JP2020042927A - Carbon material for polymer electrolyte fuel cell catalyst carrier, catalyst layer for polymer electrolyte fuel cell and polymer electrolyte fuel cell - Google Patents

Abstract

To provide a carbon material for a polymer electrolyte fuel cell catalyst carrier, a catalyst layer for a polymer electrolyte fuel cell, and a polymer electrolyte fuel cell, which are capable of achieving both low-load characteristics and high-load characteristics and which are novel and improved.SOLUTION: According to one aspect of the present invention, there is provided a carbon material for a polymer electrolyte fuel cell catalyst carrier which has: a particle size of 10-20 nm; a BET specific surface area of 200-700 m/g; a difference between a value of a nitrogen desorption isotherm and a value of a nitrogen adsorption isotherm at a relative pressure P/P=0.5 of 0.10 ml/g or less; a DBP oil absorption volume of 300-520 ml/100 g; and a half band width ▵G of the G band obtained by Raman spectroscopy of 40-70 cm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carbon material for a catalyst carrier of a polymer electrolyte fuel cell, 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, a polymer electrolyte fuel cell is known as one type of fuel cell. A polymer electrolyte fuel cell has a pair of catalyst layers disposed on both sides of a polymer electrolyte membrane, a gas diffusion layer disposed outside each catalyst layer, and a separator disposed outside each gas diffusion layer. And One of the pair of catalyst layers serves as an anode of the polymer electrolyte fuel cell, and the other catalyst layer serves as a cathode of the polymer electrolyte fuel cell. In a typical 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 anode-side separator. The gas diffusion layer on the anode side diffuses the reducing gas and then introduces the reducing gas into the anode. The anode includes a catalyst component, a catalyst carrier supporting the catalyst component, and an electrolyte material having proton conductivity. On the catalyst component, an oxidation reaction of the reducing gas occurs to generate 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. The electrons are introduced into the external circuit through the catalyst carrier, the gas diffusion layer, and the separator. The catalyst carrier is made of, for example, a carbon material. After the electrons work in an external circuit, they are introduced into the cathode-side separator. Then, the electrons are introduced into the cathode through the cathode-side separator and the cathode-side gas diffusion layer.

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

An oxidizing gas such as oxygen gas or air is introduced into the cathode-side separator. The gas diffusion layer on the cathode side diffuses the oxidizing gas and then introduces it into the cathode. 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. On the catalyst component, a reduction reaction of the oxidizing gas occurs, and water is generated. For example, when the oxidizing gas is oxygen gas or air, the following reduction reaction occurs.
O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O (E ₀ = 1.23 V)

  Water generated by the reduction reaction is discharged to the outside of the fuel cell together with unreacted oxidizing gas. As described above, in the polymer electrolyte fuel cell, power is generated using the energy difference (potential difference) between the oxidation reaction and the reduction reaction. In other words, electrons generated by the oxidation reaction work in an external circuit.

JP-A-2017-130446 JP 2017-76531 A JP-A-2006-126869 JP-A-2017-91639 International Publication No. 2016/152247 International Publication No. WO 2017/094648 International Publication No. 2014/129597 International Publication No. 2015/088025 International Publication No. WO 2016/133132

Adsorption Hysteresis of Nitrogen and Argon in Pole Networks and Characterization of Novel Micro- and Mesoporous Silicas, Langmuir 2006, 76, 22

  By the way, polymer electrolyte fuel cells are strongly required to have both low load characteristics (characteristics at the time of power generation at low current) and high load characteristics (characteristics at the time of power generation at large current). In order to meet the demand, various studies have been made on carbon materials for catalyst carriers. However, at present, there is no carbon material for a catalyst carrier that can sufficiently meet such a demand.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a new and improved solid polymer type capable of achieving 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 catalyst layer for a polymer electrolyte fuel cell fuel cell, and a polymer electrolyte fuel cell.

  The present inventor has earnestly studied characteristics of a carbon material for a catalyst carrier in order to solve the above-mentioned problems. First, the present inventor manufactured a polymer electrolyte fuel cell using a non-porous carbon material as a catalyst carrier, and evaluated its characteristics. As a result, it was found that the high load characteristics were excellent, but the low load characteristics were not sufficient.

  Then, the present inventor performed a gas activation treatment on the carbon material for the catalyst carrier in order to enhance the low load characteristics. By performing such a gas activation treatment, the carbon material for the catalyst carrier becomes porous. By using the porous carbon material for the catalyst carrier as the catalyst carrier, the catalyst particles (catalyst component) are supported not only on the surface of the catalyst carrier but also on the wall surfaces of internal pores. Therefore, more catalyst particles will be present in the catalyst layer. Therefore, further improvement of not only low load characteristics but also high load characteristics of the polymer electrolyte fuel cell can be expected.

  However, the present inventor manufactured a polymer electrolyte fuel cell using a porous carbon material for a catalyst carrier as a catalyst carrier, and evaluated the characteristics. The low load characteristics were certainly improved, but the high load characteristics were improved. On the contrary, it got worse.

  The present inventor has considered that the reduction in the strength of the catalyst carrier due to the porosity causes the reduction in the high load characteristics. That is, when producing a polymer electrolyte fuel cell, a laminate in which each catalyst layer and an electrolyte membrane are laminated is pressed under heating. It is presumed that the catalyst carrier in the catalyst layer was crushed by the hot pressing step, and the particles of the catalyst carrier were aggregated. When such aggregates are formed in the catalyst layer, pores existing in the catalyst layer (that is, pores in the carrier existing in the catalyst carrier particles and inter-carrier pores existing between the catalyst carrier particles) are crushed. Or it is so small that gas flow is impeded. In addition, flooding easily occurs, and the flooding also hinders the gas flow. Here, flooding means that water vapor (gas phase) generated by the cathode reaction is converted into a liquid phase in the catalyst layer, and pores in the catalyst layer are closed by the liquid water. At high load, a large amount of water vapor is generated at the cathode. Then, if the diffusion resistance of the pores is large, such water vapor tends to stay in the pores. The smaller the pores, the higher the diffusion resistance. Therefore, the smaller the pores, the more easily the water vapor stays 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 more easily the water vapor pressure is converted to a liquid phase in the pores, and the liquid phase closes the pores. That is, flooding occurs in the pores. Such flooding also hinders gas flow.

  Further, when the pores in the pores in the carrier are crushed or extremely small, the catalyst particles carried in the pores are less likely to be used for the power generation reaction. It is considered that the high load characteristics were reduced for these reasons.

  Then, the present inventor heat-treated the porous carbon material for catalyst carrier at a high temperature in order to increase the mechanical strength of the porous carbon material for catalyst carrier. That is, a high crystallization treatment was performed. As a result, the crystallinity of the carbon material for the catalyst carrier is increased, so that the opportunity strength can be expected to be improved.

  However, when a polymer electrolyte fuel cell was fabricated using a highly crystallized carbon material for a catalyst carrier as a catalyst carrier, and its characteristics were evaluated, no sufficient improvement in the high load characteristics was found. The present inventor has considered that the cause is that the entire catalyst carrier particles shrink due to the high crystallization, and the pores in the carrier also shrink. It is considered that the gas diffusivity in the catalyst carrier particles was reduced due to the contraction of the pores in the carrier.

  Then, the present inventor performed the gas activation treatment again on the carbon material for the catalyst carrier in order to expand the pores in the carrier. However, sufficient improvement of the high load characteristics was not found.

  Then, the present inventor paid attention to the shape of the pores in the carrier. Specifically, it was considered that the carbon material for the catalyst carrier contained bottleneck-type pores, and such bottleneck-type pores caused the above-described increase in gas diffusion resistance and flooding.

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

  As is clear from FIG. 5, since the diameter of the neck portion is smaller than the diameter of the bottle portion, the gas hardly flows in the neck portion. That is, the gas diffusion resistance increases. Further, 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 at the neck, the catalyst particles carried on the bottle hardly contribute to the power generation reaction on the cathode side.

  The presence of bottleneck-type pores can be confirmed by a nitrogen adsorption isotherm and a nitrogen desorption isotherm. The nitrogen adsorption isotherm and the nitrogen desorption isotherm are obtained by nitrogen gas adsorption measurement. The nitrogen adsorption isotherm is an isotherm on the nitrogen adsorption side, and the nitrogen desorption isotherm is an isotherm on the nitrogen desorption side. 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 a nitrogen adsorption / desorption isotherm of a conventional carbon material for a catalyst carrier. This nitrogen adsorption / desorption isotherm forms a hysteresis loop A.

  Here, there are various theories as to the cause of the hysteresis loop, but it has been proposed that the hysteresis loop is generated when a bottleneck type pore exists. In this theory, as described below, a hysteresis loop occurs due to the difference between the adsorption process and the desorption process. 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 of the bottle neck type pore is first closed by adsorption, but even if nitrogen is adsorbed to the bottle at a thickness equivalent to the neck, the diameter of the bottle is larger than the diameter of the neck. , The bottle is not completely filled yet. In this state, even when the neck is closed, the external pressure and the pressure inside the bottle are in equilibrium through the nitrogen adsorption layer. Therefore, if the relative pressure of the nitrogen gas, that is, the external pressure further increases, the pressure inside the bottle part also increases. Therefore, the adsorption corresponding to the external pressure also proceeds in the bottle part, and the nitrogen adsorption layer in the bottle part becomes thick. When the external pressure further increases, the bottle part is finally completely closed by the nitrogen adsorption layer. That is, even in the case of bottleneck type pores, adsorption proceeds in the adsorption process in the same manner as in a normal pore structure. However, strictly speaking, when the neck is closed by the nitrogen adsorption layer, at least a part of the nitrogen adsorption layer adsorbed on the neck becomes a liquid phase. It is known that the pressure inside the liquid phase (that is, the pressure inside the bottle) becomes slightly smaller than the external pressure due to the surface tension of the liquid phase. This phenomenon is called so-called capillary phenomenon. Therefore, in the adsorption isotherm of the bottleneck type pore, the relative pressure required to obtain the same adsorption amount as the non-bottleneck type pore shifts to a slightly higher value.

Next, a process of desorbing nitrogen from a state in which all the pores of the bottleneck type pores are filled will be considered. In the detachment process, the neck does not open until the external pressure drops to a pressure at which the neck can be unblocked. In the process of reducing the external pressure to a pressure at which the neck portion can be closed, the external pressure becomes a pressure at which the adsorption of the bottle portion is released. However, even in this state, the nitrogen adsorbed inside the bottle portion due to the closure of the neck portion is kept as it is (the so-called blocking phenomenon). When the desorption isotherm is measured at a liquid nitrogen temperature of, for example, 77 K using nitrogen as an adsorbate, the nitrogen adsorption layer in the neck starts boiling (cavitation) at a relative pressure higher than the pressure at which the neck is opened. Therefore, the nitrogen adsorbed on the bottle portion and the neck portion is desorbed and released at a stretch at the pressure at which the nitrogen adsorption layer starts to boil. The hysteresis loop closes at the pressure P _close at this time. The relative pressure P _close / P ₀ (P ₀ : saturated vapor pressure) when the hysteresis loop is closed (ie, cavitation occurs) is about 0.4. The value of the relative pressure P _close / P ₀ does not depend on the pore structure but depends on 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 other pores, the area of the hysteresis loop becomes small. This is because, in the process of desorbing nitrogen, the nitrogen gas adsorbed on the bottle portion is desorbed and released from pores other than the neck portion. That is, the above-described blocking phenomenon hardly occurs. Furthermore, when the bottle portion of the bottleneck type pore communicates with other pores, flooding hardly occurs in the neck portion. This is because the water vapor in the neck portion is easily discharged through other pores. That is, the gas flow between the carrier pores is improved, so that flooding is less likely to occur even if bottleneck-type pores are present.

Then, the present inventor diligently studied a technique for connecting the bottleneck-type pores with other pores, and came up with the idea of further activating the gas-activated carbon material for a catalyst carrier. By performing the catalyst activation, the difference between the value of the nitrogen desorption isotherm and the value of the nitrogen adsorption isotherm at a relative pressure P / P ₀ = 0.5, particularly the area of the hysteresis loop, could be reduced. That is, the bottleneck type pores could be communicated with other pores by the catalyst activation. Hereinafter, the catalyst used for the catalyst activation is also referred to as an activation catalyst, and the catalyst used for the power generation reaction of the polymer electrolyte fuel cell is also referred to as a fuel cell catalyst.

  Further, the present inventors have paid attention to the particle diameter of the carbon material for a catalyst carrier. The smaller the particle diameter, the shorter the distance until the gas reaches the fuel cell catalyst within the catalyst carrier particles, so that further improvement in the characteristics of the polymer electrolyte fuel cell can be expected.

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

The present invention has been made based on the above findings. According to an 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, the value of the nitrogen desorption isotherm at a relative pressure P / P ₀ = 0.5 and the nitrogen The difference from the value of the adsorption isotherm 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 . A carbon material for a solid polymer electrolyte fuel cell catalyst carrier is provided.

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

Further, 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 catalyst layer for a polymer electrolyte fuel cell, comprising the carbon material for a catalyst carrier of a polymer electrolyte fuel cell.

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

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

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

FIG. 1 is a cross-sectional view illustrating a schematic configuration of catalyst-carrying carrier particles according to an embodiment of the present invention. FIG. 1 is a schematic diagram illustrating a schematic configuration of a fuel cell according to an embodiment. FIG. 3 is a cross-sectional view illustrating a schematic configuration of catalyst-carrying carrier particles according to a comparative example. FIG. 3 is a cross-sectional view illustrating a schematic configuration of catalyst-carrying carrier particles according to a comparative example. It is explanatory drawing which shows an example of a bottleneck type | mold micropore typically. 3 is a graph schematically showing a nitrogen adsorption / desorption isotherm of a carbon material for a catalyst carrier according to an embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

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

(1-1. Outline of Carbon Material for Catalyst Carrier)
First, the outline of the carbon material for a catalyst carrier according to the present embodiment will be described with reference to FIG. FIG. 1 shows a schematic configuration of the catalyst-carrying carrier particles 1. The catalyst carrier particles 1 have catalyst carrier particles 10 and a fuel cell catalyst 11. The catalyst carrier particles 10 are made of the carbon material for a catalyst carrier according to the present embodiment. The catalyst carrier particles 10 have a large number of pores 10a in the carrier opened on the surface and communication holes 10b communicating the pores 10a in the carrier. Some of the pores 10a in the carrier are bottleneck-type pores, but the pores 10a in the carrier communicate with each other by the communication holes 10b. The fuel cell catalyst 11 is supported not only on the surface of the catalyst carrier particles 10 but also on the wall surfaces of the pores 10a in the carrier and the communication holes 10b.

  The catalyst carrier particles 10 have small hysteresis loops and high gas diffusivity because the pores 10a in the carrier are communicated with each other through the communication holes 10b. Further, as will be described in detail later, since the catalyst carrier particles 10 have high crystallinity, the mechanical strength is increased, and the catalyst carrier particles 10 are also excellent in oxidation and wear resistance. Furthermore, since the particle diameter L of the catalyst carrier particles 10 is small (specifically, 10 to 20 nm), the distance until the gas reaches the fuel cell catalyst 11 in the catalyst carrier particles 1 is reduced. 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 carbon material for a catalyst carrier satisfies the following requirements (A) to (E).
(A) The particle size is 10 to 20 nm.
(B) The BET specific surface area is from 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 a relative pressure P / P ₀ = 0.5 is 0.10 ml / g or less.
(D) The DBP oil absorption is 300 to 520 ml / 100 g.
(E) The half-width ΔG of the G band obtained from the Raman spectrum is 40 to 70 cm ⁻¹ .

(1-1. Requirements (A))
The particle size of the carbon material for a catalyst carrier is 10 to 20 nm. The method for measuring the particle diameter will be described in Examples. Therefore, it can be said that the particle size of the carbon material for the catalyst carrier is relatively small. The pore diameter of the pores in the carrier formed in the particles of the carbon material for the catalyst carrier is on the order of nanometers. Therefore, most of the gas moving through the pores in the carrier is diffused by Knudsen diffusion (Knudsen diffusion is dominant). When Knudsen diffusion becomes dominant, gas becomes easier to diffuse as the length of the pores in the carrier is shorter. 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 increased. Further, since the pores in the carrier are short, the distance until the gas reaches the fuel cell catalyst in the catalyst carrier particles becomes short. Therefore, more fuel cell catalysts can be used for the power generation reaction. That is, the catalyst utilization increases. As a result, low load characteristics are particularly improved.

  On the other hand, when the particle diameter is less than 10 nm, it is advantageous from the viewpoint of gas diffusivity in the particles, but the pores between the particles become small. As a result, most of the gas is also diffused by Knudsen diffusion between particles. That is, Knudsen diffusion becomes dominant. Gas diffusion is higher when molecular diffusion is dominant. Therefore, the gas diffusion property of the entire catalyst layer is reduced, and particularly the high load characteristics are reduced. When the particle diameter is 10 nm to 20 nm, most of the gas between the particles is diffused by molecular diffusion. That is, molecular diffusion becomes dominant.

  When the particle diameter is larger than 20 nm, the gas diffusivity in the catalyst carrier particles decreases, and the distance until the gas reaches the fuel cell catalyst in the catalyst carrier particles increases. As a result, the catalyst utilization decreases, and both the low load characteristics and the high load characteristics decrease.

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

(1-2. Requirements (B))
BET specific surface area of 200~700m ² / g. The 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 a nitrogen adsorption isotherm. This makes it possible to achieve both low load characteristics and high load characteristics of the polymer electrolyte fuel cell.

When 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 for gas. As a result, the catalyst utilization decreases, and the low load characteristics decrease.

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

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

(1-3. Requirements (C))
The difference between the value of the nitrogen desorption isotherm and the value of the nitrogen adsorption isotherm at a 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, the bottleneck-type pores cause a decrease in gas diffusivity and the occurrence of flooding. In the present embodiment, the hysteresis difference is set to 0.10 ml / g or less by connecting the pores in the carrier including the bottleneck type pores with the communication holes. Thereby, the gas diffusibility of the carbon material for the catalyst carrier is enhanced, and the occurrence of flooding is suppressed. As a result, the catalyst utilization is improved, and the high load characteristics are improved.

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

(1-4. Requirements (D))
DBP oil absorption is 300 to 520 ml / 100 g. The DBP oil absorption refers to the amount of dibutyl phthalate absorbed by the carbon material for a catalyst carrier when dibutyl phthalate (DBP) is brought into contact with a carbon material for a catalyst carrier having a unit mass (here, 100 g). is there. A method for measuring the DBP oil absorption will be described in Examples. Since dibutyl phthalate is absorbed by pores in the carbon material for a catalyst carrier, particularly pores between carriers, if the three-dimensional structure of the carbon material for a catalyst carrier is developed, the DBP oil absorption tends to increase. 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 carbon material for the catalyst carrier are too small, so that the gas diffusion of the catalyst layer is reduced and flooding is likely to occur. As a result, the high load characteristics deteriorate.

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

(1-5. Requirements (E))
The half band width ΔG of the G band obtained from the Raman spectrum is 40 to 70 cm ⁻¹ . The method of measuring the half width ΔG will be described in Examples. In this case, since the carbon material for the catalyst carrier has high mechanical strength, the catalyst carrier is less likely to be crushed in the catalyst layer. As a result, gas diffusibility is improved and flooding is less likely to occur, so that 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 a catalyst carrier is too high, and the gas activation of the carbon material for a catalyst carrier (more specifically, after the high crystallization treatment, Gas activation, details of which will be described later). As a result, it becomes impossible to produce a carbon material for a catalyst carrier satisfying 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 a catalyst carrier decreases. As a result, the catalyst carrier is crushed in the catalyst layer, so that the gas diffusibility is reduced and flooding is likely to occur (that is, the drainage of water is reduced), so that the high load characteristics are reduced.

  As described above, the carbon material for a catalyst carrier according to the present embodiment satisfies the requirements (A) to (E). Therefore, the catalyst carrier made of the carbon material for the catalyst carrier has small hysteresis loops and high gas diffusivity because the pores in the carrier communicate with each other through the communication holes. Further, since the catalyst carrier has high crystallinity, the mechanical strength is increased, and the catalyst carrier has excellent resistance to oxidation and consumption. Therefore, the catalyst carrier is not easily crushed in the catalyst layer. Further, since the particle diameter of the catalyst carrier is small, the distance until the gas reaches the fuel cell catalyst in the catalyst carrier particles becomes 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 the present 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 the order described. In the present embodiment, the order of the steps is very important, and if the order of the steps is changed, the carbon material for a catalyst carrier according to the present embodiment cannot be produced. These steps modify the starting carbon material. Hereinafter, each step will be described in detail.

(2-1. Starting material)
The carbon material used as the starting material is not particularly limited, and any carbon material that can be used as a catalyst carrier for a polymer electrolyte fuel cell can be used without any particular limitation. Examples of the carbon material include, for example, carbon black and the like. Starting materials are selected that have a small particle size. Although the particle diameter of the carbon material is reduced by the first gas activation treatment and the second gas activation treatment described below, it is difficult to significantly reduce the particle size from the starting material. Therefore, the particle size of the starting material may be selected so that the particle size of the carbon material for the catalyst carrier, which is the final product, is 10 to 20 nm. Furthermore, if the crystallinity of the starting material is too high, gas activation may not be possible. 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 processing step, a carbon material as a starting material is heated in a CO ₂ gas stream for a predetermined time. This step activates the carbon material. That is, a fragile portion (for example, an amorphous portion) of the carbon material is oxidized and consumed (that is, its thickness is reduced). As a result, the carbon material is made porous and fine. The standard of the heating temperature is about 1000 to 1100 ° C., and the standard of the heating time is 1 to 6 hours. The specific heating temperature and heating time may vary depending on the type of the starting material, the type of the heating device, and the like. The concentration of the CO ₂ gas is not particularly limited, but is preferably as close as possible to 100% by volume, and 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 apparatus for performing the activation treatment. That is, the carbon material may be adjusted so that the BET specific surface area or the like becomes a value 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 the oxidation resistance of the carbon material are increased. Specifically, the half width ΔG of the G band is adjusted to 40 to 70 cm ⁻¹ by this step. The inert gas may be, for example, argon gas. The standard of the heating temperature is about 1600 to 2000 ° C., and the standard of the heating time is 1 to 3 hours. That is, by adjusting the heating temperature and the heating time within this range, the half-width ΔG of the G band may be set to a value within the above-described range. The specific heating temperature and heating time may vary depending on the type of the starting material, the type of the heating device, and the like. If the high crystallization process is performed excessively, the crystallinity of the carbon material is excessively increased, and the pores hardly expand even when the second gas activation process described below is performed. On the other hand, when the high crystallization process is insufficient, the mechanical strength of the carbon material is reduced. 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 processing step, the carbon material cannot be made porous even if the first gas activation processing step is performed. This is because the crystallinity of the carbon material is increased by the high crystallization process, so that the fragile portion is almost eliminated. 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 processing step, the carbon material after the high crystallization processing step is heated in a CO ₂ gas stream for a predetermined time. The high crystallization process increases the crystallinity of the carbon material, but on the other hand, causes the carbon material to shrink entirely. As a result, the pores in the carbon material particles (that is, the pores in the carrier) also shrink. Therefore, a second activation treatment step is performed to expand the pores in the carrier. Therefore, it can be said that the second activation treatment step is performed supplementarily. Although the crystallinity of the carbon material particles is increased by the high crystallization process, many pores are already formed in the carbon material particles. Gas activation to the extent that such pores are expanded is possible.

In this step, the BET specific surface area is adjusted to 200 to 700 m ² / g, the particle diameter is adjusted to 10 to 20 nm, and the DBP oil absorption is adjusted to 300 to 520 ml / 100 g. The standard of the heating temperature is about 1000 to 1100 ° C., and the standard of the heating time is 1.0 to 3.5 hours. That is, by adjusting the heating temperature and the heating time within this range, the BET specific surface area, the particle diameter, and the DBP oil absorption may be set to values within the above-described ranges. The specific heating temperature and heating time may vary depending on the type of the starting material, the type of the heating device, and the like. The concentration of the CO ₂ gas is not particularly limited, but is preferably as close as possible to 100% by volume, and 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 apparatus for performing the activation treatment. That is, the carbon material may be adjusted so that the BET specific surface area or the like becomes a value within the above range.

  It is important to perform the second activation process after the high crystallization process. This is because, as described above, the pores in the particles are contracted by the high crystallization process, and it is necessary to expand the pores.

(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. In this step, the pores in the particles are communicated with each other. Thereby, the hysteresis difference is adjusted to 0.10 ml / g or less. Hereinafter, the catalyst activation treatment step will be described in detail.

(2-5-1. Catalyst loading treatment)
First, a utilization catalyst is carried in pores in carbon material particles, that is, pores in the particles. The activation catalyst may be any catalyst that promotes the activation reaction of the carbon material (that is, the oxidative consumption of the carbon portion). The activation catalyst promotes an activation reaction of the carbon layer existing around the activation catalyst.

  Examples of the utilization catalyst include a 3d element (Ni, Fe, Co, Ti) and a noble metal element (Ru, Cu, Ag, Pt, Pd). Of these, Ni, Fe, Co, and Pt are preferred. The utilization catalyst may be particles composed of a simple substance of these elements, or may be particles of an alloy with another metal. For example, alloy particles of the 3d element and Pt may be used as the utilization catalyst.

  Ni, Fe, and Co are preferable because (1) high catalytic activity, (2) easy removal after the catalyst activation treatment step, and (3) activation when an alloy with Pt is used as an activation catalyst. For example, a catalyst for fuel cells can be diverted as it is to a catalyst for fuel cells. Pt is preferable because (1) Pt used as a utilization catalyst can be diverted to a fuel cell catalyst as it is. (2) Nano-sized particles are easily formed in the carbon material, which are easily reduced as compared with the 3d element. And the like.

  The method for supporting the utilization catalyst in the pores of the carbon material is not particularly limited. Specific methods include, for example, the following methods. First, a mixed solution of a carbon material, a salt (or complex) of a utilization catalyst, and a reducing agent is prepared. Here, examples of the salt of the utilization catalyst include nitrate of the utilization catalyst. Further, examples of the complex of the utilization catalyst include an acetylacetonate complex of the utilization catalyst. Reducing agents include, for example, ethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, polyols such as hexadecanediol, formaldehyde, sodium borohydride, potassium borohydride, lithium borohydride, lithium aluminum hydride, And sodium aluminum hydride. Tetraethylene glycol is a reducing agent and also functions as a solvent for the mixed solution.

  Next, the utilized catalyst ions in the mixed solution are reduced by the reducing agent. Thereby, the utilization catalyst precipitates as clusters in the pores of the carbon material. The utilized catalysts come together by contact and grow into a larger utilized catalyst. Thereby, the utilization catalyst is supported in the pores of the carbon material. In addition, the utilization catalyst ion may be reduced in a high-temperature solvent, and such a treatment is also preferably performed. For example, hexadecanediol or the like is dissolved as a polyol in a high boiling point solvent such as diphenyl ether, dibenzyl ether or octyl ether tetraethylene glycol, and the mixed solution is heated to 200 ° C. or higher. This treatment can also reduce the complex or salt of the 3d element.

  Other methods include the following method. That is, a coagulated and dried product is produced by impregnating a carbon material with a solution of a salt (or complex) of a utilization catalyst and drying the solution. Then, the coagulated and dried product is heated in a reducing gas (for example, hydrogen) atmosphere to reduce the utilization catalyst ions in the coagulated and dried product. Thereby, the utilization catalyst is supported in the pores of the carbon material. Hereinafter, the carbon material supporting the utilization catalyst is also referred to as a utilization catalyst-supporting carbon material. The loading ratio of the utilized catalyst in the utilized catalyst-supporting carbon material (mass% of the utilized catalyst with respect to the total mass of the utilized catalyst-supporting carbon material) is preferably 0.5% or more and less than 10%.

(2-5-2. Catalyst activation treatment)
Next, the activated catalyst-carrying carbon material is heated in air for a predetermined time. Thereby, catalyst activation is performed. That is, the carbon portion existing around the utilization catalyst is reduced in thickness by oxidation. Preferably, the air is allowed to flow during the heating. The standard of the heating temperature is about 370 to 410 ° C., and the standard of the 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 above-described range. The specific heating temperature and heating time can vary depending on the type of the starting material, the type of the utilized catalyst, the type of the heating device, and the like. In addition, when the catalyst activation treatment is performed excessively, the mechanical strength of the carbon material is reduced. Therefore, it is preferable to adjust the heating temperature and the heating time within the above range. The concentration of air is not particularly limited, but is preferably as close as possible to 100% by volume, and 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 apparatus for performing the activation process. That is, the hysteresis difference of the carbon material may be adjusted so as to be a value within the above range.

  It is important that the catalyst activation process is performed after the second gas activation process. As described above, since the catalyst activation treatment step is a treatment in which pores in the carbon material particles communicate with each other, it is necessary that pores are formed in the carbon material particles.

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

<3. Configuration of polymer electrolyte fuel cell>
The carbon material for a catalyst carrier according to the present embodiment is applicable to, for example, a 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 a separator on the anode side, and introduces a fuel gas such as hydrogen into the gas diffusion layer 130. The separator 120 is a cathode-side separator, 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, and may be any separator used in a conventional fuel cell, for example, a polymer electrolyte fuel cell.

  The gas diffusion layer 130 is a gas diffusion layer on the anode side, and after diffusing the fuel gas supplied from the separator 110, supplies the fuel gas to the catalyst layer 150. The gas diffusion layer 140 is a gas diffusion layer on the cathode side, and after diffusing the oxidizing gas supplied from the separator 120, supplies the oxidizing gas to the catalyst layer 160. The type of the gas diffusion layers 130 and 40 is not particularly limited, and may be any gas diffusion layer used in a conventional fuel cell, for example, a polymer electrolyte fuel cell. 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. In addition, as a preferable example of the gas diffusion layers 130 and 140, the layer on the separator side of the gas diffusion layer is a gas diffusion fiber layer mainly containing a fibrous carbon material, and the layer on the catalyst layer side mainly contains carbon black. And a gas diffusion layer having a two-layer structure to be a micropore layer.

The catalyst layer 150 is a so-called anode. In the catalyst layer 150, an oxidation reaction of the fuel gas occurs, and protons and electrons are generated. For example, when the fuel gas is hydrogen gas, the following oxidation reaction occurs.
H ₂ → 2H ⁺ + 2e ⁻ (E ₀ = 0 V)

  Protons generated by the oxidation reaction reach the catalyst layer 160 through the catalyst layer 150 and the electrolyte membrane 170. The electrons generated by the oxidation reaction reach the external circuit through the catalyst layer 150, the gas diffusion layer 130, and the separator 110. The electrons are introduced into the separator 120 after working 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 serving as the anode is not particularly limited. That is, the configuration of the catalyst layer 150 may be the same as that of the conventional anode, may be the same as the configuration of the catalyst layer 160, or may be a configuration having higher hydrophilicity than the catalyst layer 160. You may.

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

  As described above, the polymer electrolyte fuel cell 100 generates power by utilizing the energy difference (potential difference) between the oxidation reaction and the reduction reaction. In other words, electrons generated by the oxidation reaction work in an external circuit.

  The catalyst layer 160 preferably contains the carbon material for a catalyst carrier according to the present embodiment as a catalyst carrier. That is, the catalyst layer 160 includes a catalyst carrier composed of the carbon material for a catalyst carrier according to the present embodiment, an electrolyte material, and a fuel cell catalyst. Thereby, the gas diffusion property, mechanical strength, and oxidation resistance of the catalyst layer 160 can be improved, and thus both low load characteristics and high load characteristics can be achieved.

  In addition, the loading ratio of the catalyst for a fuel cell in the catalyst layer 160 is not particularly limited, but is preferably 30% by mass or more and less than 80% by mass. Here, the fuel cell catalyst loading rate is preferably the mass% of the fuel cell catalyst with respect to the total mass of the catalyst carrier particles (particles of the catalyst carrier carbon material carrying the fuel cell catalyst). In this case, the catalyst utilization rate is further increased. If the fuel cell catalyst loading is less than 30% by mass, the thickness of the catalyst layer 160 may need to be increased so that the polymer electrolyte fuel cell 100 can withstand practical use. On the other hand, when the fuel cell catalyst loading is 80% by mass or more, catalyst aggregation is likely to occur. Further, there is a possibility that the catalyst layer 160 becomes too thin and flooding occurs.

  The mass ratio I / C of the mass I (g) of the electrolyte material to the mass C (g) of the carbon material for the catalyst carrier in the catalyst layer 160 is not particularly limited, but is preferably more than 0.5 and less than 5.0. . In this case, the pore network and the electrolyte material network can be compatible, and the catalyst utilization 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. When the mass ratio I / C is 5.0 or more, the pore network may be separated by the electrolyte material. In either case, the catalyst utilization may decrease.

  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 is easily diffused into the catalyst layer 160, and flooding is unlikely to occur. When the thickness of the catalyst layer 160 is 5 μm or less, flooding easily occurs. When the thickness of the catalyst layer 160 is 20 μm or more, the oxidizing gas hardly diffuses in the catalyst layer 160, and the fuel cell catalyst in the vicinity of the electrolyte membrane 170 does not work easily. That is, the catalyst utilization 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 serving as a cathode. Here, the type of the electrolyte material is not particularly limited, and may be any electrolyte material used in a conventional fuel cell, for example, a polymer electrolyte fuel cell. A preferred example is an electrolyte material used in a polymer electrolyte fuel cell, that is, an electrolyte resin. Examples of the electrolyte resin include a polymer into which a phosphoric acid group, a sulfonic acid group, or the like is introduced, such as a polymer into which a perfluorosulfonic acid polymer or benzenesulfonic acid is introduced. Of course, the electrolyte material according to the present embodiment may be another type of electrolyte material. Examples of such an electrolyte material include an inorganic material, an inorganic-organic hybrid material, and the like. In addition, the polymer electrolyte fuel cell 100 may be a fuel cell that operates within a range of normal temperature to 150 ° C.

<4. Manufacturing method of polymer electrolyte fuel cell>
The method for producing the polymer electrolyte fuel cell 100 is not particularly limited, and may be any method as long as it is a conventional method. However, it is preferable to use the carbon material for a catalyst carrier according to the present embodiment as the catalyst carrier on the cathode side.

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

(1-1. Method for measuring particle diameter)
The shape of 100 samples arbitrarily selected was observed by electron microscope observation (SU9000, manufactured by Hitachi High-Technologies Corporation), the major axis and the minor axis were measured, and the arithmetic average value was defined as the particle diameter.

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

(1-3. Method of measuring Raman spectrum)
Approximately 3 mg of a sample is measured and taken, and using a laser Raman spectrophotometer (Model NRS-7100, manufactured by JASCO Corporation), excitation laser wavelength: 532 nm, laser power: 100 mW (sample irradiation power: 0.1 mW), microscopic arrangement: Backscattering, slit dimensions: 100 μm × 100 μm, objective lens: × 100, spot diameter: 1 μm, exposure time: 30 sec, observation wave number: 3200 to 750 cm ⁻¹ , and the number of integrations: 2 times The Raman spectrum of the sample is measured. did. Then, a peak in the range of 1550 to 1650 cm ^-1 called G band was extracted from the Raman 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 into a DBP oil absorption per 100 g of the sample.

<2. Examples 1 to 6>
Next, Examples 1 to 6 will be described. In Examples 1 to 6, a polymer electrolyte fuel cell was manufactured by the following steps and evaluated.

(2-1. Preparation of Starting Material)
Niteron # 3350 (Niteron Carbon Co., Ltd .: NT3), Niteron # 415UD (Nippon Carbon Co., Ltd .: Niteron: NT4), BP2000 (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), a carbon material as a starting material was heated in a 100% by volume CO ₂ gas stream for a predetermined time. In this step, the sample was charged into a cylindrical tube having an inner diameter of 50 mm and a length of 400 mm, and was performed under the conditions of a CO ₂ gas flow rate of 0.5 liter / min. Thereby, the carbon material was activated. Table 1-1 shows the heating temperature and the heating time.

(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. By this step, the crystallinity of the carbon material was improved. Table 1-1 shows the heating temperature and the heating time.

(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 this step, the sample was charged into a cylindrical tube having an inner diameter of 50 mm and a length of 400 mm, and was performed under the conditions of a CO ₂ gas flow rate of 0.5 liter / min. As a result, the pores in the carrier contracted in the high crystallization treatment step were expanded again. Table 1-1 shows the heating temperature and the heating time.

(2-5. Catalyst activation treatment step)
In the catalyst activation treatment step, the carbon material after the second activation treatment step was activated using an activation catalyst. In this step, the pores in the carbon material particles were communicated with each other. Specifically, the following processing was performed.
(2-5-1. Catalyst loading treatment)
The carbon material after the second gas activation treatment step was dispersed in distilled water. Then, formaldehyde was added to the 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., the same as that of the bath, an aqueous solution of dinitrodiamine Pt complex nitric acid was slowly poured into the dispersion with stirring. Then, after stirring was continued for about 2 hours, the dispersion was filtered and the obtained solid was washed. The solid obtained in this manner was vacuum-dried at 90 ° C. and then pulverized in a mortar to produce an activated catalyst-carrying carbon material supporting platinum particles as an activated catalyst.

  The platinum loading of the activated catalyst-carrying carbon material 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 was measured and confirmed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).

(2-5-2. Catalyst activation treatment)
Next, the activated catalyst-carrying carbon material was heated in 100% by volume of air for a predetermined time. In this step, the sample was charged into a cylindrical tube having an inner diameter of 50 mm and a length of 400 mm, and was performed under the conditions of an air flow rate of 0.5 L / min. This activated the catalyst. Table 1-1 shows the heating temperature and the heating time. Through the above steps, a carbon material for a catalyst carrier was produced. Table 2-1 summarizes the physical property values of the carbon materials for catalyst carriers. In Examples 1 to 6, Pt, which is a utilization catalyst, was used as it was as a fuel cell catalyst. Therefore, the utilization catalyst removal step was not performed.

(2-6. Production of Fuel Cell)
Next, a fuel cell was prepared using the carbon material for a catalyst carrier prepared above. The specific steps are as follows.

(2-6-1. Preparation of catalyst-carrying carrier)
Since Pt as a fuel cell catalyst is insufficient at the stage after the catalyst activation treatment step, Pt was further supported on the carbon material for the catalyst carrier. Specifically, the catalyst carrier carbon material prepared above was dispersed in an aqueous chloroplatinic acid solution. Formaldehyde was added to the 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., the same as that of the bath, an aqueous solution of dinitrodiamine Pt complex nitric acid was slowly poured into the dispersion with stirring. Then, after stirring was continued for about 2 hours, filtration was performed and the obtained solid was washed. The solid thus obtained was vacuum-dried at 90 ° C. and then pulverized in a mortar to prepare a catalyst carrier carrying platinum particles as a fuel cell catalyst, that is, a catalyst carrier (Pt carrier).

  The platinum loading of the catalyst 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 was measured and confirmed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES).

(2-6-2. Production of coating ink)
The catalyst-carrying support is placed in a container, and a 5% by mass Nafion solution (DE2020CS manufactured by DuPont, registered trademark: Nafion) is added thereto such that the ratio of Nafion is 0.6 parts by mass relative to 1 part by mass of the catalyst-carrying carrier. Was. The dispersion was then gently stirred. Thereafter, the catalyst-carrying carrier was pulverized by ultrasonic waves. Thereafter, the dispersion was further stirred to obtain a coating ink.

(2-6-3. Preparation of catalyst layer)
The spray conditions were adjusted such that the mass of platinum per unit area of the catalyst layer (hereinafter, referred to as “platinum weight”) was 0.2 mg / cm ^2, and the applied ink was sprayed on a Teflon (registered trademark) sheet. Subsequently, a catalyst layer was prepared by performing a drying treatment in argon at 120 ° C. for 60 minutes.

(2-6-4. Production of membrane electrode assembly (MEA))
A 6 cm-square electrolyte membrane was cut out from a Nafion membrane (NR211 manufactured by Dupont). In addition, each of the anode and cathode catalyst layers applied on the Teflon (registered trademark) sheet was cut into a square having a side of 2.5 cm with a cutter knife. The electrolyte membrane was sandwiched between the thus-cut anode and cathode catalyst layers such that the catalyst layers were in contact with each other across the center of the electrolyte membrane and were not displaced from each other. Next, the laminate was pressed at 120 ° C. and 100 kg / cm ² for 10 minutes. When the mechanical strength of the catalyst carrier is low, the catalyst carrier is crushed in this step. Next, the laminate was cooled to room temperature. Subsequently, only the Teflon (registered trademark) sheet was carefully peeled off for 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 measuring 2.5 cm on a side were cut out from carbon paper (39BC manufactured by SGL Carbon Co., Ltd.) as a gas diffusion layer. Next, the catalyst layer-electrolyte membrane assembly was sandwiched between these carbon papers so that the positions of the anode and cathode catalyst layers did not shift. Then, the laminate was pressed at 120 ° C. and 50 kg / cm ² for 10 minutes. Through the above steps, an MEA was manufactured. Next, a fuel cell was produced by incorporating the produced MEA into a cell.

(2-7. Evaluation test of fuel cell performance)
A fuel cell power generation performance test and a fuel cell durability performance test of the fuel cell were performed using the 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 became 35% and 70%, respectively. The cell temperature was set at 80 ° C. Air was supplied to the fuel cell and pure hydrogen was passed through distilled water kept at 65 ° C. in a humidifier (ie, bubbling was performed) to humidify. Thereby, the relative humidity of the anode and the cathode was set to about 100%.

Under the conditions in which gas was supplied to the cell under such a setting, the load was gradually increased, and the voltage between cell terminals at a current density of 100 mA / cm ² was set as low load performance. The performance evaluation of the fuel cell was performed with the current density set to high load performance.

Regarding the evaluation of the low load performance of the obtained fuel cell, the case where “the cell terminal voltage at 100 mA / cm ² is 0.87 V or more” is evaluated as “◎”, and the “cell terminal voltage at 100 mA / cm ² is 0”. The case where “less than 0.87 V and 0.86 V or more” was satisfied was evaluated as “O”, and the case where “the voltage between cell terminals at 100 mA / cm ² was less than 0.86 V” was evaluated as “fail”.

Regarding the high load performance evaluation of the obtained fuel cell, the case where “the current density at 0.3 V satisfies 1450 mA / cm ² or more” is “◎”, and the “current density at 0.3 V is less than 1450 mA / cm ^{2 and} 1400 mA. / Cm ² or more ”was evaluated as“ ○ ”, and“ if the current density at 0.3 V was less than 1400 mA / cm ² ”was evaluated as“ poor ”.

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

Then, regarding the low-load performance evaluation of the obtained fuel cell, when the “voltage between cell terminals at 100 mA / cm ² satisfies 0.86 V or more” is “◎”, and “voltage between cell terminals at 100 mA / cm ² ” Is less than 0.86 V and not less than 0.85 V ”is rated“ 、 ”, and“ if the voltage between cell terminals at 100 mA / cm ² is less than 0.85 V ”is rated“ fail ”.

Regarding the evaluation of the high-load performance of the obtained fuel cell, the case where the current density at 0.3 V satisfies 1450 mA / cm ² or more is evaluated as “◎”, and the current density at 0.3 V is less than 1450 mA / cm ^{2 and} 1400 mA / cm ^2. cm ² or more "to meet the as" ○ "," current density at 0.3V was a "×" the failure in the case of less than 1400 mA / cm ² ".

  Then, based on these four evaluation results, as an overall evaluation, a case where ◎ is 3 or more is “◎”, a case where 2 is 2 or more and there is no × is “○”, and The case where there was at least one was evaluated as "Failed". The results are shown in Table 3-1.

<3. Comparative Examples 1-37>
In Comparative Examples 1 to 35, as the carbon materials serving as starting materials, Niteron # 3350 (Niteron: NT3 manufactured by Nippon Carbon Co., Ltd.), Niteron # 415 (Niteron: NT4 manufactured by Nippon Carbon Co., Ltd.), EC300J (Lion Specialty) EC300J: EC manufactured by Chemicals, and acetylene black (acetylene black: AB, manufactured by Denka) were prepared.

  Then, a first gas activation treatment step, a high crystallization treatment step, a second gas activation treatment step, and a catalyst activation treatment step were performed 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 property values of the carbon material for the catalyst carrier. Comparative Example 30 was obtained by omitting the first gas activation treatment step from Example 1, Comparative Example 31 was obtained by omitting the high crystallization treatment step from Example 1, and Comparative Example 32 was obtained by Comparative Example 33 is obtained by omitting the catalyst activation treatment step from Example 1 except that the second gas activation treatment step is omitted from Example 1. 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 the first gas activation treatment step → the second gas activation treatment step → the catalyst activation treatment step → the high crystallization treatment step. In Comparative Example 35, the above four steps were performed in the order of the first gas activation treatment step → the catalyst activation treatment step → the second gas activation treatment step → the high crystallization treatment step.

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

<4. Discussion>
(4-1. Examples 1 to 6)
The carbon materials for catalyst carriers according to Examples 1 to 6 all satisfy the requirements (A) to (E) of the present embodiment. Therefore, both the low load characteristics and the high load characteristics were good. Furthermore, according to Examples 3 to 5, when the particle diameter or the BET specific surface area was within a preferable range, the low load characteristics and the 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 diameter of Example 1 is less than the range of the present embodiment. Since the particle diameter is too small, the pores between the carriers are small, the gas diffusion performance is reduced, and the high load performance is deteriorated.

  In Comparative Example 2, the particle diameter of Example 1 exceeds the range of the present embodiment. Since the particle diameter is too large, the distance until the gas reaches the fuel cell catalyst in the catalyst carrier particles becomes long. Further, the pores in the carrier become longer. Here, Knudsen diffusion becomes dominant in the catalyst carrier particles, so that the longer the pores in the carrier, the worse the gas diffusivity becomes. For these reasons, the catalyst utilization decreased, and both the low load characteristics and the 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 short, and the catalysts compete for oxygen. For this reason, the utilization rate of the catalyst was deteriorated, and the low load performance was deteriorated.

  In Comparative Example 4, the BET specific surface area of Example 1 exceeds the range of the present embodiment. In Comparative Example 4, the carbon material for the catalyst carrier was too thin, and the mechanical strength was low. For this reason, since the catalyst carrier was crushed in the catalyst layer, gas diffusion performance was reduced, and high load performance was deteriorated.

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

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

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

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

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

(4-3. Comparison between Example 2 and Comparative Examples 10 to 18)
Comparative Examples 10 to 18 correspond to Example 2. The details are the same as in Comparative Examples 1 to 9. When Example 2 was compared with Comparative Examples 10 to 18, the same results as those described above were obtained.

(4-4. Comparison between Example 3 and Comparative Examples 19 to 27)
Comparative Examples 19 to 27 correspond to Example 3. The details are the same as in Comparative Examples 1 to 9. When Example 3 was compared with Comparative Examples 19 to 27, results similar to the above considerations were obtained.

(4-5. Comparative Example 28)
Comparative Example 28 uses acetylene black having high crystallinity as a starting material. In Comparative Example 28, the gas activation could not be sufficiently performed because the starting material had high crystallinity. That is, sufficient pores could not be formed in the carbon material particles for the catalyst carrier. FIG. 3 shows an outline of the catalyst-carrying carrier particles 200 produced in Comparative Example 28. The catalyst carrier particles 200 include a catalyst carrier 201 composed of a catalyst carrier carbon material and a fuel cell catalyst 202. In the catalyst carrier 201, pores 201a in the carrier are formed, but the size thereof is small, and the pores are not communicated with each other. For this reason, the particle diameter and the DBP oil absorption are out of the range of the present embodiment. In Comparative Example 28, the gas diffusivity was extremely poor, and both the low load characteristics and the high load characteristics were poor.

(4-6. Comparative Example 29)
Comparative Example 29 uses EC300J as a starting material. Since EC300J has a very large particle size, the particle size of the carbon material for the catalyst carrier also greatly exceeds the range of the present embodiment. However, other parameters have values within the range of the present embodiment. FIG. 4 shows an outline of the catalyst-carrying carrier particles 300 produced in Comparative Example 29. The catalyst carrier particles 300 include a catalyst carrier 301 made of a carbon material for a catalyst carrier, and a fuel cell catalyst 302. In the catalyst carrier 301, pores 301a in the carrier are formed, and the pores 301a in the carrier are connected to each other by a communication hole 301b. However, the particle diameter L greatly exceeds the range of the present embodiment. Therefore, the distance until the gas reaches the fuel cell catalyst 302 in the catalyst carrier 301 becomes longer. Further, the pores 301a in the carrier become longer. Here, Knudsen diffusion becomes dominant in the catalyst carrier 301, so that the longer the pores 301a in the carrier are, the worse the gas diffusivity becomes. For these reasons, the utilization rate of the catalyst is lowered, and the high load characteristics are deteriorated.

(4-7. Comparative Example 30)
Comparative Example 30 is different from Example 1 in that the first gas activation treatment step was omitted. 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 were below the ranges of the present embodiment. As a result, the catalyst utilization decreased, and the low-load characteristics deteriorated.

(4-8. Comparative Example 31)
Comparative Example 31 is different from Example 1 in that the high crystallization treatment step was omitted. Therefore, the half width ΔG of the G band exceeds the range of the present embodiment. For this reason, the mechanical strength of the carbon material for the catalyst carrier was reduced. As a result, the catalyst carrier was crushed in the catalyst layer, the gas diffusibility was reduced, and the high load performance was deteriorated. In addition, the oxidation resistance was low, and the durability 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 were contracted by the high crystallization treatment step. In this case, even if the catalyst activation treatment step is performed, the communication between the bottleneck type pores is not improved. As a result, the hysteresis difference exceeds 0.10 ml / g, the gas diffusibility of the carbon material for the catalyst carrier decreases, and flooding easily occurs. As a result, the catalyst utilization decreased, and the high load characteristics decreased.

(4-10. Comparative Example 33)
In Comparative Example 33, the catalyst activation treatment step was omitted from Example 1. Therefore, the hysteresis difference exceeds 0.10 ml / g, the gas diffusibility of the carbon material for the catalyst carrier decreases, and flooding easily occurs. As a result, the catalyst utilization decreased, and the high load characteristics decreased.

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

(4-12. Comparative Examples 36 and 37)
In Comparative Examples 36 and 37, the raw materials of Examples 1 to 6, Niteron # 3350 (Niteron Carbon Co., Ltd .: NT3) and Niteron # 415 (Nippon Carbon Co., Ltd., Niteron: NT4) are not modified. Used in In Comparative Example 36, the BET specific surface area is less than the range of the present embodiment. The distance between the fuel cell catalysts becomes shorter, and the catalysts compete for oxygen. For this reason, the utilization rate of the catalyst was deteriorated, and the low load performance was deteriorated. In Comparative Example 37, the DBP oil absorption was less than the range of the present embodiment. As a result, the catalyst utilization decreased, and the low-load characteristics deteriorated.

  As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is apparent that those skilled in the art to which the present invention pertains can conceive various changes or modifications within the scope of the technical idea described in the claims. It is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF REFERENCE NUMERALS 1 catalyst-supporting carrier particles 10 catalyst carrier 10a carrier pore 10b communication hole 11

Claims (6)

The particle size is 10 to 20 nm,
A BET specific surface area of 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 a relative pressure P / P ₀ = 0.5 is 0.10 ml / g or less;
DBP oil absorption is 300 to 520 ml / 100 g,
A carbon material for a solid polymer electrolyte fuel cell catalyst carrier, wherein a half-width ΔG of a G band obtained from a Raman spectrum is 40 to 70 cm ⁻¹ .   The carbon material according to claim 1, wherein the particle size is 15 to 19 nm. 3. The carbon material for a polymer electrolyte fuel cell catalyst carrier according to claim 1, wherein the BET specific surface area is 210 to 450 m ² / g. 4.   A catalyst layer for a polymer electrolyte fuel cell, comprising the carbon material for a catalyst carrier of a polymer electrolyte fuel cell according to claim 1.   A polymer electrolyte fuel cell, comprising the catalyst layer for a polymer electrolyte fuel cell according to claim 4. The polymer electrolyte fuel cell according to claim 5, wherein the catalyst layer for a polymer electrolyte fuel cell is a catalyst layer on a cathode side.

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