Fuel cell catalyst

Abstract

To provide a fuel cell catalyst capable of suppressing an increase in proton resistance after endurance, and suppressing a decrease in high load performance after the endurance.SOLUTION: A fuel cell catalyst includes: a platinum-supporting carbon; and an ionomer covering the platinum-supporting carbon. The platinum-supporting carbon includes: a carbon support having a specific surface area of 950 to 1350 m2 / g; and Pt particles having an average particle diameter of 3.5 to 4.2 nm supported on the carbon support at a support density of 52 to 68% by mass. The carbon support has a pore volume of 0.4 mL / g or more when a pore diameter is in a range of 2 to 10 nm, and a mass ratio I / C of an ionomer content I to a carbon carrier content C is 1.1 to 1.4.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application relates to a catalyst for fuel cells.

Background Art

[0002] Regarding the catalyst for fuel cells, Patent Document 1 describes "In a catalyst for a polymer electrolyte fuel cell in which platinum particles are supported on a carbon powder carrier, the carbon powder carrier has hydrophilic groups bonded thereto in an amount of 0.7 to 3.0 mmol / g (based on the weight of the carrier), the platinum particles have an average particle diameter of 3.5 to 8.0 nm, and the platinum specific surface area (COMSA) by CO adsorption is 40 to 100 m 2 / g, and it is a catalyst for a polymer electrolyte fuel cell characterized by this."

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a catalyst having a carbon carrier with a high specific surface area (SSA) and a high pore volume has high initial performance, but after durability, the phenomenon that the proton resistance increases and the performance deteriorates easily occurs.

[0005] The present invention provides a catalyst for a fuel cell capable of suppressing an increase in proton resistance after durability and suppressing a decrease in high-load performance after durability.

Means for Solving the Problems

[0006] One embodiment of the present invention includes platinum-supported carbon and an ionomer covering the platinum-supported carbon, and the platinum-supported carbon has a specific surface area of 950 to 1350 m 2A carbon carrier with a specific surface area of 1000 to 2000 m² / g, Pt particles with an average particle diameter of 3.5 to 4.2 nm supported on the carbon carrier at a supported density of 52 to 68% by mass, the pore volume of the carbon carrier in the pore diameter range of 2.0 to 10.0 nm is 0.40 mL / g or more, and the mass ratio I / C of the content I of the ionomer to the content C of the carbon carrier is 1.10 to 1.40, which is a catalyst for fuel cells.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a catalyst for fuel cells that can suppress an increase in proton resistance after durability and reduce a decrease in high-load performance after durability.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] It should be noted that the content in you provided seems to be incomplete or inaccurate in some parts. I have made translations based on the existing content as accurately as possible. If there are any specific corrections or supplements, please let me know.Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments. Note that the drawings do not necessarily reflect exact dimensions. Also, some reference numerals may be omitted in the figures. In this specification, unless otherwise specified, the notation "A to B" for numerical values A and B means "A or more and B or less". When a unit is attached only to numerical value B in such notation, the unit shall also apply to numerical value A. Also, the words "or" and "alternatively" mean logical sum unless otherwise specified. Also, the notation "E1 and / or E2" for elements E1 and E2 means "E1 or E2, or a combination thereof", and for elements E1, …, E N (where N is an integer of 3 or more) means "E1, …, E N-1 , and / or E N " means "E1, …, E N-1 , or E N , or a combination thereof".

[0010] FIG. 1 is a cross-sectional view schematically illustrating a fuel cell catalyst 100 (hereinafter sometimes simply referred to as "catalyst 100") according to one embodiment. The catalyst 100 includes a platinum-supported carbon 10 and an ionomer 20 covering the platinum-supported carbon 10. The platinum-supported carbon 10 includes a carbon carrier 1 and Pt particles 2, 2, … (hereinafter sometimes simply referred to as "Pt particles 2") supported on the carbon carrier. Note that the fuel cell catalyst 100 may be formed in a layer including a plurality of platinum-supported carbon particles 10, 10, …. When the fuel cell catalyst 100 is formed in a layer as a fuel cell catalyst layer, for example, its thickness may preferably be, for example, 3 μm or more and 20 μm or less.

[0011] (carbon carrier) As the carbon carrier 1, a high specific surface area carbon carrier capable of supporting platinum particles can be used. Examples of the carbon carrier include carbon particles such as carbon black, graphite, graphite, activated carbon, and fullerene; carbon fibers such as carbon nanotubes and carbon nanofibers; and porous carbon and the like. Among these, from the viewpoint of improving the power generation performance of the fuel cell, carbon particles can be preferably used. From the viewpoint of reducing the increase rate of proton resistance after durability, and from the viewpoint of enhancing the initial performance and reducing the performance degradation after durability, the specific surface area of the carbon carrier 1 is 950 m 2 / g or more, and from the viewpoint of carbon oxidation resistance, it is 1350 m 2 / g or less. The specific surface area of the carbon carrier 1 is determined by BET adsorption measurement.

[0012] From the viewpoint of reducing the increase rate of proton resistance after durability, and from the viewpoint of enhancing the initial performance and reducing the performance degradation after durability, the pore volume of the carbon carrier 1 in the range of pore diameters of 2.0 to 10.0 nm (that is, the total volume of pores having pore diameters of 2.0 to 10.0 nm) is 0.40 mL / g or more, and in one embodiment, it can be 0.40 to 0.70 mL / g. The pore volume of the carbon carrier 1 in the range of pore diameters of 2.0 to 10.0 nm can be determined by the DH method.

[0013] From the viewpoint of improving the power generation performance of the fuel cell, the carbon carrier 1 is preferably in a particulate form. From the viewpoint of improving the gas diffusibility of the catalyst layer, the average particle diameter of the carbon carrier 1 can preferably be 10 nm or more. Also, from the viewpoints of improving the dispersibility of the carbon carrier and suppressing cracks in the catalyst layer, it can preferably be 500 nm or less. The average particle diameter of the particles can be calculated by the following procedure. First, in a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image at an appropriate magnification (for example, 50,000 to 1,000,000 times), for a certain particle, the particle diameter when the particle is regarded as spherical is calculated. The particle diameter R when the particle is regarded as spherical is obtained from the area S occupied by the particle in the image, R = (S / π) 1 / 2It can be calculated as such. Here, π represents the ratio of a circle's circumference to its diameter. The particle size calculation by such TEM or SEM observation is performed for 200 to 300 particles of the same type, and the average of the calculated values is taken as the average particle size.

[0014] (Pt particles) As Pt particles 2, platinum particles used as a catalyst for fuel cells can be used. The method for supporting Pt particles 2 on the carbon carrier 1 is not particularly limited, and conventionally known methods can be appropriately employed. From the viewpoint of reducing the performance degradation after durability, the average particle size of Pt particles 2 is 3.5 to 4.2 nm. The average particle size (average primary particle size) of Pt particles 2 can be determined by an image analysis method based on a TEM image or an SEM image as described above for the carbon carrier.

[0015] The loading density of Pt particles 2 is 52 mass% or more from the viewpoints of reducing the initial and post-durability proton resistance and reducing the increase rate of the post-durability proton resistance, and from the viewpoints of enhancing the initial performance and reducing the performance degradation after durability, and is 68 mass% from the viewpoints of reducing the increase rate of the post-durability proton resistance and reducing the performance degradation after durability. In this specification, the loading density of Pt particles 2 (unit: mass%) means the mass% of Pt particles 2 supported in the platinum-supported carbon 10 based on the total mass of the platinum-supported carbon 10 (100 mass%).

[0016] (Ionomer) Ionomers are also referred to as cation exchange resins. As the ionomer 20, ionomers known in the art can be used. Examples of ionomers include fluororesin-based electrolytes such as perfluorosulfonic acid resin materials; sulfonated resin-based electrolytes such as sulfonated polyether ketone, sulfonated polyether sulfone, sulfonated polyether ether sulfone, sulfonated polysulfone, sulfonated polysulfide, sulfonated polyphenylene; sulfonalkylated resin-based electrolytes such as sulfonalkylated polyether ether ketone, sulfonalkylated polyether sulfone, sulfonalkylated polyether ether sulfone, sulfonalkylated polysulfone, sulfonalkylated polysulfide, sulfonalkylated polyphenylene, and the like.

[0017] The mass ratio I / C of the content I of the ionomer 20 to the content C of the carbon support 1 is 1.10 to 1.40 from the viewpoints of reducing the increase rate of the proton resistance after durability and reducing the performance degradation after durability.

[0018] The catalyst for a fuel cell of the present invention can be used as a cathode catalyst of a fuel cell and can also be used as an anode catalyst.

Examples

[0019] Hereinafter, the present invention will be described more specifically based on examples.

[0020] <Example 1> An evaluation fuel cell equipped with the catalyst for a fuel cell of the present invention was fabricated. (Preparation of platinum-supported carbon) By an impregnation method using chloroplatinic acid, a carbon support (average primary particle diameter 100 nm, BET specific surface area 1250 m 2 / g, Pt particles were supported on the pore volume (0.651 mL / g) measured by the DH method corresponding to a pore diameter in the range of 2 to 10 nm, thereby obtaining platinum-supported carbon. The supported density of the Pt particles was 64% by mass based on the total amount of the platinum-supported carbon. The average primary particle diameter of the Pt particles supported on the carbon carrier, measured by an image analysis method based on a TEM image, was 4.0 nm.

[0021] (Preparation of Catalyst (Layer) for Fuel Cell and Fuel Cell) A catalyst ink was prepared by mixing the obtained platinum-supported carbon and an ionomer (perfluorosulfonic acid-based resin) in a water / ethanol mixed solvent. The ratio I / C of the mass I of the ionomer to the mass C of the carbon carrier was 1.3. This was spray-coated and dried on both sides of a perfluorocarbon sulfonic acid resin membrane (thickness 10 μm) as the electrolyte layer to form an anode catalyst layer and a cathode catalyst layer. The areal density of the Pt particles in both catalyst layers was 0.3 mg / cm 2 was obtained. Next, the obtained electrolyte membrane-catalyst layer assembly was sandwiched between carbon papers for gas diffusion layers and thermocompression-bonded to obtain a membrane electrode assembly (MEA). Further, this membrane electrode assembly was sandwiched between two separators (made of carbon) to fabricate a fuel cell having the catalyst layer for fuel cell of Example 1.

[0022] <Examples 2 to 6, Comparative Examples 1 to 10> Evaluation fuel cells (Examples 2 to 6) equipped with the catalyst for fuel cell of the present invention and evaluation fuel cells (Comparative Examples 1 to 10) equipped with a comparative catalyst for fuel cell were fabricated by the same procedure as in Example 1, except that the conditions were changed as described in Table 1 below.

[0023]

Table 1

[0024] <Evaluation Method> For each of the fuel cells of Examples 1 to 6 and Comparative Examples 1 to 10, while humidifying the fuel cell under the conditions of a fuel cell temperature of 60°C and a bubbler temperature of 55°C (relative humidity 80%RH), hydrogen was supplied to the anode electrode side and air was supplied to the cathode electrode side, and an initial proton resistance and an initial high current density (2.0 A / m 2 ) were measured. Further, as a durability process, after operating for 500 hours under the condition of a potential fluctuation range of 0.1 V to 1.0 V, an IV curve was obtained in the same manner, and the proton resistance after durability and the voltage at the high current density after durability (2.0 A / m 2 ) were measured.

[0025] Figure 2(A) is a graph plotting the initial and post-durability proton resistances of each fuel cell against the average particle size of the Pt particles. Figure 2(B) is a graph plotting the voltages under the initial and post-durability high current density conditions of each fuel cell against the average particle size of the Pt particles. Figure 2(C) is a graph plotting the initial and post-durability proton resistances of each fuel cell against the loading density of the Pt particles. Figure 2(D) is a graph plotting the voltages under the initial and post-durability high current density conditions of each fuel cell against the loading density of the Pt particles. Figure 3(A) is a graph plotting the initial and post-durability proton resistances of each fuel cell against the mass ratio I / C of the ionomer content I to the carbon carrier content C. Figure 3(B) is a graph plotting the voltages under the initial and post-durability high current density conditions of each fuel cell against the mass ratio I / C.

Explanation of symbols

[0026] 1: Carbon carrier, 2: Pt particles, 10: Platinum-supported carbon, 20: Ionomer, 100: Catalyst for fuel cell

Claims

Claim 1 A catalyst for a fuel cell, comprising: platinum-supported carbon; and an ionomer covering the platinum-supported carbon, wherein the platinum-supported carbon contains A carbon carrier having a specific surface area of 950 to 1350 m ２ / g, and Pt particles having an average particle diameter of 3.5 to 4.2 nm supported on the carbon carrier at a supported density of 52 to 68% by mass; and the pore volume of the carbon carrier in the pore diameter range of 2.0 to 10.0 nm is 0.40 mL / g or more; and the mass ratio I / C of the content I of the ionomer to the content C of the carbon carrier is 1.10 to 1.

40. A catalyst for a fuel cell.

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