JP7110842B2 - Carbon material for polymer electrolyte fuel cell catalyst carrier, catalyst layer for polymer electrolyte fuel cell fuel cell, and polymer electrolyte fuel cell - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carbon material for a polymer electrolyte fuel cell catalyst carrier, a catalyst layer for a polymer electrolyte fuel cell fuel cell, and a polymer electrolyte fuel cell.

For example, as disclosed in Patent Documents 1 to 9, polymer electrolyte fuel cells are known as one type of fuel cell. A polymer electrolyte fuel cell consists of a pair of catalyst layers arranged on both sides of a solid polymer electrolyte membrane, a gas diffusion layer arranged outside each catalyst layer, and a separator arranged outside each gas diffusion layer. and One of the pair of catalyst layers serves as the anode of the polymer electrolyte fuel cell, and the other catalyst layer serves as the cathode of the polymer electrolyte fuel cell. In addition, in a normal polymer electrolyte fuel cell, a plurality of unit cells having the above components are stacked in order to obtain a desired output.

A reducing gas such as hydrogen is introduced into the separator on the anode side. The gas diffusion layer on the anode side diffuses the reducing gas and then introduces it into the anode. The anode includes a catalyst component, a catalyst carrier supporting the catalyst component, and an electrolyte material having proton conductivity. An oxidation reaction of the reducing gas takes place on the catalyst component to produce protons and electrons. For example, when the reducing gas is hydrogen gas, the following oxidation reaction occurs.
H ₂ →2H ⁺ +2e ⁻ (E ₀ =0 V)

Protons generated by this oxidation reaction are introduced into the cathode through the electrolyte material in the anode and the solid polymer electrolyte membrane. Electrons are also introduced into the external circuit through the catalyst carrier, gas diffusion layer, and separator. The catalyst carrier is made of, for example, a carbon material. The electrons are introduced into the separator on the cathode side after doing work in an external circuit. These electrons are introduced into the cathode through the separator on the cathode side and the gas diffusion layer on the cathode side.

A solid polymer electrolyte membrane is composed of an electrolyte material having proton conductivity. The solid polymer electrolyte membrane introduces protons generated by the oxidation reaction to the cathode.

Oxidizing gas such as oxygen gas or air is introduced into the separator on the cathode side. The gas diffusion layer on the cathode side introduces the oxidizing gas into the cathode after diffusing it. The cathode includes a catalyst component, a catalyst carrier supporting the catalyst component, and an electrolyte material having proton conductivity. The catalyst carrier is made of, for example, a carbon material. A reduction reaction of the oxidizing gas takes place on the catalyst component to produce water. For example, when the oxidizing gas is oxygen gas or air, the following reduction reactions occur.
O ₂ +4H ⁺ +4e ⁻ →2H ₂ O (E ₀ =1.23 V)

Water produced by the reduction reaction is discharged outside the fuel cell together with unreacted oxidizing gas. In this way, polymer electrolyte fuel cells generate electricity by utilizing the energy difference (potential difference) between the oxidation reaction and the reduction reaction. In other words, the electrons produced in the oxidation reaction do work in the external circuit.

JP 2017-130446 A JP 2017-76531 A JP 2016-126869 A JP 2017-91639 A WO2016/152447 WO2017/094648 WO2014/129597 WO2015/088025 WO2016/133132

Adsorption Hysteresis of Nitrogen and Argon in Pore Networks and Characterization of Novel Micro- and Mesoporous Silicas, Langmuir 2006, 22, 756-764

By the way, polymer electrolyte fuel cells are strongly required to have both low load characteristics (characteristics during power generation at low current) and high load characteristics (characteristics during power generation at large current). In order to meet the demand, various studies have been made on carbon materials for catalyst carriers. However, the current situation is that a carbon material for a catalyst carrier that can sufficiently meet such demands has not yet been proposed.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a novel and improved solid polymer type that can achieve both low load characteristics and high load characteristics. An object of the present invention is to provide a carbon material for a fuel cell catalyst carrier, a polymer electrolyte fuel cell fuel cell catalyst layer, and a polymer electrolyte fuel cell.

In order to solve the above problems, the present inventors have earnestly studied the characteristics of carbon materials for catalyst carriers. First, the present inventor produced a solid polymer fuel cell using a non-porous carbon material as a catalyst carrier, and evaluated its characteristics. As a result, it was found that although the high load characteristics were excellent, the low load characteristics were not sufficient.

Therefore, the present inventor performed a gas activation treatment on the catalyst carrier carbon material in order to improve the low-load characteristics. By performing such a gas activation treatment, the carbon material for a catalyst carrier becomes porous. By using a porous carbon material for a catalyst support as a catalyst support, the catalyst particles (catalyst components) are supported not only on the surface of the catalyst support but also on the walls of the internal pores. Therefore, more catalyst particles will be present in the catalyst layer. Therefore, not only the low-load characteristics of polymer electrolyte fuel cells, but also further improvements in high-load characteristics can be expected.

However, when the present inventor produced a polymer electrolyte fuel cell using a porous carbon material for catalyst support as a catalyst support and evaluated its characteristics, the low load characteristics were certainly improved, but the high load characteristics were improved. It got worse.

The present inventor considered that the decrease in the strength of the catalyst carrier due to the porosity is the cause of the decrease in high-load characteristics. That is, when fabricating a polymer electrolyte fuel cell, a laminate obtained by laminating each catalyst layer and an electrolyte membrane is pressed under heating. It is presumed that the catalyst carrier in the catalyst layer was crushed by this hot pressing process, and the particles of the catalyst carrier were agglomerated. When such aggregates are generated in the catalyst layer, the pores present in the catalyst layer (that is, intra-support pores present in the catalyst support particles and inter-support pores present between the catalyst support particles) are crushed. or becomes extremely small, obstructing the gas flow. In addition, flooding is likely to occur, and this flooding also obstructs the gas flow. Here, flooding means that the water vapor (gas phase) generated by the cathode reaction is converted to a liquid phase within the catalyst layer, and the pores within the catalyst layer are clogged with the liquid water. At high load, a large amount of water vapor is generated at the cathode. Such water vapor tends to remain in the pores when the diffusion resistance of the pores is high. And the smaller the pores, the greater the diffusion resistance. Therefore, the smaller the pores, the easier it is for water vapor to stay in the pores. That is, the water vapor pressure tends to increase. On the other hand, the smaller the pores, the lower the saturated vapor pressure. Therefore, the smaller the pores, the easier it is for the water vapor pressure to convert to the liquid phase within the pores, and the liquid phase clogs the pores. That is, flooding occurs within the pores. Such flooding also obstructs gas flow.

Furthermore, when the pores in the carrier are crushed or become extremely small, the catalyst particles supported in the pores become difficult to use for the power generation reaction. For these reasons, it is considered that the high load characteristics were degraded.

Therefore, the present inventor heat-treated the porous carbon material for catalyst support at a high temperature in order to increase the mechanical strength of the porous carbon material for catalyst support. That is, high crystallization treatment was performed. As a result, the crystallinity of the carbonaceous material for catalyst support is enhanced, and an improvement in mechanical strength can be expected.

However, when polymer electrolyte fuel cells were fabricated using highly crystallized carbon materials for catalyst supports as catalyst supports and their characteristics were evaluated, sufficient improvement in high load characteristics was still not observed. The present inventor considered that the reason for this is that the catalyst carrier particles as a whole shrunk due to high crystallization, and the pores inside the carrier also shrunk. It is believed that the gas diffusivity within the catalyst carrier particles decreased due to the contraction of the pores within the carrier.

Therefore, the present inventor performed a gas activation treatment again on the carbon material for a catalyst carrier in order to expand the pores in the carrier. However, a sufficient improvement in high-load characteristics was still not observed.

Therefore, the present inventor focused on the shape of the pores in the carrier. Specifically, the carbon material for a catalyst support contains bottleneck pores, and it is thought that such bottleneck pores cause the above-described increase in gas diffusion resistance and flooding.

FIG. 5 shows a bottleneck pore 30 as an example of the bottleneck pore. The bottleneck pore 30 is composed of a bottle portion 30a and a neck portion 30b communicating with the bottle portion 30a. The diameter of the bottle portion 30a is greater than the diameter of the neck portion 30b. Also, the neck portion 30b is formed on the outer surface of the carbon material.

As is clear from FIG. 5, the diameter of the neck is smaller than the diameter of the bottle, so the gas is less likely to flow through the neck. That is, gas diffusion resistance increases. Furthermore, since the saturated vapor pressure at the neck portion is lower than the saturated vapor pressure at the bottle portion, flooding is likely to occur at the neck portion. When flooding occurs in the neck portion, the catalyst particles carried on the bottle portion are less likely to contribute to the power generation reaction on the cathode side.

The presence of bottleneck pores can be confirmed by nitrogen adsorption isotherms and nitrogen desorption isotherms. Nitrogen adsorption isotherms and nitrogen desorption isotherms are obtained from nitrogen gas adsorption measurements. The nitrogen adsorption isotherm is the nitrogen adsorption isotherm, and the nitrogen desorption isotherm is the nitrogen desorption isotherm. Hereinafter, an isotherm combining the nitrogen adsorption isotherm and the nitrogen desorption isotherm (that is, an isotherm connecting these isotherms) is also referred to as a nitrogen adsorption/desorption isotherm.

FIG. 6 shows an example of a nitrogen adsorption/desorption isotherm. The nitrogen adsorption/desorption isotherm shown in FIG. 6 schematically shows the nitrogen adsorption/desorption isotherm of a conventional catalyst carrier carbon material. This nitrogen adsorption/desorption isotherm forms a hysteresis loop A.

Here, there are various theories as to why the hysteresis loop is generated, and one theory has been proposed that the hysteresis loop is generated when bottleneck pores are present. In this theory, the difference between the adsorption and desorption processes causes a hysteresis loop, as explained next. That is, in the adsorption process, the adsorption thickness of nitrogen gradually increases according to the relative pressure of the nitrogen gas. In the process, the neck portion of the bottleneck type pores is first blocked by adsorption. , the bottle part is not yet completely filled. In this state, even if the neck portion is closed, the external pressure and the pressure inside the bottle portion are in equilibrium through the nitrogen adsorption layer. Therefore, if the relative pressure of the nitrogen gas, that is, the external pressure increases, the pressure inside the bottle also increases. Therefore, the adsorption corresponding to the external pressure also progresses in the bottle portion, and the nitrogen adsorption layer in the bottle portion becomes thicker. When the external pressure further increases, the bottle portion is finally completely closed by the nitrogen adsorption layer. That is, even in the case of bottleneck pores, adsorption proceeds in the same manner as in a normal pore structure in the adsorption process. Strictly speaking, however, when the neck portion is clogged with the nitrogen adsorption layer, at least part of the nitrogen adsorption layer adsorbed on the neck portion becomes a liquid phase. It is known that the pressure inside the liquid phase (that is, the pressure inside the bottle portion) is slightly lower than the external pressure due to the surface tension of the liquid phase. This phenomenon is called so-called capillary action. Therefore, the adsorption isotherm for bottleneck pores shifts to a slightly higher value for the relative pressure required to obtain the same amount of adsorption as for non-bottleneck pores.

Next, let us consider the desorption process of nitrogen from the state in which all the pores of the bottleneck type are filled. During the detachment process, the neck does not open until the external pressure drops to a pressure that unoccludes the neck. In the process in which the external pressure is reduced to the pressure at which the neck portion is unblocked, the external pressure becomes the pressure at which the bottle portion is unsealed. However, even in this state, the nitrogen adsorbed inside the bottle portion is retained as it is due to the blockage of the neck portion (so-called blocking phenomenon). When measuring the desorption isotherm at a liquid nitrogen temperature of, for example, 77 K using nitrogen as an adsorbate, the nitrogen adsorption layer in the neck begins to boil (cavitation) at a relative pressure higher than the pressure at which the neck opens. Therefore, the nitrogen adsorbed in the bottle portion and the neck portion is desorbed and released at once at a pressure at which the nitrogen adsorption layer begins to boil. The hysteresis loop is closed by the pressure P _close at this time. The relative pressure P _close /P ₀ (P ₀ : saturated vapor pressure) when the hysteresis loop closes (that is, cavitation occurs) is about 0.4. The value of the relative pressure P _close /P ₀ does not depend on the pore structure, but is determined by the adsorbate and the measurement temperature. The phenomenon of hysteresis is described in detail in Non-Patent Document 1, for example.

When the bottle portion of the bottleneck type pore communicates with another pore, the area of the hysteresis loop is reduced. This is because, in the nitrogen desorption process, the nitrogen gas adsorbed on the bottle portion is desorbed and released from pores other than the neck portion. That is, the blocking phenomenon described above is less likely to occur. Furthermore, when the bottle portion of the bottleneck type pore communicates with other pores, flooding is less likely to occur within the neck portion. This is because water vapor in the neck portion is easily discharged through other fine pores. In other words, since the gas flowability between the carrier pores is improved, flooding is less likely to occur even if bottleneck pores are present.

Accordingly, the present inventors have made intensive studies on techniques for communicating bottleneck pores with other pores, and have come up with the idea of further catalytically activating a gas-activated carbon material for a catalyst carrier. Activation of the catalyst made it possible to reduce the area of the hysteresis loop, particularly the difference between the nitrogen desorption isotherm value and the nitrogen adsorption isotherm value at relative pressure P/P ₀ =0.5. That is, the catalyst activation enabled the bottleneck pores to communicate with other pores. Hereinafter, the catalyst used for catalyst activation is also referred to as an activation catalyst, and the catalyst used for the power generation reaction of a solid polymer fuel cell is also referred to as a fuel cell catalyst.

Furthermore, the present inventor also paid attention to the particle size of the carbon material for catalyst support. The smaller the particle diameter, the shorter the distance for the gas to reach the fuel cell catalyst within the catalyst support particles, so further improvement in the properties of polymer electrolyte fuel cells can be expected.

A polymer electrolyte fuel cell was fabricated using the catalyst carrier carbon material subjected to the above treatment as a catalyst carrier, and the characteristics of the polymer electrolyte fuel cell were evaluated. As a result, the high load characteristics could be improved. . As a result, it was possible to achieve both low load characteristics and high load characteristics.

The present invention has been made based on the above findings. According to one aspect of the present invention, the particle diameter is 10 to 20 nm, the BET specific surface area is 200 to 700 m ² /g, and the value of the nitrogen desorption isotherm at relative pressure P/P ₀ = 0.5 and nitrogen The difference from the adsorption isotherm value is 0.10 ml / g or less, the DBP oil absorption is 300 to 520 ml / 100 g, and the half width ΔG of the G band obtained from the Raman spectrum is 40 to 70 cm ^-1 . There is provided a carbon material for a polymer electrolyte fuel cell catalyst carrier, characterized by:

Here, the particle size may be 15 to 19 nm.

Also, the BET specific surface area may be 210 to 450 m ² /g.

According to another aspect of the present invention, there is provided a polymer electrolyte fuel cell catalyst layer comprising the carbon material for polymer electrolyte fuel cell catalyst support described above.

According to another aspect of the present invention, there is provided a polymer electrolyte fuel cell comprising the above catalyst layer for a polymer electrolyte fuel cell.

Here, the polymer electrolyte fuel cell catalyst layer may be a catalyst layer on the cathode side.

As described above, according to the present invention, since the carbon material for catalyst support has the above-described characteristics, a polymer electrolyte fuel cell using this carbon material for catalyst support as a catalyst support has low load characteristics and high load characteristics. Excellent properties. That is, according to the present invention, both low load characteristics and high load characteristics of a polymer electrolyte fuel cell can be achieved.

1 is a cross-sectional view showing a schematic configuration of a catalyst-supporting carrier particle according to an embodiment of the present invention; FIG. 1 is a schematic diagram showing a schematic configuration of a fuel cell according to an embodiment; FIG. FIG. 3 is a cross-sectional view showing a schematic configuration of a catalyst-supporting carrier particle according to a comparative example; FIG. 3 is a cross-sectional view showing a schematic configuration of a catalyst-supporting carrier particle according to a comparative example; It is an explanatory view showing an example of a bottleneck type pore typically. 4 is a graph schematically showing the nitrogen adsorption/desorption isotherm of the carbon material for catalyst support according to the embodiment of the present invention.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

<1. Carbon material for polymer electrolyte fuel cell catalyst carrier>
First, the configuration of the carbon material for polymer electrolyte fuel cell catalyst support (hereinafter also referred to as "carbon material for catalyst support") according to the present embodiment will be described. In the following description, the term "carbon material for catalyst support" means an aggregate of particles constituting the carbon material for catalyst support, unless otherwise specified. A "catalyst carrier" shall mean an aggregate of particles constituting a catalyst carrier, unless otherwise specified.

(1-1. Outline of carbon material for catalyst carrier)
First, based on FIG. 1, the outline of the carbon material for a catalyst carrier according to the present embodiment will be described. FIG. 1 shows a schematic configuration of catalyst-supporting carrier particles 1 . The catalyst-carrying carrier particles 1 have catalyst carrier particles 10 and fuel cell catalysts 11 . The catalyst carrier particles 10 are composed of the catalyst carrier carbon material according to the present embodiment. The catalyst carrier particles 10 have a large number of intra-carrier pores 10a opened on the surface and communication pores 10b communicating between the intra-carrier pores 10a. Although some of the intra-carrier pores 10a are bottleneck pores, the intra-carrier pores 10a are communicated with each other through the communication pores 10b. The fuel cell catalyst 11 is supported not only on the surfaces of the catalyst carrier particles 10, but also on the walls of the intra-carrier pores 10a and the communication holes 10b.

In the catalyst carrier particles 10, the intra-carrier pores 10a communicate with each other through the communication holes 10b, so that the hysteresis loop is reduced and the gas diffusion is high. Furthermore, although the details will be described later, the catalyst carrier particles 10 have high crystallinity, so that they have high mechanical strength and are excellent in resistance to oxidative wear and tear. Furthermore, since the particle diameter L of the catalyst-supporting particles 10 is small (specifically, 10 to 20 nm), the distance for the gas to reach the fuel cell catalyst 11 within the catalyst-supporting support particles 1 is short. Therefore, the polymer electrolyte fuel cell using the catalyst-carrying carrier particles 1 has characteristics that achieve both low load characteristics and high load characteristics.

Specifically, the catalyst carrier carbon material satisfies the following requirements (A) to (E).
(A) The particle size is 10 to 20 nm.
(B) a BET specific surface area of 200 to 700 m ² /g;
(C) The difference between the value of the nitrogen desorption isotherm and the value of the nitrogen adsorption isotherm at relative pressure P/P ₀ =0.5 is 0.10 ml/g or less.
(D) DBP oil absorption is 300-520ml/100g.
(E) The half width ΔG of the G band obtained from Raman spectroscopy is 40 to 70 cm ⁻¹ .

(1-1. Requirement (A))
The particle size of the catalyst carrier carbon material is 10 to 20 nm. A method for measuring the particle size will be described in Examples. Therefore, it can be said that the particle size of the carbon material for catalyst support is relatively small. The pore diameter of the intra-support pores formed in the particles of the carbon material for catalyst support is nano-order. Therefore, most of the gas moving through the intra-carrier pores diffuses by Knudsen diffusion (Knudsen diffusion becomes dominant). When Knudsen diffusion is dominant, the shorter the pore length in the carrier, the easier the gas diffusion. Therefore, by setting the particle diameter to 10 to 20 nm, the length of the pores in the carrier can be shortened, and the gas diffusibility can be enhanced. In addition, since the pores in the carrier are short, the distance for the gas to reach the fuel cell catalyst within the catalyst carrier particles is short. Therefore, more fuel cell catalyst can be used for the power generation reaction. That is, the catalyst utilization rate increases. As a result, especially low load characteristics are improved.

On the other hand, when the particle diameter is less than 10 nm, it is advantageous from the viewpoint of gas diffusion in the particles, but the pores between particles become small. As a result, most of the gas diffuses between particles by Knudsen diffusion. That is, Knudsen diffusion becomes dominant. The diffusion of gas is higher when molecular diffusion is dominant. Therefore, the gas diffusibility of the catalyst layer as a whole deteriorates, and particularly the high load characteristics deteriorate. If the particle diameter is 10 nm to 20 nm, most of the gas between particles diffuses by molecular diffusion. That is, molecular diffusion becomes dominant.

If the particle diameter is larger than 20 nm, the gas diffusibility within the catalyst carrier particles is reduced, and the distance for the gas to reach the fuel cell catalyst within the catalyst carrier particles is lengthened. As a result, the catalyst utilization rate is lowered, and both low load characteristics and high load characteristics are deteriorated.

A preferred range of particle size is 15 to 19 nm. In this case, at least one of low load characteristics and high load characteristics is further improved.

(1-2. Requirement (B))
It has a BET specific surface area of 200 to 700 m ² /g. A method for measuring the BET specific surface area will be described in Examples. Here, the BET specific surface area is a value obtained by BET analysis of the nitrogen adsorption isotherm. This makes it possible to achieve both low load characteristics and high load characteristics of the polymer electrolyte fuel cell.

If the BET specific surface area is less than 200 m ² /g, the distance between the fuel cell catalysts in the catalyst carrier particles becomes too short, and the fuel cell catalysts compete with each other for gas. As a result, the catalyst utilization rate is lowered, and the low load characteristics are deteriorated.

If the BET specific surface area exceeds 700 m ² /g, the thickness of the carbon material for catalyst support is excessively reduced, resulting in a decrease in the mechanical strength of the carbon material for catalyst support. As a result, the catalyst carrier is crushed in the catalyst layer, gas diffusibility is reduced, flooding is likely to occur (that is, water drainage is reduced), and high load characteristics are deteriorated.

A preferred range for the BET specific surface area is 210-450 m ² /g. In this case, at least one of low load characteristics and high load characteristics is further improved.

(1-3. Requirement (C))
The difference between the value of the nitrogen desorption isotherm and the value of the nitrogen adsorption isotherm at relative pressure P/P ₀ =0.5 (hereinafter also referred to as “hysteresis difference”) is 0.10 ml/g or less. A method for measuring the hysteresis difference will be described in Examples. As described above, bottleneck-type pores cause deterioration of gas diffusion and generation of flooding. In the present embodiment, the hysteresis difference is set to 0.10 ml/g or less by connecting pores in the carrier including bottleneck type pores with communicating pores. As a result, the gas diffusibility of the catalyst carrier carbon material is enhanced, and the occurrence of flooding is suppressed. As a result, the catalyst utilization rate is improved and the high load characteristics are improved.

If the hysteresis difference exceeds 0.10 ml/g, the communication between the bottleneck pores becomes poor, so that the gas diffusibility of the carbon material for the catalyst carrier is lowered, and flooding is likely to occur. As a result, the catalyst utilization rate is lowered and the high load characteristics are deteriorated.

(1-4. Requirement (D))
DBP oil absorption is 300-520ml/100g. The DBP oil absorption is the amount of dibutyl phthalate absorbed by the carbon material for catalyst support when dibutyl phthalate (DBP) is brought into contact with a unit mass (here, 100 g) of the carbon material for catalyst support. be. A method for measuring the DBP oil absorption will be described in Examples. Since dibutyl phthalate is absorbed in the pores in the carbon material for catalyst support, particularly in the pores between supports, the DBP oil absorption tends to increase when the three-dimensional structure of the carbon material for catalyst support is developed. When the DBP oil absorption is 300 to 520 ml/100 g, both low load characteristics and high load characteristics of the polymer electrolyte fuel cell can be achieved.

If the DBP oil absorption is less than 300 ml/100 g, the pores in the carbonaceous material for catalyst support are too small, so that the gas diffusibility of the catalyst layer is reduced and flooding is likely to occur. As a result, the high load characteristics deteriorate.

When the DBP oil absorption exceeds 520 ml/100 g, the pores in the carbon material for catalyst support are too large, and the mechanical strength of the carbon material for catalyst support decreases. As a result, the catalyst carrier is crushed in the catalyst layer, gas diffusibility is reduced, flooding is likely to occur (that is, water drainage is reduced), and high load characteristics are deteriorated.

(1-5. Requirement (E))
The half width ΔG of the G band obtained from Raman spectroscopy is 40 to 70 cm ⁻¹ . A method for measuring the half width ΔG will be described in Examples. In this case, since the carbon material for the catalyst support has high mechanical strength, the catalyst support is less likely to be crushed in the catalyst layer. As a result, gas diffusibility is improved, flooding is less likely to occur, and high load characteristics are improved.

When the half width ΔG of the G band is less than 40 cm ⁻¹ , the crystallinity of the carbon material for catalyst support is too high, and gas activation of the carbon material for catalyst support (more specifically, after high crystallization treatment Gas activation (details will be described later) cannot be performed. As a result, it becomes impossible to produce a catalyst carrier carbon material that satisfies the requirements (A) to (D) described above.

When the half width ΔG of the G band exceeds 70 cm ⁻¹ , the mechanical strength of the carbon material for catalyst support is lowered. As a result, the catalyst carrier is crushed in the catalyst layer, gas diffusibility is reduced, flooding is likely to occur (that is, water drainage is reduced), and high load characteristics are deteriorated.

As described above, the catalyst carrier carbon material according to the present embodiment satisfies requirements (A) to (E). Therefore, the catalyst carrier composed of the carbon material for a catalyst carrier has a small hysteresis loop and high gas diffusibility because the pores in the carrier communicate with each other through the communicating pores. Furthermore, since the catalyst carrier has high crystallinity, it has high mechanical strength and excellent oxidative wear resistance. Therefore, the catalyst carrier is less likely to be crushed within the catalyst layer. Furthermore, since the particle diameter of the catalyst carrier is small, the distance for the gas to reach the fuel cell catalyst within the catalyst carrier particles is short. Therefore, a polymer electrolyte fuel cell using this catalyst carrier has characteristics that achieve both low-load characteristics and high-load characteristics.

<2. Method for producing carbon material for catalyst carrier>
Next, a method for producing a carbon material for a catalyst carrier will be described. The method for producing a carbon material for a catalyst carrier according to this embodiment includes a first gas activation treatment step, a high crystallization treatment step, a second gas activation treatment step, and a catalyst activation treatment step. Each step is performed in this order. In this embodiment, the order of each step is very important, and if the order of each step is changed, the carbon material for a catalyst carrier according to this embodiment cannot be produced. These steps modify the starting carbon material. Each step will be described in detail below.

(2-1. Starting material)
The starting carbon material is not particularly limited, and any carbon material that can be used as a catalyst carrier for polymer electrolyte fuel cells can be used without particular limitation. Examples of carbon materials include carbon black and the like. The starting material is selected to have a small particle size. Although the particle size of the carbon material is reduced by the first gas activation treatment and the second gas activation treatment, which will be described later, it is difficult to significantly reduce the particle size from the starting material. Therefore, the particle size of the starting material should be selected so that the particle size of the carbon material for catalyst support, which is the final product, is 10 to 20 nm. Furthermore, gas activation may not be possible if the starting material is too crystalline. Therefore, the half width ΔG of the G band of the starting material is preferably larger than 70 cm ⁻¹ .

(2-2. First gas activation treatment step)
In the first gas activation treatment step, the starting carbon material is heated in a CO ₂ gas stream for a predetermined period of time. This step activates the carbon material. That is, the fragile portion (for example, amorphous portion) of the carbon material is oxidized and consumed (that is, the thickness is reduced). As a result, the carbon material is made porous and fine. A standard heating temperature is about 1000 to 1100° C., and a standard heating time is 1 to 6 hours. Specific heating temperature and heating time may vary depending on the type of starting material, the type of heating device, and the like. Although the concentration of the CO ₂ gas is not particularly limited, it is preferably close to 100% by volume, most preferably 100% by volume. The flow rate of the CO ₂ gas is not particularly limited, and may be appropriately adjusted in consideration of the volume of the device for activation treatment. That is, the BET specific surface area and the like of the carbon material may be adjusted so as to fall within the above range.

(2-3. High crystallization treatment step)
In the high crystallization treatment step, the carbon material after the first gas activation treatment step is heat-treated at a high temperature for a predetermined time in an inert gas stream. This step enhances the crystallinity of the carbon material. That is, the mechanical strength and oxidation wear resistance of the carbon material are enhanced. Specifically, this step adjusts the half width ΔG of the G band to 40 to 70 cm ⁻¹ . The inert gas may be argon gas, for example. A standard heating temperature is about 1600 to 2000° C., and a standard heating time is 1 to 3 hours. That is, by adjusting the heating temperature and the heating time within this range, the half-value width ΔG of the G band can be set to a value within the above-described range. Specific heating temperature and heating time may vary depending on the type of starting material, the type of heating device, and the like. If the high crystallization treatment step is excessively performed, the crystallinity of the carbon material is excessively increased, and the pores hardly expand even if the second gas activation treatment step described later is performed. On the other hand, when the high crystallization treatment process is insufficient, the mechanical strength of the carbon material is lowered. Therefore, it is preferable to adjust the heating temperature and the heating time within the above range.

If the heat treatment step is performed before the first gas activation treatment step, the carbon material cannot be made porous even if the first gas activation treatment step is performed. This is because, as a result of increasing the crystallinity of the carbon material by the high crystallization treatment step, there are almost no weak portions. Therefore, it is very important to perform the first gas activation treatment step before the high crystallization treatment step.

(2-4. Second activation treatment step)
In the second gas activation treatment step, the carbon material after the high crystallization treatment step is heated in a CO ₂ gas stream for a predetermined time. The high crystallization treatment step increases the crystallinity of the carbon material, but at the same time causes the carbon material to shrink as a whole. As a result, the pores within the carbon material particles (that is, pores within the carrier) are also shrunk. Therefore, a second activation treatment step is performed in order to expand the pores in the carrier. Therefore, it can be said that the second activation treatment step is performed auxiliary. Although the crystallinity of the carbon material particles is enhanced by the high crystallization treatment step, many pores are already formed in the carbon material particles. Gas activation to the extent that such pores are expanded is possible.

By this step, the BET specific surface area is adjusted to 200-700 m ² /g, the particle diameter is adjusted to 10-20 nm, and the DBP oil absorption is adjusted to 300-520 ml/100 g. A standard heating temperature is about 1000 to 1100° C., and a standard heating time is 1.0 to 3.5 hours. That is, by adjusting the heating temperature and heating time within these ranges, the BET specific surface area, particle size, and DBP oil absorption may be set within the ranges described above. Specific heating temperature and heating time may vary depending on the type of starting material, the type of heating device, and the like. Although the concentration of the CO ₂ gas is not particularly limited, it is preferably close to 100% by volume, most preferably 100% by volume. The flow rate of the CO ₂ gas is not particularly limited, and may be appropriately adjusted in consideration of the volume of the device for activation treatment. That is, the BET specific surface area and the like of the carbon material may be adjusted so as to fall within the above range.

It is important to perform the second activation treatment step after the high crystallization treatment step. This is because, as described above, the intra-particle pores must be expanded due to the shrinkage of the intra-particle pores due to the high crystallization treatment step.

(2-5. Catalyst activation treatment step)
In the catalyst activation treatment step, the carbon material after the second activation treatment step is activated using an activation catalyst. Through this step, the intra-particle pores are communicated with each other. Thereby, the hysteresis difference is adjusted to 0.10 ml/g or less. The catalyst activation treatment step will be described in detail below.

(2-5-1. Catalyst supporting treatment)
First, the pores in the carbon material particles, that is, the intra-particle pores are loaded with the catalyst for activation. Any activation catalyst may be used as long as it promotes the activation reaction of the carbon material (that is, the oxidative consumption of the carbon portion). The activation catalyst accelerates the activation reaction of the carbon layer existing around the activation catalyst.

Examples of activation catalysts include 3d elements (Ni, Fe, Co, Ti) and noble metal elements (Ru, Cu, Ag, Pt, Pd). Among these, Ni, Fe, Co and Pt are preferred. The activation catalyst may be particles composed of these elements alone, or may be particles of alloys with other metals. For example, alloy particles of the 3d element and Pt may be used as activation catalysts.

The reasons why Ni, Fe, and Co are preferred are that (1) they have high catalytic activity, (2) they are easy to remove after the catalyst activation treatment step, and (3) when an alloy with Pt is used as an activation catalyst, activation For example, the catalyst for fuel cells can be used as it is as a catalyst for fuel cells. The reasons why Pt is preferable are: (1) Pt used as an activation catalyst can be used as it is as a fuel cell catalyst; easy, etc.

There is no particular limitation on the method of supporting the activation catalyst in the pores of the carbon material. Specific methods include, for example, the following methods. First, a mixed solution of a carbon material, a salt (or complex) of an activating catalyst, and a reducing agent is prepared. Here, examples of the salt of the activation catalyst include nitrates of the activation catalyst. In addition, examples of the activation catalyst complex include an activation catalyst acetylacetonate complex and the like. Examples of reducing agents include polyols such as ethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, hexadecanediol, formaldehyde, sodium borohydride, potassium borohydride, lithium borohydride, lithium aluminum hydride, and sodium aluminum hydride. Tetraethylene glycol functions both as a reducing agent and as a solvent for the mixed solution.

Next, the catalyst ions for activation in the mixed solution are reduced by a reducing agent. As a result, the activation catalyst is deposited as clusters in the pores of the carbon material. When the activation catalysts come into contact with each other, they coalesce and grow into a larger activation catalyst. As a result, the activation catalyst is carried in the pores of the carbon material. In addition, the catalyst ion for activation may be reduced in a high-temperature solvent, and such treatment is also preferably performed. For example, a polyol such as hexadecanediol is dissolved in a high boiling point solvent such as diphenyl ether, dibenzyl ether, octyl ether tetraethylene glycol, etc., and the mixed solution is heated to 200° C. or higher. This treatment can also reduce the 3d element complexes and salts.

Other methods include the following methods. That is, a carbon material is impregnated with a solution of a salt (or complex) of an activating catalyst and dried to prepare a coagulated and dried product. Then, the coagulated and dried product is heated in a reducing gas (for example, hydrogen) atmosphere to reduce the catalyst ions for activation in the coagulated and dried product. As a result, the activation catalyst is carried in the pores of the carbon material. Hereinafter, the carbon material on which the activation catalyst is supported is also referred to as an activation catalyst-supporting carbon material. The loading ratio of the activation catalyst in the activation catalyst-supporting carbon material (% by mass of the activation catalyst with respect to the total mass of the activation catalyst-supporting carbon material) is preferably 0.5% or more and less than 10%.

(2-5-2. Catalyst activation treatment)
Next, the activation catalyst-carrying carbon material is heated in the air for a predetermined period of time. Thereby, catalyst activation is performed. That is, the carbon portion existing around the activation catalyst is reduced in thickness by oxidation. Air flow is preferred during heating. A standard heating temperature is about 370 to 410° C., and a standard heating time is 0.5 to 1.5 hours. That is, by adjusting the heating temperature and the heating time within this range, the hysteresis difference may be set to a value within the range described above. Specific heating temperature and heating time may vary depending on the type of starting material, the type of activation catalyst, the type of heating device, and the like. If the catalyst activation treatment is excessively performed, the mechanical strength of the carbon material is lowered, so it is preferable to adjust the heating temperature and the heating time within the range of the above standard. Although the concentration of air is not particularly limited, it is preferably as close to 100% by volume as possible, most preferably 100% by volume. The flow rate of the air is not particularly limited, and may be appropriately adjusted in consideration of the volume of the device that performs the activation treatment. In other words, the hysteresis difference of the carbon material should be adjusted to a value within the above range.

It is important that the catalyst activation treatment step is performed after the second gas activation treatment step. This is because, as described above, the catalyst activation treatment step is a treatment for communicating the pores in the carbon material particles, and therefore the pores must be formed in the carbon material particles as a premise.

(2-5-3. Activation catalyst removal treatment)
The activation catalyst remains in the activation catalyst-carrying carbon material after the catalyst activation treatment. When the activation catalyst cannot be used as a fuel cell catalyst, the activation catalyst is removed from the activation catalyst-carrying carbon material in this step. The method for removing the catalyst for activation is not particularly limited, but examples thereof include a method of immersing the catalyst-activated carbon material in an acidic solution (eg, aqueous nitric acid solution, etc.). Through the steps described above, the carbon material for a catalyst carrier according to the present embodiment is produced.

<3. Configuration of Polymer Electrolyte Fuel Cell>
The catalyst carrier carbon material according to the present embodiment can be applied to, for example, the polymer electrolyte fuel cell 100 shown in FIG. The polymer electrolyte fuel cell 100 includes separators 110 and 120 , gas diffusion layers 130 and 140 , catalyst layers 150 and 160 and an electrolyte membrane 170 .

The separator 110 is an anode-side separator and introduces a fuel gas such as hydrogen into the gas diffusion layer 130 . The separator 120 is a separator on the cathode side, and introduces an oxidizing gas such as oxygen gas or air into the gas diffusion layer 140 . The type of the separators 110 and 120 is not particularly limited as long as they are separators used in conventional fuel cells such as polymer electrolyte fuel cells.

The gas diffusion layer 130 is a gas diffusion layer on the anode side, and supplies the catalyst layer 150 after diffusing the fuel gas supplied from the separator 110 . The gas diffusion layer 140 is a cathode-side gas diffusion layer, and after diffusing the oxidizing gas supplied from the separator 120 , supplies the gas to the catalyst layer 160 . The type of gas diffusion layers 130 and 40 is not particularly limited as long as they are gas diffusion layers used in conventional fuel cells, such as polymer electrolyte fuel cells. Examples of the gas diffusion layers 130 and 40 include porous carbon materials such as carbon cloth and carbon paper, and porous metal materials such as metal mesh and metal wool. As a preferred example of the gas diffusion layers 130 and 140, the separator-side layer of the gas diffusion layer is a gas diffusion fiber layer containing a fibrous carbon material as a main component, and the catalyst layer-side layer contains carbon black as a main component. A gas diffusion layer having a two-layer structure that serves as a microporous layer is exemplified.

The catalyst layer 150 is a so-called anode. An oxidation reaction of the fuel gas occurs in the catalyst layer 150 to generate protons and electrons. For example, when the fuel gas is hydrogen gas, the following oxidation reactions occur.
H ₂ →2H ⁺ +2e ⁻ (E ₀ =0 V)

Protons generated by the oxidation reaction reach catalyst layer 160 through catalyst layer 150 and electrolyte membrane 170 . Electrons generated by the oxidation reaction pass through the catalyst layer 150, the gas diffusion layer 130, and the separator 110 and reach the external circuit. The electrons are introduced into separator 120 after doing work in the external circuit. After that, the electrons reach the catalyst layer 160 through the separator 120 and the gas diffusion layer 140 .

The configuration of the catalyst layer 150 that serves as the anode is not particularly limited. That is, the structure of the catalyst layer 150 may be the same as that of a conventional anode, or the same as that of the catalyst layer 160, or may be more hydrophilic than the catalyst layer 160. may

The catalyst layer 160 is a so-called cathode. A reduction reaction of the oxidizing gas occurs in the catalyst layer 160 to produce water. For example, when the oxidizing gas is oxygen gas or air, the following reduction reactions occur. Water generated by the oxidation reaction is discharged outside the solid polymer fuel cell 100 together with unreacted oxidizing gas.
O ₂ +4H ⁺ +4e ⁻ →2H ₂ O (E ₀ =1.23 V)

In this manner, the polymer electrolyte fuel cell 100 generates electricity using the energy difference (potential difference) between the oxidation reaction and the reduction reaction. In other words, the electrons produced in the oxidation reaction do work in the external circuit.

The catalyst layer 160 preferably contains the carbon material for catalyst support according to the present embodiment as a catalyst support. That is, the catalyst layer 160 includes a catalyst carrier made of the carbon material for catalyst carrier according to the present embodiment, an electrolyte material, and a fuel cell catalyst. As a result, the gas diffusibility, mechanical strength, and resistance to oxidation consumption of the catalyst layer 160 can be enhanced, and both low-load characteristics and high-load characteristics can be achieved.

Although the fuel cell catalyst loading rate in the catalyst layer 160 is not particularly limited, it is preferably 30% by mass or more and less than 80% by mass. Here, the fuel cell catalyst support rate is preferably mass % of the fuel cell catalyst with respect to the total mass of the catalyst-supporting carrier particles (particles in which the fuel cell catalyst is supported on the carbon material for catalyst support). In this case, the catalyst utilization rate is further increased. When the fuel cell catalyst support rate is less than 30% by mass, it may be necessary to increase the thickness of the catalyst layer 160 in order to make the polymer electrolyte fuel cell 100 practically usable. On the other hand, when the fuel cell catalyst support rate is 80% by mass or more, catalyst aggregation tends to occur. Also, the catalyst layer 160 may become too thin, causing flooding.

The mass ratio I/C between the mass I (g) of the electrolyte material and the mass C (g) of the carbon material for catalyst support in the catalyst layer 160 is not particularly limited, but is preferably more than 0.5 and less than 5.0. . In this case, both the pore network and the electrolyte material network can be achieved, and the catalyst utilization rate increases. On the other hand, when the mass ratio I/C is 0.5 or less, the electrolyte material network tends to be poor and the proton conduction resistance tends to be high. If the mass ratio I/C is 5.0 or more, the electrolyte material may disrupt the pore network. In either case, catalyst utilization may decrease.

Moreover, the thickness of the catalyst layer 160 is not particularly limited, but is preferably more than 5 μm and less than 20 μm. In this case, the oxidizing gas easily diffuses into the catalyst layer 160, and flooding is less likely to occur. When the thickness of the catalyst layer 160 is 5 μm or less, flooding is likely to occur. When the thickness of the catalyst layer 160 is 20 μm or more, it becomes difficult for the oxidizing gas to diffuse in the catalyst layer 160, and the fuel cell catalyst in the vicinity of the electrolyte membrane 170 becomes difficult to work. That is, the catalyst utilization rate may decrease.

The electrolyte membrane 170 is made of an electrolyte material having proton conductivity. The electrolyte membrane 170 introduces the protons generated by the oxidation reaction into the catalyst layer 160, which is the cathode. Here, the type of electrolyte material is not particularly limited as long as it is an electrolyte material used in conventional fuel cells such as polymer electrolyte fuel cells. A suitable example is an electrolyte material used in a polymer electrolyte fuel cell, ie, an electrolyte resin. Examples of electrolyte resins include polymers into which phosphoric acid groups and sulfonic acid groups have been introduced, such as perfluorosulfonic acid polymers and polymers into which benzenesulfonic acid has been introduced. Of course, the electrolyte material according to this embodiment may be other types of electrolyte materials. Examples of such electrolyte materials include inorganic electrolyte materials, inorganic-organic hybrid electrolyte materials, and the like. The polymer electrolyte fuel cell 100 may be a fuel cell that operates within the range of room temperature to 150.degree.

<4. Method for Producing Polymer Electrolyte Fuel Cell>
The method of manufacturing the polymer electrolyte fuel cell 100 is not particularly limited as long as it is a conventional manufacturing method. However, it is preferable to use the carbon material for catalyst support according to the present embodiment for the catalyst support on the cathode side.

<1. Measurement method of each parameter>
Next, an example of this embodiment will be described. First, the method of measuring each parameter will be described.

(1-1. Particle size measurement method)
The shapes of 100 arbitrarily selected samples were observed by electron microscopic observation (SU9000 manufactured by Hitachi High-Technologies Corporation), the major axis and minor axis were measured, and the arithmetic mean value of these was taken as the particle size.

(1-2. Method for measuring nitrogen adsorption/desorption isotherm)
About 30 mg of sample was weighed out and vacuum dried at 120° C. for 2 hours. Next, the sample was set in an automatic specific surface area measuring device (BELSORPmini manufactured by Microtrac Bell), and the nitrogen adsorption/desorption isotherm was measured at a measurement temperature of 77K using nitrogen gas as an adsorbate. Then, the difference between the value of the nitrogen desorption isotherm and the value of the nitrogen adsorption isotherm at relative pressure P/P ₀ =0.5, that is, the hysteresis difference was calculated. Furthermore, the BET specific surface area was calculated by BET analysis of the nitrogen adsorption isotherm in the range of relative pressure P/P ₀ from 0.05 to 0.15.

(1-3. Method for measuring Raman spectrum)
About 3 mg of a sample is measured and a laser Raman spectrophotometer (manufactured by JASCO Corporation, model NRS-7100) is used, excitation laser wavelength: 532 nm, laser power: 100 mW (sample irradiation power: 0.1 mW), microscopic arrangement: Backscattering, slit size: 100 μm × 100 μm, objective lens: × 100, spot diameter: 1 μm, exposure time: 30 sec, observation wave number: 3200 to 750 cm ⁻¹ , number of times of integration: 2 times Measurement conditions: Measure the Raman spectrum of the sample. did. A peak in the range of 1550 to 1650 cm ⁻¹ called the G band was extracted from the Raman spectroscopic spectrum obtained in each measurement, and the half width (ΔG) of this peak was calculated.

(1-4. DBP oil absorption)
The DBP oil absorption was measured using an absorbometer (manufactured by Brabender). Specifically, the amount of DBP added at 70% of the maximum torque was converted to the DBP oil absorption per 100 g of the sample.

<2. Examples 1-6>
Next, Examples 1 to 6 will be described. In Examples 1 to 6, polymer electrolyte fuel cells were produced by the following steps and evaluated.

(2-1. Preparation of starting materials)
Niteron #3350 (Niteron manufactured by Shin Nikka Carbon Co., Ltd.: NT3), Niteron #415UD (Niteron manufactured by Shin Nikka Carbon Co., Ltd.: NT4), BP2000 (manufactured by Cabot Specialty Chemicals Inc.: A carbon material of BP2) was prepared.

(2-2. First gas activation treatment step)
In the first gas activation treatment step (first CO ₂ gas activation treatment step), the starting carbon material was heated in a 100% by volume CO ₂ gas stream for a predetermined time. In addition, this process was carried out under the conditions of a CO ₂ gas flow rate of 0.5 liter/min with a sample inserted into a cylindrical tube having an inner diameter of 50 mm and a length of 400 mm. This activated the carbon material. Table 1-1 shows heating temperatures and heating times.

(2-3. High crystallization treatment step)
In the high crystallization treatment step, the carbon material after the first gas activation treatment step was heat-treated at a high temperature for a predetermined time in an argon gas stream. This step enhanced the crystallinity of the carbon material. Table 1-1 shows heating temperatures and heating times.

(2-4. Second activation treatment step)
In the second gas activation treatment step (second CO ₂ gas activation treatment step), the carbon material after the high crystallization treatment step was heated in a CO ₂ gas stream for a predetermined time. In addition, this process was carried out under the conditions of a CO ₂ gas flow rate of 0.5 liter/min with a sample inserted into a cylindrical tube having an inner diameter of 50 mm and a length of 400 mm. As a result, the pores in the carrier that had shrunk in the high crystallization treatment step were expanded again. Table 1-1 shows heating temperatures and heating times.

(2-5. Catalyst activation treatment step)
In the catalyst activation treatment step, the activation catalyst was used to activate the carbon material after the second activation treatment step. Through this step, the pores in the carbon material particles were communicated with each other. Specifically, the following processes were performed.
(2-5-1. Catalyst supporting treatment)
The carbon material after the second gas activation treatment step was dispersed in distilled water. Then, formaldehyde was added to this dispersion, and the container containing the dispersion was set in a water bath set at 40°C. Then, after the temperature of the dispersion reached 40° C., which was the same as that of the bath, the dinitrodiamine Pt complex nitric acid aqueous solution was slowly poured into this dispersion while stirring. Then, after continuing stirring for about 2 hours, the dispersion was filtered and the obtained solid was washed. The solid matter thus obtained was vacuum-dried at 90° C. and then pulverized in a mortar to prepare an activating catalyst-carrying carbon material carrying platinum particles as an activating catalyst.

The platinum loading ratio of the catalyst-supporting carbon material for activation was adjusted so that the mass of the platinum particles was 2% by mass with respect to the total mass of the carbon material and the platinum particles. The platinum loading rate was measured and confirmed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).

(2-5-2. Catalyst activation treatment)
Then, the activation catalyst-carrying carbon material was heated in 100% by volume air for a predetermined time. In addition, this step was carried out under the condition that the sample was put into a cylindrical tube having an inner diameter of 50 mm and a length of 400 mm, and the flow rate of air was 0.5 liter/min. Thus, catalyst activation was performed. Table 1-1 shows heating temperatures and heating times. Through the steps described above, a carbon material for a catalyst carrier was produced. Table 2-1 summarizes the physical properties of the carbon materials for catalyst carriers. In Examples 1 to 6, Pt, which is an activation catalyst, was used as it is as a fuel cell catalyst. Therefore, the activation catalyst removal step was not performed.

(2-6. Fabrication of fuel cell)
Next, a fuel cell was produced using the carbon material for a catalyst carrier produced above. Specific steps are as follows.

(2-6-1. Preparation of catalyst-supporting carrier)
Since Pt as a fuel cell catalyst was insufficient at the stage after the catalyst activation treatment step, Pt was further supported on the catalyst carrier carbon material. Specifically, the catalyst-supporting carbon material prepared above was dispersed in an aqueous solution of chloroplatinic acid. Formaldehyde was added to this dispersion, and the container containing the dispersion was set in a water bath set at 40°C. Then, after the temperature of the dispersion reached 40° C., which was the same as that of the bath, the dinitrodiamine Pt complex nitric acid aqueous solution was slowly poured into this dispersion while stirring. Then, after continuing stirring for about 2 hours, it filtered and the solid substance obtained was washed. The solid matter thus obtained was vacuum-dried at 90° C. and then pulverized in a mortar to prepare a catalyst carrier supporting platinum particles as a fuel cell catalyst, that is, a catalyst-carrying carrier (Pt-carrying carrier).

The platinum loading ratio of the catalyst-carrying carrier was adjusted so that the mass of the platinum particles was 30% by mass with respect to the total mass of the catalyst carrier and the platinum particles. The platinum loading rate was measured and confirmed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).

(2-6-2. Preparation of coating ink)
The catalyst-supporting carrier was placed in a container, and a 5% by mass Nafion solution (DE2020CS manufactured by DuPont, registered trademark: Nafion) was added thereto so that the ratio of Nafion to 1 part by mass of the catalyst-supporting carrier was 0.6 parts by mass. rice field. The dispersion was then gently stirred. After that, the catalyst-carrying carrier was pulverized with ultrasonic waves. After that, the dispersion liquid was further stirred to obtain a coating ink.

(2-6-3. Production of catalyst layer)
The spray conditions were adjusted so that the mass of platinum per unit area of the catalyst layer (hereinafter referred to as “platinum coating weight”) was 0.2 mg/cm ² , and the coating ink was sprayed onto a Teflon (registered trademark) sheet. Then, a drying treatment was performed in argon at 120° C. for 60 minutes to prepare a catalyst layer.

(2-6-4. Preparation of membrane electrode assembly (MEA))
A 6 cm square electrolyte membrane was cut from a Nafion membrane (NR211 manufactured by Dupont). In addition, each of the catalyst layers of the anode and cathode coated on the Teflon (registered trademark) sheet was cut into a square shape with a side of 2.5 cm using a utility knife. The electrolyte membrane was sandwiched between the catalyst layers of the anode and the cathode thus cut out so that the catalyst layers were in contact with each other with the center of the electrolyte membrane interposed therebetween and were not displaced from each other. Then, this laminate was pressed at 120° C. and 100 kg/cm ² for 10 minutes. In addition, when the mechanical strength of the catalyst carrier is low, the catalyst carrier is crushed in this step. The laminate was then cooled to room temperature. Then, only the Teflon (registered trademark) sheets were carefully peeled off from both the anode and the cathode. Through the above steps, a catalyst layer-electrolyte membrane assembly in which the anode and cathode catalyst layers were fixed to the electrolyte membrane was produced.

Next, two square-shaped carbon papers each having a side of 2.5 cm were cut out from the carbon paper (39BC manufactured by SGL Carbon Co., Ltd.) to be the gas diffusion layer. Next, the catalyst layer-electrolyte membrane assembly was sandwiched between the carbon papers so that the positions of the catalyst layers of the anode and cathode were not displaced. Then, this laminate was pressed at 120° C. and 50 kg/cm ² for 10 minutes. An MEA was produced by the above steps. Then, a fuel cell was produced by incorporating the produced MEA into a cell.

(2-7. Fuel cell performance evaluation test)
A fuel cell power generation performance test and a fuel cell durability performance test were conducted using a fuel cell measurement device.

(2-7-1. Fuel cell power generation performance test)
Air was supplied to the cathode and pure hydrogen was supplied to the anode under 0.2 MPa so that the utilization rates were 35% and 70%, respectively. The cell temperature was set at 80°C. Also, the air and pure hydrogen supplied to the fuel cells were humidified by respectively passing them through distilled water kept at 65° C. in a humidifier (that is, by bubbling). As a result, the relative humidity of the anode and cathode was set to about 100%.

Under the conditions in which the gas was supplied to the cell under such settings, the load was gradually increased, and the voltage across the cell terminals at a current density of 100 ^mA /cm The performance evaluation of the fuel cell was performed with the current density as high load performance.

Regarding the evaluation of the low-load performance of the obtained fuel cell, the case where "the voltage between the cell terminals at 100 mA/cm ² is 0.87 V or more" is evaluated as "⊚", and "the voltage between the cell terminals at 100 mA/cm ² is 0. 0.86V or more less than 0.87V” was rated as “◯”, and “the voltage between the cell terminals at 100 mA/cm ² was less than 0.86V” was rated as “×” for failure.

Regarding the high-load performance evaluation of the obtained fuel cell, the case where "current density at 0.3 V is 1450 mA / cm ² or more" is rated as "⊚", and "current density at 0.3 V is less than 1450 mA / cm ² 1400 mA /cm ² or more” was rated as “◯”, and “current density at 0.3 V is less than 1400 mA/cm ² ” was rated as failed with “x”.

(2-7-2. Fuel cell durability performance test)
The durability performance test was conducted in the following steps. That is, after the power generation performance test, the cathode gas was changed to Ar and the gas was sufficiently replaced. Here, the argon gas was humidified by passing it through distilled water kept at 80° C. (that is, by bubbling). Then, using a potentiostat, the process of holding the cathode at 0.6 V for 4 seconds and holding the cathode at 1.3 V for 4 seconds was repeated 200 times with reference to the anode through which hydrogen gas flows. After that, the cathode gas was replaced with air, and a power generation performance test was conducted under the conditions of the fuel cell performance evaluation test.

Then, regarding the low load performance evaluation of the obtained fuel cell, the case where "the voltage between the cell terminals at 100 mA/cm ² is 0.86 V or more" is given as "⊚", and the "voltage between the cell terminals at 100 mA/cm ² "0.85 V or more less than 0.86 V" was evaluated as "○", and "the voltage between the cell terminals at 100 mA/cm ² was less than 0.85 V" was evaluated as "X" for failure.

Regarding the high-load performance evaluation of the obtained fuel cell, the case where "current density at 0.3 V is 1450 mA/cm ² or more" is evaluated as "⊚", and "current density at 0.3 V is less than 1450 mA/cm ² 1400 mA/ cm ² or more” was rated as “◯”, and “current density at 0.3 V is less than 1400 mA/cm ² ” was rated as failed with “x”.

Then, based on these four evaluation results, as a comprehensive evaluation, if there are 3 or more ◎, it will be "◎", if there are 2 or more ○ and no x, it will be "○", and × If there was at least one, it was set as "x" of failure. The results are summarized in Table 3-1.

<3. Comparative Examples 1 to 37>
In Comparative Examples 1 to 35, Niteron #3350 (Niteron manufactured by Shin Nikka Carbon Co., Ltd.: NT3), Niteron #415 (Niteron manufactured by Shin Nikka Carbon Co., Ltd.: NT4), EC300J (Lion Specialty Chemicals EC300J: EC) and acetylene black (Denka acetylene black: AB) were prepared.

Then, the first gas activation treatment step, the high crystallization treatment step, the second gas activation treatment step, and the catalyst activation treatment step were carried out in the same manner as in Examples 1 to 6 to produce a carbon material for a catalyst carrier. Tables 1-1 to 1-4 show the conditions of each step, and Tables 2-1 and 2-2 show the physical properties of the catalyst carrier carbon material. In Comparative Example 30, the first gas activation treatment step was omitted from Example 1, in Comparative Example 31, the high crystallization treatment step was omitted from Example 1, and in Comparative Example 32, the first gas activation treatment step was omitted. The second gas activation treatment step is omitted from Example 1, and Comparative Example 33 is Example 1 without the catalyst activation treatment step. Comparative Examples 34 and 35 are obtained by changing the order of the above steps. Specifically, in Comparative Example 34, the above four steps were performed in the order of first gas activation treatment step → second gas activation treatment step → catalyst activation treatment step → high crystallization treatment step. In Comparative Example 35, the above four steps were performed in the order of first gas activation treatment step→catalyst activation treatment step→second gas activation treatment step→high crystallization treatment step.

Then, using this catalyst carrier carbon material, fuel cells were produced in the same manner as in Examples 1 to 6, and the performance of the fuel cells was evaluated. The results are shown in Tables 3-1 to 3-3.

<4. Discussion>
(4-1. Examples 1 to 6)
All of the catalyst carrier carbon materials according to Examples 1 to 6 satisfy the requirements (A) to (E) of the present embodiment. Therefore, both low load characteristics and high load characteristics were good. Furthermore, according to Examples 3 to 5, when the particle size or BET specific surface area was within the preferred range, the low load characteristics and high load characteristics were further improved.

(4-2. Comparison between Example 1 and Comparative Examples 1 to 9)
Comparative Examples 1 to 9 correspond to Example 1. Specifically, in Comparative Example 1, the particle size of Example 1 is less than the range of the present embodiment. Since the particle size is too small, the inter-support pores become small, the gas diffusion performance deteriorates, and the high-load performance deteriorates.

In Comparative Example 2, the particle size of Example 1 exceeds the range of the present embodiment. Since the particle size is too large, the distance for the gas to reach the fuel cell catalyst within the catalyst support particles is long. Furthermore, the intra-carrier pores are lengthened. Here, since Knudsen diffusion is dominant in the catalyst carrier particles, the longer the pores in the carrier, the worse the gas diffusibility. For these reasons, the catalyst utilization rate decreased, and both the low load characteristics and high load characteristics deteriorated.

In Comparative Example 3, the BET specific surface area of Example 1 is less than the range of the present embodiment. In Comparative Example 3, the distance between the fuel cell catalysts is shortened, and the catalysts compete with each other for oxygen. As a result, the catalyst utilization rate deteriorated, and the low-load performance deteriorated.

In Comparative Example 4, the BET specific surface area of Example 1 exceeds the range of this embodiment. In Comparative Example 4, the thickness of the catalyst carrier carbon material was excessively reduced, resulting in low mechanical strength. As a result, the catalyst carrier collapsed in the catalyst layer, resulting in a decrease in gas diffusion performance and deterioration in high-load performance.

In Comparative Example 5, the hysteresis difference of Example 1 exceeds the range of this embodiment. For this reason, the communication between pores in the carrier is poor, flooding is likely to occur, and the drainage of water generated by flooding is also poor. Furthermore, gas diffusivity is also reduced. As a result, the high load performance deteriorated.

In Comparative Example 6, the DBP oil absorption of Example 1 is less than the range of this embodiment. For this reason, the pores in the catalyst layer were too small, gas diffusibility was lowered, and flooding was likely to occur. As a result, high load performance deteriorated.

In Comparative Example 7, the DBP oil absorption exceeds the range of this embodiment. For this reason, the pores in the catalyst layer were too large, and the mechanical strength of the carbon material for catalyst support was lowered. As a result, the catalyst carrier was crushed in the catalyst layer, the gas diffusibility decreased, and the high-load performance deteriorated.

In Comparative Example 8, the half width ΔG of the G band is less than the range of this embodiment. Therefore, in Comparative Example 8, gas activation could not be performed by the second gas activation treatment. Specifically, even if gas activation was performed, the carbon material only burned. As a result, the particle diameter, the BET specific surface area, and the DBP oil absorption were also outside the range of the present embodiment. Almost the same results were obtained in Comparative Examples 17 and 26 as well.

In Comparative Example 9, the half width ΔG of the G band exceeds the range of this embodiment. As a result, the mechanical strength of the carbon material for the catalyst carrier decreased. As a result, the catalyst carrier was crushed in the catalyst layer, the gas diffusibility decreased, and the high-load performance deteriorated. Furthermore, since the resistance to oxidation and wear was low, the durability performance test results were also poor.

(4-3. Comparison between Example 2 and Comparative Examples 10 to 18)
Comparative Examples 10-18 correspond to Example 2. The details are the same as in Comparative Examples 1-9. Comparing Example 2 with Comparative Examples 10 to 18 yielded results similar to those discussed above.

(4-4. Comparison between Example 3 and Comparative Examples 19 to 27)
Comparative Examples 19-27 correspond to Example 3. The details are the same as in Comparative Examples 1-9. Comparing Example 3 with Comparative Examples 19 to 27 yielded results similar to those discussed above.

(4-5. Comparative Example 28)
Comparative Example 28 uses highly crystalline acetylene black as the starting material. In Comparative Example 28, gas activation could not be sufficiently performed due to the high crystallinity of the starting material. In other words, sufficient pores could not be formed in the catalyst carrier carbon material particles. FIG. 3 shows an outline of catalyst-supporting carrier particles 200 produced in Comparative Example 28. As shown in FIG. The catalyst-carrying carrier particles 200 have a catalyst carrier 201 made of a catalyst carrier carbon material and a fuel cell catalyst 202 . Intra-carrier pores 201a are formed in the catalyst carrier 201, but the size thereof is small and the pores are not communicated with each other. Therefore, the particle size and the DBP oil absorption are out of the range of the present embodiment. In Comparative Example 28, gas diffusibility was extremely poor, and both low load characteristics and high load characteristics were deteriorated.

(4-6. Comparative Example 29)
Comparative Example 29 uses EC300J as the starting material. Since EC300J has a very large particle size, the particle size of the carbonaceous material for a catalyst support also greatly exceeds the range of the present embodiment. However, other parameters were values within the range of this embodiment. FIG. 4 shows an overview of the catalyst-supporting carrier particles 300 produced in Comparative Example 29. As shown in FIG. The catalyst-carrying carrier particles 300 have a catalyst carrier 301 made of a catalyst carrier carbon material and a fuel cell catalyst 302 . Intra-carrier pores 301a are formed in the catalyst carrier 301, and the intra-carrier pores 301a are communicated with each other through communicating pores 301b. However, the particle diameter L greatly exceeds the range of this embodiment. Therefore, the distance for the gas to reach the fuel cell catalyst 302 in the catalyst carrier 301 is long. Furthermore, the intra-carrier pores 301a become longer. Here, since Knudsen diffusion is dominant in the catalyst carrier 301, the longer the intra-carrier pores 301a, the worse the gas diffusibility. For these reasons, the catalyst utilization rate decreased and the high load characteristics deteriorated.

(4-7. Comparative Example 30)
Comparative Example 30 is obtained by omitting the first gas activation treatment step from Example 1. Therefore, in Comparative Example 30, gas activation is performed after high crystallization. In this case, the carbon material only burns and does not become porous. Specifically, the BET specific surface area and the DBP oil absorption fell below the range of the present embodiment. As a result, the catalyst utilization rate decreased and the low load characteristics deteriorated.

(4-8. Comparative Example 31)
Comparative Example 31 is obtained by omitting the high crystallization treatment step from Example 1. Therefore, the half width ΔG of the G band exceeds the range of this embodiment. As a result, the mechanical strength of the carbon material for the catalyst carrier decreased. As a result, the catalyst carrier was crushed in the catalyst layer, the gas diffusibility decreased, and the high-load performance deteriorated. Furthermore, since the resistance to oxidation and wear was low, the durability performance test results were also poor.

(4-9. Comparative Example 32)
Comparative Example 32 is obtained by omitting the second gas activation treatment step from Example 1. Therefore, in Comparative Example 32, the catalyst activation treatment step is performed without expanding the pores in the carrier that have shrunk due to the high crystallization treatment step. In this case, even if the catalyst activation treatment step is performed, the communication between the bottleneck pores is not improved. As a result, the hysteresis difference exceeds 0.10 ml/g, the gas diffusibility of the catalyst carrier carbon material is lowered, and flooding is likely to occur. As a result, the catalyst utilization rate decreased and the high-load characteristics deteriorated.

(4-10. Comparative Example 33)
Comparative Example 33 is obtained by omitting the catalyst activation treatment step from Example 1. Therefore, the hysteresis difference exceeds 0.10 ml/g, the gas diffusibility of the catalyst carrier carbon material is lowered, and flooding is likely to occur. As a result, the catalyst utilization rate decreased and the high-load characteristics deteriorated.

(4-11. Comparative Examples 34 and 35)
In Comparative Examples 34 and 35, since the high crystallization treatment step is performed after a series of activation treatment steps, the pores in the carrier are crushed by such a high crystallization treatment step. Specifically, the BET specific surface area and the DBP oil absorption fell below the range of the present embodiment. As a result, the catalyst utilization rate decreased and the low load characteristics deteriorated.

(4-12. Comparative Examples 36 and 37)
In Comparative Examples 36 and 37, Niteron #3350 (Niteron manufactured by Shin Nikka Carbon Co., Ltd.: NT3) and Niteron #415 (Niteron manufactured by Shin Nikka Carbon Co., Ltd.: NT4), which are the raw materials of Examples 1 to 6, were not modified. used in Comparative Example 36 has a BET specific surface area less than the range of this embodiment. The distance between the fuel cell catalysts becomes closer, and the catalysts compete with each other for oxygen. As a result, the catalyst utilization rate deteriorated, and the low-load performance deteriorated. In Comparative Example 37, the DBP oil absorption was less than the range of this embodiment. As a result, the catalyst utilization rate decreased and the low load characteristics deteriorated.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

1 Catalyst-supporting carrier particles 10 Catalyst carrier 10a Pore 10b in carrier 10b Communication hole 11 Fuel cell catalyst

Claims (6)

The particle size is 10 to 20 nm,
BET specific surface area is 200 to 700 m ² /g,
the difference between the value of the nitrogen desorption isotherm and the value of the nitrogen adsorption isotherm at relative pressure P/P ₀ =0.5 is 0.10 ml/g or less;
DBP oil absorption is 300-520ml/100g,
A carbon material for a polymer electrolyte fuel cell catalyst support, characterized in that the half width ΔG of the G band obtained from Raman spectroscopy is 40 to 70 cm ⁻¹ . 2. The carbon material for polymer electrolyte fuel cell catalyst carrier according to claim 1, wherein said particle diameter is 15 to 19 nm. 3. The carbon material for polymer electrolyte fuel cell catalyst carrier according to claim 1, wherein said BET specific surface area is 210 to 450 m ² /g. A catalyst layer for a polymer electrolyte fuel cell, comprising the carbon material for a catalyst support for a polymer electrolyte fuel cell according to any one of claims 1 to 3. A polymer electrolyte fuel cell comprising the polymer electrolyte fuel cell catalyst layer according to claim 4 . 6. The polymer electrolyte fuel cell according to claim 5, wherein said polymer electrolyte fuel cell catalyst layer is a catalyst layer on the cathode side.

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