JP2014039910A - Pt-SUPPORTED MICROTUBE AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Pt-supported microtube useful as a catalyst body or the like, which is obtained by supporting platinum nano particles having catalytic functions to a porous microtube formed from ceramic, and to provide a production method for suitably producing the Pt-supported microtube having such a constitution.SOLUTION: A Pt-supported microtube is such that platinum (Pt) particles are supported on the surface of a ceramic microtube in which ceramic particles are bonded into a hollow tubular shape, and is obtained by a production method including: a step for preparing a spinning raw material liquid containing a ceramic source, a platinum (Pt) source, and a resin component; a step for preparing a fibriform precursor by spinning the spinning raw material liquid; a first firing step for firing the precursor at a first firing temperature set within a temperature range of 450°C to 900°C in an inert gas stream; and a second firing step for firing the fired material fired in the first firing step at a second firing temperature set within a temperature range of 400°C or more and not exceeding the first firing temperature in an oxidizing atmosphere.

Description

  The present invention relates to a Pt-supported microtube in which platinum (Pt) nanoparticles having high catalytic activity are supported on a microtube and a method for producing the same. Moreover, it is related with utilization of this Pt carrying | support microtube. More specifically, the present invention relates to a Pt-supported microtube useful as a catalyst body in which Pt nanoparticles are supported on a porous microtube made of ceramic.

  Fuel cells are attracting attention as a new power source with low environmental impact because they can generate electromotive force with relatively high efficiency and clean exhaust gas. This fuel cell is classified into various types according to the type of electrolyte used. Among them, a polymer electrolyte fuel cell (PEMFC), which is a fuel cell using a polymer electrolyte membrane, is described below. , May be simply referred to as “PEMFC”), because it can be reduced in size and weight, and in principle it can be increased in output density and cost, so that it can be used as a power source for electric vehicles, portable devices, etc. Practical use is being promoted as a home power supply for household use that co-generates electricity and heat.

  A PEMFC is generally constituted by a membrane-electrode assembly including an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and the cathode. The anode of the PEMFC is equipped with a catalyst that promotes a hydrogen oxidation reaction (HOR) that mainly oxidizes hydrogen used as a fuel, and the cathode has an oxygen reduction reaction (ORR: Oxygen) that reduces the oxidant. A catalyst that promotes reduction reaction is provided. Such a catalyst is often used as a noble metal-supported catalyst body in which a noble metal (typically a platinum group element) having catalytic action is supported on the surface of an appropriate carrier.

International Publication No. 2008/093731 JP 2011-072981 A JP 2012-001865 A JP 2009-263802 A JP 2009-235629 A JP 2009-007697 A JP 2008-062163 A JP 2009-174066 A

In these noble metal-supported catalyst bodies, in order to reduce the amount of expensive noble metal catalyst used and to realize an efficient catalytic reaction, a three-phase interface between a gas such as fuel or air, an electrolyte, and a catalyst Has been studied (see, for example, Patent Documents 1 and 2). For example, according to the noble metal-supported catalyst body disclosed in Patent Document 1, such a three-phase interface functions well. For example, there is a CO selective catalyst in which only CO is selectively oxidized without oxidizing hydrogen. It is known that it can be realized.
However, the noble metal-supported catalyst body constituted by a special carrier disclosed in Patent Documents 1 and 2 is supported by impregnating a solution containing a desired noble metal catalyst colloid or the like.

  The present invention has been created in view of such a situation, and the object of the present invention is useful as a catalyst body in which platinum nanoparticles having a catalytic function are supported on a porous microtube made of ceramic. Is to provide a Pt-supported microtube. Another object of the present invention is to provide a production method for suitably producing a Pt-supported microtube having such a configuration.

The Pt-supported microtube provided by the invention disclosed herein is characterized in that platinum (Pt) particles are supported on the surface of a ceramic microtube formed by bonding ceramic particles into a hollow tube.
The microtube having such a configuration has a very large specific surface area because the microtube is formed by bonding ceramic particles in addition to being hollow. Therefore, a large amount of Pt particles can be supported per unit volume, and a catalyst with high catalytic ability can be realized.

In a preferred embodiment of the Pt-supporting microtube disclosed herein, the average particle size of the Pt particles is 15 nm or less.
The Pt particles described above can be nanoparticles having a particle size that is essentially nanometer sized (typically in the range of 1-100 nm). In such a configuration, the average particle size of Pt particles (hereinafter sometimes referred to as “Pt nanoparticles”) is preferably 15 nm or less, typically 10 nm or less, more preferably 5 nm or less. It can be. Therefore, it is possible to secure a large catalytically active surface while reducing the amount of expensive Pt used, and to realize a Pt-supported microtube with high catalytic performance at low cost.

In a preferred embodiment of the Pt-supported microtube disclosed herein, the ceramic particles have an average particle size of 200 nm or less.
When the ceramic particles are coarse, the specific surface area of the microtube decreases, which is not preferable. Further, the bonding area between the particles is relatively reduced, and the strength of the microtube can be reduced. The average particle size of the ceramic particles is preferably 200 nm or less, typically 100 nm or less, more preferably 75 nm or less.

In a preferred embodiment of the Pt-supporting microtube disclosed herein, the Pt particles are supported on the inner wall and the outer wall of the microtube, respectively.
According to this configuration, both the outer wall and the inner wall of the microtube serve as the Pt particle supporting surface, and more Pt particles can be supported.

In a preferred embodiment of the Pt-supported microtube disclosed herein, the Pt particles are supported at a ratio of 1% by mass to 40% by mass with the entire Pt-supported microtube as 100% by mass. Yes.
According to such a configuration, although the Pt particles are nanoparticles, the specific surface area of the microtube as a carrier is large, so that the Pt particles can be supported in a desired amount in the range of 1% by mass to 40% by mass. It can be supported in a large amount of mass%. Thereby, a Pt-supporting microtube with higher catalytic ability is realized.

In a preferred embodiment of the Pt-supported microtube disclosed herein, the microtube has an average outer diameter of 200 nm to 700 nm and an average inner diameter of 40 nm to 600 nm.
The average outer diameter of the microtube can be prepared in the range of about 200 nm to 700 nm, and the average inner diameter of the microtube can be prepared in the range of about 40 nm to 600 nm. Thereby, for example, when such a Pt-supported microtube is used as an electrode catalyst for PEMFC, it is possible to control the form of a three-phase interface between a gas such as fuel or air, an electrolyte, and a catalyst. .

In a preferred embodiment of the Pt-supporting microtube disclosed herein, the microtube has a porous structure.
Although the microtube is configured by bonding ceramic particles, pores are formed in the tube wall in a portion where the intervals of the ceramic particles are sparse, and the whole can have a porous structure. Since such pores include pores (mesopores) having a size of 1 nm to several tens of nm, the specific surface area of the carrier can be extremely increased. Thus, when the microtube has a porous structure including mesopores, the specific surface area of the carrier is further greatly increased, and more Pt particles can be supported. Further, a passage connecting the inside and the outside of the microtube is formed through the pores, and the contact efficiency between the Pt particles carried on the inner wall of the microtube and the gas or the like is increased.

  In a preferred embodiment of the Pt-supported microtube disclosed herein, the ceramic particles are tin oxide particles. Tin (IV) oxide is a semiconductor material having relatively high conductivity as a ceramic. Further, tin (IV) oxide is a material having transparency and excellent physical and chemical stability, and is a material expected as a novel functional material in the electric / electronic field. Since such a Pt-supported microtube can constitute a microtube with the tin oxide particles, a Pt / tin oxide composite having a possibility of developing a new function is provided.

  According to another aspect of the invention disclosed herein, a method for producing a Pt-supported microtube includes a step of preparing a spinning raw material solution including a ceramic source, a platinum (Pt) source, and a resin component, and spinning the above-described spinning raw material solution. A step of preparing a fibrous precursor, a first baking step of baking the precursor at a first baking temperature set in a temperature range of 450 ° C. or higher and 900 ° C. or lower in an inert air current, and The second firing step of firing the fired product fired by the first firing step in an oxidizing atmosphere at a second firing temperature set at a temperature range of 400 ° C. or higher and not exceeding the first firing temperature. It is characterized by including.

  That is, in the invention disclosed herein, at the stage of adjusting the spinning raw material liquid, the spinning raw material liquid contains both ceramic and Pt raw materials that constitute the Pt-supporting microtube. Then, the spinning raw material liquid is shaped into a fiber to form a precursor, and the Pt-supported microtube disclosed herein is manufactured by performing the characteristic two-stage baking process as described above. I have to. In the above spinning raw material liquid, the ceramic source and the Pt source are present in a substantially uniformly mixed state. Also in the precursor, the ceramic source and the Pt source exist in a substantially uniformly mixed state. Here, the precursor is solid, i.e., filled fibrous. Then, the resin component is burned out by a two-stage baking process to form a microtube in which ceramic particles are bonded to a hollow tube from a ceramic source, and Pt nanoparticles are formed on the surface thereof. Although the details are unknown, the present inventors, in the above-described two-stage baking treatment, (1) by the first baking performed in an inert air current, the precursor has the resin component as the core, It is transformed into a core-sheath structure having a ceramic source and a Pt source as a sheath part, and (2) the core part in the core-sheath structure disappears and constitutes the sheath part by the second firing performed in an oxidizing atmosphere. It is considered that the ceramic source and the Pt source are oxidized into ceramic particles and Pt particles. Hereinafter, unless otherwise specified, when simply described as “fibrous” in the present specification, it means a solid fiber form and does not include a hollow fiber form (including a tube form or the like).

According to such a configuration, for example, after forming a micro tube made of ceramic, it is possible to support Pt on the surface simultaneously with the formation of the micro tube without requiring the trouble of supporting Pt nanoparticles on the surface. Moreover, the ceramic particles and the ceramic particles and the Pt particles are firmly bonded by sintering. Therefore, it is possible to obtain a Pt-supporting microtube with a low possibility that the Pt particles will slide down.
Moreover, since the ratio of ceramic particles and Pt nanoparticles can be controlled at the stage of preparing the spinning raw material liquid, the amount of Pt nanoparticles supported can be controlled relatively accurately.
Further, since the ceramic raw material and the Pt raw material form a uniform system at the stage of adjusting the spinning raw material liquid, the Pt nanoparticle is uniformly dispersed on the surface of the ceramic particles in the obtained Pt-supported microtube Can be supported.
In addition, since the form of the Pt-supported microtube is derived from the form of the precursor formed by spinning, a desired tube shape can be realized depending on the spinning mode, and the aggregated form of microtubes can be changed to the desired form. It is also possible to control. This makes it possible to easily manufacture a Pt-supporting microtube with a higher degree of freedom in shape.

In a preferred embodiment of the method for producing a Pt-supporting microtube disclosed herein, the temperature increase rate in the first firing step is set to 5 ° C./min or more and 20 ° C./min or less.
By setting the rate of temperature increase in the first firing step within the above range, a hollow tubular Pt-supported microtube can be suitably obtained from the fibrous precursor. When the rate of temperature increase is less than 5 ° C./min, it may be difficult to form a tube shape with ceramic particles even if two-stage firing is performed. The temperature rising rate is preferably 7 ° C./min or more, for example, 8 ° C./min or more, more preferably 10 ° C./min or more. The upper limit of the heating rate is not particularly limited, but as a guideline for the smooth transformation into the core-sheath structure as described above and the upper limit of the general heating rate in a widely used firing furnace, for example, 20 It is exemplified that the temperature is not more than ° C / min.

In a preferred embodiment of the method for producing a Pt-supported microtube disclosed herein, the temperature is lowered to 100 ° C. or lower after the completion of the first firing step, and then the temperature raising rate is 5 ° C. to the second firing temperature. The temperature is increased at a rate of not less than / min and not more than 20 ° C./min.
The temperature increase rate in the second firing step is important in controlling the particle size of the Pt nanoparticles supported on the surface of the microtube. As the rate of temperature increase in the second firing step is increased, the particle size of the Pt nanoparticles tends to decrease. And the average particle diameter of Pt nanoparticles can be made into the range of about 1 nm-15 nm by setting a temperature increase rate in the said range. More specifically, when the rate of temperature rise is about 5 ° C./min or more and 15 ° C./min or less, the particle size of the Pt nanoparticles can be about 2 nm to 10 nm. Further, when the rate of temperature rise is about 10 ° C./min or more and about 15 ° C./min or less, the particle size of the Pt nanoparticles can be about 2 nm to 5 nm. When the rate of temperature increase is less than 5 ° C./min, the particle size of the Pt nanoparticles may exceed 15 nm.

In a preferred embodiment of the method for producing a Pt-supported microtube disclosed herein, the ratio of the ceramic source and the platinum source in the spinning raw material liquid is the mass of the ceramic and platinum obtained after the second firing step. The ratio (ceramic mass: platinum mass) is adjusted to be in a range of 60:40 to 99: 1.
The proportion of Pt nanoparticles supported on the surface of the microtube made of ceramic can be adjusted so as to obtain a desired mass ratio at the stage of the spinning raw material liquid. In addition, since the ceramic source and the platinum source are uniformly dispersed in the spinning raw material liquid within the range of the above mass ratio, the Pt nanoparticles are supported in a uniformly dispersed state without aggregating on the surface of the microtube. The

In a preferred embodiment of the method for producing a Pt-supported microtube disclosed herein, the ceramic source is one or more selected from the group consisting of tin halides, nitrates, sulfates, acetates, and oxalates. It is characterized by including. According to such a configuration, SnO ₂ microtubes in which tin (IV) (SnO ₂ ) particles are formed as ceramic particles and Pt particles are supported can be obtained. Tin (IV) oxide has transparency and is a material having high electrical conductivity as a ceramic material. Since such a Pt-supported microtube can be constituted by the tin oxide particles, a Pt-supported microtube useful as a catalyst body is provided.

In a preferred embodiment of the method for producing a Pt-supporting microtube disclosed herein, the precursor is formed by ejecting the spinning raw material liquid from a nozzle by an electrospinning method.
Conventionally, a technique for obtaining a fibrous ceramic material having a micrometer diameter (fiber diameter) by using an electrospinning method is known (see, for example, Patent Documents 3 to 7). Typically, a spinning material containing an inorganic material and a resin is spun into a long fiber to form a precursor, which is oxidized and fired to form a fibrous ceramic. According to the electrospinning method, a long fibrous ceramic material in which the fiber diameter is controlled to some extent at a micro level (for example, in the range of about 100 nm to 1000 nm) can be produced relatively easily. However, it has not yet been realized to form such a long fibrous ceramic material into a tube shape (that is, a microtube). At the same time, it has not been realized that the tube wall has a porous structure and that the surface of the microtube is loaded with a different material.
On the other hand, in the manufacturing method disclosed here, by combining the characteristic spinning process as described above with the electrospinning method, it is possible to easily realize the manufacture of a Pt-supported microtube that has not been known so far. It is possible.

A technique for spinning a fiber having a core-sheath structure using an electrospinning method is also known. In this technique, for example, a core material and a sheath material are prepared as separate spinning raw material liquids, and spinning is performed using a spinneret (spinneret) for a core-sheath structure or a hollow structure with a special configuration (for example, , See Patent Document 8).
On the other hand, in the manufacturing method disclosed here, the spinneret having such a special configuration is not necessary, and the spout can be spun using a nozzle having a very simple tubular configuration such as an injection needle. In addition, as the spinning raw material liquid, only one liquid containing a ceramic source and a platinum (Pt) source needs to be prepared, which is an extremely simple method.

In a preferred embodiment of the method for producing a Pt-supporting microtube disclosed herein, the inner diameter of the nozzle is in the range of 0.2 mm to 1.2 mm.
With such a configuration, the hollow shape of the Pt-supporting microtube can be suitably formed, and dimensions such as the outer diameter can be controlled. For example, by controlling the inner diameter of the nozzle within the above range, it is possible to produce a Pt-supported microtube whose tube diameter (outer diameter) is controlled in the range of about 200 nm to 700 nm on average.

  The above-described Pt-supported microtube disclosed here constitutes a porous microtube by combining particles of nanometer order. And the surface carries the Pt nanoparticle which shows a catalytic action. Therefore, such a Pt-supported microtube can be suitably used, for example, as a catalyst body for promoting various chemical reactions. In addition, the ceramic porous microtube as the support has a large number of fine pores on the order of nanometers on the tube wall, so that reaction selectivity can be imparted to such catalytic ability. For example, this Pt-supported microtube can control the inner diameter of the tube and the pore diameter of the tube wall, etc., to properly arrange the three-phase interface between the gas to be reacted, the electrolyte, and the catalyst. , It can function as a catalyst for preferentially promoting the HOR reaction over the ORR reaction. Therefore, these Pt-supported microtubes can be preferably used as, for example, a catalyst body used for a polymer electrolyte fuel cell, particularly an anode catalyst. Accordingly, the present invention can suitably provide a polymer body for a polymer electrolyte fuel cell including the above-described Pt-supporting microtube and other various articles. In addition, the present invention can suitably provide a polymer body fuel cell catalyst body including the Pt-supported microtube manufactured by the above-described method for manufacturing a Pt-supported microtube, and other various articles. .

It is a perspective view explaining the structure of a polymer electrolyte fuel cell. It is sectional drawing which showed the structure of the membrane-electrode assembly of a polymer electrolyte fuel cell. It is the figure which showed notionally the mode that a Pt carrying | support microtube was manufactured. It is an electron microscope image of the sample 1 produced in the Example. It is an electron microscope image of the sample 2 produced in the Example. It is a principal part enlarged view of FIG. 5A. It is an electron microscope image of the sample 3 produced in the Example. It is an electron microscope image about the same sample as FIG. 6A, Comprising: It is an observation image in higher magnification. It is an electron microscope image which shows the surface state of the sample 4 produced in the Example. It is an elemental map of Sn in the same visual field as FIG. 7A. It is an element map of Pt in the same visual field as FIG. 7A. It is the figure which illustrated the cyclic voltammogram of Pt carrying | support microtube of the sample 4 produced in the Example.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

In the Pt-supported microtube disclosed herein, platinum (Pt) particles are supported on the surface of a ceramic microtube.
Such a microtube forms a long hollow tubular tube by continuously bonding a plurality of ceramic particles to each other. In the plurality of ceramic particles, adjacent ceramic particles are firmly bonded to each other (typically including solid phase bonding, for example, sintering, liquid phase sintering, etc.). The ceramic particles may be, for example, granular particles which are bonded to each other with a point or a relatively small area while maintaining the outer shape thereof, or a plurality of ceramic particles are closely bonded with a relatively large area. Also good.
When the microtube is viewed as a whole, pores are formed in the tube wall, and the microtube can be porous. The pores are formed by creating gaps between several ceramic particles and communicating the hollow portion of the microtube with the outside. For example, pores that are sufficiently larger than voids formed when a plurality of spherical ceramic particles are bonded together in close-packing can be formed.
As described above, the microtube disclosed herein has a large specific surface area because a plurality of ceramic particles are bonded together. Furthermore, the specific surface area is further increased due to the presence of pores in the tube wall of the microtube. Further, since the microtube is made of ceramic, it has high strength and durability, and has desirable characteristics as a catalyst carrier, for example.

As the ceramic constituting the microtube, oxide ceramics which are oxides of various metals and composites thereof can be considered. Specific examples of such oxide ceramics include silica (SiO ₂ ), alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), yttria (Y ₂ O ₃ ), and ferrite (Fe ₂ O). ₃ ), titanium oxide (TiO ₂ ), tin oxide (SnO ₂ ), zinc oxide (ZnO ₂ ), calcium oxide (CaO ₂ ), magnesium oxide (MgO ₂ ), etc. are exemplified. Examples include indium tin oxide (ITO), sialon (Si ₃ N ₄ .Al ₂ O ₃ ), mullite (Al ₆ Si ₂ O ₁₃ ), perovskite oxide, yttria stabilized zirconia (YSZ), and the like. Among these, for example, SnO ₂ or ITO can be used to impart semiconductor level conductivity (electron conductivity) to the microtube.

The form of the microtube is not particularly limited, but typically the average tube diameter (that is, the average outer diameter) may be in the range of about 200 nm to 700 nm. The average outer diameter may typically be about 300 nm to 600 nm, for example, about 400 nm to 500 nm.
About the average diameter (namely, average internal diameter) of the hollow part of a microtube, it may be 40 nm or more and 600 nm or less. The average inner diameter is typically about 100 nm to 500 nm, for example, about 200 nm to 300 nm.

The particle diameter of the ceramic particles constituting the microtube is not particularly limited, but typically the average particle diameter is about 200 nm or less, more typically 50 nm or more and 100 nm or less, for example, 50 nm or more. The range is 75 nm or less.
The length of the microtube is also not limited, and can typically be 1 μm or longer, for example, several μm or longer.
And although the magnitude | size of the pore formed in a tube wall is not restrict | limited especially, For example, an average pore diameter may be a mesopore of a magnitude | size about 5-100 nm. More typically, the average pore diameter is about 10 nm to 75 nm, and more limited to about 15 nm to 30 nm.
The dimensions represented by “average outer diameter”, “average inner diameter”, “average particle diameter” and the like in this specification are arithmetic average values of the dimensions of 20 or more particles measured by observation with an electron microscope or the like. Defined.

  The cross-sectional shape of the above microtube is not particularly limited, and may be various forms such as a substantially circular shape, a substantially elliptical shape, and a substantially rectangular shape. Typically, the cross-sectional shape of the microtube can be substantially circular. Further, the microtubes do not necessarily have the same cross-sectional shape, and may vary to some extent (for example, about ± 30% as a dimension). For example, the diameter does not necessarily have to be constant as seen in carbon nanotubes, and there may be a thicker portion or a thinner portion in one microtube. The same applies to the inner diameter of the tube and the thickness of the tube wall, and it is not always necessary to have a constant size and thickness. Further, the microtube may be relatively straight or curved. Further, a two-dimensional or three-dimensional structure may be formed by connecting one or more microtubes at a part thereof.

The Pt particles can contain Pt as a main component. Here, “containing Pt as a main component” means that when the mass of Pt particles is 100% by mass, the proportion of Pt is 50% by mass or more, typically 70% by mass. As mentioned above, Pt is preferably 90% by mass or more, more preferably 98% by mass or more (for example, 99% by mass or more).
The average particle size of the Pt particles can typically be nanoparticles of 100 nm or less. Although the surface area per unit mass can be increased when the average particle diameter of the Pt particles is small, the catalytic activity is lowered when the particles are excessively refined, and the Pt-supported microtube is used as a catalyst body. Is not preferable from the viewpoint of maintaining performance. Further, too small catalyst fine particles are expected to cause a problem in durability. The average particle diameter of the Pt particles disclosed herein is in the range of 1 nm to 30 nm, typically 1 nm to 15 nm, for example, 2 nm to 10 nm, more preferably 2 nm to 5 nm. The Pt particles having such an average particle diameter can be provided with durability when used as a catalyst in addition to an increase in mass activity.

Such Pt particles are carried on the inner wall and the outer wall of the microtube. Specifically, it is carried on the surface of ceramic particles constituting the microtube. Here, the ceramic particles and the Pt particles are firmly bonded to each other. Typically, both are firmly bonded by solid phase bonding, such as sintering.
The proportion of Pt particles supported on the microtube can be adjusted within a desired range. Such a microtube may have a large specific surface area because the ceramic particles are bonded in a state where the granular shape is substantially maintained. Therefore, a relatively large amount of Pt particles can be supported. However, if too much Pt particles are supported, a situation may occur in which the Pt particles come into contact with each other. Then, the active surface area per unit mass of Pt is reduced, and there is a possibility that the catalytic ability cannot be efficiently expressed. Therefore, for example, when the total amount of the Pt-supporting microtube is 100% by mass, Pt particles are preferably supported at a ratio of 1% by mass to 40% by mass. In other words, a preferable range is about 60:40 to 99: 1 as a mass ratio (ceramic mass: Pt mass) of the ceramic and the Pt particles constituting the microtube. By setting such a ratio, the nano-sized Pt particles as described above can be suitably supported in a highly dispersed state on the surface of the microtube.

In the Pt-supported microtube configured as described above, Pt showing catalytic action is supported as nanoparticles, so that the amount of platinum necessary for obtaining a predetermined catalytic ability is reduced, and the cost is reduced. It has excellent practicality. As the catalytic performance of such a Pt-supported microtube, specifically, for example, the active surface area per 1 g of platinum supported on the Pt-supported microtube is 40 m ² / gPt or more, for example, 40 m ² / gPt or more, preferably Can achieve 60 m ² / gPt or more.

  Moreover, even if this Pt carrying | support microtube is a long thing, the internal space and the exterior of a microtube are connected by the pore formed in a tube wall, for example. Therefore, the outside and inside of the microtube are configured such that substances can enter and exit through the pores. That is, more Pt particles can be carried per unit volume. Further, any substance that can pass through such pores can easily contact the Pt particles carried on the inner wall of the microtube even if the substance exists outside the microtube. Therefore, a special reaction field limited by the size of the pores can be formed inside the microtube. According to this, it is possible to exhibit excellent performance such as having a selective catalytic activity peculiar in the pores.

  The Pt-supporting microtube disclosed herein can be suitably manufactured by, for example, the manufacturing method shown below. Hereinafter, the production method of the Pt-supported microtube disclosed herein will be described in detail while showing a preferred embodiment. That is, the manufacturing method disclosed here is a method for manufacturing a Pt-supported microtube in which platinum (Pt) particles are supported on the surface of a ceramic microtube formed by bonding ceramic particles into a hollow tube. The following steps are included.

(1) A step of preparing a spinning raw material liquid containing a ceramic source, a platinum (Pt) source, and a compound containing a resin component.
(2) A step of spinning a spinning raw material solution to prepare a fibrous precursor.
(3) A first firing step of firing the precursor at a first firing temperature set in a temperature range of 450 ° C. or higher and 900 ° C. or lower in an inert air current.
(4) Second firing step of firing the fired product fired in the first firing step in an oxidizing atmosphere at a second firing temperature set to a temperature range of 400 ° C. or higher and not exceeding the first firing temperature. .

  That is, in this manufacturing method, platinum is supported on the surface of a ceramic substrate by preparing a spinning raw material solution containing a ceramic source and a platinum (Pt) source simultaneously and uniformly, and molding and firing the solution. The obtained Pt-supported microtube is obtained. In addition, a Pt-supported microtube having a shape different from that of the precursor is created as a fired body by the characteristic two-stage firing process as described above. That is, a tube-shaped fired body is obtained from the fibrous precursor.

(1) Adjustment process of spinning raw material liquid As a ceramic source used as a raw material of the Pt-supporting microtube, various materials may be used as long as ceramics can be generated by oxidation firing. For example, various salts of metal elements constituting the ceramic can be preferably used. Examples of such salts include chlorides, hydroxides, borides, bromides, iodides, sulfides, carbonates, sulfates, nitrates, oxalates, perchlorates, and the like. More specifically, for example, when the ceramic is tin oxide (SnO ₂ ), examples of the ceramic source include tin (II) chloride dihydrate (SnCl ₂ .2H ₂ O), tin chloride. Pentahydrate (SnCl ₂ .5H ₂ O), tin nitrate 20 hydrate (Sn (NO ₃ ) ₂ .20H ₂ O), tin (II) 2-ethylhexanoate (Co [OOCCH (C ₂ H ₅ ) C ₄ H ₉ ] ₂ ), tin (II) diperchlorate (Sn (ClO ₄ ) ₂ ), tin (II) acetate (Sn (CH ₃ COO) ₂ ), tin (II) tartrate (Sn (C Any one of ₄ H ₄ O ₆ )) or a mixture of two or more thereof is exemplified. If the ceramic is a composite oxide, prepare the salt as described above for each metal element constituting the composite ceramic, and use the salt of each element in a predetermined ratio according to the ceramic composition. Good.

As the Pt source, various salts or complexes of platinum (Pt) can be preferably used. Examples of platinum salts include halides such as platinum chloride, bromide and iodide, hydroxides, sulfides, sulfates and nitrates, and potassium composite oxides, ammonium composite oxides and sodium composites. A composite oxide such as an oxide can be used. As the platinum complex, a platinum ammine complex, a cyano complex, a halogeno complex, a hydroxy complex, or the like can be used. Specifically, as an example, for example, platinum chloride hexahydrate (H ₂ (PtCl ₆ ) · 6H ₂ O), platinum (IV) chloride, platinum (II) bromide, platinum (IV) iodide, platinum (IV) sulfide, potassium tetrachloroplatinate (II), ammonium tetrachloroplatinate (II), sodium hexachloroplatinate (IV) hexahydrate, platinum (II) hexafluoroacetylacetonate complex, platinum (II ) Acetylacetonato complex and the like are exemplified.

  The ratio of the ceramic source and the Pt source can be adjusted to a desired ratio from the relationship between the ceramic microtube and the Pt particles supported on the ceramic microtube. Although there is no restriction | limiting in particular about this ratio, For example, it is preferable to prepare so that the mass ratio of a ceramic and platinum may become a ratio of about 60: 40-99: 1 as ceramic mass: platinum mass. If the proportion of platinum (Pt) in the entire Pt-supported microtube (that is, the total of ceramic and platinum) is less than 1% by mass, a catalyst body with high catalytic ability cannot be obtained, which is not preferable. For example, Pt is preferably 5% by mass or more, and more preferably 15% by mass or more. In addition, since this Pt is carried as a nanoparticle, Pt exceeding 40% by mass is not preferable because there is a risk of joining the Pt particles on the surface of the microtube. From this point of view, Pt is preferably 25% by mass or less, and more preferably 20% by mass or less.

  In addition to the raw material for the Pt-supported microtube, the spinning raw material liquid contains a resin component for the purpose of enhancing the moldability of the precursor and maintaining the shape of the precursor after molding. Although there is no restriction | limiting in particular as this resin component, It is preferable that it is resin which has appropriate viscosity at the time of shaping | molding of a precursor, and can be provided with shape maintainability, such as appropriate hardness after shaping | molding. For example, although depending on the molding method of the precursor, a thermoplastic resin, an ultraviolet curable resin, or the like can be preferably used. Specific examples of such resin components include polystyrene, polycarbonate, polymethyl methacrylate, polyvinyl pyrrolidone, polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), carboxymethyl cellulose (CMC), polyacrylamide (PAM), and the like. Can be preferably used. Such resin components may be used alone or in combination of two or more.

Such a resin component can be blended in the spinning raw material liquid in a mass ratio of the above ceramic source and a ratio of resin component: ceramic source of about 1: 3 to 1: 0.1. More specifically, the resin component can be blended at a ratio of 1: 2 to 1: 1, for example, about 1: 0.5 to 1: 0.25. Such a resin component has a role of improving moldability when the precursor is molded into a fiber. In essence, this resin component is burned off by the subsequent baking. However, although details are not clear, it is considered that the resin component plays an important role in forming the Pt-supported microtube in the present invention. That is, it is considered that it has a role as a template when knitting microtubes from a fibrous precursor in a subsequent firing step.
In addition to the materials described above, various additives typified by a dispersant, a thickener and the like may be added to the spinning raw material liquid as necessary.

  The spinning raw material liquid may be a solution obtained by dissolving the above-described raw material in a solvent, or may be a dispersion liquid in which each raw material is dispersed in a dispersion medium. In addition, the spinning raw material liquid has a viscosity adjusted, gel-like or sol-like shape in order to keep the ceramic source and the platinum source in a uniform dispersed state and facilitate molding into a fibrous precursor described later. It may be prepared in the state of. Of course, the state of the raw material liquid may be changed according to the molding process. The solvent (hereinafter also including a dispersion medium) constituting the spinning raw material liquid may be an aqueous solvent or an organic solvent. When the spinning raw material liquid is composed of an aqueous solvent, water (pure water, ion exchange water, purified water, etc.) or a mixed liquid containing water (for example, a mixed solution of water and ethanol) can be used as the solvent. In the case of an organic solvent (organic dispersion medium), alcohols such as methanol and ethanol; ketones such as acetone and methyl ketone; esters such as ethyl acetate; N, N-dimethylformamide Aprotic polar solvents such as (DMF), dimethylacetamide (DMA), dimethylsulfoxide (DMSO), acetonitrile, N-methyl-2-pyrrolidone (NMP) are used alone or in admixture of two or more. be able to.

The solid content concentration in the spinning raw material liquid (that is, the ratio of the ceramic source, the platinum source and the resin component) varies depending on the molding method for forming into a fiber shape, but is prepared with, for example, about 10% by mass to 30% by mass. can do. More specifically, it is exemplified that the content is 10% by mass or more and 20% by mass or less, for example, 10% by mass or more and 15% by mass or less.
When preparing the spinning raw material liquid, the raw materials may be sufficiently stirred so that the raw materials are uniformly dispersed in the liquid. For example, at about room temperature (typically 25 ° C.), using a rotary stirring device, for example, at a speed of about 100 rpm to 500 rpm, more preferably about 200 rpm to 300 rpm, for several tens of minutes to several hours. For example, stirring for about 30 minutes to 1 hour is exemplified.

(2) Precursor preparation step Next, a precursor of a Pt-supported microtube is prepared by forming the spinning raw material liquid prepared above into a fibrous form. Such a forming technique is not particularly limited, and various spinning methods can be used. Examples of techniques that can be spun into a fiber having a micro-level fiber diameter include, for example, a self-assembly method, a phase separation method, and an electrospinning method. In particular, the electrospinning method can be used to form the precursor disclosed herein because fibers having a diameter of nano-level to sub-micron level can be obtained by a relatively simple operation using a relatively simple apparatus. preferable.

FIG. 3 illustrates an outline of an electrospinning apparatus. The electrospinning apparatus 20 generally includes a container 4 for storing a spinning raw material liquid 2, a nozzle 6 for discharging the spinning raw material liquid 2 from the container 4, a pump 12 for sending the spinning raw material liquid 2 to the nozzle 6, a spinning raw material liquid 2 is composed of a high-voltage power supply 8 for charging 2 and a grounded current collecting plate 14.
In the apparatus 20, the spinning raw material liquid 2 is extruded from the container 4 to the nozzle 6 at a constant speed, and a voltage is applied to the nozzle 6 to be positively charged. When the electric attractive force of the positively charged spinning raw material liquid 2 exceeds the surface tension, the spinning raw material liquid 2 is jetted toward the current collecting plate 14 in a jet shape. Since the solvent in the spun raw material liquid 2 that has been ejected gradually evaporates during the flight, when it reaches the current collector plate 14, it becomes a fiber having a diameter reduced from the nano level to the micro level. Thereby, the fibrous precursor 10 whose diameter is nano level to micro level can be formed.

In electrospinning, if the humidity is high, the volatilization of the solvent is hindered, making it difficult to obtain a fibrous precursor. Therefore, an environment in which the humidity is controlled and a chamber capable of humidity management (not shown) It is also a preferable aspect to carry out internally. In this case, for example, specifically, the conditions of an environmental temperature of about 30 ° C. (for example, 30 ° C. ± 5 ° C.) and a relative humidity of about 30% (for example, 30% ± 10%) are exemplified as approximate guidelines. Is done.
In addition, the voltage applied to the spinning raw material liquid 2 cannot be generally described because the optimum value varies depending on conditions such as the preparation state of the spinning raw material liquid 2 and the distance between the nozzle 6 and the current collector plate 14. When the extrusion speed (flow rate) of the spinning raw material liquid 2 is 10 to 40 μL / min and the distance between the nozzle 6 and the current collector 14 is 20 to 30 cm, the applied voltage is in the range of about 10 to 30 kV. The adjustment is exemplified. In addition, the conditions illustrated here are only one embodiment, and do not limit the invention disclosed here.

In the manufacturing method disclosed herein, a Pt-supported microtube is obtained from a fibrous precursor by performing a two-step firing process on the precursor obtained above. Such a two-stage firing process will be described below.
(3) First firing step In the first firing step, first, the precursor obtained above is first fired at a first firing temperature set in a temperature range of 450 ° C to 900 ° C in an inert air stream. Bake.
As the inert air flow, the concentration of rare gas such as helium (He), neon (Ne), argon (Ar), nitrogen (N ₂ ) gas, and oxygen (O ₂ ) is reduced (for example, 8 mass% or less). ) Gas, a gas obtained by mixing these gases, and the like may be introduced into a firing furnace or the like at an appropriate flow rate. The flow rate of the inert gas is, for example, about 5 L / min to 40 L / min, preferably about 10 L / min to 30 L / min, for example, about 20 L / min to 30 L / min, depending on the reaction system. Illustrated.

The firing temperature (first firing temperature) in the first firing step is 450 ° C. or higher and 900 ° C. or lower as described above, preferably 500 ° C. or higher and 900 ° C. or lower, more preferably 600 ° C. or higher and 800 ° C. or lower. When the first baking temperature is lower than 450 ° C. or exceeds 900 ° C., it is not preferable because a hollow microtube cannot be finally obtained.
Moreover, it is preferable that the temperature increase rate to this baking temperature shall be 5 to 20 degree-C / min. A temperature increase rate of less than 5 ° C./min is not preferable because a hollow microtube cannot be finally obtained. The temperature rising rate is preferably 5 ° C./min or more and 15 ° C./min or less, for example, 10 ° C./min or more and 15 ° C./min or less. A temperature increase rate of about 20 ° C./min or less is sufficient, and a rapid temperature increase exceeding 20 ° C./min is not preferable in terms of equipment and cost.
The precursor is held for about 0.5 hours to 4 hours (for example, 1 hour to 3 hours) under such first firing conditions, and then subjected to the next second firing step.

(4) Second firing step In the second firing step, the fired product fired in the first firing step is set in a temperature range not lower than the first firing temperature at 400 ° C or higher in an oxidizing atmosphere. Baking is performed at the second baking temperature.
The firing atmosphere can be an oxygen-containing atmosphere such as an air atmosphere. By firing in such an oxidizing atmosphere, the ceramic source is fired to form a ceramic microtube formed by bonding ceramic particles into a hollow tube. Further, the Pt source is baked to form Pt particles on the surface of the microtube.

  The firing temperature (second firing temperature) in the second firing step is set to a temperature range of 400 ° C. or higher and not exceeding the first firing temperature as described above. Here, the adjustment to the second firing temperature may be performed by cooling the temperature in the furnace to, for example, 100 ° C. or lower after the first firing step and then raising the temperature to the second firing temperature, or firing atmosphere. The temperature may be lowered from the first firing temperature to the second firing temperature by switching from an inert air current to an oxidizing atmosphere. For example, the second firing temperature can be 400 ° C. or higher and 800 ° C. or lower, preferably 400 ° C. or higher and 700 ° C. or lower, and more preferably 500 ° C. or higher and 600 ° C. or lower. More preferred. When the second firing temperature is less than 500 ° C., there is a possibility that the ceramic source is not sufficiently oxidized and ceramic particles cannot be obtained. If the first baking temperature exceeds 800 ° C., a porous shape cannot be obtained, which is not preferable.

  In the second firing step, it is preferable to cool the temperature in the furnace to 100 ° C. or lower and then raise the temperature to the second firing temperature. In this case, the temperature rising rate is preferably adjusted in the range of 5 ° C./min to 20 ° C./min. By adjusting the temperature rising rate, it is possible to control the particle size of the Pt particles carried on the microtube. By increasing the heating rate, it is possible to promote nucleation of Pt particles on the surface of the nanotube, suppress nucleation, and form fine Pt particles. Specifically, for example, Pt particles having an average particle diameter of about 20 nm or less can be formed by setting the temperature rising rate to 5 ° C./min or more. Moreover, Pt particles of about 2 to 3 nm can be formed by setting the temperature rising rate to 10 ° C./min or more. The Pt-supported microtube disclosed herein can be obtained by holding it for about 1 hour under the second baking conditions and then cooling it in a furnace, for example.

In the above two-stage firing, if the firing in the first firing step is performed in an air atmosphere or an air stream, a microtube cannot be obtained. Moreover, it has been confirmed that a microtube cannot be obtained simply by using an inert atmosphere. In the production method disclosed herein, it is an indispensable requirement to carry out the first firing step in an inert air stream.
From the above, it is considered that preparations for modifying the fibrous (solid) precursor into a tube shape are made in the first firing step. For example, the present inventors believe that in this first firing step, the fibrous precursor is transformed into a core-sheath structure with the resin component as the core and the ceramic source and the Pt source as the sheath. . In the second firing step, the core part of the core-sheath structure disappears, and the sheath part is oxidized and fired to obtain a ceramic microtube. Regarding Pt particles, it is not clear at which stage the Pt component moves to the surface of the microtube (ceramic particles), but it is considered that Pt particles are formed in the second firing step.

In the Pt-supported microtube thus obtained, the ceramic particles are sintered to form a microtube, and therefore the ceramic particles are bonded very firmly. The Pt particles are fired on the surface of the ceramic particles, and the Pt particles are firmly bonded to the surface of the ceramic particles by sintering. Therefore, such Pt particles are supported on the microtube which is a substrate by a strong bond.
Further, since the ceramic source and the Pt source are homogeneously dispersed in the precursor, the Pt particles are highly dispersed without being segregated on the surface of the microtube as the substrate.
Therefore, for example, the Pt-supported microtube disclosed herein is in a state in which the Pt particles are more uniformly dispersed as compared with a Pt catalyst support obtained by supporting Pt particles prepared in advance on a mesoporous substrate, and the like. It can be supported more firmly on the substrate.

  The Pt-supported microtube thus obtained is excellent in catalytic activity. Therefore, for example, it can be suitably used as a catalyst body in a polymer electrolyte fuel cell (PEMFC). Moreover, since the selectivity of the catalytic action is provided by utilizing the porosity of the microtube as the substrate, it can be suitably used as an anode catalyst for PEMFC, for example.

A general PEMFC (fuel cell) will be briefly described with reference to FIGS. FIG. 1 is an exploded perspective view showing an embodiment of the fuel cell 100, and FIG. 2 is a cross-sectional view schematically showing a membrane-electrode assembly (MEA) 110 that is a basic structure of the fuel cell 100.
The fuel cell 100 shown in FIG. 1 conceptually shows a configuration (stack) in which two unit cells 130 are connected in series and sandwiched between a pair of holders 140 and 140. The unit cell 130 includes a membrane-electrode assembly 110 and bipolar plates 120 and 120 disposed on both sides of the membrane-electrode assembly 110 in the thickness direction. The bipolar plates 120 and 120 are made of a conductive material (typically, a highly conductive metal or carbon) in which a reaction gas supply channel is engraved, and are joined to the membrane-electrode assembly 110, respectively. Thus, oxygen and fuel can be supplied to the catalyst layer of the membrane-electrode assembly 110 while functioning as a current collector.

  The membrane-electrode assembly 110 includes a sheet-like solid polymer membrane (electrolyte membrane) 200 and a fuel electrode (negative electrode) 210 applied to one surface (the left surface in FIG. 2) of the solid polymer membrane 200. And an oxidation electrode (positive electrode) 220 applied to the other surface of the solid polymer film 200 (the right surface in FIG. 2). The fuel electrode 210 and the oxidation electrode 220 also have a function as a catalyst layer, and are each configured to include a catalyst and a binder. A first fuel circulation layer 212 and a second fuel circulation layer 214 are sequentially laminated on the outer surface of the fuel electrode 210, and the first air circulation layer 222 and the second air are laminated on the outer surface of the oxidation electrode 220. The circulation layer 224 is laminated in order. Since the Pt-supported microtube disclosed herein can be a catalyst body having a large electrochemical surface area, it can be suitably used as a material constituting such a catalyst layer (the fuel electrode 210 and the oxidation electrode 220). For example, it can be particularly preferably used as a catalyst body included in the fuel electrode 210. By using such a Pt-supported microtube as a catalyst body, it is possible to reduce the manufacturing cost of the fuel cell 100 while maintaining good catalytic activity.

The present invention has been described based on the preferred embodiments. Next, examples relating to the present invention will be described. The examples described below are not intended to limit the present invention.
[Production of Pt-supported microtube]
[Preparation of spinning raw material liquid]
Platinum source was used hexachloroplatinic (IV) acid hexahydrate and _{(H 2 PtCl 6 · 6H 2} O). Tin tetrachloride (SnCl ₄ ) was used as the ceramic source. N, N-dimethylformamide (DMF: N, N-dimethylformamide) was used as the resin component. As the solvent, polyacrylonitrile (PAN) having a weight average molecular weight of 150,000 was used.

(P1): Using a chloroplatinic acid hexahydrate, a platinum chloride aqueous solution containing 10% by mass of Pt was prepared to obtain a platinum raw material solution.
(P2): 9 parts by mass of DMF was mixed with 1 part by mass of this platinum raw material solution and stirred at 80 ° C. for 2 hours.

(S1): PAN was mixed at a ratio of 1 part by mass with 9 parts by mass of DMF, and dissolved by stirring at 80 ° C. for 1 hour.
(S2): 1 part by mass of tin tetrachloride was mixed with 2 parts by mass of DMF, and the mixture was stirred at 80 ° C. for 30 minutes.
(S3): With respect to 10 parts by mass of the solution prepared in (S1) above, the mixture prepared in (S2) above was mixed at a ratio of 3 parts by mass and stirred for 1 hour.

  (Spinning raw material liquid): For 15 parts by weight of the solution prepared in (P2) above, the solution prepared in (S3) above is mixed at a ratio of 85 parts by weight and stirred for 1 hour, for electrospinning. The spinning raw material liquid was adjusted.

[Precursor preparation]
By using the electrospinning apparatus 20 having the configuration shown in FIG. 3, the spinning raw material liquid 2 prepared above was spun onto a target substrate (current collector plate 14) to produce a precursor 10. As the spinning nozzle 6, a syringe having an inner diameter of 0.4 μm was used. An aluminum foil was used as the target substrate 14. The spinning conditions when this apparatus 20 was used were as follows. The precursor spun under such conditions was a fiber having a diameter of 300 nm to 800 nm and a length of 1 μm or more.
Applied voltage (V): 14 kV
Ejection speed (Q): 10 to 40 μL / min
Nozzle-target distance (d): 23 cm
Relative humidity: 30%

[Baking]
The precursor obtained above is subjected to two-stage firing comprising a first firing step and a second firing step under the firing conditions shown in Table 1 below, using an electric furnace capable of controlling the firing atmosphere. Thus, samples 1 to 4 were obtained.

  (Sample 1) That is, the firing conditions of the first firing step of Sample 1 are as follows. In an inert air flow with a flow rate of 20 L / min, the temperature is increased to 300 ° C. at a temperature increase rate of 2 ° C./min and held at 300 ° C. for 1 hour. It was supposed to be. In this embodiment, the sample 1 after the first firing step was in a furnace-cooled state in which the sample 1 was left for a predetermined time without being removed from the furnace after the heating and holding time. The firing conditions of the second firing step were that the temperature was raised to 600 ° C. at a temperature rising rate of 6 ° C./min in an air atmosphere and held at 600 ° C. for 1 hour.

  (Sample 2) The firing conditions of the first firing step of Sample 2 were the same except that the temperature increase rate in the firing conditions of the first firing step of Sample 1 was changed to 10 ° C./min. The firing conditions for the second firing step were the same as the firing conditions for the second firing step of Sample 1.

  (Sample 3) The firing conditions of the first firing step of Sample 3 were the same except that the firing temperature in the firing conditions of the first firing step of Sample 2 was changed to 700 ° C. The firing conditions for the second firing step were the same as the firing conditions for the second firing step of Sample 1.

  (Sample 4) The firing conditions of the first firing step of sample 4 were the same as the firing conditions of the first firing step of sample 3. The firing conditions of the second firing step were the same except that the temperature increase rate in the firing conditions of the second firing step of Sample 1 was changed to 15 ° C./min.

[Evaluation of fired product]
The fired product (samples 1 to 4) obtained through the above manufacturing process was observed with a scanning electron microscope (SEM). The observation results are shown in FIGS. FIG. 4 is an SEM image of Sample 1. FIG. 5A is an SEM image of Sample 2, and FIG. 5B is an enlarged view of a main part thereof. 6A is an SEM image of Sample 3, and FIG. 6B is a TEM image when the same sample is observed with a transmission electron microscope (TEM) at a higher magnification. Note that the result of observation of the sample 4 with the electron microscope was almost the same as that of the sample 3.
Moreover, the X-ray-diffraction (XRD) analysis of the surface of the baking products of samples 1-4 was performed.

(Sample 1)
As a result of SEM observation of Sample 1, as shown in FIG. 4, it was confirmed that a fibrous fired body having a form in which the precursor was fired and solidified was obtained. This fiber had an average diameter of about 700 nm. When the fired body is observed closely, particles having a diameter of 25 nm to 35 nm (average particle diameter of about 30 nm) are formed on the surface where relatively large particles having a diameter of about 100 nm to 200 nm are closely bonded to each other in a fibrous form. I was able to confirm that was wearing. As a result of XRD analysis, it was confirmed that the large particles constituting the substrate were SnO ₂ and the fine particles bonded to the surface were Pt.

(Sample 2)
As a result of SEM observation of Sample 2, as shown in FIG. 5A, it was confirmed that a fired body having a shape as if a hollow tube was ruptured was obtained. When the fired body is observed closely, this fibrous material is a hollow tube having a diameter of about 50 nm to 150 nm and a relatively large pore on the tube wall. It was found that a substrate was formed. Further, as shown in FIG. 5B, it was found that relatively fine particles having a diameter of about 15 nm to 20 nm (average particle diameter of about 17 nm) were bonded and supported on the surface of the substrate.
The approximate shape of the entire tube was about 800 nm in diameter and about 2 μm in length. As a result of XRD analysis, it was confirmed that the large particles constituting the substrate were SnO ₂ and the fine particles bonded to the surface were Pt.

(Sample 3)
As a result of SEM observation of sample 3, as shown in FIG. 6A, it was confirmed that the precursor was fired to obtain a porous fibrous fired body. When the fired body is further observed by TEM, as shown in FIG. 6B, the fibrous material has a hollow tube shape in which particles having a diameter of about 50 nm to 100 nm are bonded, and pores are formed in the tube wall. It was found that a porous substrate having the same was formed. It was also found that fine particles were bonded and supported on the surface of the particles constituting the substrate.
The approximate shape of this tube was an outer diameter of about 500 nm, an inner diameter of about 200 nm, and a length of about 2 μm. The diameter of the pore formed in the tube wall was approximately 20 nm to 30 nm. The particles carried on the surface of the substrate had a diameter of about 6 nm to 8 nm (average particle size of about 7 nm). As a result of XRD analysis, it was confirmed that the portion constituting the substrate was SnO ₂ and the particles bonded to the surface were Pt.

(Sample 4)
As a result of SEM observation of sample 4, it was confirmed that the precursor was fired and a porous fibrous fired body was obtained. When the fired body is further observed, the fibrous material is bonded with particles having a diameter of about 50 nm to 100 nm to form a hollow substrate and a porous substrate having pores on the tube wall. I understood. It was found that fine particles were bonded and supported on the surface of the substrate as compared with Sample 3.
The approximate shape of this tube was approximately the same as that of sample 3, with a diameter of approximately 500 nm and a length of approximately 2 μm. The diameter of the pore formed in the tube wall was approximately 20 nm to 30 nm. The particles carried on the surface of the substrate of sample 4 had a diameter of about 3 nm to 4 nm (average particle diameter of about 3 nm) and were finer than the Pt particles of sample 3. As a result of XRD analysis, it was confirmed that the portion constituting the substrate was SnO ₂ and the particles bonded to the surface were Pt.

From the above, after subjecting the precursor to the first firing step of firing in a predetermined firing temperature range (first firing temperature) in an inert stream, the precursor is subjected to a predetermined temperature range (first It was found that a Pt-supported microtube having a micro-tube made of porous ceramic as a base and Pt nanoparticles supported on the surface can be manufactured by performing a second firing step of firing at a second firing temperature). .
From the observation results of Sample 1 and Sample 2, it can be seen that if the firing temperature in the first firing step is too low, a hollow shape may not be formed suitably. Further, it has been found that if the inert atmosphere in the first firing step does not have a sufficient flow, the ceramic substrate may be densely sintered and a porous substrate or a hollow substrate may not be formed.
From the observation results of Sample 3 and Sample 4, it was found that the particle size of the Pt particles supported on the ceramic substrate (ceramic microtube) can be controlled by changing the temperature increase rate in the second firing step.

[Manufacture of electrodes]
In order to evaluate the catalytic activity of the Pt-supported microtube obtained in Sample 4, cyclic voltammetry (CV) was measured by the following procedure.
(1) Cyclic voltammetry measurement Using the Pt-supported microtube obtained in Sample 4 as a catalyst, a working electrode is constructed, platinum is used as a reference electrode, a reversible hydrogen electrode is used as a counter electrode, and 0 is used as an electrolyte. A tripolar cell was made using a 1 M perchloric acid (HClO ₄ ) solution. The working electrode was prepared by dropping a solution in which the catalyst body to be measured was dispersed in pure water onto the disk electrode so as to be 3.76 × 10 ⁻⁵ g / cm ² , drying, and then perfluorocarbon. It was prepared by fixing with a proton conductive membrane composed of Further, nitrogen (N ₂ ) gas was blown into the electrolyte solution for 30 minutes before the measurement, and the inside of the cell was saturated with nitrogen (N ₂ ). Thereafter, the potential was swept at 25 ° C. under the conditions of 50 mV / s and a potential width of 0 V to 1.2 V with respect to the reversible hydrogen electrode, and the response current was measured.

FIG. 8 shows cyclic voltammograms at the 10th cycle, 100th cycle, 500th cycle and 900th cycle when the potential is changed for 1000 cycles. As shown in FIG. 8, an adsorption / desorption peak characteristic of platinum is observed in the low voltage side region of CV, and it can be said that Pt in the Pt-supported microtube is electrochemically active. Further, it was confirmed that the electrochemically active surface area of the Pt-supported microtube calculated from the area of this peak was a very high value of 60 m ² / gPt.
Further, although not shown in the figure, the peak intensity increases by repeating the potential fluctuation up to 200 cycles between the potential fluctuations of 10 to 1000 cycles, and thereafter the peak intensity can be kept almost constant. It could be confirmed. That is, the Pt-supported microtube showed almost no desorption or deterioration of the catalyst characteristics, indicating that the cycle characteristics and durability were high.

Although the present invention has been described with reference to specific examples, these are merely examples and do not limit the present invention. The invention disclosed herein can include various modifications and alterations of the specific examples described above.
For example, in the above embodiment, a Pt-supported microtube in which the ceramic source and the platinum source in the spinning raw material liquid are uniformly mixed and Pt particles are extremely uniformly dispersed (highly dispersed) on the surface of the microtube. However, the ratio (for example, concentration) of the ceramic source and the platinum source in the spinning raw material liquid is not used for the purpose of, for example, partially changing the amount of Pt particles supported in the Pt-supported microtube. It may be made uniform.
Further, in the above embodiment, the spinning raw material liquid is spun from one nozzle to form a fibrous precursor. For example, the spinning raw material liquid is spun from a plurality of nozzles and the fibers are intertwined. A shaped precursor may be formed. Further, the precursor may be further shaped into an arbitrary shape and then fired to obtain a Pt-supported microtube having a desired shape.

  The present invention provides a Pt-supported microtube in which Pt nanoparticles are supported on the inner wall and the outer wall of a porous ceramic microtube. Since such a Pt-supported microtube has a high active specific surface area, it can be used as a catalyst for various reactions. For example, it can be suitably used when forming an anode catalyst layer in a polymer electrolyte fuel cell (PEMFC).

2 Spinning raw material liquid 4 Container 6 Nozzle 8 High-voltage power supply 10 Precursor 12 Pump 14 Current collector 20 Electrospinning device 100 Fuel cell (PEMFC)
110 Membrane-electrode assembly (MEA)
120 Bipolar plate 130 Unit cell 140 Holder 200 Solid polymer membrane (electrolyte membrane)
210 fuel electrode 212 first fuel circulation layer 214 second fuel circulation layer 220 oxidation electrode 222 first air circulation layer 224 second air circulation layer

Claims (19)

  A Pt-supported microtube in which platinum (Pt) particles are supported on the surface of a ceramic microtube formed by bonding ceramic particles into a hollow tube.   The Pt-supporting microtube according to claim 1, wherein an average particle diameter of the Pt particles is 15 nm or less.   The Pt-supported microtube according to claim 2, wherein the ceramic particles have an average particle size of 200 nm or less.   The Pt-supporting microtube according to any one of claims 1 to 3, wherein the Pt particles are respectively supported on an inner wall and an outer wall of the microtube.   The Pt-supported microtube according to any one of claims 1 to 4, wherein the Pt particles are supported at a ratio of 1% by mass to 40% by mass with the entire Pt-supported microtube as 100% by mass. .   The Pt-supporting microtube according to any one of claims 1 to 5, wherein the microtube has an average outer diameter of 200 nm to 700 nm and an average inner diameter of 40 nm to 600 nm.   The Pt-supporting microtube according to any one of claims 1 to 6, wherein the microtube has a porous structure.   The Pt-supporting microtube according to any one of claims 1 to 7, wherein the ceramic particles are tin oxide particles. Preparing a spinning raw material liquid comprising a ceramic source, a platinum (Pt) source and a resin component;
Spinning the spinning raw material liquid to prepare a fibrous precursor,
A first firing step of firing the precursor at a first firing temperature set in a temperature range of 450 ° C. or more and 900 ° C. or less in an inert air flow; and
A second firing step in which the fired product fired in the first firing step is fired in an oxidizing atmosphere at a second firing temperature set at a temperature range of 400 ° C. or higher and not exceeding the first firing temperature;
The manufacturing method of Pt carrying | support microtube containing this.   The manufacturing method of the Pt carrying | support microtube of Claim 9 which makes the temperature increase rate in said 1st baking process 5 degrees C / min or more and 20 degrees C / min or less. After the temperature is lowered to 100 ° C. or less after the first firing step,
The method for producing a Pt-supported microtube according to claim 9 or 10, wherein the temperature is raised to a temperature of 5 ° C / min to 20 ° C / min up to the second firing temperature. The ratio of the ceramic source and the platinum source in the spinning raw material liquid is:
The mass ratio of ceramic and platinum obtained after the second firing step (ceramic mass: platinum mass) is prepared to be in a range of 60:40 to 99: 1. The manufacturing method of Pt carrying | support microtube of description.   The Pt-supported micro of any one of claims 9 to 12, wherein the ceramic source includes one or more selected from the group consisting of tin halides, nitrates, sulfates, acetates, and oxalates. Tube manufacturing method.   The method for producing a Pt-supported microtube according to claim 9, wherein the precursor is formed by ejecting the spinning raw material liquid from a nozzle by an electrospinning method.   The manufacturing method of the Pt carrying | support microtube of Claim 14 which is the range whose inner diameter of the said nozzle is 0.2 mm or more and 1.2 mm or less. An article comprising the Pt-supporting microtube according to any one of claims 1 to 8.   A catalyst body for a polymer electrolyte fuel cell, comprising the Pt-supported microtube according to any one of claims 1 to 8.   An article comprising a Pt-supported microtube manufactured by the manufacturing method according to any one of claims 9 to 15.   A catalyst body for a polymer electrolyte fuel cell, comprising the Pt-supported microtube manufactured by the manufacturing method according to any one of claims 9 to 15.