JP2023011964A - Electrode catalyst and electrode catalyst layer for electrochemical device, membrane/electrode assembly, and electrochemical device - Google Patents

Abstract

To provide an electrode catalyst for an electrochemical device capable of having high device durability.SOLUTION: An electrode catalyst 1 for an electrochemical device contains: mesoporous carbon particles 2 in which the average crystallite size of the 002 plane is 1.6 nm or more; and catalytic metal particles 3 supported on the mesoporous carbon particles 2.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to electrocatalysts and electrocatalyst layers for electrochemical devices, membrane/electrode assemblies, and electrochemical devices.

Electrocatalysts disclosed in Patent Documents 1 and 2 are known as conventional electrode catalysts. In this electrode catalyst, a catalyst metal is supported inside mesoporous carbon.

JP 2018-181838 A Japanese Patent No. 6063039

However, there is still room for improvement in the durability required for the electrochemical reaction of the electrochemical device (hereinafter referred to as device durability) compared to the conventional techniques described in Patent Documents 1 and 2 above.

The present disclosure solves the problems of the prior art, and provides an electrochemical device electrode catalyst and electrode catalyst layer, a membrane/electrode assembly, and an electrochemical device that can have high device durability. purpose.

One aspect of the electrode catalyst of the electrochemical device according to the present disclosure includes mesoporous carbon particles having an average crystallite size of 1.6 nm or more on the 002 plane, and catalyst metal particles supported on the mesoporous carbon particles.

One aspect of the electrode catalyst layer of the electrochemical device according to the present disclosure includes mesoporous carbon particles having an average crystallite size of 1.6 nm or more on the 002 plane, and catalyst metal particles supported on the mesoporous carbon particles. It contains an electrode catalyst and a proton-conducting resin.

One aspect of the membrane/electrode assembly according to the present disclosure includes a proton-conducting electrolyte membrane, an anode provided on one main surface of the proton-conducting electrolyte membrane, and the other main surface of the proton-conducting electrolyte membrane. at least one of the anode and the cathode is mesoporous carbon particles having an average crystallite size of 002 plane of 1.6 nm or more; and catalyst metal particles supported on the mesoporous carbon particles. and an electrode catalyst layer containing a proton-conducting resin.

One aspect of the electrochemical device according to the present disclosure includes a proton-conducting electrolyte membrane, an anode provided on one main surface of the proton-conducting electrolyte membrane, and an anode provided on the other main surface of the proton-conducting electrolyte membrane. a cathode, wherein at least one of the anode and the cathode is mesoporous carbon particles in which the average crystallite size of the 002 plane is 1.6 nm or more; and catalyst metal particles supported on the mesoporous carbon particles; and a membrane/electrode assembly including an electrode catalyst layer containing a proton-conducting resin.

INDUSTRIAL APPLICABILITY The present disclosure provides an electrode catalyst and an electrode catalyst layer of an electrochemical device, a membrane/electrode assembly, and an effect that the electrochemical device can have high device durability.

The above and other objects, features, and advantages of the present disclosure will become apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

FIG. 1 is a diagram schematically showing an example of an electrode catalyst for an electrochemical device according to a first embodiment; FIG. FIG. 2A is a diagram schematically showing an example of an electrode catalyst layer of an electrochemical device according to a second embodiment; FIG. 2B is an enlarged view of a portion of FIG. 2A. FIG. 3 is a cross-sectional view schematically showing an example of a membrane/electrode assembly according to the third embodiment. FIG. 4 is a cross-sectional view schematically showing an example of an electrochemical device according to the fourth embodiment. FIG. 5 is a graph showing the relationship between the average crystallite diameter of the 002 plane of mesoporous carbon particles and the voltage drop in the potential cycle test of the fuel cell. FIG. 6 is a graph showing the relationship between the DTA peak temperature and the particle diameter for mesoporous carbon particles having an average crystallite diameter of 0.8 nm on the 002 plane. FIG. 7 is a graph showing the relationship between the DTA peak temperature and the particle size for mesoporous carbon particles having an average crystallite size of 2.2 nm on the 002 plane. FIG. 8A is a cross-sectional image of mesoporous carbon particles having an average crystallite diameter of 0.8 nm on the 002 plane before the potential cycle test. FIG. 8B is a cross-sectional image of mesoporous carbon particles having an average crystallite size of 0.8 nm on the 002 plane after the potential cycle test. FIG. 8C is a cross-sectional image of mesoporous carbon particles having an average crystallite size of 2.2 nm on the 002 plane after the potential cycle test.

(Knowledge underlying the present disclosure)
The present inventors have extensively studied the device durability of electrode catalysts for electrochemical devices. As a result, it was found that the device durability of an electrochemical device is affected by the average crystallite size of the 002 plane in the mesoporous carbon used as a support for the electrode catalyst of the electrochemical device.

Specifically, as described in Patent Document 2, when the crystallite diameter of the 002 plane is large, the mesopores of the mesoporous carbon are crushed depending on the temperature of the heat treatment, and it has been considered unsuitable.

However, the inventors have found that a larger average crystallite diameter of the 002 plane is more appropriate for the device durability of the electrochemical device against start-stop of the fuel cell system. Specifically, in order to make the device durability in the case of using an electrode catalyst having mesoporous carbon particles as a carrier equal to or higher than the device durability in the case of using an electrode catalyst having carbon black as a carrier, 002 It has been found that the average crystallite size of the face is suitable to be 1.6 nm or more.
The present disclosure is made based on this finding. Therefore, the present disclosure specifically provides the following aspects.

The electrode catalyst of the electrochemical device according to the first aspect of the present disclosure includes mesoporous carbon particles having an average crystallite size of 1.6 nm or more on the 002 plane, and catalytic metal particles supported on the mesoporous carbon particles. include. According to this configuration, the electrode catalyst can have high device durability by having high electrochemical durability.

In the electrode catalyst of the electrochemical device according to the second aspect of the present disclosure, in the first aspect, the mesoporous carbon particles have an average particle size of 500 nm or more. According to this configuration, the mesoporous carbon particles have high oxidation durability, so that the electrode catalyst can have high device durability.

In the electrode catalyst for an electrochemical device according to a third aspect of the present disclosure, in the first or second aspect, the mesoporous carbon particles have a mode radius of 1 nm or more and 25 nm or less before supporting the catalytic metal particles. and has mesopores with a pore volume of 1.0 cm ³ /g or more and 3.0 cm ³ /g or less. With this configuration, the electrode catalyst can have high catalytic activity and durability.

An electrode catalyst layer of an electrochemical device according to a fourth aspect of the present disclosure includes the electrode catalyst according to any one aspect of the first to third aspects and a proton-conducting resin. According to this configuration, the electrode catalyst layer can have high device durability by containing the electrode catalyst.

A membrane/electrode assembly according to a fifth aspect of the present disclosure comprises a proton-conducting electrolyte membrane, an anode provided on one main surface of the proton-conducting electrolyte membrane, and an anode on the other main surface of the proton-conducting electrolyte membrane. and a cathode provided on the main surface, wherein at least one of the anode and the cathode includes the electrode catalyst layer of the fourth aspect. According to this configuration, the membrane/electrode assembly can have high device durability by including the electrode catalyst layer.

A membrane/electrode assembly according to a sixth aspect of the present disclosure is the fifth aspect, wherein at least the cathode includes the electrode catalyst layer. According to this configuration, the membrane/electrode assembly can have high device durability by including the electrode catalyst layer.

An electrochemical device according to a seventh aspect of the present disclosure comprises the membrane/electrode assembly of the fifth or sixth aspect. According to this configuration, the electrochemical device can have high device durability by including the membrane/electrode assembly.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In addition, hereinafter, the same reference numerals may be given to the same or corresponding constituent members throughout all the drawings, and the description thereof may be omitted.

(First embodiment)
The electrode catalyst 1 of the electrochemical device according to the first embodiment of the present disclosure includes mesoporous carbon particles 2 and catalytic metal particles 3, as shown in FIG. A fuel cell will be described below as an example of an electrochemical device. However, the electrochemical device is not limited to a fuel cell as long as it undergoes an electrochemical reaction. For example, it may be a water electrolysis device that electrolyzes water to produce hydrogen and oxygen. .

The mesoporous carbon particles 2 are porous materials having a large number of mesopores 4 and are carriers on which the catalytic metal particles 3 are supported. The mesoporous carbon particles 2 are produced, for example, by heat-treating mesoporous carbon. The pore structure of mesoporous carbon can be freely controlled by changing manufacturing conditions such as a template, carbon source, and reaction temperature during synthesis.

The average particle size of the primary particles of the mesoporous carbon particles 2 is, for example, 500 nm or more. The average particle size is the median size (d50) of the particle size distribution of the mesoporous carbon particles 2 . Thus, when the average particle size is 500 nm or more, the oxidation durability of the electrode catalyst 1 can be improved to be higher than that of a general electrode catalyst using carbon black as a carrier, and the device durability of the electrode catalyst 1 can be improved. Improvement is planned. In addition, even if the mesoporous carbon particles 2 are in contact with the proton conductive resin, the ratio of the catalyst metal particles 3 coated with the proton conductive resin is small, and the decrease in the catalytic activity of the electrode catalyst 1 is reduced. can do.

The average particle size of the mesoporous carbon particles 2 may be adjusted by pulverization. A method such as a roller mill, a ball mill, or a bead mill is used for this pulverization treatment, for example. Among these, for the refinement of the mesoporous carbon particles 2, a roller mill is used, a ball mill is more preferably used, and a bead mill is more preferably used.

In addition, for example, in a bead mill, the particle size of the mesoporous carbon particles 2 is controlled by the rotational speed (peripheral speed) and time of the stirring mechanism and the diameter of the beads. The peripheral speed is 6 m/s or more and 18 m/s or less. This peripheral speed may be 8 m/s or more and 16 m/s or less, and more preferably 10 m/s or more and 14 m/s. The rotation time of the stirring mechanism may be from 10 minutes to 30 minutes, from 14 minutes to 26 minutes, or from 18 minutes to 22 minutes.

The average particle diameter of the mesoporous carbon particles 2 can be measured by a measuring device such as a laser diffraction particle size distribution measuring device, a scanning electron microscope (SEM), and a transmission electron microscope (TEM) while the mesoporous carbon particles 2 are dispersed in a solvent. ) is measured using an observation device such as

The mesopores 4 are pores provided in the mesoporous carbon particles 2 , open to the outer surface of the mesoporous carbon particles 2 , and extend long inside the mesoporous carbon particles 2 from these openings. The mesopores 4 are connecting pores and are connected to other mesopores 4 . Thereby, the plurality of mesopores 4 communicate with each other.

The mesopores 4 have a mode radius of 1 nm or more and 25 nm or less before the catalyst metal particles 3 are supported on the mesoporous carbon particles 2 . The mode radius is the most frequent diameter (radius with maximum value) in the diameter distribution of the mesopores 4 of the mesoporous carbon particles 2 . The radius of the mesopores 4 is half the dimension perpendicular to their extending direction.

The mode radius of the mesopores 4 may be 3 nm or more and 6 nm or less, more preferably 3 nm or more and 4 nm or less. If the mode radius of the mesopores 4 is 3 nm or more, gas can easily flow through the mesopores 4 . If the mode radius is 6 nm or less, even if the proton conductive resin comes into contact with the electrode catalyst 1 , it becomes difficult for the proton conductive resin to enter the mesopores 4 .

The mesopores 4 may have a pore volume of 1.0 cm ³ /g or more and 3.0 cm ³ /g or less before supporting the catalyst metal particles 3 . If the pore volume of the mesopores 4 is 1.0 cm ³ /g or more, many catalyst metal particles 3 are supported inside the mesoporous carbon particles 2 (that is, the mesopores 4), and the electrode catalyst 1 has high catalytic activity. can have If the pore volume is 3.0 cm ³ /g or less, the mesoporous carbon particles 2 can have high strength as a structure.

In addition, the pore volume and mode radius of the mesopores 4 are determined by the measurement data of the nitrogen adsorption desorption isotherm, the Barrett-Joyner-Halenda (BJH) method, the density functional (DFT) method, the quench fixed density functional (QSDFT) ) is obtained by analyzing by a method such as the method.

Mesoporous carbon particles 2 have an average crystallite size of 002 plane of 1.6 nm or more. As a result, the electrochemical durability of the electrode catalyst 1 can be enhanced beyond that of a general electrode catalyst using carbon black as a carrier. For this reason, the device durability when using the electrode catalyst 1 with mesoporous carbon particles 2 as a carrier is equal to or higher than the device durability when using an electrode catalyst with carbon black as a carrier, and the electrode catalyst 1 is high. It can have device durability.

The average crystallite size of the 002 plane is controlled, for example, by the heat treatment temperature of the mesoporous carbon. The heat treatment temperature of mesoporous carbon is 1000°C or higher and lower than 2000°C. The heat treatment temperature may be 1400°C or higher and lower than 1700°C, and preferably 1600°C or higher and lower than 1680°C.

The mesoporous carbon particles 2 have a specific surface area of 1000 m ² /g or more. This specific surface area is the surface area per unit weight of the mesoporous carbon particles 2 . The surface area of the mesoporous carbon particles 2 includes the surface (inner surface) of the mesoporous carbon particles 2 defining the mesopores 4 and the surface appearing outside the mesoporous carbon particles 2 (outer surface).

The specific surface area is obtained, for example, by evaluating the mesoporous carbon particles 2 by the Brunauer-Emmett-Teller (BET) method. In this BET method, for example, the surface area of the mesoporous carbon particles 2 is obtained by applying the BET formula to the region of the relative pressure of 0.05 or more and 0.35 or less on the nitrogen adsorption/desorption isotherm.

The mesoporous carbon particles 2 having a specific surface area of 1000 m ² /g or more have less agglomeration of the catalyst metal particles 3 supported on the mesoporous carbon particles 2 than the mesoporous carbon particles 2 having a specific surface area of less than 1000 m ² /g. be. Therefore, it is possible to reduce the reduction in the specific surface area of the catalyst metal particles 3 due to aggregation, and reduce the deterioration in the catalytic activity of the electrode catalyst 1 .

Catalyst metal particles 3 are carried on mesoporous carbon particles 2 . The catalyst metal particles 3 are supported at least inside the mesoporous carbon particles 2 . That is, the catalyst metal particles 3 are supported on the inner surfaces of the mesoporous carbon particles 2 defining the mesopores 4 . The catalyst metal particles 3 may or may not be supported on the outer surface of the mesoporous carbon particles 2 .

The catalyst metal particles 3 are made of, for example, platinum (Pt), ruthenium (Ru), palladium (Pd), iridium (Ir), silver (Ag), gold (Au), and the like. Platinum and its alloys are suitable as the electrode catalyst 1 for fuel cells because they have high catalytic activity for oxidation-reduction reactions and good durability in the power generation environment of fuel cells. Moreover, the catalyst metal particles 3 have a suitable particle shape.

The average particle size of the catalyst metal particles 3 is, for example, 1 nm or more and 20 nm or less. This average particle size may be 2 nm or more and 10 nm or less. When the average particle size of the catalyst metal particles 3 is 10 nm or less, the surface area (specific surface area) per unit weight of the catalyst metal particles 3 is large, and the catalytic metal particles 3 have high catalytic activity. Further, when the average particle size of the catalytic metal particles 3 is 1 nm or more, the catalytic metal particles 3 are chemically stable, and for example, the catalytic metal particles 3 are difficult to dissolve even under the power generation environment of the fuel cell.

(Second embodiment)
As shown in FIGS. 2A and 2B, the electrode catalyst layer 5 of the electrochemical device according to the second embodiment of the present disclosure includes the plurality of electrode catalysts 1 of the first embodiment and the proton conductive resin 6. contains. The electrode catalyst layer 5 may be, for example, a thin film having a thin plate shape.

The proton-conducting resin 6 coats the outer surface of the electrode catalyst 1 and is a polymer electrolyte having proton-conducting properties. Among ion-exchange resins, perfluorosulfonic acid resin has high proton conductivity and stably exists even under the electrochemical reaction of an electrochemical device. be done. Moreover, the proton conductivity of the proton conductive resin 6 improves the operating efficiency of the electrochemical device.

The ion exchange capacity of the ion exchange resin may be greater than or equal to 0.9 and less than or equal to 2.0 meq/g dry resin. When the ion exchange capacity is 0.9 meq/g dry resin or more, the proton conductive resin 6 tends to have high proton conductivity. When the ion exchange capacity is 2.0 meq/g dry resin or less, swelling of the resin due to water absorption is suppressed, and gas diffusion in the electrode catalyst layer 5 is less likely to be inhibited.

In the electrode catalyst layer 5, the ratio of the weight of the proton conductive resin 6 to the total weight of carbon including the mesoporous carbon particles 2 may be 0.3 or more and 2.0 or less. Further, the weight ratio may be 0.6 or more and 1.5 or less, preferably 0.8 or more and 1.2 or less.

The electrode catalyst layer 5 may further contain at least one carbon material selected from carbon black and carbon nanotubes. The average particle size of the carbon material is smaller than the average particle size of the mesoporous carbon particles 2, for example, 10 nm or more and 100 nm or less. Such a carbon material is arranged between the mesoporous carbon particles 2 adjacent to each other and fills the gaps.

Therefore, since carbon black and/or carbon nanotube carbon materials generate capillary action, water is prevented from staying in the gaps of the mesoporous carbon particles 2, the drainage property in the electrode catalyst layer 5 is improved, and the electrochemical device can increase the efficiency of the electrochemical reaction of In addition, since the carbon material has conductivity, it can assist the conductivity between the mesoporous carbon particles 2, reduce the resistance of the electrode catalyst layer 5, and increase the efficiency of the electrochemical reaction of the electrochemical device.

Moreover, the electrode catalyst layer 5 may contain materials other than the mesoporous carbon particles 2 and the catalyst metal (for example, metal oxides, etc.). Thereby, the electron conductivity, proton conductivity, oxygen diffusibility, etc. of the electrode catalyst layer 5 can be improved.

As described above, the electrode catalyst layer 5 has the electrode catalyst 1 including the mesoporous carbon particles 2 having an average crystallite size of 1.6 nm or more on the 002 plane and the catalytic metal particles 3 supported on the mesoporous carbon particles 2 . Thereby, the electrode catalyst layer 5 can have high device durability.

(Third embodiment)
A membrane electrode assembly 7 (MEA: Membrane Electrode Assembly) according to the third embodiment of the present disclosure includes a proton-conducting electrolyte membrane 8, an anode 9 and a cathode 10, as shown in FIG. At least one of the anode 9 and cathode 10 contains the electrode catalyst layer 5 of the electrochemical device of the second embodiment. Here, at least the cathode 10 may contain the electrode catalyst layer 5 .

The proton-conducting electrolyte membrane 8 has both proton conductivity and gas barrier properties, and is, for example, a solid polymer electrolyte membrane and is composed of an ion-exchangeable fluororesin membrane, an ion-exchangeable hydrocarbon-based resin membrane, or the like. Among them, the perfluorosulfonic acid resin membrane has high proton conductivity and can stably exist even in the power generation environment of a fuel cell, for example.

A proton-conducting electrolyte membrane 8 is sandwiched between an anode 9 and a cathode 10 for ionic (proton) conduction therebetween. The proton-conducting electrolyte membrane 8 is an ion exchange capacity of 0.9 or more and 2.0 or less meq/g dry resin. When the ion exchange capacity is 0.9 meq/g dry resin or more, the proton conductive electrolyte membrane 8 tends to have high proton conductivity. When the ion exchange capacity is 2.0 meq/g dry resin or less, swelling of the resin due to water absorption is suppressed in the proton conductive electrolyte membrane 8, and dimensional change is suppressed.

The proton-conducting electrolyte membrane 8 has a pair of surfaces (principal surfaces), and the dimension (film thickness) therebetween is, for example, 5 μm or more and 50 μm or less. When the film thickness is 5 μm or more, the proton conductive electrolyte membrane 8 can obtain high gas barrier properties. When the film thickness is 50 μm or less, the proton conductive electrolyte membrane 8 can obtain high proton conductivity.

The anode 9 and cathode 10 are the electrodes of the membrane/electrode assembly 7 and sandwich the proton-conducting electrolyte membrane 8 therebetween. The anode 9 is arranged on one main surface of the pair of main surfaces of the proton-conducting electrolyte membrane 8, and the cathode 10 is arranged on the other main surface.

The anode 9 includes an electrode catalyst layer (first electrode catalyst layer 9a) and a gas diffusion layer (first gas diffusion layer 9b). One surface of the first electrode catalyst layer 9a is arranged on one main surface of the proton conductive electrolyte membrane 8, and one surface of the first gas diffusion layer 9b is arranged on the other surface of the first electrode catalyst layer 9a. are placed.

The cathode 10 includes an electrode catalyst layer (second electrode catalyst layer 10a) and a gas diffusion layer (second gas diffusion layer 10b). One surface of the second electrode catalyst layer 10a is arranged on the other main surface of the proton conductive electrolyte membrane 8, and one surface of the second gas diffusion layer 10b is arranged on the other surface of the second electrode catalyst layer 10a. are placed.

Each of the gas diffusion layers 9b and 10b is a layer having both current collecting action and gas permeability. Each gas diffusion layer 9b, 10b is, for example, a material having excellent conductivity and gas and liquid permeability, and examples thereof include porous materials such as carbon paper, carbon fiber cloth, and carbon fiber felt. .

A water-repellent layer may be provided between the first gas diffusion layer 9b and the first electrode catalyst layer 9a and between the second gas diffusion layer 10b and the second electrode catalyst layer 10a. The water-repellent layer is a layer for improving liquid permeability (drainage). The water-repellent layer is mainly composed of, for example, a conductive material such as carbon black and a water-repellent resin such as polytetrafluoroethylene (PTFE).

Each of the electrode catalyst layers 9a and 10a is a layer that accelerates the power generation reaction speed of the electrode. At least one of the first electrode catalyst layer 9 a and the second electrode catalyst layer 10 a includes the electrode catalyst layer 5 . Thus, the membrane/electrode assembly 7 can have high device durability because the anode 9 and/or cathode 10 includes the electrode catalyst layer 5 .

For example, at least the second electrode catalyst layer 10 a may include the electrode catalyst layer 5 . In this case, the first electrode catalyst layer 9a may be composed of the electrode catalyst layer 5, or may have the same structure as the conventional electrode catalyst layer generally used in the membrane/electrode assembly 7 of the fuel cell. may be Further, the second electrode catalyst layer 10 a is composed of the electrode catalyst layer 5 .

The membrane/electrode assembly 7 is produced, for example, as follows. A catalyst paste is prepared by dispersing the conductive material, catalyst metal particles 3 and proton conductive resin 6 in a solvent such as water or alcohol. The catalyst paste is applied to both sides of the proton-conducting electrolyte membrane 8 or other base material and dried to form the anode 9 and the cathode 10 on the proton-conducting electrolyte membrane 8 or the base material. A proton conductive electrolyte membrane 8 is sandwiched between the anode 9 and the cathode 10 to produce a membrane/electrode assembly 7 .

Here, the cathode 10 composed of the electrode catalyst layer 5 is formed by using the mesoporous carbon particles 2 having an average crystallite diameter of 1.6 nm or more on the 002 plane as the conductive material of one of the catalyst pastes. . Mesoporous carbon particles 2, carbon black, or the like is used as the conductive material of the other catalyst paste, and the anode 9 is formed.

(Fourth embodiment)
An electrochemical device 11 according to the fourth embodiment, as shown in FIG. 4, includes a membrane/electrode assembly 7 according to the third embodiment. In FIG. 4, the electrochemical device 11 is composed of a single cell having one cell, but may be composed of a stack in which a plurality of cells are laminated.

A membrane/electrode assembly 7 is sandwiched between a pair of separators 12 and 13 . One separator 12 of the pair of separators 12 and 13 is arranged on the anode 9 and has a surface facing the other surface of the first gas diffusion layer 9b (the surface opposite to the first electrode catalyst layer 9a side). A supply path for supplying a fuel gas such as hydrogen to the anode 9 is provided on this surface. The other separator 13 is arranged on the cathode 10 and has a surface facing the other surface of the second gas diffusion layer 10b (the surface opposite to the second electrode catalyst layer 10a side). A supply path is provided for supplying the cathode 10 with an oxidant gas such as .

Thus, the fuel gas and the oxidant gas supplied to the electrochemical device 11 undergo an electrochemical reaction in the membrane/electrode assembly 7 . This electrochemical device 11 can have high device durability by including the membrane/electrode assembly 7 .

(Example 1)
<Production of electrode catalyst and fuel cell>
In the production of the fuel cell of Example 1, first, a commercially available mesoporous carbon (CNovel manufactured by Toyo Tanso Co., Ltd.) having a specific surface area of 1600 m ² /g and a designed pore diameter of 10 nm was subjected to heat treatment. As long as mesoporous carbon having an average crystallite diameter of 1.6 nm or more on the 002 plane can be produced, the method for producing mesoporous carbon is not limited to heat treatment.

In this heat treatment, 1 g of mesoporous carbon was subdivided into an alumina crucible, heated from room temperature over 2 hours using a Tammann tube atmosphere furnace, fired at 1650 ° C. for 2 hours, and then left at room temperature overnight. The temperature was lowered to As a result, mesoporous carbon having an average crystallite diameter of 2.2 nm on the 002 plane was produced. The heat treatment is not limited to the above method as long as mesoporous carbon having an average crystallite diameter of 1.6 nm or more in the 002 plane can be produced.

The optimum method for changing the average crystallite size differs depending on the type of mesoporous carbon. For example, Patent Document 2, which is a prior art, describes that the average crystallite size does not change before and after heat treatment in mesoporous carbon.

Then, the heat-treated mesoporous carbon was added to a mixed solvent containing equal amounts of water and ethanol, and the solid content was adjusted to 1 wt. % slurry was adjusted. Zirconia beads with a diameter of 0.5 mm were added to this slurry, and pulverization was performed for 20 minutes at a peripheral speed of 12 m/s using a medium agitation type wet bead mill (Labo Star Mini manufactured by Ashizawa Fine Tech). Thus, mesoporous carbon particles having an average particle size of 800 nm were produced.

After removing the zirconia beads from the slurry after the pulverization treatment and evaporating the solvent, the resulting aggregates were ground in a mortar to prepare dispersed mesoporous carbon particles. The method for producing the mesoporous carbon particles is just an example, and the method is not limited to this as long as the method can control the average crystallite size and particle size on the 002 plane of the mesoporous carbon particles.

1 g of the obtained mesoporous carbon particles was added to 400 mL of a mixed solvent of water:ethanol=1:1 (weight ratio), and ultrasonically dispersed for 15 minutes. While stirring this dispersion in a nitrogen atmosphere, a 14 wt % dinitrodiamineplatinum nitric acid solution was added dropwise to the mesoporous carbon particles so that the platinum content was 50 wt %, followed by heating and stirring at 80° C. for 6 hours.

After allowing the stirred material to cool, it was filtered and washed, and the filtered material was dried at 80° C. for 15 hours to obtain aggregates. This aggregate was ground in a mortar and heat-treated at 220° C. for 2 hours in a gas atmosphere of nitrogen:hydrogen=85:15. As a result, an electrode catalyst was produced in which the mesoporous carbon particles carried the catalyst metal particles. The method for producing the electrode catalyst described above is merely an example, and is not limited to this method as long as the catalytic metal particles are supported inside the mesopores of the mesoporous carbon particles.

The prepared electrode catalyst and Ketjenblack (EC300J, manufactured by Lion Specialty Chemicals Co., Ltd.) of half the weight of the mesoporous carbon particles contained in this electrode catalyst are mixed with equal amounts of water and ethanol. Pour into the solvent and stir. An ionomer (Nafion, manufactured by DuPont) was added to the obtained slurry so that the weight ratio to the total carbon (mesoporous carbon particles + Ketjenblack) was 0.8, and ultrasonic dispersion treatment was performed. The catalyst ink thus obtained is applied onto one main surface of a solid polymer electrolyte membrane (manufactured by Gore Japan Co., Ltd., Gore Select III) by a spray method to form a second electrode catalyst layer containing an electrode catalyst. was made.

In addition, a commercially available platinum-supported carbon black catalyst (TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was put into a mixed solvent containing equal amounts of water and ethanol and stirred. An ionomer (manufactured by DuPont, Nafion) was added to the resulting slurry so that the weight ratio to carbon was 0.8, followed by ultrasonic dispersion treatment to obtain a catalyst ink. This catalyst ink was applied onto the other main surface (the surface opposite to the second electrode catalyst layer side) of the solid polymer electrolyte membrane by a spray method to prepare a first electrode catalyst layer.

Then, a first gas diffusion layer (GDL25BC, manufactured by SGL Carbon Japan) is placed on the first electrode catalyst layer, and a second gas diffusion layer (GDL25BC, manufactured by SGL Carbon Japan) is placed on the second electrode catalyst layer. bottom. By applying a pressure of 7 kgf/cm ² for 5 minutes at a high temperature of 140° C., a membrane/electrode assembly was produced.

Then, the resulting membrane/electrode assembly is sandwiched between a pair of separators provided with serpentine-shaped flow paths. Then, this sandwiched object was incorporated into a predetermined jig to fabricate a single cell fuel cell.

(Example 2)
In Example 2, 1 g of the same mesoporous carbon as in Example 1 was subdivided into an alumina crucible, heated from room temperature over 2 hours using a Tammann tube atmosphere furnace, and fired at 1800 ° C. for 2 hours. After that, the temperature was lowered to room temperature overnight. As a result, mesoporous carbon having an average crystallite diameter of 3.4 nm on the 002 plane was produced. In Example 2, other methods for producing the electrode catalyst and the fuel cell are the same as in Example 1.

(Comparative example 1)
In Comparative Example 1, 1 g of the same mesoporous carbon as in Example 1 was subdivided into an alumina crucible, heated from room temperature over 2 hours using a Tammann tube atmosphere furnace, and fired at 1500° C. for 2 hours. After that, the temperature was lowered to room temperature overnight. As a result, mesoporous carbon having an average crystallite diameter of 0.8 nm on the 002 plane was produced. In Comparative Example 1, other methods for producing the electrode catalyst and the fuel cell are the same as in Example 1.

(Comparative example 2)
In Comparative Example 2, 1 g of the same mesoporous carbon as in Example 1 was subdivided into an alumina crucible, heated from room temperature over 2 hours using a Tammann tube atmosphere furnace, and fired at 1000 ° C. for 2 hours. was allowed to cool to room temperature overnight. As a result, mesoporous carbon having an average crystallite diameter of 0.8 nm on the 002 plane was produced. In Comparative Example 2, other methods for producing the electrode catalyst and the fuel cell are the same as in Example 1.

<Evaluation of Electrode Catalyst and Fuel Cell>
In this way, the mesoporous carbon particles of the electrode catalyst and the fuel cell were produced. Measurements of the average crystallite size, average particle size, and oxidation resistance of the mesoporous carbon particles on the 002 plane were carried out as follows. Further, as a test simulating the potential state of starting and stopping the fuel cell, a potential cycle test of the fuel cell was performed as follows. These results are shown in FIGS. 5-7.

The average crystallite size of the 002 plane in the mesoporous carbon particles was measured by the X-ray diffraction method. An X-ray diffractometer (RINT-RAPID, manufactured by Rigaku Corporation) was used, and a glass sample stage was used. The tube voltage was set to 40 kV, the tube current to 30 mA, the irradiation angle to 10° (ω axis), the irradiation time to 15 minutes, the collimator to 300 μmΦ, and the rotation speed to 5°/min. The average crystallite size was calculated from the (002) peak in the mesoporous carbon particle measurement results.

The average particle size of the mesoporous carbon particles was measured with a laser diffraction particle size distribution analyzer (Microtrac HRA, manufactured by Microtrac Bell). An ionomer dispersion is added to the mesoporous carbon particles so that the weight ratio of the ionomer and carbon is 2:1, and ultrasonic treatment is performed in an ultrasonic bath for 60 minutes to obtain a slurry in which the mesoporous carbon particles are monodispersed. rice field. The particle size distribution of this slurry was measured by a laser diffraction method, and the obtained median size was used as the average particle size of the mesoporous carbon particles.

The oxidation durability of the mesoporous carbon particles was measured by ThermoGravimeter-Differential Thermal Analyzer (TG-DTA), which continuously measures the weight change of the sample while heating the sample in an oxygen atmosphere. A thermogravimetric differential thermal analyzer (STA7200RV, manufactured by Hitachi High-Tech Science Co., Ltd.) was used, and a measurement vessel made of platinum was used. The heating conditions were set from room temperature to 900° C., a heating rate of 5° C./min, a gas atmosphere of air, and a gas flow rate of 100 mL/min. A DTA peak was detected from the results of measurement by this TG-DTA method. Since the temperature of this DTA peak represents the decomposition temperature (oxidation temperature) of the mesoporous carbon particles in an oxygen atmosphere, it was used as an evaluation value of the oxidation durability of the electrode catalyst.

In the potential cycle test of the fuel cell, the fuel cell was connected to a potentio-galvanostat (HAL30001, manufactured by Hokuto Denko Co., Ltd.). Then, the temperature of the fuel cell was kept at 80° C., hydrogen having a dew point of 80° C. was supplied to the anode, and nitrogen having a dew point of 80° C. was supplied to the cathode. The potentio-galvanostat was set to a scanning potential range of 1 V to 1.3 V, a potential scanning rate of 0.5 V/s, and a cycle number of 5000, respectively. Before and after this potential cycle test, the voltage of the fuel cell when generating electricity at a predetermined current was measured, and the difference (lowered voltage) obtained by subtracting the voltage before the potential cycle test from the voltage after the potential cycle test was calculated as the electrochemical reaction of the electrode catalyst. durability.

In the graph of FIG. 5, the horizontal axis indicates the voltage drop of the fuel cell in the potential cycle test, and the vertical axis indicates the average crystallite size of the 002 plane in the mesoporous carbon particles. The drop in voltage was plotted against the average crystallite size, as indicated by the black circles in FIG. Based on this plot, the relationship between the average crystallite size and the voltage drop was determined as indicated by the solid line 103 . Each plot shown in FIG. 5 corresponds to the results of the potential cycle test for the fuel cells of Comparative Example 2, Comparative Example 1, Example 1, and Example 2 in order from the right.

As indicated by the solid line 103, the smaller the average crystallite diameter, the larger the voltage drop. As a result, the electrochemical durability of the electrode catalyst with a small average crystallite size is lowered. This is presumed for the following reason.

FIG. 8A is a cross-sectional image of mesoporous carbon particles of Comparative Example 2 having an average crystallite size of 002 plane of 0.8 nm before the potential cycle test. FIG. 8B is a cross-sectional image of mesoporous carbon particles of Comparative Example 2 having an average crystallite size of 002 plane of 0.8 nm after the potential cycle test. FIG. 8C is a cross-sectional image of the mesoporous carbon particles of Example 1 having an average crystallite size of 2.2 nm on the 002 plane after the potential cycle test. A cross-sectional image of the mesoporous carbon particles is taken in the following procedure. After processing the cross section of the electrode catalyst layer according to the embodiment of the present disclosure with a broad ion beam (BIB), a focused ion beam (FIB), or the like, it is imaged using a scanning electron microscope (SEM).

As shown in FIG. 8B, in the mesoporous carbon particles with a small average crystallite size, many of the mesopores are collapsed by repeated potential cycles, so the catalytic metal particles in the mesopores do not function effectively. On the other hand, as shown in FIG. 8C, in mesoporous carbon particles with a large average crystallite diameter, the mesopores are less collapsed than in mesoporous carbon particles with a small average crystallite diameter, so the catalyst metal particles in the mesopores are effectively used. Function. Therefore, the smaller the average crystallite size, the larger the voltage drop in the potential cycle test.

Further, the dashed line 101 in FIG. 5 indicates the drop in voltage of a polymer electrolyte fuel cell (general fuel cell) using carbon black, which is generally used as a carrier for electrodes of fuel cells. Comparing the dashed line 101 and the solid line 103, as indicated by the asterisk 102, the average crystallite diameter of the 002 plane is 1.6 nm or more, which is equivalent to or higher than the electrochemical durability of general fuel cells. It has electrochemical durability. Thereby, the electrode catalyst can have high device durability.

In the graphs of FIGS. 6 and 7, the horizontal axis indicates the average particle size of the mesoporous carbon particles, and the vertical axis indicates the DTA peak temperature of the mesoporous carbon particles. Here, the black circle indicates the top temperature at which the slope of the DTA peak obtained from the measurement by the TG-DTA method is 0.

In FIG. 6, for mesoporous carbon particles having an average crystallite size of 0.8 nm on the 002 plane, the temperature of the DTA peak is plotted against the average particle size, as indicated by the black circles. From this value, a relational expression between the average particle size and the temperature of the DTA peak was obtained as indicated by the dotted line 201 . Further, the ratio of the DTA peak temperature to the average particle size (DTA peak temperature/average particle size) was calculated from the slope of this relational expression.

Also, in FIG. 7, for mesoporous carbon particles having an average crystallite size of 2.2 nm on the 002 plane, the temperature of the DTA peak is plotted against the average particle size, as indicated by the black circles in FIG. Here, the error bars extending vertically from the black circles indicate the temperature of the half width of the DTA peak.

The slope of the dotted line 201 in FIG. 6 (the ratio of the DTA peak temperature to the average grain size) does not depend on the average crystallite size. Therefore, when this slope is applied to the temperature of the DTA peak in FIG. A relational expression is required.

As indicated by the dotted line 301, the smaller the average particle size of the mesoporous carbon particles, the lower the temperature of the DTA peak. As a result, the smaller the mesoporous carbon particles, the lower the oxidation durability of the electrode catalyst.

Furthermore, dashed line 302 in FIG. 7 indicates the temperature of the DTA peak of carbon black (a common carrier), which is commonly used as a carrier in fuel cell electrodes. Comparing the dashed line 302 and the dotted line 301, as indicated by asterisks 303, the average particle diameter is 500 nm or more and the temperature of the DTA peak is higher than the temperature of a general carrier. As described above, the electrode catalyst having mesoporous carbon particles with an average particle diameter of 500 nm or more has an oxidation durability equal to or higher than that of an electrode catalyst containing a general carrier. Thereby, the electrode catalyst can have high device durability.

It is noted that many modifications and other embodiments of the disclosure will be apparent to those skilled in the art from the above description. Accordingly, the above description is to be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the disclosure. Details of its structure and/or function may be changed substantially without departing from the spirit of the disclosure.

The electrode catalyst and electrode catalyst layer of the electrochemical device, the membrane/electrode assembly, and the electrochemical device according to the present disclosure can have high device durability. It is useful as an electrode assembly and an electrochemical device.

1: Electrode catalyst 2: Mesoporous carbon particles 3: Catalyst metal particles 4: Mesopores 5: Electrode catalyst layer 6: Proton conductive resin 7: Electrode assembly 8: Proton conductive electrolyte membrane 9: Anode 10: Cathode

Claims (7)

Mesoporous carbon particles having an average crystallite size of 1.6 nm or more on the 002 plane;
and catalyst metal particles supported on the mesoporous carbon particles. 2. The electrode catalyst for an electrochemical device according to claim 1, wherein said mesoporous carbon particles have an average particle size of 500 nm or more. The mesoporous carbon particles have a mode radius of 1 nm or more and 25 nm or less and a pore volume of 1.0 cm ³ /g or more and 3.0 cm ³ /g or less before supporting the catalyst metal particles. The electrode catalyst for an electrochemical device according to claim 1 or 2, comprising: The electrode catalyst according to any one of claims 1 to 3,
An electrocatalyst layer of an electrochemical device, comprising a proton-conducting resin. a proton-conducting electrolyte membrane;
an anode provided on one main surface of the proton-conducting electrolyte membrane;
a cathode provided on the other main surface of the proton-conducting electrolyte membrane,
5. A membrane/electrode assembly, wherein at least one of said anode and said cathode comprises an electrocatalyst layer according to claim 4. 6. The membrane/electrode assembly according to claim 5, wherein at least said cathode comprises said electrocatalyst layer. An electrochemical device comprising the membrane/electrode assembly according to claim 5 or 6.

Images