selected from a nitric acid group, an amino group, a sulfonic acid group, a hydroxyl group and a halogen group.