JP2006015345A - Carbon supported catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve dispersibility and increase activity by preventing local aggregation of catalyst fine particles on a carbon support without lowering the conductivity of the carbon support.
A carbon support 1 forms a higher order structure in which crystallites 7 having a diameter of 5 nm to 100 nm are three-dimensionally connected, and a neck portion 9 which is a boundary portion where the crystallites 7 are connected to each other. It has. The neck portion 9 is covered with a masking material 3 made of inorganic fine particles or organic fine particles, and in this state, catalyst fine particles 5 made of platinum or the like are adsorbed on the surface of the carbon support 1.
[Selection] Figure 1

Description

  The present invention relates to a carbon-supported catalyst in which catalyst fine particles are supported on the surface of a carbon support.

  A carbon-supported catalyst in which catalyst fine particles are supported on the surface of a carbon support is widely used for promoting various chemical reactions, but is currently often used as an electrode for a solid polymer electrolyte fuel cell. Yes.

  In such a carbon-supported catalyst, it is important to reduce the particle size of the catalyst particles and uniformly support them on the support in order to more effectively use the activity of the catalyst and minimize the amount of catalyst particles used. become. In particular, various methods as described below have been proposed in order to uniformly and highly support noble metal fine particles having a small particle size used as an electrode catalyst for a solid polymer electrolyte fuel cell on a carbon support.

1. Japanese Patent Publication No. 8-8989 In order to disperse and carry the noble metal fine particles on the carbon support in a highly dispersed manner, the three-dimensional structure of the carbon support is destroyed and the adsorption sites of the noble metal fine particles are increased. As a result, the noble metal fine particles are individually located at the adsorption sites and most of the noble metal fine particles are exposed on the surface, thereby preventing the surface area of the catalyst from being reduced due to the overlap or bonding between the noble metal fine particles.

2. JP, 2001-325964, A By using the effect that oxygen combined with conductive carbon as a carrier suppresses the growth of platinum particles as catalyst fine particles, even if the amount of platinum supported is increased, the crystallite particles of platinum The electrode has a high electrochemical metal surface area as a catalyst.

3. JP-A-6-106076 (JP-A-6-114274)
Carbon monoxide (ethylene and / or acetylene) coexists in the reaction solution in the process of dispersing the support in the reaction solution containing the supported metal ion and reducing the supported metal ion by the reducing agent and supporting it on the support. Thus, the growth of metal fine particles is suppressed, and a catalyst carrying monodispersed metal fine particles having a particle size of about 20 angstroms or less and a narrow particle size distribution width is obtained.
Japanese Patent Publication No. 8-8989 JP 2001-325964 A JP-A-6-106076 JP-A-6-114274

  The method of destroying the three-dimensional structure of carbon in prior art 1 and increasing the dispersibility by increasing the adsorption sites of the catalyst fine particles reduces the conductivity by destroying the three-dimensional structure of carbon. When a catalyst is used as an electrode of a fuel cell, it becomes a factor that reduces the efficiency of the fuel cell.

  On the other hand, carbon as a catalyst carrier forms a higher order structure in which crystallites having a diameter of 5 nm to 100 nm are three-dimensionally linked. A portion having a large surface area per unit volume, such as a neck portion which is a boundary portion where crystallites are connected to each other, has a high surface energy, and adsorption of catalyst fine particles occurs more easily than other portions. That is, when the catalyst fine particles are supported and adsorbed on the carbon support, the catalyst fine particles are easily adsorbed on the neck portion of the carbon support, and as a result, the catalyst fine particles tend to aggregate on the neck portion in the carbon microstructure. In such a state, it cannot be said that the atomized catalyst is working effectively.

  For this reason, the methods of suppressing the particle diameter of the catalyst particles in order to increase the catalyst specific surface area in the prior arts 2 and 3 described above, the catalyst fine particles having the small particle diameter are the above-mentioned necks on the carbon support. As a result, the surface area of the catalyst is reduced, so that the high activity is not exhibited.

  That is, in order to give the catalyst high activity, it is desirable that fine catalyst particles are uniformly and highly dispersedly supported on the carbon support surface without agglomeration.

  Accordingly, an object of the present invention is to increase the dispersibility and enhance the activity by preventing local aggregation of the catalyst fine particles on the carbon support without lowering the conductivity of the carbon support.

  In order to achieve the above object, the invention according to claim 1 is the carbon supported catalyst in which the catalyst fine particles are supported on the surface of the carbon support, wherein a part of the surface of the carbon support is coated with a masking material, The catalyst fine particles are supported.

  The invention according to claim 2 is the carbon-supported catalyst according to claim 1, wherein the carbon support forms a higher order structure in which crystallites are connected, and a part of the surface of the carbon support is formed by connecting the crystallites to each other. It is the neck part used as the boundary part which is present.

  The invention of claim 3 is the carbon-supported catalyst of claim 1 or 2, wherein the masking material is made of fine particles.

  The invention of claim 4 is the carbon-supported catalyst of claim 3, wherein the fine particles of the masking material have a diameter of 1 nm to 10 nm.

  When the diameter of the fine particles of the masking material exceeds 10 nm, it becomes impossible to selectively mask a specific portion of the carbon support where the catalyst fine particles are likely to aggregate. On the other hand, when the diameter of the fine particles of the masking material is less than 1 nm, it becomes difficult to disperse the colloid and the masking material does not function as a suitable masking material.

  According to a fifth aspect of the present invention, in the carbon support catalyst according to any one of the first to fourth aspects, the masking material is 4% to 40% by volume with respect to the carbon support.

  If the added amount of the masking material is less than 4% by volume with respect to carbon, the specific part of the carbon support where catalyst fine particles are likely to aggregate cannot be sufficiently covered, and the aggregation of catalyst fine particles can be effectively suppressed. I can't. On the other hand, when the addition amount of the masking material exceeds 40% by volume with respect to the carbon, the ratio of the masking material covering the carbon surface increases, so that the catalyst fine particles are not sufficiently supported on the carbon support. End up.

  According to the first aspect of the present invention, the portion of the carbon support surface on which the aggregation is likely to occur is previously covered with the masking material, whereby the aggregation of the catalyst fine particles on the carbon support surface can be suppressed. Further, by using the carbon-supported catalyst while adsorbing on the carbon support without removing the masking material described above, the masking material removal work becomes unnecessary, so that the catalyst fine particles are more easily deposited on the carbon support. A carbon-supported catalyst supported in a dispersed state can be obtained.

  According to the invention of claim 2, the catalyst fine particles are adsorbed on the carbon support in a state in which the neck portion of the carbon support on which the catalyst fine particles are likely to be adsorbed is previously coated with the masking material. Can be supported on a carbon support.

  According to the invention of claim 3, by using the fine-particulate masking material, the masking material is evenly distributed in the fine structure of the carbon support having a complicated higher order structure, and the part on which the carbon support surface is likely to aggregate is likely to occur. It can be reliably coated.

  According to the invention of claim 4, by setting the diameter of the fine particle-shaped masking material to 1 nm to 10 nm, it is possible to more reliably cover the portion where the carbon carrier surface is likely to aggregate.

  According to the invention of claim 5, it is possible to mask only a specific part of the surface of the carbon support where the aggregation of the catalyst fine particles is likely to occur without insufficient support of the catalyst fine particles on the carbon support. Can be supported in a highly dispersed state.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a method for producing a carbon-supported catalyst according to an embodiment of the present invention. (A) shows the carbon support 1 schematically. The carbon support 1 has a higher order structure in which crystallites 7 having a diameter of 5 nm to 100 nm are three-dimensionally connected, and includes a neck portion 9 that is a boundary portion where the crystallites 7 are connected to each other. Yes. As shown in FIG. 1B, the masking material 3 is adsorbed and covered on the neck portion 9.

  Next, from the state of FIG. 1B, the catalyst fine particles 5 are adsorbed on the surface of the carbon support 1 as shown in FIG. 1C. Further, the masking material 3 can be removed from the state of FIG. 1C as shown in FIG.

  As described above, the catalyst fine particles 5 are adsorbed on the carbon support 1 in a state where the neck portion 9 on which the catalyst fine particles 5 are likely to adsorb is coated with the masking material 3 in advance. It is carried on the carrier 1.

  The masking material 3 described above is an inorganic fine particle or organic fine particle that can be selectively removed after the step (c) of adsorbing on the surface of the carbon support 1 and supporting the catalyst fine particles 5 is completed. Any diameter may be used as long as the diameter is 1 nm to 10 nm.

  For example, metal colloid such as copper colloid, iron colloid, nickel colloid, cobalt colloid, zinc colloid, copper oxide colloid, iron oxide colloid, nickel oxide colloid, metal oxide colloid such as cobalt oxide colloid, or polyethylene colloid, There are polymer colloids such as polystyrene colloid, polymethyl acrylate colloid, polypropylene colloid, polyacrylonitrile colloid, polycarbonate colloid, and the masking material 3 is preferably easy to remove.

  That is, the masking material 3 is dissolved and removed by a suitable acidic solution that dissolves only the masking material 3 when a metal colloid or metal oxide colloid is used, and the masking material 3 is used when a polymer colloid is used. It is dissolved and removed by a suitable organic solvent that dissolves only the solvent.

  The masking material 3 is preferably made of an inorganic material or an organic material, and can remove the masking material supported on a part of the surface of the carbon support with an acidic solution or an organic solvent that does not dissolve the catalyst fine particles. According to this, it is possible to selectively remove only the masking material 3 while ensuring that the catalyst fine particles are supported on the carbon support.

  Here, if the diameter of the fine particles of the masking material 3 exceeds 10 nm, it becomes impossible to selectively mask the above-described neck portion 9 or the like where the catalyst fine particles 5 tend to aggregate. In addition, when the diameter of the fine particles of the masking material 3 is less than 1 nm, it is difficult to disperse the colloid, and the masking material 3 may not function as a suitable masking material 3. In any case, the intended effect cannot be obtained. A possibility arises.

  The fine particles of the masking material 3 are 4% to 40% by volume with respect to the carbon support 1. When the addition amount of the fine particles of the masking material 3 is less than 4% by volume with respect to the carbon support 1, a specific portion (neck portion 9) on the surface of the carbon support 1 where aggregation easily occurs is sufficiently covered. Therefore, the aggregation of the catalyst fine particles 5 cannot be effectively suppressed. On the other hand, when the addition amount of the fine particles of the masking material 3 exceeds 40%, the ratio of covering the surface of the carbon support 1 increases, so that the catalyst fine particles 5 cannot be supported on the carbon support 1. there is a possibility.

  The method for selectively adsorbing the masking material 3 to a specific part of the surface of the carbon support 1 typified by the neck portion 9, where the catalyst fine particles 5 tend to aggregate, is given priority over such a part. Therefore, it is only necessary to adsorb the appropriate amount of the masking material 5 to the carbon support 1 before the catalyst supporting step (c).

  In addition, when the carbon support catalyst obtained as described above is used as an electrode catalyst for a solid polymer electrolyte fuel cell, the masking material 3 is used if the masking material 3 does not affect the fuel cell performance. Even if it is not removed, it can be used as it is as an electrode catalyst. This eliminates the need for a masking material removal step, and thus a carbon-supported catalyst in which the catalyst fine particles 5 are supported on the carbon support 1 in a highly dispersed state can be obtained more easily.

  The carbon carrier 1 used as the electrode catalyst is not particularly limited as long as it has a large specific surface area and conductivity, and acetylene black, ketjen black, furnace black, activated carbon, graphite powder and the like can be used.

  Examples of the fine catalyst particles 5 that can be used as the electrode catalyst include platinum, platinum alloys, palladium, and iridium.

  In addition, by covering a portion of the carbon support surface where the catalyst fine particles 5 are likely to aggregate with the masking material 3 in advance, the aggregation of the catalyst fine particles 5 on the surface of the carbon support can be suppressed. 5 can be supported in a highly dispersed state, and the activity as a catalyst can be enhanced. Further, in this case, since the carbon three-dimensional structure is not destroyed, a decrease in carbon conductivity is avoided, so that the efficiency of the fuel cell when this carbon-supported catalyst is used as an electrode of the fuel cell is reduced. Can be prevented. Further, by using the carbon-supported catalyst without covering the above-described masking material 3 without removing the masking material 3, a masking material removing step is not required, so that the catalyst fine particles 5 can be more easily attached to the carbon carrier. A carbon-supported catalyst supported in a highly dispersed state can be obtained.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  1 g of carbon was dispersed in purified water, and 1 wt. 100 g of a copper colloid solution containing 1% copper (colloid particle diameter: 2 nm) is added, and a masking step is performed while stirring at room temperature.

  After completion of the masking process, after filtering and washing, and drying, carbon powder containing the carbon carrier 1 having a part of the surface coated with the masking material 3 is 0.2 wt. The solution is dispersed in 500 g of a chloroplatinic acid aqueous solution containing 1% platinum, 3 g of sodium citrate is added thereto, and the mixture is heated to 70 ° C. while refluxing to carry out reduction loading of platinum. After carrying platinum, it is allowed to cool, and the carbon carrying platinum is filtered off.

  Thereafter, as a step of removing the masking material 3, the platinum-supported carbon support 1 is added to concentrated nitric acid, the copper colloid as the masking material 3 is dissolved and removed, and the remaining platinum-supported carbon support 1 is filtered and washed. An electrode catalyst is obtained.

  On the other hand, as a comparative example, an electrode catalyst is obtained by producing by the same method as the above-described example except that the masking step and the masking material removing step are omitted.

Next, a solid polymer electrolyte fuel cell single cell was manufactured using the above-described Example electrode catalyst and Comparative Example electrode catalyst. The platinum content per 1 cm ^{2 of} electrode area was 0.5 mg.

  The performance of the manufactured fuel cell was measured. In this measurement, hydrogen was supplied as fuel to the anode side, and air was supplied to the cathode side. For both gases, the supply pressure was atmospheric pressure, hydrogen was 80 ° C., air was saturated and humidified at 60 ° C., the temperature of the fuel cell body was set to 80 ° C., and the current density-cell voltage characteristics were examined.

  FIG. 2 shows the relationship between the current density and the cell voltage measured for each fuel cell as described above. As shown in FIG. 2, it can be seen that the cell voltage obtained in the fuel cell using the example electrode catalyst is higher than that in the fuel cell using the comparative example electrode catalyst. As described above, according to the present invention, a highly active electrode catalyst can be produced, and the performance of the fuel cell can be greatly improved.

  The above-mentioned carbon-supported catalyst is not only used as an electrode catalyst for a solid polymer electrolyte fuel cell, but can be widely used to promote various other chemical reactions.

In the manufacturing process diagram of the carbon support catalyst according to one embodiment of the present invention, (a) schematically shows the carbon support, (b) shows a state where the masking material is adsorbed on the carbon support of (a), (C) shows a state where catalyst fine particles are adsorbed on the surface of the carbon support of (c), and (d) shows a state where the masking material is removed from the state of (c). It is a correlation diagram of the current density and cell voltage in each fuel cell which respectively used the Example electrode catalyst and the comparative example electrode catalyst.

Explanation of symbols

1 Carbon support 3 Masking material 5 Catalyst fine particles

Claims (5)

In the carbon-supported catalyst in which catalyst fine particles are supported on the surface of the carbon support,
A carbon-supported catalyst characterized in that a part of the surface of the carbon support is coated with a masking material, and the catalyst fine particles are supported at other sites. The carbon support forms a higher order structure in which crystallites are connected,
2. The carbon-supported catalyst according to claim 1, wherein a part of the surface of the carbon support is a neck portion that becomes a boundary portion where the crystallites are connected to each other.   The carbon-supported catalyst according to claim 1 or 2, wherein the masking material comprises fine particles.   The carbon-supported catalyst according to claim 3, wherein the fine particles of the masking material have a diameter of 1 nm to 10 nm.   The carbon-supported catalyst according to any one of claims 1 to 4, wherein the masking material is 4% to 40% by volume with respect to the carbon support.