JP2007123049A - Electrode catalyst carrier, manufacturing method of electrode catalyst carrier, manufacturing device of electrode catalyst carrier, membrane electrode assembly for fuel cell, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high performance fuel cell by enabling efficient manufacture of an excellent electrode catalyst carrier and a membrane electrode assembly. <P>SOLUTION: A CO<SB>2</SB>supply part 23, a surface active agent supply part 22, and a plating solution supply part 21 are connected to a chamber 40. A stirring unit 34 and a pair of electrodes (an anode 30 and a cathode 32) for conducting electrolytic plating are installed in the chamber 40. Mixed fluid of CO<SB>2</SB>, the surface active agent, and a plating solution are introduced in the chamber 40. Conductive powder is previously mixed to the mixed fluid. By controlling the pressure and temperature in the chamber 40, CO<SB>2</SB>is made in a supercritical state, and the mixed fluid is stirred to form dispersions. By passing electricity to the anode 30 and the cathode 32, electrode catalyst metal is formed on the surface of the conductive powder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrode catalyst carrier, a method for producing an electrode catalyst carrier, an apparatus for producing an electrode catalyst carrier, a membrane electrode assembly for a fuel cell, and a fuel cell.

  In recent years, materials in which an electrode catalyst such as a metal is supported on a powder (carrier) have been applied to various technologies. This is because, by using this powder, a large surface area can be secured, so that an electrocatalytic action can be obtained with a small amount. One of the applied technologies is a fuel cell with high energy conversion efficiency. This fuel cell is also attracting attention as a clean energy source that does not generate harmful substances. The fuel cell is classified into a phosphoric acid type, a molten carbonate type, a solid electrolyte type, a solid polymer type, and the like depending on the type of electrolyte.

  For example, in a polymer electrolyte fuel cell, a fuel such as hydrogen is supplied to the fuel electrode, and an oxidizing gas such as air is supplied to the oxygen electrode, and a chemical reaction occurs at each electrode. Hydrogen ions (protons) generated at the fuel electrode move to the oxygen electrode through the electrolyte membrane. In the oxygen electrode, hydrogen ions and oxygen ions are combined to generate water and at the same time generate energy. As described above, in the polymer electrolyte fuel cell, the chemical energy of the fuel can be directly converted into electric energy and extracted using the electrochemical reaction.

  In order to realize such a function, in the polymer electrolyte fuel cell, as shown in FIG. 3, an electrolyte membrane 14 having proton conductivity and a pair of electrode catalyst membranes and gas diffusion layers sandwiching the electrolyte membrane 14 are provided. A membrane electrode assembly MEA (Membrane Electrode Assembly) is used. Battery cells having separators on both sides of the membrane electrode assembly MEA are produced. A fuel cell is configured by stacking a plurality of these battery cells.

  The membrane electrode assembly MEA generally uses an electrode catalyst-supporting carbon in which an electrocatalyst material such as platinum (Pt) is supported on a conductive catalyst carrier such as carbon particles (for example, carbon black). It has been. For the electrolyte membrane 14, a perfluorosulfonic acid polymer having proton conductivity is used. In the three-dimensional structure formed by mixing the carbon particles and the electrolyte membrane 14, a porous electrode having a plurality of pores formed therein is formed.

  Here, the carbon particles form an electron conduction channel, and the electrolyte membrane 14 forms a proton conduction channel. In addition, the pores form a supply and discharge channel that supplies oxygen or hydrogen and discharges the product water. In the electrode, these three channels are in three-dimensional contact with each other, and a large number of three-phase interfaces capable of simultaneously transferring gas, proton (H +) and electron (e-) are formed. Is promoted.

  In order to produce such an electrode catalyst-supported carbon, a solid polymer electrolyte solution is mixed with a solution in which carbon black in which platinum is previously supported in an organic solvent is mixed, so that the solid polymer electrolyte layer is placed on the carbon black surface. A technique for precipitation is disclosed (see, for example, Patent Document 1). By depositing the electrolyte layer on the surface of carbon black, a material having a three-phase interface can be mass-produced.

Further, during the electrode reaction, “CO poisoning” may occur in which carbon monoxide (CO) as a reaction product intermediate and a CO component in the fuel are strongly adsorbed on the surface of Pt which is an electrode catalyst material. In this case, the output voltage of the fuel cell decreases. Therefore, in order to realize high CO poisoning resistance, a technique is also disclosed in which an alloy of a second metal such as ruthenium (Ru) is supported on Pt (see, for example, Patent Document 2).

  In Patent Document 2, first, a cation exchange resin solution and carbon particles are mixed, concentrated with stirring at 70 ° C., then formed into a film shape on a polymer film using a screen printing method, and dried. To produce a mixture containing cation exchange resin and carbon particles.

  Next, the electrocatalyst metal colloid is infiltrated into the Nafion (registered trademark) film, the metal colloid is reduced, and an electrode catalyst of several nm is chemically deposited in the Nafion (registered trademark) film. Specifically, by immersing in an aqueous solution containing tetraammine Pt (divalent) cation and hexaammine Ru (trivalent) cation for 15 hours, tetraammine is added to the ion exchange group of the ion cluster portion of the cation exchange resin. A Pt cation and a hexaammine Ru cation are adsorbed by an ion exchange reaction. Next, it is reduced in a hydrogen atmosphere for about 7 hours to form an alloy of Pt and Ru on the surface of carbon particles in contact with the ion cluster part of the cation exchange resin. Thereby, a Pt—Ru alloy having high CO poisoning resistance can be supported as an electrode catalyst.

  On the other hand, in order to perform satisfactory plating, a plating technique using a supercritical fluid is disclosed (for example, refer to Patent Document 3). In the technique described in Patent Document 3, the reaction is performed in a bath containing a substance in a supercritical state and an electrolyte solution. In this technique, since the bath contains a substance in a supercritical state, ions are diffused and efficiently supplied to the surface of an electrode or the like, and the reactivity can be increased.

Furthermore, a technique relating to a method for producing conductive fine particles that are plated in a state where a supercritical fluid or subcritical fluid and a plating solution coexist in electroplating is also disclosed (for example, see Patent Document 4). By using this technique, it is possible to produce conductive fine particles having a plating layer with an extremely uniform thickness and excellent surface smoothness.
JP 2001-283868 A (first page) JP 2001-291520 A (FIGS. 1-2) Japanese Unexamined Patent Publication No. 2003-321791 (FIG. 1) JP 2004-277833 A (first page)

  Here, even in the technique described in Patent Document 1, a three-phase interface can be formed, but since the supported platinum particles are not strongly fixed to the carbon particles, when immersed in a polymer electrolyte solution, Easy to physically fall off. In addition, since the size of the platinum particles cannot be increased to a certain extent, the electrode catalyst metal may be chemically dissolved in a solid polymer electrolyte solution that is strongly acidic.

  In the technique described in Patent Document 2, an electrode catalyst-supporting carbon is formed by depositing an electrode catalyst in a cation exchange resin. Furthermore, since the electrode catalyst metal is formed in the cation exchange resin, it is possible to prevent the electrode catalyst metal from being detached. However, this technique requires several hours for the catalyst deposition treatment and is not efficient.

In addition, one of the important factors that influence the discharge performance of the fuel cell is that pores serving as reaction gas supply paths at the interface between the electrolyte membrane and the electrode, an electrolyte having proton conductivity, and an electrode material It is the width of the reaction area at the three-phase interface formed by and. However, in the technique described in Patent Document 2, since the electrode catalyst metal is deposited in the cation exchange resin film, the electrode catalyst metal and the surface of the carbon particles are not always in contact with each other. For this reason, it is difficult to reliably form a three-phase interface.

The technique described in Patent Document 3 is a technique for plating an object installed on the cathode side, and does not use a powdery object as a plating object.
Furthermore, the technique described in Patent Document 4 is intended to form a plating layer with a uniform thickness on the surface of the conductive fine particles. With such conductive fine particles, the specific area of the electrode catalyst is small, The area of the three-phase interface involving the catalyst is very small.

  The present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a high-performance fuel cell that enables efficient production of a good electrode catalyst carrier and a membrane electrode assembly. is there.

  In order to solve the above-mentioned problems, the invention described in claim 1 has pores in a dispersion of a plating solution containing a metal atom serving as an electrocatalyst metal and a diffusion fluid that enhances the diffusing power of the plating solution. The gist is that the electrocatalyst is mixed on the surface of the conductive powder by mixing the conductive powder and performing electroplating while stirring the dispersion, thereby precipitating particles.

  According to a second aspect of the present invention, in the electrode catalyst carrier according to the first aspect, the electrode catalyst carrier comprises a coating layer that covers a conductive powder carrying the electrode catalyst metal, and the coating layer Is made up of a solid electrolyte.

  The invention according to claim 3 is the electrode catalyst carrier according to claim 1 or 2, wherein in the conductive powder, the electrocatalyst metal is introduced and supported in the pores, and the conductivity The gist is that the surface of the powder is deposited so as not to cover the electrode catalyst metal.

  The invention according to claim 4 is the electrode catalyst carrier according to any one of claims 1 to 3, wherein the conductive powder includes at least one of carbon particles, carbon nanotubes, and carbon nanohorns. Inclusion is included.

  In the invention according to claim 5, conductive powder is mixed in a dispersion of a plating solution containing a metal atom that becomes an electrode catalyst metal and a diffusion fluid that enhances the diffusing power of the plating solution, and the mixture is stirred in a reaction vessel. A step of energizing the electrode in the reaction vessel, reducing the electrocatalyst metal on the surface of the conductive powder, and forming an electrode catalyst support in which particles are deposited, and from the dispersion to the electrode And a step of separating the catalyst carrier.

  According to a sixth aspect of the present invention, in the method for producing an electrode catalyst carrier according to the fifth aspect, in the step of forming the electrode catalyst carrier, the surface of the conductive powder is covered with the electrode catalyst metal. The gist of the present invention is that the process is finished in a state where it is deposited.

  According to a seventh aspect of the present invention, there is provided a reaction vessel in which a conductive powder is mixed with a dispersion of a plating solution containing a metal atom serving as an electrode catalyst metal and a diffusion fluid, and the dispersion is stirred in the reaction vessel. An agitation means, an electrode for performing electroplating on the conductive powder in the reaction vessel, a power source for supplying electric power to the electrode, and an electrocatalyst carrying an electrocatalyst metal from the dispersion The gist of the present invention is to provide a separating means for separating the body.

  The invention according to claim 8 is the electrode catalyst carrier manufacturing apparatus according to claim 7, wherein the power source is deposited so that the electrode catalyst metal does not cover the surface of the conductive powder. The gist is to terminate the electrolytic plating.

  According to the ninth aspect of the present invention, a conductive powder is mixed in a dispersion of a plating solution containing a metal atom serving as an electrocatalyst metal and a diffusion fluid that enhances the diffusion power of the plating solution, and the dispersion is stirred. Electrocatalyst plating while depositing the electrocatalyst powder so that the electrocatalyst metal does not cover the surface of the conductive powder, and using the electrocatalyst carrier as an electrode catalyst layer, the electrolyte membrane and gas diffusion The gist is that it is sandwiched between the layers.

  In the invention according to claim 10, conductive powder is mixed in a dispersion of a plating solution containing a metal atom serving as an electrocatalyst metal and a diffusion fluid that enhances the diffusing power of the plating solution, and the dispersion is stirred. Electrocatalyst plating while depositing the electrocatalyst powder so that the electrocatalyst metal does not cover the surface of the conductive powder, and using the electrocatalyst carrier as an electrode catalyst layer, the electrolyte membrane and gas diffusion The gist is that a membrane electrode assembly sandwiched between layers and a hydrogen gas introduction unit and an oxidizing gas introduction unit facing the membrane electrode assembly are provided.

(Function)
According to the first aspect of the present invention, the conductive powder can be plated by stirring the dispersion. In this case, since the diffusion fluid is used, the coating of the conductive powder as the material to be plated is good.

According to the invention described in claim 2, since the supported electrocatalyst metal and conductive powder are coated with the electrolyte, a three-phase interface can be formed.
According to the invention described in claim 3, the electrocatalyst metal is introduced and supported in the pores of the conductive powder. For this reason, the introduction part in this pore becomes an anchor, the electrocatalyst metal is firmly fixed to the conductive powder, and the physical strength can be increased. Furthermore, since the surface of the conductive powder is deposited so as not to cover the electrode catalyst metal, the electrode catalyst becomes fine particles, and a large surface area can be secured.

  According to the invention described in claim 4, the electroconductive powder can form an electrode catalyst carrier by containing at least one of carbon particles, carbon nanotubes, and carbon nanohorns.

According to invention of Claim 5 or 7, an electrocatalyst carrier can be mass-produced efficiently by using electroplating.
According to invention of Claim 6 or 8, electroplating is complete | finished in the state which deposited so that the surface of the electroconductive powder might not cover an electrode catalyst metal. Thereby, an electrode catalyst metal can be partially deposited on the surface of the conductive powder, and an electrode catalyst carrier capable of forming a three-phase interface can be manufactured. In this case, since the surface of the conductive powder is deposited so that the electrode catalyst metal does not cover it, the electrode catalyst becomes fine particles, and a large surface area can be secured.

  According to the invention described in claim 9 or 10, a membrane electrode assembly with high energy conversion efficiency and a fuel cell using the same are manufactured using an electrode catalyst carrier in which a three-phase interface is reliably formed. be able to.

  According to the present invention, it is possible to efficiently produce a good electrode catalyst carrier and membrane electrode assembly, and to produce a high-performance fuel cell.

DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS. In the present embodiment, as shown in FIG. 3, a description will be given using a fuel cell that includes Pt-supported carbon particles in a fuel electrode or an air electrode as an electrode catalyst layer. First, the structure of the polymer electrolyte fuel cell according to the present embodiment will be described.

(Fuel cell structure)
FIG. 3 shows a cross-sectional structure of the fuel cell according to the embodiment of the present invention. The fuel cell is composed of flat cells 10, and separators 11 are provided on both sides of the cells 10. Although only one cell is shown in FIG. 3, a plurality of cells 10 may be stacked via the separator 11 to constitute a fuel cell having a cell stack structure.

  The cell 10 includes a membrane electrode assembly MEA. This membrane electrode assembly MEA includes an electrolyte membrane 14, a fuel electrode 12b as an electrode catalyst layer, and an air electrode 13b. The fuel electrode 12b and the air electrode 13b are supported by a gas diffusion layer 12a and a gas diffusion layer 13a each made of a porous material (a material that ensures air permeability such as carbon paper or carbon cloth). The fuel electrode 12b and the air electrode 13b are provided to face each other with the electrolyte membrane 14 interposed therebetween.

  The separator 11 on the fuel electrode 12b side is provided with a gas flow path as hydrogen gas introduction means, and fuel gas (for example, hydrogen gas) is supplied to the cell 10 through this gas flow path. Similarly, the separator 11 on the air electrode 13b side is also provided with a gas flow path as an oxidizing gas introduction means, and an oxidizing gas (for example, air) is supplied to the cell 10 through this gas flow path.

  When hydrogen gas is supplied to the fuel electrode 12b via the gas diffusion layer 12a, hydrogen in the gas becomes protons, and these protons move through the electrolyte membrane 14 toward the air electrode 13b. At this time, the emitted electrons move to the external circuit and flow from the external circuit to the air electrode 13b. On the other hand, when air is supplied to the air electrode 13b through the gas diffusion layer 13a, oxygen is combined with protons to become water. As a result, in the external circuit, electrons flow from the fuel electrode 12b toward the air electrode 13b, and electric power can be taken out.

  The electrolyte membrane 14 is preferably a solid that exhibits good ion conductivity in a wet state, and functions as an ion exchange membrane that moves protons between the fuel electrode 12b and the air electrode 13b. The electrolyte membrane 14 is formed of a solid polymer material such as a fluorine-containing polymer or a non-fluorine polymer, and for example, a sulfonic acid type perfluorocarbon polymer, a polysulfone resin, a perfluorocarbon polymer having a phosphonic acid group or a carboxylic acid group. Etc. can be used. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (registered trademark). Examples of non-fluorine polymers include sulfonated aromatic polyetheretherketone and polysulfone.

  The fuel electrode 12b and the air electrode 13b are porous membranes, and in this embodiment, the fuel electrode 12b and the air electrode 13b are composed of an ion exchange resin and carbon particles carrying an electrode catalyst. In this embodiment, platinum (Pt) is used as the electrode catalyst metal to be supported.

(Plating equipment)
Hereinafter, in the present embodiment, Pt-supported carbon particles used for the electrodes are manufactured by electrolytic plating using a diffusion fluid. Here, supercritical carbon dioxide (hereinafter referred to as “CO 2”) is used as the diffusion fluid. The critical point of carbon dioxide is 7.4 MPa at 31 ° C.

First, the outline of the plating apparatus of this embodiment is demonstrated using FIG.
As shown in FIG. 1, the plating apparatus of the present embodiment includes a chamber 40 as a reaction vessel constituted by a pressure vessel that can be sealed. Then, the plating solution supply unit 21, the surfactant supply unit 22, and the CO2 supply unit 23 are connected to the chamber 40, respectively.

  The plating solution supply unit 21 supplies the plating solution from the plating solution tank to the chamber 40 via the plating solution supply pipe. The plating solution tank contains an aqueous solution (plating solution) containing metal atoms (here, Pt) that forms a plating film. In addition, the plating solution supply unit 21 includes a heating / heat retaining means, and is always maintained at a temperature at which the components of the plating solution do not precipitate.

  The surfactant supply unit 22 supplies the surfactant from the surfactant tank to the chamber 40 via the surfactant supply pipe. In this embodiment, a fluorosurfactant is used as a surfactant that acts on CO2 and the plating solution. The fluorine-based surfactant has a parent CO2 portion and a hydrophilic portion composed of fluorine groups. Desirable surfactants as the fluorosurfactant used in the present invention include nonionic surfactants. This fluorine-based nonionic surfactant exhibits a good surface active function in high-pressure CO2.

  Further, examples of the fluorine group include those containing a hetero atom in a carbon chain including a linear or branched perfluoroalkyl group or a perfluoropolyether group. Of these, those having a carbon chain length of about 3 to 15 for a perfluoroalkyl group and about 3 to 50 for a hetero atom in the carbon chain can be used.

  Further, examples of the hydrophilic group include ether, ester, thioether, thioester, amide, and alcohol groups. Among these, those in which the fluorine group mentioned in this example is a perfluoropolyether group and the hydrophilic group is a short-chain polyethylene glycol group are particularly excellent.

  Further, since conventional hydrocarbon surfactants have a long-chain polyethylene glycol group, there is a problem in chemical stability. Compared to this, since the fluorosurfactant is more stable, durability against repeated use over a long period can be expected. In addition, the possibility of contamination by foreign substances derived from the decomposition product of the surfactant is reduced.

  Since the fluorosurfactant is a hydrophobic fluorine group, the time during which CO2 and the plating solution maintain a stable dispersion state (dispersion holding time) is short, and separation of the plating solution from CO2 is easy. There is also excellent operability. When this surfactant is used, when the dispersion operation is stopped, the plating dispersion is separated into CO2 and a plating solution in about several seconds to several tens of seconds, for example.

  The CO2 supply unit 23 supplies CO2 from the CO2 tank to the chamber 40 via the CO2 supply pipe. In this embodiment, CO2 is supplied to the chamber 40 and is brought into a supercritical state at a predetermined temperature and pressure.

  Here, the surfactant supply pipe and the CO2 supply pipe are provided with a liquid pump, a heating unit, and a supply valve. The liquid pump is used to pressurize the fluid to be supplied. The heating unit is used to heat the fluid to be supplied. The supply valve is controlled to be opened and closed, thereby connecting / blocking each tank to the chamber 40 and controlling supply or stop of supply of each fluid.

  Further, the chamber 40 is provided with a stirring unit 34. Specifically, the stirring unit 34 includes a rotor with a mesh to which a permanent magnet is attached inside the chamber 40 and a stator to which a coil is attached outside the chamber 40. By controlling the current flowing through the stator, the rotational speed and direction of the meshed rotor are controlled. The rotational speed of the rotor can be controlled, for example, from about 100 rpm to about 1000 rpm. Using this agitating unit 34, the plating solution, CO2 and surfactant are mixed and diffused in the chamber 40 at a ratio suitable for plating treatment, and rotated under a temperature and pressure condition above the critical point of CO2. The plating dispersion is formed by stirring with an attached rotor.

  Further, this chamber 40 is provided with a block heater (not shown), and CO2 contained in the plating dispersion in the chamber 40 is brought into a supercritical state and maintained at a temperature suitable for further plating.

In addition, a pair of electrodes (anode 30 and cathode 32) are disposed inside the chamber 40. The anode 30 and the cathode 32 are connected to the power supply unit 33.
Further, the chamber 40 is provided with a discharge pipe connected to the separation unit 50. This discharge pipe includes an on-off valve and a regulating valve, and can discharge the fluid from the chamber 40 while managing the pressure.

The separation unit 50 separates the plating dispersion discharged from the chamber 40 into CO 2 containing a surfactant and a plating solution using a difference in specific gravity between them. Here, the specific gravity of the plating solution is about 1.0 to 1.3 (g / cm ³ ), which is heavier than CO 2 containing a surfactant. Therefore, in the separation part 50, it isolate | separates into the upper layer which consists of CO2 containing surfactant, and the lower layer which consists of a plating solution. The CO2 separated in the separation unit 50 is regenerated in a CO2 regenerator (not shown), and is returned to the CO2 supply unit 23 again.

(Production of electrode catalyst support)
Next, a method for producing an electrode catalyst carrier using the above-described plating apparatus will be described with reference to FIG. First, in a state where the chamber 40 is shut off from the respective supply units (21, 22, 23), the chamber 40 is opened, and conductive powder for supporting the electrode catalyst is introduced (step S1). In the present embodiment, carbon particles 101 are used as the conductive powder. As the carbon particles 101, those having a size of 0.03 μm to 0.05 μm are used. The carbon particles 101 are a porous body, and many pores are formed.

  Next, stirring plating of the conductive powder is performed (step S2). Specifically, the chamber 40 into which the carbon particles 101 are introduced is sealed, the supply valve of each supply unit (21, 22, 23) is opened, the CO2 from the CO2 supply unit 23, the interface from the surfactant supply unit 22 The plating solution from the activator and the plating solution supply unit 21 is supplied to the chamber 40 at a predetermined ratio to generate a mixed fluid. In this case, the fluid is heated in each supply unit, and each liquid pump is driven to control the pressure and temperature so that CO 2 is in a supercritical state in the chamber 40.

  Next, when a predetermined amount is accumulated in the chamber 40, the chamber 40 is sealed, and a current is supplied to the stator of the chamber 40 to rotate the meshed rotor of the stirring unit 34. Thereby, in the chamber 40, the mixed fluid of CO2, surfactant, and plating solution is stirred, and a plating dispersion is formed. Here, stirring is performed at about 500 rpm. In this case, the carbon particles 101 dispersed in the plating dispersion are also stirred.

  Then, power is supplied from the power supply unit 33 to the anode 30 and the cathode 32 disposed in the chamber 40, and electrolytic plating is performed on the carbon particles 101 in the plating dispersion in the chamber 40. In the present embodiment, while the plating process is being performed, the meshed rotor is continuously driven, and the plating process is performed while stirring and mixing and dispersing the dispersion in the chamber 40.

  In this case, the carbon particles 101 dispersed in the plating dispersion are repeatedly contacted and detached from the cathode 32 as the plating dispersion is stirred. At the moment when the carbon particles 101 come into contact with the cathode 32, the carbon particles 101 are energized, and the metal ions of the plating dispersion are reduced on the surface of the carbon particles 101. And the metal nucleus is produced | generated on this surface and a nucleus growth is accelerated | stimulated. In the present embodiment, Pt particles 102 are formed on the surfaces of the carbon particles 101.

  In particular, in the present embodiment, a plating dispersion using supercritical CO2 and a plating solution is used. For this reason, the plating solution enters the pores on the surface of the carbon particles 101 by the diffusion force of the supercritical CO2, and the Pt particles 102 that enter the pores are formed. When the carbon particles 101 are detached from the cathode 32 as the plating dispersion is agitated, the metal nucleus growth stops.

By repeating such contact with the cathode 32 and detachment from the cathode 32, a large number of Pt particles 102 are formed on the surface of the carbon particles 101.
Then, stirring plating is finished in a state where the metal deposited by reduction does not cover the surface of the carbon particles 101, that is, in a state where the Pt particles 102 are partially deposited on the surface of the carbon particles 101, and the dispersed Pt support The carbon powder 110 is separated (S3). In this embodiment, in about 10 minutes, the energization between the anode 30 and the cathode 32 and the rotation of the rotor are stopped, and the dispersion in the chamber 40 is discharged to the separation unit 50. In this case, the dispersion is separated into CO2 containing the surfactant and the plating solution by specific gravity. Here, the surfactant layer generated by saturation from the CO2 layer or the Pt-supported carbon powder dispersed in the CO2 layer is recovered by solid-liquid separation (filtration, evaporation to dryness, etc.).

  Then, the mixed fluid from which the Pt-supported carbon powder 110 is separated is separated into CO 2 and a plating solution. This CO2 is regenerated in a CO2 regenerator. On the other hand, each component of the plating solution separated in the separation unit 50 is adjusted by a plating solution regenerator. Then, the regenerated plating solution is returned to the plating solution supply unit 21. Thus, the plating process is completed.

  Next, polymer coating of the Pt-supported carbon powder 110 is performed (S4). Here, a dispersion liquid in which Pt-supported carbon powder 110 is added to an organic solvent and sufficiently mixed and dispersed is used. A Nafion (registered trademark) solution as a solid electrolyte is added to the dispersion as a solid polymer electrolyte, and the mixture is sufficiently stirred and mixed. As a result, as shown in FIG. 2, the solid electrolyte membrane 104 is coated on the surface of the Pt-supported carbon powder 110.

The Pt-supported carbon powder 110 and the ion exchange resin thus obtained are dispersed in a solvent to produce an electrode catalyst ink. Then, this electrode catalyst ink is applied to, for example, carbon paper to be a gas diffusion layer (12a, 13a), heated and dried to form an electrode catalyst layer, and the fuel electrode 12b and the air electrode 13b are produced. As the coating method, for example, brush coating, spray coating, screen printing, transfer technology or the like is used. Subsequently, the electrolyte membrane 14 is sandwiched between the fuel electrode 12b and the air electrode 13b and bonded by hot pressing. Thereby, the membrane electrode assembly MEA is produced.
Further, a separator is provided on the membrane electrode assembly MEA to manufacture the cell 10.

According to this embodiment, the following effects can be obtained.
In this embodiment, the carbon particles 101 dispersed in a dispersion of a plating solution and CO 2 are subjected to electrolytic plating in the chamber 40. In this case, the carbon particles 101 dispersed in the plating dispersion are repeatedly contacted and detached from the cathode 32 as the plating dispersion is stirred. Thereby, only when the carbon particles 101 come into contact with the cathode 32, the electrocatalyst metal is electroplated by energization. Therefore, the electrode catalyst plating can be efficiently formed in a short time. This plating state changes by controlling the current value at the time of electrolytic plating. For example, when a large number of crystal nuclei are formed at a time, it can be realized by flowing a large current in a short time. It is also possible to apply a voltage in pulses.

In the present embodiment, during the plating process, the plating dispersion in which the carbon particles 101 are dispersed is stirred, so that the electrocatalyst metal is plated only at the moment when the carbon particles 101 contact the cathode 32. Unlike the method of depositing the electrode catalyst metal in the cation exchange resin membrane, the electrode catalyst metal is deposited so that the surface of the conductive powder (carbon particles 101) is not covered with the electrode catalyst metal. A three-phase interface can be reliably formed by coating. Furthermore, since the surface of the conductive powder is deposited so as not to cover the electrode catalyst metal, the electrode catalyst becomes fine particles, and a large surface area can be secured.

  In the present embodiment, the carbon particles 101 are plated using a plating dispersion containing CO2 in a supercritical state. Since CO2 in a supercritical state is mixed, the diffusion force of this CO2 improves the coating film coating, and Pt particles 102 that enter the pores of the porous carbon particles 101 are formed. Therefore, the electrocatalyst metal is strongly fixed to the carrier by the anchor effect of the Pt particles 102, and dissolution and desorption can be suppressed.

  In this embodiment, a fluorochemical surfactant is used to mix and disperse the supercritical CO2 and the plating solution. When this surfactant is used, the time during which a uniform dispersion can be maintained is short, and after the stirring is stopped, the plating solution and CO2 are promptly separated. And it isolate | separates in the isolation | separation part 50 using a specific gravity difference. Therefore, in this separated state, the carbon particles 101 dispersed in the dispersion can be separated. Further, since separation is easy, it is easy to collect and regenerate CO2 and plating solution.

Moreover, you may change the said embodiment as follows.
In the present embodiment, the carbon particles 101 are used as the conductive powder. However, the present invention is not limited to this, and acetylene black, ketjen black, carbon nanotubes, and carbon nanohorn-like carbon may be used. Also in this case, the electrocatalyst metal can be supported in the carbon structure by using a plating dispersion containing CO2 in a supercritical state.

  In this embodiment, Pt is used as the electrode catalyst metal, but the present invention is not limited to this. As the electrode catalyst material, one or a mixture or alloyed electrode catalyst selected from noble metals such as Pd, Ru, Os, Ir, Rh, Au and the like can be used in addition to Pt.

  In the present embodiment, Nafion (registered trademark) is used as the electrolyte membrane 14, but is not particularly limited thereto. In addition, it is possible to adopt a sol-gel method that can easily form a thin film having a uniform thickness easily and inexpensively because the thickness can be easily reduced and the thickness can be made uniform and adjusted. If a thin electrolyte thin film having a uniform thickness is formed by the sol-gel method, it is possible to easily and reliably cover all the electrocatalytic active materials with the electrolyte thin film while ensuring good gas permeability. In the case of forming an electrolyte membrane by the sol-gel method, a preparation step for preparing a sol solution, a coating step for applying the sol solution to the surface of the electrode substrate on which the electrode catalytic active substance is supported, and the surface of the electrode substrate The sol solution applied to the gel is gelled to obtain an electrolyte thin film made of a gel material.

  In this embodiment, CO2 in a supercritical state is used as the diffusion fluid. Any diffusion fluid that enhances the diffusing power of the plating solution need not be in a supercritical state and may be in a subcritical state. A substance other than CO2 may be used as the diffusion fluid.

In this embodiment, stirring plating is completed in a state where the metal particles are deposited so as not to cover the surfaces of the carbon particles 101. Alternatively, the stirring plating may be terminated with the surface of the conductive powder coated with the electrode catalyst metal. In this case, after the plating process, the electrode catalyst metal is etched until the surfaces of the carbon particles 101 (conductive powder) are exposed. In this case, the etching rate of the electrode catalyst metal in the pores is slower than the etching rate of the electrode catalyst metal on the surface, so that the electrode catalyst metal can remain in the pores. As a result, an electrocatalyst metal can be carried on the pores of the conductive powder, and an electrocatalyst carrier that can form a three-phase interface can be produced.

  In the present embodiment, the chamber 40 into which the carbon particles 101 are introduced is sealed, and a mixed fluid is generated by supplying CO2, a surfactant, and a plating solution. In the chamber 40, electrolytic plating is performed by stirring a mixed fluid of CO2, a surfactant, and a plating solution. Instead, during the plating process, conductive powder is mixed, and a plating dispersion in which CO2 is in a supercritical state is formed outside the chamber 40, and this plating dispersion is continuously supplied and discharged. You may make it circulate by. In this case, a circulation system is configured in which a mixer and a disperser are connected to the chamber 40 through a supply pipe, and a discharge pipe from the chamber 40 to the mixer / disperser is provided. Furthermore, the anode 30 can also be composed of a platinum mesh. Thereby, anode 30 itself functions as a rotor with a mesh. The residence time of the plating dispersion in the chamber 40 is set to several tens of seconds or less. The chamber 40 may be a shell and tube type, and the plating fluid may be sprayed onto the platinum electrode (anode). Thereby, contact and separation of the carbon particles 101 from the cathode 32 can be repeated in the chamber 40 while maintaining the relative speed between the plating dispersion and the electrode.

  In this embodiment, the Pt-supported carbon particles used for the fuel electrode 12b and the air electrode 13b of the polymer electrolyte fuel cell have been described as an example. However, a metal (electrode catalyst) is supported on a conductive powder (support). The application of the electrode catalyst carrier is not limited to this. Regarding fuel cells, not only anodes and cathodes of polymer electrolyte fuel cells (PEFC) but also anodes and cathodes of direct methanol fuel cells (DMFC) and anodes and cathodes of phosphoric acid fuel cells (PAFC) Is possible. The gas generator can also be applied to anodes and cathodes of solid polymer water electrolyzers, anodes and cathodes of solid polymer hydrogen / oxygen generators, anodes and cathodes of solid polymer ozone generators. is there. In addition, in gas sensors, it can be used as a sensor for detecting the concentration of electrodes of solid polymer type humidity sensors, oxidizing gases such as oxygen and ozone, or reducing gases such as hydrogen, carbon monoxide and hydrogen sulfide. It can accurately measure even a small amount of gas components.

The schematic explanatory drawing of the plating apparatus which performs the electroplating in embodiment. The schematic explanatory drawing of the process in embodiment. Schematic explanatory drawing of a fuel cell.

Explanation of symbols

  MEA ... Membrane electrode assembly, 10 ... Cell, 11 ... Separator, 12a, 13a ... Gas diffusion layer, 12b ... Fuel electrode as electrode catalyst layer, 13b ... Air electrode as electrode catalyst layer, 14 ... Electrolyte membrane, 21 ... Plating solution supply unit, 22 ... surfactant supply unit, 23 ... CO2 supply unit, 30 ... anode, 32 ... cathode, 34 ... stirring unit, 40 ... chamber, 101 ... carbon particles as conductive powder, 102 ... electrode Pt particles as a catalyst metal, 104... Solid electrolyte membrane.

Claims (10)

  Electrolytic plating is performed while mixing the conductive powder having pores in a dispersion of a plating solution containing a metal atom serving as an electrocatalyst metal and a diffusion fluid that enhances the diffusivity of the plating solution, and stirring the dispersion. An electrode catalyst carrier, wherein the electrode catalyst metal is reduced on the surface of the conductive powder to precipitate particles.   2. The electrode catalyst carrier according to claim 1, wherein the electrode catalyst carrier comprises a coating layer covering the conductive powder carrying the electrode catalyst metal, and the coating layer is made of a solid electrolyte. .   The electroconductive powder is characterized in that the electrocatalyst metal is introduced and supported in the pores and is deposited so that the electrocatalyst metal does not cover the surface of the electroconductive powder. The electrode catalyst carrier according to claim 1 or 2.   The electrode catalyst carrier according to any one of claims 1 to 3, wherein the conductive powder includes at least one of carbon particles, carbon nanotubes, and carbon nanohorns. A step of mixing conductive powder in a dispersion of a plating solution containing metal atoms to be an electrocatalyst metal and a diffusion fluid that enhances the diffusing power of the plating solution, and stirring in a reaction vessel;
Energizing an electrode in the reaction vessel, reducing the electrocatalyst metal on the surface of the conductive powder, and forming an electrocatalyst carrier having deposited particles;
And a step of separating the electrode catalyst carrier from the dispersion.   6. The electrode catalyst carrier according to claim 5, wherein the step of forming the electrode catalyst carrier is completed in a state where the surface of the conductive powder is deposited so as not to cover the electrode catalyst metal. Body manufacturing method. A reaction vessel in which a conductive powder is mixed with a dispersion of a plating solution containing a metal atom serving as an electrode catalyst metal and a diffusion fluid;
A stirring means for stirring the dispersion in the reaction vessel;
In the reaction vessel, an electrode for performing electroplating on the conductive powder, a power source for supplying power to the electrode,
An apparatus for producing an electrode catalyst carrier, comprising: separation means for separating an electrode catalyst carrier carrying an electrode catalyst metal from the dispersion.   The said power supply finishes the said electroplating in the state which deposited the surface of the said electroconductive powder so that the said electrode catalyst metal may not cover, The manufacture of the electrode catalyst support body of Claim 7 characterized by the above-mentioned. apparatus. Conductive powder is mixed in a dispersion of a plating solution containing metal atoms to be an electrocatalyst metal and a diffusion fluid that enhances the diffusing power of the plating solution, and electroplating while stirring the dispersion, An electrocatalyst carrier deposited such that the electrocatalyst metal does not cover the surface of the conductive powder;
A membrane electrode assembly for a fuel cell, wherein the electrode catalyst carrier is sandwiched between an electrolyte membrane and a gas diffusion layer as an electrode catalyst layer. Conductive powder is mixed in a dispersion of a plating solution containing metal atoms to be an electrocatalyst metal and a diffusion fluid that enhances the diffusing power of the plating solution, and electroplating while stirring the dispersion, An electrocatalyst carrier deposited such that the electrocatalyst metal does not cover the surface of the conductive powder;
A membrane electrode assembly in which the electrode catalyst support is sandwiched between an electrolyte membrane and a gas diffusion layer as an electrode catalyst layer;
A fuel cell comprising a hydrogen gas introducing means and an oxidizing gas introducing means opposed to the membrane electrode assembly.

Images