JP7063831B2 - How to create a simulation model of the catalyst layer for fuel cells - Google Patents

Description

The present invention relates to a method for creating a simulation model of a catalyst layer for a fuel cell, and more specifically, a method for creating a simulation model of a catalyst layer for a fuel cell capable of expressing the formation of a carbon laminated structure closer to the real thing and the arrangement of ionomers.

A solid polymer fuel cell is attracting attention as an energy source as a fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas. Since the polymer electrolyte fuel cell can operate at room temperature and has a high output density, it is being actively studied as a form suitable for automobile applications and the like.

Since the members that make up a fuel cell are expensive, simulation techniques are widely used when designing and manufacturing fuel cells. In the fuel cell performance prediction simulation, a catalyst layer model equivalent to the actual one is required.

For example, Patent Document 1 discloses a model creating means for modeling a catalyst layer from geometrical shape and characteristic data of the catalyst layer.

Patent Document 2 discloses a method for creating a porous body model including a skeleton composed of a plurality of granules based on information on pores such as porosity and pore size distribution. In Patent Document 2, the pore size of the pores for which the allocation number is calculated is corrected based on the thickness of the ionomer formed at the interface between the pores and the granules.

Patent Document 3 is a fuel cell simulation method for calculating the performance of the catalyst layer of a fuel cell in which catalyst layers are arranged on both main surfaces of an electrolyte membrane, and is a model of the Boltzmann equation describing the material transport of the catalyst layer. We disclose a fuel cell simulation method that calculates the performance of the catalyst layer based on the actual structure of the catalyst layer by using the lattice Boltzmann method to solve the equation.

Further, Non-Patent Document 1 discloses a carbon arrangement based on DLVO potential, and the shape of the carbon is a virtual shape formed from a series of spheres.

JP-A-2009-193672 Japanese Unexamined Patent Publication No. 2010-128746 Japanese Unexamined Patent Publication No. 2017-139158

G. Inoue and M.M. Kawase, "Understanding formation mechanism of hydrogen geneus porous structure of catalyst layer in polymer, electrolyte fuel cell", International 21352-21365, 2016

However, Patent Documents 1 to 3 do not disclose a method for specifically modeling the 3D solid geometry of the catalyst layer. Further, even in Non-Patent Document 1, the influence of steric interference based on the actual shape of the catalyst layer is not reflected in the 3D steric structure.

For example, FIG. 1 shows a method for creating a simulation model of a catalyst layer for a fuel cell described in Non-Patent Document 1. In FIG. 1, black indicates carbon and gray indicates ionomer. In FIG. 1, since the shape of carbon is virtually generated from a series of spheres, even if carbon having that shape is laminated to form a carbon laminated structure and an ionomer is placed (attached) there, the carbon is formed. It is not possible to generate a structure equivalent to the structure of the actual catalyst layer.

That is, in the conventional method for creating a simulation model of a catalyst layer for a fuel cell, carbon having pores (voids) inside used in an actual catalyst layer is expressed (for example, a void smaller than the carbon diameter is represented). It is difficult to set it at an arbitrary position), and the obtained carbon laminated structure may have a shape different from the actual one.

Further, even if a carbon model having an internal void is used as the carbon, the ionomer may be clogged in the carbon void, and the arrangement of the ionomer may differ from the actual one.

In the actual catalyst layer, the catalyst inside the hollow is more active than the catalyst at other positions, which is presumed to be because the catalyst not coated with ionomer is highly active without being poisoned by the catalyst. To. Therefore, it is necessary to create a model in which the voids inside the carbon are not clogged by ionomers.

Therefore, it is an object of the present invention to provide a method for creating a simulation model of a catalyst layer for a fuel cell, which can express the formation of a carbon laminated structure closer to the real thing and the arrangement of ionomers.

The catalyst layer structure is composed of a laminated structure of carbon aggregates carrying a catalyst (also referred to as “carbon laminated structure” in the present specification and the like) and ionomers arranged in the structure, and is at the micro level. And it is complicated. Therefore, in order to simulate the catalyst layer structure, dedicated software is used instead of general CAD software. At that time, since the structure generation method that meets the needs is often not prepared, it is necessary to proceed with the development independently.

As a result of various studies on means for solving the above-mentioned problems, the present inventors virtually generated in the method for creating a simulation model of a catalyst layer for a fuel cell described in Non-Patent Document 1, as shown in FIG. We have developed a method to replace the shape of the carbon with a 3D image (3D-TEM image) obtained by a transmission electron microscope (TEM).

However, in the above method of expressing the shape of carbon by a 3D-TEM image, when the shape of carbon is a hollow structure, the ionomer is clogged in the voids of the carbon when the ionomer is arranged, which is seen in the actual catalyst layer structure. It turns out that it produces a structure that is not possible. FIG. 3 shows a cross-sectional view of a catalyst layer structure in which ionomers are clogged in carbon voids in a method for creating a simulation model of a catalyst layer for a fuel cell. In FIG. 3, voids (black), carbon, and ionomers are shown in order from the darkest color.

Therefore, as a result of further studying various means for solving the above-mentioned problems, the present inventors have first described in the method of creating a simulation model of the catalyst layer for a fuel cell by using a transmission electron microscope to obtain 3D- of carbon as a raw material. A TEM image is acquired, and secondly, when the carbon represented by the 3D-TEM image has a hollow structure, the voids in the hollow structure are replaced with the substance X to be removed later, and thirdly, carbon is laminated and carbon is laminated. A fuel in which an ionomer is arranged in a carbon laminated structure closer to the real thing by creating a laminated structure, fourthly arranging an ionomer, and fifthly removing the substance X and causing a void portion to appear again. We have found that it is possible to express a catalyst layer for a battery, and completed the present invention.

That is, the gist of the present invention is as follows.
(1) A method for creating a simulation model of a catalyst layer for a fuel cell.
(I) A step of acquiring a 3D-TEM image of carbon as a raw material by a transmission electron microscope,
(Ii) The step of replacing the voids existing in the carbon represented by the 3D-TEM image acquired in (i) with a substance X other than the substance existing in the catalyst layer for a fuel cell.
(Iii) The step of laminating carbon whose voids are replaced with the substance X in (ii) to create a carbon laminated structure,
(Iv) A method for creating a simulation model, which comprises a step of arranging an ionomer in the carbon laminated structure created in (iv) and (iv), and a step of removing the substance X from the carbon laminated structure in which the ionomer is arranged in (v) (iv).
(2) The method for creating a simulation model according to (1), wherein in the step (ii), the void portion having a size of 8 nm or less is replaced with the substance X.

INDUSTRIAL APPLICABILITY The present invention provides a method for creating a simulation model of a catalyst layer for a fuel cell, which can generate a carbon laminated structure closer to the real thing and express the arrangement of ionomers.

It is a figure which shows the simulation model making method of the catalyst layer for a fuel cell described in Non-Patent Document 1. It is a figure which shows the simulation model creation method of the fuel cell catalyst layer which replaced the shape of the virtually generated carbon with 3D-TEM image in the simulation model creation method of the fuel cell catalyst layer which is described in Non-Patent Document 1. .. It is a figure which shows the cross-sectional view of the catalyst layer structure in which ionomer is packed in the void part of carbon in the method of making the simulation model of the catalyst layer for a fuel cell. It is a figure which shows an example of the simulation model making method of the catalyst layer for a fuel cell of this invention schematically. It is a figure which shows the cross-sectional view of the catalyst layer structure created by an example of the simulation model creation method of the catalyst layer for a fuel cell of this invention. It is a figure which shows typically the method of making the simulation model of the catalyst layer for a fuel cell in the comparative example. It is a figure which shows typically the method of making the simulation model of the catalyst layer for a fuel cell in an Example. It is a figure which shows the pore diameter distribution of a comparative example and an Example. It is a figure which shows the proton conductivity of a comparative example and an Example. It is a figure which shows the IV characteristic of a comparative example and an Example. It is a figure which shows the result of the overvoltage separation of the comparative example and the Example.

Hereinafter, preferred embodiments of the present invention will be described in detail.
In the present specification, the features of the present invention will be described with reference to the drawings as appropriate. The drawings exaggerate the dimensions and shapes of each part for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of the parts shown in these drawings. The method for creating a simulation model of the catalyst layer for a fuel cell of the present invention is not limited to the following embodiment, and changes and improvements that can be made by those skilled in the art are made without departing from the gist of the present invention. It can be carried out in various forms.

The method for creating a simulation model of the catalyst layer for a fuel cell of the present invention is as follows: (i) a step of acquiring a 3D-TEM image of carbon as a raw material by a transmission electron microscope, and (ii) a void portion existing in carbon for a fuel cell. The steps of substituting a substance X other than the substance existing in the catalyst layer, (iii) laminating carbon to create a carbon laminated structure, (iv) arranging an ionomer, and (v) removing the substance X are performed. include.

The details of the steps (i) to (v) are shown below.

(I) Step of Acquiring a 3D-TEM Image of Raw Material Carbon by Transmission Electron Microscope In step (i), a 3D-TEM image of raw material carbon is acquired by a transmission electron microscope.

In the present invention, a 3D-TEM image of carbon as a raw material can be obtained by a transmission electron microscope known in the art, and the length is usually 100 nm to 400 nm, preferably 150 nm to 250 nm, and the width is horizontal. However, it is a 3D-TEM image having a depth of usually 100 nm to 400 nm, preferably 100 nm to 200 nm, and a depth of usually 100 nm to 400 nm, preferably 100 nm to 150 nm.

As the 3D-TEM image of carbon as a raw material, one image may be acquired, or a plurality of images, for example, two images to an image of the number of carbons constituting the catalyst layer may be acquired.

By acquiring a 3D-TEM image of carbon as a raw material by a transmission electron microscope in the step (i), a carbon laminated structure closer to the real thing can be created in the step (iii).

(Ii) The step of replacing the voids existing in the carbon with a substance X other than the substance existing in the catalyst layer for the fuel cell In the step of (ii), the carbon represented by the 3D-TEM image obtained in (i) is used. The existing void is replaced with a substance X other than the substance existing in the fuel cell catalyst layer.

Since the substance X other than the substance existing in the fuel cell catalyst layer is removed in the step (v), any substance other than the substance existing in the fuel cell catalyst layer (for example, carbon, ionomer, and platinum) can be used. Not limited.

In the step (ii), by replacing the voids existing in the carbon represented by the 3D-TEM image acquired in (i) with a substance X other than the substance existing in the catalyst layer for the fuel cell, (iv). When the ionomer is arranged in the above step, the voids inside the carbon are not clogged by the ionomer, and the difference between the finally obtained fuel cell simulation and the actual product can be reduced.

The voids existing in the carbon represented by the 3D-TEM image obtained in (i) may be all replaced with the substance X, but the size of the voids replaced with the substance X is defined as the equivalent circle diameter. When it is used, it may be adjusted to 8 nm or less.

In the step (ii), of the voids existing in the carbon represented by the 3D-TEM image acquired in (i), the voids having the size in the above range are substances other than the substance existing in the catalyst layer for the fuel cell. By substituting with X, when voids of various sizes are present in the carbon represented by the 3D-TEM image obtained in (i), ionomers are present in the large voids in the step (iv). It is possible to create a model in which ionomers do not enter into small gaps.

(Iii) Step of laminating carbon to create a carbon laminated structure In the step of (iii), carbon whose voids are replaced with the substance X in (iii) is laminated to create a carbon laminated structure.

In the step (iii), the method for laminating carbon in which the voids are replaced with the substance X in (iii) is not limited. For example, in the step (iii), a carbon laminated structure is created by randomly laminating carbon whose voids are replaced with the substance X in (iii).

The carbon whose voids are replaced with the substance X in (ii) may be of one type, for example, two types to a catalyst layer, depending on the number of images acquired in the step (i). It may be of the type of the number of carbons constituting.

Further, a mirror image of the carbon may be used as the carbon in which the void portion is replaced with the substance X in (ii). Therefore, even if the image acquired in the step (i) is one image, there are two types of carbon, in which the voids obtained from the image in (ii) are replaced with the substance X, and a mirror image of the carbon. A carbon laminated structure can be created from carbon.

By laminating carbon based on the 3D-TEM image acquired by the transmission electron microscope in step (i) in step (iii), a carbon laminated structure closer to the real thing can be created.

(Iv) Step of arranging ionomers In the step of (iv), ionomers are arranged in the carbon laminated structure created in (iii).

In the step (iv), the amount of ionomers arranged is not limited and can be changed according to the desired fuel cell catalyst layer as a simulation model. For example, in a specific fuel cell catalyst layer, when it is desired to simulate a change in fuel cell power generation performance due to a difference in the amount of ionomer, the amount of ionomer is set to an amount smaller or larger than the amount normally used in the art. Can be changed to various quantities.

By arranging the ionomer in the carbon laminated structure created in (iii) in the step (iv), the ionomer is clogged in the voids inside the carbon of the carbon laminated structure substituted with the substance X, particularly small voids. It is placed between carbon and carbon. Therefore, in the step (v), the catalyst layer after removing the substance X becomes closer to the real thing in which the voids inside the carbon are usually not clogged by the ionomer.

(V) Step of removing substance X In step (v), the substance X is removed from the carbon laminated structure in which the ionomer is arranged in (iv).

In the simulation of the catalyst layer for a fuel cell obtained by removing the substance X from the carbon laminated structure in which the ionomer is arranged in the step (v), the voids inside the carbon are usually not clogged by the ionomer. It will be closer to the real thing.

In the method for creating a simulation model of the catalyst layer for a fuel cell of the present invention, platinum is used between steps (i) and (ii) and / or between steps (ii) and (iv). Can be placed in.

FIG. 4 schematically shows an example of a method for creating a simulation model of a catalyst layer for a fuel cell of the present invention, and FIG. 5 shows a catalyst layer structure created by the method for creating a simulation model of a catalyst layer for a fuel cell of the present invention. A cross-sectional view is shown. In FIG. 4, black indicates carbon and gray indicates ionomer. In FIG. 5, voids (black), carbon, and ionomers are shown in order from the darkest color.

From FIGS. 4 and 5, according to the method for creating a simulation model of the catalyst layer for a fuel cell of the present invention, there are voids inside the carbon, and the voids inside the carbon are not clogged by ionomers. It can be seen that the catalyst layer for a fuel cell having the arrangement of can be expressed.

From the above, by the method for creating a simulation model of the catalyst layer for a fuel cell of the present invention, it is possible to express a catalyst layer for a fuel cell in which an ionomer is arranged in a state closer to the real thing in a carbon laminated structure closer to the real thing. It is possible to express the pore size peak derived from the carbon hollow structure in the relationship between the pore size and the body integration rate in the fuel cell catalyst layer, which could not be expressed in the past, and further, the characteristics in the conventional simulation, such as proton conduction. It is possible to express characteristics such as degree, relationship between current density and cell voltage, overvoltage separation, and different simulation results.

Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

As a comparative example, a simulation model of a catalyst layer for a fuel cell prepared by using the method described in Non-Patent Document 1 (FIG. 6) was used. In FIG. 6, black indicates carbon and gray indicates ionomer.

As an example, (i) a 3D-TEM image (length x width x depth = 200 nm x 150 nm x 120 nm) of carbon as a raw material was acquired by a transmission electron microscope, and the 3D-TEM acquired in (ii) and (i). The voids of 4 nm or less present in the carbon represented by the image are replaced with a substance X other than the substance existing in the catalyst layer for the fuel cell, and the voids are replaced with the substance X in (iii) and (ii). From the carbon laminated structure in which the mirror image of the carbon is randomly laminated to create a carbon laminated structure, the ionomer is arranged in the carbon laminated structure created in (iv) and (iii), and the ionomer is arranged in (v) and (iv). The simulation model of the catalyst layer for a fuel cell prepared by removing the substance X (FIG. 7) was used. In FIG. 7, black indicates carbon and gray indicates ionomer.

Structural analysis and power generation calculation were performed using the simulation models of Comparative Examples and Examples.

Regarding the results of the structural analysis, FIG. 8 shows the pore size distribution, and FIG. 9 shows the proton conductivity. From FIG. 8, it was found that in the example, the peak caused by the carbon hollow structure peculiar to the 3D-TEM image, which could not be expressed in the comparative example, can be expressed. Further, from FIG. 9, it was found that the examples and the comparative examples show different proton conductivitys.

Regarding the results of power generation calculation, FIG. 10 shows the IV characteristics, and FIG. 11 shows the results of overvoltage separation. From FIG. 10, it was found that the examples and the comparative examples exhibited different IV characteristics. Further, from FIG. 11, it was found that the examples and the comparative examples showed different overvoltage separations.

From the above, it is considered that the present invention has made it possible to capture the characteristics derived from the actual shape of the fuel cell catalyst layer, which could not be captured by the conventional method. Therefore, according to the present invention, it is possible to evaluate the influence of the actual carbon shape on the characteristics of the catalyst layer structure and the power generation characteristics, and the present invention is based on the carbon shape that improves the power generation performance of FC, that is, the catalyst. Useful for layer structure design.

Claims (2)

It is a method of creating a simulation model of a catalyst layer for a fuel cell.
(I) A step of acquiring a 3D-TEM image of carbon as a raw material by a transmission electron microscope,
(Ii) The step of replacing the voids existing in the carbon represented by the 3D-TEM image acquired in (i) with a substance X other than the substance existing in the catalyst layer for a fuel cell.
(Iii) The step of laminating carbon whose voids are replaced with the substance X in (ii) to create a carbon laminated structure,
(Iv) A method for creating a simulation model, which comprises a step of arranging an ionomer in the carbon laminated structure created in (iv) and (iv), and a step of removing the substance X from the carbon laminated structure in which the ionomer is arranged in (v) (iv). The simulation model creating method according to claim 1, wherein in the step (ii), the void portion having a size of 8 nm or less is replaced with the substance X.

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