JP7277770B2 - Porous carbon material for catalyst carrier for polymer electrolyte fuel cell, catalyst layer for polymer electrolyte fuel cell, and fuel cell - Google Patents

Description

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

A polymer electrolyte fuel cell, which is a kind of fuel cell, comprises a pair of catalyst layers arranged on both sides of a solid polymer electrolyte membrane, gas diffusion layers arranged outside each catalyst layer, and gas diffusion layers arranged on the outside of each catalyst layer. and a separator arranged on the outside. 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 fuel gas such as hydrogen is introduced into the separator on the anode side. The gas diffusion layer on the anode side diffuses the fuel and then introduces it into the anode. The anode includes a catalyst component, a catalyst carrier supporting a fuel cell catalyst, and an electrolyte material having proton conductivity. Hereinafter, a catalyst component that promotes a power generation reaction (an oxidation reaction or a reduction reaction to be described later) in a fuel cell is also referred to as a "fuel cell catalyst". Catalyst carriers are often composed of porous carbon materials. On the fuel cell catalyst, an oxidation reaction of the fuel gas occurs 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 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 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 fuel cell catalyst, a catalyst carrier supporting the fuel cell catalyst, and an electrolyte material having proton conductivity. Catalyst carriers are often composed of porous carbon materials. On the fuel cell catalyst, a reduction reaction of the oxidizing gas occurs 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. As described above, the polymer electrolyte fuel cell generates electricity by utilizing the free energy difference (potential difference) generated by the oxidation reaction of the fuel gas. In other words, it converts the free energy produced by the oxidation reaction into work done by electrons in an external circuit.

By the way, cost reduction and durability improvement are important issues for the further spread of polymer electrolyte fuel cells. For cost reduction, it is essential to reduce the amount of platinum (Pt) used in the catalyst, and for durability, it is essential to improve the durability of the catalyst, especially the oxidation wear resistance of the carbon material used as the carrier. In order to reduce the amount of platinum or precious metals used, one important solution is to improve the utilization rate of the catalyst. It is one solution. It is known that control of the porous structure of the carrier is effective for improving the former utilization rate. That is, since catalytic metal particles such as platinum and platinum-based alloys usually have a size (diameter) of several nanometers, a size suitable for supporting the catalytic metal particles, that is, a so-called mesopore region, In particular, it is important to increase the volume of mesopores of 10 nm or less and increase the surface area for supporting.

On the other hand, in order to improve the large current characteristics, it is important to increase the diffusion of oxygen, which is the reaction gas of the cathode, in the catalyst layer. For this purpose, it is important that pores with a diameter of 100 nm or more exist in the catalyst layer so that the molecular mobility of the gas does not appear. Pores generated in the catalyst layer can be controlled by the three-dimensional structure of the catalyst support. That is, if the carrier has a dendritic structure with a length of 100 nm or more, it is possible to form pores of 100 nm corresponding to the dendritic structure in the catalyst layer.

In recent years, as disclosed in Patent Documents 1 to 4, from the two viewpoints of such mesopore volume of 10 nm or less, specific surface area and dendritic structure of about 100 nm, porous carbon having a three-dimensional dendritic structure Techniques using materials (hereinafter also referred to as "three-dimensional dendritic carbon materials") as catalyst supports have been proposed. A three-dimensional dendritic carbon material has a characteristic structure not found in other carbon materials. Specifically, the three-dimensional dendritic carbon material has a structure that combines a highly developed pore structure (porous structure) and a large-scale dendritic structure. In other words, the carrier particles that constitute the three-dimensional dendritic carbon material have a large number of pores capable of supporting fuel cell catalysts therein and have a large dendritic structure.
Further, as disclosed in Patent Document 5, a porous carbon material produced using MgO as a template has attracted attention as a material whose pores are less likely to collapse even when subjected to high-temperature heat treatment.
Also, as disclosed in Patent Document 6, a porous carbon material produced using carbon black as a starting material has attracted attention as a material whose pores are less likely to collapse even when subjected to high-temperature heat treatment.

Other porous carbon materials include gas-activated porous carbon using water vapor or carbon dioxide as an oxidizing agent, carbon material activated with alkali metal (Non-Patent Document 1), template carbon material using zeolite or magnesium oxide as a template (Non-Patent Document 1). Document 2), CDC (Non-Patent Document 3) produced by heat-treating carbide such as SiC in a chlorine atmosphere, and three-dimensional dendritic carbon materials made from silver acetylide (Non-Patent Document 4) are typical examples. .

WO2014/129597 WO2015/088025 WO2015/141810 WO2016/133132 JP 2012-188309 A JP 2017-052967 A Adsorption characteristics of alkaline activated carbon exemplified by water vapor, H2S, and CH3SH gas, Separation science and technology, 35, 903-918, 2000) A review of the controle of pore structure in MgO-templated nanoporous carbons, Carbon, 48, 2690-2707(2010)) Carbide-derived-carbon, Nanoporous carbide-derived carbonwith tunable pore size, Nature Materials 2, 591-594(2003) Meso-Carbon-Nano-dendrite, Synthesis and characterization of mesoporous carbon nano-dendrites with graphitic ultra-thin walls and teir application to supercapacitor electrodes, Carbon 47, 306-312(2009)

In recent years, polymer electrolyte fuel cells are required to have durability (especially resistance to oxidative exhaustion) when operated at high temperatures. In particular, in automobile applications, the demand is strong. For example, the standard operating temperature at present is 70 to 80°C, but the final goal of the industry is to operate at 120°C.
However, when the polymer electrolyte fuel cell is operated at a high temperature, the oxidation progresses due to the heat, and the pores of the carbon material for the catalyst carrier are crushed, resulting in deterioration of output characteristics at low current.
In order to suppress collapse of pores when the polymer electrolyte fuel cell is operated at high temperature, heat treatment at high temperature is required for the porous carbon material.

Among porous carbon materials, porous carbon materials having mainly small pore diameters, such as micropores, tend to have pores that are easily crushed due to changes in the carbon structure due to heat treatment at 2000° C. or higher. On the other hand, in the template carbon material and the three-dimensional dendritic carbon material, mesopores are the major pore diameters, so even if the carbon structure slightly changes due to heat treatment at 2000° C. or higher, the pores are less crushed.

However, at a temperature of 2300° C. or higher, it was difficult to avoid collapsing of the pores even with conventionally reported template carbon and three-dimensional dendritic carbon materials.

Therefore, an object of the present invention is to provide a catalyst layer for a polymer electrolyte fuel cell that has excellent durability (especially resistance to oxidation and consumption of carbon) with less change over time in output characteristics at low current even when operated at high temperatures. It is an object of the present invention to provide a porous carbon material for a catalyst carrier suitable for producing a polymer electrolyte fuel cell catalyst layer and a fuel cell using the same.

Means for solving the problems include the following aspects.
<1>
A porous carbon material for a catalyst carrier for polymer electrolyte fuel cells that satisfies the following requirements (A), (B), (C), and (D).
(A) Specific surface area determined by BET analysis of nitrogen adsorption isotherm is 450 to 700 m ² /g.
(B) The adsorption amount difference V _0.4-0.9 obtained by subtracting the adsorption amount at a relative pressure of 0.4 from the adsorption amount at a relative pressure of 0.9 in the nitrogen adsorption/desorption isotherm is 150 to 450 mL/g.
(C) After heat treatment at 2400 ° C., when the difference in the adsorption amount obtained by subtracting the adsorption amount at a relative pressure of 0.1 from the adsorption amount at a relative pressure of 0.4 in the nitrogen adsorption and desorption isotherm is V _0.1-0.4 The difference ΔV 0.1-0.4 in adsorption amount obtained by subtracting V _0.1-0.4 after heat treatment at ₂₂₀₀ ° C. from V _0.1-0.4 is 10 to 30 mL/g.
(D) The half width of the G band detected in the range of 1500 to 1700 cm ^-1 by Raman spectroscopy is 35 to 45 cm ^-1 .
<2>
A porous carbon material for a catalyst carrier for polymer electrolyte fuel cells according to <1>, which satisfies the following requirement (E).
(E) The intensity ratio l _D /l _G of the peak intensity I _G in the range of G band 1500 to 1700 cm ⁻¹ and the peak intensity I _D in the range of D band 1200 to 1400 ^cm −1 obtained from the Raman spectroscopy spectrum is 1.0 to 1.7.
<3>
The porous carbon material for a catalyst carrier for polymer electrolyte fuel cells according to <1> or <2>, wherein the adsorption amount difference V _0.4-0.9 is 200 to 400 mL/g.
<4>
The porous carbon material for a catalyst carrier for polymer electrolyte fuel cells according to any one of <1> to <3>, wherein the adsorption amount difference ΔV _0.1-0.4 is 15 to 25 mL/g.
<5>
A catalyst layer for a polymer electrolyte fuel cell, comprising the porous carbon material for a catalyst carrier for a polymer electrolyte fuel cell according to any one of <1> to 4>.
<6>
A fuel cell comprising the polymer electrolyte fuel cell catalyst layer according to <5>.
<7>
The fuel cell according to <6>, wherein the polymer electrolyte fuel cell catalyst layer is a cathode-side catalyst layer.

According to the present invention, a catalyst layer of a polymer electrolyte fuel cell is manufactured that has excellent durability (particularly resistance to oxidation and consumption of carbon) with less change over time in output characteristics at low current even when operated at high temperatures. It is possible to provide a porous carbon material for a catalyst carrier, a catalyst layer for a polymer electrolyte fuel cell, and a fuel cell using the same.

1 is a graph showing an example of a nitrogen adsorption/desorption isotherm of a porous carbon material for a catalyst carrier of a polymer electrolyte fuel cell of the present disclosure. 1 is a graph showing an example of nitrogen adsorption and desorption isotherms after heat treatment at 2200° C. and 2400° C. in a porous carbon material for a catalyst carrier of a polymer electrolyte fuel cell according to the present invention. 1 is a schematic diagram showing a schematic configuration of a fuel cell according to an embodiment; FIG.

The present invention will be described below.
In this specification, a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.
In the numerical ranges described stepwise, the upper limit value or lower limit value described in a certain numerical range may be replaced with the upper limit value or lower limit value of another numerical range described stepwise.
In numerical ranges, the upper limit or lower limit described in a certain numerical range may be replaced with the values shown in the examples.
The term "process" is included in this term not only as an independent process, but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes.
A "combination of preferred aspects" is a more preferred aspect.

<Porous carbon material for catalyst carrier of polymer electrolyte fuel cell>
The porous carbon material for a catalyst carrier for a polymer electrolyte fuel cell of the present invention (hereinafter also referred to as "porous carbon material") is the following (A), (B), (C), and (D) meet the requirements.
(A) Specific surface area determined by BET analysis of nitrogen adsorption isotherm is 450 to 700 m ² /g.
(B) The adsorption amount difference V _0.4-0.9 obtained by subtracting the adsorption amount at a relative pressure of 0.4 from the adsorption amount at a relative pressure of 0.9 in the nitrogen adsorption/desorption isotherm is 150 to 450 mL/g.
(C) After heat treatment at 2400 ° C., when the difference in the adsorption amount obtained by subtracting the adsorption amount at a relative pressure of 0.1 from the adsorption amount at a relative pressure of 0.4 in the nitrogen adsorption and desorption isotherm is V _0.1-0.4 The difference ΔV 0.1-0.4 in adsorption amount obtained by subtracting V _0.1-0.4 after heat treatment at ₂₂₀₀ ° C. from V _0.1-0.4 is 10 to 30 mL/g.
(D) The half width of the G band detected in the range of 1500 to 1700 cm ^-1 by Raman spectroscopy is 35 to 45 cm ^-1 .

The porous carbon material of the present invention is a catalyst for a polymer electrolyte fuel cell that has excellent durability (especially resistance to oxidation and consumption of carbon) with little change over time in output characteristics at low current even when operated at high temperatures. Layers can be manufactured.
The porous carbon material of the present invention was discovered based on the following findings.

First, in order to improve the output characteristics at low current, it is important to secure both the area and the volume for carrying the metal catalyst particles in the pores at the same time. In order for the metal catalyst particles to be evenly subjected to the oxygen reduction reaction at the oxygen electrode, it is said that the distance between the particles should be at least as large as the diameter with respect to the particle diameter of several nanometers. For example, in the case of metal catalyst particles with a diameter of 3 nm, it is sufficient that one metal catalyst particle exists in approximately 36 nm ² . Converting this to an area, assuming that the metal catalyst particles are Pt particles, a specific area of about 120 m ² /g is a necessary condition, assuming that the catalyst support rate is 50% by mass.
The pores having the above-mentioned specific surface area must be of such a size that even if metal catalyst particles with a size of several nanometers are supported, pores for gas flow can still be secured. That is, the pore size (diameter) must be at least the same as that of the metal catalyst particles, and desirably, the pore diameter must be larger than that of the metal catalyst particles.
It is known that in the case of porous carbon materials, the specific surface area due to so-called micropores with a diameter of 2 nm or less generally reaches from several tenths to more than half, and in the case of activated carbon, it reaches as much as 90%. Therefore, the BET specific surface area obtained from the nitrogen adsorption/desorption isotherm must be ensured to be 120 m ² /g or more as described above only at the portion of the pores having a diameter of several nanometers or more. ² /g (that is, 700 m ² /g or less).

On the other hand, the adsorption amount difference V _0.4-0.9 obtained by subtracting the adsorption amount at a relative pressure of 0.4 from the adsorption amount at a relative pressure of 0.9 in the nitrogen adsorption/desorption isotherm is the well-known BJH (Barrett-Joyner-Halenda) According to analysis, when converted to pore diameter, it corresponds to a mesopore volume with a pore diameter (diameter) of 4 nm to 20 nm. It is believed that the metal catalyst particles supported in the pores corresponding to this pore diameter mainly contribute to the catalytic reaction. This is because mesopores with a pore diameter of 4 nm to 20 nm have sufficient space even when catalytic metal particles of this size are supported, because the size of the catalytic metal particles is usually 2 to 6 nm. For example, assuming that a representative pore diameter is 5 nm, and Pt particles with a diameter of 3 nm are supported there as metal catalyst particles, assuming a slit-shaped pore with a slit width of 5 nm, the area in the slit is When calculated, it is approximately 200 cm ³ /g, which is also the value of the adsorption amount difference V _0.4-0.9 obtained by subtracting the adsorption amount at a relative pressure of 0.4 from the adsorption amount at a relative pressure of 0.9 specified in the present invention.

In addition, the difference ΔV _0.1-0.4 in the amount of adsorption obtained by subtracting V _0.1-0.4 after heat treatment at 2200 ° C. from V _0.1-0.4 after heat treatment at 2400 ° C. is the volume in the high temperature range of 2200 ° C. to 2400 ° C. This indicates that the change is small. When this volume change is small, the mechanical strength of the carbon skeleton of the porous carbon material is high, and it is possible to maintain the pore structure against the mechanical shear applied to the carrier in making a uniformly dispersed ink. Therefore, a catalyst layer in which the catalyst is uniformly dispersed can be produced. At the same time, the improvement in mechanical strength leads to minimization of collapse of the pore structure due to oxidative consumption. As a result, the durability (resistance to oxidative consumption of carbon) is improved. In this way, by focusing on the volume change in the high temperature range of 2200 ° C. to 2400 ° C., it is possible to bring out the characteristics that the pores are difficult to collapse even in the temperature range of 2400 ° C. or higher and the durability is excellent. .

The half width of the G band indicates the crystallinity of the porous carbon material. If the crystallinity is high, the area of the edge portion of the graphene, which is the starting point of oxidation, becomes smaller, so the durability (resistance to oxidation and consumption of carbon) can be improved in the sense that oxidation consumption is less likely to occur.
In addition, it should be noted that in the present invention, conventional porous carbon If so, the aim is to perform heat treatment in a temperature range of 2400° C. or higher where the pores are crushed and the carrier does not function. In the present invention, by using such a special material system, we have succeeded in further improving the durability while maintaining the same level of power generation characteristics as in the past. The above-mentioned specific surface area, V _0.1-0.4 , difference ΔV _0.1-0.4 , and ΔG are areas in which conventional porous carbon materials cannot satisfy these simultaneously, and the porous carbon material of the present invention is the first to reach them. It is possible.

Based on the above findings, the porous carbon material of the present invention is a solid polymer that has excellent durability (especially resistance to oxidation and consumption of carbon) with little change over time in output characteristics at low current even when operated at high temperatures. It has been found that it is possible to produce catalyst layers for shaped fuel cells.

The porous carbon material of the present invention will be described in detail below.

(Requirement (A))
The specific surface area determined by BET analysis of the nitrogen adsorption isotherm (hereinafter also referred to as "BET specific surface area") is 450 to 700 m ² /g. As a result, more metal catalyst particles can be supported on the pore walls, and output characteristics at low current are improved.
If the BET specific surface area is less than 450 m ² /g, the amount of supported metal catalyst particles is reduced, and the output characteristics at low flow are deteriorated. When the BET specific surface area exceeds 700 m ² /g, the mechanical strength of the porous carbon material and the durability during high-temperature operation (oxidative wear resistance of carbon) are lowered.

The lower limit of the BET specific surface area is preferably 500 m ² /g or more, and more preferably 550 m ² /g or more, from the viewpoint of suppressing the deterioration of the supportability of the metal catalyst particles and improving the output characteristics at low current.
On the other hand, the upper limit of the BET specific surface area is 680 m ² /g from the viewpoint of reducing the carbon content and improving the physical strength (mechanical strength) of the porous carbon material and the durability during high-temperature operation (oxidation wear resistance). The following is preferable, and 650 m ² /g or less is more preferable.

Here, the BET specific surface area is a value measured by a measuring method shown in Examples described later.

(Requirement (B))
In the nitrogen adsorption/desorption isotherm, the difference V _0.4-0.9 (see FIG. 1) of the adsorption amount obtained by subtracting the adsorption amount at a relative pressure (P/P ₀ ) of 0.4 from the adsorption amount at a relative pressure of 0.9 is 150 to 450 mL/g (preferably 200-400 mL/g). As a result, the mesopore volume is high and the output characteristics at low current are improved.
If the adsorption amount difference V _0.4-0.9 is less than 150 mL/g, the mesopore volume is not ensured, and the output characteristics at low currents deteriorate. On the other hand, when the adsorption amount difference V _0.4-0.9 exceeds 450 mL/g, the mechanical strength of the porous carbon material and the durability during high-temperature operation (oxidative consumption resistance of carbon) decrease.

The lower limit of the adsorption amount difference V _0.4-0.9 is preferably 200 mL/g or more, more preferably 250 mL/g or more, from the viewpoint of increasing the mesopore volume and improving the output characteristics at low current.
The upper limit of the adsorption amount difference V _0.4-0.9 is preferably 400 mL/g or less from the viewpoint of improving the physical strength (mechanical strength) of the porous carbon material and the durability during high-temperature operation (oxidation wear resistance). , 395 mL/g or less.

Here, the adsorption amount difference V _0.4-0.9 is a value measured by a measurement method shown in Examples described later.
The adsorption amount difference V _0.4-0.9 is calculated by determining the nitrogen adsorption/desorption isotherm without subjecting the porous carbon material to be measured to heat treatment.

(Requirement (C))
Heat treatment at 2400 ° C., where V _0.1-0.4 is the difference in the adsorption amount obtained by subtracting the adsorption amount at a relative pressure (P/P ₀ ) of 0.1 from the adsorption amount at a relative pressure of 0.4 in the nitrogen adsorption and desorption isotherm The adsorption amount difference ΔV _0.1-0.4 (see FIG. 2) obtained by subtracting V _0.1-0.4 after heat treatment at 2200° C. from V _0.1-0.4 after heat treatment is 10 to 30 mL/g. As a result, collapse of pores is suppressed even when heat treatment is performed at a temperature of 2200° C. or higher, and durability (oxidative consumption resistance of carbon) during high-temperature operation is improved.
In general, at a temperature of 1800° C. or higher, hydrogen atoms in functional groups and aromatic compounds are decomposed and eliminated from carbon materials, bonds between aromatic molecules are formed, and a graphene structure begins to grow. Furthermore, in the temperature range of 2200 to 2400° C., it is believed that a laminated structure begins to develop due to the mutual movement of the graphene layers as the graphene grows. In the case of porous carbon materials, the growth of graphene does not lead to fatal collapse of the pore structure, but the development of the layered structure causes the rearrangement and structural change of the walls that make up the pores, i.e., the pore structure directly linked to the collapse of In order to improve the durability (especially the resistance to oxidation and consumption of carbon) with less change over time in the output characteristics at low current even when operated at a high temperature, a higher heat treatment temperature than before, that is, a high temperature of 2400 ° C. or higher It is essential to suppress the collapse of pores in the region. For that purpose, it is essential that the change in the pore structure at 2200 to 2400° C. is small, that is, the development of the laminated structure is suppressed. Therefore, in the present invention, the adsorption amount difference ΔV _0.1-0.4 obtained by subtracting V _0.1-0.4 after heat treatment at 2200° C. from V _0.1-0.4 after heat treatment at 2400° C. is used as an index. The degree of development was defined as physical property.
When the difference ΔV _0.1-0.4 in the amount of adsorption is less than 10 mL/g, the thickness of the walls made of carbon constituting the pores is large, resulting in high structural stability. The problem arises that the pore volume and pore surface area are too small.
On the other hand, when the adsorption amount difference ΔV _0.1-0.4 is more than 30 mL/g, the pores are significantly crushed by heat treatment in a high temperature range of 2400 ° C. or higher. It may not be possible to maintain the required specific surface area, mesopore volume (that is, V _0.1-0.4 ).

The lower limit of the adsorption amount difference ΔV _0.1-0.4 corresponds to the mechanical strength of the pores. and the specific surface area per unit weight becomes smaller. Thus, from the viewpoint of the balance between pore strength and specific surface area, the lower limit of the difference ΔV _0.1-0.4 in adsorption amount is preferably 12 mL/g or more, more preferably 15 mL/g or more.
The upper limit of the adsorption amount difference ΔV _0.1-0.4 is 28 mL / g or less from the viewpoint of suppressing pore collapse due to heat treatment at 2200 ° C. and improving durability during high-temperature operation (oxidation resistance of carbon). Preferably, 25 mL/g or less is more preferable.

Here, the adsorption amount difference ΔV _0.1-0.4 is a value measured by a measurement method shown in Examples described later.
The adsorption amount difference V _0.4-0.9 is obtained by subjecting the porous carbon material to be measured to heat treatment at 2200° C. and 2400 °C, and then obtaining the nitrogen adsorption and desorption isotherms of the porous carbon material after each heat treatment. calculated by

(Requirement (D))
The half width of the G band detected in the range of 1500 to 1700 cm ^-1 by Raman spectroscopy is 35 to 45 cm ^-1 . As a result, the carbon network surface of the porous carbon material is expanded, the crystallinity is enhanced, and the durability (oxidative consumption resistance of carbon) during high-temperature operation is improved.
When the half-value width of the G band is less than 35 cm ⁻¹ , the carbon network plane of the porous carbon material spreads too much, the edge amount of the carbon network plane forming the pore wall decreases, and the catalytic metal fine particles on the pore wall The supporting properties of the are lowered. As a result, the output characteristics at low current are degraded.
On the other hand, when the half-value width of the G band exceeds 45 cm ⁻¹ , the crystallinity of the porous carbon material is low and the carbon network planes become narrow. durability (oxidative wear resistance of carbon) is reduced.

The lower limit of the half-value width of the G band is preferably 37 cm ⁻¹ or more, more preferably 39 cm ⁻¹ or more, from the viewpoint of improving output characteristics at low current.
The upper limit of the half-value width of the G band is preferably 44 cm ⁻¹ or less, more preferably 43 cm ⁻¹ or less, from the viewpoint of improving the durability (oxidative consumption resistance of carbon) during high-temperature operation.

(Requirement (E))
The porous carbon material of the present invention preferably satisfies the following requirement (E).
(E) The intensity ratio l _D /l _G of the peak intensity I _G in the range of G band 1500 to 1700 cm ⁻¹ and the peak intensity I _D in the range of D band 1200 to 1400 ^cm −1 obtained from the Raman spectroscopy spectrum is 1.0 to 1.7.
The intensity ratio l _D /l _G is an index indicating the crystallinity of the porous carbon material. (oxidative consumption resistance of carbon) is improved.

The lower limit of the intensity ratio l _D /l _G is preferably 1.1 or more, more preferably 1.2 or more, from the viewpoint of maintaining the output voltage at a low current density and further improving durability.
The upper limit of the intensity ratio l _D /l _G is preferably 1.6 or less, more preferably 1.5 or less, from the viewpoint of maintaining the output voltage at a low current density and further improving durability.

<Method for Producing Porous Carbon Material for Catalyst Carrier of Polymer Electrolyte Fuel Cell>
An example of the method for producing the porous carbon material of the present invention will be described below.

(MgO template method)
The inventors studied a method for producing a porous carbon material using MgO as a template (MgO template method). As a result, the following findings were obtained.
In the case of a porous carbon material made of carbon walls containing polycyclic condensed aromatics with high aromaticity as a constituent element, even if it is heat-treated, the condensation does not easily proceed, and the pores are not easily collapsed. In order to suppress pore collapse due to carbon rearrangement due to heat, a structure in which graphene ribbons are sterically bonded is preferable.
In order to obtain such a porous carbon material having a carbon wall with high aromaticity, magnesium carbonate is used as an MgO source, and as a carbon source, a condensed polycyclic aromatic group having two or more rings is added to the molecular structure. polyimide (specifically, polyamic acid, which is a precursor of polyimide) is used. In the production method using these MgO sources and carbon sources, for example, graphene ribbons with a width of 3 to 4 or less carbon hexagonal network planes surround nano-sized MgO particles as constituent units, thereby forming bonds between the ribbons. . As a result, the graphene ribbons themselves do not deform even when heat-treated at 2300 to 2600° C., and are less likely to bond to each other. Since the bonds are formed so as to surround the MgO particles, rearrangement due to heat is less likely to occur.

In addition, when pre-synthesized MgO particles are used as the MgO source, it is difficult to make the crystallite size of MgO several nm. At least, the minimum crystallite size of commercially available magnesium oxide was 7 nm. As described above, the metal catalyst particles are several nanometers in size, the diameter of the pores containing them is 3 to 10 nm, preferably about 4 to 8 nm, and the MgO particles with a crystallite size of 7 nm are used as the template raw material. Then, at least the porous carbon to be formed has a pore size of 7 nm or more, which is not necessarily suitable for porous carbon for a carrier.
On the other hand, magnesium carbonate gradually thermally decomposes at 200 to 430° C., forming MgO fine particles in the process. When the thermal decomposition of the raw material carbon source is superimposed in the same temperature range as this thermal decomposition process, the carbon source decomposition product suppresses the growth of MgO particles, and as a result, MgO particles of several nanometers are formed, resulting in porous A pore diameter of several nanometers can also be obtained in the carbonaceous material.

Furthermore, in the process of heat-treating the raw material polyamic acid, an imidization reaction occurs due to dehydration condensation, but this imide structure is the key to heat-resistant stability. It is possible to increase the formation rate of By doing so, the aromaticity is increased, the crystallinity is increased, and the durability (oxidative consumption resistance) during high-temperature operation is increased.

As a result, in the MgO template method of the present invention, mesopores having a predetermined specific surface area and a pore diameter of 4 nm to 10 and several nm can be formed. It becomes possible to manufacture a porous carbon material having properties. That is, it is possible to manufacture a porous carbon material that satisfies the above (A) to (D).

An example of the MgO template method is described below.
The MgO template method includes a step of mixing an MgO source and a carbon source, a first heating step, a MgO removal step, and a second heating step. Each step will be described in detail below.

(Mixing step of MgO source and carbon source)
In this step, an MgO source and a carbon source are mixed.
Then, magnesium carbonate is applied as the MgO source.
On the other hand, as the carbon source, a polyamic acid which is a polyimide precursor and has a condensed polycyclic aromatic group of two or more rings (preferably two to four rings) is used. Here, the condensed polycyclic aromatic group is a group obtained by condensing a plurality of aromatic rings, and naphthalene for bicyclic rings, anthracene and phenanthrene for tricyclic rings, tetracene, chrysene, pyrene, 5 Examples of rings include pentacene, benzopyrene, triphenylene, colannulene, and the like.
By applying magnesium carbonate as the MgO source and polyamic acid having a condensed polycyclic aromatic group with two or more rings (preferably two to four rings) as the carbon source, the target adsorption amount difference ΔV _0.1- A porous carbon material with _0.4 is obtained.

A polyamic acid is a condensation polymer of a tetracarboxylic dianhydride and a diamine compound. Examples of tetracarboxylic dianhydrides and diamine compounds are shown below. However, at least one of the tetracarboxylic dianhydride and the diamine compound applies a compound having a condensed polycyclic aromatic group of two or more rings.

Aromatic tetracarboxylic dianhydrides: pyromellitic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 3,3′,4,4′-biphenylsulfone tetracarboxylic acid acid dianhydride, 2,3,5,6-cyclohexane dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 4,4-oxyphthalic dianhydride, 3,4-oxyphthalic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, etc.

Aliphatic or alicyclic tetracarboxylic dianhydrides: butanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2,3, 4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,5-tricarboxycyclopentylacetic dianhydride, 3,5,6-tricarboxynol Bonane-2-acetic acid dianhydride, 2,3,4,5-tetrahydrofurantetracarboxylic dianhydride, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2- Dicarboxylic dianhydride, bicyclo[2,2,2]-oct-7-ene-2,3,5,6-tetracarboxylic dianhydride

Aromatic diamine compounds: p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylethane, 4,4'-diaminodiphenyl ether, 1,5-naphthalenediamine, 2,6 -Naphthalenediamine, 9,10-anthracenediamine and the like, as well as melamine, hexamethylenetetramine and the like can also be used.
Aliphatic or alicyclic diamine compounds; 1,1-metaxylylenediamine, 1,3-propanediamine, tetramethylenediamine, pentamethylenediamine, octamethylenediamine, nonamethylenediamine, 4,4-diaminoheptamethylenediamine , 1,4-diaminocyclohexane, isophoronediamine, tetrahydrodicyclopentadienylenediamine, hexahydro-4,7-methanoindanidimethylenediamine, tricyclo[6,2,1,0 ^2.7 ]-undecylenedimethyl diamine, 4,4'-methylenebis(cyclohexylamine), etc.

The mixing ratio of the MgO source and the carbon source (MgO source/carbon source) is, for example, 1.0 or more and 15.0 or less in terms of the molar ratio of MgO and carbon C in the carbon source. As a result, a porous carbon material having the desired BET specific surface area and pore size distribution (difference V _0.4-0.9 in adsorbed amount) can be obtained.

(First heating step)
In the first heating step, for example, a mixture of an MgO source and a carbon source is heated to 800 to 1100° C. at a temperature elevation rate of 5 to 30° C./min under an inert gas atmosphere. Hold for ~200 minutes.
By this heat treatment, magnesium carbonate is thermally decomposed and converted to MgO in parallel with the polyimidation and carbonization of the polyamic acid to obtain a carbon-MgO composite.

When the polyamic acid is heated, it undergoes dehydration condensation and polyimide is formed. However, in the process of raising the temperature, the polyamic acid is thermally decomposed while imidization is incomplete. Therefore, it is preferable to maintain the temperature at 300° C. to 450° C. for 1 hour or more during the temperature rise to increase the imidization rate. By increasing the imidization rate, the heat resistance of the polyimide is improved, and the carbonization yield after holding at 800 to 1100° C. is increased. In addition, the graphene ribbon becomes longer, the fragrance increases, the crystallinity increases, and the durability (resistance to oxidative wear and tear) during high-temperature operation improves.

(MgO removal step)
In the MgO removal step, the carbon-MgO composite is pickled to dissolve the MgO template in the pickling solution. This removes the MgO template from the carbon-MgO composite. Thereby, a porous carbon material intermediate is obtained.
The acid used for pickling may be any acid that dissolves MgO, and a preferred example is sulfuric acid. After pickling, the carbon material is washed with water and dried.

(Second heating step)
In the second heating step, for example, the obtained porous carbon material intermediate is held at 2300 to 2600° C. for 0.5 to 3.0 hours in an inert gas atmosphere.
This heat treatment further increases the crystallinity of the porous carbon material and improves the durability (resistance to oxidation consumption) during high-temperature operation.

The intended porous carbon material can be obtained by the MgO template method described above.

(Silver acetylide method)
The inventors also investigated a method for producing a porous carbon material using silver acetylide as a raw material (silver acetylide method). As a result, the following findings were obtained.
The carbon structure generated by the thermal decomposition of silver acetylide is basically characterized by high crystallinity as well as aromaticity. On the other hand, in the production method using silver acetylide as a raw material, it is possible to control the size of silver nanoparticles by adjusting the environment during decomposition. That is, it is possible to control the pore size distribution and form mesopores.
On the other hand, conventionally, a silver particle-encapsulating intermediate derived from silver acetylide is dried and then exploded. . Then, silver acetylide explodes over a longer period of time than before, promoting the formation of a structure in which graphene ribbons are sterically bonded, and suppressing pore collapse due to carbon rearrangement due to heat.
Therefore, in the silver acetylide method of the present invention, mesopores having a predetermined specific surface area and a pore diameter of 4 nm to 10 and several nm are formed, and the pores are not crushed even by heat treatment at 2300 ° C. or higher, and high crystallinity is achieved. It becomes possible to form a porous carbon material having That is, it is possible to manufacture a porous carbon material that satisfies the above (A) to (D).

An example of the silver acetylide method is described below.
The silver acetylide method includes a silver acetylide production step, a first heat treatment step, a second heat treatment step, a washing treatment step, and a third heat treatment step. Each step will be described in detail below.

(Silver acetylide production step)
In the silver acetylide production step, acetylene gas is blown into a solution containing silver or a silver salt to produce metal acetylide.

(First heat treatment step)
In the first heat treatment step, silver acetylide is heated at a temperature of 60° C. or higher and 80° C. or lower to segregate silver as silver particles to obtain a silver particle-encapsulated intermediate in which the silver particles are encapsulated. The heating time in this first heat treatment step is usually 1 hour or more, preferably 1 to 10 hours.

(Second heating step)
In the second heating step, the metal particle-encapsulated intermediate is heated at a temperature of 200° C. or higher and 400° C. or lower to induce self-decomposition explosion reaction of silver acetylide and explode the silver particle-encapsulated intermediate. As a result, metal particles are ejected from the silver particle-containing intermediate to obtain a porous carbon material intermediate (decomposition product composed of a composite of silver and carbon).

In the process of the explosion of the silver particle-encapsulated intermediate, silver nano-sized particles (silver nanoparticles) are generated, and at the same time, a hexagonal mesh plane carbon layer is formed surrounding the silver nanoparticles, resulting in the shape of silver acetylide. The skeleton of the three-dimensional dendritic structure is composed of the carbon layer as it is. Further, the generated silver nanoparticles are melted by the explosion energy, and ejected to the outside through the pores formed by the carbon layer surrounding the nanoparticles to form aggregates of silver (silver particles). In a series of processes from this explosion to the ejection of silver, a composite of porous carbon and silver having a three-dimensional dendritic structure is formed.

Here, in the second heating step, a slurry is prepared by dispersing the silver acetylide-derived metal particle-encapsulating intermediate in water, and this slurry is dropped onto a hot plate heated at 300° C. or higher and 500° C. or lower. The dropped slurry first evaporates water on the heating plate, and then causes explosive decomposition of silver acetylide. The importance of the process of pyrolyzing the slurry lies in two effects. The first effect is that water remains during the explosive decomposition of silver acetylide, and part of the explosion energy is allocated to evaporation of water and heating of steam, thereby reducing heating of silver acetylide. The second effect is that, at the same time, the explosion locations and timings are dispersed, so that the scale of each explosion itself becomes smaller.

Compared to the conventional decomposition process in which the silver acetylide after the first heating step is vacuum-dried, then heated in a vacuum and exploded at once by heat, in the above-mentioned second heating step, on a slurry heating plate, A two-fold effect of the decomposition of , lengthens the time to form the hexagonal carbon layers surrounding the silver grains and develops connections between the carbon layers. As a result, the formation of a structure in which graphene ribbons are sterically bonded is promoted, and pore collapse due to carbon rearrangement due to heat is suppressed.

Further, in the second heating step, a material having as large a heat capacity as possible and high thermal conductivity is used for the heating plate in order to fully exhibit the above effects. Specifically, it is preferable to use a metal plate as the heating plate. The concentration of the slurry is 0.5 to 30% by mass based on the dry mass of the silver acetylide as a solid content, and the amount of the slurry dropped is 0.2 with respect to the volume obtained by multiplying the area of the heating plate by the height of 1 mm. Double to 1.5 times. The heating plate is desirably controlled so that the surface temperature of the heating plate is kept at least 200° C. or higher from the time the slurry is dropped until the decomposition is completed.
By heating under these conditions, a porous carbon material having the desired BET specific surface area and mesopores with a pore size of 4 nm to 10 and several nm (that is, the difference V _0.4-0.9 ) is formed.

(Washing process)
In the washing step, the porous carbon material intermediate (a decomposition product composed of a composite of silver and carbon) is subjected to silver dissolution treatment (washing treatment). Thereby, silver particles and other unstable carbon compounds present on the surface of the porous carbon material intermediate are removed.
Here, for example, nitric acid and sulfuric acid are used for dissolving treatment (cleaning treatment) of silver. The concentration is 5 to 30% by mass, the temperature is from room temperature to about 80° C., and the time is from several hours to ten and several hours. This step can also be performed multiple times.

(Third heating step)
In the third heating step, the cleaned porous carbon material intermediate is held at 2300 to 2600° C. for 0.5 to 3.0 hours in an inert gas atmosphere. This heat treatment further increases the crystallinity of the porous carbon material and improves the durability (resistance to oxidation consumption) during high-temperature operation.

The desired porous carbon material can be obtained by the silver acetylide method described above.

<Structure of polymer electrolyte fuel cell>
The catalyst carrier carbon material according to this embodiment can be applied 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 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 and aggregation phase. 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 (carbon cloth, carbon paper, etc.), porous metal materials (metal mesh, metal wool, etc.), and the like.
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 contains the catalyst carrier carbon material according to the present embodiment. That is, the catalyst layer 160 includes the catalyst carrier carbon material according to the present embodiment, the electrolyte material, and the fuel cell catalyst. Thereby, the catalyst utilization rate in the catalyst layer 160 can be increased. As a result, the catalyst utilization rate of the polymer electrolyte fuel cell 100 can be increased.

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 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. If 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, sulfonic acid groups, etc. are introduced (for example, perfluorosulfonic acid polymers or polymers into which benzenesulfonic acid is 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.

<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, the catalyst carrier carbon material according to the present embodiment is used for the catalyst carrier on the cathode side.

<Method of measuring each parameter>
Next, examples of the present invention will be described. First, the method of measuring each parameter will be described.

(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 (BELSORP MAX manufactured by Microtrack Bell), and the nitrogen adsorption/desorption isotherm was measured at a measurement temperature of 77K using nitrogen gas as an adsorbate.
In the measurement of the nitrogen adsorption-desorption isotherm, the measurement interval of the relative pressure P/P ₀ is set smaller than in general measurement (specifically, the measurement interval of P/P ₀ is set at increments of 0.005. ) was set. That is, the measurement accuracy of the relative pressure P/ _P0 on measurement was set to 0.005.

Next, the BET specific surface area S _BET was calculated by BET analysis of the nitrogen adsorption isotherm when the relative pressure P/P ₀ was in the range of 0.05 to 0.15.

Next, from the nitrogen adsorption/desorption isotherm, the adsorption amount at a relative pressure of 0.9 and the adsorption amount at a relative pressure of 0.4 are obtained, and the adsorption amount difference V _0.4-0.9 (= adsorption amount at a relative pressure of 0.9 - relative The amount of adsorption at a pressure of 0.4) was calculated.

Next, the sample is heat-treated at 2200° C. for 1.0 hour in an inert gas atmosphere. The nitrogen adsorption/desorption isotherm is measured for the sample after this heat treatment in the same manner as described above.
From the obtained nitrogen adsorption and desorption isotherms, the adsorption amount at a relative pressure of 0.4 and the adsorption amount at a relative pressure of 0.1 are obtained, and the difference in the adsorption amount is V _0.1-0.4 @ 2200 ° C (= relative pressure of 0.4 Adsorption amount - adsorption amount at a relative pressure of 0.1) was calculated.
Next, the sample is heat-treated at 2400° C. for 1.0 hour in an inert gas atmosphere. The nitrogen adsorption/desorption isotherm is measured for the sample after this heat treatment in the same manner as described above.
From the obtained nitrogen adsorption and desorption isotherms, the adsorption amount at a relative pressure of 0.4 and the adsorption amount at a relative pressure of 0.1 are obtained, and the difference in the adsorption amount is V _0.1-0.4 @ 2400 ° C (= relative pressure of 0.4 Adsorption amount - adsorption amount at a relative pressure of 0.1) was calculated.
Then, the adsorption amount difference ΔV _0.1-0.4 (=V _0.1-0.4 @2400° C.−V _0.1-0.4 @2200° C.) is obtained.

(Method for measuring Raman spectrum)
About 3 mg of a sample was weighed and Raman spectrum was measured using a laser Raman spectrophotometer (manufactured by JASCO Corporation, model NRS-3100). A peak in the range of 1500 to 1700 cm ⁻¹ called the G band and a peak in the range of 1200 to 1400 cm ⁻¹ called the D band were extracted from the Raman spectrum obtained under the following measurement conditions.
Then, the half width (Δ _G ) of the G band peak was measured. Also, the peak intensity I _G of the G band and the peak intensity I _D of the D band were measured, and the intensity ratio l _D /l _G was calculated.
-Measurement condition-
Excitation laser: 532 nm, Laser power: 10 mW (Sample irradiation power: 1.1 mW), Microscopic arrangement: Backscattering, Objective lens: ×100, Spot diameter: 1 μm, Exposure time: 30 sec, Observation wave number: 2000 cm ^-1 to 300 cm ^{- 1} , Accumulated times: 6 times

<Method for producing template carbon>
(Test Examples Nos. 1 to 5: Magnesium citrate template carbon)
Commercially available trimagnesium dicitrate (manufactured by Kanto Chemical Co., Ltd., abbreviated as CitMg) is sintered in a horizontal gas-flowing tubular electric furnace while an inert gas is circulated to form a composite of MgO particles and carbon. Obtained. Argon was flowed at a linear velocity of 3 cm/min, heated from room temperature to 400°C at a temperature elevation rate of 20°C/min, held at 400°C for 1 hour, and then heated to 900°C at the same temperature elevation rate. After being held at 900° C. for 30 minutes, it was allowed to cool and taken out when the temperature reached 100° C. or lower to obtain a composite of MgO particles and carbon. After lightly pulverizing with a mortar, it was dispersed in a 20% by mass sulfuric acid aqueous solution, stirred at 90° C. for 40 hours, suction filtered with a membrane filter, dispersed again in distilled water, and washed by repeating filtration twice. After removing moisture with a hot air dryer at 100° C., it was vacuum-dried at 90° C. for 5 hours to obtain a porous carbon material. In order to increase the crystallinity, the porous carbon material is subjected to graphitization (heat treatment) for 0.5 to 1.0 hours under heating temperature conditions in the range of 2000° C. to 2600° C. in an inert gas atmosphere. was carried out and used as a sample of a porous carbon material for a catalyst carrier. Table 1 summarizes the preparation conditions.

(Test Example Nos. 6 to 10: Magnesium oxide-based mold carbon)
Magnesium oxide PSF-150 manufactured by Kojima Kagaku Kogyo Co., Ltd. was used as magnesium oxide (referred to as MgO), and fine powder of polyvinyl alcohol manufactured by Denka Co., Ltd. (trade name: Poval B05S) was used as the carbon source. After thoroughly mixing both powders in a mortar, a porous carbon material was obtained by the same preparation method as for the magnesium citrate-based template carbon described above. Several levels were prepared with varying mixing ratios of magnesium oxide and PVA. In order to increase the crystallinity, the porous carbon material is subjected to graphitization (heat treatment) for 0.5 to 1.0 hours under heating temperature conditions in the range of 2000° C. to 2600° C. in an inert gas atmosphere. was carried out and used as a sample of a porous carbon material for a catalyst carrier. Table 1 summarizes the preparation conditions.

(Test Examples Nos. 11 to 47: Template carbon using magnesium carbonate and polyimide (its precursor, polyamic acid))
4 g of basic magnesium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., abbreviated as CarMg) powder and 12 g of a polyamic acid solution (DMAc solution of polyamic acid) having a solid concentration of 12% by mass synthesized by the following method (solid content: 14.0 g). 4g) was placed in a mortar and, if necessary, DMAc was added in small portions with a pipette to adjust the viscosity and mixed well in a highly viscous state. The mixed solution is transferred to a petri dish, placed in a gas-exchanged electric furnace, and treated at 150 ° C. for 5 hours under a flow of argon at 200 mL / min to evaporate the solvent DMAc and dry basic carbonate. A solid mixture of magnesium powder and polyamic acid was obtained.
Next, this solid is placed in a horizontal tubular electric furnace, argon is flowed at a linear velocity of 3 cm per minute, the temperature is raised to 900° C. at 20° C./min, and the temperature is maintained at 900° C. for 30 minutes. Polyimidization and carbonization of polyamic acid, and in parallel, thermal decomposition of basic magnesium carbonate and subsequent conversion to MgO were performed. Further, if necessary, an intermediate heat treatment was also performed under the conditions shown in Table 1 during the temperature rising process to 900° C. at 20° C./min.
After being held at 900°C for 30 minutes, it was allowed to cool in the furnace and was taken out after being cooled to 100°C. After sufficiently pulverizing in a mortar, put the powder after carbonization into an eggplant flask, add 100 to 150 times by mass of a 20% by mass aqueous solution of sulfuric acid to the solids, and stir at 90 ° C. for 40 hours or more, MgO was dissolved off with sulfuric acid.
Next, it is filtered through a membrane filter, and the residue is further stirred and washed with distilled water and filtered again. This operation is repeated twice. Vacuum drying yielded porous carbon.

In addition, porous carbon was obtained in the same manner by increasing or decreasing the mass ratio of polyimide (its precursor, polyamic acid) as a carbon source to basic magnesium carbonate.
Moreover, using various polyamic acids prepared by the synthesis method described below, porous carbon was obtained in the same manner as described above, except that the type of polyamic acid was different.
Then, in order to increase the crystallinity, the porous carbon is subjected to graphitization treatment (heat treatment) for 0.5 to 1.0 hours under heating temperature conditions in the range of 2000 ° C. to 2600 ° C. in an inert gas atmosphere. ) was carried out to obtain a sample of a porous carbon material for a catalyst carrier. Table 1 summarizes the preparation conditions.

(Synthesis of polyamic acid)
First, the compounds to be used and their abbreviations are shown below.
ATDA: 9,10-anthracenediamine (manufactured by ChemTik)
NTDA: 2,6-naphthalenediamine (manufactured by Matrix Scientific, USA)
p-PhDA: 1,4-phenylenediamine (manufactured by Tokyo Kasei Co., Ltd.)
PMDA: pyromellitic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
BPDA: Biphenyl-3,4,3',4'-tetracarboxylic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
DMAc: N,N-dimethylacetamide (manufactured by Kanto Chemical Co., Ltd.)

-Synthesis Example 1-
Synthesis was performed using a 2 L reaction vessel. 40 g of ATDA was dissolved in 500 g of DMAc. Next, an equimolar amount of PMDA was added to this solution and stirred, DMAc was added so that the solid content became 12 wt %, and the mixture was stirred at room temperature for 5 hours to carry out a polymerization reaction. After the reaction, a viscous and transparent polyamic acid solution was obtained. This polyamic acid is referred to as PM-AT.

-Synthesis Example 2-
Synthesis was performed using a 2 L reaction vessel. 40 g of ATDA was dissolved in 500 g of DMAc. Next, an equimolar amount of BPDA was added to this solution and stirred, DMAc was added so that the solid content was 12 wt %, and the mixture was stirred at room temperature for 5 hours to carry out a polymerization reaction. After the reaction, a viscous and transparent polyamic acid solution was obtained. This polyamic acid is referred to as BP-AT.

-Synthesis Example 3-
Synthesis was performed using a 2 L reaction vessel. 40 g of NTDA was dissolved in 500 g of DMAc. Next, an equimolar amount of PMDA was added to this solution and stirred, DMAc was added so that the solid content became 12 wt %, and the mixture was stirred at room temperature for 5 hours to carry out a polymerization reaction. After the reaction, a viscous and transparent polyamic acid solution was obtained. This polyamic acid is referred to as PM-NT.

-Synthesis Example 4-
Synthesis was performed using a 2 L reaction vessel. 40 g of NTDA was dissolved in 500 g of DMAc. Next, an equimolar amount of BPDA was added to this solution and stirred, DMAc was added so that the solid content was 12 wt %, and the mixture was stirred at room temperature for 5 hours to carry out a polymerization reaction. After the reaction, a viscous and transparent polyamic acid solution was obtained. This polyamic acid is referred to as BP-NT.

-Synthesis Example 5-
Synthesis was performed using a 2 L reaction vessel. 40 g of p-PhDA was dissolved in 500 g of DMAc. Next, an equimolar amount of BPDA was added to this solution and stirred, DMAc was added so that the solid content was 12 wt %, and the mixture was stirred at room temperature for 5 hours to carry out a polymerization reaction. After the reaction, a viscous and transparent polyamic acid solution was obtained. This polyamic acid is referred to as BP-Ph.

-Synthesis Example 6-
Synthesis was performed using a 2 L reaction vessel. 40 g of p-PhDA was dissolved in 500 g of DMAc. Next, an equimolar amount of PMDA was added to this solution and stirred, DMAc was added so that the solid content became 12 wt %, and the mixture was stirred at room temperature for 5 hours to carry out a polymerization reaction. After the reaction, a viscous and transparent polyamic acid solution was obtained. This polyamic acid is referred to as PM-Ph.

<Test Example No. 48-49: carbon black-based porous carbon>
In order to increase the crystallinity of Ketjenblack "EC600JD" manufactured by Lion Corporation, a heat treatment (graphitization treatment) was performed at 2100°C and 2300°C using a graphitization furnace manufactured by Tokyo Shinku Co., Ltd. The powder to be heat-treated was placed in a graphite crucible and set in a graphitization furnace. The temperature was raised at 20° C./min to 1200° C., the temperature was raised to 1800° C. at 15° C., and in the higher temperature range, the temperature was raised at 10° C./min, and heat treatment was performed at a predetermined temperature for a predetermined time. The heat treatment time was 1 hour. The atmosphere was argon, and heat treatment was performed under a flow rate of 2 L/min.

<Silver acetylide-based porous carbon>
(Test Example Nos. 50 to 52: Silver acetylide-based porous carbon 01)
(1) Silver acetylide production step Ammonia was mixed into an aqueous solution of silver nitrate adjusted to a concentration of 5% by mass so as to have a molar ratio of eight times that of silver nitrate to prepare an aqueous solution of ammoniacal silver nitrate. First, nitrogen gas was blown in for 40 to 60 minutes to replace dissolved oxygen with an inert gas to eliminate the risk of decomposition explosion of silver acetylide produced in this silver acetylide producing step.
Next, acetylene gas is blown into the ammoniacal silver nitrate aqueous solution thus prepared at room temperature for about 10 minutes, and when acetylene gas starts to be released as bubbles from the reaction solution, the acetylene gas is stopped. The reaction was stopped and silver nitrate and acetylene in the reaction solution reacted to form a white precipitate of silver acetylide.
The precipitate of silver acetylide produced was recovered by filtration with a membrane filter, the recovered precipitate was re-dispersed in methanol, and the precipitate obtained by filtering again was taken out in a petri dish.

(2) First heat treatment step About 0.5 g of the silver acetylide obtained in the silver acetylide production step was placed in a stainless steel cylindrical container with a diameter of 5 cm while it was impregnated with methanol, and this was vacuumed. It was placed in a heating electric furnace and vacuum-dried at 60° C. for 1 to 3 hours to prepare a silver particle-encapsulating intermediate derived from silver acetylide of each example and comparative example.

(3) Second heat treatment step The silver particle-encapsulating intermediate at 60°C immediately after vacuum drying obtained in the first heat treatment step is further heated to 200°C without being removed from the vacuum heating electric furnace. In this process, the silver acetylide was heated to induce a self-decomposition explosion reaction to obtain a carbon material intermediate (decomposition product composed of a composite of silver and carbon).

(4) Washing treatment process Silver dissolution treatment (washing treatment) is performed on the carbon material intermediate (decomposition product composed of a composite of silver and carbon) with concentrated nitric acid having a concentration of 30% by mass at 60 ° C. Then, the silver particles and other unstable carbon compounds existing on the surface of the carbon material intermediate were removed to obtain a cleaned carbon material intermediate.

(5) Third heat treatment step (graphitization treatment)
The carbon material intermediate cleaned in the cleaning treatment step is subjected to graphitization treatment (heat treatment) for 0.5 hour to 1.0 hour under heating temperature conditions in the range of 2000 ° C. to 2600 ° C. in an inert gas atmosphere. ) was carried out to obtain a sample of a carbon material for a catalyst carrier. Table 1 summarizes the preparation conditions.

(Test Example Nos. 53 to 56: Silver acetylide-based porous carbon 02)
(1) Silver acetylide production step (2) First heat treatment step Test Example No. After silver acetylide was produced in the same manner as in 50-52, a silver particle-encapsulating intermediate derived from silver acetylide was obtained.

(3) Second heat treatment step Next, the silver particle-containing intermediate was dispersed in water to prepare a slurry containing the silver particle-containing intermediate. The solid content concentration of the slurry was adjusted to about 2% by mass.
Next, a second heat treatment step was performed. First, a stainless steel plate heated to 350 to 450° C. is placed in a stainless steel vacuum container with a volume of 10 L, and 1 mL of the above slurry is added dropwise. Explosion was carried out to obtain a carbon material intermediate (a decomposition product composed of a composite of silver and carbon).

(4) Washing treatment process Silver dissolution treatment (washing treatment) is performed on the carbon material intermediate (decomposition product composed of a composite of silver and carbon) with concentrated nitric acid having a concentration of 30% by mass at 60 ° C. Then, the silver particles and other unstable carbon compounds existing on the surface of the carbon material intermediate were removed to obtain a cleaned carbon material intermediate.

(5) Third heat treatment step (graphitization treatment)
The carbon material intermediate cleaned in the cleaning treatment step is subjected to graphitization treatment (heat treatment) for 0.5 hour to 1.0 hour under heating temperature conditions in the range of 2000 ° C. to 2600 ° C. in an inert gas atmosphere. ) was carried out to obtain a sample of a carbon material for a catalyst carrier. Table 1 summarizes the preparation conditions.

<Preparation of catalyst, preparation of catalyst layer, preparation of MEA, assembly of fuel cell, and evaluation of cell performance>
Next, using the catalyst support carbon material prepared and prepared as described above, a polymer electrolyte fuel cell catalyst supporting a catalyst metal is prepared and obtained as follows. A catalyst layer ink liquid is prepared using the obtained catalyst, then a catalyst layer is formed using this catalyst layer ink liquid, and a membrane electrode assembly (MEA: Membrane Electrode Assembly) is formed using the formed catalyst layer. The manufactured MEA was assembled into a fuel cell, and a power generation test was performed using a fuel cell measuring device. Hereinafter, cell evaluation by preparation of each member and power generation test will be described in detail.

(1) Preparation of polymer electrolyte fuel cell catalyst (platinum-supporting carbon material) The porous carbon material for catalyst support prepared above or a commercially available carbon material is dispersed in distilled water, and formaldehyde is added to the dispersion. was added, and set in a water bath set at 40°C. After the temperature of the dispersion reached 40°C, the same as that of the bath, the dinitrodiamine Pt complex nitric acid aqueous solution was slowly poured into the dispersion while stirring. Then, after continuing stirring for about 2 hours, it filtered and the solid substance obtained was washed. The solid thus obtained was vacuum-dried at 90° C., pulverized in a mortar, and then heat-treated at 200° C. for 1 hour in an argon atmosphere containing 5% by volume of hydrogen to produce a carbon material supporting platinum catalyst particles. bottom.
The amount of platinum supported by the platinum-supporting carbon material was adjusted to 40% by mass with respect to the total mass of the carbon material for catalyst support and platinum particles, and inductively coupled plasma atomic emission spectrometry (ICP-AES: Inductively Measured and confirmed by Coupled Plasma—Atomic Emission Spectrometry).

(2) Preparation of catalyst layer Using the platinum-supported carbon material (Pt catalyst) prepared as described above, Nafion manufactured by Dupont (registered trademark: Nafion; persulfonic acid-based ion exchange resin) was used as the electrolyte resin. Using these Pt catalysts and Nafion in an Ar atmosphere, the mass of the Nafion solid content is 1.0 times the mass of the platinum catalyst particle-supporting carbon material, and the mass of the non-porous carbon is 0.5 times. After blending and stirring lightly, the Pt catalyst is crushed with ultrasonic waves, and ethanol is added to adjust the total solid content concentration of the Pt catalyst and the electrolyte resin to be 1.0% by mass, A catalyst layer ink liquid in which the Pt catalyst and the electrolyte resin were mixed was prepared.

Ethanol was further added to each catalyst layer ink solution having a solid content concentration of 1.0% by mass thus prepared to prepare a catalyst layer ink solution for spray coating having a platinum concentration of 0.5% by mass. The spray conditions were adjusted so that the mass per unit area of the layer (hereinafter referred to as "platinum coating weight") was 0.2 mg/cm2, and the catalyst layer ink for spray coating was sprayed onto a Teflon (registered trademark) sheet. After that, drying treatment was performed in argon at 120° C. for 60 minutes to prepare a catalyst layer.

(3) Production of MEA Using the catalyst layer produced as described above, an MEA (membrane electrode assembly) was produced by the following method.
A 6 cm square electrolyte membrane was cut from a Nafion membrane (NR211 manufactured by Dupont). Further, each of the catalyst layers of the anode and cathode coated on the Teflon (registered trademark) sheet was cut into a square shape of 2.5 cm on each side with a utility knife.
The electrolyte membrane was sandwiched between the catalyst layers of the anode and the cathode cut out in this way so that the catalyst layers were in contact with each other with the central part of the electrolyte membrane sandwiched therebetween and there was no displacement with each other. /cm2 for 10 minutes, then cooled to room temperature, and then carefully peeled off only the Teflon sheet on both the anode and cathode to prepare a catalyst layer-electrolyte membrane assembly in which each catalyst layer of the anode and cathode was fixed to the electrolyte membrane. .

Next, as gas diffusion layers, carbon paper (35BC manufactured by SGL Carbon Co., Ltd.) was cut into a pair of square-shaped carbon papers with a size of 2.5 cm on each side. The catalyst layer-electrolyte membrane assembly was sandwiched so that there was no deviation, and pressed at 120° C. and 50 kg/cm 2 for 10 minutes to prepare an MEA.
The basis weight of each component of the catalyst metal component, the carbon material, and the electrolyte material in each MEA produced was calculated from the difference between the mass of the Teflon sheet with the catalyst layer before pressing and the mass of the Teflon sheet peeled off after pressing. The mass of the catalyst layer fixed to the membrane (electrolyte membrane) was obtained, and calculated from the mass ratio of the composition of the catalyst layer.

(4) Evaluation of fuel cell power generation characteristics (evaluation before endurance: evaluation of low current characteristics)
Each of the MEAs prepared in each test example and prepared using the prepared porous carbon material for catalyst support is assembled into a cell, set in a fuel cell measurement device, and evaluated for fuel cell performance by the following procedure. did
The reaction gas was air on the cathode side, and pure hydrogen on the anode side, and the pressure was adjusted by a back pressure valve provided downstream of the cell under atmospheric pressure so that the utilization rates were 40% and 70%, respectively. , at a back pressure of 0.04 MPa. The cell temperature was set to 80° C., and both the cathode and the anode were supplied with distilled water kept at 60° C. in a humidifier by bubbling. ℃ humidified gas was supplied and power generation evaluation was performed.

Under the condition that the reactant gas was supplied to the cell under such settings, the load was gradually increased, and the voltage between the cell terminals at a current density of 100 mA/cm ² was recorded as the output voltage to evaluate the performance of the fuel cell. , was evaluated according to the criteria for the following pass rank and fail rank. Table 1 shows the results.
[passing rank]
5: Output voltage at 100 mA/cm ² is 0.880 V or more.
4: An output voltage of 0.875 V or higher at 100 mA/cm ² .
3: The output voltage at 100 mA/cm ² is 0.870 V or higher.
[Fail rank]
2: The output voltage at 100 mA/cm ² is 0.850 V or more and less than 0.870 V.
1: Output voltage at 100mA/cm ² is less than 0.850V.

(Evaluation after endurance: Evaluation of durability)
In the above cell, while leaving the anode as it is and flowing argon gas under the same humidified conditions as above to the cathode, the cell voltage is set to 1.0 V and held for 4 seconds, and the cell voltage is set to 1.3 V and held for 4 seconds. (repeated operation of rectangular wave voltage fluctuation) is defined as one cycle, and after performing this repeated operation of rectangular wave voltage fluctuation for 4000 cycles, durability is evaluated in the same manner as the above evaluation of low current characteristics. investigated. Evaluation was performed according to the criteria for the following pass rank and fail rank. Table 1 shows the results.
[passing rank]
5: Output voltage at 100 mA/cm ² is 0.880 V or higher.
4: An output voltage of 0.875 V or higher at 100 mA/cm ² .
3: The output voltage at 100 mA/cm ² is 0.870 V or higher.
[Fail rank]
2: The output voltage at 100 mA/cm ² is 0.850 V or more and less than 0.870 V.
1: Output voltage at 100mA/cm ² is less than 0.850V.

From the above results, the porous carbon material of the example of the present invention is a porous carbon material considered to be the current world standard Ketjenblack "EC600JD" at a temperature higher than normal heat treatment (2000 ° C. or less) (2100 , 2300 ° C)), the output characteristics at low current and the output characteristics at low current change over time even when operated at high temperatures, compared to Test Examples 48 and 49, which were heat-treated at 2300 ° C.) to greatly improve durability. It can be seen that a polymer electrolyte fuel cell catalyst layer having excellent durability (especially resistance to oxidation and consumption of carbon) can be produced.

100 polymer electrolyte fuel cell 110, 120 separator 130, 140 gas diffusion layer 150, 160 catalyst layer 170 electrolyte membrane

Claims (7)

A porous carbon material for a catalyst carrier for polymer electrolyte fuel cells that satisfies the following requirements (A), (B), (C), and (D).
(A) Specific surface area determined by BET analysis of nitrogen adsorption isotherm is 450 to 700 m ² /g.
(B) The adsorption amount difference V _0.4-0.9 obtained by subtracting the adsorption amount at a relative pressure of 0.4 from the adsorption amount at a relative pressure of 0.9 in the nitrogen adsorption/desorption isotherm is 150 to 450 mL/g.
(C) After heat treatment at 2400 ° C., when the difference in the adsorption amount obtained by subtracting the adsorption amount at a relative pressure of 0.1 from the adsorption amount at a relative pressure of 0.4 in the nitrogen adsorption and desorption isotherm is V _0.1-0.4 The difference ΔV 0.1-0.4 in adsorption amount obtained by subtracting V _0.1-0.4 after heat treatment at ₂₂₀₀ ° C. from V _0.1-0.4 is 10 to 30 mL/g.
(D) The half width of the G band detected in the range of 1500 to 1700 cm ^-1 by Raman spectroscopy is 35 to 45 cm ^-1 . 2. The porous carbon material for a catalyst carrier for polymer electrolyte fuel cells according to claim 1, which satisfies the following requirement (E).
(E) The intensity ratio l _D /l _G of the peak intensity I _G in the range of G band 1500 to 1700 cm ⁻¹ and the peak intensity I _D in the range of D band 1200 to 1400 ^cm −1 obtained from the Raman spectroscopy spectrum is 1.0 to 1.7. 3. The porous carbon material for a catalyst carrier of a polymer electrolyte fuel cell according to claim 1, wherein the adsorption amount difference V _0.4-0.9 is 200 to 400 mL/g. 4. The porous carbon material for a catalyst carrier of a polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the difference ΔV _0.1-0.4 in adsorption amount is 15 to 25 mL/g. A catalyst layer for a polymer electrolyte fuel cell, comprising the porous carbon material for a catalyst carrier for a polymer electrolyte fuel cell according to any one of claims 1 to 4. A fuel cell comprising the polymer electrolyte fuel cell catalyst layer according to claim 5 . 7. The fuel cell according to claim 6, wherein the polymer electrolyte fuel cell catalyst layer is a cathode-side catalyst layer.

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