KR101586147B1 - Fuel cell catalyst structure, method of manufacturing the same, fuel cell including the same, and metal nano tube - Google Patents

Abstract

The catalyst structure for a fuel cell according to the present invention comprises a conductive base material and a plurality of metal nanotubes arranged on the conductive base material, wherein each of the metal nanotubes has an outer side wall in the form of a tube having a first hollow portion, And an upper wall connecting an upper end of the outer sidewall and an upper end of the inner sidewall, the inner sidewall being in the form of a tube having a second hollow portion formed therein.

Description

Technical Field [0001] The present invention relates to a catalyst structure for a fuel cell, a method for manufacturing the same, a fuel cell including the fuel cell and a metal nanotube,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst structure for a fuel cell, a method for manufacturing the same, a fuel cell and a metal nanotube including the same, and more particularly to a catalyst structure for a fuel cell capable of improving the performance of the fuel cell, This invention relates to metal nanotubes.

Generally, a catalyst for a fuel cell uses powder-like nanoparticles and uses a carbon support to connect the nanoparticles to each other. The conductivity of the carbon support itself is good, but the use of a carbon support has the disadvantage of complicating the electron transport path, resulting in ineffective electron transport and reducing the active surface area of the nanoparticles. In addition, the use of a carbon support also lowers the stability of the catalyst for a fuel cell.

In order not to use a carbon support for a catalyst for a fuel cell, it is required to stably form the structure of the nanoparticles and have an active surface area wider than that of the powder form. To this end, platinum-based plates, dentrites, nanowires or tubular nanostructures have been continuously studied to increase the active surface area of nanoparticles.

It is an object of the present invention to solve the above-mentioned problems, and an object of the present invention is to provide a metal nanotube having a novel stable structure and capable of improving an active surface area and a catalyst structure for a fuel cell including the same.

Another object of the present invention is to provide a method of manufacturing the catalyst structure for a fuel cell.

It is still another object of the present invention to provide a fuel cell including a catalyst structure for a fuel cell.

The catalyst structure for a fuel cell according to an embodiment of the present invention includes a conductive substrate and a plurality of metal nanotubes disposed on the conductive substrate. Each of the metal nanotubes includes an outer side wall in the form of a tube having a first hollow portion, an inner side wall in the form of a tube disposed inside the first hollow portion and formed with a second hollow portion, And an upper wall connecting the upper end of the inner side wall and the upper end of the inner side wall.

In one embodiment, the metal nanotubes may be formed of platinum.

In one embodiment, the conductive substrate may be formed of gold, platinum, silver, palladium, ruthenium, rhodium, osmium, and / or iridium.

In one embodiment, the metal nanotubes may extend in a perpendicular or inclined direction from the surface of the conductive substrate, and may be spaced apart from each other on the conductive substrate surface.

In one embodiment, the surface roughness of the inner sidewall may be greater than the surface roughness of the outer sidewall.

In one embodiment, the inner sidewalls include micropores through which gas molecules pass, and the density of the inner sidewalls may be less than the density of the outer sidewalls.

In the manufacturing method of a catalyst structure for a fuel cell according to an embodiment of the present invention, an electrically conductive substrate is formed on a lower surface of a first template having a through hole, and the electro- A noble metal is deposited on the inner surface of the hole to form a second tube-shaped template. After removing the first template and depositing a noble metal on the exposed surface of the second template using an electrochemical deposition method using the second template to form a double walled noble metal nanotube, The catalyst structure for a fuel cell is produced by removing the template.

In one embodiment, the first template may be formed by anodizing the surface of an aluminum substrate to form an aluminum oxide layer having a porous structure, and then removing the aluminum substrate.

In one embodiment, the conductive substrate may be formed by depositing a noble metal on the lower surface of the first template.

In one embodiment, the step of forming the second template includes the steps of immersing the conductive base and the first template in a first electrolytic solution containing palladium ions, and immersing the conductive base and the first template in a solution And applying a different voltage to the working electrode to deposit palladium on the inner surface of the through hole. At this time, a plurality of protruding minute fibers may be formed on the inner surface of the second template.

In one embodiment, the step of forming the double walled noble metal nanotubes includes the steps of immersing the conductive base and the second template in a second electrolytic solution containing platinum ions, and a step of immersing the conductive base and the second template in the second template and the second electrolytic solution And applying a different voltage to the immersed working electrode to deposit platinum on the entire exposed surface of the second template. At this time, the protruding fine fibers of the second template may penetrate the platinum layer deposited on the inner surface of the second template.

In one embodiment, the second template may be removed using a strong acid aqueous solution.

In one embodiment, the step of removing the second template comprises the steps of removing the protruding microfibers of the second template using the strong acid aqueous solution and removing the pores of the platinum layer formed by the removed protruding microfibers And passing the aqueous strong acid solution through the interior of the double walled noble metal nanotube to remove the second template.

A fuel cell according to an embodiment of the present invention includes two electrodes spaced apart from each other and an electrolyte interposed therebetween, and one electrode of the electrode includes a conductive base material and a plurality of noble metal nano- Wherein each of the metal nanotubes comprises an outer sidewall in the form of a tube having a first hollow portion, an inner sidewall in the form of a tube disposed in the first hollow portion and formed with a second hollow portion, And an upper wall connecting the upper end of the outer sidewall and the upper end of the inner sidewall.

The metal nanotube according to an embodiment of the present invention includes an outer side wall in the form of a tube having a first hollow portion, an inner side wall in the form of a tube disposed inside the first hollow portion and having a second hollow portion, And an upper wall connecting the upper end of the outer side wall and the upper end of the inner side wall.

In one embodiment, the outer sidewall, the inner sidewall, and the top wall may be formed of platinum (Pt).

In one embodiment, the outer sidewall, the inner sidewall, and the top wall are integrally formed, and the platinum may have a polycrystalline structure.

In one embodiment, the surface roughness of the inner sidewall may be greater than the surface roughness of the outer sidewall.

In one embodiment, the inner sidewalls include micropores through which gas molecules pass, and the density of the inner sidewalls may be less than the density of the outer sidewalls.

According to the present invention, in the catalyst structure for a fuel cell comprising metal nanotubes formed directly on a conductive substrate without a carbon support, the electron transport path can be shortened to the electron transport path of the catalyst containing the carbon support. In addition, the metal nanotubes constituting the catalyst structure for a fuel cell have a double wall structure, thereby maximizing the active surface area. In addition, since the metal nanotubes have surface roughness, the active surface area can be further increased as the interfacial area is increased. Therefore, the efficiency of the fuel cell per unit area can be improved by using the catalyst structure for a fuel cell according to the present invention in a fuel cell. Since the plurality of metal nanotubes can be regularly arranged on the conductive substrate, the mass transfer efficiency of the catalyst structure for a fuel cell can be further improved as compared with the non-regular arrangement.

In addition, since the catalyst structure for a fuel cell does not include a carbon support, the problem of carbon corrosion can be prevented originally. In addition, since the metal nanotubes have a micro-scale length, they are less soluble or cohesive than a catalyst made of powder nanoparticles. Therefore, it is possible to provide a catalyst structure for a fuel cell having improved durability.

Since the catalyst structure for a fuel cell is synthesized electrochemically, the productivity of the catalyst structure for a fuel cell can be improved because the loss ratio of the metal nanotubes in the manufacturing process is almost zero.

1 is a perspective view illustrating a catalyst structure for a fuel cell according to an embodiment of the present invention.
FIGS. 2A, 2B and 2C are views for explaining the metal nanotube shown in FIG.
FIGS. 3 to 9 are process diagrams for explaining the method of manufacturing the catalyst structure for a fuel cell shown in FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and similarities. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the term "comprises" or "having" is intended to designate the presence of stated features, elements, etc., and not one or more other features, It does not mean that there is none.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

1 is a perspective view illustrating a catalyst structure for a fuel cell according to an embodiment of the present invention.

Referring to FIG. 1, a catalyst structure 500 for a fuel cell includes a plurality of metal nanotubes 100 and a conductive substrate 200.

The conductive base material 200 is a base material for supporting the metal nanotubes 100, and has conductivity. The conductive substrate 200 may be used as one electrode for electrochemical plating in the process of forming the metal nanotubes 100. The conductive substrate 200 may be formed of gold, platinum, silver, palladium, ruthenium, rhodium, osmium, and iridium. Since the metal nanotubes 100 are formed directly on the conductive base material 200 having conductivity, the electron transfer path between the conductive base material 200 and the metal nanotubes 100 can be shortened.

The metal nanotubes 100 have a lengthwise direction perpendicular or inclined from the surface of the conductive base material 200 and are disposed on the conductive base material 200 so as to be spaced apart from each other. In one example, the length of each of the metal nanotubes 100 may be about 1 to 10, and the diameter may be about 200 nm to 300 nm. The metal nanotubes 100 may be formed of platinum. At this time, platinum may have a polycrystalline structure. The specific structure of the metal nanotube 100 will be described in detail below with reference to FIG. 2A, FIG. 2B, and FIG. 2C together with FIG.

FIGS. 2A, 2B and 2C are views for explaining the metal nanotube shown in FIG.

2A is a perspective view showing the metal nanotube 100 in a normal direction, which is a direction disposed on the conductive base 200, FIG. 2B is a cross-sectional view taken along line II of FIG. 2A, and FIG. 2C is a cross- 1 is a perspective view showing a metal nanotube 100 according to an embodiment of the present invention.

2A, 2B and 2C, the metal nanotube 100 includes an outer sidewall OP, an inner sidewall IP, and a top wall 110. [

The outer side wall OP has a tube shape in which the first hollow portion A is formed and the inner side wall IP has a tube shape in which the second hollow portion B is formed. Each of the outer side wall OP and the first hollow portion A may have a circular shape and the inner side wall IP and the second hollow portion B may each have a circular shape in plan view. A circle means not only a circle having the same curvature at all points but also an ellipse or a curved shape.

The inner side wall IP is disposed inside the first hollow portion A and the upper end of the outer side wall OP and the upper end of the inner side wall IP are connected to the upper wall 110. [ The inner side wall IP is disposed so as to be surrounded by the outer side wall OP. The first opening 112 is defined on the upper side of the metal nanotube 100 by the outer side wall OP, the inner side wall IP and the upper wall 110. The depth of the first hollow portion A may be substantially equal to or less than the length of the metal nanotubes 100.

The lower end of the outer side wall OP may be directly connected to the conductive base 200. The lower end of the inner side wall IP may be connected by the lower wall 120 to have a U-shaped cross section. At this time, the lower wall 120 is disposed apart from the conductive base material 200. A second opening 122 is defined below the metal nanotubes 100 by the outer sidewall OP, the inner sidewall IP, and the top wall 110. The depth of the second hollow portion (B) may be smaller than the length of the metal nanotube (100).

Alternatively, the lower end of the inner sidewall IP may be directly connected to the conductive substrate 200. That is, the lower wall 120 is removed, and the lower end of the inner side wall IP is disposed in contact with or spaced from the conductive base material 200. The first hollow portion A penetrates the metal nanotube 100 . ≪ / RTI > The inner side wall IP and the outer side wall OP may be integrated without the lower wall 120 because the upper end of the inner side wall IP is connected to the upper wall 110. [

Each of the outer side wall OP and the inner side wall IP has a predetermined surface roughness and the surface roughness of the inner side wall IP can be larger than the surface roughness of the outer side wall OP. At the same time, the inner sidewall IP comprises micropores through which the gas molecules pass, so that the density of the inner sidewall IP may be less than the density of the outer sidewall OP.

Each of the outer side wall OP, the inner side wall IP, the top wall 110 and the bottom wall 120 may be formed of platinum, and they may be integrally connected. When the outer sidewall OP, the inner sidewall IP, the top wall 110 and the bottom wall 120 are integrally connected, the cross-sectional shape may have an M-shape.

The metal nanotubes 100 described above have a double wall structure including an outer side wall OP and an inner side wall IP. Thus, the active surface area of the metal nanotube 100 can be maximized. In addition, the surface area of the metal nanotubes 100 can be increased by the surface roughness of the metal nanotubes 100 due to the minute pores formed in the outer side wall OP and the inner side wall IP.

Hereinafter, a method of manufacturing the catalyst structure 500 for a fuel cell as described with reference to FIGS. 1, 2A to 2C will be described with reference to FIGS. 3 to 9. FIG.

FIGS. 3 to 9 are process diagrams for explaining the method of manufacturing the catalyst structure for a fuel cell shown in FIG.

3 and 4 are cross-sectional views for explaining the process of forming the conductive base material 200 on the first template 322. FIG.

Referring to FIG. 3, an aluminum substrate 310 is prepared, and an aluminum oxide layer 320 having a porous structure 330 is formed on the surface of the aluminum substrate 310.

The aluminum oxide layer 320 may be formed on the surface of the aluminum substrate 310 through an anodizing process. In the anodic oxidation process, sulfuric acid, phosphoric acid, oxalic acid, or the like can be used as an electrolyte, and the porous aluminum oxide layer 320 can be formed while the electrolyte penetrates the surface of the aluminum substrate 310. The plurality of pores 330 forming the porous structure may be formed to have a predetermined depth, and the cross-section may have a U-shape and a circular planar shape.

Referring to FIG. 4, a first template 322 is formed using an aluminum oxide layer 320, and a conductive base material 200 is formed on a lower surface of the first template 322.

The conductive substrate 200 is formed on the aluminum oxide layer 320 and the aluminum substrate 310 and the aluminum oxide layer 320 are partially removed on the aluminum substrate 310 on which the aluminum oxide layer 320 is formed, The conductive base material 200 can be formed on the lower surface of the first template 322. At this time, the conductive base material 200 can be formed by sputtering a noble metal.

The first template 322 includes a plurality of through holes 332 as the aluminum oxide layer 320 partially remains on the conductive base material 200. [ Each of the through holes 332 may correspond to each of the pores 330 of the porous structure.

5, 6, and 7 are sectional views for explaining a process of forming the second template 410 using the first template 322, and FIG. 6 is an enlarged sectional view of the portion A of FIG. 5 .

5 to 7, a noble metal layer is formed on the conductive base material 200 on which the first template 322 is formed. By forming the noble metal layer, a second template 410 which is recessed corresponding to the central region of the through holes 332 of the first template 322 is formed. At this time, the noble metal layer includes palladium.

The noble metal layer may be formed using an electrochemical deposition method. The conductive base material 200 on which the first template 322 is formed is immersed in the first electrolytic solution containing palladium ions. A working electrode is immersed in the first electrolytic solution and a voltage is applied to each of the working electrode and the conductive base material 200 to deposit the noble metal layer on the inner surface of the through holes 332. At this time, a plurality of protruding minute fibers as shown in FIG. 6 are formed on the inner surface of the second template 410. The surface of the second template 410 may have a predetermined roughness due to the fine fibers.

After the noble metal layer is formed, only the second template 410 having a tube shape remains on the conductive base 200 by removing the first template 322. At this time, the first template 322 may be removed with a strongly basic solution. For example, the first template 322 may be removed using a sodium hydroxide solution.

FIGS. 8 and 9 are process diagrams illustrating a process of forming the metal nanotubes 100 using the second template 410.

8, a noble metal layer is formed on the conductive base material 200 on which the second template 410 is formed, whereby the metal moldings 410 form a core and a shell layer SH covering the core. Thereby forming a nanotube. The noble metal layer may be partially formed on the second template 410 and the conductive base 200. The thickness of the noble metal layer formed on the bottom surface of the second template 410 is several nm and may be formed thinner than the thickness of the noble metal layer formed on the sidewall of the second template 410. [

Since the second template 410 includes a plurality of protruding microfibers, the noble metal layer is formed and a plurality of pores are formed in the shell layer SH. That is, the protruding fine fibers of the second template 410 may penetrate the shell layer SH deposited on the inner surface of the second template 410. The noble metal layer may include platinum.

For example, when the conductive base material 200 and the second template 410 are immersed in a second electrolytic solution containing platinum ions and a voltage is applied to the conductive base material 200 and the working electrode, respectively, Platinum can be deposited entirely on the exposed surface. The working electrode is immersed in the second electrolytic solution.

9, the second template 410 may be removed to form the metal nanotubes 101 having openings having substantially the same shape as the second template 410 on the conductive base 200 have.

The second template 410 may be removed using an etching solution containing a strong acid aqueous solution. For example, the etchant may be an aqueous nitric acid solution. The etchant may reach the second template 410 through pores formed in the shell layer SH by the protruding microfibers to remove the second template 410.

For example, when the etching solution is applied to the conductive base material 200 on which the double-walled noble metal nanotubes are formed to remove the protruding minute fibers of the second template 410, the shell layer SH formed by the removed protruding minute fibers The etchant penetrates into the second template 410 to remove the second template 410. At this time, the noble metal layer formed on the bottom surface of the second template 410 may be removed together with the second template 410. When the noble metal layer formed on the bottom surface of the second template 410 is removed, the lower wall 120 shown in Figs. 2A and 2B is removed and the inner sidewall IP is slightly spaced from the conductive base 200 So that the first hollow portion of the outer side wall IP passes through the metal nanotube 101 as shown in Fig.

Alternatively, in the step of removing the second template 410, when the noble metal layer formed on the bottom surface of the second template 410 remains, the inner side wall IP is separated from the lower wall 410 shown in Figs. The metal nanotubes 100 having a structure connected to each other by the first electrode 120 can be formed.

Accordingly, the catalyst structural body 500 for a fuel cell described with reference to FIGS. 1, 2A, 2B and 2C can be formed.

Since the catalyst structure 500 for a fuel cell according to the present invention includes a plurality of metal nanotubes 100 and each of the metal nanotubes 100 has a double wall structure and has a wide active surface area, The efficiency of the battery can be improved. The fuel cell includes two electrodes facing each other and an electrolyte solution interposed therebetween, and the catalyst structure 500 for a fuel cell can be used as one electrode of the fuel cell. The electrolyte solution may include methanol.

Carbon dioxide, which is the final product in the methanol fuel cell, can be easily accumulated in the metal nanotubes 100 during methanol oxidation. Since the catalytic reaction depends on the surface area of the catalyst, when the carbon dioxide is accumulated in the catalyst, the catalytic active area is reduced, so that the oxidation activity can be drastically reduced. However, the metal nanotube 100 according to the present invention has a double-walled structure and has a hollow structure, so that it has sufficient pores for discharging carbon dioxide.

As described above, since the metal nanotubes 100 are directly formed on the conductive base material 200, the electron transport path can be shortened in the catalyst structure 500 for a fuel cell. Accordingly, the efficiency of the fuel cell per unit area can be improved by using the catalyst structure 500 for a fuel cell according to the present invention in a fuel cell. Since the plurality of metal nanotubes 100 can be regularly arranged on the conductive base material 200, the mass transfer efficiency of the catalyst structure 500 for a fuel cell can be further improved as compared with the non-regular arrangement.

The description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features presented herein.

500: catalyst structure for fuel cell 100: metal nanotube
200: conductive base material 112: first opening
122: second opening IP: inner side
OP: outer side 130: upper wall
310 aluminum substrate 320 aluminum oxide layer
322: First Template

Claims (19)

Conductive substrates; And
And a plurality of metal nanotubes spaced apart from each other on the conductive substrate,
Each of the metal nanotubes
An outer sidewall in the form of a tube having a first hollow portion;
An inner side wall in the form of a tube disposed inside the first hollow portion and having a second hollow portion; And
Wherein the outer sidewall, the inner sidewall, and the upper wall are all formed of the same metal so that the outer sidewall and the inner sidewall are spaced apart from each other And,
Wherein the metal nanotubes are arranged vertically with respect to the surface of the conductive base so that the upper wall of each of the metal nanotubes faces the surface of the conductive base.
Catalyst structure for fuel cells.
The method according to claim 1,
Wherein the metal nanotubes are formed of platinum.
3. The method of claim 2,
Wherein the conductive substrate is formed of one material selected from the group consisting of gold, platinum, silver, palladium, ruthenium, rhodium, osmium, and iridium.
delete The method according to claim 1,
Wherein the surface roughness of the inner sidewall is larger than the surface roughness of the outer sidewall.
The method according to claim 1,
Wherein the inner sidewalls comprise micropores through which gas molecules pass,
Wherein the density of the inner sidewalls is less than the density of the outer sidewalls.

Forming a conductive base on the lower surface of the first template having the through-hole;
Depositing a noble metal on the inner surface of the through hole using an electrochemical deposition method using the conductive base to form a tube-type second template;
Removing the first template;
Depositing a noble metal on the exposed surface of the second template using an electrochemical deposition method using the second template to form a double walled noble metal nanotube; And
And removing the second template. ≪ Desc / Clms Page number 19 >
8. The method of claim 7,
Wherein the first template is formed by anodizing the surface of the aluminum substrate to form an aluminum oxide layer having a porous structure, and then removing the aluminum substrate.
9. The method of claim 8,
Wherein the conductive substrate is formed by depositing a noble metal on the lower surface of the first template.
9. The method of claim 8,
Wherein the forming of the second template comprises:
Immersing the conductive base and the first template in a first electrolytic solution containing palladium ions; And
Depositing palladium on the inner surface of the through hole by applying different voltages to the conductive base and the working electrode immersed in the first electrolytic solution,
And a plurality of protruding microfibers are formed on the inner surface of the second template.
11. The method of claim 10,
The step of forming the double walled noble metal nanotubes comprises:
Immersing the conductive base and the second template in a second electrolytic solution containing platinum ions; And
And applying a different voltage to the second template and the working electrode immersed in the second electrolytic solution to deposit platinum on the entire exposed surface of the second template,
Wherein protruding fine fibers of the second template pass through a platinum layer deposited on the inner surface of the second template.
12. The method of claim 11,
Wherein the second template is removed using a strong acid aqueous solution.
13. The method of claim 12,
Wherein the removing the second template comprises:
Removing the protruding minute fibers of the second template using the strong acid aqueous solution; And
And removing the second template by penetrating the strong acid aqueous solution into the double walled noble metal nanotube through pores of the platinum layer formed by the removed protruding microfibers. Gt;
And two electrodes spaced apart from each other and an electrolyte interposed therebetween,
Wherein one of the electrodes comprises a conductive substrate and a plurality of noble metal nanotubes disposed on the conductive substrate,
Each of the metal nanotubes may include a metal,
An outer sidewall in the form of a tube having a first hollow portion;
An inner side wall in the form of a tube disposed inside the first hollow portion and having a second hollow portion; And
And an upper wall connecting the upper end of the outer side wall and the upper end of the inner side wall, wherein the outer side wall, the inner side wall, and the upper wall are all formed of the same metal, And,
Wherein the metal nanotubes are arranged vertically with respect to the surface of the conductive base so that the upper wall of each of the metal nanotubes faces the surface of the conductive base.
Fuel cell.
An outer sidewall in the form of a tube having a first hollow portion;
An inner sidewall disposed in the interior of the first hollow and in the form of a tube having a second hollow; And
Wherein the outer sidewall, the inner sidewall, and the upper wall are all formed of the same metal so that the outer sidewall and the inner sidewall are spaced apart from each other And,
Wherein the inner sidewalls comprise micropores through which gas molecules pass and the density of the inner sidewalls is less than the density of the outer sidewalls.
Metal nanotubes.
16. The method of claim 15,
Wherein the outer sidewall, the inner sidewall, and the top wall are formed of platinum (Pt).
17. The method of claim 16,
Wherein the outer sidewall, the inner sidewall, and the upper wall are integrally formed, and the platinum has a polycrystalline structure.
16. The method of claim 15,
Wherein the surface roughness of the inner sidewall is larger than the surface roughness of the outer sidewall.
16. The method of claim 15,
Wherein the inner sidewalls comprise micropores through which gas molecules pass,
Wherein the density of the inner sidewalls is less than the density of the outer sidewalls.

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