JP2017208240A - Metal particle-supporting catalyst, method for manufacturing the same, and fuel cell arranged by use of metal particle-supporting catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a platinum group metal particle-supporting catalyst, which enables the improvement in durability as a fuel cell.SOLUTION: To achieve the object, a method for manufacturing a metal particle-supporting catalyst is used, which comprises: a pre-treatment step of performing a thermal treatment of carbon; a metal particle-supporting step of causing the carbon to support metal particles, thereby forming a metal particle-supporting carbon; and an oxidation treatment step of forming the metal particle-supporting catalyst by processing the metal particle-supporting carbon in an acidic solution. In the method, a kind of carbon which does not produce a carbon-originating gas as a gas produced by raising the temperature from a room temperature to 500°C is used; the carbon is made to support the metal particles to form the metal particle-supporting carbon; and the metal particle-supporting catalyst is formed by processing the metal particle-supporting carbon in the acidic solution. A fuel cell comprises the above metal particle-supporting catalyst.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a metal particle supported catalyst, a production method thereof, and a fuel cell using the metal particle supported catalyst. In particular, the present invention relates to a platinum particle supported catalyst, a method for producing the same, and a fuel cell using the platinum particle supported catalyst.

  Fuel cells including solid polymer are expected as next-generation power generation systems. Among them, the polymer electrolyte fuel cell has a low operating temperature and is compact compared to other fuel cells. For this reason, the polymer electrolyte fuel cell is expected to be used as a power source for households and automobiles.

  With the recent widespread use of fuel cells, various improvements have been demanded for solid polymer fuel cell catalysts. The solid polymer fuel cell catalyst is excellent in activity, but further improvement is required. In particular, improvement of the durability of the catalyst is required for the polymer electrolyte fuel cell catalyst, and many studies have been made.

  Among them, the following technologies have been developed as technologies attracting attention in recent years. For example, in order to improve the power generation activity, development of immersing the platinum group metal particle-supported catalyst in an acidic solution has been made as a post-treatment of the synthesized platinum group metal particle-supported catalyst. Here, the platinum group metal particle-supported catalyst is a catalyst in which metal particles containing at least a platinum group metal are supported on carbon.

  The post-treatment of the platinum group metal particle-supported catalyst described above is a treatment method in which the platinum group metal particle-supported catalyst is immersed in an oxidizing solution having a predetermined concentration and heated for a predetermined time. By this treatment, the amount of hydrophilic functional groups on the carbon surface of the platinum group metal particle-supported catalyst is increased, and the power generation characteristics as a fuel cell are improved (Patent Document 1).

  Further, for the purpose of improving the durability of the platinum group metal particle-supported catalyst, the carbon is crystallized by heat-treating the carbon at a high temperature of 1500 ° C. or higher before the platinum group metal particles are supported on the carrier carbon. Thus, it is described that deterioration of power generation characteristics due to carbon deterioration can be reduced, that is, durability can be improved (prior art document 2).

JP2012-124001A JP 2012-129059 A

(Patent Document 1)
In the catalyst production method shown in Patent Document 1, platinum group metal particle-supported carbon in which platinum group metal particles are supported on carbon as a carrier is brought into contact with an acidic solution to impart a hydrophilic functional group to the surface of the carbon. We produce platinum group metal particle supported catalysts.

  However, in carbon, there are variations in high density and low density areas. For example, FIG. 1A and FIG. 1B show STEM images of platinum group metal particle-supported catalysts using Ketjen Black (manufactured by Lion) as an example.

  FIG. 1A shows a low density state, and FIG. 1B shows a high density state. In any figure, the part where the density of carbon is low is mixed by the place. In this state, when carbon is brought into contact with the acidic solution described above, the acidic solution penetrates from the portion where the density of carbon is low to the inside of the carbon, and the entire carbon is oxidized. For this reason, the platinum group metal particle supported catalyst treated with the acidic solution is weak in strength.

  FIG. 2 shows, as an example, the results of mass analysis of gas generated by heating a platinum group metal particle-supported catalyst before and after the platinum group metal particle supported catalyst using Ketjen Black (manufactured by Lion) is treated with an acidic solution. It is shown.

  The data “a” indicates the spectrum of a gas having a molecular weight of 78 (benzene) generated when the temperature is raised from room temperature to 500 ° C. at a rate of 10 ° C./min before the acidic solution treatment, and the data of b.

This is a gas generated from carbon, and gas is generated from carbon by treatment with an acidic solution. In other words, the surface of the carbon is decomposed and weakened. When this carbon is used as an electrode of a fuel cell to generate power, the carbon is deteriorated by H ₂ O ₂ generated at the electrode along with power generation, and the power generation characteristics are deteriorated.

(Patent Document 2)
Further, in the carbon treatment method disclosed in Patent Document 2, carbon is heat-treated at a high temperature of 1500 ° C. or higher to crystallize the carbon surface. This improves the durability of the carbon.

  However, by crystallizing carbon, the specific surface area of carbon is reduced. Therefore, when the metal particles are supported on the carbon surface, the metal particles are densely supported because the carbon specific surface area is low. Or carbon will aggregate. As a result, the surface of the metal particles is difficult to be used effectively, and there is a problem that power generation characteristics are lowered when power is generated using the fuel cell electrode.

  Accordingly, an object of the present invention is to provide a metal particle-supported catalyst using carbon that does not have a low density portion and has a specific surface area, a method for manufacturing the same, and a fuel cell using the metal particle-supported catalyst. I will do it.

  In order to achieve the above object, a pretreatment step of heat treating carbon, a metal particle supporting step of forming metal particle supporting carbon by supporting metal particles on the carbon, and treating the metal particle supporting carbon in an acidic solution Thus, an oxidation treatment step for forming a metal particle-supported catalyst and a method for producing the metal particle-supported catalyst are used.

  Further, as a gas generated by raising the temperature from room temperature to 500 ° C., carbon that does not generate a carbon-derived gas is used, metal particles are supported on carbon, metal particle-supported carbon is formed, and metal particle-supported carbon is acidic. A metal particle-supported catalyst formed by processing in a solution is used.

  Further, a fuel cell using the metal particle supported catalyst is used.

  According to the present invention, a fuel cell catalyst having high power generation characteristics and high durability can be produced.

(A) An image diagram showing a portion where the density of conventional carbon is low, (b) An image diagram showing a portion where the density of conventional carbon is high Figure showing the gas analysis spectrum of a conventional catalyst Schematic showing the configuration of the fuel cell of the embodiment The figure which shows the manufacturing method of the catalyst in embodiment The figure which shows the TG analysis spectrum of carbon explaining the evaluation method of an Example

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all of the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. The present invention will be described in detail below, but the present invention is not limited to the following description, and various modifications can be made within the scope of the gist of the present invention.

<Structure of fuel cell>
FIG. 3 is a cross-sectional view showing the basic configuration of the fuel cell according to the embodiment of the present invention. The fuel cell according to this embodiment electrochemically reacts a fuel gas containing hydrogen with an oxidant gas containing oxygen such as air. This is a polymer electrolyte fuel cell that simultaneously generates electric power and heat. The embodiment is not limited to the polymer electrolyte fuel cell, and can be applied to various fuel cells.

  As shown in FIG. 3, the fuel cell according to the present embodiment includes a membrane electrode assembly 10 (MEA) and a pair of plate-like anode separators 20 </ b> A and 20 </ b> C disposed on both surfaces of the membrane electrode assembly 10. A cell 5 (single cell) is provided. Note that the fuel cell according to the present embodiment may be configured by stacking one or a plurality of the cells 5. In this case, the stacked cells 5 are fastened at a predetermined fastening pressure by a fastening member (not shown) such as a bolt so that the fuel gas and the oxidant gas do not leak and the contact resistance is reduced. It is preferable that

  The membrane electrode assembly 10 includes a polymer electrolyte membrane 11 that selectively transports hydrogen ions, and a pair of electrode layers formed on both surfaces of the polymer electrolyte membrane 11. One of the pair of electrode layers is an anode electrode (also referred to as a fuel electrode) 12A, and the other is a cathode electrode (also referred to as an air electrode) 12C.

  The anode electrode 12A is formed on one surface of the polymer electrolyte membrane 11, formed on the anode catalyst layer 13A mainly composed of carbon powder carrying a white metal catalyst, and the anode catalyst layer 13A. It has an anode gas diffusion layer 14A having both electric action, gas permeability and water repellency.

  The cathode electrode 12C is formed on the other surface of the polymer electrolyte membrane 11, and is formed on the cathode catalyst layer 13C mainly composed of carbon powder carrying a white metal catalyst and the cathode catalyst layer 13C. It has a cathode gas diffusion layer 14C having both electric action, gas permeability and water repellency.

  The anode separator 20A disposed on the anode electrode 12A side is provided with a fuel gas passage 21A for flowing fuel gas on the main surface in contact with the anode gas diffusion layer 14A.

  The fuel gas channel 21A is constituted by, for example, a plurality of grooves that are substantially parallel to each other. The cathode separator 20C disposed on the cathode electrode 12C side is provided with an oxidant gas flow channel 21C for flowing an oxidant gas on the main surface in contact with the cathode gas diffusion layer 14C.

  The oxidant gas flow path 21C is constituted by, for example, a plurality of grooves that are substantially parallel to each other.

  The anode separator 20A and the cathode separator 20C may be provided with a cooling water passage (not shown) through which cooling water or the like passes. The fuel gas is supplied to the anode electrode 12A through the fuel gas flow path 21A, and the oxidant gas is supplied to the cathode electrode 12C through the oxidant gas flow path 21C, whereby an electrochemical reaction occurs, and electric power and heat are generated. Occur. Here, in order to cause an electrochemical reaction more efficiently, it is important to humidify the fuel gas and the oxidant gas and maintain the anode electrode 12A and the cathode electrode 12C described above in a predetermined water retention state. This is because the reactants move through moisture, and the humidification conditions are appropriately adjusted according to the configuration and specifications of the fuel cell.

  In this embodiment, the fuel gas passage 21A is provided in the anode separator 20A, but the present invention is not limited to this. For example, the fuel gas channel 21A may be provided in the anode gas diffusion layer 14A. In this case, the anode separator 20A may be flat. Similarly, in this embodiment, the oxidant gas flow path 21C is provided in the cathode separator 20C, but the present invention is not limited to this. For example, the oxidant gas flow path 21C may be provided in the cathode gas diffusion layer 14C. In this case, the cathode separator 20C may be flat.

  Between the anode separator 20A and the polymer electrolyte membrane 11, an anode separator 15A is disposed as a sealing material so as to cover the side surfaces of the anode catalyst layer 13A and the anode gas diffusion layer 14A in order to prevent fuel gas from leaking to the outside. Has been. Further, between the cathode separator 20C and the polymer electrolyte membrane 11, in order to prevent the oxidant gas from leaking to the outside, the cathode separator is used as a sealing material so as to cover the side surfaces of the cathode catalyst layer 13C and the cathode gas diffusion layer 14C. 15C is arranged.

  As the anode separator 15A and the cathode separator 15C, a general thermoplastic resin, thermosetting resin, or the like can be used. For example, as the anode separator 15A and the cathode separator 15C, silicon resin, epoxy resin, melamine resin, polyurethane resin, polyimide resin, acrylic resin, ABS resin, polypropylene, liquid crystalline polymer, polyphenylene sulfide resin, polysulfone, glass fiber reinforced resin Etc. can be used.

  The anode separator 20A and the cathode separator 20C are preferably partially impregnated in the peripheral portion of the anode gas diffusion layer 14A or the cathode gas diffusion layer 14C. Thereby, power generation durability and strength can be improved.

  Further, instead of the anode separator 20A and the cathode separator 20C, the polymer electrolyte membrane 11, the anode catalyst layer 13A, the anode gas diffusion layer 14A, the cathode catalyst layer 13C, and the cathode gas diffusion are provided between the anode separator 20A and the cathode separator 20C. A separator may be disposed so as to cover the side surface of the layer 14C. Thereby, deterioration of the polymer electrolyte membrane 11 can be suppressed, and the handling property of the membrane electrode assembly 10 and the workability at the time of mass production can be improved.

<Method for producing catalyst>
As a catalyst for the anode catalyst layer 13A or the cathode catalyst layer 13C constituting the anode electrode 12A and / or the cathode electrode 12C in the structure of the fuel cell, the platinum group metal particle-supported catalyst of the present embodiment (hereinafter referred to as the catalyst) , Described as catalyst).

  The manufacturing method of the catalyst concerning embodiment is demonstrated using FIG.

  (1) A step of pretreating a carbon material as a carrier to remove carbon having a low density (hereinafter referred to as a pretreatment step) is performed.

  (2) Next, using carbon that has been subjected to a predetermined treatment in the pretreatment step, metal particles containing at least platinum are supported on the carbon (hereinafter referred to as a metal particle support step).

  (3) Further, carbon carrying metal particles is impregnated in an oxidizing solution, and functional groups are introduced on the carbon surface (hereinafter referred to as an oxidation treatment step). By this process, carbon can be made more hydrophilic, and when the above-described fuel cell is constructed and power is generated, the water retention effect of the anode electrode layer and / or the cathode electrode layer can be obtained and power can be generated efficiently. Can do.

  As described above, the pretreatment process, the metal particle supporting process, and the oxidation treatment process are performed in this order.

  The detailed content in each process mentioned above is demonstrated below.

[1. Pretreatment process]
As the carbon 111 used in the present embodiment, it is desirable to apply a carbon powder having a specific surface area of 250 to 1200 m ² / g.

By setting the specific surface area to 250 m ² / g or more, the area to which the catalyst adheres can be increased, so that the catalyst particles can be dispersed in a high state and the effective surface area can be increased.

On the other hand, when the specific surface area exceeds 1200 m ² / g, the existence ratio of ultrafine pores (less than about 20 mm) into which the ion exchange resin is difficult to enter when forming the electrode is increased, and the utilization efficiency of the catalyst particles is decreased.

  Specific examples of the carbon 111 include carbon black, acetylene black, ketjen black, and carbon nanotube. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

  Carbon 111 was heat-treated at 600-1500 ° C. Here, the means for the heat treatment is not limited to the advantage, and a batch-type firing furnace, a rotary kiln, a gas circulation firing furnace, and the like can be used.

In addition, when heated in an atmosphere in which oxygen is present, the carbon 111 is combusted, so that it is desirable to perform the treatment in an inert gas.
Further, when the heat treatment is 600 ° C. or lower, the removal of the carbon 111 having a low density is insufficient, and when the heat treatment is 1500 ° C. or higher, the entire carbon 111 is crystallized and the surface area is reduced. It is desirable that the temperature be 600 ° C. or higher and 1500 ° C. or lower.

  Therefore, it is necessary to manage the heat treatment time. It is necessary to adjust the temperature and processing time at which carbon 111 having a low density to be removed is thermally decomposed and carbon 111 having a high density to be left is not decomposed.

  Furthermore, it is also effective to use atmospheric plasma, UV light, or laser light, which is a high-temperature treatment for a short time, as another means of this pretreatment process. As a result, the manufacturing cost can be reduced by shortening the processing time, the variation in processing due to temperature unevenness and the like can be reduced, and the effect of stabilizing the quality can be expected. In the present embodiment, processing is performed using a general atmospheric pressure plasma processing machine and air as a gas species.

[2. Metal particle support process]
Using the carbon 111 that has been subjected to the pretreatment described above, the carbon 111 and the metal precursor 121 that is the raw material of the metal particles and, if necessary, the additive 122 are mixed / dispersed in the solvent 123, under conditions of a predetermined temperature and time. Stir.

  While stirring, the solution was adjusted to a pH in the range of 4 to 10 using the pH adjusting agent 124, and the temperature was maintained at 30 to 40 ° C. Here, the pH adjustment range is not particularly limited. In order to uniformly disperse and dissolve the carbon 111 and the metal precursor 121, the zeta potential on the surface of the carbon 111 and the solubility of the metal precursor are controlled. It is. Therefore, it is necessary to adjust according to the material to be used.

  Thereafter, a reducing agent 125 is added, and metal ions constituting the metal precursor 121 are reduced, thereby supporting the metal particles on the carbon 111. Thereafter, the platinum group metal particle-supporting carbon is taken out by filtration, washed, dried and fired, and the solvent adhering to the surface and impurities adhering in the previous steps are removed. This procedure of washing, drying and firing is a general method and is not particularly limited.

  Each material in this platinum group metal particle carrying | support process is further demonstrated below.

[Metal precursor 121]
In the present embodiment, a platinum group metal particle-supported catalyst using platinum group particles as the metal particles was manufactured. As metal precursors used for that purpose, platinum group inorganic compounds (platinum group oxides, nitrates, sulfates, etc.), halides (platinum group chlorides, etc.), organic acid salts (platinum group acetates, etc.), Examples thereof include complex salts (such as platinum group ammine complexes) and organometallic compounds (such as platinum group acetolacetonate complexes). Further, the platinum group metal itself may be used after dissolved in the reaction solution. Note that the platinum group includes elements such as Ru, Rh, Pd, Os, and Ir in addition to Pt, as is generally known.

  Among them, as the platinum group salt, it is preferable to use an inorganic compound containing a platinum group, a platinum group halide, or an organometallic compound containing a platinum group. Specifically, a platinum group chloride is used. Is particularly preferred.

  In addition, a platinum group salt may be used individually by 1 type, and may be used combining 2 or more types by arbitrary combinations and ratios.

[Additive 122]
Next, the additive will be described. This additive is used to uniformly disperse / dissolve the carbon 111 and the metal precursor 121 in the solvent. Therefore, the additive dissolves or disperses in the solvent itself, does not hinder the dissolution of the metal precursor in the solvent, improves the affinity of the carbon 111 to the solvent, and does not agglomerate the metal particles and carbon in the subsequent steps. It is necessary to select within the range.

If it is the range mentioned above, the additive called a general complex agent, a dispersing agent, or surfactant can be used as an additive. Specific examples of the complexing agent include ethylenediamine (abbreviation EDA: molecular formula: H ₂ N (CH ₂ ) ₂ NH ₂ ) and diethanolamine (abbreviation DEA: molecular formula: (HOCH ₂ CH ₂ ) ₂ NH. A compound containing a nitrogen atom or an oxygen atom, such as In addition, as a surfactant, a hydrophilic amino group such as hexadecyltrimethylammonium bromide (abbreviation CTAB: molecular formula (CH ₃ (CH ₂ ) ₁₅ N (CH ₃ ) ₃ Br)) and a hydrophobic group are used. Compounds composed of hydrocarbons are desirable, and compounds having the properties of both a complexing agent and a surfactant can be used, but the types of complexing agents and surfactants are not limited here. .

[Solvent 123]
The type of the solvent is not limited as long as it solves the problems of the present invention and has an effect, but usually water or an organic solvent is used. Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, and 2-propanol.

  Among these, water is preferable as the solvent from the viewpoint of easy control of pH, and distilled water or ion exchange water is particularly preferable.

  In addition, a solvent may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio. However, from the viewpoint of pH control, the mixing ratio of water and alcohols is desirably 50% or less of the mixing capacity of alcohols with respect to the total volume.

[PH adjuster 124]
Next, the pH of the mixed solution in which the metal precursor 121, carbon, and additive 122 described above were dissolved and dispersed in the solvent 123 was adjusted with the pH adjuster 124. In general, fine particles in a solution have a charge on the surface, and the charge is generally pH-dependent. Therefore, the electric charge changes from plus to 0 to minus depending on pH. If the electric charge is close to 0, the carbon aggregates, and there is a concern that the carrying position of the metal particles carried on the carbon in the subsequent process may be biased.

  In that case, it is desirable to adjust the pH to the acidic side or the alkaline side to prevent carbon aggregation.

  Moreover, although the method of adjusting pH is not restrict | limited, Usually, a pH adjuster is used. Examples of the pH adjuster include nitric acid, sulfuric acid, hydrochloric acid, ammonia, potassium hydroxide, sodium hydroxide and the like. Of these, hydrochloric acid, nitric acid, and sodium hydroxide are preferable. In addition, a pH adjuster may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

[Reducing agent 125]
The kind of the reducing agent 125 is not limited as long as it is soluble in the solvent in which the metal precursor 121 and the carbon 111 are dissolved / dispersed.

  Specific examples of the reducing agent include nitrogen compounds such as hydrazine, boron compounds such as sodium borohydride, aldehydes such as formaldehyde, L-ascorbic acid and similar carboxylic acids, alcohols such as methanol, and the like.

  Of these, sodium borohydride and hydrazine are preferable as the reducing agent.

  In addition, any one of the reducing agents illustrated above may be used alone, or two or more may be used in any combination and ratio.

  The amount of the reducing agent used is preferably an amount that can sufficiently reduce all the platinum group complexes contained in the platinum group salt solution to the platinum group.

  In general, it may be usually 1-fold equivalent or more with respect to 1 equivalent of metal, and preferably 1.2-fold equivalent or more, more preferably 1.5-fold equivalent or more, considering the efficiency of the reduction reaction. More preferably, a double equivalent or more is desirable. In consideration of post-treatment of unreacted materials, the upper limit is usually 500 times equivalent or less, preferably 100 times equivalent or less, and more preferably 40 times equivalent or less.

  Further, the method for bringing the platinum group salt solution, the carbon powder dispersion, and the reducing agent 125 into contact with each other is not limited. Usually, the reducing agent 125 may be added to a mixed solution obtained by mixing the above platinum group salt solution and the above carbon powder dispersion and mixed to perform a platinum group metal reduction reaction.

  The reducing agent 125 may be added directly to the platinum group salt solution and mixed. However, in order to facilitate mixing and dissolution in the platinum group salt solution, the reducing agent 125 is previously dissolved in a solvent, and this solution is added. (Hereinafter referred to as “reducing agent solution”) may be added to the platinum group salt solution and mixed.

  In this case, the type of the solvent is not limited as long as it can dissolve the reducing agent 125. One kind of solvent may be used alone, or two or more kinds of solvents may be used in any combination and ratio. However, the same type of solvent as that of the platinum group salt solution is usually used.

  The concentration of the reducing agent 125 in the reducing agent solution and the amount of the reducing agent solution used are not particularly limited. What is necessary is just to adjust suitably so that the quantity of the reducing agent with respect to the metal in a platinum group salt solution may satisfy | fill the said range, when a reducing agent solution is added to a platinum group salt solution.

  The temperature during the reduction reaction is usually 4 ° C. or higher, preferably 10 ° C. or higher, and usually lower than the boiling point, preferably 95 ° C. or lower, more preferably 90 ° C. or lower. If the temperature at the time of the reduction reaction is too high, the reduction reaction proceeds faster, so that other than the target platinum group compound may be generated. On the other hand, if the temperature is too low, the reducing power is too weak and the target platinum group compound is You may not get it.

  In addition, as a procedure for starting the reduction reaction, the following two methods (1) and (2) may be mentioned, but any procedure may be used.

  (1) The platinum group at such a low temperature that the reduction reaction does not proceed even when a reducing agent is added (temperature below the above-mentioned normal reduction temperature range, usually room temperature or lower, preferably 10 ° C. or lower, more preferably 5 ° C. or lower). A method of adding a reducing agent (reducing agent solution) to a mixed solution of a salt solution and a carbon powder dispersion, mixing the mixture, and then raising the temperature to a temperature sufficient for the reduction reaction to proceed (a temperature within the specified temperature range). .

  (2) The mixed solution of the platinum group salt solution and the carbon powder dispersion is heated in advance to a temperature at which the reduction reaction of the platinum group salt sufficiently proceeds (temperature within the above specified temperature range). In addition, a technique to start a reduction reaction.

  Through the steps so far, a solution in which metal particle-supporting carbon in which metal particles are supported on carbon is dispersed can be produced. The dispersed metal particle-supporting carbon was separated by filtration and thoroughly washed with water or ethanol. Here, the washing was completed after confirming that the filtrate was not alkaline but sufficiently neutral.

  Moreover, in order to remove the solvent component adhering to the metal particle carrying | support carbon separated by filtration, it dried at 50-110 degreeC, or was left to stand in a pressure-reduced atmosphere. Further, if necessary, if a complexing agent or surfactant residue remains, it can be removed by baking at 100 to 400 ° C.

[3. Acid treatment process]
The metal particle-supporting carbon separated by filtration described above was dispersed again in water. And at least 1 or more types of acid solution 131 was added from nitric acid, a sulfuric acid, and hydrochloric acid, and pH was adjusted so that it might become 1-2.

  The acid concentration was set to 1 to 3 mol / L, the temperature was set to 50 to 80 ° C., and after stirring for 0.5 to 12 hours, the metal particle-supported carbon was separated by filtration and sufficiently washed with water or ethanol. The washing here confirmed that the filtrate was not acidic and became sufficiently neutral. By this step, the carbon surface can be made more hydrophilic, and the water retention effect of the anode electrode layer and / or the cathode electrode layer can be obtained when the above-described fuel cell is configured to generate power. As a result, the reactant is easily conducted through moisture, and can efficiently generate power.

[4. Catalyst completed]
[1. Pretreatment step], [2. Metal particle supporting step], [3. Through the oxidation treatment step, the metal particle-supporting carbon 144 is obtained.

(Example)
Furthermore, a comparison and an Example are shown below about the manufacturing method of the platinum group metal particle carrying | support catalyst in this Embodiment. An example of a basic manufacturing method is shown below.

  First, Ketjen Black EC (manufactured by Lion Corporation) was used as carbon, and a batch-type firing furnace and a plasma processing apparatus were used as heat treatment means, and the carbon pretreatment process was changed and examined.

Next, hexachloroplatinic (tetravalent) acid hexahydrate (H ₂ Cl ₆ Pt · 6H ₂ O) was used as the metal precursor 121, and ethylenediamine was used as a complexing agent as an additive. The mixing ratio of the metal precursor 121 and the additive 122 is a molar ratio of 1: 2 to 1:10 and dissolved in an aqueous ethanol solution having a water: ethanol ratio of 1: 0.1 to 1: 0.4. It was. The solution was heated and stirred at 30 to 50 ° C. for 12 to 24 hours. Here, in order to improve the dispersibility of the carbon 111, it is also possible to add a surfactant. Further, nitric acid and sodium hydroxide were used as the pH adjusting agent 124, and the pH was adjusted to be maintained at a predetermined pH.

  Next, sodium borohydride was added to the above-mentioned solution after stirring, and platinum was reduced by stirring for a predetermined time to support the metal particles on the carbon 111, and the metal particle-supporting carbon was produced in the solution. .

  Thereafter, the carbon carrying metal particles was obtained by filtering, washing and drying.

  Detailed conditions of the carbon 111 used here are shown below, and Tables 1 and 2 show the evaluation results when each carbon 111 is used. Table 1 and Table 2 differ in the pretreatment heat treatment means. In Table 1, carbon 111 was heat-treated in a batch furnace, and in Table 2, it was treated with atmospheric pressure plasma and UV irradiation.

[Comparative Example 1]
The carbon 111 used in the metal particle supporting step was used without being pretreated.
[Comparative Example 2]
As the carbon 111 used in the metal particle supporting step, carbon heat-treated at 300 ° C. was used, and the catalyst was produced by the same method as in Comparative Example 1 except that.
[Example 1]
As the carbon 111 used in the metal particle supporting step, carbon heat-treated at 600 ° C. was used, and the catalyst was produced by the same method as in Comparative Example 1 except that.
[Example 2]
As the carbon 111 used in the metal particle supporting step, carbon heat-treated at 900 ° C. was used, and the catalyst was produced by the same method as in Comparative Example 1 except that.
[Example 3]
Carbon 111 used in the metal particle supporting step was carbon 111 that had been heat-treated at 1500 ° C., and a catalyst was produced by the same method as in Comparative Example 1 except that.
[Example 4]
The carbon 111 used in the metal particle supporting step was carbon 111 that was heat-treated at 2000 ° C., and a catalyst was produced by the same method as in Comparative Example 1 except that.
[Comparative Example 3]
As the carbon 111 used in the metal particle supporting step, the carbon 111 which was subjected to the atmospheric pressure plasma treatment for 0.1 sec was used, and the catalyst was produced by the same method as in Comparative Example 1 except that.
[Example 5]
The carbon 111 used in the metal particle supporting step was carbon 111 that was subjected to an atmospheric pressure plasma treatment for 0.3 sec, and a catalyst was produced by the same method as in Comparative Example 1 except that.
[Example 6]
The carbon 111 used in the metal particle supporting step was carbon 111 that had been subjected to atmospheric pressure plasma treatment for 0.5 sec, and a catalyst was produced by the same method as in Comparative Example 1 except that.
[Example 7]
As the carbon 111 used in the metal particle supporting step, the carbon 111 which was subjected to the atmospheric pressure plasma treatment for 5 times for 0.1 sec was used, and the catalyst was produced by the same method as in Comparative Example 1 except that.
[Example 8]
As the carbon 111 used in the metal particle supporting step, a carbon 111 which was subjected to UV irradiation treatment for 5 times for 0.1 sec was used, and the catalyst was produced by the same method as in Comparative Example 1 except that.

<Evaluation items>
[Evaluation of weight loss by TG analysis]
An example of the thermal analysis result of the carbon processed in the pretreatment process is shown in FIG. The measurement conditions for this thermal analysis are as follows.

Measuring instrument: TG-DTA6200 (manufactured by SII)
Carrier gas: nitrogen Measurement temperature condition: r. t. ˜600 ° C. (temperature increase rate: 10 ° C./min), held at 600 ° C. for 30 min. Measured under the above measurement conditions, the initial weight is 100%, and the weight loss rate at the time of holding at 600 ° C. for 30 min (during measurement) The weight reduction amount / weight at the start of measurement * 100) <A in the figure> is shown in Tables 1 and 2 as the weight reduction amount.

  Here, this weight reduction indicates that the weight is reduced by gasification due to decomposition of carbon. In addition, this gasification is considered to be gasified from a location where the density of carbon is low, and this indicates that there is a portion with low bond strength in carbon. In other words, the greater the weight loss, the lower the durability of the carbon.

  Therefore, the success or failure of the weight reduction rate is set to -2.4% or less. If it exceeds -2.4%, there is a large amount of gas generation, and the voltage drop amount of the membrane electrode assembly described later increases, that is, the durability deteriorates.

[Gas analysis evaluation]
The gas analysis results of the carbon treated in the pretreatment process were measured under the following conditions.

Measuring instrument: JMS-Q1000GCK9 (manufactured by JEOL)
Carrier gas: helium gas (1 mL / min)
Measurement temperature conditions: 100 ° C. to 500 ° C. (temperature increase rate: 20 ° C./min)
The measurement was performed under the above measurement conditions, and it was confirmed whether or not a peak having a molecular weight of 78 was detected.

  Here, it is assumed that the molecular weight 78 indicates benzene, and when carbon is decomposed and gasified, it is estimated that it is gasified in benzene or a similar shape. Usually, when carbon is decomposed and gasified, the benzene ring constituting the carbon is cleaved, and is detected by being decomposed to a low molecular weight (molecular weight smaller than molecular weight 78).

  However, when the molecular weight 78 is detected, it is considered that the gas is gasified in a high molecular weight state, that is, the bond between the benzene rings constituting the carbon is weak. Therefore, when the molecular weight 78 was detected, it was judged that the durability of carbon was low. Those in which gas was detected were rejected, and those in which gas was not detected were considered acceptable.

  Here, it is considered that the gasification of the molecular weight 78 is generated from a portion where the density of carbon is low.

[Membrane electrode assembly voltage <initial>]
The power generation evaluation apparatus having the structure described in the item of the configuration of the fuel cell was used. In the description, a method for manufacturing the membrane electrode assembly 10 will be described.

  Specifically, the catalyst in the present embodiment is used for the cathode electrode 12C to constitute a fuel cell, and its power generation characteristics are examined. In the production of the cathode electrode 12C, the comparative example of this embodiment and the catalyst produced in the example are dispersed in an ethyl alcohol / water mixed solvent or a 2-propanol / n-propanol / water mixed solvent mixed in a predetermined ratio. It was. Ultrasound was irradiated and dispersed as necessary.

  Next, a 5% solution of an ion exchange resin (trade name: manufactured by Nafion Dupont) was added to the dispersion solution and mixed with stirring.

Next, this mixed solution was spray-coated on the electrolyte membrane, and the amount of platinum was adjusted to be a predetermined amount of 0.2 to 0.3 mg / cm ² to form a coated film.

Next, this coating film was hot-pressed at 130 to 150 ° C. and 5 to 30 kg / cm ² to form a cathode electrode.

  The anode electrode 12A was manufactured by the same manufacturing method as the cathode electrode 12C using TEC10E50E (manufactured by Tanaka Kikinzoku) as an anode standard catalyst.

  A fuel cell was constructed using the completed membrane electrode assembly 10 and power generation characteristics were evaluated under the following conditions.

Here, the evaluation voltage of the membrane electrode assembly 10 is a cell temperature of 80 ° C., a cathode and anode dew point temperature of 65 ° C., an oxygen utilization rate, and a hydrogen utilization rate of 50 to 70%. The voltage generated at a current density of 0.25 mA / cm ² was measured. Here, the reason for setting to 0.25 mA / cm ² is set assuming a current density used in a household fuel cell. However, the current density is not particularly limited in the present invention.

[Membrane electrode assembly voltage <after endurance>]
Furthermore, after measuring the membrane electrode assembly voltage <initial> described above, power was generated for 15 minutes, and then supply of oxygen and hydrogen supplied to the anode and cathode was stopped to stop power generation for 15 minutes. This operation of power generation and power generation stop was repeated, and the voltage of the membrane electrode assembly 10 after 1000 cycles was measured.

[Voltage drop before and after endurance]
The voltage difference between the voltage <initial> of the membrane electrode assembly 10 and the voltage <after endurance> of the membrane electrode assembly 10 was quantified as a voltage drop amount.

  The quality of this value depends on the specifications of the fuel cell, but first, a voltage drop of 15 mV or less was judged as good (shown as ◯), and a case where it was 15 mV or more was judged as bad (shown as ×).

  Moreover, although the voltage drop amount was 15 mV or less, a case where the initial voltage was lowered was indicated by Δ.

<Discussion>
In Comparative Example 1, the pretreatment of the carbon 111 is not performed. In Comparative Example 2, the processing temperature is low. For these reasons, it is considered that the carbon skeleton was decomposed in the oxidation treatment process at a portion where the density of the carbon 111 was low, and a portion having a low binding energy was generated. Therefore, the amount of TG weight reduction by TG analysis of carbon 111 is large. Further, it is considered that the carbon skeleton was decomposed and gasified by heat, and a peak considered to be derived from the carbon support was detected by gas analysis.

  From these results, it is considered desirable to pre-treat the carbon 111 so that the TG weight reduction amount is smaller than 2.8%. In addition, it is desirable to perform pretreatment until the carbon does not generate carbon-derived gas in the gas analysis.

  On the other hand, in Examples 1 to 3, by performing a heat treatment at 600 to 1500 ° C. as a pretreatment of carbon, the above-mentioned portion where the density of the carbon 111 is low is removed in advance, and the amount of TG weight loss by the TG analysis of carbon is increased. I think that it decreased. In addition, it is considered that a peak considered to be derived from the carbon support by gas analysis is no longer detected.

  In Example 4, a heat treatment at 2000 ° C. was performed. This confirms that the voltage drop amount of the membrane electrode assembly 10 is small and good, but the absolute value of the voltage <initial> <after durability> of the membrane electrode assembly 10 is lower than the others. This is because the pretreatment temperature of the carbon 111 was high, and accordingly, the crystallization of the carbon 111 progressed and the surface area was reduced.

  For this reason, the metal particles supported on the surface of the carbon 111 are not supported on the carbon in a highly dispersed state, and it is estimated that partial aggregation or particle enlargement occurs. Therefore, the pretreatment temperature of the carbon 111 needs to be lower than 2000 ° C. Preferably, 1550 degrees or less is preferable.

  Furthermore, the example which implemented the atmospheric pressure plasma process as a heating means is shown in the comparative example 3 of Table 2, and Examples 5-8.

  In Comparative Example 3, the processing time was 0.1 sec and the processing time was insufficient. However, as the processing time was increased to 0.3 sec as in Example 5, the removal of carbon 111 having a low density progressed, and the fuel increased. It is thought that the durability of the battery has improved.

  However, it was confirmed that the power generation voltage of the fuel cell decreases when the processing time is long as in Example 6. This is presumably because the temperature of the carbon 111 suddenly increased and the crystallization progressed due to the long processing time. Therefore, as shown in Example 7, it is also possible to eliminate the above-mentioned problem that the temperature of carbon rapidly increases by repeating short-time irradiation a plurality of times.

  Further, the same effect can be obtained not by the atmospheric pressure plasma treatment as in the embodiment 8 but also by the UV irradiation treatment. For this reason, it is important to perform the high temperature treatment in a short time so that the crystallization of carbon does not proceed. For this purpose, it is effective to repeat the pretreatment a plurality of times in a short time.

  From the above results, the processing method is not particularly limited as long as this content is realized, and it is considered that processing using laser light or the like is possible in addition to atmospheric pressure plasma processing and UV irradiation processing. Here, it is considered that when the treatment is performed for a long time by the above treatment method, the time for carbon to be 1500 ° C. or more is long and crystallization proceeds. Therefore, it is desirable to adjust the processing time, the number of times, the processing interval, etc. so that the time for heating to 1500 ° C. or more is 0.3 sec or less.

  The use of the method for producing a catalyst of the present invention is not particularly limited, but it can be used, for example, as an electrode catalyst for a polymer electrolyte fuel cell.

5 cell 10 membrane electrode assembly 11 polymer electrolyte membrane 12A anode electrode 12C cathode electrode 13A anode catalyst layer 13C cathode catalyst layer 14A anode gas diffusion layer 14C cathode gas diffusion layer 15A anode separator 15C cathode separator 20A anode separator 20C cathode separator 21A fuel Gas channel 21C Oxidant gas channel

Claims (11)

A pretreatment process for heat treating carbon;
A metal particle supporting step of supporting metal particles on the carbon to form metal particle supporting carbon;
An oxidation treatment step of forming the metal particle-supported catalyst by treating the metal particle-supported carbon in an acidic solution.   The method for producing a metal particle-supported catalyst according to claim 1, wherein in the pretreatment step, the carbon powder is heat-treated in a range of 600 to 1500 ° C.   The method for producing a metal particle-supported catalyst according to claim 1 or 2, wherein the pretreatment step is performed in an inert gas atmosphere.   The method for producing a metal particle-supported catalyst according to claim 1, wherein the pretreatment step is heat treatment only for an instant of 0.1 to 0.3 sec.   The method for producing a metal particle-supported catalyst according to claim 4, wherein the heating means in the pretreatment step uses a heating means comprising at least one of atmospheric pressure plasma treatment, UV irradiation treatment, and laser light irradiation treatment.   The method for producing a metal particle-supported catalyst according to claim 5, wherein the heat treatment in the pretreatment step is repeated a plurality of times.   The method for producing a metal particle-supported catalyst according to any one of claims 4 to 6, wherein the heat treatment in the pretreatment step is performed for 0.3 seconds or less when carbon is heated to 1500 ° C or higher. The metal particle-supported catalyst according to any one of claims 1 to 7, wherein carbon having a weight change rate of 2.4% or less when the carbon is heated to 600 ° C and held for 30 minutes in the pretreatment step is used. Manufacturing method. The method for producing a metal particle-supported catalyst according to any one of claims 1 to 7, wherein carbon that does not generate carbon-derived gas is used as the gas generated by raising the temperature from room temperature to 500 ° C. As the gas generated by raising the temperature from room temperature to 500 ° C., carbon that does not generate carbon-derived gas is used, metal particles are supported on the carbon, metal particle-supported carbon is formed, and the metal particle-supported carbon is acidic. Metal particle-supported catalyst formed by processing in solution. A fuel cell using the metal particle-supported catalyst according to claim 10.

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