Method for manufacturing catalyst ink for fuel cells

Abstract

The present invention aims to provide a method for producing catalyst ink capable of creating fuel cell electrodes with improved power generation performance. [Solution] The present invention relates to a method for producing catalyst ink for fuel cells, comprising the steps of: preparing a catalyst dispersion by dispersing catalyst-supported carrier particles, which are carrier particles on which a catalyst is supported, in a solvent; preparing a gel by mixing an ionomer with a volatile solvent; and producing a catalyst ink by stirring and mixing the catalyst dispersion and the gel, wherein the stirring and mixing of the catalyst dispersion and the gel is performed by controlling the stirring speed and stirring time.

Description

Technical Field

[0006] , , ,

[0001] The present invention relates to a method for manufacturing a catalyst ink for a fuel cell.

Background Art

[0002] A fuel cell generally includes a membrane electrode assembly. The membrane electrode assembly usually has a structure in which catalyst layers are formed on both sides of an electrolyte membrane. The catalyst layer of the membrane electrode assembly is generally formed by applying and drying a catalyst ink, which is a slurry in which catalyst-supported carrier particles obtained by supporting a catalyst on carrier particles and an ionomer are dispersed in a solvent.

[0003] Patent Document 1 describes a method for manufacturing a catalyst ink, which includes a step of preparing a catalyst dispersion liquid by dispersing catalyst-supported carrier particles, which are carrier particles supporting a catalyst, in a solvent, a step of preparing a gel body by mixing an ionomer and a volatile solvent, and a step of producing a catalyst ink by stirring and mixing the catalyst dispersion liquid and the gel body, and the particle size (D50) and storage elastic modulus Gi of the catalyst ink are specified.

[0004] However, in a conventional manufacturing method such as that of Patent Document 1, due to the state of the gel-like ionomer contained in the catalyst ink, the gas diffusion resistance of the catalyst layer and the coating state of the ionomer on the catalyst may change, which may affect the power generation performance of the fuel cell electrode.

Prior Art Documents

Patent Documents

[0007] The inventors of the present invention have found that the power generation performance of fuel cell electrodes made using catalyst ink can be improved by manufacturing catalyst ink so that the loss modulus G of the catalyst ink is within a specific range, thereby completing the present invention.

[0008] In other words, the gist of this invention is as follows: (1) A method for manufacturing catalyst ink for fuel cells, A step of preparing a catalyst dispersion by dispersing catalyst-supported carrier particles, which are carrier particles on which the catalyst is supported, in a solvent, The process involves mixing an ionomer with a volatile solvent to prepare a gel, A step of preparing a catalyst ink by stirring and mixing the catalyst dispersion and the gel body. Equipped with, In the stirring and mixing of the catalyst dispersion and the gel, the stirring speed is set to between 1000 rpm and 2000 rpm, the stirring time is set to between 2 minutes and 4 minutes, and the stirring speed and stirring time are set such that the faster the stirring speed, the shorter the stirring time. A method for manufacturing catalyst ink for fuel cells. (2) The method for producing a catalyst ink for a fuel cell according to (1), wherein the catalyst metal is platinum or a platinum alloy, and the carrier particles are carbon particles. (3) The method for producing a catalyst ink for a fuel cell according to (1) or (2), wherein the catalyst ink has a loss modulus G of 0.54 Pa or more and 0.64 Pa or less under the condition that a vibration frequency of 1 Hz is applied and the strain is 1%. [Effects of the Invention]

[0009] The present invention makes it possible to provide a method for producing catalyst ink that can be used to manufacture fuel cell electrodes with improved power generation performance. [Brief explanation of the drawing]

[0010] [Figure 1] This graph shows the relationship between the loss modulus G of the catalyst ink and the current value of the fuel cell electrode at low load (0.9V) and high load (0.6V) for the catalyst inks of Examples 1 and 2 and Comparative Examples 1 and 2. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described in detail below.

[0012] The present invention provides a method for producing a catalyst ink for fuel cells (hereinafter also referred to as catalyst ink), comprising the steps of (1) preparing a catalyst dispersion, (2) preparing a gel, and (3) producing a catalyst ink.

[0013] (1) Step of preparing a catalyst dispersion A catalyst dispersion is a solution obtained by dispersing catalyst-supported carrier particles, which are carrier particles on which a catalyst is supported, in a solvent. In the process of preparing a catalyst dispersion, catalyst-supported carrier particles, which are carrier particles on which a catalyst is supported, are dispersed in a solvent to prepare the catalyst dispersion.

[0014] As catalysts (catalytic metals), for example, platinum (Pt) and alloys (Pt alloys) consisting of Pt and other metals (e.g., cobalt, nickel) can be used.

[0015] As carrier particles for supporting the catalyst, commercially available carbon particles (carbon powder) can be used, for example, or water-repellent carbon particles, which have been heat-treated to enhance their water repellency, may also be used.

[0016] In one embodiment, the catalyst metal is platinum or a platinum alloy, and the carrier particles are carbon particles.

[0017] The solvent of the catalyst dispersion may be distilled water, a volatile solvent, etc., and the volatile solvent may be ethanol, 1-propanol, etc.

[0018] The catalyst dispersion may contain a surfactant as needed. The surfactant may be an ionomer or the like. The addition amount of the ionomer may be a mass less than 10% by mass with respect to the mass of the ionomer finally contained in the catalyst ink.

[0019] The method of dispersing the catalyst-supported carrier particles in the solvent may be, for example, a method using an ultrasonic disperser, a bead mill, etc.

[0020] (2) Step of preparing a gel body In the step of preparing the gel body, an ionomer and a volatile solvent are mixed to prepare the gel body.

[0021] The ionomer may be, for example, a fluororesin or Nafion solution (manufactured by DuPont).

[0022] The volatile solvent may be ethanol, 1-propanol, etc.

[0023] The mixing method of the ionomer and the volatile solvent is not particularly limited, and the mixing temperature may be 50°C or higher, and the mixing time may be 1 hour or longer.

[0024] [[ID=三十二]](3) Step of preparing catalyst ink In the step of preparing the catalyst ink, the catalyst dispersion prepared as described above and the gel body are stirred and mixed to prepare the catalyst ink. The prepared catalyst ink may have a loss elastic modulus G of 0.54 Pa or more and 0.64 Pa or less under the condition of applying a vibration frequency of 1 Hz and a strain of 1%.

[0025] In this invention, the loss modulus G of the catalyst ink is used as an indicator of the hardness of the gel-like ionomer contained in the catalyst ink. By controlling this, the gel-like ionomer can be controlled to a desired state, and the balance between the low-load and high-load power generation performance of the fuel cell electrode made using the catalyst ink is optimized.

[0026] The mixing ratio of the catalyst dispersion and the gel is not particularly limited; for example, they are mixed such that the proportion of ionomer in the mixture of the catalyst dispersion and the gel is between 1% by mass and 5% by mass.

[0027] The stirring and mixing of the catalyst dispersion and the gel can be performed by adjusting the stirring speed and stirring time so that the loss modulus of elasticity G of the resulting catalyst ink is between 0.54 Pa and 0.64 Pa. Specifically, in the stirring and mixing of the catalyst dispersion and the gel, the stirring speed is set to between 1000 rpm and 2000 rpm, the stirring time is set to between 2 minutes and 4 minutes, and the stirring speed and stirring time are set such that the faster the stirring speed, the shorter the stirring time.

[0028] Here, "the stirring speed and stirring time are set such that the faster the stirring speed, the shorter the stirring time" means setting the stirring conditions such that the stirring time becomes shorter as the stirring speed increases, within the range of stirring speed between 1000 rpm and 2000 rpm and stirring time between 2 minutes and 4 minutes. In other words, within this range of stirring speed and stirring time, there is a negative correlation between stirring speed and stirring time. Therefore, for example, stirring conditions of a stirring speed of 2000 rpm and a stirring time of 2 minutes, and stirring conditions of a stirring speed of 1000 rpm and a stirring time of 4 minutes satisfy the stirring conditions of the present invention, but stirring conditions of a stirring speed of 1000 rpm and a stirring time of 2 minutes, and stirring conditions of a stirring speed of 2000 rpm and a stirring time of 4 minutes do not satisfy the stirring conditions of the present invention.

[0029] More specifically, "setting the stirring speed and stirring time such that the faster the stirring speed, the shorter the stirring time" can be achieved, for example, by setting the stirring speed and stirring time to satisfy equation 1: y = -500x + 3000 (x = stirring time (minutes), y = stirring speed (rpm)). In equation 1, the stirring time x is between 2 minutes and 4 minutes, and the stirring speed y is between 1000 rpm and 2000 rpm.

[0030] In one embodiment, the catalyst dispersion and the gel are stirred and mixed under stirring conditions of a stirring speed of 2000 rpm and a stirring time of 2 minutes, or a stirring speed of 1000 rpm and a stirring time of 4 minutes.

[0031] The catalyst ink obtained by the manufacturing method of the present invention may have a loss modulus G of 0.54 Pa or more and 0.64 Pa or less under conditions where a vibration frequency of 1 Hz is applied and the strain is 1%. When the loss modulus G of the catalyst ink is 0.54 Pa or more, the power generation performance of the fuel cell electrode made using the catalyst ink is improved in the low-load range. Furthermore, when the loss modulus G of the catalyst ink is 0.64 Pa or less, the power generation performance of the fuel cell electrode made using the catalyst ink is improved in the high-load range.

[0032] The catalyst ink obtained by the manufacturing method of the present invention has a gel-like ionomer controlled to a desired state, and can be used to produce fuel cell electrodes with an optimized balance of power generation performance in the low-load and high-load ranges. Therefore, the catalyst ink of the present invention is suitably used as a catalyst ink for fuel cells (fuel cell electrodes). Fuel cell electrodes can be manufactured using the catalyst ink of the present invention by known methods. [Examples]

[0033] The present invention will be described in more detail below using examples. However, the technical scope of the present invention is not limited to these examples.

[0034] <Preparation of catalyst ink> Example 1 Distilled water was added to catalyst-supported carrier particles, which consisted of carbon particles as a support and a platinum-cobalt (PtCo) alloy as a catalyst, and then ethanol and 1-propanol were added as volatile solvents. Furthermore, an ionomer as a surfactant was added in an amount less than 10% by mass relative to the mass of ionomer to be contained in the final catalyst ink. Subsequently, the catalyst dispersion was obtained by dispersion treatment using an ultrasonic disperser and a bead mill.

[0035] A mixed solution of ionomer solution with ethanol and 1-propanol as volatile solvents was heated at 50°C for 1 hour to obtain a gel.

[0036] Using a rotation-orbit mixer (Awatori Rentaro, manufactured by Thinky Co., Ltd.), the catalyst dispersion and gel were stirred and mixed at a stirring speed of 2000 rpm and a stirring time of 2 minutes to obtain a catalyst ink. The loss modulus of elasticity G of the catalyst ink of Example 1, measured as described below, was 0.63515.

[0037] Example 2 The catalyst ink of Example 2 was obtained in the same manner as in Example 1, except that the stirring conditions between the catalyst dispersion and the gel were changed to a stirring speed of 1000 rpm and a stirring time of 4 minutes. The loss modulus of elasticity G of the catalyst ink of Example 2 was 0.54091.

[0038] Comparative Example 1 Comparative Example 1's catalyst ink was obtained in the same manner as in Example 1, except that the stirring conditions between the catalyst dispersion and the gel were changed to a stirring speed of 1000 rpm and a stirring time of 2 minutes. The loss modulus of elasticity G of Comparative Example 1's catalyst ink was 0.69509.

[0039] Comparative Example 2 Comparative Example 2 catalyst ink was obtained in the same manner as in Example 1, except that the stirring conditions between the catalyst dispersion and the gel were changed to a stirring speed of 2000 rpm and a stirring time of 4 minutes. The loss modulus of elasticity G of the catalyst ink of Comparative Example 2 was 0.4566.

[0040] <Rating> Loss modulus G of catalyst ink For each catalyst ink, the loss modulus G was measured using a rheometer (Anton Paar mcr302) under conditions of applying a vibration frequency of 1 Hz and a strain of 1%.

[0041] Current value of fuel cell electrodes Fuel cell electrodes were fabricated using each catalyst ink, and current values ​​were measured at low load (0.9V) and high load (0.6V).

[0042] Figure 1 shows the relationship between the loss modulus G of the catalyst ink and the current value of the fuel cell electrode at low load (0.9V) and high load (0.6V) for the catalyst inks of Examples 1 and 2 and Comparative Examples 1 and 2. As shown in Figure 1, at high load (0.6V), the lower the value of the loss modulus G of the catalyst ink, the higher the current value of the fuel cell electrode. Also, as shown in Figure 1, at low load (0.9V), the higher the value of the loss modulus G of the catalyst ink, the higher the current value of the fuel cell electrode. As shown in Figure 1, a fuel cell electrode with an optimized balance of power generation performance in the low-load and high-load ranges was obtained in the range where the loss modulus G of the catalyst ink is between 0.54 Pa and 0.64 Pa. When the loss modulus G of the catalyst ink is low, the ionomer is softer and the gas diffusion resistance of the catalyst layer is lower, but the coating of the catalyst with ionomer becomes more extensive. On the other hand, if the loss modulus G of the catalyst ink is high, the ionomer becomes hard, resulting in less ionomer coating on the catalyst, but the gas diffusion resistance of the catalyst layer increases. When the loss modulus G of the catalyst ink is between 0.54 Pa and 0.64 Pa, the ionomer achieves the desired hardness, and it is considered that the balance between the low-load and high-load power generation performance of the fuel cell electrode fabricated using the catalyst ink is optimized.

Claims

1. A method for manufacturing catalyst ink for fuel cells, A step of preparing a catalyst dispersion by dispersing catalyst-supported carrier particles, which are carrier particles on which the catalyst is supported, in a solvent, The process involves mixing an ionomer with a volatile solvent to prepare a gel, A step of preparing a catalyst ink by stirring and mixing the catalyst dispersion and the gel body. Equipped with, In the stirring and mixing of the catalyst dispersion and the gel, the stirring speed is set to be between 1000 rpm and 2000 rpm, the stirring time is set to be between 2 minutes and 4 minutes, and the stirring speed and stirring time are set such that the faster the stirring speed, the shorter the stirring time. A method for manufacturing catalyst ink for fuel cells.

2. A method for producing a catalyst ink for a fuel cell according to claim 1, wherein the catalyst metal is platinum or a platinum alloy, and the carrier particles are carbon particles.

3. The method for manufacturing a catalyst ink for a fuel cell according to claim 1 or 2, wherein the catalyst ink has a loss modulus G of 0.54 Pa or more and 0.64 Pa or less under the condition that a vibration frequency of 1 Hz is applied and the strain is 1%.

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