JP2013159498A - Method for coating with coating material, and method for manufacturing fuel cell electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of coating selectively the surface of a material to be treated with a coating material, especially a method capable of coating selectively the surface of a carbon nanotube oriented on a substrate at least with either of an electrolyte resin and a metal catalyst, concerning a method for coating with a coating material by utilizing temperature dependency of solubility of a supercritical fluid.SOLUTION: This method for coating the surface of a material to be treated with a coating material has: a contact step of bringing the material to be treated into contact with a supercritical fluid obtained by dissolving a precursor of the coating material and/or the coating material into a supercritical solvent; and a heating step in which the material to be treated is heated by irradiating the material to be treated with an electromagnetic wave having a wavelength in which the absorptivity of the material to be treated is higher than the absorptivity of the supercritical solvent, to thereby reduce solubility of the precursor and/or the coating material to the supercritical solvent.

Description

  The present invention relates to a method for coating the surface of a material to be treated with a coating material, and a method for manufacturing a fuel cell electrode.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes.

  An electrode of a fuel cell generally includes an electrode catalyst layer in which a catalyst and an electrolyte resin are supported on a conductive carrier. In such a fuel cell electrode catalyst layer, since the electrode reaction proceeds at the so-called three-phase interface where the conductive carrier, the electrolyte resin, and the reactive gas are in contact, it is important to efficiently form the three-phase interface. It is.

  In recent years, a method of supporting a catalyst or an electrolyte resin on the surface of a conductive carrier using a supercritical fluid has been proposed. Specifically, a method of supporting a catalyst or electrolyte resin on the surface of a conductive carrier by bringing a supercritical fluid in which a catalyst, an electrolyte resin, or a precursor thereof is dissolved into contact with the conductive carrier has been proposed. (For example, Patent Documents 1 to 3).

  For example, Patent Document 1 discloses a method for producing a carbon nanowall carrying a metal, wherein the carbon nanowall formed on a substrate is contacted with the metal compound dissolved in a supercritical fluid. A method is disclosed. Patent Document 1 describes that in the treatment step, the carbon nanowall is heated to 300 to 800 ° C. As a heating method of the carbon nanowall, there is a method of heating a heater on which the carbon nanowall is mounted. Have been described.

  On the other hand, although not a method for supporting an electrolyte resin or a catalyst, Patent Document 4 discloses a method for activating carbon nanotubes, which includes a liquid that can be easily evaporated and removed by microwave heating on at least one of the outer and inner walls of the carbon nanotubes. By irradiating the carbon nanotubes to which the liquid is adhered with microwaves by removing the liquid by heating and evaporating, the defects are formed on at least one of the outer wall and the inner wall of the carbon nanotube. A method is disclosed that includes generating.

JP 2006-273613 A JP 2007-123049 A Japanese Patent Laid-Open No. 2003-321791 JP 2003-212527 A

In a method for supporting (coating) a catalyst or an electrolyte resin using a supercritical fluid, as described in Patent Document 1, it is possible to increase the coating amount by utilizing the temperature dependence of the solubility of a substance in a supercritical fluid. it can. Specifically, for example, by heating a supercritical fluid in which a metal catalyst or an electrolyte resin or a precursor thereof is dissolved, the solubility of the coating material or precursor in the supercritical fluid can be reduced, and more A coating or precursor can be deposited.
However, when the carbon nanowall (conductive carrier) is heated by heating the substrate as in the method described in Patent Document 1, the substrate and the like become high temperature in addition to the carbon nanowall. Metal is also deposited on the high temperature member. In other words, the intended amount of metal cannot be supported on the conductive carrier.

  The present invention has been accomplished in view of the above circumstances, and an object of the present invention is to selectively coat the surface of a material to be treated in a coating method of a coating material using the temperature dependence of the solubility of a supercritical fluid. An object of the present invention is to provide a method capable of coating a material, particularly a method capable of selectively coating at least one of an electrolyte resin and a metal catalyst on the surface of carbon nanotubes oriented on a substrate.

The coating method of the present invention is a method of coating the surface of a material to be treated with a coating material,
Contacting the material to be treated with a supercritical fluid obtained by dissolving the precursor of the coating material and / or the coating material in a supercritical solvent;
By irradiating the material to be treated with an electromagnetic wave having a wavelength higher than the absorption rate of the supercritical solvent, the material to be treated is treated with the precursor and / or the super material of the coating material. A heating step of heating to a temperature at which the solubility in the critical solvent decreases;
It is characterized by having.

  In the coating method of the present invention, it is possible to heat only the workpiece by irradiation with the electromagnetic wave, and as a result, only the region in the immediate vicinity of the workpiece is typically selected on the surface of the workpiece. It is possible to deposit the coating material.

Specific embodiments of the coating method of the present invention include, for example, an embodiment in which the supercritical solvent is supercritical carbon dioxide and the wavelength of the electromagnetic wave is 2 μm or less.
In addition, as a specific aspect of the coating method of the present invention, for example, an aspect in which the supercritical solvent is supercritical carbon dioxide and the electromagnetic wave is irradiated from at least one of a semiconductor laser and a halogen lamp.

In the coating method of the present invention, examples of the coating material include platinum.
Moreover, in the coating method of this invention, electrolyte resin is mentioned as said coating | covering material, for example.

  In the coating method of the present invention, examples of the material to be treated include carbon nanotubes oriented on the substrate, and more specifically, carbon nanotubes oriented substantially vertically on the substrate.

The method for producing a fuel cell electrode of the present invention is a method for producing a fuel cell electrode in which the surface of a carbon nanotube is coated with a metal catalyst and an electrolyte resin,
Contacting the carbon nanotubes oriented on the substrate with a supercritical fluid in which a precursor of a metal catalyst and / or an electrolyte resin is dissolved in a supercritical solvent;
By irradiating the carbon nanotube with an electromagnetic wave having a wavelength higher than the absorption rate of the supercritical solvent, the carbon nanotube is converted into the precursor of the metal catalyst and / or the electrolyte resin. A heating step of heating to a temperature at which the solubility in the supercritical solvent decreases;
It is characterized by having.

In the method for producing a fuel cell electrode of the present invention, as in the coating method of the present invention, it is possible to heat only the carbon nanotubes by irradiation with the electromagnetic wave, and as a result, only the region in the immediate vicinity of the carbon nanotubes is typical. Specifically, it is possible to selectively deposit at least one of an electrolyte resin and a metal catalyst on the surface of the carbon nanotube.
An example of the metal catalyst is platinum.

  According to the coating method and the method for producing a fuel cell electrode of the present invention, the surface of the material to be treated or the carbon nanotube can be selectively coated with the coating material, or the metal catalyst or the electrolyte resin. Therefore, according to the present invention, it is possible to improve the yield of these materials while ensuring the coating amount of the coating material, the electrolyte resin, and the metal catalyst.

It is a figure which shows the flow in the 1st electromagnetic wave irradiation form in the coating method and manufacturing method of this invention. It is a schematic diagram (2A) which shows the 1st electromagnetic wave irradiation form in the coating method and manufacturing method of this invention, and a figure (2B) which shows the temperature distribution at the time of the electromagnetic wave irradiation in a 1st electromagnetic wave irradiation form. It is a schematic diagram which shows the 2nd electromagnetic wave irradiation form in the coating method and manufacturing method of this invention. It is a figure which shows the flow in the conventional coating method.

The coating method of the present invention is a method of coating the surface of a material to be treated with a coating material,
Contacting the material to be treated with a supercritical fluid obtained by dissolving the precursor of the coating material and / or the coating material in a supercritical solvent;
By irradiating the material to be treated with an electromagnetic wave having a wavelength higher than the absorption rate of the supercritical solvent, the material to be treated is treated with the precursor and / or the super material of the coating material. A heating step of heating to a temperature at which the solubility in the critical solvent decreases;
It is characterized by having.

The method for producing a fuel cell electrode of the present invention is a method for producing a fuel cell electrode in which the surface of a carbon nanotube is coated with a metal catalyst and an electrolyte resin,
Contacting the carbon nanotubes oriented on the substrate with a supercritical fluid in which a precursor of a metal catalyst and / or an electrolyte resin is dissolved in a supercritical solvent;
By irradiating the carbon nanotube with an electromagnetic wave having a wavelength higher than the absorption rate of the supercritical solvent, the carbon nanotube is converted into the precursor of the metal catalyst and / or the electrolyte resin. A heating step of heating to a temperature at which the solubility in the supercritical solvent decreases;
It is characterized by having.

It is known that the solubility of a substance in a supercritical fluid decreases as the solvent density decreases as the temperature increases under the same pressure. In addition, the solubility of a substance in a supercritical fluid is a struggle with the force that the substance (solute) tries to dissolve in the solvent, that is, the vapor pressure, so it is necessary to know the relationship between the solvent and the solute. There is a condition that the relationship where the solubility decreases as the value increases. By utilizing such temperature dependence on the supercritical fluid, it is possible to increase the amount of substances deposited from the supercritical fluid.
The inventors of the present invention make use of the temperature dependence of the solubility in the supercritical fluid as described above to manufacture an electrode in which an electrolyte resin and a metal catalyst are supported on the surface of a carbon nanotube (CNT) that is substantially vertically aligned on a substrate. As a conventional method, when a CNT-oriented substrate (CNT substrate) is placed on a heater and the CNT is heated by heating the CNT, the electrolyte resin or metal catalyst is also used on the substrate. We obtained the knowledge that precipitation of. The electrolyte resin and the metal catalyst deposited on the substrate do not contribute to the electrode reaction, leading to a decrease in material yield.
Furthermore, as a result of repeated studies by the present inventors, it is possible to locally heat only the CNT by irradiating an electromagnetic wave having a wavelength at which the absorption rate of the CNT is higher than that of the supercritical solvent. It has been found that metal catalysts can be selectively deposited on the surface of CNTs.

  The present invention will be specifically described with reference to FIGS. 1, 2, and 4. FIG. 1 shows the flow of the first electromagnetic wave irradiation form in the coating method and the fuel cell electrode manufacturing method of the present invention, and FIG. 2 is a schematic view (2A) showing the first electromagnetic wave irradiation form. It is a figure (2B) which shows the temperature distribution at the time of the electromagnetic wave irradiation in a 1st electromagnetic wave irradiation form. FIG. 4 shows a flow of a conventional coating method.

  When the platinum catalyst is supported on the surface of the substantially vertically aligned CNT of the CNT substrate, for example, as shown in FIGS. 1 and 4, first, a platinum complex that is a precursor of the platinum catalyst is dissolved in supercritical carbon dioxide. Then, by immersing the CNT substrate in supercritical carbon dioxide in which the platinum complex is dissolved, the supercritical carbon dioxide in which the platinum complex is dissolved is permeated between the CNTs.

  Next, in the conventional method, as shown in FIG. 4, the substrate is heated by heating the heater on which the CNT substrate is placed, and further the CNT is heated by heating the substrate. In this case, both the substrate and the CNT are heated, and the solubility of platinum in supercritical carbon dioxide is reduced on both the surface of the substrate and the surface of the CNT. Typically, as shown in FIG. 4, both the substrate temperature and the CNT temperature are higher than the deposition temperature of platinum. That is, platinum precipitates not only on the CNT surface but also on the substrate surface. Also, platinum may be deposited on the surface of the heater.

  On the other hand, in this invention, as shown in FIG. 1, electromagnetic waves, such as a laser which has the above specific absorption factors, are irradiated to CNT, and CNT is heated. Specifically, as shown in FIG. 2 (2A), the CNTs are heated by irradiating the CNT alignment surface of the CNT substrate with a laser. In (2A) of FIG. 2, the pressure vessel 1 is filled with a supercritical fluid (supercritical carbon dioxide in which a platinum complex is dissolved) 2. The pressure vessel 1 is provided with CNTs 3 that are substantially vertically oriented on the substrate 4. A base layer 5 is provided on the CNT orientation surface of the substrate 4. The CNT 3 on the substrate 4 is irradiated with a laser 8 emitted from a laser oscillator 7 through a window 6 provided in the pressure vessel 1. (2B) in FIG. 2 shows the temperature distribution in (2A) in FIG. 2, and shows that CNT can be selectively heated. Thus, by heating only CNT, the solubility of platinum in supercritical carbon dioxide can be lowered only on the surface of CNT. Typically, as shown in FIG. 1 and FIG. 2 (2B), the CNT temperature can be made higher than the platinum deposition temperature while the substrate temperature remains lower than the platinum deposition temperature. That is, platinum can be selectively deposited on the CNT surface without depositing platinum on the substrate.

The present invention using a supercritical fluid has the following merits.
First, supercritical fluids have both a liquid-phase behavior of dissolving solutes and a gas-phase behavior of excellent diffusivity, so they have a very fine structure like a CNT substrate. By contacting a supercritical fluid in which a coating material or a precursor of the coating material is dissolved with the material to be processed, the coating material or the precursor of the coating material can be infiltrated into the entire material to be processed. As a result, a coating material such as a metal catalyst or an electrolyte resin can be uniformly coated (supported) on the surface of the material to be treated.
In addition, since a vigorous flow is generated in the system in the process where the substance is in the supercritical state and in the process where the supercritical state is below the critical point, the cleaning effect of the material to be processed can also be obtained. For example, when an electrochemical treatment is performed on a material to be treated before the coating method according to the present invention is performed, or after a coating method according to the present invention is performed, an electrochemical treatment is performed on the material to be treated. In general, it is possible to omit a necessary cleaning step.
In addition, since the supercritical fluid has no interface between the liquid phase and the gas phase, no surface tension is generated. Therefore, when using a material to be processed having a fiber shape, for example, even when using a CNT substrate or the like in which CNTs with a high aspect ratio (the ratio of the tube length to the tube diameter is large) are aligned, By changing the phase of the critical solvent from the supercritical state to the gas phase, aggregation between fibers (between CNTs) can be suppressed without generating surface tension.

  Furthermore, in the present invention, since the coating material and the precursor are precipitated using the temperature dependency of the solubility of the coating material or the precursor of the coating material with respect to the supercritical solvent, by a simple treatment or a simple device, It can be implemented.

  The present inventors have not only applied a method for producing an electrode using a CNT substrate but also a method for coating a CNT surface of a CNT substrate to a CNT surface by electromagnetic wave irradiation as described above. It has been found that the present invention can be applied to a method for producing an electrode containing the above conductive material, and a method for coating another material to be treated with a coating material. According to the present invention, a porous structure having a fine pore structure such as a CNT substrate can be efficiently coated with a coating material. Therefore, porous structures other than the CNT substrate and other structures It can be sufficiently estimated that the method is effective as a method for coating the surface.

Hereinafter, the coating method and the method for producing a fuel cell electrode according to the present invention will be described.
The coating method of the present invention is a method of coating the surface of a material to be treated with a coating material, and the method for producing an electrode for a fuel cell of the present invention comprises a CNT substrate, a coating material as the material to be treated in the coating method of the present invention. At least one of a precursor of a metal catalyst and an electrolyte resin is used, and the surface of the CNT is coated with at least one of the metal catalyst and the electrolyte resin. Here, the coating method of the present invention will be described as appropriate while mainly explaining the method for producing the fuel cell electrode.
In the present specification, the supercritical fluid is a supercritical solvent in which a coating material precursor and / or a coating material is dissolved, or a metal catalyst precursor and / or an electrolyte resin, and other than the supercritical solvent. A supercritical solvent including a solvent and a component (entrenner) for accelerating dissolution of a component such as the precursor and the coating material in the supercritical solvent is also meant. Further, in this specification, the covering includes a form covering a part of the surface of the material to be processed and a form covering the entire surface of the material to be processed.

[Contact process]
In the contacting step, CNT (material to be treated) oriented on a substrate is dissolved in a supercritical fluid in which a precursor of a metal catalyst (precursor of a coating material) and / or an electrolyte resin (coating material) is dissolved in a supercritical solvent. , The step of contacting.
Due to the solubility and diffusibility of the supercritical fluid, the precursor of the metal catalyst and the electrolyte resin can be infiltrated between the CNTs of the CNT substrate and spread over the surface of each CNT of the CNT substrate.

The CNT oriented on the substrate refers to a state in which the CNT is fixed to the substrate surface, and can be obtained, for example, by growing the CNT on the substrate. Alternatively, it can be obtained by fixing CNTs separately generated on another substrate or the like on the substrate. The alignment form of the CNTs on the substrate is not particularly limited, but it is preferable that the alignment is substantially perpendicular on the substrate. This is because the electrode performance such as gas diffusibility, electron conductivity, and ion conductivity can be improved by forming the fuel cell electrode using a substantially vertically aligned CNT substrate.
Here, the CNT oriented substantially perpendicularly on the substrate means that the angle formed by the surface direction of the substrate and the tube length direction of the CNT is in a range of 90 ° ± 30 °. If it is in the range of 90 ° ± 30 °, the same effect as in the case of being oriented vertically (90 °) can be obtained. There are two types of CNT, straight and non-linear. In the case of non-linear CNT, the direction of the straight line connecting the centers of both end faces in the tube length direction is the tube length direction. To do.

The substrate constituting the CNT substrate is not particularly limited, and examples thereof include SUS, silicon, and aluminum. Among these, SUS is preferable from the viewpoint of achieving both substrate cost and low thermal conductivity. As will be described later, SUS has a merit that a selective heating state of only CNT can be maintained for a long time because its thermal conductivity is very low as compared with CNT.
Moreover, the base layer used when growing CNTs on the substrate may remain on the surface of the substrate. Examples of the underlayer include those containing a porous material such as alumina or silica. The porous material is used to support a growth catalyst that becomes the nucleus of CNT growth.

Even when other conductive materials other than the CNT substrate are used as the conductive material constituting the fuel cell electrode and other battery electrodes, the effects of the present invention are sufficiently exhibited. This is because according to the present invention, the surface of the material to be treated can be selectively coated with the coating material.
Other conductive materials include carbon such as carbon nanotube (CNT), carbon nanofiber, carbon black, glassy carbon, acetylene black, carbon felt, carbon cloth, carbon nanohorn (CNH), carbon nanowall (CNW), etc. Examples thereof include metals, metals such as titanium, silicon, tin, copper, titania, silica, and tin oxide, and metal oxides. These conductive materials may be used alone or in combination of two or more.
Electrodes formed using CNT substrates and conductive materials as described above have a fine pore structure (porous structure) on the surface, so the surface is covered with an electrolyte resin or metal catalyst. In the present invention, the excellent diffusibility and solubility of the supercritical fluid allows the metal catalyst precursor and the electrolyte resin to permeate into the porous structure. A sufficient amount of metal catalyst or electrolyte resin can be supported on the surface of the porous structure.

  In the fuel cell electrode manufacturing method of the present invention, the conductive material such as CNT as the material to be coated with the electrolyte resin is previously coated (supported) with a metal catalyst as described later. May be. In this case, as a method for coating the surface of the conductive material such as CNT with the metal catalyst, a general catalyst supporting method can be adopted in addition to the electrode manufacturing method of the present invention (the coating method of the present invention). Examples of a general catalyst loading method include a wet method and a dry method. Specifically, a metal catalyst salt solution (for example, a platinum salt solution) or a metal catalyst complex solution is applied to the surface and dried. And a method of firing reduction.

  As a material to be treated which is a coating target of the coating material, a material other than the above-described CNT substrate and other conductive materials can be used.

Examples of supercritical solvents include trifluoromethane (CHF ₃ ), CO ₂ , tetrafluoroethylene (CF ₂ ═CF ₂ ), 1,1,2,2-tetrafluoroethane (CHF ₂ CHF ₂ ), pentafluoroethane. Examples include (CF ₃ CHF ₂ ), water, ethanol, methanol, and the like in a supercritical state. These solvents may be used alone or in combination of two or more.
As the supercritical solvent, supercritical trifluoromethane (CHF ₃ ) and supercritical CO ₂ are particularly preferable. This is because the critical point is relatively low temperature and low pressure, so that it is easy to handle, inert, and excellent in safety.
A supercritical state can be obtained by heating the solvent to a temperature higher than the critical temperature of the solvent and pressurizing the solvent to a pressure higher than the critical pressure of the solvent.

The metal catalyst is not particularly limited as long as it can promote the electrode reaction. For example, the metal catalyst for the fuel cell electrode includes platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium. And metals such as cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, and alloys of these metals. Among these, platinum and platinum alloys, particularly platinum are preferable because of their excellent catalytic performance.
The metal catalyst is usually prepared by dissolving a precursor such as a metal complex, a metal salt, an alloy complex, or an alloy complex in a supercritical solvent, and coating the precursor on the surface of the CNT (material to be treated) according to the present invention. By changing to a metal or alloy, the surface of the CNT (material to be treated) can be coated. As a method for changing the precursor into a metal or an alloy, for example, general techniques such as thermal decomposition and reduction can be employed.
When coating the alloy catalyst, a compound containing two or more metal atoms may be used as a precursor, or two or more compounds containing different metal atoms may be used in combination as a precursor. .

Specific examples of the metal catalyst precursor include platinum catalyst precursors such as (trimethyl) methylcyclopentadienylplatinum, potassium hexachloroplatinate, and dinitrodiammine platinum (solution).
The metal catalyst itself may be dissolved in a supercritical solvent and deposited on the CNT surface.

The electrolyte resin is not particularly limited as long as it has desired ionic conductivity and can be dissolved in a supercritical solvent. For example, the electrolyte resin having proton conductivity includes a fluorine-based polymer electrolyte and a hydrocarbon-based electrolyte. Examples include polymer electrolytes.
Here, the fluoropolymer electrolyte is a perfluorocarbon sulfonic acid resin represented by Nafion (trade name, manufactured by DuPont), Aciplex (trade name, manufactured by Asahi Kasei), Flemion (trade name, manufactured by Asahi Glass), Protonic acids such as sulfonic acid groups, sulfonimide groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups, and phenolic hydroxyl groups on copolymers of fluorocarbon vinyl monomers and hydrocarbon vinyl monomers and polymers of difluorovinyl monomers Fluorine-containing polymer electrolytes such as partially fluorinated polymer electrolytes such as those having a group (proton conductive group) introduced.
The hydrocarbon-based polymer electrolyte is a polymer electrolyte that does not contain fluorine. Specifically, polyether ether ketone, polyether ketone, polyether sulfone, polyphenylene sulfide, polyphenylene ether, polyparaphenylene, etc. General purpose plastics such as engineering plastics, polyethylene terephthalate, polyethylene, polypropylene, polystyrene, and proton acid groups (proton conductive groups such as sulfonic acid groups, sulfonimide groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups, phenolic hydroxyl groups) ) Or a copolymer thereof.

  The coating material is not particularly limited as long as it can be dissolved in a supercritical solvent. In addition to the electrolyte resin and the metal catalyst, for example, a water repellent material, a water repellent material paste, and the like can be given.

  The metal catalyst precursor (coating material precursor) and electrolyte resin (coating material) are dissolved in a solvent other than the supercritical solvent and mixed with the supercritical solvent, so that the metal catalyst precursor and the electrolyte resin are mixed. It can be easily dissolved in a supercritical solvent. The solvent for the metal catalyst precursor as described above is not particularly limited as long as the precursor can be dissolved, and examples thereof include hexane. Further, the solvent for the electrolyte resin is not particularly limited as long as the electrolyte resin can be dissolved, and can be appropriately selected. Examples thereof include alcohols such as ethanol, water, and solvents such as N-methylpyrrolidone (NMP).

The method for preparing the supercritical fluid is not particularly limited, and for example, a supercritical solvent and a metal catalyst precursor and / or an electrolyte resin can be mixed.
Further, the method of bringing the carbon nanotubes (material to be treated) of the CNT substrate into contact with the supercritical fluid is not particularly limited, and examples thereof include a method of immersing the CNT substrate in the supercritical fluid.
Normally, a metal catalyst precursor (coating material precursor) and a CNT substrate (object to be processed) and a metal catalyst precursor and / or an electrolyte resin and a supercritical solvent are sealed in a pressure vessel. The CNT substrate can be immersed in a supercritical fluid in which an electrolyte resin (coating material) is dissolved.

[Heating process]
The heating step irradiates the CNT (object to be processed) with electromagnetic waves having a wavelength higher than that of the supercritical solvent to absorb the CNT (object to be processed), thereby heating the CNT, and the precursor of the metal catalyst. It is a step of heating to a temperature at which the solubility of the (precursor of the coating material) and / or the electrolyte resin (coating material) in the supercritical solvent is lowered.
In the heating step, the CNT surface is heated by reducing the solubility of the precursor of the metal catalyst (precursor of the coating material) and / or the electrolyte resin (coating material) in the supercritical fluid existing in the vicinity of the CNT. Precipitation of the precursor of the metal catalyst (precursor of the coating material) and / or the electrolyte resin (coating material) on the (surface of the object to be processed) can be promoted, and the precipitation amount (coating amount) can be ensured. In the present invention, by using an electromagnetic wave having the specific wavelength as a heating means of the CNT for reducing the solubility, it is possible to heat only the CNT (object to be processed), and to a member other than the CNT. Precipitation can be suppressed, and the precursor of the metal catalyst (precursor of the coating material) and / or the electrolyte resin (coating material) can be efficiently deposited on the surface of the CNT (object to be treated).

The electromagnetic wave should just satisfy | fill the conditions (CNT absorption rate> supercritical solvent absorption rate) that the absorption rate of CNT (material to be processed) is higher than the absorption rate of a supercritical solvent.
For example, since the absorption wavelength of carbon dioxide is about 3 μm to 12 μm (infrared region), if an electromagnetic wave having a wavelength outside this range is used, even when supercritical carbon dioxide is used as a supercritical solvent, it is supercritical. Since carbon dioxide is not heated, the supercritical fluid (atmosphere) located away from the CNT is not heated. Specifically, when supercritical carbon dioxide is used as a supercritical solvent, it is preferable to use an electromagnetic wave having a wavelength of 2 μm or less, and it is particularly preferable to use an electromagnetic wave having a wavelength of 1 μm or less.
Specific examples of the electromagnetic wave oscillation source include a semiconductor laser such as a GaAs laser (wavelength 0.6 to 1.6 μm), a solid-state laser such as a YAG laser (wavelength 1.06 μm), and a ruby laser (wavelength 0.69 μm). Gas lasers such as He—Ne laser (wavelength 0.63 μm), Ar laser (wavelength 0.51 μm), and excimer laser (wavelength 0.15 to 0.35 μm), halogen lamps, and the like. Among these, at least one of a conductor laser and a halogen lamp having a wavelength of 2 μm or less is preferable.

  On the other hand, CNTs, especially CNTs that are substantially vertically aligned, have a high absorption rate in the entire ultraviolet to far infrared region. That is, CNTs can be heated by irradiating electromagnetic waves having a wavelength in the above range, and can be appropriately selected according to the supercritical solvent to be used. Also suitable for the use of supercritical carbon dioxide as a supercritical solvent is an electromagnetic wave having a wavelength of 2 μm or less, or an electromagnetic wave having an oscillation source such as a semiconductor laser, solid laser, gas laser, or halogen lamp as described above. By irradiating, the CNT can be heated.

  The influence of the solute (coating material precursor or coating material such as a metal catalyst precursor or electrolyte resin) and the entrainer in the supercritical fluid on the absorption wavelength and absorption rate of electromagnetic waves of the supercritical solvent, In some cases, an influence due to a critical state (for example, an influence due to a phase change of the solvent from a gas phase state to a supercritical state) may occur. In this case, the intrinsic absorption wavelength of the supercritical fluid may be measured experimentally in advance, and the electromagnetic wave may be selected avoiding the wavelength.

In the heating step, only the CNTs can be heated by irradiating the electromagnetic waves only to the CNTs to be processed.
The method of irradiating electromagnetic waves only to the CNT (material to be treated) is not particularly limited. For example, as shown in FIG. 2 (2A), from the outside of the window 6 provided on the wall of the pressure vessel 1 A method of irradiating the laser 8 generated from the laser oscillator 7 is mentioned. At this time, the focal area of the laser (electromagnetic wave) can be defocused and expanded, so that the irradiation area can be expanded. Further, as shown in FIG. 2, a plurality of laser oscillators 7 may be used so that the entire surface of the CNT oriented on the substrate can be irradiated with the laser.
Note that the window need only be able to transmit the laser from the laser oscillator, and the material and shape may be appropriately selected according to the laser to be used. As a specific material of the window, for example, when supercritical carbon dioxide is used as a supercritical solvent, quartz glass and the like can be mentioned.

  Further, unlike FIG. 2, a waveguide may be introduced into the pressure vessel, an open end may be disposed in the vicinity of the CNT, and electromagnetic waves may be irradiated from the vicinity of the CNT. In this case as well, the irradiation area can be expanded by defocusing, using a plurality of oscillators, and / or introducing a plurality of waveguides.

FIG. 3 shows a method of irradiating CNT with electromagnetic waves using a halogen lamp. In FIG. 3, the electromagnetic wave 10 generated from the halogen lamp 9 from outside the window 6 provided on the wall of the pressure vessel 1 is irradiated from the upper part of the CNT substrate. At this time, as in the case of using the laser oscillator shown in FIG. 2, the electromagnetic wave can be irradiated on the entire surface of the CNT oriented on the substrate by defocusing and expanding the focal diameter of the electromagnetic wave or using a plurality of halogen lamps. You may do it.
Note that the window need only be able to transmit electromagnetic waves radiated from the halogen lamp, and the material and shape may be appropriately selected according to the wavelength of the halogen lamp to be used. As a specific material of the window, for example, when supercritical carbon dioxide is used as a supercritical solvent, quartz glass and the like can be mentioned.

  Since the radiation wavelength range of the halogen lamp is about 1 μm, in general, a material having an absorptance of a wavelength of about 1 μm of 0.3 or more can be heated satisfactorily. On the other hand, in the case of a material having an absorptance at a wavelength of about 1 μm of 0.1 or less, the heating effect is generally low.

In addition, since the absorption rate of CNT with respect to a wavelength of about 1 μm is about 0.98, heating by irradiation of electromagnetic waves with a halogen lamp is effective.
On the other hand, as described above, when the absorptivity at a wavelength of about 1 μm is 0.1 or less, the heating effect is low. It can be said that selective heating of CNTs can be performed more effectively by constituting or covering the surface with a material of 0.1 or less. For example, the inner wall of the pressure vessel is made of polished aluminum alloy (1 μm wavelength absorptivity 0.1), silver oxide (1 μm wavelength absorptivity 0.05) or the like, or CNT is emitted from the halogen lamp. The electromagnetic wave of the halogen lamp can be reflected on the inner wall surface of the pressure vessel while being absorbed and heated.

  The temperature control of the CNT as the material to be treated is controlled by the intensity of the electromagnetic wave, the defocus diameter of the electromagnetic wave, the irradiation distance of the electromagnetic wave, the irradiation time of the electromagnetic wave, the solute concentration in the atmosphere (supercritical fluid) in the pressure vessel, the heat capacity of the substrate ,It can be carried out. These conditions may be set as appropriate. Since the intensity distribution does not occur within the irradiation diameter of the electromagnetic wave, the temperature distribution of the CNT does not occur by irradiating the entire surface of the CNT with the electromagnetic wave.

  In addition, the thermal conductivity of CNT is as high as 200 to 3000 W / m · K, and the heat generated on the surface of the CNT is quickly transferred to the inside and the root of the CNT. On the other hand, the thermal conductivity of alumina and silica constituting the substrate (e.g., SUS) and the underlayer is about 10 to 400 W / m · K, and the thermal conductivity of supercritical carbon dioxide, which is a supercritical solvent. Is about 0.03 W / m · K at 60 ° C. That is, these thermal conductivities are 1 to 5 orders of magnitude lower than those of CNTs, and the heat of the heated CNTs is not instantaneously transferred to the substrate or atmosphere, but a time with a temperature difference is secured. In addition, the heat capacity ratio between the plurality of CNTs (CNT layer) oriented on the substrate and the substrate is sufficiently smaller in the CNT layer, so that the substrate is instantaneously dissolved in the supercritical fluid by heat transfer. It does not reach the deposition temperature, but only the CNT is heated to ensure a high temperature.

  A cooling means for cooling the substrate may be provided for the purpose of more reliably maintaining the temperature of the substrate below the solute precipitation temperature. As a specific form of the cooling means, for example, there is a form in which the cooling means is provided at the CNT substrate arrangement position in the pressure vessel and the CNT substrate is placed thereon.

In the heating step, after depositing the precursor of the metal catalyst and / or the electrolyte resin on the surface of the CNT (material to be treated) by electromagnetic wave irradiation, for example, by reducing the temperature and / or pressure in the pressure vessel, The supercritical solvent can be below the critical point.
The electrode manufacturing method and coating method of the present invention may include steps other than the above steps. For example, in the heating step, when a metal catalyst precursor is deposited on the CNT surface, an appropriate treatment is performed. Thus, the metal catalyst precursor on the CNT surface is changed to a metal catalyst. As a method for changing the metal catalyst precursor to a metal catalyst, general methods such as thermal decomposition and reduction can be employed as described above.
Further, after the metal catalyst is coated on the CNT surface according to the present invention, the electrolyte resin can be coated on the CNT surface coated with the metal catalyst according to the present invention.

  The electrode provided by the method for producing a fuel cell electrode of the present invention is superior in that a sufficient amount of electrolyte resin and / or metal catalyst is supported on the surface of the CNT as compared with a conventional fuel cell electrode. Electrode performance can be expressed. The electrode provided by the present invention is particularly effective as a fuel cell electrode, but can be suitably used as a battery electrode for a wide variety of fields and fields other than fuel cells.

DESCRIPTION OF SYMBOLS 1 ... Pressure vessel 2 ... Supercritical fluid 3 ... CNT
4 ... Substrate 5 ... Underlayer 6 ... Window 7 ... Laser oscillator 8 ... Electromagnetic wave (laser)
9 ... Halogen lamp 10 ... Electromagnetic wave

Claims (9)

A method of coating the surface of a material to be treated with a coating material,
Contacting the material to be treated with a supercritical fluid obtained by dissolving the precursor of the coating material and / or the coating material in a supercritical solvent;
By irradiating the material to be treated with an electromagnetic wave having a wavelength higher than the absorption rate of the supercritical solvent, the material to be treated is treated with the precursor and / or the super material of the coating material. A heating step of heating to a temperature at which the solubility in the critical solvent decreases;
A coating method characterized by comprising:   The coating method according to claim 1, wherein the supercritical solvent is supercritical carbon dioxide, and the wavelength of the electromagnetic wave is 2 μm or less.   The coating method according to claim 1, wherein the supercritical solvent is supercritical carbon dioxide, and the electromagnetic wave is irradiated from at least one of a semiconductor laser and a halogen lamp.   The coating method according to claim 1, wherein the coating material is platinum.   The coating method according to claim 1, wherein the coating material is an electrolyte resin.   The coating method according to claim 1, wherein the material to be treated is a carbon nanotube oriented on a substrate.   The coating method according to claim 6, wherein the carbon nanotubes are substantially vertically aligned on the substrate. A method for producing an electrode for a fuel cell in which the surface of a carbon nanotube is coated with a metal catalyst and an electrolyte resin,
Contacting the carbon nanotubes oriented on the substrate with a supercritical fluid in which a precursor of a metal catalyst and / or an electrolyte resin is dissolved in a supercritical solvent;
By irradiating the carbon nanotube with an electromagnetic wave having a wavelength higher than the absorption rate of the supercritical solvent, the carbon nanotube is converted into the precursor of the metal catalyst and / or the electrolyte resin. A heating step of heating to a temperature at which the solubility in the supercritical solvent decreases;
A method for producing an electrode for a fuel cell, comprising:   The method for producing a fuel cell electrode according to claim 8, wherein the metal catalyst is platinum.