JP6097015B2 - Acetylene black and fuel cell catalyst using the same - Google Patents

Description

  The present invention relates to acetylene black having a high specific surface area and high dispersibility.

  The cell structure of the polymer electrolyte fuel cell has a structure in which a gas diffusion layer, a catalyst layer, and an electrolyte membrane are sandwiched between separators provided with gas flow paths. This catalyst layer is composed of carbon black on which platinum particles and / or platinum alloy particles (hereinafter referred to as “platinum particles”) are supported, and the platinum particles are supported on the carbon black surface in a highly dispersed manner. . Here, the term “supported” refers to a state in which another particle is attached to the carbon black surface by a chemical bond or a physical bond. Since the raw material gas such as hydrogen or oxygen is activated by contact with particles such as platinum to generate water, the reaction efficiency is higher when the particles such as platinum in the catalyst layer are supported in a highly dispersed state. On the other hand, if the particles such as platinum are supported on carbon black with low dispersion, that is, if they are aggregated and supported, the contact area between the source gas and the particles such as platinum is reduced, and the reaction efficiency is lowered.

  In order to increase the reaction efficiency of particles such as platinum, carbon black having a high specific surface area is good, and furnace black has been conventionally used. However, since furnace black has low crystallinity, long-term stability is not sufficient, and impurities derived from raw materials such as sulfur, chlorine, potassium, lead, sodium, calcium, etc. are contained in the order of several tens of ppm to several percent. There were many, and long-term stability was inhibited further.

Therefore, it is conceivable to use acetylene black, which has much less impurities than furnace black, but the specific surface area of normal acetylene black is 30 to ²⁰⁰ m ² / g, and the supported area compared to furnace black with a high specific surface area. However, the particles such as platinum are aggregated and supported, and cannot be supported in a highly dispersed state. Therefore, it is necessary to increase the specific surface area of acetylene black. A specific surface area of acetylene black can be increased by oxidizing the surface of acetylene black with air, oxygen or the like at a temperature of 500 ° C. or higher (Patent Document 1). The acetylene black having a high specific surface area as described above is used as a fuel cell catalyst carrier, but there are agglomerated particles in which acetylene blacks are partly aggregated.

  As fuel cell technology has been improved in recent years, the catalyst layer of fuel cells has been made thinner, and there has been a demand for reducing the above-mentioned aggregated particles. When the aggregated particles are present, protrusions due to the aggregated particles are generated in the catalyst layer, which may damage the electrolyte membrane-electrode assembly (MEA) obtained by sandwiching the catalyst layer and the electrolyte membrane. In acetylene black, a bonded body of primary particles called a structure is developed in a branch shape, and it is necessary to loosen the entanglement between the structures to reduce the aggregated particles, but it is not easy.

  As a technique for reducing the carbon black aggregated particles, an external shearing machine (bead mill, ball mill, three rolls, etc.) and an internal shearing machine (ultrasonic homogenizer, jet) (Patent Document 2) has been proposed. In addition, methods have been proposed in which the carbon black itself is pulverized with various pulverization apparatuses (jet mill, planetary mill, etc.) in the form of powder (Patent Documents 3 and 4). However, acetylene black used in this application not only has a structure developed more than that of general carbon black, but also has a high specific surface area, so that there is a limit to crushing by post-treatment.

JP-A-61-66759 JP 2005-216661 A JP-A-2005-41967 JP 2006-274189 A

  An object of the present invention is to provide acetylene black having a high specific surface area and high dispersibility.

The present invention employs the following means in order to solve the above problems.
(1) Agglomerated particles having a specific surface area of 500 to 1100 m ² / g and an aggregate of primary particles of 20 μm or more that are entangled with each other in a branched structure are 10 ppm or less, 0.1 g of acetylene black and 30 g of dibutyl phthalate are homogenizers (Nippon Seiki BM-2) mixed at 2000 rpm for 1 minute, the dispersion by JIS K 5600-2-5 tube gauge is 40 μm or less, the total pore volume is 0.8 ml / g or more, and the water content is 0 Acetylene black, characterized in that it is from 6 to 9.1%.
(2) A catalyst for a polymer electrolyte fuel cell, characterized in that platinum particles and / or platinum alloy particles are supported on the acetylene black described in (1).
(3) After acetylene gas having a high specific surface area is generated by incomplete combustion reaction of acetylene gas in the reaction furnace, and after containing 1.0 to 10.0% (inner percent) of moisture in this acetylene black The method for producing acetylene black according to claim 1, wherein oxidation treatment is performed using an oxidizing gas.

  The acetylene black of the present invention can be dispersed with high dispersion when mixed with water, alcohol or other solvents. Therefore, a uniform plane can be obtained without special consideration when the catalyst layer is formed by coating the slurry after catalysis. In addition, since aggregated particles are reduced, platinum particles and / or platinum alloy particles can be more uniformly supported on the surface of acetylene black in the catalyzing step, leading to improved performance of the solid polymer fuel cell.

The acetylene black of the present invention has a specific surface area of 500 to 1100 m ² / g. If it is less than 500 m < ² > / g, particles, such as platinum, cannot fully disperse | distribute, and reaction efficiency cannot be made high. When the specific surface area exceeds 1100 m ² / g, it is difficult to sufficiently immerse the particles in the supporting liquid, so that it is difficult to support particles such as platinum in a highly dispersed state, and also in this case, the reaction efficiency cannot be increased. . Here, the reaction efficiency is the catalytic activity per unit mass of particles such as platinum, and when the supported amount is constant, the current potential curve in the fuel cell evaluation is compared, and it is determined by the voltage level at the same current value. Is possible. The higher the voltage, the higher the reaction efficiency.

  The acetylene black of the present invention has agglomerated particles of 20 μm or more and 10 ppm or less. If the aggregated particle size of 20 μm or more exceeds 10 ppm, when coated as a catalyst layer, the surface smoothness cannot be maintained due to the aggregated particle, and when the MEA is assembled, there is a possibility of causing an internal short circuit through the counter electrode side. Rise.

  Further, acetylene black having a dispersity of 40 μm or less by a tube gauge is preferable. A high numerical value of the tab gauge indicates that the average aggregate particle size is large, and 40 μm or less is preferable.

Since the fuel cell can obtain a high output when the contact frequency between the catalyst and the gas is high, a fuel cell having a high porosity, that is, a high total pore volume is preferable. Further, when the total pore volume is high, there is an effect of facilitating the discharge of the generated water. Here, the preferable total pore volume is 0.8 ml / g or more.

  As an example of the method for producing acetylene black of the present invention, acetylene black having a high specific surface area is first generated by incomplete combustion reaction of acetylene gas in a reaction furnace. The acetylene black having a high specific surface area can be produced by containing water in an amount of 1.0 to 10.0% (inner percent) and then oxidizing it using an oxidizing gas such as air or ozone. . The reason for this is not clear, but it is considered that by introducing acetylene black containing water into a reaction field of 500 ° C. or higher, the aggregated particles are crushed by the action of rapid steaming. However, if the water content is less than 1.0%, the effect of water vapor cannot be sufficiently obtained, and aggregation cannot be reduced. On the other hand, if the water content exceeds 10.0%, the temperature of the reactor is lowered, and not only the aggregation cannot be reduced but also the specific surface area is difficult to increase.

  The oxidation treatment using the oxidizing gas uses a horizontal furnace maintained at a temperature of 500 to 800 ° C., and a method in which acetylene black and the oxidizing gas are brought into contact with each other, preferably while stirring the acetylene black, and the oxidizing gas at the above temperature. It can be performed by a method of spraying acetylene black from the top of the vertical furnace maintained in an atmosphere. In order to perform uniform surface oxidation, it is preferable to use an electric furnace in which the raw material is continuously stirred and uniformly contacted with an appropriate amount of oxidizing gas, but if there is a small amount of acetylene black, the contact surface with the gas will be Since the distribution is not so large, a general electric furnace is also possible.

  In the form of an electric furnace, more preferably, an autoclave that can be pressurized and an apparatus having a mechanism equivalent thereto can be mentioned, and the effect of water vapor can be further enhanced. A preferable internal pressure is 0.1 kPa or more.

  The acetylene black of the present invention has reduced aggregated particles, but the remaining aggregated particles themselves are also easily loosened, so it is possible to further reduce the aggregated particles using a ball mill, vibration mill, jet mill, etc. It is. In particular, the use of a jet mill can reduce aggregated particles more effectively.

  The fuel cell catalyst of the present invention is obtained by precipitating (supporting) particles such as platinum with high dispersion on the surface of the acetylene black of the present invention. From the viewpoint of long-term stability of fuel cell performance, it is preferable that particles such as platinum are strongly supported on the surface of carbon black, and a method for supporting the particles will be described later. The size of particles such as platinum is preferably 10 to 50 mm.

  As a material such as platinum, platinum alloy is used in addition to platinum. Examples of the platinum alloy-forming metal include palladium, rhodium, iridium, ruthenium, iron, titanium, nickel, cobalt, gold, silver, copper, chromium, manganese, molybdenum, tungsten, aluminum, silicon, rhenium, zinc, and tin. Among these, in the case of a direct methanol fuel cell, a platinum-ruthenium alloy is preferable because it is effective in preventing carbon monoxide poisoning. If an example of a platinum alloy composition is shown, platinum will be 30-90 mass%, and the metal to alloy will be 10-70 mass%.

  Although there is no restriction | limiting in particular in the support method of particles, such as platinum, to acetylene black, For example, the following method is preferable. Acetylene black is suspended in water to form a slurry, and an aqueous solution of hexachloroplatinic acid (IV) containing particles such as platinum is added thereto to obtain a mixed solution A. To this, 10 times equivalent sodium borohydride is added to the particles such as platinum. After adding (reducing treatment) and precipitating platinum particles and the like on the surface of acetylene black, a fuel cell catalyst is produced by filtration, washing and drying.

  In order to use platinum or the like as a platinum alloy, hexachloroplatinic acid (IV) containing platinum and an alloy-forming metal is used. For example, when ruthenium is used as the alloy-forming metal, a mixed solution B is prepared by adding a ruthenium (III) trichloride aqueous solution containing a predetermined amount of ruthenium to the mixed solution A. The blending amount of ruthenium is preferably 10 to 70% by mass with respect to platinum. Next, sodium borohydride equivalent to 10 times the platinum particles is added to the mixed solution B (reduction treatment), and the platinum particles are precipitated on the surface of the acetylene black in the mixed solution B, followed by filtration, washing, A fuel cell catalyst is produced by drying.

  Regardless of whether the particles such as platinum are platinum particles or platinum alloy particles, a pH adjusting agent such as an aqueous solution of sodium hydroxide can be added as appropriate when the particles are precipitated on the surface of acetylene black. An example of the supported amount of particles such as platinum is 10 to 80 parts by mass with respect to 100 parts by mass of acetylene black.

  The evaluation of the fuel cell catalyst of the present invention can be performed as follows, for example, in the case of a polymer electrolyte fuel cell. A fuel cell catalyst is mixed with tetrafluoride resin powder, and a paste obtained by adding alcohol is applied to one side of carbon paper to form a catalyst layer. And a Nafion solution is uniformly apply | coated to the surface of a catalyst layer, and it is set as an electrode. An electrode is placed on both sides of a Nafion membrane (perfluorosulfonic acid electrolyte membrane) so that the electrodes are in contact with each other and thermocompression bonded by a hot press to obtain an electrolyte membrane-electrode assembly (MEA). A single cell is completed if the MEA is sandwiched between a separator and a current collector, and a fuel cell can be evaluated by connecting an electronic load device and a gas supply device. Moreover, if the commercially available fuel cell single cell evaluation apparatus is used, the said evaluation can be performed more simply.

Examples 1-9, Comparative Examples 1-4
Acetylene gas and oxygen gas are mixed under the conditions shown in Table 1 and sprayed from a nozzle installed at the top of a carbon black manufacturing furnace (furnace total length 5 m, furnace diameter 0.5 m) to utilize the thermal decomposition and combustion reaction of acetylene. Thus, acetylene black A was produced. Thereafter, acetylene black A is collected from the bag filter directly connected to the lower part of the furnace, and is hydrated with a constant temperature and humidity device for an arbitrary time until the moisture content shown in Table 1 is reached at a temperature of 30 ° C. and a humidity of 50%. Acetylene black B was obtained. 200 g of water-containing acetylene black B was sampled and placed in an electric furnace heated to 700 ° C., and then the pressure in the furnace was maintained at 0.1 kPa and air was introduced at 30 L / hour for 1 hour oxidation treatment. To obtain acetylene black C. Here, the comparative example 1 performed the oxidation process, without making it water-containing with a constant temperature and humidity apparatus.

About the obtained acetylene black, the following physical properties were measured. The results are shown in Table 1.
(1) Specific surface area: Measured according to JIS K 6217-2.
(2) Moisture: Measured according to JIS K 1469.
(3) Sieve residue: Measured according to JIS K 6218-3 except that the sieve was changed to 635 mesh (opening: 20 μm).
(4) Dispersity: As a pretreatment, 0.1 g of acetylene black and 30 g of dibutyl phthalate were placed in a centrifugal sedimentation tube, and mixed under a condition of 2000 rpm for 1 minute using a homogenizer (BM-2 manufactured by Nippon Seiki). In accordance with JIS K 5600-2-5, the particle diameter of the tube was measured with a grind gauge (100 μm and 50 μm grooves).
(5) Total pore volume: Using a fully automatic gas adsorption / desorption measuring device (OMNISORP-360CX, manufactured by Coulter, Inc.), adsorption / desorption measurement by a continuous volume method was performed with nitrogen gas (flow rate = 0.3 ml / min). The pore volume was calculated.

  Next, in order to evaluate the acetylene black of Example 1, Examples 5-9, and Comparative Examples 1-4 as a fuel cell catalyst, a platinum-ruthenium alloy was supported by the following method. That is, acetylene black was mixed with chloroplatinic acid and a ruthenium chloride aqueous solution. The mixing ratio was acetylene black / platinum / ruthenium = 40/40/20 by mass ratio. The mixture was stirred at 80 ° C. for 30 minutes and then cooled to room temperature. 0.5M sodium borohydride is added in 5 portions to precipitate platinum and ruthenium as an alloy, filtered, washed and dried to carry platinum-ruthenium having an average particle size of 10-50１０〜 A battery catalyst was obtained.

  2500 g of Nafion was mixed with 1 g of the obtained fuel cell catalyst to form a paste, applied to carbon paper, and then dried at 80 ° C. to obtain a fuel electrode. The surface smoothness of the fuel electrode was evaluated by observing 10 fields of view using an SEM and evaluating the number of aggregated particles of 10 μm or more contained in a 100 μm square. As a result, Example 1 averaged three, Example 5 averaged four, Example 6 averaged one, Example 7 averaged three, Example 8 averaged nine, and Example 9 averaged five In contrast, Comparative Example 1 had 25, Comparative Example 2 had an average of 15, Comparative Example 3 had an average of 18 and Comparative Example 4 had an average of 1.

Next, Pt-black was used for the oxygen electrode, and the Nafion membrane was sandwiched between the fuel electrode and pressed at 135 ° C. for 10 minutes at 9.8 MPa to obtain MEA. The fuel cell was configured by sandwiching and integrating the separator and the current collector plate. The initial output voltage was measured when the fuel cell was continuously operated at a constant current of 500 mA / cm ² by introducing methanol at 4 ml / min and air at 60 ml / min under the condition of 90 ° C. As a result, the initial voltages were 0.44 V in Example 1, 0.42 V in Example 5, 0.41 V in Example 6, 0.47 V in Example 7, 0.43 V in Example 8, and 9 in Example 9. Was 0.41V, while Comparative Example 1 was 0.35V, Comparative Example 2 was 0.37V, and Comparative Example 4 was 0.37V.

  From Table 1, the acetylene black obtained by the Example of this invention was excellent in the dispersibility compared with the comparative example, and the catalyst layer had few number of aggregated particles, and was excellent in smoothness. In addition, the fuel cell produced using the acetylene black obtained by the example was excellent in that the initial output voltage was higher than that of the comparative example. The difference in the initial output voltage between Examples 6 and 9 and Comparative Examples 2 and 4 is 0.04 V, which is a significant difference in this technical field.

The acetylene black of the present invention can be used as a catalyst for various fuel cells such as solid polymer fuel cells and phosphoric acid fuel cells.

Claims (3)

A homogenizer (Nippon Seiki Co., Ltd.) has a specific surface area of 500 to 1100 m ² / g, aggregates of 10 ppm or less of aggregated particles that are entangled with a structure in which a combination of primary particles of 20 μm or more is branched, and 0.1 g of acetylene black and 30 g of dibutyl phthalate. The dispersion of the solution mixed for 1 minute at 2000 rpm using BM-2) is 40 μm or less with a JIS K 5600-2-5 tube gauge, the total pore volume is 0.8 ml / g or more, and the water content is 0.6 to Acetylene black, characterized in that it is 9.1%. A catalyst for a polymer electrolyte fuel cell, wherein platinum particles and / or platinum alloy particles are supported on the acetylene black according to claim 1. Acetylene gas having a high specific surface area is produced by incomplete combustion reaction of acetylene gas in the reactor, and the acetylene black contains water in an amount of 1.0 to 10.0% (internal content), and then oxidized. The method for producing acetylene black according to claim 1, wherein oxidation treatment is performed using a gas.