Manufacturing method for catalyst ink

Abstract

To provide a manufacturing method for a catalyst ink that can reduce the sedimentation of catalyst particles within the catalyst ink.SOLUTION: There is provided a manufacturing method for a catalyst ink, the catalyst ink Including: catalyst particles including a metal catalyst supported on a carbon carrier; a solvent; and an ionomer. The method includes a step of stirring and mixing, by using beads having a bead diameter of 2 mm or less, the catalyst particles, the solvent, and the ionomer, thereby, an average particle diameter of the catalyst particles becomes 2.2 μm or less after the stirring and mixing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for making a catalyst ink. [Background technology]

[0002] Various technologies have been proposed regarding fuel cells such as those disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-034773 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a method for producing a catalyst ink for fuel cell electrodes, which includes a step of stirring and mixing a catalyst, a solvent, and a gel-like ionomer. Because the stirring and mixing is performed without consideration of the particle size of the catalyst, the catalyst particles in the catalyst ink tend to settle.

[0005] The present disclosure has been made in consideration of the above-described circumstances, and has as its main object to provide a method for producing a catalyst ink that can make catalyst particles in the catalyst ink less likely to settle. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> A method for producing a catalyst ink containing catalyst particles including a metal catalyst supported on a carbon support, a solvent, and an ionomer, the method comprising: a step of stirring and mixing the catalyst particles, the solvent, and the ionomer using beads having a bead diameter of 2 mm or less, A method for producing a catalyst ink, wherein the catalyst particles have an average particle size of 2.2 μm or less after stirring and mixing. [Effects of the Invention]

[0007] The method for producing a catalyst ink according to the present disclosure can make it difficult for catalyst particles in the catalyst ink to settle. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a flowchart showing an example of a method for producing a catalyst ink according to the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing an example of a compounding machine used for stirring and mixing according to the present disclosure. [Figure 3] FIG. 3 is a graph showing the average particle size of catalyst particles versus the time elapsed while stirring and mixing the catalyst ink in Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiments of the present disclosure will be described below. It should be noted that matters necessary for implementing the present disclosure other than those specifically mentioned in this specification (for example, the general configuration and manufacturing process of catalyst inks that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. Furthermore, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect the actual dimensional relationships. In this disclosure, the gas supplied to the anode of a fuel cell is a fuel gas (anode gas), and the gas supplied to the cathode of a fuel cell is an oxidant gas (cathode gas). The fuel gas is a gas that contains mainly hydrogen and may be hydrogen. The oxidant gas is a gas that contains oxygen and may be oxygen, air, etc. In this disclosure, the fuel gas and the oxidant gas are collectively referred to as reactant gases or gases.

[0010] The present disclosure provides a method for producing a catalyst ink including catalyst particles including a metal catalyst supported on a carbon support, a solvent, and an ionomer, the method comprising: a step of stirring and mixing the catalyst particles, the solvent, and the ionomer using beads having a bead diameter of 2 mm or less, The method for producing a catalyst ink is characterized in that the catalyst particles after stirring and mixing have an average particle size of 2.2 μm or less.

[0011] In the MEGA mass production process, after preparing the catalyst ink, there is a process of applying the catalyst ink to a Teflon sheet or similar material and drying it to produce a catalyst sheet. In the conventional process, the catalyst particles settle immediately after preparing the catalyst ink, making it impossible to apply the catalyst ink uniformly. In addition, the prepared catalyst ink cannot be stored for a certain period of time, so it must be used up. In the present disclosure, by stirring and mixing with beads of a specified diameter, the average particle diameter of the catalyst particles can be controlled, making it possible to make the catalyst particles in the catalyst ink less likely to settle.

[0012] The catalyst ink of the present disclosure includes catalyst particles including a metal catalyst supported on a carbon support, a solvent, and an ionomer. As the carbon support, a solid carbon support, a hollow carbon support, a highly crystalline carbon support, etc. can be used. The metal catalyst supported on the carrier reacts at the electrodes of the MEA. Oxidant electrode (cathode): O2+ 4H + + 4e - → 2H2O Fuel electrode (anode): 2H2 → 4H + + 4e - Any material that exhibits catalytic activity in the above reaction may be used. As the metal catalyst, for example, platinum (Pt) and alloys of Pt with other metals (for example, Pt alloys mixed with cobalt and nickel, etc.) can be used. Examples of the solvent include water, alcohol, and a mixture thereof. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, and diacetone alcohol (DAA). The ionomer may be a fluorine-based ionomer, etc. The ionomer may be a gel or a non-gel.

[0013] FIG. 1 is a flowchart showing an example of a method for producing a catalyst ink according to the present disclosure. The method for producing a catalyst ink of the present disclosure includes a step of stirring and mixing the catalyst particles, the solvent, and the ionomer using beads having a diameter of 2 mm or less. The average particle size of the catalyst particles after the stirring and mixing may be 2.2 μm or less, or may be 1.5 μm or less. By including a stirring and mixing (crushing) process that reduces the average particle size of the catalyst particles in the catalyst ink to 2.2 μm or less, separation of the catalyst particles in the catalyst ink after production can be suppressed, making it possible to produce a homogeneous catalyst layer sheet. After the stirring and mixing step, the catalyst ink may be filtered and degassed. FIG. 2 is a schematic diagram showing an example of a compounding machine used for stirring and mixing according to the present disclosure. The compounding machine used for stirring and mixing may be a compounding machine that has both the function of crushing the materials in the catalyst ink and the function of stirring the materials in the catalyst ink, and examples of such a machine include a ball mill and a bead mill. The compounder may have a rotation speed of 300 rpm or more. The diameter of the beads used for stirring and mixing may be 2 mm or less, or may be 1 mm or less. The stirring and mixing time may be a time that does not cause over-dispersion, and may be 6 hours or less. If the temperature of the catalyst ink increases during stirring and mixing, the compounding machine may be provided with a mechanism for preventing the temperature of the catalyst ink from increasing.

[0014] The mechanism by which separation does not occur in the catalyst ink according to the present disclosure is presumed to be as follows. <Up and down movement: Stokes' law> Stokes' equation: v=a 2 (ρ-ρ0)g / 18η v: Terminal velocity: (1μm / s) a: Particle diameter (1μm) ρ: Particle specific gravity (carbon specific gravity 1.8 g / cm 3 (Assuming ρ0: Continuous phase specific gravity (based on JIS B 7548:2009 Appendix A), water / ethanol (59.37 / 40.63 wt%) 0.93839 g / cm 3 ) g: Gravitational acceleration (9.8m / s 2 ) η: Continuous phase viscosity (Japan Society of Mechanical Engineers, Technical Data on Thermophysical Properties of Fluids, pp. 436, 474 (1983); Chemical Society of Japan, Handbook of Chemistry (5th Revised Edition), Basics, p. II-49 (2012), 2.350 mPa·s (25°C, 40 wt%) *assuming no influence of ionomer) <Movement by diffusion (Brownian motion): Einstein-Stokes equation> Mean square moving distance: L=(2Dt) 1 / 2 Einstein-Stokes equation: D=kT / 3πηa D: Diffusion coefficient t: elapsed time (1 second) k: Boltzmann constant (1.380649×10 -23 J / K) T: Absolute temperature (298K (25℃)) a: Particle diameter (1μm) η: Continuous phase viscosity (Japan Society of Mechanical Engineers, Technical Data on Thermophysical Properties of Fluids, pp. 436, 474 (1983); Chemical Society of Japan, Handbook of Chemistry (5th Revised Edition), Basics, p. II-49 (2012), 2.350 mPa·s (25°C, 40 wt%) *assuming no influence of ionomer) Consider the vertical movement of catalyst particles and their movement due to diffusion. The vertical movement is expressed by the Stokes equation, while the diffusion movement is expressed by the mean square movement distance L, which includes the diffusion coefficient D obtained from the Einstein-Stokes equation. Each parameter was confirmed from publicly known information, and calculations were made assuming no influence of the ionomer, resulting in the results in Table 1. When the catalyst particle diameter is 1.5 μm, the orders of vertical movement and diffusion movement are roughly the same. When the catalyst particle diameter is 1.5 μm or more, vertical movement becomes dominant, and it is thought that ink sedimentation occurs. Conversely, when the catalyst particle diameter is less than 1.5 μm, diffusion movement becomes dominant over vertical movement, and it is thought that catalyst ink sedimentation does not occur. In the present disclosure, by setting the average particle size of the catalyst particles in the catalyst ink to 2.2 μm or less, separation of the catalyst ink is less likely to occur compared to conventional techniques.

[0015] [Table 1]

[0016] The catalyst ink of the present disclosure may be used for a catalyst layer of a fuel cell. The fuel cell may have only one unit cell (cell), or may be a fuel cell stack, which is a cell laminate formed by stacking multiple cells. In this disclosure, both cells and fuel cell stacks may be referred to as fuel cells. The number of cells stacked in the fuel cell stack is not particularly limited, and may be, for example, from 2 to several hundred. A cell of the fuel cell may have a pair of separators, a resin frame that bonds the pair of separators, and a power generation section. The power generation section may be a membrane electrode assembly (MEA) including an electrolyte membrane and two electrodes that sandwich the electrolyte membrane. The two electrodes are an anode (fuel electrode) and a cathode (oxidant electrode). The electrodes include a catalyst layer and may optionally include a gas diffusion layer. The power generation section may be a membrane electrode gas diffusion layer assembly (MEGA). In this case, the cell may include a cathode separator, an anode separator, and a membrane electrode gas diffusion layer assembly disposed between the cathode separator and the anode separator. The membrane electrode gas diffusion layer assembly has, in this order, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer. [Example]

[0017] (Examples 1 and 2) The catalytic ink was verified according to the following experimental procedure. <Experimental Procedure> The solid content in the catalyst ink was 9.0 wt %, and a mixed solvent of water / ethanol = 60 / 40 wt % was used as the solvent. 1. Catalyst particles containing a metal catalyst supported on a carbon support weighed 1.8 g 2. Weigh 11.87g of water (mix after weighing) 3. Weigh 0.32 g of ionomer 1 (I (amount of ionomer) / C (amount of carbon support in catalyst particles) = 0.1) (mixed after weighing) 4. Weigh 3.12g of ethanol (mix after weighing) 5. Weigh 3.77g of diacetone alcohol (DAA) (mix after weighing) 6. Stir and mix for 3 hours in a bead mill (bead diameter 1 mm (Example 1), bead diameter 2 mm (Example 2), 300 rpm) 7. Ionomer 2 weighed 6.72g (I / C=0.8) 8. Starting from step "6" in the experimental procedure, the particle size of the catalyst particles was measured every hour of stirring and mixing in a bead mill (bead diameter 1 mm (Example 1), bead diameter 2 mm (Example 2), 300 rpm), and the results shown in Figure 1 were obtained. The particle size was the average value of the volume-based distribution. FIG. 1 is a graph showing the average particle size of catalyst particles versus the time elapsed while stirring and mixing catalyst inks in Examples 1 and 2. Stirring and mixing the catalyst ink for more than six hours results in over-dispersion, which leads to the generation of active sites on the particle surface due to the crushing of primary particles, resulting in an abnormal increase in viscosity, aggregation, changes in physical properties, and an increase in the average particle size of the catalyst particles. After the catalyst ink was prepared, it was left to stand and the state of separation of the catalyst ink was observed. Bead diameter 1 mm (Example 1): It was confirmed that the catalyst ink did not separate for about 7 days. Bead diameter 2 mm (Example 2): Sedimentation of the catalyst ink was confirmed on the sixth day. It was confirmed that the catalyst ink did not separate for at least about three days.

[0018] (Comparative Example 1) The catalytic ink was verified according to the following experimental procedure. <Experimental Procedure> The solid content in the catalyst ink was 9.0 wt %, and a mixed solvent of water / ethanol = 60 / 40 wt % was used as the solvent. 1. Catalyst particles containing a metal catalyst supported on a carbon support weigh 1.85g 2. Weigh 13.94g of water (stir and mix after weighing) 3. Weigh 0.33 g of ionomer 1 (I (amount of ionomer) / C (amount of carbon support in catalyst particles) = 0.1) (mixed after weighing) 4. Weigh 3.70g of DAA (mix after weighing) 5. Weigh 4.45g of ethanol (mix after weighing) 6. Ionomer 2 (gel) weighed 2.86 g (I / C=0.7) (mixed after weighing) 7. Mix in the groove Filmix for 180 seconds. 8. Particle size measurement The particle size measurement results for Comparative Example 1 showed that the average particle size of the catalyst particles in the catalyst ink was approximately 2.5 μm. Observation of the catalyst ink confirmed that the catalyst ink separated within one day.

Claims

[Claim 1] A method for producing a catalyst ink containing catalyst particles including a metal catalyst supported on a carbon support, a solvent, and an ionomer, the method comprising: a step of stirring and mixing the catalyst particles, the solvent, and the ionomer using beads having a bead diameter of 2 mm or less, The method for producing a catalyst ink, wherein the catalyst particles after stirring and mixing have an average particle size of 2.2 μm or less.

Images