JP2023129770A - Catalyst layer for fuel cell and electrolyte membrane-electrode assembly - Google Patents

Abstract

To provide a highly efficient catalyst layer for a fuel cell that can supply protons to the catalyst inside the pores of a catalyst carrier while suppressing poisoning of the catalyst by an ionomer.SOLUTION: A catalyst layer for a fuel cell according to the present disclosure includes a catalyst support material including a conductive catalyst carrier having pores and a catalyst at least partially supported inside the pores, and a proton-conducting ionomer coating at least a portion of the outer surface of the catalyst support material, and the catalyst support material has an amount of acidic functional groups modifying the outer surface and inside of the pores of the catalyst support of 0.2 mmol or more per unit weight gram of the catalyst support.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a catalyst layer for a fuel cell and an electrolyte membrane-electrode assembly.

Patent Document 1 discloses a catalyst supporting material that suppresses poisoning of the catalyst by an ionomer by supporting the catalyst in the pores of a catalyst carrier. This catalyst support material includes a conductive catalyst support having pores and a catalyst at least partially supported within the pores of the catalyst support, and at least a part of the outer surface is covered with an ionomer. .

JP2020-64852A

The present disclosure provides a highly efficient catalyst layer for a fuel cell that can supply protons to the catalyst inside the pores of a catalyst carrier while suppressing poisoning of the catalyst by an ionomer.

A catalyst layer for a fuel cell according to the present disclosure includes a catalyst supporting material including a conductive catalyst carrier having pores and a catalyst at least partially supported inside the pores, and at least one of the outer surfaces of the catalyst supporting material. A proton-conducting ionomer covering a portion thereof.

The catalyst supporting material is characterized in that the amount of acidic functional groups modifying the outer surface and the inside of the pores of the catalyst carrier is 0.2 mmol or more per unit weight gram of the catalyst carrier.

The fuel cell catalyst layer of the present disclosure can retain moisture inside the pores of the catalyst carrier by modifying the catalyst carrier with an acidic functional group, so that protons can be transferred to the catalyst supported inside the pores of the catalyst carrier. can be supplied.

The catalyst supported inside the pores is not coated with ionomer and protons are supplied by the water held inside the pores, which increases the efficiency of catalyst utilization and creates a highly efficient fuel. A catalyst layer for a battery can be provided.

A schematic diagram showing a cross section of a catalyst supporting material of a catalyst layer for a fuel cell in Embodiment 1 of the present invention A schematic diagram enlarging a part of the cross section of the catalyst supporting material of the catalyst layer for a fuel cell in Embodiment 1 of the present invention A schematic diagram showing the state of functional groups inside the pores of the catalyst supporting material of the catalyst layer for a fuel cell in Embodiment 1 of the present invention A schematic diagram showing a cross section of an electrochemical device equipped with an electrolyte membrane-electrode assembly according to Embodiment 1 of the present invention Schematic diagram showing the structure of the ionomer used in the fuel cell catalyst layer in Embodiment 1 of the present invention Characteristic diagram showing the relationship between the amount of functional groups modified in the catalyst supporting material of Examples 1 to 4 of the fuel cell catalyst layer in Embodiment 1 of the present invention and the comparative example and the normalized mass activity Flowchart showing the manufacturing process of a catalyst layer for a fuel cell in Embodiment 1 of the present invention

(Findings, etc. that formed the basis of this disclosure)
At the time the inventors arrived at the present disclosure, the technology of forming a three-phase interface in the catalyst layer of a fuel cell was based on the belief that bringing the catalyst into contact with the ionomer would lead to improved performance from the perspective of proton supply. However, in recent years, it has been found that when the ionomer comes into contact with the catalyst, the catalyst is poisoned by the ionomer, and the catalytic activity is actually reduced.

Therefore, in order to suppress the poisoning of catalysts by ionomers, the industry has developed a method of supporting catalysts inside the pores of catalyst carriers that have large mesopores (pores) such as mesoporous materials. It has been common practice to design products so that the ionomer does not come into contact with the catalyst.

However, when the catalyst is supported inside the pores of the catalyst carrier, the structure of the catalyst carrier prevents the ionomer from penetrating into the pores of the catalyst carrier. There was a problem in that the supply of protons to the catalyst inside the pores of the support material was insufficient.

Not bringing the ionomer into contact with the catalyst and supplying protons to the catalyst are contradictory phenomena, and it is difficult to achieve both using normal thinking.

Under such circumstances, the inventors took a hint from the fact that protons move in water, and by adsorbing water into the pores of the catalyst carrier, the catalyst supported inside the pores of the catalyst carrier was I got the idea of supplying protons to the human body.

The inventors discovered that in order to realize this idea, there was a problem that the amount of water adsorbed inside the pores of the catalyst carrier was insufficient, and in order to solve this problem, the present disclosure This led to the composition of the theme.

Therefore, the present disclosure supplies protons to the catalyst inside the pores of the catalyst carrier by retaining water inside the pores of the catalyst carrier, thereby providing a highly efficient catalyst layer.

Hereinafter, embodiments will be described in detail with reference to the drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanations of well-known matters or redundant explanations of substantially the same configurations may be omitted.

The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

(Embodiment 1)
Embodiment 1 will be described below using FIGS. 1 to 7.

[1-1. composition]
(electrochemical device)
As shown in FIG. 4, the electrochemical device 40 has a structure in which an electrolyte membrane-electrode assembly 30 is sandwiched between a cathode separator 24 and an anode separator 28.

(Electrolyte membrane-electrode assembly)
As shown in FIG. 4, the electrolyte membrane-electrode assembly 30 includes an electrolyte membrane 21, a cathode 34 including a cathode catalyst layer 22, and a cathode gas diffusion layer 23, and an anode catalyst layer 26 and an anode gas diffusion layer 27. The anode 35 includes an anode 35. The electrolyte membrane-electrode assembly 30 has a structure in which the electrolyte membrane 21 is sandwiched between a cathode 34 and an anode 35.

The electrolyte membrane 21 is a membrane that conducts protons between the cathode 34 and the anode 35, and must have both proton conductivity and gas barrier properties. In the electrolyte membrane-electrode assembly 30 of this embodiment, a perfluorosulfonic acid resin membrane is used as the electrolyte membrane 21. This perfluorosulfonic acid resin membrane has high proton conductivity and can exist stably even in the power generation environment of a fuel cell, for example. The thickness of the electrolyte membrane 21 is 10 μm. If the thickness of the electrolyte membrane 21 is 10 μm, high gas barrier properties and high proton conductivity can be obtained.

The gas diffusion layer (the cathode gas diffusion layer 23 and the anode gas diffusion layer 27) is a layer that has a current collecting function, gas permeability, and water repellency, and has a base material and a coating layer.

In the electrolyte membrane-electrode assembly 30 of this embodiment, carbon paper, which is a material with excellent conductivity and gas/liquid permeability, is used as the base material of the gas diffusion layer.

The coating layer is interposed between the base material and the catalyst layer (cathode catalyst layer 22 and anode catalyst layer 26) to reduce the contact resistance between the base material and the catalyst layer and improve water drainage. This is the layer of

In the electrolyte membrane-electrode assembly 30 of this embodiment, carbon black, which is a conductive material, and polytetrafluoroethylene, which is a water-repellent resin, are used as the coating layer of the gas diffusion layer.

The cathode catalyst layer 22 is a layer that accelerates the rate of electrochemical reaction of the electrode. The cathode catalyst layer 22 includes the catalyst supporting material 5 shown in FIG.

(Catalyst supporting material)
As shown in FIG. 1, the catalyst supporting material 5 includes an electrically conductive catalyst carrier 1 having pores 4, a catalyst 2 supported on the catalyst carrier 1, a hydrophilic functional group (side chain) and a hydrophobic functional group (side chain). It has an ionomer 3 with a main chain. The catalyst supporting material 5 supports the catalyst 2 in at least the pores of the porous and conductive catalyst carrier 1, and a part of the outer surface of the catalyst carrier 1 is coated with the ionomer 3.

The catalyst 2 includes an extra-pore catalyst 2a supported on the outer surface of the catalyst carrier 1, and a pore supported in a portion deeper than the opening in the pore 4 that communicates from the outer surface of the catalyst carrier 1 to the inside. It is distinguished into an internal catalyst 2b.

In this embodiment, mesoporous carbon is used as an example of the catalyst carrier 1 used in the catalyst supporting material 5, but the catalyst carrier 1 is not limited to this mesoporous carbon. Other materials may be used as long as they have the same pore diameter and pore volume as mesoporous carbon and are electrically conductive.

Other mesoporous carbon materials that can be used for the catalyst carrier 1 include, for example, materials made of oxides of titanium, tin, niobium, tantalum, zirconium, aluminum, silicon, and the like.

The mesoporous carbon used for the catalyst carrier 1 in this embodiment has pores 4 communicating from the outer surface to the inside, as shown in FIGS. 1 and 2.

The mode diameter of the pores 4 is 6 nm. If the mode diameter of the pores 4 is 6 nm or more, a large amount of the catalyst 2 can be supported inside the catalyst carrier 1.

The mesoporous carbon used for the catalyst carrier 1 is configured to have an average particle size of 200 nm or more and 1000 nm or less. If the average particle size is 200 nm or more, the particle size of the mesoporous carbon is sufficiently large relative to the length of the ionomer 3, so the area where the ionomer 3 enters the pore 4 is smaller than the pore volume of the pore 4. Since the ionomer 3 becomes smaller, the proportion of the catalyst 2 that is affected by poisoning by the ionomer 3 becomes smaller.

As shown in FIG. 3, functional groups 7 modify the surface of the catalyst carrier 1. In this embodiment, an acidic phenolic hydroxyl group is used as the functional group 7 of the catalyst supporting material 5. The acidic functional group 7 can adsorb moisture 6 on the surface.

Protons supplied from the outside of the catalyst support material 5 are transported to the entrance of the pores 4 via the ionomer 3 adsorbed on the surface of the catalyst support 1 . The ionomer 3 and the water 6 adsorbed on the functional group 7 are in contact with each other, and the protons transported to the entrance of the pore 4 are further transported via the water 6 to the catalyst 2b in the pore.

The material of the catalyst 2 (the extra-pore catalyst 2a and the intra-pore catalyst 2b) includes platinum and a metal different from platinum. Examples of metals different from platinum include cobalt, nickel, manganese, titanium, aluminum, chromium, iron, molybdenum, tungsten, ruthenium, palladium, rhodium, iridium, osmium, copper, and silver. Among these, an alloy of platinum and cobalt is suitable because it has high catalytic activity for the oxygen reduction reaction and good durability in the power generation environment of the fuel cell.

In the catalyst 2 used for the catalyst supporting material 5 in the first embodiment, the molar ratio of platinum and metals different from platinum contained in the catalyst 2 to all metals contained in the catalyst 2 is 0.25 or more. The metal different from platinum contained in catalyst 2 is cobalt. Catalyst 2 having such a composition exhibits high activity.

Cobalt, for example, is easily eluted in the power generation environment of a fuel cell, and when power is generated for a long time, it causes a decrease in the power generation performance of the fuel cell. Therefore, by setting the molar ratio of platinum and cobalt contained in the catalyst 2 to 1 or less, such a decrease in power generation performance can be suppressed. The composition of the catalyst 2 is represented by the composition of PtxCo (x is 1 or more and 4 or less).

The ionomer 3 transmits protons that have passed through the electrolyte membrane 21 to the catalyst 2 in the cathode catalyst layer 22, and has a polymer having a repeating structure as a main chain and an acidic functional group.

In this embodiment, perfluorosulfonic acid resin, which is a solid polymer material of the same quality as the electrolyte membrane 21, is used as the ionomer 3. This perfluorosulfonic acid resin has high proton conductivity among ion exchange resins, and is suitable because it exists stably even in the power generation environment of a fuel cell.

As shown in Figure 5, Ionomer 3 has an agglomerated structure of a polymer chain consisting of a random copolymer of a hydrophilic part with a sulfonic acid group and a hydrophobic part, and a hydrophilic part bonded to the end of the polymer chain. A hydrophilic block consisting of.

Here, the polymer chain refers to a random copolymer of a hydrophilic part and a hydrophobic part, and the molecular structure of the polymer chain is not particularly limited. Further, the ratio of the hydrophilic part to the hydrophobic part contained in the polymer chain is not particularly limited. Furthermore, the polymer chain is a fluorine-based polymer containing a C—F bond.

The hydrophilic portion in the ionomer 3 refers to the smallest repeating unit of the portion to which the sulfonic acid group is bonded in the polymer chain, as shown in FIG. The hydrophilic part has a sulfonic acid group in either part. The number of hydrophilic parts affects the poisoning of the catalyst 2. The hydrophilic portion easily binds to the catalyst 2, and the catalyst 2 combined with the hydrophilic portion inhibits the oxygen reduction reaction with oxygen in the gas, resulting in a decrease in the catalytic activity of the catalyst 2.

In the ionomer 3 in the solution, protons are dissociated from the sulfonic acid group, which is an ion exchanger, and the sulfonic acid group becomes negatively charged. Since the surface of the catalyst 2 is positively charged, the sulfonic acid group of the ionomer 3 is easily adsorbed onto the surface of the catalyst 2.

As shown in FIG. 5, the hydrophobic portion in the ionomer 3 refers to the smallest repeating unit in a portion of the polymer chain to which no acid group (sulfonic acid group, carboxylic acid group, phosphonic acid group, etc.) is bonded. The structure of the hydrophobic part is not particularly limited.

The weight ratio of the ionomer 3 to the total weight of carbon contained in the cathode catalyst layer 22 is 0.8 to 1.5. This carbon is mesoporous carbon.

The ionomer 3 coats at least a portion of the outer surface of the catalyst carrier 1. Since the catalyst carrier 1 has a large number of pores 4, it is useful for suppressing poisoning of the catalyst 2 by the ionomer 3 and for obtaining a fuel cell catalyst in which the catalyst 2 is supported at a high density.

(Manufacturing process of catalyst layer)
Based on the above content, the manufacturing process of the cathode catalyst layer 22 in the electrochemical device 40 will be explained. FIG. 7 is a flowchart showing the manufacturing process of the catalyst layer.

(Hydrophilic treatment process)
First, based on FIG. 1, a method for manufacturing the cathode catalyst layer 22 in the electrochemical device 40 will be described.

A catalyst support material 5 (manufactured by Tanaka Kikinzoku Co., Ltd., TECCо (PMPC-S2) 52-PN), in which the designed pore diameter of the catalyst support 1 is 6 nm and the loading rate of the catalyst 2 on the catalyst support 1 is 50 wt%, was added at 1 mol/L. Impregnation in nitric acid solution. The concentration of the nitric acid solution is not particularly limited, but is preferably 0.1 to 3 mol/L. In this embodiment, the temperature of the nitric acid solution impregnating the catalyst supporting material 5 is maintained at 75°C. The temperature of the nitric acid solution that impregnates the catalyst support material 5 is not limited to 75°C, but the temperature of the nitric acid solution that impregnates the catalyst support material 5 is preferably in the temperature range of 50°C to 90°C.

The hydrophilic treatment of the catalyst supporting material 5 is carried out by placing the catalyst supporting material 5, nitric acid solution, and pure water in a beaker, and heating the contents of the beaker while stirring with a stirrer. Although the time for making the catalyst supporting material 5 hydrophilic is not particularly limited, it is preferable that the time for making the catalyst supporting material 5 hydrophilic is 0.5 h to 5 h.

After the hydrophilic treatment of the catalyst-supporting material 5, the catalyst-supporting material 5 is washed to remove the nitric acid solution remaining in the pores 4 of the catalyst-supporting material 5. The catalyst-supporting material 5 is washed by placing the catalyst-supporting material 5 in pure water and impregnating the catalyst-supporting material 5 with pure water. After confirming that the pH of the cleaning liquid is 6 or more, the cleaning of the catalyst supporting material 5 is completed. If the removal of nitric acid from the catalyst support material 5 is insufficient, the catalytic activity of the catalyst 2 will decrease due to the nitric acid adhering to the surface of the catalyst 2, and the efficiency of the electrochemical device 40 will decrease.

After cleaning the catalyst supporting material 5, the catalyst supporting material 5 is heated to a temperature of 100° C. or higher to evaporate the pure water impregnated into the catalyst supporting material 5, thereby drying the catalyst supporting material 5. In this embodiment, the catalyst supporting material 5 was heated at a temperature of 120° C. for 12 hours to dry the catalyst supporting material 5. The hydrophilic treatment step (S01) was carried out as described above.

(Ink adjustment process)
The catalyst supporting material 5 that has been subjected to the hydrophilic treatment in the hydrophilic treatment step (S01) is added to a mixed solvent of ethanol:water at a weight ratio of 1:1. Ionomer 3 is added in an amount such that the weight ratio is 1.0 to the carbon weight of catalyst supporting material 5 to prepare a slurry having a solid content concentration of 7%.

This prepared slurry was pulverized at 100 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine). Thereafter, the pulverized slurry was stirred for 20 minutes using a rotation-revolution variable mixer (manufactured by Kurabo Industries, Ltd., Mazel Star). The catalyst ink, which was a slurry that had been stirred, was aged for 12 hours at room temperature for defoaming treatment. In this way, the ink adjustment step (S02) was carried out.

(Coating process)
The cathode catalyst layer 22 was prepared by applying the catalyst ink prepared as described above to the approximate center of one main surface of the electrolyte membrane 21 by a spray method (S03) and drying it. Examples and comparative examples of the cathode catalyst layer 22 prepared as described above will be described.

(Example 1)
In the hydrophilic treatment step, the impregnation time of the catalyst supporting material 5 in the nitric acid solution was set to 0.5 h. The cathode catalyst layer 22 was produced under the above conditions except for the above conditions.

(Example 2)
In the hydrophilic treatment step, the catalyst supporting material 5 was immersed in the nitric acid solution for 1 hour. The cathode catalyst layer 22 of Example 2 was manufactured in the same manner as in Example 1 with respect to other conditions.

(Example 3)
In the hydrophilic treatment step, the time for impregnating the catalyst supporting material 5 in the nitric acid solution was set to 3 hours. The cathode catalyst layer 22 of Example 3 was manufactured in the same manner as in Example 1 with respect to other conditions.

(Example 4)
In the hydrophilic treatment step, the catalyst supporting material 5 was immersed in the nitric acid solution for 5 hours. The cathode catalyst layer 22 of Example 4 was manufactured in the same manner as in Example 1 with respect to other conditions.

(Comparative example)
For the comparative example, the above hydrophilic treatment step was not performed. The other conditions, such as the ink adjustment step and the coating step, were carried out in the same manner as in Examples 1 to 4, and the cathode catalyst layer 22 of the comparative example
was created.

Subsequently, an anode catalyst layer 26 was formed approximately in the center of the main surface of the electrolyte membrane 21 on the side opposite to the surface on the cathode catalyst layer 22 side of the electrolyte membrane 21 provided with the cathode catalyst layer 22 of Examples 1 to 4 and the comparative example. did.

The anode catalyst layer 26 is produced as follows. First, a commercially available platinum-supported carbon black catalyst (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., TEC10E50E) was added to a mixed solvent containing equal amounts of water and ethanol and stirred. Ionomer (manufactured by AGC Co., Ltd., IQ100B) was added to the obtained slurry so that the weight ratio to the carbon of the platinum carbon black catalyst was 0.6, and it was mixed with a rotation-revolution variable mixer (manufactured by Kurabo Industries, Mazel Star). Stirring treatment was performed for 20 minutes.

The catalyst ink thus prepared was applied to the approximate center of the main surface of the electrolyte membrane 21 on the side opposite to the cathode catalyst layer 22 side of the electrolyte membrane 21 provided with the cathode catalyst layer 22 of Examples 1 to 4 and the comparative example. The anode catalyst layer 26 was prepared by applying it by a spray method and drying it.

A gas diffusion layer (manufactured by SGL Carbon Japan Co., Ltd., GDL25BC) was placed on each exposed surface of the cathode catalyst layer 22 and anode catalyst layer 26 of Examples 1 to 4 and the comparative example produced in this way. By applying a pressure of 1 MPa for 5 minutes in a high temperature environment of 140° C., electrolyte membrane-electrode assemblies 30 of Examples 1 to 4 and a comparative example were produced.

The obtained electrolyte membrane-electrode assemblies 30 of Examples 1 to 4 and comparative example were used as a cathode separator in which a serpentine-shaped channel was formed in the form of a groove on the surface of the electrolyte membrane-electrode assembly 30 facing the cathode 34. 24 and an anode separator 28 in which a serpentine-shaped channel is formed in the groove shape on the surface facing the anode 35 of the electrolyte membrane-electrode assembly 30, and by incorporating it into a predetermined jig, the fuel can be removed. Electrochemical devices 40 of Examples 1 to 4 and a comparative example, which serve as battery cells, were manufactured.

[1-2. motion]
The operation and effect of the electrochemical device 40 configured as described above will be explained below.

The temperature of the electrochemical device 40 created as described above was maintained at 65° C., and hydrogen with a dew point of 60° C. was introduced into the flow path between the anode separator 28 and the anode 35 between the cathode separator 24 and the cathode 34. Oxygen with a dew point of 65° C. is flowed through the flow channels at a flow rate sufficiently higher than the amount consumed by the electrochemical reaction (oxidation/reduction reaction) of the fuel cell, and the anode 35 and cathode 34 are connected to the electronic load. Electrical connection was made through the device.

At this time, each voltage of the electrochemical device 40 was measured during constant current operation using an electronic load device (PLZ-664WA, manufactured by Kikusui Electronics Co., Ltd.). Additionally, during the measurement, the electrical resistance of the electrochemical device 40 was measured in-situ using a low resistance meter with a fixed frequency of 1 kHz.

Then, the current value at 0.9 V is read from the current-voltage curve corrected for the electrical resistance of the electrochemical device 40, and the current value is normalized by the amount of platinum contained in the cathode catalyst layer 22, which can be used as an index of catalytic activity. did. This is called mass activity at 0.9V and is generally used as an indicator of catalytic activity in fuel cells.

The amount of functional groups modified on the catalyst supporting material 5 was calculated by a water vapor adsorption method. The catalyst supporting materials 5 of Examples 1 to 4 and Comparative Example were placed in a cell with a constant volume, water vapor was introduced, and the pressure fluctuation before and after the introduction was regarded as monomolecular adsorption of water vapor, and the water vapor adsorption per unit weight was determined. The functional group amount (mmol/L) was calculated from the amount (mmol/g).

FIG. 6 shows the relationship between the amount of functional groups modified in the catalyst supporting material 5 and the mass activity at 0.9 V in the electrochemical devices 40 of Examples 1 to 4 and the comparative example. Note that in FIG. 6, the values of Examples 1 to 4 are normalized by setting the mass activity value at 0.9 V of the comparative example to 1.

In the cathode catalyst layer 22 of Example 1, the amount of functional groups was 0.2 mmol/L, and in the cathode catalyst layer 22 of Example 2, the amount of functional groups was 1.3 mmol/L, and the catalyst supporting material had more functional groups than the comparative example. It can be seen that it has been modified to 5.

It can also be seen that the mass activity of the cathode catalyst layers 22 of Examples 1 and 2 is 1.2 to 1.3 times higher than that of the comparative example, indicating an improvement. This is because, as shown in FIG. 3, in the cathode catalyst layers 22 of Examples 1 and 2, protons can be supplied to the pore catalysts 2b existing in the pores 4 through the water 6. Therefore, it seems that the surface area of the catalyst 2 that can be utilized within the catalyst supporting material 5 is increased and the normalized activity is improved.

On the other hand, in the cathode catalyst layer 22 of Example 3, the amount of functional groups is 2.0 mmol/L, and in the cathode catalyst layer 22 of Example 4, the amount of functional groups is 3.6 mmol/L. It can be seen that more functional groups are modified than in the cathode catalyst layer 22 of Example 2.

However, the normalized activity of the cathode catalyst layer 22 of Example 4 was lower than the normalized activity of the cathode catalyst layer 22 of Examples 1 and 2. This is because in the cathode catalyst layer 22 of Example 4, the adsorption amount of moisture 6 existing in the pores 4 becomes excessive, and by partially blocking the pores 4, the moisture 6 is diffused into the pores. This is considered to be because the flow rate of oxygen supplied to the catalyst 2b decreased, and the usable surface area of the catalyst 2b within the pores began to decrease.

From the above, by performing an appropriate hydrophilic treatment process as in the case of the cathode catalyst layer 22 in Examples 1 to 3, the surface area of the available pore catalyst 2b can be increased and the mass activity of the cathode catalyst layer 22 can be increased. You can improve.

[1-3. Effects, etc.]
As described above, in the present embodiment, the cathode catalyst layer 22 is a catalyst-supported catalyst including the conductive catalyst carrier 1 having pores 4 and the catalyst 2 at least partially supported inside the pores 4. A proton-conducting ionomer 3 that covers at least a portion of the outer surface of the catalyst-supporting material 5 is provided. In the catalyst support material 5, the amount of acidic functional groups 7 that modify the outer surface and the inside of the pores of the catalyst support 1 is 0.2 mmol or more per unit weight gram of the catalyst support 1.

In the cathode catalyst layer 22 of this embodiment, the catalyst support material 5 of the cathode catalyst layer 22 has acidic functional groups on the outer surface and inside the pores of the catalyst support 1 at 0.00% per unit weight of the catalyst support 1 in grams. By modifying the amount by 2 mmol or more, the moisture 6 can be adsorbed to the vicinity of the catalyst 2 (in-pore catalyst 2b) inside the pores of the catalyst supporting material 5.

Therefore, by creating a moist environment inside the pores 4, protons can be supplied to the intra-pore catalyst 2b via the moisture 6 within the pores 4. The catalyst 2 (pore catalyst 2b) supported inside the pores 4 is not covered with the ionomer 3 and is supplied with protons by the moisture 6 held inside the pores 4, so that the catalyst 2 , and a highly efficient cathode catalyst layer 22 can be obtained.

As in this embodiment, the average pore diameter of the pores 4 of the catalyst carrier 1 in the catalyst supporting material 5 of the cathode catalyst layer 22 may be 3 nm or more and 10 nm or less. If the average pore diameter of the pores 4 of the catalyst carrier 1 is 3 nm or more and 10 nm or less, the ionomer 3 is prevented from penetrating into the pores 4 of the catalyst carrier 1, and the catalyst supported inside the catalyst support material 5 is prevented. The moisture 6 of the electrolyte membrane-electrode assembly 30 can be adsorbed up to a level close to 2.

Therefore, while preventing the catalyst 2 from being poisoned by the ionomer 3, it is possible to create a moist environment inside the pores 4 of the catalyst carrier 1, thereby increasing the utilization efficiency of the catalyst 2 and creating a highly efficient cathode catalyst layer 22. can be obtained.

As in this embodiment, the catalyst support material 5 of the cathode catalyst layer 22 has an amount of acidic functional groups 7 that modify the outer surface and inside of the pores of the catalyst support 1 per unit weight gram of the catalyst support 1. It may be 2.0 mmol or less.

If the amount of acidic functional groups 7 modified on the outer surface of the catalyst carrier 1 and inside the pores is 2.0 mmol or less per unit weight gram of the catalyst carrier 1, the interior of the pores 4 can be blocked by the functional groups 7. You can prevent it from happening. Therefore, since oxygen can be supplied to the vicinity of the catalyst 2 supported inside the catalyst carrier 1 of the catalyst supporting material 5, the utilization efficiency of the catalyst 2 can be increased, and a highly efficient cathode catalyst layer 22 can be formed. Obtainable.

As in this embodiment, the functional group 7 that modifies the surface of the catalyst carrier 1 may be a phenolic hydroxyl group or a carboxyl group. If the functional group 7 modifying the surface of the catalyst carrier 1 is a phenolic hydroxyl group or a carboxyl group, the contact angle of the water 6 adsorbed in the pores 4 can be reduced.

Therefore, by preventing the inside of the pore 4 from being blocked by moisture 6, protons can be supplied to the catalyst 2 via the moisture 6 in the pore 4, and oxygen can be supplied to the catalyst 2 via the pore 4. Since both supply can be achieved, the utilization efficiency of the catalyst 2 can be further increased, and a more efficient cathode catalyst layer 22 can be obtained.

As in this embodiment, the electrolyte membrane-electrode assembly 30 includes an electrolyte membrane 21, an anode 35 disposed on one main surface of the electrolyte membrane 21, and an anode 35 disposed on the other main surface of the electrolyte membrane 21. A cathode 34 may be provided, and the cathode 34 may include the cathode catalyst layer 22 of this embodiment.

If the cathode 34 in the electrolyte membrane-electrode assembly 30 includes the cathode catalyst layer 22 of this embodiment, the cathode catalyst layer 22 of the cathode 34 in the electrolyte membrane-electrode assembly 30 will have a reduced amount of water vapor adsorption by the hydrophilic treatment. The catalyst supporting material 5 has improved properties.

Therefore, the catalyst 2 supported inside the catalyst supporting material 5 in the cathode 34 can supply protons while suppressing poisoning by the ionomer 3, so that it becomes a highly efficient cathode catalyst layer 22 and the electrolyte membrane-electrode assembly 30 can be made more efficient.

(Other embodiments)
As mentioned above, Embodiment 1 has been described as an example of the technology disclosed in this application. However, the technology in the present disclosure is not limited to this, and can also be applied to embodiments in which changes, replacements, additions, omissions, etc. are made. Furthermore, it is also possible to create a new embodiment by combining the components described in the first embodiment.

Therefore, other embodiments will be illustrated below.

In Embodiment 1, the catalyst supporting material 5 in which the mode diameter of the pores 4 was 6 nm was described. The mode diameter of the pores 4 of the catalyst supporting material 5 may be 3 nm or more and 10 nm or less. Therefore, the mode diameter of the pores 4 of the catalyst supporting material 5 is not limited to 6 nm.

However, if the catalyst supporting material 5 in which the mode diameter of the pores 4 is 3 nm or more is used, the partial pressure of oxygen in the air (oxygen-containing gas) within the pores 4 can be increased. Furthermore, if a catalyst supporting material 5 in which the mode diameter of the pores 4 is 10 nm or less is used, the ionomer 3 is difficult to penetrate into the pores 4, so that a highly efficient cathode catalyst layer 22 can be obtained.

In Embodiment 1, the cathode catalyst layer 22 was described using mesoporous carbon having pores 4 of a size called mesopores as the catalyst carrier 1 used for the catalyst support material 5. The catalyst carrier 1 used as the catalyst supporting material 5 only needs to have excellent electrical conductivity and water repellency. Therefore, the catalyst carrier 1 used for the catalyst supporting material 5 is not limited to a mesoporous material.

However, if a mesoporous material having mesopores is used as the catalyst carrier 1 used in the catalyst supporting material 5, a highly efficient cathode catalyst layer 22 can be obtained since it has a high mass activity. Further, as the catalyst carrier 1 used for the catalyst supporting material 5, Ketjenblack may be used. If Ketjen Black is used as the catalyst carrier 1 used in the catalyst supporting material 5, it can have excellent conductivity and drainage properties, and therefore a highly efficient cathode catalyst layer 22 can be obtained.

In the first embodiment, the cathode catalyst layer 22 was described in which the catalyst 2 supported inside the pores 4 of the catalyst supporting material 5 was made of platinum and a metal different from platinum. The catalyst 2 of the cathode catalyst layer 22 may undergo an oxidation-reduction reaction. Therefore, the material of the catalyst 2 supported inside the pores 4 of the catalyst support material 5 of the cathode catalyst layer 22 is not limited to platinum.

The metals different from platinum in the catalyst 2 supported inside the pores 4 of the catalyst support material 5 of the cathode catalyst layer 22 include cobalt, nickel, manganese, titanium, aluminum, chromium, iron, molybdenum, tungsten, ruthenium, palladium, If rhodium, iridium, osmium, copper, silver, or the like is used, a highly efficient cathode catalyst layer 22 can be obtained because it has high mass activity.

Further, cobalt may be used as a metal different from platinum in the catalyst 2. If cobalt is used as a metal different from platinum in the catalyst 2, the catalyst 2 with excellent mass activity and durability can be produced.

In the first embodiment, the electrolyte membrane-electrode assembly 30 using the electrolyte membrane 21 with a membrane thickness of 10 μm was described. The thickness of the electrolyte membrane 21 used in the electrolyte membrane-electrode assembly 30 may be 5 μm or more and 50 μm or less. Therefore, the thickness of the electrolyte membrane 21 used in the electrolyte membrane-electrode assembly 30 is not limited to 10 μm.

If the thickness of the electrolyte membrane 21 used in the electrolyte membrane-electrode assembly 30 is 5 μm or more, high gas barrier properties can be obtained. Further, if the thickness of the electrolyte membrane 21 used in the electrolyte membrane-electrode assembly 30 is 50 μm or less, the resistance of protons moving through the electrolyte membrane 21 can be reduced, so that high proton conductivity can be obtained.

In Embodiment 1, a spray method was described as a method for manufacturing the cathode catalyst layer 22. The cathode catalyst layer 22 may be fabricated using a method generally used for the electrolyte membrane-electrode assembly 30. Therefore, the method for producing the cathode catalyst layer 22 is not limited to the spray method.

However, if a spray method is used as a method for producing the cathode catalyst layer 22, the solvent can be dried during spraying, so the catalyst layer can be produced in a short time. Furthermore, if the coating and drying method is used as a method for producing the cathode catalyst layer 22, the interface between the cathode catalyst layer 22 and the cathode gas diffusion layer 23 becomes flat, so that the adhesion between the cathode catalyst layer 22 and the cathode gas diffusion layer 23 is improved. As a result, a highly efficient cathode catalyst layer 22 can be obtained.

Note that the above-described embodiments are for illustrating the technology of the present disclosure, and therefore various changes, substitutions, additions, omissions, etc. can be made within the scope of the claims or equivalents thereof.

The present disclosure is useful, for example, in an electrode catalyst used in an electrolyte membrane-electrode assembly that constitutes a fuel cell. Specifically, the present disclosure is applicable to fuel cell stacks and the like.

1 Catalyst carrier 2 Catalyst 2a Extra-pore catalyst 2b In-pore catalyst 3 Ionomer 4 Pore 5 Catalyst supporting material 6 Moisture 7 Functional group 21 Electrolyte membrane 22 Cathode catalyst layer 23 Cathode gas diffusion layer 24 Cathode separator 26 Anode catalyst layer 27 Anode Gas diffusion layer 28 Anode separator 30 Electrolyte membrane-electrode assembly 34 Cathode 35 Anode 40 Electrochemical device

Claims (5)

A catalyst supporting material comprising a conductive catalyst carrier having pores and a catalyst at least partially supported inside the pores, and a proton conductive material covering at least a part of the outer surface of the catalyst supporting material. ionoma and,
A catalyst layer for a fuel cell, characterized in that the amount of acidic functional groups modified on the outer surface of the catalyst carrier and inside the pores is 0.2 mmol or more per unit weight gram of the catalyst carrier. The catalyst layer for a fuel cell according to claim 1, wherein the pores have an average pore diameter of 3 nm or more and 10 nm or less. The catalyst layer for a fuel cell according to claim 1 or 2, wherein the amount of acidic functional groups modified on the outer surface of the catalyst carrier and inside the pores is 2.0 mmol or less per unit weight gram of the catalyst carrier. . The fuel cell catalyst layer according to any one of claims 1 to 3, wherein the acidic functional group is a phenolic hydroxyl group or a carboxyl group. An electrolyte membrane, an anode disposed on one main surface of the electrolyte membrane, and a cathode disposed on the other main surface of the electrolyte membrane,
An electrolyte membrane-electrode assembly, wherein the cathode includes the fuel cell catalyst layer according to claim 1.

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