Carbon carrier 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 a carbon support material for a fuel cell. [Background technology]

[0002] In recent years, research into fuel cells has been progressing in order to address environmental issues such as air pollution. This type of fuel cell has a laminated structure in which an anode and a cathode face each other with an electrolyte sandwiched between them. The anode and cathode are electrically connected by a conductive member such as an electric wire. In a fuel cell with such a 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 (H + ) and electrons (e - ) and then transported through the electrolyte to hydrogen ions (H + ) is transferred to the cathode, and electrons (e - ) moves to the cathode. Meanwhile, the cathode is supplied with an oxygen-containing gas such as air. At the cathode, hydrogen ions (H + ) and electrons (e - ) reacts with oxygen (O2) to produce water (H2O).

[0003] The electrodes (anode, cathode) of the fuel cell configured as described above use electrode materials in which a catalytic metal is supported on a carbon support material. One example of the carbon support material for this fuel cell is a support material containing carbon particles with minute pores inside (mesoporous carbon). This mesoporous carbon has an extremely large specific surface area, which 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, including a first step of preparing mesoporous silica to serve as a template; a second step of depositing carbon within 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. This production method uses mesoporous silica with a bead-and-reel structure in which multiple primary particles are connected as the template. As a result, the produced mesoporous carbon has a bead-and-reel structure similar to that of the template (mesoporous silica). Patent Document 1 states that mesoporous carbon with this bead-and-reel structure can ensure an appropriate amount of voids in the air electrode catalyst layer (electrode), thereby suppressing flooding. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-84852 Summary of the Invention [Problem to be solved by the invention]

[0006] In general, fuel cells are constrained along the lamination direction of the anode, electrolyte, and cathode. This prevents gaps from forming at the interface between the layers. However, if the structure of the support material is destroyed by the constraining pressure, the voids in the electrode are blocked, resulting in a significant decrease in power generation performance. Furthermore, since the cathode is exposed to water during power generation, the strength of the support material gradually decreases due to oxidation of the carbon. In particular, mesoporous carbon has a large specific surface area, making it prone to strength loss due to oxidation. From these perspectives, there has been a recent demand for highly durable carbon support materials that can maintain excellent power generation performance even when power generation is continued for long periods of time. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present inventors investigated the causes of the low durability of conventional carbon support materials (mesoporous carbon) and discovered the following. As described above, conventional support materials have a bead-and-loop structure in which multiple primary particles (carbon particles) are connected to ensure voids within the electrode. However, this bead-and-loop structure is prone to weakening the strength of the junctions because multiple carbon particles are joined at points. Furthermore, if the strength of the junctions is further weakened by oxidation, structural destruction originating from the junctions can easily occur. Based on this finding, the present inventors believed that a highly durable support material could be realized if multiple carbon particles could be joined via strong beam-like connecting portions (bridges) having a certain thickness or greater (typically 70 nm or greater). Furthermore, in a support material with such a structure, external pores surrounded by the bridges and carbon particles are formed, ensuring a sufficient specific surface area and enabling favorable power generation efficiency. Based on this finding, the present inventors conducted various experiments and studies and ultimately developed a carbon support material having the following configuration.

[0008] The carbon support material (1) disclosed herein is a material containing a plurality of carbon particles. In a number-based particle size distribution based on surface SEM observation of such a carbon support material, the proportion of large-diameter particles having a circle-equivalent diameter of 100 nm or more is 70% by number or more, and internal pores having a pore diameter of 10 nm or less are formed inside the large-diameter particles. Furthermore, in the carbon support material disclosed herein, the plurality of carbon particles are bonded via bridges having an average diameter of 70 nm to 150 nm, and external pores are formed in regions surrounded by the plurality of carbon particles and the bridges.

[0009] First, the carbon support material disclosed herein contains a large number of large-diameter particles of 100 nm or more. This reduces the number of junctions between carbon particles. Furthermore, in this support material, beam-like connecting portions (bridges) with an average thickness of 70 nm or more are formed at the junctions between carbon particles. These configurations enable the realization of a support material with excellent durability. Furthermore, in this support material, internal pores of 10 nm or less are formed inside the large-diameter particles. Furthermore, by limiting the thickness of the bridges to 150 nm or less, sufficiently large external pores are formed. These configurations enable the support of a large amount of catalytic 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 can achieve both high levels of durability and power generation efficiency.

[0010] In the carbon support material (2) disclosed herein, the carbon support material described in (1) above has an external pore having an average pore diameter of 10 nm or more and 150 nm or less based on surface SEM observation, thereby achieving both durability and power generation efficiency at an even higher level.

[0011] The carbon support material (3) disclosed herein is the carbon support material according to (1) or (2) above, in which the volume of pores having a pore diameter of 10 nm or less as determined by a nitrogen adsorption method is 0.18 ml / g or more and 0.5 ml / g or less, thereby achieving both durability and power generation efficiency at an even higher level.

[0012] The carbon support material (4) disclosed herein is the carbon support material according to any one of the above (1) to (3), in which the volume of pores having a pore diameter of 10 nm to 150 nm as determined by mercury porosimetry is 0.5 ml / g to 1.4 ml / g, thereby achieving both durability and power generation efficiency at an even higher level.

[0013] The carbon support material (5) disclosed herein is the carbon support material according to any one of the above (1) to (4), and has a bulk density of 0.6 g / ml or less when a load of 4 kN is applied, thereby ensuring higher durability. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of the carbon support material disclosed herein. [Figure 2] FIG. 2 is a flow chart illustrating an example of a method for producing the carbon support material shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of a conventional carbon support material. [Figure 4] FIG. 4 is a surface SEM image (200,000x magnification) of Example 3. [Figure 5] FIG. 5 is a cross-sectional SEM image (200,000x 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 endurance testing for each example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the technology disclosed herein are described below with reference to the drawings. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (such as the detailed structure of a fuel cell) can be understood as design matters for 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 common technical knowledge in the relevant field. Furthermore, the expression "A to B" indicating a numerical range in this specification means "greater than A and less than B," and includes "greater than A and less than B."

[0016] 1. Carbon support material An embodiment of the carbon support material disclosed herein will be described below: Fig. 1 is a cross-sectional view schematically showing one example of the carbon support material disclosed herein.

[0017] The carbon support material 1 shown in FIG. 1 contains a plurality of carbon particles 10. In this carbon support material 1, in a number-based particle size distribution based on surface SEM observation, the proportion of large-diameter particles 10L having a circle-equivalent diameter of 100 nm or more is 50% or more by number, and internal pores 12 having an average pore diameter of 10 nm or less are formed inside these large-diameter particles 10L. Furthermore, the plurality of carbon particles 10 are joined via beam-like connecting portions (bridge portions 20) having an average diameter of 70 nm to 150 nm. External pores 30 are formed in the region surrounded by the plurality of carbon particles 10 and the bridge portions 20. A carbon support material 1 having such a configuration can realize a fuel cell that achieves both high levels of power generation efficiency and durability. A specific description will be given below.

[0018] (1) Components of carbon support material First, the carbon support material 1 is a structure whose main component is carbon. Here, "mainly composed of carbon" means that elements other than carbon are not intentionally included. Therefore, the carbon support material 1 may contain unavoidable impurities (metal elements, metalloid elements) derived from raw materials, manufacturing processes, etc. Examples of impurities that may be contained in the carbon support 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, the term "carbon support material" as used herein refers to a structure in which the carbon content is 70% or more (preferably 75% or more, more preferably 80% or more, and particularly preferably 85% or more) when the total number of atoms of metal elements, metalloid elements, and carbon elements is taken as 100%. The upper limit of the carbon content is not particularly limited and may be 100%, 95% or less, or 90% or less.

[0019] (2) Carbon particles The carbon support material 1 disclosed herein includes a plurality of carbon particles 10. The carbon particles 10 shown in FIG. 1 include large-diameter particles 10L and small-diameter particles 10S. In this specification, "large-diameter particles 10L" refers to carbon particles 10 having a particle diameter of 100 nm or more in surface SEM observation. Meanwhile, "small-diameter particles 10S" refers to carbon particles 10 having a particle diameter of less than 100 nm in surface SEM observation. The "particle diameter in surface SEM observation" in this specification is measured according to the following procedure. First, any carbon particle is selected in a surface SEM photograph at a predetermined magnification (e.g., 200,000 times). Next, an auxiliary line is drawn to form a rectangle circumscribing the selected carbon particle. 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." The area of ​​an ellipse having these major and minor axes is then calculated. The diameter of a circle having the same area as the ellipse is considered to be the "particle diameter of the carbon particle."

[0020] In the carbon support material 1 disclosed herein, the proportion of large-diameter particles 10L in the number-based particle size distribution based on surface SEM observation is 70% by number or more. In other words, this carbon support material 1 contains more large-diameter particles 10L than small-diameter particles 10S. This reduces the number of bonding portions between carbon particles 10, thereby contributing to improved durability of the support material 1. The proportion of large-diameter particles 10L is preferably 75% by number or more, more preferably 80% by number or more, and particularly preferably 88% by number or more. This further improves the durability of the support material 1. On the other hand, as the proportion of large-diameter particles 10L decreases, the specific surface area of ​​the support material 1 increases, which makes it easier to improve power generation efficiency. From this perspective, the upper limit of the proportion of large-diameter particles 10L is preferably 98% by number or less, more preferably 96% by number or less, even more preferably 94% by number or less, and particularly preferably 92% by number 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 support material. Next, the particle diameter of each carbon particle is measured according to the procedure described above. Next, the particle diameters (circle-equivalent diameters) of the measured carbon particles are arranged in order of particle diameter to create a number-based particle size distribution. Then, the proportion of large-diameter particles (carbon particles with a particle diameter of 100 nm or more) among the selected 50 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 10L. Although not shown in FIG. 1, these internal pores 12 are connected to the outside of the large-diameter particles 10L. Therefore, in this carbon support material 1, a catalytic metal can be supported in the internal pores 12 (inside the large-diameter particles 10L). Furthermore, when a fuel cell electrode is formed, a target fluid (fuel gas, oxygen-containing gas, etc.) can be introduced into the internal pores 12. As a result, despite containing many large-diameter particles 10L, a large specific surface area can be ensured, thereby achieving excellent power generation efficiency. Note that the "pore diameter of the internal pores" in this specification is measured according to the following procedure. Specifically, any carbon particle is selected from a cross-sectional SEM photograph taken at a predetermined magnification (e.g., 200,000 times). Next, a binary image of the selected carbon particle is obtained. Then, the largest circle inscribed in the pore (internal pore) present inside the large particle is drawn, and the diameter of this largest circle is defined as the "pore diameter of the internal pore."

[0022] The average number of internal pores 12 present within one 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 support 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 one large-diameter particle 10L, the strength of the support material 1 may decrease. From this perspective, 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 within an arbitrary area of ​​the large-diameter particle 10L is measured in a cross-sectional SEM image of the support material 1. Next, the number of internal pores 12 is divided by the area to obtain the number of internal pores per unit area. Next, in the number-based particle size distribution based on surface SEM observation, the average particle size of large 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 size and the number of internal pores per unit area.

[0023] The carbon support 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) as determined by a nitrogen adsorption method. This ensures a larger specific surface area, thereby achieving even better power generation efficiency. Note that the term "mesopores" as used herein refers not only to the internal pores 12 and external pores 30, but also to minute pores present in the carbon support material 1. Specifically, mesopores refer to pores with a pore diameter of 10 nm or less in a nitrogen adsorption isotherm measured using a nitrogen adsorption method. Experiments conducted by the present inventors have confirmed that the carbon support material 1 disclosed herein has a tendency to have an increased mesopore volume because a large number of internal pores 12 with a pore diameter of 10 nm or less are formed within the large-diameter particles 10L. On the other hand, if the mesopore volume becomes too large, the strength of the large-diameter particles 10L may be reduced. From this viewpoint, the upper limit of the mesopore volume 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 bridged portions 20 refer to beam-shaped connections with an average thickness of 70 nm or more among the connections connecting multiple carbon particles 10. Specifically, SEM observation of a carbon support material reveals point-bonded connections where carbon particles are directly bonded to each other, as well as beam-shaped connections spanning spaced carbon particles. In this specification, the term "bridged portion" refers to a beam-shaped connection having a certain thickness or greater among these connections. More specifically, when the thicknesses of 100 beam-shaped connections are measured during SEM observation of a carbon support material, if the average thickness is 70 nm or greater, the carbon support material can be said to contain bridged portions. In the support material 1 disclosed herein, the average thickness of the bridged portions 20 is set to 70 nm or greater and 150 nm or less. This significantly improves the durability of the support material 1. Below, the bridged portions 20 of the carbon support material 1 disclosed herein will be described in comparison with a conventional carbon support material 100 shown in FIG. 3.

[0025] First, as shown in FIG. 3 , a conventional carbon support material 100 includes multiple carbon particles 110 with minute internal pores 112. This carbon support material 100 has a bead-and-loop structure in which the multiple carbon particles 110 are connected to one another. In a carbon support material 100 with this bead-and-loop structure, the majority of the carbon particles are directly joined to one another through point-bonding, which tends to reduce the strength of the connecting portions 100J. Furthermore, the connecting portions 100J of this bead-and-loop structure are easily oxidized to the interior when exposed to water, resulting in a more significant decrease in strength. Therefore, in a fuel cell using the conventional carbon support material 100, structural destruction originating from the connecting portions 100J is likely to occur during long-term power generation. As a result, the external pores surrounded by the multiple carbon particles 110 collapse, and the performance of the fuel cell declines as power generation continues.

[0026] On the other hand, as shown in FIG. 1, the carbon support material 1 disclosed herein has a plurality of carbon particles 10 bonded together via bridges 20, which are beam-shaped connecting portions with an average thickness of 70 nm or more. These bridges 20 have higher strength than the connecting portions 100J (see FIG. 3) of the conventional support material 100. Furthermore, even when exposed to water or the like, the bridges 20 only oxidize on the surface, and the internal strength is easily maintained. Therefore, the support material 1 disclosed herein is less likely to suffer structural breakdown originating from the bonding portions (bridges 20) between the carbon particles 10, even when power generation in a fuel cell is continued for a long period of time. As a result, the support material 1 disclosed herein can exhibit superior durability compared to conventional support materials.

[0027] Note that as the crosslinked portions 20 become thicker, the strength of the crosslinked portions 20 tends to improve. Furthermore, as the crosslinked portions 20 become thicker, they become less susceptible to a decrease in strength due to oxidation. From these viewpoints, the average thickness of the crosslinked portions 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 crosslinked portions 20 become too thick, the pore volume of the external pores 30 described below decreases, which may result in a decrease in power generation efficiency. From this viewpoint, the average thickness of the crosslinked portions 20 is set to 150 nm or less. Furthermore, from the viewpoint of achieving more favorable power generation efficiency, the average thickness of the crosslinked portions 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 crosslinking moieties 20 connected per 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 allows for a support material 1 with even greater durability. Meanwhile, the upper limit of the average number of crosslinking moieties 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, the "average number of crosslinking moieties 20" refers to the average number of crosslinking moieties in a planar view measured based on a surface SEM image. This average number of crosslinking moieties is measured by the following procedure. First, 50 carbon particles 10 are arbitrarily selected from the surface SEM image of the support material 1. Next, the number of crosslinking moieties 20 connected in each of the selected carbon particles 10 is measured, and the average number of crosslinking moieties 20 connected for the selected carbon particles 10 is calculated.

[0029] (4) External pores The external pores 30 are cavities formed in an area surrounded by multiple carbon particles 10 and bridging portions 20. These external pores 30 serve as flow paths for various fluids (fuel gas, oxygen-containing gas, water, etc.). As shown in FIG. 1, in the support material 1 disclosed herein, bridging portions 20 are interposed between multiple carbon particles 10, thereby forming a bridged bead-and-seal structure containing many external pores 30 of suitable sizes. Therefore, the support material 1 disclosed herein can exhibit superior power generation efficiency compared to a conventional support material 100 (see FIG. 3) in which multiple carbon particles 110 are directly bonded to each other. Furthermore, as described above, the support material 1 disclosed herein has bridging portions 20 with excellent strength, and therefore can maintain this bridged bead-and-seal structure with external pores 30 for a long period of time.

[0030] 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 increases the specific surface area of ​​the support material 1 and makes it easier for fluid to pass through, thereby 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 support material 1. The "average pore diameter of the external pores 30" in this specification is measured by the following procedure. First, 100 external pores 30 are arbitrarily selected in the surface SEM image of the support material 1. Next, a rectangular auxiliary line is drawn circumscribing the selected external pores 30. Next, the length of the long side of the rectangular auxiliary line is defined as the "long diameter of the external pore," and the length of the short side is defined as the "short diameter of the external pore." Next, the area of ​​the ellipse having the major axis and minor axis is calculated. Next, the diameter of a circle having the same area as the ellipse is regarded as the "pore diameter of the external pores." Then, the average value of the pore diameters of the selected external pores 30 is calculated.

[0031] Furthermore, in the carbon support material 1 disclosed herein, the volume of the macropores measured by mercury intrusion porosimetry is preferably 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 more optimal fluid flow paths, thereby improving power generation efficiency. Note that the term "macropores" as used herein refers not only to the internal pores 12 and the external pores 30, but also to large pores present in the carbon support material 1. Specifically, it refers to pores with a pore diameter of 10 nm or more and 150 nm or less in the pore size distribution measured by mercury intrusion porosimetry. Note that if the volume of the macropores becomes too large, the strength of the support material 1 may decrease. From this perspective, the upper limit of the volume of the support 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 support material 1 disclosed herein contains a large number of large-diameter particles 10L of 100 nm or more. This reduces the number of bonding portions between the carbon particles 10. Furthermore, in this support material 1, bridges 20 with an average thickness of 70 nm or more are formed at the bonding portions between the carbon particles 10. This allows the carbon particles 10 to be firmly bonded together. These configurations enable the support material 1 to have excellent durability.

[0033] Furthermore, in this carrier material 1, internal pores 12 of 10 nm or less are formed inside the large-diameter particles 10L. In this carrier material 1, the thickness of the bridge portions 20 is limited to 150 nm or less. These configurations ensure a sufficient specific surface area of ​​the carrier material 1. As a result, a large amount of catalytic metal can be supported, and the target fluid can pass through efficiently, thereby 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 both high levels of durability and high power generation efficiency.

[0035] As described above, the carrier material 1 disclosed herein has high-strength crosslinks 20, and therefore can maintain a bridged bead-and-seal structure having a plurality of external pores 30 even when a 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. The carrier material 1 having such excellent strength can particularly contribute to improving the durability of fuel cells.

[0036] 2.Method for producing carbon support material Next, an example of a method for producing the carbon support material disclosed herein will be described with reference to Fig. 2. Fig. 2 is a flowchart showing an example of the method for producing the carbon support material disclosed herein. Note that the following description is not intended to limit the support material disclosed herein to one produced by the following production method.

[0037] 2, the method for producing a support material disclosed herein includes 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 template. Examples of mesoporous particle materials include ceramic materials such as silica, magnesia, alumina, and zeolite. Among these, silica is particularly preferred. Examples of mesoporous particles made of silica include mesoporous silica and fumed silica. Using these materials makes it easy to control the particle size of the large particles 10L and the pore size of the internal pores 12. For example, the average particle size of the mesoporous particles is preferably 7 nm or more and 200 nm or less. This allows for easy production of large 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 1 nm or more and 10 nm or less. This facilitates the formation of internal pores 12 with a size of 2 nm or more and 10 nm or less within the large particles 10L. The specific means for preparing mesoporous particles is not particularly limited, and conventional production means can be used without particular limitation. Furthermore, mesoporous particles may be used as purchased.

[0039] (2) Carbon adhesion process S20 In this step, a carbon component is attached to the mesoporous particles. This produces a composite material containing the mesoporous particles, carbon particles 10, and crosslinked portions 20. The carbon attachment step S20 shown in Fig. 2 includes a carbon source spraying step S22 and a first heat treatment step S24. Each step will be described below.

[0040] (a) Carbon source attachment step S22 In this process, a liquid carbon source is attached to the mesoporous particles. The carbon source is attached 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 producing carbon through pyrolysis. Examples of such carbon sources include sugars such as sucrose, wood sugar, and glucose, and polymer precursors such as furfuryl alcohol and aniline. In this process, the mesoporous particles may be added dropwise to the liquid carbon source and stirred. This allows the carbon source to be attached appropriately. Alternatively, a spray-drying method or the like may 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 (particularly the internal pores 12 of the large-diameter particles 10L) is adsorbed into the gaps between the mesoporous particles. This carbon source adsorbed into the gaps between the mesoporous particles serves as a precursor for the crosslinked portions 20. The amount of carbon source supplied in this step is preferably 1.5 times or more 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 facilitates the formation of beam-like connecting portions (crosslinked portions 20) with a diameter of 70 nm or more. Note that if an excessive amount of carbon source is supplied, the external pores 30 may be filled. From this perspective, the upper limit of the amount of carbon source supplied is preferably 6.0 times or less 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 bridge portion 20 from becoming excessively thick.

[0042] (b) First heat treatment step S24 In this step, the mesoporous particles to which the carbon source is attached are heated. This step is not particularly limited, and any conventionally known method can be used. 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, vacuum, etc.). This carbonizes (or partially graphitizes) the carbon source attached to the interior and surfaces of the mesoporous particles. As a result, carbon particles 10 (typically large-diameter particles 10L) are produced. Meanwhile, the carbon source adsorbed in the gaps between the mesoporous particles is carbonized (or partially graphitized) to form bridged portions 20. As described above, in this manufacturing method, the dispersed mesoporous particles are used as a template, and a carbon source exceeding the volume of the internal pores of the mesoporous particles is attached. This allows the production of a support material 1 in which multiple carbon particles 10 are bonded together via bridged portions 20.

[0043] The heating temperature in this step is preferably 500°C or higher and 1200°C or lower. This allows the carbon source to be appropriately carbonized (or partially graphitized) while suppressing the reaction between silica and carbon. Furthermore, in this step, 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, making it easier to produce a support material 1 with a suitable structure.

[0044] It is preferable that the carbon attachment step S20 is repeated multiple times until the desired carbon particles 10 and crosslinked portions 20 are formed. For example, the carbon attachment step S20 is preferably performed once or more, more preferably twice or more, and particularly preferably three times or more. This makes it possible to form carbon particles 10 of an appropriate size and crosslinked portions 20 of an appropriate thickness. On the other hand, the upper limit of the number of times the carbon attachment step S2 is performed is preferably six times or less, more preferably five times or less, and particularly preferably four times or less. This prevents the formation of crosslinked portions 20 that are thicker than necessary, and allows the formation of external pores 30 of sufficient size.

[0045] (4) Template removal step S30 In this step, only the mesoporous particles are removed from the composite material containing mesoporous particles, carbon particles 10, and crosslinked portions 20. This results in a support material 1 having carbon particles 10 and crosslinked portions 20. The means for removing the template (mesoporous particles) is not particularly limited, and any conventionally known means appropriate for the components of the mesoporous particles can be used. For example, when removing mesoporous silica, methods such as heating the support material in an alkaline solution (such as an aqueous NaOH solution) or etching with an aqueous hydrofluoric acid solution can be used.

[0046] (5) Second heat treatment step S40 In this step, the support material 1 is heated again. This promotes carbonization (or graphitization) of the support material 1, thereby improving performance such as durability. The second heat treatment step S40 is preferably performed after the template removal step S30. This prevents the carbon components (carbon particles, crosslinked portions, etc.) from reacting with the 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 the support material 1 to be appropriately graphitized. On the other hand, from the viewpoint of energy efficiency, the upper limit of the heating temperature is preferably 2300°C or lower, more preferably 2200°C or lower.

[0047] As described above, the support material 1 shown in Fig. 1 can be appropriately produced by the production method shown in Fig. 2. The produced support material 1 has strong crosslinked portions 20 and a large specific surface area, and therefore can achieve both high levels of durability and power generation efficiency.

[0048] 3.Applications The carbon support material disclosed herein has been described above. A fuel cell electrode material can be produced by supporting a predetermined catalytic metal on this carbon support material. Specifically, the support material disclosed herein is first dispersed in a solution of the catalytic metal. Next, the catalytic metal in the dispersion is precipitated by heating or the like. This allows the catalytic metal to be supported on the support material. As described above, the support material disclosed herein has a large specific surface area, allowing it to support a large amount of catalytic metal. Furthermore, the support material disclosed herein is resistant to structural destruction during use, allowing the fluid to be treated to maintain proper contact with the catalytic 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 (Pt, Pd, Rh, etc.) can be used without any particular restrictions. The amount of metal catalyst supported is also not particularly limited, and can be changed as appropriate depending on the specifications of the fuel cell. The support material disclosed herein can be used for both the anode and cathode of a fuel cell. However, because the support material disclosed herein has the property 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] [Test example] Test examples relating to the technology disclosed herein will be described below, but it is not intended that the technology disclosed herein be limited to those shown in these test examples.

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

[0052] 1. Preparation of test samples (1) Example 1 In Example 1, 33.1 g of mesoporous silica was prepared as a template. A liquid carbon source was then added dropwise to the mesoporous silica, followed by stirring for 5 minutes to attach the carbon source to the template. Next, the template with the attached carbon source was subjected to a drying treatment and a heat treatment (first heat treatment) to carbonize and partially graphitize the carbon source. In this experiment, three carbon generation treatments were performed under different conditions. The conditions for each carbon generation treatment were as follows:

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

[0054] [Second and third times] Carbon source: furfuryl alcohol Amount of carbon source: 1.5 times the pore volume of mesoporous silica Drying treatment: Air atmosphere, 110℃, 9 hours Firing treatment: Nitrogen atmosphere, 800°C, 1 hour

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

[0056] Next, the dried carbon material was subjected to a second heat treatment. The heating temperature in this second heat treatment was set to 1900°C. The heating time was set to 0.5 hours. The heating atmosphere was set to a vacuum atmosphere. In this way, the carbon support material of Example 1 was produced.

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

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

[0059] (4) Comparative Examples 1 to 3 In this test, a commercially available carbon support material was prepared as a comparative example. The carbon support materials used in each example are as follows:

[0060] Comparative Example 1: Carbon black manufactured by Tokai Carbon Co., Ltd. (product number: TOKABLACK #3845) Comparative Example 2: Conductive carbon black manufactured by Cabot Corporation (product number: VULCAN XC72R (registered trademark)) Comparative Example 3: Carbon black (product number: Li-400) manufactured by Denka Co., Ltd.

[0061] (5) Comparative Example 4 In this test, a carbon support similar to that described in Japanese Patent No. 7153005 was prepared as Comparative Example 4. In Comparative Example 4, furfuryl alcohol (FA) was added to mesoporous silica in an amount 0.95 times the pore volume and allowed to penetrate into the silica pores. This was heat-treated at 110°C for 9 hours to polymerize the FA. This was then heat-treated in a nitrogen atmosphere at 800°C for 1 hour to carbonize and graphitize the FA. This process was repeated twice to obtain a mesoporous silica / carbon composite. The template (mesoporous silica) was then removed using the same procedure as in Example 1. The composite was then heat-treated at 1800°C for 0.5 hours in a vacuum atmosphere. 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 support materials (1)SEM analysis In this test, the structure of the carbon support material of each example was analyzed. Specifically, a surface SEM image and a cross-sectional SEM image of the carbon support material of each example were obtained. The surface SEM image of Example 3 is shown in FIG. 4, and the cross-sectional SEM image is shown in FIG. 5. Meanwhile, the surface SEM image of Comparative Example 3 is shown in FIG. 6, and the cross-sectional SEM image is shown in FIG. 7.

[0063] In this test, the particle size distribution of carbon particles in the support material was measured by image analysis of surface SEM images of each sample. Based on this particle size distribution, the proportion (%) of large-diameter particles (carbon particles with a circle-equivalent diameter of 100 nm or more) was measured. In addition, in this image analysis of the surface SEM images, the average thickness of the beam-like connections between the carbon particles was also measured. If the average thickness of the beam-like connections was 70 nm or more, it was determined that strong bridges had been formed between the carbon particles. Note that in this test, connections where carbon particles were point-bonded together were not included in the measurement of the thickness of the connections. In this test, the pore size distribution of internal pores inside the carbon particles was measured for Example 3 by image analysis of cross-sectional SEM images. The proportion of internal pores with a diameter of 10 nm or less was then measured. The measurement results for each item are shown in Table 1.

[0064] (2) Mesopore measurement by nitrogen adsorption In this evaluation, nitrogen adsorption measurements were performed to measure the pore volume of mesopores in the support material. Specifically, each carbon support material was subjected to a drying treatment (120°C, 6 hours). Then, the surface area of ​​the support material was measured. 2 The support material was weighed so that the pore size was 10 nm or less, and then the nitrogen adsorption isotherm was measured at 77 K using an Anton-Paar nitrogen adsorption measuring device (QUADRASORB SI). The nitrogen adsorption isotherm was then analyzed to obtain the pore volume of 10 nm or less. Specifically, the pore volume of 2 to 10 nm was determined from the nitrogen adsorption isotherm using analysis based on the BJH method. The pore volume of 2 nm or less was then determined using the MP method. The pore volume of 2 to 10 nm and the pore volume of 2 nm or less were then added together to calculate the mesopore volume (pore volume of 10 nm or less). This mesopore volume is the total volume of pores with a pore 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 the carbon support material. Specifically, each carbon support material was dried (120°C, 4 hours). Then, using a mercury porosimetry measurement device (Autopore IV9520) manufactured by Micromeritics, the pore size distribution (distribution width: approximately 0.0018 to 100 μm) of the dried support material was determined. The pore size was calculated using the Washburn equation. The pore volume of macropores, mainly external pores (pore volume at 10 to 150 nm), was calculated from the pore size distribution based on mercury porosimetry. The results are shown in Table 1.

[0066] (3) Load density measurement In this evaluation, the bulk density was measured when a load of 4 kN was applied to the carbon support material. Specifically, a drying treatment (110°C, 12 hours) was performed on each carbon support material. Then, 1.0 g of the support material was subjected to a low-resistance resistivity meter (Loresta GX MCP-T700, manufactured by Nitto Seiki Air Analytec 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 materials (1) Preparation of evaluation cell A dispersion was prepared by dispersing each support material in a 0.1N nitric acid solution. Next, a dinitrodiammine platinum nitrate solution was added to this dispersion and stirred for 30 minutes. After stirring, ethanol was added to the solution and heated under reflux for 2 hours. This produced an electrode material in which Pt was supported on a carbon support material. The electrode material was then separated by filtration, washed with pure water, and dried (80°C, 15 hours). This electrode material was then calcined at 700°C for 2 hours.

[0068] Next, a dispersion was prepared by dispersing the calcined electrode material and ionomer in an organic solvent. This dispersion was then applied to a fluororesin sheet to fabricate an air electrode (cathode). For the hydrogen electrode (anode), an electrode material consisting of a catalyst metal supported on a Ketjen Black carbon material was used. The anode was fabricated using the same procedure as the cathode. The anode and cathode were then positioned so that they faced each other with a polymer electrolyte membrane (NR-211) in between. After bonding the layers together using a hot press, diffusion layers were installed on both sides to construct an evaluation cell.

[0069] (2) Initial performance evaluation The performance of each test cell was evaluated using a fuel cell power generation characteristic evaluation system manufactured by MicLab Co., Ltd. Specifically, under an environment of a cell temperature of 90°C and 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. Then, the current density was 0.1 to 1.0 A / cm. 2 The voltage values ​​were measured in the range of 1000 to 12000. The measurement results are shown in Table 1.

[0070] (3) Evaluation of performance after endurance A durability test was conducted in which power generation was continued for 120 minutes at 1.3 V under the same conditions as in the evaluation of initial performance in (2) above, and then a current density of 0.1 to 1.0 A / cm was applied under the same conditions. 2 The voltage values ​​were measured in the range of 100%. These were the voltage values ​​after the durability test. The measurement results are shown in Table 1. Note that the "voltage values ​​after the durability test" in Table 1 are relative values ​​with the voltage value of the initial performance set as 100%.

[0071] [Table 1]

[0072] First, as shown in Table 1 and Figures 4 and 5, in Examples 1 to 3, support materials containing a large number of carbon particles (large-diameter particles) of 100 nm or larger were prepared. Furthermore, in Examples 1 to 3, bridges, which are beam-like portions with a thickness of 70 nm or larger, were formed. Multiple carbon particles were connected via these bridges. This is presumably due to the use of a template in which multiple mesoporous silica particles were dispersed and a large amount of carbon source was attached to the template. The carbon support materials of Examples 1 to 3 simultaneously achieved excellent initial performance of 0.8 V or higher and excellent durability performance 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 to 3), in which improved initial performance resulted in decreased durability. On the other hand, in Examples 1 to 3, this trade-off relationship was overcome, and both initial performance and durability performance were achieved at a high level. Furthermore, Comparative Example 4 had excellent initial voltage but low post-durability voltage. This is presumably because the bridges were not formed thick enough, causing the carrier structure to break during the test.

[0073] While specific examples of the technology disclosed herein have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0074] 1 Carbon support material (support material) 10 carbon particles 10L Large particles 10S small diameter particles 12 Internal pores 20 Crosslinked part 30 external pores

Claims

1. 1. A carbon support material comprising a plurality of carbon particles, In a particle size distribution based on the number of particles obtained by surface SEM observation, the proportion of large particles having an equivalent circle diameter of 100 nm or more is 70% by number or more, internal pores having a pore diameter of 10 nm or less are formed inside the large-diameter particles, the plurality of carbon particles are bonded together via bridges having an average thickness of 70 nm or more and 150 nm or less; a carbon support material, wherein external pores are formed in a region surrounded by the plurality of carbon particles and the bridge portion;

2. The carbon support material according to claim 1 , wherein the external pores have an average pore diameter of 10 nm or more and 150 nm or less, as determined by surface SEM observation.

3. 3. The carbon support material according to claim 1, wherein the volume of mesopores having a pore diameter of 2 nm or more and 10 nm or less, as determined by a nitrogen adsorption method, is 0.18 ml / g or more and 0.5 ml / g or less.

4. 3. The carbon support material according to claim 1, wherein the volume of macropores having a pore diameter of 10 nm or more and 150 nm or less as determined by mercury intrusion porosimetry is 0.5 ml / g or more and 1.4 ml / g or less.

5. 3. The carbon support material according to claim 1, which has a bulk density of 0.6 g / ml or less when a load of 4 kN is applied thereto.

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