Method for measuring the concentration distribution of cerium

Abstract

This invention provides a method for measuring the concentration distribution of cerium, which allows for the simple and rapid analysis of the distribution and concentration of cerium present in a membrane electrode assembly. [Solution] The method for measuring the concentration distribution of cerium includes the steps of: preparing a reference sample that serves as a standard for which multiple concentrations of cerium have been specified in advance, and a membrane electrode assembly to be measured for the cerium concentration distribution; measuring the distribution of cerium in the membrane electrode assembly by simultaneously performing X-ray fluorescence analysis on the reference sample and the membrane electrode assembly; and calculating the concentration of cerium corresponding to the intensity of X-ray fluorescence emitted from the cerium in the membrane electrode assembly, based on the intensity of X-ray fluorescence emitted from the cerium in the reference sample and the concentration of cerium in the reference sample that has been specified in advance.

Description

Technical Field

[0001] The present invention relates to a method for measuring the concentration distribution of cerium that measures the distribution and concentration of cerium present in a membrane electrode assembly used in a fuel cell.

Background Art

[0002] Conventionally, when a fuel cell is used, cerium contained in the electrolyte membrane of a membrane electrode assembly (MEA) is likely to move, so the distribution and concentration of cerium present in the membrane electrode assembly are measured. For example, in Patent Document 1, the distribution of cerium in the membrane electrode assembly is measured by performing fluorescent X-ray analysis on the membrane electrode assembly.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as shown in Patent Document 1, when fluorescent X-ray analysis is performed on the membrane electrode assembly, the relative distribution of cerium present in the membrane electrode assembly can be measured, but the concentration of cerium present in the membrane electrode assembly cannot be measured. Therefore, in such a case, it is common to measure the concentration of cerium present in the membrane electrode assembly by performing inductively coupled plasma (ICP) emission analysis on the membrane electrode assembly. However, two types of analysis methods are required, and a considerable amount of analysis time is required.

[0005] The present invention has been made in view of such points, and an object thereof is to provide a method for measuring the concentration distribution of cerium that can analyze the distribution and concentration of cerium present in a membrane electrode assembly used in a fuel cell simply and in a short time. [Means for solving the problem]

[0006] In view of the above issues, the present invention provides a method for measuring the concentration distribution of cerium, which is a method for measuring the distribution and concentration of cerium present in a membrane electrode assembly used in a fuel cell, and is characterized by comprising: a preparation step of preparing a reference sample that serves as a standard for which multiple concentrations of cerium have been specified in advance, and the membrane electrode assembly to be measured for which the cerium concentration distribution is to be measured; a distribution measurement step of measuring the distribution of cerium in the membrane electrode assembly by simultaneously performing fluorescent X-ray analysis on the reference sample and the membrane electrode assembly; and a concentration calculation step of calculating the concentration of cerium corresponding to the intensity of fluorescent X-rays emitted from the cerium in the membrane electrode assembly, based on the intensity of fluorescent X-rays emitted from the cerium in the reference sample and the concentration of cerium in the reference sample that has been specified in advance. [Effects of the Invention]

[0007] According to the present invention, the distribution of cerium in a reference sample and a membrane electrode assembly can be measured by performing X-ray fluorescence analysis. The intensity of X-ray fluorescence emitted from the cerium in the reference sample and the membrane electrode assembly is correlated with the concentration of cerium, and the concentration of cerium in the reference sample is predetermined. As a result, the concentration of cerium in the membrane electrode assembly can be determined simply and quickly based on the intensity of X-ray fluorescence emitted from the cerium in the reference sample and the predetermined concentration of cerium in the reference sample, without performing inductively coupled plasma (IPC) emission analysis. [Brief explanation of the drawing]

[0008] [Figure 1] This is a flowchart illustrating a method for measuring the concentration distribution of cerium according to an embodiment of the present invention. [Figure 2] (a) is a schematic cross-sectional view of the membrane electrode assembly prepared in the preparation step, (b) is a schematic diagram illustrating the method for measuring the cerium concentration distribution of the membrane electrode assembly, and (c) is an image of the membrane electrode assembly and an image of a reference sample. [Figure 3] This is a schematic diagram illustrating the calculation process shown in Figure 1. [Modes for carrying out the invention]

[0009] The method for measuring the cerium concentration distribution according to the present invention will be described below with reference to Figures 1 to 3. The method for measuring the cerium concentration distribution is a method for measuring the distribution and concentration of cerium present in a membrane electrode assembly used in a fuel cell.

[0010] 1. About fuel cells and MEA10 The fuel cell (single cell) referred to here is a polymer electrolyte fuel cell that generates electromotive force through an electrochemical reaction between an oxidizing gas (e.g., air) and a fuel gas (e.g., hydrogen gas). The fuel cell has a rectangular plate-shaped MEA (Membrane Electrode Assembly) 10 as shown in Figure 2(a). The MEA 10 has a pair of catalyst layers 12 (i.e., a cathode-side electrode catalyst layer 12A and an anode-side electrode catalyst layer 12B) formed so as to sandwich an electrolyte membrane 11. The fuel cell is manufactured by sandwiching the MEA 10 with a pair of metal separators (not shown) while a pair of gas diffusion layers (not shown) are placed on both sides of the MEA 10.

[0011] During power generation, an oxidizing gas is flowed through a gas channel formed in one separator, and a fuel gas is flowed through a gas channel formed in the other separator, generating an electromotive force in the MEA10 through an electrochemical reaction. Here, the electrolyte membrane 11 contains cerium, and during the manufacture of the fuel cell, the cerium is uniformly dispersed in the electrolyte membrane 11. When such a fuel cell is subjected to durability tests, the cerium in the electrolyte membrane 11 may migrate and become unevenly distributed within the MEA10.

[0012] Previously, after durability testing, the distribution of cerium within MEA10 was measured by placing it into an X-ray fluorescence (XRF) analyzer. Then, multiple sections of MEA10 were cut out, each section was dissolved in a solution, and the concentration of cerium in each section was measured using an inductively coupled plasma (ICP) emission spectrometer. Thus, measuring the distribution and concentration of cerium within MEA10 required sequentially performing two analytical methods—X-ray fluorescence analysis and inductively coupled plasma emission spectrometer—on the MEA10, which was time-consuming. Furthermore, because the cerium was measured on a portion of the MEA10 cut out using inductively coupled plasma emission spectrometer, only the average concentration of cerium in the cut section could be measured.

[0013] From this perspective, in this embodiment, the distribution of cerium that has moved within the MEA10 is measured by a series of steps shown in Figure 1 below, such as durability tests, and the concentration of cerium is also measured.

[0014] 2. Method for measuring the concentration distribution of cerium 2-1. Regarding preparation process S1 First, preparation step S1 is performed as shown in Figure 1. Specifically, in this step, as shown in Figure 2(b), a reference sample 20 with pre-specified concentrations of cerium, a membrane electrode assembly 10 to be measured for the cerium concentration distribution, and an organic film 13 are prepared.

[0015] In this embodiment, the reference sample 20 is prepared, for example, by preparing multiple (e.g., five) MEA22A to 22E with different concentrations along the longitudinal direction of the organic film 21 on the surface of a strip-shaped organic film 21. The cerium contained in each of the MEA22A to 22E is uniformly dispersed, and its concentration can be determined in advance during the formation of the MEA22A to 22E.

[0016] 2-2. Distribution measurement process S2 Next, as shown in Figure 1, the distribution measurement process S2 is performed. Specifically, in this process, as shown in Figure 2(b), the distribution of cerium in the membrane electrode assembly 10 is measured by simultaneously performing fluorescent X-ray analysis on the reference sample 20 and the membrane electrode assembly 10. Specifically, when X-rays are irradiated from the X-ray irradiation device 31 onto the membrane electrode assembly 10 and the reference sample 20, fluorescent X-rays with energies (wavelengths) specific to the cerium elements that make up the MEA22A~22E of the membrane electrode assembly 10 and the reference sample 20 are emitted. By measuring the energy (intensity) of these fluorescent X-rays with the detector 41, the distribution of the contained cerium can be determined.

[0017] The obtained cerium distribution can be represented by the relative intensity of X-rays, specifically, as shown in Figure 2(c), by the shades of color in image 12a of the membrane electrode assembly 10 and images 22a to 22e of the reference sample 20 (MEA22A to 22E). However, this X-ray intensity represents the qualitative amount of cerium present.

[0018] 2-3. Regarding the concentration calculation process S3 Next, as shown in Figure 1, the concentration calculation step S3 is performed. Specifically, the concentration of cerium is calculated based on the intensity of fluorescent X-rays emitted from the cerium in the reference sample 20 and the previously identified concentration of cerium in the reference sample 20, corresponding to the intensity of fluorescent X-rays emitted from the cerium in the membrane electrode assembly 10. Specifically, as shown in Figure 3, the fluorescent X-ray intensities p1 to p5 for each MEA22A to 22E are identified from the RGB values ​​of the pixels in images 22a to 22e of MEA22A to 22E of the reference sample 20. The relationship between the cerium concentration and the fluorescent X-ray intensity is identified from the cerium concentrations (average concentrations) d1 to d5 for each MEA22A to 22E and the obtained fluorescent X-ray intensities p1 to p5. For example, as shown in Figure 3, the cerium concentration and the fluorescent X-ray intensity may be plotted on a graph, an approximation line passing through the plotted points may be calculated, and the relationship between the cerium concentration and the fluorescent X-ray intensity may be formulated.

[0019] Next, from the RGB values of each pixel of the image 12a of the membrane electrode assembly 10, the intensity of the fluorescent X-ray of the MEA at the position corresponding to each pixel is specified. From the specified intensity of the fluorescent X-ray of the MEA, the concentration of cerium in the membrane electrode assembly 10 at the position corresponding to each pixel is calculated. For example, by substituting the value of the intensity of the fluorescent X-ray of the membrane electrode assembly 10 at the position corresponding to each pixel into the formulated relationship between the concentration of cerium and the intensity of the fluorescent X-ray, the concentration of cerium in the membrane electrode assembly 10 at the position corresponding to each pixel is calculated.

[0020] Note that the intensity of the fluorescent X-ray used in the concentration calculation step S3 may be directly obtained from the intensity of the fluorescent X-ray emitted from cerium in the image 12a of the membrane electrode assembly 10 and the images 22a to 22e of the MEAs 22A to 22E of the reference sample 20 in the distribution measurement step S2.

[0021] In this way, while measuring the distribution of cerium in the membrane electrode assembly 10 by fluorescent X-ray (XRF) analysis, based on the intensity of the fluorescent X-ray of cerium in the reference sample 20 and the concentration of cerium in the reference sample 20, the concentration distribution of cerium in the membrane electrode assembly 10 can be obtained simply and in a short time.

[0022] As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various design changes can be made without departing from the spirit of the present invention described in the claims.

Explanation of Reference Numerals

[0023] 10: Membrane electrode assembly, 11: Electrolyte membrane, 12: Catalyst layer, 13·21: Organic film, 20: Reference sample, 22: MEA for reference sample, S1: Preparation step, S2: Distribution measurement step, S3: Concentration calculation step

Claims

[Claim 1] A method for measuring the distribution and concentration of cerium present in a membrane electrode assembly used in a fuel cell, A preparation step involves preparing a reference sample with pre-specified concentrations of cerium, and the membrane electrode assembly to be measured for the cerium concentration distribution. A distribution measurement step involves simultaneously performing X-ray fluorescence analysis on the reference sample and the membrane electrode assembly to measure the distribution of cerium in the membrane electrode assembly. A concentration calculation step, which calculates the concentration of cerium corresponding to the intensity of fluorescent X-rays emitted from the cerium of the membrane electrode assembly, based on the intensity of fluorescent X-rays emitted from the cerium of the reference sample and the predetermined concentration of cerium of the reference sample; A method for measuring the concentration distribution of cerium, characterized by including [a specific substance].

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