Method for producing catalyst ink for fuel cell

Abstract

The purpose of the present invention is to provide a method for producing a catalyst ink capable of producing a fuel cell electrode having improved power generation performance. The present invention pertains to a method for producing a catalyst ink for a fuel cell, the method comprising: a step for preparing a catalyst dispersion liquid by dispersing catalyst-supporting carrier particles, which are carrier particles supporting a catalyst, in a solvent; mixing the ionomer and a volatile solvent to prepare a gel; and preparing a catalyst ink by stirring and mixing the catalyst dispersion liquid and the gel, wherein the stirring and mixing of the catalyst dispersion liquid and the gel are performed by controlling the stirring speed and the stirring time.

Description

Technical Field

[0001] This invention relates to a method for manufacturing catalyst ink for fuel cells. Background Technology

[0002] Fuel cells typically include a membrane electrode assembly (MEA). The MEA typically has a structure in which catalyst layers are formed on both sides of the electrolyte membrane. The catalyst layers of the MEA are usually formed by coating and drying a catalyst ink, which is a slurry in which catalyst-supported carrier particles and ionomers are dispersed in a solvent.

[0003] In Patent Document 1, as a method for manufacturing catalyst ink, there is a method comprising the following steps: dispersing catalyst support particles, which serve as support particles for carrying the catalyst, in a solvent to prepare a catalyst dispersion; mixing an ionomer and a volatile solvent to prepare a gel; and stirring and mixing the catalyst dispersion and the gel to produce catalyst ink, wherein the particle size (D50) and storage modulus Gi of the catalyst ink are determined.

[0004] However, in conventional manufacturing methods such as Patent Document 1, the gas diffusion resistance of the catalyst layer or the coating state of the catalyst by the ionomer varies depending on the state of the gel-like ionomer contained in the catalyst ink, which can sometimes affect the power generation performance of the fuel cell electrode.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-82005 Summary of the Invention

[0006] As described above, in conventional methods for manufacturing catalyst inks, there is room for improvement in enhancing the power generation performance of fuel cell electrodes made using catalyst inks. Therefore, the object of the present invention is to provide a method for manufacturing catalyst inks capable of producing fuel cell electrodes with improved power generation performance.

[0007] The inventors discovered that by manufacturing catalyst ink in a manner where the loss modulus G of the catalyst ink is within a defined range, the power generation performance of fuel cell electrodes made using the catalyst ink is improved, thus completing the present invention.

[0008] That is, the essence of the present invention is as follows.

[0009] (1) A method for manufacturing catalyst ink for fuel cells, comprising the following steps:

[0010] A catalyst dispersion is prepared by dispersing catalyst support particles, which serve as the support particles for the catalyst, in a solvent.

[0011] To prepare a gel by mixing ionomers and volatile solvents; and

[0012] The catalyst dispersion and the gel are mixed by stirring to prepare a catalyst ink.

[0013] In the stirring and mixing of the catalyst dispersion and the gel, the stirring speed is set in the range of 1000 rpm to 2000 rpm, and the stirring time is set in the range of 2 minutes to 4 minutes. The stirring speed and the stirring time are set such that the faster the stirring speed, the shorter the stirring time.

[0014] (2) The method for manufacturing catalyst ink for fuel cells according to (1), wherein the catalyst metal is platinum or a platinum alloy and the carrier particles are carbon particles.

[0015] (3) The method for manufacturing catalyst ink for fuel cells according to (1) or (2), wherein the loss modulus G of the catalyst ink under the condition of applying a vibration frequency of 1 Hz and a strain of 1% is 0.54 Pa or more and 0.64 Pa or less.

[0016] Invention Effects

[0017] This invention provides a method for manufacturing catalyst ink for fuel cell electrodes that improve power generation performance. Attached Figure Description

[0018] Figure 1 This is a graph showing the relationship between the loss modulus G of the catalyst ink and the current value of the fuel cell electrode under low load (0.9V) and high load (0.6V) for the catalyst inks of Examples 1 and 2 and Comparative Examples 1 and 2. Detailed Implementation

[0019] The preferred embodiments of the present invention will now be described in detail.

[0020] The method for manufacturing the catalyst ink for fuel cells (hereinafter also referred to as catalyst ink) of the present invention includes: (1) a step of preparing a catalyst dispersion; (2) a step of preparing a gel; and (3) a step of manufacturing the catalyst ink.

[0021] (1) Steps for preparing catalyst dispersion

[0022] A catalyst dispersion is a solution obtained by dispersing catalyst support particles, which serve as carrier particles holding the catalyst, in a solvent. In the process of preparing a catalyst dispersion, the catalyst support particles, which serve as carrier particles holding the catalyst, are dispersed in a solvent to prepare the catalyst dispersion.

[0023] As a catalyst (catalyst metal), for example, platinum (Pt) and alloys of Pt with other metals (e.g., cobalt, nickel) (Pt alloys) can be used.

[0024] As the carrier particles used to support the catalyst, commercially available carbon particles (carbon powder) can be used, or hydrophobic carbon particles whose water-repellent properties have been improved by heat treatment can be used.

[0025] In one embodiment, the catalyst metal is platinum or a platinum alloy, and the support particles are carbon particles.

[0026] The solvent for the catalyst dispersion can be distilled water, volatile solvents, etc., and the volatile solvents can be ethanol, 1-propanol, etc.

[0027] The catalyst dispersion may contain surfactants as needed. Surfactants may include ionomers, etc. The amount of ionomer added may be less than 10% by mass relative to the final mass of the ionomer contained in the catalyst ink.

[0028] Methods for dispersing catalyst support particles in a solvent include, for example, using an ultrasonic disperser and a bead mill.

[0029] (2) Procedures for preparing gel

[0030] In the gel preparation process, ionomers and volatile solvents are mixed to prepare the gel.

[0031] Ionomers can be, for example, fluorinated resins or Nafion solutions (manufactured by DuPont).

[0032] Volatile solvents can include ethanol, 1-propanol, etc.

[0033] There are no particular limitations on the mixing method of the ionomer and the volatile solvent. The mixing temperature can be above 50°C and the mixing time can be above 1 hour.

[0034] (3) Process of making catalyst ink

[0035] In the process of producing catalyst ink, the catalyst dispersion and gel prepared as described above are stirred and mixed to produce catalyst ink. The produced catalyst ink can achieve a loss 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%.

[0036] 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 indicator, the gel-like ionomer is controlled in a desired state, and the balance of power generation performance in the low-load and high-load regions of the fuel cell electrode made using the catalyst ink is optimized.

[0037] There is no particular limitation on the mixing ratio of the catalyst dispersion and the gel. For example, they can be mixed in such a way that the proportion of ionomers in the mixture of the catalyst dispersion and the gel is more than 1% by mass and less than 5% by mass.

[0038] The stirring and mixing of the catalyst dispersion and the gel can be carried out by adjusting the stirring speed and stirring time so that the loss modulus G of the obtained catalyst ink is 0.54 Pa or higher and 0.64 Pa or lower. Specifically, in the stirring and mixing of the catalyst dispersion and the gel, the stirring speed is set in the range of 1000 rpm or higher and 2000 rpm or lower, and the stirring time is set in the range of 2 minutes or higher and 4 minutes or lower, and the stirring speed and the stirring time are set such that the faster the stirring speed, the shorter the stirring time.

[0039] Here, "setting the stirring speed and the stirring time such that the faster the stirring speed, the shorter the stirring time" means setting the stirring conditions within a range of stirring speed above 1000 rpm and below 2000 rpm and stirring time above 2 minutes and below 4 minutes, in a manner that the faster the stirring speed, the shorter the stirring time. That is, within this range of stirring speed and stirring time, the stirring speed and stirring time are negatively correlated. Therefore, for example, stirring conditions of 2000 rpm and 2 minutes, and stirring conditions of 1000 rpm and 4 minutes, satisfy the stirring conditions of the present invention, but stirring conditions of 1000 rpm and 2 minutes, and stirring conditions of 2000 rpm and 4 minutes, do not satisfy the stirring conditions of the present invention.

[0040] More specifically, "setting the stirring speed and the 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 the 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 more than 2 minutes and less than 4 minutes, and the stirring speed y is more than 1000 rpm and less than 2000 rpm.

[0041] In one embodiment, the catalyst dispersion and the gel are mixed under stirring conditions of 2000 rpm and 2 minutes or 1000 rpm and 4 minutes.

[0042] The catalyst ink obtained by the manufacturing method of the present invention has a loss 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%. If 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 higher in the low load region. Furthermore, if 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 higher in the high load region.

[0043] The catalyst ink obtained by the manufacturing method of the present invention can be used to produce fuel cell electrodes in which the gel-like ionomer is controlled in a desired state and the balance of power generation performance in low-load and high-load regions is optimized. Therefore, the catalyst ink of the present invention is preferably 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 and by known methods.

[0044] Example

[0045] The present invention will now be described in more detail using examples. However, the scope of the present invention is not limited to these examples.

[0046] <Preparation of Catalyst Ink>

[0047] Example 1

[0048] Distilled water was added to catalyst support particles, which held a platinum-cobalt (PtCo) alloy as a catalyst, on carbon particles as a support. Ethanol and 1-propanol were then added as volatile solvents. Next, an ionomer as a surfactant was added at a mass of less than 10% by mass relative to the mass of the ionomer ultimately contained in the catalyst ink. The catalyst dispersion was then obtained by dispersion treatment using an ultrasonic disperser and a bead mill.

[0049] A gel was obtained by heating a mixed solution of ethanol and 1-propanol as volatile solvents in an ionomer solution at 50°C for 1 hour.

[0050] Catalyst ink was obtained by mixing the catalyst dispersion and gel using a rotation-revolution mixer (Awa Tori Renshurou manufactured by THINKY CORPORATION) at a stirring speed of 2000 rpm for 2 minutes. The loss modulus G of the catalyst ink of Example 1, as described below, was 0.63515.

[0051] Example 2

[0052] The stirring conditions for the catalyst dispersion and gel were changed to a stirring speed of 1000 rpm and a stirring time of 4 minutes. Otherwise, the catalyst ink of Example 2 was obtained in the same manner as in Example 1. The loss modulus G of the catalyst ink of Example 2 was 0.54091.

[0053] Comparative Example 1

[0054] The stirring conditions for the catalyst dispersion and gel were changed to a stirring speed of 1000 rpm and a stirring time of 2 minutes. Otherwise, the catalyst ink of Comparative Example 1 was obtained in the same manner as in Example 1. The loss modulus G of the catalyst ink of Comparative Example 1 was 0.69509.

[0055] Comparative Example 2

[0056] The stirring conditions for the catalyst dispersion and gel were changed to a stirring speed of 2000 rpm and a stirring time of 4 minutes. Otherwise, the catalyst ink of Comparative Example 2 was obtained in the same manner as in Example 1. The loss modulus G of the catalyst ink of Comparative Example 2 was 0.4566.

[0057] <Evaluation>

[0058] Loss modulus G of catalyst ink

[0059] For each catalyst ink, the loss modulus G was measured using a rheometer (mcr302 manufactured by Anton Paar) under conditions of applied vibration frequency of 1 Hz and strain of 1%.

[0060] Current value of fuel cell electrode

[0061] Fuel cell electrodes were fabricated using various catalyst inks, and current values ​​were measured under low load (0.9V) and high load (0.6V).

[0062] exist Figure 1 The diagram shows the relationship between the loss modulus G of the catalyst ink and the current values ​​of the fuel cell electrode under low load (0.9V) and high load (0.6V) conditions, relating to the catalyst inks of Examples 1 and 2 and Comparative Examples 1 and 2. Figure 1As shown, under high load (0.6V), the lower the loss modulus G of the catalyst ink, the higher the current value of the fuel cell electrode. Furthermore, as... Figure 1 As shown, under low load (0.9V), the higher the loss modulus G of the catalyst ink, the higher the current value of the fuel cell electrode. Figure 1 As shown, a fuel cell electrode with optimized power generation performance in both low-load and high-load regions was obtained within the range of a loss modulus G of the catalyst ink being 0.54 Pa or higher and 0.64 Pa or lower. When the loss modulus G of the catalyst ink is low, the ionomer is soft, resulting in lower gas diffusion resistance of the catalyst layer, but also increased ionomer coating on the catalyst. Conversely, when the loss modulus G of the catalyst ink is high, the ionomer becomes harder, resulting in less ionomer coating on the catalyst, but also increased gas diffusion resistance of the catalyst layer. It is believed that when the loss modulus G of the catalyst ink is 0.54 Pa or higher and 0.64 Pa or lower, the ionomer achieves the desired hardness, thus optimizing the balance of power generation performance in both low-load and high-load regions of the fuel cell electrode fabricated using the catalyst ink.

Claims

1. A method for producing a catalyst ink for a fuel cell, characterized by, comprises the steps of: preparing a catalyst dispersion liquid by dispersing the catalyst-supporting carrier particles, which are carrier particles supporting a catalyst, in a solvent; preparing a gel by mixing an ionomer and a volatile solvent; and stirring the catalyst dispersion liquid and the gel to produce a catalyst ink, in the stirring of the catalyst dispersion liquid and the gel, the stirring speed is set to a range of 1000 rpm or more and 2000 rpm or less, the stirring time is set to a range of 2 minutes or more and 4 minutes or less, and the stirring speed and the stirring time are set such that the faster the stirring speed, the shorter the stirring time.

2. The method of manufacturing a catalyst ink for fuel cells according to claim 1, characterized in that the catalyst metal is platinum or platinum alloy, and the carrier particles are carbon particles.

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

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