KR20080103123A - Analysis method of membrane-electrode assembly using scanning electron microscope - Google Patents

Abstract

An analytical method of the membrane electrode assembly using the scanning electron microscope is provided to perform the structure and section analysis of the membrane electrode assembly accurately. An analytical method of the membrane electrode assembly using the scanning electron microscope includes the step of collection of the specimen by using the sawing machine; the step for cutting the specimen which collects in the state that cools by using the liquid nitrogen; the step for coating the conductive metal using the coating equipment in the surface of the specimen cut; the step for analyzing the specimen which is kept in the space blocked with the external air by using the scanning electron microscope.

Description

Analysis method of membrane-electrode assembly using scanning electron microscope

1 is a schematic diagram of a basic reaction of a membrane-electrode assembly in a fuel cell stack;

2 is a flow chart showing a specimen preparation and analysis process according to the present invention,

3, 4 and 5 are photographs observing the structure of the MEA specimen prepared according to the conventional method,

6, 7, 8 and 9 are photographs observing the structure of the MEA specimen prepared according to the method according to the invention.

The present invention relates to a method for analyzing a membrane-electrode assembly (MEA), and more particularly, to a specimen preparation and analysis method for analyzing a membrane-electrode assembly in a fuel cell stack using a scanning electron microscope.

In general, a fuel cell is a device that converts chemical energy of a fuel into electrochemical energy directly in a cell without being converted into heat by combustion, and is a pollution-free power generation device that has been recently studied with interest.

Fuel cells produce electrical energy by electrochemically reacting fuel and oxygen. These fuel cells can be applied not only to supply power for industrial, domestic and vehicle driving, but also for power supply of small electrical / electronic products, especially portable devices. Can be.

1 is a schematic diagram illustrating a basic reaction of a membrane-electrode assembly (MEA) in a fuel cell stack, and illustrates a reaction that actually occurs in a Proton Exchange Membrane Fuel Cell (PEMFC).

When hydrogen enters the anode, protons and electrons are generated. Protons flow through the central hydrogen-conducting membrane, and electrons flow through the outer conductor, reacting when oxygen enters the cathode. Where this happens is called the membrane-electrode assembly (MEA).

In the membrane-electrode assembly, electrodes (anode and cathode) are places where the reaction occurs as described above, and the membrane serves as a passage for delivering protons.

On the other hand, since the cross-sectional structure of the membrane-electrode assembly (hereinafter referred to as MEA) (anode, cathode, electrode thickness and shape, components) has a great effect on performance, accurate analysis of the cross-section of the MEA is very important.

Scanning electron microscopy can be used to analyze the MEA. Until now, the method for preparing the scanning electron microscope specimens of MEA has not been standardized in some way. It has been manufactured by speculation.

Here, the scanning electron microscope (Scanning Electron Microscopy; SEM) is described as follows.

Scanning electron microscopy refers to the surface of a specimen placed in a vacuum of 10 ^-3 Pa or more in a two-dimensional direction of xy with a fine electron beam of about 1 to 100 nm, and generates secondary electrons, reflected electrons, transmission electrons, visible light, Detects signals such as infrared rays, X-rays, internal electromotive force, etc. and displays or records magnified images on the cathode ray tube (Brown tube) screen to analyze the shape of specimen, microstructure, distribution of members, qualitative and quantitative analysis. Device.

Secondary electrons are mainly used to observe the shape of the specimen, and reflected electrons or X-rays are used for the component analysis.

The electron beam is heated by the cathode in the cylinder of the electron gun, and electrons are accelerated to the anode. Usually, the electron beam accelerated to 0.5 to 30 kV is the diameter of 3 to 100 nm due to the action of the focusing lens and the electron lens of the objective lens. After being fined down to the surface of the specimen.

This finer electron beam is called an electron probe, which scans a newly set area in the two-dimensional direction (normal television) of X and Y on the electron surface by the scanning coil.

On the CRT screen synchronized with the scanning of the electron probe, the signal generated from the specimen is detected and amplified by the detector converted into the respective signals and displayed as an image.The result obtained by fixing to a point on the specimen without scanning the electron probe is obtained. Elemental analysis of irradiation points is possible using X-rays.

Scanning electron microscope for secondary electron image and elemental analysis for quality observation or quality control of metals, minerals, minerals, ceramics, cement, glass, plastics, rubber, petroleum, paints, biologics, semiconductor ICs, integrated circuits and electronic components It can be applied to reflected electron image or X-ray image.

On the other hand, in analyzing the MEA using such a scanning electron microscope, since the cross-sectional structure of the MEA (anode, cathode, electrode thickness, shape, composition) has a great effect on performance, accurate analysis of the cross section of the MEA is very important. In addition, since MEA is a non-conductive material (teflon-based), a conductive metal must be coated for conduction.

The reason is to increase the emission rate of secondary electrons.

If the secondary electrons are not emitted, the phase cannot be seen accurately, and the conductive metal coating layer must be properly formed so that a clear and clear phase and accurate structure and wavefront can be analyzed.

If the coating is not performed in the high vacuum it is impossible to analyze due to the charging (charging), it can be observed in the low vacuum, but the resolution is lower than the high vacuum, the accurate analysis is impossible.

In addition, in order to observe and analyze the cross-sectional structure and film of MEA, the MEA should be cut. At this time, it is difficult to cut at room temperature, and since it is in the form of a thin film, the cut of the cross section and the state deformation of each layer are cut when cutting with a knife. This occurs and accurate observation is impossible.

As described above, there are various difficulties in analyzing the MEA using the scanning electron microscope, and since the specimen preparation and analysis process are not standardized in a certain way, it is usually difficult to perform accurate analysis because it is carried out depending on the experience and speculation of the analyst.

Therefore, the present invention was invented to solve the above problems, and in analyzing the membrane-electrode assembly using a scanning electron microscope, all the matters of the preparation and preparation of the specimen were established to prepare and analyze the specimen. By separating and organizing the whole process for each step, the structure of the membrane-electrode assembly using a scanning electron microscope can be more accurately compared to the conventional structure and cross-sectional analysis of the membrane-electrode assembly without depending on the analyst's experience and speculation. The purpose is to provide analytical methods.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In order to achieve the above object, the present invention, (a) a step of first cutting the specimen from the membrane-electrode assembly to be analyzed using a cutting equipment to prepare a membrane-electrode assembly specimen for scanning electron microscope Wow; (b) cutting the collected specimen while cooled with liquid nitrogen; (c) coating the conductive metal on the surface of the cut specimen using coating equipment; It provides a method for analyzing a membrane-electrode assembly using a scanning electron microscope, comprising: (d) storing the specimen coated with a conductive metal in a space separated from the outside air and analyzing it using a scanning electron microscope.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

2 is a flowchart illustrating a specimen preparation and analysis process according to the present invention.

In the method of analyzing a membrane-electrode assembly using a scanning electron microscope according to the present invention, in order to prepare a membrane-electrode assembly specimen for a scanning electron microscope, a step of collecting a specimen from the membrane-electrode assembly to be analyzed and the collected specimen After cooling with liquid nitrogen and cutting, coating the conductive metal on the surface of the cut specimen, and storing the conductive metal coated specimen in a space isolated from outside air and using a scanning electron microscope And analyzing.

First, in the specimen collection process, the specimen is first cut from the membrane-electrode assembly to be analyzed according to the purpose of observation and analysis using a cutting device, that is, a cutting machine, and is collected from the membrane-electrode assembly in the chamber of the scanning electron microscope. It is collected by cutting to a size that can fit, such as 50 mm or less in width, 50 mm or less in height, and 70 mm or less in height.

Next, in the cutting process, the specimen is cut into an appropriate size in accordance with the purpose of observation and analysis while cooled in liquid nitrogen.

In the cutting process, scratches of about 1mm or less are first scratched on the surface for easy cutting of the analysis and observation parts, and 50% of liquid nitrogen is filled in a 2-liter stainless steel container, and the specimen is placed therein, followed by 15 to 20 minutes in liquid nitrogen. After holding, hold the cooled specimen by both sides with forceps and cut it.

At this time, the cutting should be carried out in the state of the liquid nitrogen, cutting the specimen by cooling sufficiently in liquid nitrogen does not cause damage to the cross section of the specimen is easy to observe.

Next, in the conductive metal coating process, the conductive metal is coated on the surface of the dried specimen after cutting as described above using a coating equipment.

In the conductive metal coating process, it is preferable to use gold (Au) having a purity of 99.99% or more with excellent conductivity as the conductive metal coated on the surface of the specimen.

Then, in the coating process, after opening the specimen mounting portion of the coating equipment is mounted on the specimen mounting portion, wherein the distance between the specimen and gold is mounted at a distance of 5 ~ 6 cm.

Here, if the mounting distance is not appropriate, the coating state becomes unstable.

Then, the coating is completed when the vacuum is 1 × 10 ^-1 mbar after the installation as described above, the coating time is 200 ~ 250 sec, the current strength is 20 ~ 25 ㎃.

Here, if the coating time is too long exceeding 250 sec, the thickness of the coating layer becomes thick, affecting the EDX results, so pay attention to the time adjustment.

When the coating is completed, the vacuum is released and the specimen mounting part is opened to check the coated state of gold, and then the specimen is taken out.

When the coating is performed under the above conditions, a coating layer having a thickness of about 70 to 80 Å is formed on the surface of the specimen. When the gold coating layer is 100 Å or more, the image structure phenomenon occurs.

In the phase structure, the measured value tends to be small because the overcoated Au film penetrates into the center of the specimen sheet.

Next, in the storage process, the specimen is coated with a conductive metal so that the surface of the specimen is recorded so that it is stored in a tessellator blocked from outside air.

In this way, by storing the specimen in a desiccator blocked from the outside air, it is possible to eliminate the influence of humidity and temperature, and to prevent contamination by the atmosphere.

Next, during the analysis, the specimen stored in the desiccator is observed and analyzed by using a scanning electron microscope. The specimen is mounted on a stage in the chamber, and a high vacuum of 1.17 × 10 ^-4 Torr or less is applied. .

After the beam is turned on, the cross-sectional shape and each layer component are analyzed, and at this time, the acceleration voltage is 20 kV or more and the spot size is 4.5 or more.

3 and 4 are photographs (2000 times) of the structure of the MEA specimen prepared according to the conventional method, and are photographs of the specimen cut using a knife at room temperature without coating a conductive metal.

Scanning electron microscope (model name: FEI INSPECT) was used as the analysis equipment, and the analysis conditions are as follows.

Vacuum degree: 6.52 × 10 ^-2 Torr

Acceleration voltage: 25 kV

Spot size: 4.5

Beam type: SE (Secondary Electron)

3 and 4, the electrode layer located on the upper side of the specimen section was pushed down into the electrolyte layer to observe the cross-sectional structure, and it was difficult to clearly distinguish the layers by analyzing in low vacuum, and thus accurate interpretation was impossible. It was.

FIG. 5 is a photograph (1200 times) of the structure of the MEA specimen prepared according to the conventional method. The conductive metal is coated at a high vacuum, but the specimen is cut using a knife at room temperature.

Referring to this, since the specimen was cut at room temperature with a knife, it was difficult to clearly distinguish the structure because the layer of the cross section of the specimen was pushed out, which made it impossible to accurately interpret the specimen.

6, 7, 8, and 9 are photographs (2000 times) of observing the structure of the MEA specimen prepared according to the method according to the present invention.

Scanning electron microscope (model name: FEI INSPECT) was used as the analysis equipment, and the analysis conditions are as follows.

Vacuum degree: 1.17 × 10 ^-4 Torr

Acceleration voltage: 25 kV

Spot size: 4.5

Beam type: SE (Secondary Electron)

6 to 9, since the coating state of the conductive metal was very good and the specimen was cut in a state of cooling with liquid nitrogen, the cross section of the material was not damaged and it was easy to clearly distinguish the state of the electrode layer and the electrolyte layer. .

Therefore, the state of the structure could be accurately observed and evaluated, and the reliability of the test could be improved.

In the case of FIGS. 8 and 9, the cross-sectional shape is clearly observed, and thus the thickness of the layer may be measured, and the reduced cathode layer may be confirmed and applied to performance evaluation.

As described above, according to the analysis method of the membrane-electrode assembly according to the present invention, in the process of manufacturing a specimen for analysis using a scanning electron microscope, by cutting the specimen from the membrane-electrode assembly by using a cutting equipment The specimen is placed in liquid nitrogen and cooled in order to see the cross section, and then manufactured by coating a conductive metal on the surface of the cut specimen. By dividing and organizing the whole process for the preparation and analysis of each step by step, it is possible to perform the structure and cross-sectional analysis of the membrane-electrode assembly more accurately than the conventional one without relying on the analyst's experience and speculation, And by excluding the difference of the method according to the proficiency difference can reduce the error of interpretation when observing the cross section and structure Will be.

Claims (5)

(a) firstly cutting the specimen from the membrane-electrode assembly to be analyzed using a cutting device to prepare the membrane-electrode assembly specimen for the scanning electron microscope; (b) cutting the collected specimen while cooled with liquid nitrogen; (c) coating the conductive metal on the surface of the cut specimen using coating equipment; (d) storing the specimen coated with the conductive metal in a space isolated from outside air and analyzing the sample using a scanning electron microscope; Analysis method of a membrane-electrode assembly using a scanning electron microscope comprising a. The method according to claim 1, In step (b), scratches of 1 mm or less are made on the surface of the specimen taken in step (a) to facilitate cutting, and then maintained in liquid nitrogen for 15 to 20 minutes, and then the specimen is clamped on both sides with forceps. Analysis method of a membrane-electrode assembly using a scanning electron microscope, characterized in that the holding and cutting. The method according to claim 1, In the step (c), the method of analyzing the membrane-electrode assembly using a scanning electron microscope, characterized in that the coating of gold as the conductive metal on the surface of the specimen cut in the step (b). The method according to claim 3, In the coating process of step (c), the distance between the specimen and the gold is 5 ~ 6 cm, vacuum degree 1 × 10 ^-1 mbar, coating time 200 ~ 250 sec, working current 20 ~ 25 20, coating thickness 70 ~ Analysis method of the membrane-electrode assembly using a scanning electron microscope, characterized in that the coating with 80 kHz. The method according to claim 1, In the step (d), after mounting the specimen on the stage in the chamber of the scanning electron microscope of the membrane-electrode assembly using a scanning electron microscope, characterized in that the observation under a high vacuum of 1.17 × 10 ^-4 Torr Analytical Method.

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