JP5092381B2 - Catalyst powder for fuel cell, method for producing catalyst powder for fuel cell, and fuel cell - Google Patents

Description

  The present invention relates to a catalyst powder used in a fuel cell, in particular, a polymer electrolyte fuel cell using a solid polymer electrolyte, a production method thereof, and a fuel cell including the catalyst powder in an electrode.

  A single cell of a polymer electrolyte fuel cell (PEFC) has a structure in which a membrane / electrode assembly is sandwiched between a pair of gas flow plates. The membrane / electrode assembly is obtained by joining an anode to one surface of a polymer electrolyte membrane and a cathode to the other surface. A gas flow path is processed in the gas flow plate. For example, electric power can be obtained by supplying hydrogen as fuel to the anode and oxygen as oxidant to the cathode. In the anode and the cathode, the following electrochemical reaction proceeds.

Ano - ^{_{de: 2H 2 → 4H + + 4e}} - (1)
Cathode - ^{_{de: O 2 + 4H + + 4e}} - → H 2 O (2)
The above-described electrochemical reaction proceeds at an interface where a reactant such as an oxidant or fuel and protons (H ⁺ ) and electrons (e ⁻ ) exist (hereinafter, this interface is referred to as a reaction interface). . In addition, protons move the polymer electrolyte membrane from the anode to the cathode with several hydrated waters.

The catalyst layers of the anode and the cathode are a mixture of a cation exchange resin that is a solid polymer electrolyte, carbon, and a catalyst metal. Here, carbon as a catalyst metal carrier forms an electron conduction channel, a cation exchange resin forms a proton conduction channel, and pores form a supply and discharge channel of water as a reaction gas and a product. is there. The cation exchange resin is composed of a proton conduction path called a hydrophilic cluster part through which protons and reaction gases pass and a hydrophobic skeleton part. The reaction interface is formed at the contact surface between the proton conduction path and carbon. By selectively supporting a catalytic metal on the interface, there is an ultra-small amount of platinum-supporting electrode whose utilization of the metal is significantly higher than that of a conventional fuel cell electrode. In order to produce this electrode, an ultra-small amount of platinum-supported carbon, which is a catalyst powder in which the catalyst metal is mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface, has been developed. This catalyst powder is produced by adsorbing the catalyst metal cation on a mixture of carbon and cation exchange resin and then exposing it to a heated reducing atmosphere containing hydrogen gas, and its average particle size. In the range of 0.1 μm to 200 μm, especially 0.1 to 10 μm, the surface of the catalyst layer produced using the powder becomes smooth, and the current distribution in the electrode surface becomes uniform, resulting in improved output performance. Therefore, it is disclosed in Patent Document 1 that this is good.
JP 2003-257439 A

However, although the cell voltage of PEFC to which the above catalyst powder having an average particle size in the range of 0.1 to 10 μm is applied is high when pure hydrogen and pure oxygen are used for the fuel and the oxidizer, respectively, the oxidation voltage is high. There has been a problem of reduction when air containing the agent or hydrogen containing CO ₂ and CO is used as the fuel. The decrease in performance indicates that the gas diffusivity of the electrode is low, and therefore, when the partial pressure of hydrogen or oxygen as a reaction gas is low, the electrode is easily affected by the diffusivity. The low gas diffusivity is that the catalyst powder composing the electrode has a wide particle size distribution, that is, the coexistence of large particles and small particles clogs the pores, making the gas diffusion path remarkably. This is thought to be due to the narrowing. Therefore, when a powder having a narrow particle size distribution is applied, the size of the particles becomes relatively uniform, so that it is expected that gas diffusibility in the electrode is improved by suppressing pore blockage.

Therefore, an object of the present invention is to apply a catalyst metal having a narrow particle size distribution to a catalyst powder in which a catalyst metal is mainly supported on a contact surface between a proton conduction path of a cation exchange resin and a carbon surface. Even when hydrogen containing CO ₂ and CO is used as air or fuel, the cell voltage of the fuel cell is improved.

  In the present invention, the volume cumulative frequency of the catalyst metal is 50% and 90%, respectively, as an index of the particle size distribution of the catalyst powder in which the catalyst metal is mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. The cell voltage is improved by applying the above catalyst powder satisfying the condition of (D90 / D50) ≦ 2.5 to the electrode of the fuel cell, when the particle diameter is reached and the diameter is D50 and D90, respectively. It is based on the discovery of doing. In particular, it has been found that the cell voltage is remarkably improved by applying to PEFC.

  The invention of claim 1 is directed to a fuel cell catalyst powder having an average particle size of 0.1 μm or more and 10 μm or less mainly supported on the proton conduction path of the cation exchange resin and the carbon surface. It is characterized by satisfying the condition of (D90 / D50) ≦ 2.5 when the particle diameter when the volume accumulation frequency reaches 50% and 90%, respectively, is D50 and D90.

  According to a second aspect of the present invention, there is provided a method for producing a catalyst powder according to the first aspect, wherein a mixture containing 3.0% by mass or less of cation exchange resin and carbon is spray-dried to obtain a cation exchange resin and carbon. After the mixed powder containing is manufactured, the mixed powder contains a cation of a catalytic metal element, and the cation is reduced in a gas containing hydrogen.

  According to a third aspect of the present invention, in the fuel cell, the catalyst powder is provided in an electrode.

By applying the catalyst powder of the present invention to a fuel cell, particularly a catalyst layer of PEFC, a high cell voltage can be obtained even when air containing oxidant or hydrogen containing CO and CO ₂ is used. This is because by using a powder with a narrow particle size distribution, that is, with a relatively uniform particle size, blockage of pores due to diffusion of reaction gas is suppressed, and continuous pores are formed. As a result, the gas diffusibility was remarkably improved.

  Further, when the production method of the present invention is used, the particle diameter when the volume cumulative frequency of the particle size distribution reaches 50% and 90%, respectively, where D50 and D90, respectively, (D90 / D50) ≦ 2.5 A catalyst powder with a narrow particle size distribution that satisfies the above can be obtained. In addition, by applying the catalyst powder of the present invention to a fuel cell, particularly a PEFC electrode, the cell voltage is improved even when a reaction gas with a low partial pressure is used. Energy conversion efficiency can be improved.

  The present invention relates to a catalyst powder having an average particle size of 0.1 μm or more and 10 μm or less in which the catalyst metal is mainly supported on the proton conduction path of the cation exchange resin and the carbon surface, and the volume cumulative frequency of the particle size distribution is 50%. When the particle diameters D50 and D90 when reaching 90% satisfy the condition of (D90 / D50) ≦ 2.5, the gas diffusibility of the catalyst layer using the catalyst powder is improved.

  The fuel cell catalyst powder of the present invention comprises a step of preparing a mixed solution containing a total amount of cation exchange resin and carbon of 3.0% by mass or less, and spray-drying the mixed solution to contain carbon and cation exchange resin. The mixed powder is manufactured through a process of including a catalyst metal element cation in the mixture and reducing the cation in a gas containing hydrogen.

Here, the volume cumulative frequency of the particle size distribution indicates the number of powder particles with respect to each particle size range, and the particle sizes when the distribution reaches 50% and 90% are D50 and D90, respectively. At this time, a large value of D90 / D50 indicates that the particle size distribution is wide and the particle size varies, and a small value indicates that the distribution is narrow and the particle size is relatively uniform. The catalyst powder of the present invention satisfies the condition of (D90 / D50) ≦ 2.5, and its particle size distribution is narrow. When a fuel cell to which a catalyst layer manufactured using this powder is applied is operated using air as an oxidant or hydrogen containing CO and CO ₂ as a fuel, the cell voltage is (D90 / D50). Significantly higher than when using powders larger than 2.5. This is due to the fact that the gas diffusibility of the catalyst layer produced using a powder having a narrow particle size distribution, that is, a relatively uniform particle size, is extremely high.

  The catalyst metal of the present invention refers to a platinum group metal such as platinum, palladium, osnium, rhodium, ruthenium, iridium and an alloy containing the same having a high catalytic activity for oxygen reduction reaction or hydrogen oxidation reaction, and includes a cation exchange resin. Indicates a proton conductive resin such as a perfluorocarbon sulfonic acid type styrene-divinylbenzene sulfonic acid type cation exchange resin resin. These resins are described in reports by HL Yeager et al. (J. Electrochem. Soc., 128, 1880 (1981)) and Kokumi et al. (J. Electrochem. Soc., 132, 2601 (1985)). It is a polymer with a microphase-separated structure between the hydrophobic region where the main chain is assembled and the proton conduction path of the hydrophilic region called the cluster where the side chain is assembled. Since the hydrophobic region is a structure similar to polytetrafluoroethylene, there is significantly less permeation of reactants and water. On the other hand, in the proton conduction path, the ion exchange group bonded to the tip of the side chain forms a cluster, and when water is taken into the cluster, the counter ion becomes movable. That is, water, protons and reactants (hydrogen or oxygen) can move through the hydrophilic region. Therefore, the catalytic metal supported on the contact surface between the proton conduction path and the carbon surface is active against the electrode reaction. The EW value of the cation exchange resin is preferably in the range of 800 to 1150. If it is smaller than this, the strength of the resin is insufficient, and if it is larger than this, the amount of ion-exchange groups is reduced and proton conductivity is lowered. The carbon of the present invention refers to a carbon material having electron conductivity, such as carbon black such as acetylene black, furnace black, channel black, and activated carbon.

  In the present invention, “mainly” means that the proportion of the catalyst metal in the total catalyst metal is 80% or more. The ratio is, for example, that an electrode including a catalyst to be evaluated and a cation exchange resin is manufactured using a known method (Japanese Patent Laid-Open No. 2003-257439), and the catalyst supported on the electrode The quantity of electricity based on the adsorption and desorption reaction of hydrogen to and from is determined by measurement in argon gas and sulfuric acid aqueous solution, respectively. The amount of electricity determined by cyclic voltammetry in argon gas is based on the adsorption / desorption reaction of hydrogen on the catalyst supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. From the quantity of electricity obtained by this method, the surface area involved in this reaction is calculated. The calculation formula is as follows.

S = Q × a
In this formula, S is the surface area involved in the reaction (unit is cm ² ), Q is the charge amount (unit is C), and a is the amount of electricity associated with the hydrogen adsorption / desorption reaction on 1 cm ^{2 of the} catalyst surface (unit is C). / cm ² ). This coefficient is 210 × 10 ⁻⁶ when the catalyst involved in the reaction is platinum. Since the adsorption / desorption reaction of hydrogen occurs on the surface of the electrochemically active catalyst, the surface area determined by this calculation is supported on the contact surface between the carbon surface and the proton conduction path of the cation exchange resin. It means the surface area of the catalyst only. This surface area to S _1.

Next, by the same method, the amount of electricity by hydrogen adsorption / desorption reaction when the same electrode is immersed in sulfuric acid aqueous solution and cyclic voltammetry is calculated. In this case, since the electrode is immersed in an aqueous sulfuric acid solution, the catalyst supported on the carbon surface can exchange protons regardless of the contact with the proton conduction path of the cation exchange resin. The surface areas of all the catalysts contained in the electrode are calculated. This surface area and S _2.

By using the values of S ₁ and S ₂ calculated above, the catalyst metal supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface is added to all the catalysts contained in the catalyst particles. The occupying ratio (X) can be calculated as follows.

X = S ₁ / S ₂ × 100
Here, FIG. 1 shows a schematic diagram of the vicinity of the carbon surface of the catalyst powder for fuel cells in which the catalytic metal of the present invention is mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. . The surface of the carbon 1 is covered with a cation exchange resin 2. A catalytic metal 5 is mainly supported on the contact surface between the proton conduction path 3 and the surface of the carbon 1. When a large amount of the cation exchange resin 2 is mixed, the electron conductivity is lowered. Further, the cation exchange resin 2 includes a proton conduction path 3 and a hydrophobic region 4 which are hydrophilic regions.

  The method for producing the catalyst powder of the present invention will be described in detail below.

  First, a mixed solution containing a cation exchange resin and carbon is prepared. The solid content concentration of the mixed solution is 3.0% by mass or less. Here, the solid content concentration is the total amount of solids including a cation exchange resin and carbon, and in addition to these, a fluorine resin for improving the water repellency of the catalyst powder may be included. By using a mixed solution having a solid content concentration of 3.0% by mass or less, the particle size of the resulting mixture of cation exchange resin and carbon can be reduced to 9.0 μm or less, and the particle size distribution of the particle size (D90 / D50 ) ≦ 2.5 can be obtained. Here, it is preferable to use a mixed solution having a solid content concentration of more than 0.5% by mass because the production efficiency of the powder can be increased. Furthermore, the content of the cation exchange resin in the mixture containing carbon and the cation exchange resin is preferably 35% by mass or more and 60% by mass or less with respect to the carbon. The content can be adjusted by the mixing ratio of the liquid mixture containing cation exchange resin and carbon and carbon. If the content of the cation exchange resin is 35% by mass or less, not only the proton conductivity between the catalyst powders is decreased, but also the amount of the cation adsorbed is lowered, resulting in a decrease in the content of the catalyst. The problem is that the thickness increases. On the other hand, when the content is larger than 60% by mass, the content of the cation exchange resin is high, so that the conductivity of the cation exchange resin, which is an insulator, is mixed between the carbon particles, thereby reducing the electronic conductivity. As a result, resistance polarization increases and the cell voltage of PEFC decreases.

Next, a cation of a catalytic metal is included in the mixture of the cation exchange resin and carbon. In this step, the cation is adsorbed on the proton conduction path of the cation exchange resin in the mixture. For example, a solution containing a cation of a catalytic metal is prepared. Next, a cation exchange path of the cation exchange resin in the mixture is adsorbed by immersing a mixture containing carbon and the cation exchange resin in this solution. This is due to an ion exchange reaction between the counter ion of the cation exchange resin and the cation of the catalyst metal. In this step, two or more kinds of ions can be adsorbed to the cation exchange resin by using two or more kinds of ions as the cation to be ion-exchanged. The precursor cation is difficult to adsorb on the exposed carbon without being coated with the cation exchange resin, but the cation exchange resin is not adsorbed by the counter ion of the cation exchange resin. Those that preferentially adsorb to the proton conduction path are preferred. Cations having such adsorption characteristics include [Pt (NH ₃ ) ₄ ] ²⁺ , [Pt (NH ₃ ) ₅ Cl] ³⁺ , [Ru (NH ₃ ) ₆ ] ²⁺ , [Ru (NH ₃ ) ₅ Cl] ²⁺ , [Ru (NH ₃ ) ₆ ] ^{3+ and the} like can be used. Also, in this process, a catalyst metal cation solution is prepared, and a cation exchange resin and carbon mixture is immersed in this solution to adsorb the catalyst metal cation to the cation exchange resin. Can be made. Furthermore, the average particle size of the mixture of carbon and cation exchange resin used here is preferably 0.05 μm or more and 9.0 μm or less. By using a mixture in this range, it becomes easy to control the particle diameter of the catalyst powder obtained after the next step to a range of 0.1 μm or more and 10 μm or less.

  Finally, the cation contained in the mixture of cation exchange resin and carbon is reduced by exposure to a gas atmosphere containing hydrogen. The gas containing hydrogen is preferably a mixed gas of hydrogen and an inert gas such as nitrogen, helium, or argon, and preferably contains 10 vol% or more of hydrogen. Here, it is possible to control the content of the catalyst metal with respect to the total mass of the cation exchange resin and carbon by repeating the step of including a cation in the mixture and the step of exposing to a gas atmosphere containing hydrogen several times. it can. The content can also be adjusted by the content of the cation exchange resin contained in the mixture, the EW value of the resin, and the cation valence of the catalyst metal. The temperature of the gas containing hydrogen is preferably in the range of 80 to 150 ° C. in which the cation of the catalyst metal is sufficiently reduced and the softening of the cation mixed resin contained in the mixture is suppressed. The higher the temperature, the more the particles agglomerate with the softening, so the average particle diameter increases.

  The present invention will be described below with reference to preferred embodiments.

[Experiment 1]
Fuel cell cathodes using various catalyst powders with different D90 / D50 values were fabricated as follows. First, 150 g of a cation exchange resin solution (Aldrich, Nafion 5% by mass solution), 100 g of 2-propanol (Nacalai tesque) and 50 g of deionized water were mixed using a stirrer (Rotary shaker, TAITEC). Mix well for hours. After adding 11.25 g of carbon powder (Cabot, Vulcan XC-72) to 300 g of this mixed solution and dispersing with a vacuum mixer (UH-600S, SMT) for 30 minutes, the mixture was irradiated with ultrasonic waves for 2 minutes. After adding 2-propanol to the prepared dispersion and diluting each to the prescribed solid content concentration, each diluted dispersion is spray-dried at 120 ° C using a spray dryer, so that carbon and cation are obtained. A powder containing an exchange resin was obtained.

Add [Pt (NH ₃ ) ₄ ] to 10 g of each mixed powder prepared using the diluted dispersion of the prescribed concentration. [Pt (NH ₃ ) ₄ ] ²⁺ ions were adsorbed on the proton conduction path of the cation exchange resin by adding 125 ml of 50 ml mol l- ¹ aqueous solution of Cl ₂ and stirring at 60 ° C for 6 hours . After adsorption, [Pt (NH ₃ ) ₄ ] ²⁺ ions adsorbed excessively on the mixture of carbon and cation exchange resin are washed with deionized water and dried at 60 ° C., and then hydrogenated at a predetermined temperature for 6 hours. Under the atmosphere, the [Pt (NH ₃ ) ₄ ] ²⁺ ion was reduced. Furthermore, catalyst powders A to G having different particle size distributions were obtained by repeating the cation adsorption step and the ion reduction step twice. Table 1 shows the concentration of the diluted dispersion used for the production of the catalyst powder, the average particle size of the mixture of the cation exchange resin and carbon obtained using the dispersion, and the reduction temperature.

A paste was prepared by mixing 2.0 g of this catalyst powder and 8.2 g of N-methyl-2-pyrrolidone (NMP, Nacalai tesque) with a hybrid mixer (HM500, KEYENCE) for 30 minutes, and after applying the paste on Ti foil The electrode for a fuel cell as a cathode was manufactured by drying at 80 ^° C. for 30 minutes. This electrode supported 0.15 mg cm ^{−2 of} platinum. The electrode cut into a size of 5 cm × 5 cm was applied to a fuel cell.

The fuel cell anode used in Experiment 1 was manufactured by the following method. First, 150 g of a cation exchange resin solution (Aldrich, Nafion 5% by mass solution), 100 g of 2-propanol (Nacalai tesque) and 50 g of deionized water were mixed using a stirrer (Rotary shaker, TAITEC). Mix well for hours. After adding 11.25 g of carbon powder (Cabot, Vulcan XC-72) to 300 g of this mixed solution and dispersing with a vacuum mixer (UH-600S, SMT) for 30 minutes, the mixture was irradiated with ultrasonic waves for 2 minutes. Cation exchange with carbon is performed by adding 2-propanol to the prepared dispersion and diluting it to a solid concentration of 1.5% by mass, and then spray-drying the diluted dispersion at 120 ° C using a spray dryer. A powder containing resin was obtained. [Pt (NH ₃ ) ₄ ] was prepared so that the atomic ratio Pt: Ru = 20: 80 was applied to 10 g of the powder. By adding 250 ml of a 25 mMol ^-1 mixed aqueous solution containing Cl ₂ and [Ru (NH ₃ ) ₅ Cl] Cl ₂ and stirring for 24 hours, [Pt ( NH ₃ ) ₄ ] ²⁺ ions and [Ru (NH ₃ ) ₅ Cl] ²⁺ ions were adsorbed. After adsorption, the [Pt (NH ₃ ) ₄ ] ²⁺ and [Ru (NH ₃ ) ₅ Cl] ²⁺ ions adsorbed excessively on the mixture of carbon and cation exchange resin were washed with deionized water at 60 ° C. After drying, the [Pt (NH ₃ ) ₄ ] ²⁺ ion and [Ru (NH ₃ ) ₅ Cl] ²⁺ ion were reduced at 120 ° C. for 24 hours under a hydrogen atmosphere. Furthermore, a catalyst powder was obtained by repeating the cation adsorption step and the ion reduction step twice.

A paste was prepared by mixing 2.0 g of this catalyst powder and 8.2 g of N-methyl-2-pyrrolidone (NMP, Nacalai tesque) with a hybrid mixer (HM500, KEYENCE) for 30 minutes, and after applying the paste on Ti foil The anode was fabricated by drying at 80 ^° C. for 30 minutes. On this electrode, platinum and ruthenium as catalytic metals were supported at 0.12 mg cm ⁻² and 0.18 mg cm ⁻² , respectively. The electrode cut into a size of 5 cm × 5 cm was applied to a fuel cell.

Electrode and polymer electrolyte membrane assemblies using various fuel cell catalyst powders with different D90 / D50 were produced by the following procedure. First, a polymer electrolyte membrane (DuPont Nafion 112 membrane, film thickness of about 50 mm) was kept in 0.5 mol l- ¹ sulfuric acid at 80 ° C for 1 hour, and then deionized water at 80 ° C for 1 hour. Washing was carried out by holding the plate. Subsequently, the cathode and the anode were arranged on both sides of the membrane, and then the membrane and the electrode were joined together by thermocompression bonding (160 ° C., 0.2 MPa). Thus, the membrane / electrode assembly provided with the electrode for fuel cells using the catalyst powder of the present invention was obtained. Finally, the membrane / electrode assembly was sandwiched between a pair of gas flow plates to produce fuel cells having various catalyst powders having different D90 / D50 values on the cathode.

The fuel cell using the catalyst powder of Experiment 1 was operated by supplying oxygen or air humidified at 80 ° C. and hydrogen humidified at 80 ° C. to the cathode and the anode, respectively, while keeping the temperature at 80 ° C. Table 2 shows the solid content concentration of the diluted dispersion when producing the catalyst powder (A to G) applied to the cathode, the value of D90 / D50, and the cell voltage at 300 mAcm ^-2 when operated by supplying air to the cathode. . Furthermore, the particle diameter when the volume cumulative frequency of the particle size distribution reaches 10% is D10, and the value of D10 / D50 is also shown for reference.

Fig. 2 shows the current-voltage curve when the fuel cell using the catalyst powder A shown in Table 2 and the fuel cell using the catalyst powder F are operated under pure hydrogen / oxygen conditions. FIG. 3 shows current-voltage curves when supplied and operated. From FIG. 2, the output characteristics when oxygen is supplied to the cathode are similar regardless of the catalyst powder, but from FIG. 3, the characteristics when air is supplied to the cathode are the values of D90 / D50. It turns out that it is excellent when using catalyst powder A as small as 1.55. Furthermore, it can be seen from Table 2 that a high cell voltage is exhibited when the catalyst powders A to D shown in the thick frame are used. FIG. 4 shows the relationship between the D90 / D50 values of the catalyst powders A to G and the cell voltage at 300 mAcm ⁻² . From the figure, it can be seen that the value of D90 / D50 is 2.5 or less, that is, the cell voltage is high when catalyst powders A to D are used. Furthermore, all of these catalyst powders were found to have a D10 / D50 value of 0.4 or more at the same time. In other words, it was found that by satisfying the condition of D90 / D50 ≦ 2.5, D10 / D50 ≧ 0.4 was satisfied at the same time, and a powder having a narrow particle size distribution was obtained. From the above results, in the cell to which the catalyst powder having a narrow particle size distribution is applied, continuous pores for the reaction gas to diffuse are formed due to the relatively uniform size of the particles in the catalyst layer. Therefore, as a result of sufficient gas diffusivity being obtained, diffusion polarization is reduced, and it is considered that a high cell voltage was obtained even when air was used as the oxidant.

[Experiment 2]
Fuel cell anodes using various catalyst powders with different D90 / D50 values were fabricated as follows. First, 150 g of a cation exchange resin solution (Aldrich, Nafion 5% by mass solution), 100 g of 2-propanol (Nacalai tesque) and 50 g of deionized water were mixed using a stirrer (Rotary shaker, TAITEC). Mix well for hours. After adding 11.25 g of carbon powder (Cabot, Vulcan XC-72) to 300 g of this mixed solution and dispersing with a vacuum mixer (UH-600S, SMT) for 30 minutes, the mixture was irradiated with ultrasonic waves for 2 minutes. After further adding 2-propanol to the prepared dispersion and diluting each to a predetermined solid content concentration, each diluted dispersion is spray-dried at 120 ^° C. using a spray dryer. A powder containing an ion exchange resin was obtained.

[Pt (NH ₃ ) ₄ ] prepared to have an atomic ratio of Pt: Ru = 20: 80 to 10 g of each mixed powder produced using a dilute dispersion with a predetermined concentration By adding 250 ml of a 25 mMol ^-1 mixed aqueous solution containing Cl ₂ and [Ru (NH ₃ ) ₅ Cl] Cl ₂ and stirring for 24 hours, [Pt ( NH ₃ ) ₄ ] ²⁺ ions and [Ru (NH 3) 5 Cl] ²⁺ ions were adsorbed. After adsorption, the [Pt (NH ₃ ) ₄ ] ²⁺ and [Ru (NH ₃ ) ₅ Cl] ²⁺ ions adsorbed excessively on the mixture of carbon and cation exchange resin were washed with deionized water at 60 ° C. After drying, the [Pt (NH ₃ ) ₄ ] ²⁺ ion and [Ru (NH ₃ ) ₅ Cl] ²⁺ ion were reduced at a predetermined temperature for 24 hours under a hydrogen atmosphere. Furthermore, catalyst powders H to N having different particle size distributions were obtained by repeating the cation adsorption step and the ion reduction step twice. Table 3 shows the concentration of the diluted dispersion used for the production of the catalyst powder, the average particle diameter of the mixture of the cation exchange resin and carbon obtained using the dispersion, and the reduction temperature.

A paste was prepared by mixing 2.0 g of this catalyst powder and 8.2 g of N-methyl-2-pyrrolidone (NMP, Nacalai tesque) with a hybrid mixer (HM500, KEYENCE) for 30 minutes, and after applying the paste on Ti foil The anode was fabricated by drying at 80 ^° C. for 30 minutes. This electrode supported 0.18 mg cm ^{-2 of} platinum and 0.12 mg cm ^{-2 of} ruthenium. The electrode cut into a size of 5 cm × 5 cm was applied to a fuel cell.

  Using these anodes having different catalyst powders and the cathode to which the catalyst powder A manufactured in Experiment 1 was applied, a fuel cell including the fuel cell catalyst powder of the present invention was manufactured in the same manner as in Experiment 1.

While maintaining the temperature of the fuel cell to which the catalyst powder of Experiment 2 was applied at 80 ° C., the cathode and the anode were respectively humidified with air humidified at 80 ° C. and CO ₂ 20% and H ₂ 80% containing 10 ppm CO. And a gas mixture of 300 mAcm ^-2 was supplied. Table 4 shows the solid content concentration of the diluted dispersion, the value of D90 / D50 when the catalyst powder (H to L) applied to the anode was manufactured, and the cell voltage at 300 mAcm ^-2 when operated by supplying air to the cathode. . For reference, the value of D10 / D50 is also shown.

It can be seen from the table that a high cell voltage is exhibited when the catalyst powders H to K shown in the thick frame are used. Next, FIG. 5 shows the relationship between the D90 / D50 values of the catalyst powders H to N and the cell voltage at 300 mAcm ⁻² . From the figure, it can be seen that the value of D90 / D50 is 2.5 or less, that is, the cell voltage is high when the catalyst powders H to K are used. Furthermore, all of these catalyst powders were found to have a D10 / D50 value of 0.4 or more at the same time. In other words, it was found that by satisfying the condition of D90 / D50 ≦ 2.5, D10 / D50 ≧ 0.4 was satisfied at the same time, and a powder having a narrow particle size distribution was obtained. When a gas containing CO and CO ₂ is used for the anode, the hydrogen partial pressure is lower than when pure hydrogen is used, so that hydrogen, which is a reactant of the anode, hardly diffuses to the reaction interface. Therefore, it is easily affected by gas diffusibility in the catalyst layer. However, the particle size distribution of the catalyst powder showing the above D90 / D50 value is narrow and the particle size is relatively uniform, so that continuous pores are formed without dense packing of particles, and high gas As a result of ensuring diffusivity, it is considered that high cell voltage was obtained by reducing the polarization of the anode by discharging CO ₂ or CO out of the system and supplying sufficient hydrogen to the reaction interface. .

  From the above results, it was clarified that the PEFC using the cathode and the anode manufactured using the catalyst powder having a D90 / D50 value of 2.5 or less in the particle size distribution shows a high voltage.

  In addition, the method for producing the catalyst powder of the present invention defines the concentration of the spray solution containing the cation exchange resin so that a mixed solution having a total amount of the cation exchange resin and carbon of 3.0% by mass or less is used. Is found to have a critical impact. Furthermore, the temperature condition when the cation adsorbed on the cation exchange resin is reduced by exposure to hydrogen may be in the range of 110 to 160 ° C., and can be produced by appropriately setting.

The figure which showed typically the carbon surface of the electrode by which the catalyst metal was selectively carry | supported mainly on the contact surface of the proton conduction path | route of a cation exchange resin, and a carbon surface. A current-voltage curve when a fuel cell using catalyst powder A as a cathode and a fuel cell using catalyst powder F as a cathode are measured by supplying hydrogen and air to the cathode and anode, respectively. Measurements of a fuel cell using catalyst powder A as the cathode and a fuel cell using catalyst powder F as the cathode when hydrogen and air containing 20% CO ₂ and 10 ppm CO are supplied to the cathode and anode, respectively. Current-voltage curve. The figure which shows the relationship between the value of D50 / D90 of catalyst powder, and the cell voltage in 300 mAcm ^<-2 > when air and air are each supplied to the cathode and anode of PEFC using the powder. 300 mA cm when the value of D50 / D90 of the catalyst powder and hydrogen and air containing 20% CO ₂ and 10 ppm CO, respectively, and air are supplied to the cathode and anode of PEFC using the powder. ^The figure which shows the relationship with the cell voltage in ^-2 .

Explanation of symbols

1 Carbon Particle 2 Cation Exchange Resin 3 Proton Conduction Path 4 Hydrophobic Region 5 Catalytic Metal

Claims (3)

Hydrogen containing CO ₂ and CO in air or fuel to the catalyst metal cation exchange resin of the proton conduction paths and 80% supported average particle diameter 0.1μm or 10μm or less of the oxidizing agent of the total catalyst metal at the interface of the carbon In the fuel cell catalyst powder used, when the particle size distribution when the volume cumulative frequency of the particle size distribution of the powder reaches 50% and 90%, respectively, is D50 and D90, respectively, (D90 / D50) ≦ 2.5 A fuel cell catalyst powder characterized by satisfying the conditions. By spray-drying a mixed solution having a total amount of the cation exchange resin and carbon of 3.0% by mass or less, a mixed powder containing the cation exchange resin and carbon is manufactured. The method for producing a catalyst powder according to claim 1, wherein ions are included and the cations are reduced in a gas containing hydrogen. A fuel cell comprising the fuel powder catalyst powder according to claim 1 on an electrode.