Carbon support material

Abstract

To provide a carbon carrier material that achieves both durability and power generation efficiency at high levels.SOLUTION: A carbon carrier material 1 according to the present disclosure is a material that comprises a plurality of carbon particles 10. In this carbon carrier material 1, large-diameter particles 10L account for 70% or more in number, and internal pores 12 with a pore diameter of 10 nm or less are formed inside the large-diameter particles 10L. In the carbon carrier material 1 as disclosed herein, the plurality of carbon particles 10 are connected by cross-link parts 20 whose average thickness is between 70 nm and 150 nm inclusive, and external pores 30 are provided in regions defined by the plurality of carbon particles 10 and the cross-link parts 20. This structure of the carbon carrier material achieves both durability and power generation efficiency at high levels.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to carbon carrier materials for fuel cells. [Background technology]

[0002] In recent years, research on fuel cells has been progressing to address environmental problems such as air pollution. This type of fuel cell has a layered structure in which the anode and cathode face each other with an electrolyte in between. The anode and cathode are electrically connected by conductive materials such as electric wires. In a fuel cell with this configuration, a fuel gas such as hydrogen gas is supplied to the anode. At this anode, hydrogen (H2) in the fuel gas is converted into hydrogen ions (H2). + ) and electrons (e - It is broken down into ) and then hydrogen ions (H) via an electrolyte. + As ) is transmitted to the cathode, electrons (e) are also transmitted through the conductive material. - ) moves to the cathode. Meanwhile, oxygen-containing gas such as air is supplied to the cathode. Then, hydrogen ions (H) move to the cathode. + ) and electrons (e - ) reacts with oxygen (O2) to produce water (H2O).

[0003] In the fuel cell with the above configuration, electrode materials are used for the electrodes (anode and cathode), in which a catalytic metal is supported on a carbon support material. An example of a carbon support material for this fuel cell is a support material containing carbon particles with tiny pores inside (mesoporous carbon). Because this mesoporous carbon has a very large specific surface area, it can contribute to improving the reaction efficiency at the electrodes.

[0004] Patent Document 1 (JP 2021-84852 A) discloses technology related to mesoporous carbon. Specifically, Patent Document 1 discloses a method for producing mesoporous carbon, comprising a first step of preparing mesoporous silica to serve as a template, a second step of precipitating carbon in the mesopores of the mesoporous silica to produce a mesoporous silica / carbon composite, and a third step of removing the mesoporous silica from the composite. In this manufacturing method, mesoporous silica having a beaded structure in which multiple primary particles are linked together is used as the template. As a result, the manufactured mesoporous carbon has a beaded structure similar to the template (mesoporous silica). Patent Document 1 states that this beaded mesoporous carbon can suppress flooding because it can secure an appropriate amount of voids in the air electrode catalyst layer (electrode). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-84852 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In typical fuel cells, the anode, electrolyte, and cathode are constrained along the stacking direction. This prevents gaps from forming at the interfaces of each layer. However, if the structure of the support material is destroyed by this constraining pressure, the voids within the electrodes become blocked, significantly reducing power generation performance. Furthermore, since the cathode is exposed to water during power generation, the strength of the support material gradually decreases due to carbon oxidation. Mesoporous carbon, in particular, has a large specific surface area, making it susceptible to strength degradation due to oxidation. From these perspectives, there is a growing demand for durable carbon support materials that can maintain excellent power generation performance even when power generation is continued for extended periods. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the inventors investigated the reasons for the low durability of conventional carbon carrier materials (mesoporous carbon) and obtained the following findings. As described above, conventional carrier materials construct a beaded structure in which multiple primary particles (carbon particles) are linked together in order to secure voids within the electrode. However, in this beaded structure, multiple carbon particles are joined at points, so the strength of the joints tends to be low. Furthermore, if the strength of the joints decreases further due to oxidation, structural failure starting from the joints easily occurs. Based on these findings, the inventors considered that if multiple carbon particles could be joined via strong beam-like connecting parts (bridged parts) having a certain thickness or more (typically 70 nm or more), a carrier material with high durability could be realized. In addition, in a carrier material with such a structure, external pores surrounded by the bridged parts and carbon particles are formed, so a sufficient specific surface area can be secured and suitable power generation efficiency can be achieved. Based on these findings, the inventors conducted various experiments and studies and have realized a carbon carrier material with the following configuration.

[0008] The carbon carrier material (1) disclosed herein is a material containing multiple carbon particles. In the particle size distribution based on the number of particles observed on the surface using SEM, the proportion of large-diameter particles with an equivalent circular diameter of 100 nm or more is 70% or more, and internal pores with a pore diameter of 10 nm or less are formed inside the large-diameter particles. Furthermore, in the carbon carrier material disclosed herein, the multiple carbon particles are joined together via cross-linking portions with an average thickness of 70 nm to 150 nm, and external pores are formed in the region surrounded by the multiple carbon particles and the cross-linking portions.

[0009] First, the carbon support material disclosed herein contains many large-diameter particles of 100 nm or more. This reduces the number of bonding points between carbon particles. Furthermore, in this support material, beam-like connecting parts (bridged parts) with an average thickness of 70 nm or more are formed at the bonding points between carbon particles. These configurations enable the realization of a support material with excellent durability. In addition, internal pores of 10 nm or less are formed inside the large-diameter particles of this support material. Furthermore, by limiting the thickness of the bridged parts to 150 nm or less, sufficiently sized external pores are formed. These configurations allow for the support of a large amount of catalyst metal and ensure sufficient flow paths for the target fluid (fuel gas, oxygen-containing gas, etc.). As a result, the support material with the above configuration can contribute to the construction of fuel cells with excellent power generation efficiency. As described above, the carbon support material disclosed herein makes it possible to achieve a high level of both durability and power generation efficiency.

[0010] In the carbon support material (2) disclosed herein, the average pore diameter of the external pores, based on surface SEM observation, is 10 nm or more and 150 nm or less, compared to the carbon support material described in (1) above. This makes it possible to achieve an even higher level of both durability and power generation efficiency.

[0011] In the carbon support material (3) disclosed herein, the pore volume of the pores with a diameter of 10 nm or less, based on the nitrogen adsorption method, is 0.18 ml / g or more and 0.5 ml / g or less, in the carbon support material described in (1) or (2) above. This makes it possible to achieve an even higher level of both durability and power generation efficiency.

[0012] In the carbon support material (4) disclosed herein, in the carbon support material described in any one of (1) to (3) above, the volume of pores with a pore diameter of 10 nm or more and 150 nm or less, based on the mercury intrusion method, is 0.5 ml / g or more and 1.4 ml / g or less. This makes it possible to achieve an even higher level of both durability and power generation efficiency.

[0013] In the carbon carrier material (5) disclosed herein, in the carbon carrier material according to any one of the above (1) to (4), the bulk density when a load of 4 kN is applied is 0.6 g / ml or less. Thereby, higher durability can be ensured.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the carbon carrier material disclosed herein. [Figure 2] FIG. 2 is a flowchart explaining an example of a method for manufacturing the carbon carrier material shown in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of a conventional carbon carrier material. [Figure 4] FIG. 4 is a surface SEM image (200,000 times magnification) of Example 3. [Figure 5] FIG. 5 is a cross-sectional SEM image (200,000 times magnification) of Example 3. [Figure 6] FIG. 6 is a surface SEM image (200,000 times magnification) of Comparative Example 2. [Figure 7] FIG. 7 is a cross-sectional SEM image (200,000 times magnification) of Comparative Example 2. [Figure 8] FIG. 8 is a graph showing the relationship between the initial voltage and the voltage after durability for each example.

Modes for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the technology disclosed herein will be described based on the drawings. In addition, matters other than those specifically mentioned in this specification, which are necessary for the implementation of the technology disclosed herein (for example, the detailed structure of a fuel cell, etc.), can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the common technical knowledge in the relevant field. Also, the notation "A to B" indicating a numerical range in this specification means "A or more and B or less" and includes "more than A and less than B".

[0016] 1. Carbon carrier material Hereinafter, an embodiment of the carbon carrier material disclosed herein will be described. FIG. 1 is a cross-sectional view schematically showing an example of the carbon carrier material disclosed herein.

[0017] The carbon carrier material 1 shown in FIG. 1 includes a plurality of carbon particles 10. In this carbon carrier material 1, in the particle size distribution based on the number standard by surface SEM observation, the ratio of the large-diameter particles 10L having an equivalent circle diameter of 100 nm or more is 50% or more by number. Inside the large-diameter particles 10L, internal pores 12 having an average pore diameter of 10 nm or less are formed. Further, the plurality of carbon particles 10 are joined via a beam-shaped connecting portion (crosslinking portion 20) having an average thickness of 70 nm or more and 150 nm or less. And external pores 30 are formed in the region surrounded by the plurality of carbon particles 10 and the crosslinking portion 20. According to the carbon carrier material 1 having such a configuration, a fuel cell in which both power generation efficiency and durability are achieved at a high level can be realized. Hereinafter, it will be specifically described.

[0018] (1) Components of the carbon carrier material First, carbon carrier material 1 is a structure mainly composed of carbon. Here, "mainly composed of carbon" means that elements other than carbon are intentionally not included. Therefore, carbon carrier material 1 may contain unavoidable impurities (metallic elements, metalloid elements) derived from raw materials and manufacturing processes. Examples of impurities that may be contained in carbon carrier material 1 include silica (Si), sodium (Na), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), aluminum (Al), calcium (Ca), potassium (K), zinc (Zn), magnesium (Mg), zinc (Zn), molybdenum (Mo), cerium (Ce), barium (Ba), palladium (Pd), and silver (Ag). More specifically, in this specification, "carbon carrier material" refers to a structure in which, when the total number of atoms of metallic elements, metalloid elements, and carbon elements is taken as 100%, the carbon element content is 70% or more (preferably 75% or more, more preferably 80% or more, and especially preferably 85% or more). Furthermore, the upper limit of the carbon element content is not particularly limited and may be 100%, 95% or less, or 90% or less.

[0019] (2) Carbon particles The carbon carrier material 1 disclosed herein contains a plurality of carbon particles 10. The carbon particles 10 shown in Figure 1 include large-diameter particles 10L and small-diameter particles 10S. In this specification, "large-diameter particles 10L" refers to carbon particles 10 with a particle diameter of 100 nm or more as observed by surface SEM. On the other hand, "small-diameter particles 10S" refers to carbon particles 10 with a particle diameter of less than 100 nm as observed by surface SEM. In this specification, "particle diameter as observed by surface SEM" is measured according to the following procedure. First, an arbitrary carbon particle is selected in a surface SEM image at a predetermined magnification (e.g., 200,000x). Next, a rectangular auxiliary line is drawn circumscribing the selected carbon particle. Next, the length of the long side of the auxiliary line of the rectangle is defined as the "major axis of the carbon particle," and the length of the short side is defined as the "minor axis of the carbon particle." Next, the area of ​​an ellipse having this major axis and minor axis is calculated. Finally, the diameter of a circle having the same area as the ellipse is considered the "particle diameter of the carbon particle."

[0020] Furthermore, in the carbon carrier material 1 disclosed herein, the proportion of large-diameter particles 10L in the particle size distribution based on the number of particles observed by surface SEM is 70% or more. In other words, this carbon carrier material 1 contains more large-diameter particles 10L than small-diameter particles 10S. This reduces the bonding areas between carbon particles 10, thus contributing to improved durability of the carrier material 1. The proportion of large-diameter particles 10L is preferably 75% or more, more preferably 80% or more, and particularly preferably 88% or more. This further improves the durability of the carrier material 1. On the other hand, as the proportion of large-diameter particles 10L decreases, the specific surface area of ​​the carrier material 1 increases, making it easier to improve power generation efficiency. From this viewpoint, the upper limit of the proportion of large-diameter particles 10L is preferably 98% or less, more preferably 96% or less, even more preferably 94% or less, and particularly preferably 92% or less. In this specification, the "proportion of large-diameter particles in the number-based particle size distribution" can be determined as follows: First, 50 carbon particles are randomly selected from the carbon carrier material. Next, the particle size of each carbon particle is measured according to the procedure described above. Then, a number-based particle size distribution is created by arranging the measured particle sizes (equivalent circle diameters) of the carbon particles in order of particle size. Finally, the proportion of large-diameter particles (carbon particles with a particle size of 100 nm or more) among the 50 selected carbon particles is calculated.

[0021] Next, internal pores 12 with a pore diameter of 10 nm or less are formed inside the large-diameter particles 10 L. Although not shown in Figure 1, these internal pores 12 communicate with the outside of the large-diameter particles 10 L. Therefore, in this carbon support material 1, a catalytic metal can be supported in the internal pores 12 (inside the large-diameter particles 10 L). Furthermore, when forming electrodes for a fuel cell, the fluid to be acted upon (fuel gas, oxygen-containing gas, etc.) can be introduced into the internal pores 12. As a result, a large specific surface area can be secured despite containing many large-diameter particles 10 L, thus enabling excellent power generation efficiency. In this specification, the "pore diameter of the internal pores" is measured according to the following procedure. Specifically, an arbitrary carbon particle is selected in a cross-sectional SEM image at a predetermined magnification (e.g., 200,000x). Next, a binarized image of the selected carbon particle is obtained. Then, the largest circle inscribed in the pores (internal pores) present inside the large particles is drawn, and the diameter of this largest circle is defined as the "pore diameter of the internal pores".

[0022] The average number of internal pores 12 present within a single large-diameter particle 10L is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more. As the number of internal pores 12 increases, the specific surface area of ​​the carrier material 1 increases, which tends to improve the power generation efficiency of the fuel cell. On the other hand, if too many internal pores 12 are formed in a single large-diameter particle 10L, the strength of the carrier material 1 may decrease. From this viewpoint, the average number of internal pores 12 is preferably 60 or less, more preferably 55 or less, even more preferably 50 or less, and particularly preferably 45 or less. The average number of internal pores 12 can be measured by the following procedure. First, the number of internal pores 12 in an arbitrary area within the large-diameter particle 10L is measured in a cross-sectional SEM image of the carrier material 1. Next, the number of internal pores per unit area is obtained by dividing the number of internal pores 12 by the area. Next, in the particle size distribution based on surface SEM observation, the average particle diameter of large-diameter particles with an equivalent circle diameter of 100 nm or more is calculated, and the number of internal pores is calculated from the product of the cross-sectional area at the average particle diameter and the number of internal pores per unit area.

[0023] The carbon carrier material 1 disclosed herein preferably has a mesopore volume of 0.18 ml / g or more (more preferably 0.2 ml / g or more, even more preferably 0.22 ml / g or more, and particularly preferably 0.24 ml / g or more) based on the nitrogen adsorption method. This allows for a larger specific surface area, thereby achieving even better power generation efficiency. Herein, "mesopore" refers to minute pores present in the carbon carrier material 1, not limited to internal pores 12 and external pores 30. Specifically, mesopores refer to pores with a diameter of 10 nm or less in the nitrogen adsorption isotherm measured using the nitrogen adsorption method. According to the inventors' experiments, the carbon carrier material 1 disclosed herein has been confirmed to have a tendency for the mesopore volume to increase because a large number of internal pores 12 with a diameter of 10 nm or less are formed within the large-diameter particles 10 L. On the other hand, if the mesopore volume becomes too large, the strength of the large-diameter particles 10 L may decrease. From this viewpoint, the upper limit of the volume of the mesopores is preferably 0.5 ml / g or less, more preferably 0.48 ml / g or less, even more preferably 0.46 ml / g or less, and particularly preferably 0.44 ml / g or less.

[0024] (3)Bridge part The crosslinking portion 20 refers to a beam-shaped connecting portion with an average thickness of 70 nm or more, among the connecting portions that join multiple carbon particles 10. Specifically, when a carbon carrier material is observed with an SEM, point connections where carbon particles are directly joined to each other, and beam-shaped connecting portions that span between spaced carbon particles can be observed. In this specification, "crosslinking portion" refers to a beam-shaped connecting portion among these connecting portions that has a certain thickness or more. More specifically, if the thickness of 100 beam-shaped connecting portions is measured in an SEM observation of a carbon carrier material and the average thickness is 70 nm or more, then the carbon carrier material can be said to have a crosslinking portion. In the carrier material 1 disclosed herein, the average thickness of the crosslinking portion 20 is set to 70 nm or more and 150 nm or less. This significantly improves the durability of the carrier material 1. The crosslinking portion 20 of the carbon carrier material 1 disclosed herein will be described below in comparison with the conventional carbon carrier material 100 shown in Figure 3.

[0025] First, as shown in Figure 3, the conventional carbon carrier material 100 contains multiple carbon particles 110 having minute internal pores 112. This carbon carrier material 100 has a beaded structure in which multiple carbon particles 110 are linked together. In the carbon carrier material 100 with this beaded structure, the majority of the connection points are point joints where carbon particles are directly joined together, so the strength of the connection points 100J tends to be low. In addition, the connection points 100J of this beaded structure oxidize easily to the inside when exposed to water, etc., resulting in a more significant decrease in strength. For this reason, in fuel cells using the conventional carbon carrier material 100, structural failure starting from the connection points 100J is likely to occur when power generation is continued for a long period of time. As a result, the external pores surrounded by multiple carbon particles 110 collapse, and the performance of the fuel cell deteriorates as power generation continues.

[0026] On the other hand, as shown in Figure 1, the carbon carrier material 1 disclosed herein has multiple carbon particles 10 joined together via a cross-linking portion 20, which is a beam-shaped connecting portion with an average thickness of 70 nm or more. This cross-linking portion 20 has higher strength than the connecting portion 100J of the conventional carrier material 100 (see Figure 3). Furthermore, even when exposed to water or the like, only the surface of this cross-linking portion 20 oxidizes, and it is easy to maintain its internal strength. For this reason, even when the carrier material 1 disclosed herein is used to generate electricity in a fuel cell for a long period of time, structural failure starting from the joining portion (cross-linking portion 20) between the carbon particles 10 is less likely to occur. As a result, the carrier material 1 disclosed herein can exhibit superior durability compared to conventional materials.

[0027] Furthermore, as the cross-linked portion 20 becomes thicker, its strength tends to improve. Also, as the cross-linked portion 20 becomes thicker, it becomes less susceptible to strength reduction due to oxidation. From these viewpoints, the average thickness of the cross-linked portion 20 is preferably 76 nm or more, more preferably 78 nm or more, even more preferably 80 nm or more, and particularly preferably 82 nm or more. On the other hand, if the cross-linked portion 20 becomes too thick, the pore volume of the external pores 30 described later decreases, which may reduce power generation efficiency. From this viewpoint, the average thickness of the cross-linked portion 20 is set to 150 nm or less. Also, from the viewpoint of achieving more favorable power generation efficiency, the average thickness of the cross-linked portion 20 is preferably 140 nm or less, more preferably 130 nm or less, even more preferably 120 nm or less, and particularly preferably 110 nm or less.

[0028] The average number of connections of the crosslinking portion 20 to a single carbon particle 10 is preferably 0.5 or more, more preferably 1 or more, even more preferably 1.5 or more, and particularly preferably 2 or more. This makes it possible to realize a carrier material 1 with even greater durability. On the other hand, the upper limit of the average number of connections of the crosslinking portion 20 is not particularly limited and may be 8 or less, 7.5 or less, 7 or less, 6.5 or less, or 6 or less. In this specification, "average number of connections of the crosslinking portion 20" refers to the average number of connections in a plan view measured based on a surface SEM image. This average number of connections is measured by the following procedure. First, 50 arbitrary carbon particles 10 are selected from the surface SEM image of the carrier material 1. Next, the number of connections of the crosslinking portion 20 in each of the selected carbon particles 10 is measured, and the average value of the number of connections of the crosslinking portion 20 for the selected carbon particles 10 is calculated.

[0029] (4) External pores The external pores 30 are cavities formed in a region surrounded by multiple carbon particles 10 and the bridging portion 20. These external pores 30 serve as channels for various fluids (fuel gas, oxygen-containing gas, water, etc.) to pass through. As shown in Figure 1, in the carrier material 1 disclosed herein, since the bridging portion 20 is interposed between multiple carbon particles 10, a bridging bead structure containing many external pores 30 of a suitable size is constructed. For this reason, the carrier material 1 disclosed herein can exhibit superior power generation efficiency compared to conventional carrier materials 100 (see Figure 3) in which multiple carbon particles 110 are directly joined together. Furthermore, as described above, since the carrier material 1 disclosed herein is equipped with bridging portions 20 that have excellent strength, this bridging bead structure with external pores 30 can be maintained for a long period of time.

[0030] Furthermore, the average pore diameter of the external pores 30 based on surface SEM observation is preferably 10 nm or more, more preferably 20 nm or more, even more preferably 30 nm or more, and particularly preferably 40 nm or more. This improves the specific surface area of ​​the carrier material 1 and makes it easier for fluid to pass through, thus further improving power generation efficiency. On the other hand, the average pore diameter of the external pores 30 is preferably 150 nm or less, more preferably 140 nm or less, even more preferably 130 nm or less, and particularly preferably 120 nm or less. This further improves the durability of the carrier material 1. In this specification, the "average pore diameter of the external pores 30" is measured by the following procedure. First, 100 arbitrary external pores 30 are selected from the surface SEM image of the carrier material 1. Next, a rectangular auxiliary line is drawn that circumscribes the selected external pores 30. Then, the length of the long side of the rectangular auxiliary line is defined as the "major axis of the external pore," and the length of the short side is defined as the "minor axis of the external pore." Next, the area of ​​the ellipse having this major axis and minor axis is calculated. Then, the diameter of a circle having the same area as the ellipse is considered to be the "pore diameter of the external pore". Finally, the average value of the pore diameters of the selected multiple external pores 30 is calculated.

[0031] Furthermore, in the carbon carrier material 1 disclosed herein, it is preferable that the volume of macropores based on the mercury intrusion method is 0.3 ml / g or more (more preferably 0.4 ml / g or more, even more preferably 0.5 ml / g or more, and particularly preferably 0.6 ml / g or more). This allows for a more favorable securing of fluid flow paths, thereby improving power generation efficiency. Herein, "macropores" refers to large pores present in the carbon carrier material 1, not limited to internal pores 12 and external pores 30. Specifically, it refers to pores with a diameter of 10 nm to 150 nm in the pore size distribution measured based on the mercury intrusion method. However, if the volume of macropores becomes too large, the strength of the carrier material 1 may decrease. From this viewpoint, the upper limit of the volume of the carrier material 1 is preferably 1.7 ml / g or less, more preferably 1.6 ml / g or less, even more preferably 1.5 ml / g or less, and particularly preferably 1.4 ml / g or less.

[0032] (5) Overall structure As described above, the carrier material 1 disclosed herein contains a large number of large-diameter particles 10L with a diameter of 100 nm or more. This reduces the number of bonding points between carbon particles 10. Furthermore, in this carrier material 1, crosslinking portions 20 with an average thickness of 70 nm or more are formed at the bonding points between carbon particles 10. This allows for strong bonding between carbon particles 10. These configurations enable the realization of a carrier material 1 with excellent durability.

[0033] Furthermore, in this carrier material 1, internal pores 12 of 10 nm or less are formed inside the large-diameter particles 10 L. In addition, the thickness of the cross-linking portion 20 in this carrier material 1 is limited to 150 nm or less. These configurations ensure a sufficient specific surface area of ​​the carrier material 1. As a result, it is possible to support a large amount of catalyst metal and efficiently allow the target fluid to pass through, thus achieving excellent power generation efficiency.

[0034] As described above, by using the carbon support material 1 disclosed herein, it is possible to realize a fuel cell that achieves a high level of both durability and power generation efficiency.

[0035] As described above, the carrier material 1 disclosed herein has high-strength crosslinked portions 20, and therefore can maintain a crosslinked bead structure with multiple external pores 30 even when strong confining pressure is applied. Specifically, the carrier material 1 disclosed herein can have a bulk density of 0.6 g / ml or less (more preferably 0.55 g / ml or less, even more preferably 0.5 g / ml or less, and particularly preferably 0.45 g / ml or less) when a load of 4 kN is applied. Such a carrier material 1 with excellent strength can particularly contribute to improving the durability of fuel cells.

[0036] 2. Method for manufacturing carbon carrier material Next, with reference to Figure 2, an example of a method for manufacturing the carbon carrier material disclosed herein will be described. Figure 2 is a flowchart of an example of a method for manufacturing the carbon carrier material disclosed herein. It should be noted that the following description is not intended to limit the carrier material disclosed herein to those manufactured by the following manufacturing method.

[0037] As shown in Figure 2, the method for manufacturing the carrier material disclosed herein comprises a mold preparation step S10, a carbon deposition step S20, a mold removal step S30, and a second heat treatment step S40. Each step will be described below.

[0038] (1) Mold preparation process S10 In this process, a powder material containing mesoporous particles is prepared as a mold. Examples of materials for the mesoporous particles include ceramic materials such as silica, magnesia, alumina, and zeolite. Among these, silica is particularly preferred. Examples of silica-based mesoporous particles include mesoporous silica and fumed silica. By using these materials, the particle size of the large-diameter particles 10L and the pore size of the internal pores 12 can be easily controlled. For example, the average particle size of the mesoporous particles is preferably between 7 nm and 200 nm. This makes it easy to produce large-diameter particles 10L (carbon particles 10 with a particle size of 100 nm or more). Furthermore, the average pore size of the internal pores of the mesoporous particles is preferably between 1 nm and 10 nm. This makes it easier for internal pores 12 between 2 nm and 10 nm to form inside the large-diameter particles 10L. The specific means for preparing the mesoporous particles are not particularly limited, and conventionally known production methods can be used without particular restriction. Furthermore, the mesoporous particles can be used as they are after purchase.

[0039] (2) Carbon adhesion process S20 In this process, carbon components are attached to mesoporous particles. This creates a composite material containing mesoporous particles, carbon particles 10, and crosslinking portions 20. The carbon attachment process S20 shown in Figure 2 comprises a carbon source spraying process S22 and a first heat treatment process S24. Each of these processes will be described below.

[0040] (a) Carbon source attachment step S22 In this process, a liquid carbon source is attached to mesoporous particles. The carbon source adheres to the surface and interior of the mesoporous particles. Furthermore, a portion of the carbon source penetrates between two adjacent mesoporous particles. The carbon source used in this process is a material capable of generating carbon through thermal decomposition. Examples of such carbon sources include sugars such as sucrose, wood sugar, and glucose, as well as polymer precursors such as furfuryl alcohol and aniline. In this process, it is preferable to drop the mesoporous particles into the liquid carbon source and stir. This allows for proper attachment of the carbon source. Additionally, spray drying methods can also be used in this process.

[0041] In the carbon source attachment step S22, a carbon source exceeding the volume of the internal pores of the mesoporous particles is attached. As a result, the carbon source that could not penetrate the internal pores of the mesoporous particles (especially the internal pores 12 of the large-diameter particles 10L) is adsorbed into the gaps between the multiple mesoporous particles. This carbon source adsorbed into the gaps between the mesoporous particles becomes a precursor to the cross-linked portion 20. Furthermore, the amount of carbon source supplied in this step is preferably 1.5 times or more the volume of the internal pores of the mesoporous particles, more preferably 1.8 times or more, even more preferably 2.0 times or more, and particularly preferably 2.5 times or more. This makes it easy to form beam-shaped connecting portions (cross-linked portions 20) of 70 nm or more. However, supplying an excessive amount of carbon source may clog the external pores 30. From this viewpoint, the upper limit of the amount of carbon source supplied is preferably 6.0 times or less the volume of the internal pores of the mesoporous particles, more preferably 5.0 times or less, even more preferably 4.0 times or less, and particularly preferably 3.0 times or less. This prevents the width of the bridged section 20 from becoming excessive.

[0042] (b) First heat treatment process S24 In this process, mesoporous particles to which a carbon source is attached are heated. This process is not particularly limited, and conventionally known methods can be employed without particular restriction. For example, in the first heat treatment step S24, the carbon source may be heated in a non-oxidizing atmosphere (e.g., an inert atmosphere, a vacuum, etc.). This causes the carbon source attached to the inside and surface of the mesoporous particles to carbonize (or partially graphitize). As a result, carbon particles 10 (typically large-diameter particles 10L) are produced. On the other hand, the carbon source adsorbed in the gaps between the mesoporous particles carbonizes (or partially graphitizes) to form a crosslinked portion 20. As described above, in this manufacturing method, dispersed mesoporous particles are used as a mold, and a carbon source exceeding the volume of the internal pores of the mesoporous particles is attached. This makes it possible to manufacture a carrier material 1 in which multiple carbon particles 10 are joined via crosslinked portions 20.

[0043] In this process, the heating temperature is preferably between 500°C and 1200°C. This suppresses the reaction between silica and carbon, allowing for proper carbonization (or partial graphitization) of the carbon source. Furthermore, in this process, it is preferable to perform a drying treatment before the heat treatment. This makes it easier to maintain the shape of the carbon source during the heat treatment, thus making it easier to manufacture a carrier material 1 with a suitable structure.

[0044] Furthermore, it is preferable to repeat the carbon deposition process S20 multiple times until the desired carbon particles 10 and crosslinked portions 20 are formed. For example, the number of times the carbon deposition process S20 is carried out is preferably one or more, more preferably two or more, and particularly preferably three or more. This makes it possible to form carbon particles 10 of a suitable size and crosslinked portions 20 of an appropriate thickness. On the other hand, the upper limit of the number of times the carbon deposition process S2 is carried out is preferably six or less, more preferably five or less, and particularly preferably four or less. This suppresses the formation of crosslinked portions 20 that are thicker than necessary and makes it possible to form external pores 30 of a sufficient size.

[0045] (4) Mold removal process S30 In this process, only the mesoporous particles are removed from a composite material containing mesoporous particles, carbon particles 10, and crosslinking portions 20. This yields a carrier material 1 having carbon particles 10 and crosslinking portions 20. The means for removing the mold (mesoporous particles) are not particularly limited, and conventionally known methods can be appropriately employed depending on the composition of the mesoporous particles. For example, when removing mesoporous silica, methods such as heating the carrier material in an alkaline solution (such as an aqueous NaOH solution) or etching with an aqueous hydrofluoric acid solution can be employed.

[0046] (5) Second heat treatment process S40 In this step, the carrier material 1 is heated again. This promotes carbonization (or graphitization) of the carrier material 1, thereby improving performance such as durability. It is preferable that the second heat treatment step S40 be performed after the mold removal step S30. This prevents the reaction between carbon components (carbon particles, crosslinked parts, etc.) and mesoporous particles. The heating temperature in this step is preferably 400°C or higher, more preferably 1000°C or higher, and particularly preferably 1600°C or higher. This allows for proper graphitization of the carrier material 1. On the other hand, from the viewpoint of energy efficiency, the upper limit of the heating temperature is preferably 2300°C or lower, and more preferably 2200°C or lower.

[0047] As described above, the carrier material 1 shown in Figure 1 can be appropriately manufactured according to the manufacturing method shown in Figure 2. Furthermore, the manufactured carrier material 1 has a strong cross-linking portion 20 and a large specific surface area, thus achieving a high level of both durability and power generation efficiency.

[0048] 3.Applications The carbon support material disclosed herein has been described above. By supporting a predetermined catalyst metal on this carbon support material, an electrode material for a fuel cell can be manufactured. Specifically, first, the support material disclosed herein is dispersed in a solution of the catalyst metal. Next, the catalyst metal in the dispersion is precipitated by heating or other means. This allows the catalyst metal to be supported on the support material. As described above, the support material disclosed herein has a large specific surface area and can support a large amount of catalyst metal. Furthermore, the support material disclosed herein is less prone to structural failure during use, so it can maintain a state in which the fluid being processed can come into proper contact with the catalyst metal. As a result, a fuel cell with excellent power generation performance and durability can be realized.

[0049] The type of metal catalyst is not limited to the technology disclosed herein, and conventionally known metal catalysts (such as Pt, Pd, and Rh) can be used without particular restriction. Furthermore, the amount of metal catalyst supported is not particularly limited and can be appropriately changed according to the specifications of the fuel cell. The carrier material disclosed herein can be used in both the anode and cathode of a fuel cell. However, because the carrier material disclosed herein has the characteristic of maintaining high durability even when exposed to water, it is particularly preferable to use it in the cathode where water is generated during power generation.

[0050] [Example Test] The following describes test examples relating to the technologies disclosed herein, but it is not intended that the technologies disclosed herein are limited to those shown in such test examples.

[0051] In this study, seven types of carbon support materials (Examples 1-3, Comparative Examples 1-4) were prepared, and the structure and performance of each support material were investigated.

[0052] 1. Preparation of test samples (1) Example 1 In Example 1, 33.1 g of mesoporous silica was prepared as a mold. A liquid carbon source was then dropped onto the mesoporous silica and stirred for 5 minutes to allow the carbon source to adhere to the mold. Next, the mold with the attached carbon source was subjected to drying and heat treatment (first heat treatment) to carbonize and partially graphitize the carbon source. In this experiment, three carbon generation treatments with different conditions were performed. The conditions for each carbon generation treatment are as follows.

[0053] [First time] Carbon source: 45 wt% sucrose solution Amount of carbon source: 0.95 times the pore volume of mesoporous silica Drying process: Air atmosphere, 110°C, 1 hour Firing process: Nitrogen atmosphere, 800°C, 1 hour

[0054] [2nd time, 3rd time] Carbon source: furfuryl alcohol Amount of carbon source: 1.5 times the pore volume of mesoporous silica Drying process: Air atmosphere, 110°C, 9 hours Firing process: Nitrogen atmosphere, 800°C, 1 hour

[0055] Next, the mold (mesoporous silica) was removed from the composite material after the carbon generation treatment. Specifically, first, the calcined material was suspended in 42 times the weight of the mesoporous silica in pure water. Next, 0.65 times the weight of the mesoporous silica in NaOH was dissolved in the suspension. The suspension was then heated at 80°C for 3 hours while stirring. After filtering the suspension using a suction filter, a washing treatment was repeated five times, in which 30 times the weight of the mesoporous silica in pure water was added. Next, the filtered composite material was dispersed in an acid solution. The acid solution used was a mixture of 0.45 times the weight of the mesoporous silica in 13N nitric acid and 9 times the weight of the mesoporous silica in pure water. After filtering the suspension using a suction filter, a washing treatment was repeated three times, in which 30 times the weight of the mesoporous silica in pure water was added. Finally, the carbon material separated by filtration was dried (110°C, 12 hours).

[0056] Next, a second heat treatment was performed on the dried carbon material. The heating temperature for this second heat treatment was set to 1900°C, and the heating time was set to 0.5 hours. The heating atmosphere was set to a vacuum atmosphere. This produced the carbon support material of Example 1.

[0057] (2) Example 2 In Example 2, the carbon support material was prepared according to the same procedure as in Example 1, except that the amount of furfuryl alcohol sprayed during the second and third carbon generation treatments was increased to "2.0 times the pore volume of the mesoporous silica".

[0058] (3) Example 3 In Example 2, the carbon support material was prepared according to the same procedure as in Example 1, except that the amount of furfuryl alcohol sprayed during the second and third carbon generation treatments was increased to "2.5 times the pore volume of the mesoporous silica".

[0059] (4) Comparative Examples 1-3 In this study, commercially available carbon carrier materials were prepared as comparative examples. The carbon carrier materials used in each example are as follows:

[0060] Comparative Example 1: Carbon Black manufactured by Tokai Carbon Co., Ltd. (Product No.: TOKABLACK#3845) Comparative Example 2: Conductive carbon black manufactured by Cabot Corporation (Product No.: VULCAN XC72R (registered trademark)) Comparative Example 3: Denka Co., Ltd. Carbon Black (Product No.: Li-400)

[0061] (5) Comparative Example 4 In this study, a comparative example 4 was created, which was similar to the carbon support described in Japanese Patent No. 7153005. In Comparative Example 4, furfuryl alcohol (FA) was added to mesoporous silica in an amount equal to 0.95 times the pore capacity, and allowed to permeate into the silica pores. This was then heat-treated at 110°C for 9 hours to polymerize the FA. Furthermore, this was heat-treated at 800°C for 1 hour in a nitrogen atmosphere to promote carbonization and graphitization of the FA. This was repeated twice to obtain a mesoporous silica / carbon composite. Then, following the same procedure as in Example 1, the mold (mesoporous silica) was removed. Subsequently, heat treatment was performed by heating at 1800°C for 0.5 hours in a vacuum atmosphere. Furthermore, the carbon support of Comparative Example 4 was obtained by heating at 450°C for 1 hour and then crushing.

[0062] 2. Structural analysis of carbon carrier materials (1)SEM analysis In this study, the structure of the carbon support material in each example was analyzed. Specifically, surface SEM images and cross-sectional SEM images were obtained for each carbon support material. The surface SEM image of Example 3 is shown in Figure 4, and the cross-sectional SEM image is shown in Figure 5. On the other hand, the surface SEM image of Comparative Example 3 is shown in Figure 6, and the cross-sectional SEM image is shown in Figure 7.

[0063] In this study, the particle size distribution of carbon particles in the carrier material was measured by image analysis of surface SEM images of each sample. Based on this particle size distribution, the percentage of large-diameter particles (carbon particles with an equivalent circle diameter of 100 nm or more) was measured. In addition, the average thickness of the beam-like connecting parts between carbon particles was also measured in the image analysis of the surface SEM images. If the average thickness of the beam-like connecting parts was 70 nm or more, it was determined that a strong cross-linking part had been formed between the carbon particles. In this study, connecting parts where carbon particles were joined at points were not included in the measurement of the thickness of the connecting parts. Furthermore, in this study, the pore size distribution of internal pores inside the carbon particles was measured by image analysis of cross-sectional SEM images of Example 3. The percentage of internal pores smaller than 10 nm was measured. The measurement results for each item are shown in Table 1.

[0064] (2) Measurement of mesopores by nitrogen adsorption In this evaluation, nitrogen adsorption measurements were performed to determine the pore volume of mesopores in the carrier material. Specifically, each carbon carrier material was subjected to a drying treatment (120°C, 6 hours). Then, the surface area was 1000 m². 2 After weighing the carrier material to the specified values, the nitrogen adsorption isotherm at 77K was measured using an Anton-Paar QUADRASORB SI nitrogen adsorption analyzer. The nitrogen adsorption isotherm was then analyzed to obtain the pore volume of pores smaller than 10 nm. Specifically, the pore volume of pores between 2 and 10 nm was determined from the nitrogen adsorption isotherm using the BJH method. Then, the pore volume of pores smaller than 2 nm was determined using the MP method. Finally, the pore volume of mesopores (pore volume of pores smaller than 10 nm) was calculated by adding the pore volume of pores between 2 and 10 nm and the pore volume of pores smaller than 2 nm. This mesopore volume is the sum of the volumes of pores with a diameter of 10 nm or less (internal pores and minute external pores). The calculation results are shown in Table 1.

[0065] (2) Measurement of macropores by mercury porosimetry In this evaluation, mercury porosimetry was performed to measure the pore volume of macropores in carbon support materials. Specifically, each carbon support material was subjected to a drying treatment (120°C, 4 hours). Then, using a mercury porosimetry analyzer (Autopore IV9520) manufactured by micromeritics, the pore size distribution (distribution range: approximately 0.0018 to 100 μm) of the dried support material was determined. The pore size was calculated using Washburn's formula. From the pore size distribution based on mercury porosimetry, the pore volume of macropores, mainly external pores (pore volume at l0 to l50 nm) was calculated. The results are shown in Table 1.

[0066] (3) Measurement of load density In this evaluation, the bulk density of carbon carrier materials was measured when a load of 4 kN was applied. Specifically, each carbon carrier material was subjected to a drying treatment (110°C, 12 hours). Then, 1.0 g of the carrier material was subjected to a low-resistivity resistivity meter (Rolester GX MCP-T700, manufactured by Nitto Seiki Airanatech Co., Ltd.) and the bulk density when a load of 4 kN was applied was calculated. The results are shown in Table 1.

[0067] 3. Performance evaluation test of carbon support material (1) Preparation of evaluation cells Dispersions were prepared by dispersing each example's carrier material in a 0.1N nitric acid solution. Next, a dinitrodiammineplatinum nitric acid solution was added to the dispersion and stirred for 30 minutes. Then, ethanol was added to the stirred solution and heated under reflux for 2 hours. This produced electrode materials in which Pt was supported on carbon carrier materials. Next, the electrode materials were separated by filtration, washed with pure water, and then dried (80°C, 15 hours). Finally, these electrode materials were calcined at 700°C for 2 hours.

[0068] Next, a dispersion liquid in which the fired electrode material and the ionomer were dispersed in an organic solvent was prepared. Then, by applying this dispersion liquid to a fluororesin sheet, an electrode for an air electrode (cathode) was fabricated. On the other hand, for the hydrogen electrode (anode), an electrode material in which a catalytic metal was supported on a carbon material of Ketjen black was used. Note that the anode was fabricated by the same procedure as the cathode. Then, the respective electrodes were arranged such that the anode and the cathode faced each other through a polymer electrolyte membrane (NR-211). And after laminating each layer using hot pressing, diffusion layers were provided on both outer sides to construct an evaluation cell.

[0069] (2) Evaluation of Initial Performance Using a fuel cell power generation characteristic evaluation system manufactured by Mikura Laboratory Co., Ltd., the performance of the evaluation cell of each example was evaluated. Specifically, in an environment with a cell temperature of 90°C and a humidity of 83%, air was supplied to the cathode side at a flow rate of 2.0 L / min, and hydrogen was supplied to the anode side at a flow rate of 0.5 L / min. And the voltage value was measured within the range of a current density of 0.1 to 1.0 A / cm 2 . The measurement results are shown in Table 1.

[0070] (3) Evaluation of Performance after Durability After conducting a durability test in which power generation under the same conditions as the above (2) evaluation of initial performance was continued at 1.3 V for 120 minutes, the voltage value within the range of a current density of 0.1 to 1.0 A / cm 2 was measured. This was taken as the voltage value after the durability test. The measurement results are shown in Table 1. Note that the "voltage value after durability test" in Table 1 describes the relative value when the voltage value of the initial performance is taken as 100%.

[0071]

Table 1

[0072] First, as shown in Table 1 and Figures 4-5, in Examples 1-3, carrier materials containing a large number of carbon particles (large-diameter particles) of 100 nm or more were fabricated. In Examples 1-3, cross-linked sections, which are beam-like portions with a thickness of 70 nm or more, were formed. Multiple carbon particles were connected via these cross-linked sections. This is presumed to be because a mold containing dispersed mesoporous silica was used, allowing a large amount of carbon source material to adhere to the mold. The carbon carrier materials in Examples 1-3 achieved both excellent initial performance of 0.8V or higher and excellent durability of 97% or higher. In particular, as shown by the dotted line in Figure 8, a trade-off relationship was observed in conventional commercially available products (Comparative Examples 1-3), where improved initial performance led to decreased durability. On the other hand, Examples 1-3 overcame this trade-off relationship, achieving a high level of both initial performance and durability. Comparative Example 4, while possessing excellent initial voltage, resulted in a low post-durability voltage. This is presumed to be because a sufficiently thick cross-linking section was not formed, and the carrier structure was damaged during durability testing.

[0073] The specific examples of the technologies disclosed herein have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples described above. [Explanation of symbols]

[0074] 1. Carbon carrier material (carrier material) 10 Carbon particles 10L Large-diameter particles 10S small diameter particles 12 Internal pores 20 Bridge 30 External pores

Claims

1. A carbon support material containing multiple carbon particles, In the particle size distribution based on the number of particles observed using surface SEM, the proportion of large-diameter particles with an equivalent circle diameter of 100 nm or more was 70% or more. Internal pores with a diameter of 10 nm or less are formed inside the aforementioned large-diameter particles. The aforementioned plurality of carbon particles are joined together via cross-linking portions having an average thickness of 70 nm to 150 nm. A carbon support material in which external pores are formed in the region surrounded by the plurality of carbon particles and the crosslinking portion.

2. The carbon carrier material according to claim 1, wherein the average pore diameter of the external pores, based on surface SEM observation, is 10 nm or more and 150 nm or less.

3. The carbon carrier material according to claim 1 or 2, wherein the volume of mesopores, which have a pore diameter of 2 nm or more and 10 nm or less based on nitrogen adsorption, is 0.18 ml / g or more and 0.5 ml / g or less.

4. The carbon carrier material according to claim 1 or 2, wherein the volume of macropores with a pore diameter of 10 nm or more and 150 nm or less, based on the mercury intrusion method, is 0.5 ml / g or more and 1.4 ml / g or less.

5. The carbon carrier material according to claim 1 or 2, wherein the bulk density when a load of 4 kN is applied is 0.6 g / ml or less.

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