JP2016081596A - Inspection method of electrolyte membrane for fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection method of an electrolyte membrane for a fuel battery that can determine defect or non-defect for an electrolyte membrane which is not detected as a defect in breakdown voltage inspection, and prevent effluence of defectives.SOLUTION: An inspection method of an electrolyte membrane for a fuel battery comprises: a step of applying a voltage to a membrane electrode assembly MEA until the voltage reaches a first voltage value, and determining success in breakdown voltage inspection when current flowing in the membrane electrode assembly is not more than a first predetermined value; a step of keeping an accepted product to a fixed voltage lower than the first voltage value for a predetermined time; and a step of measuring a leak current value of an electrolyte membrane 42 contained in the membrane electrode assembly MEA and determining defect when the leak current value exceeds a second predetermined value. For the predetermined time, the fixed voltage is kept so that the amount of heat occurring due to application of the fixed voltage is less than the amount of heat of dissolution of the electrolyte membrane 42.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for inspecting an electrolyte membrane for a fuel cell.

  A fuel cell, for example, a polymer electrolyte fuel cell, has a reaction gas in a membrane electrode assembly (hereinafter also referred to as “MEA (Membrane Electrode Assembly)”) formed by sandwiching an electrolyte membrane between a pair of electrodes (anode and cathode). By supplying (fuel gas and oxidizing gas) and causing an electrochemical reaction, the chemical energy of the substance is directly converted into electrical energy.

  In order to improve proton conductivity, MEA has been studied to make it thinner. Along with this, there is a concern that the probability of MEA generation with a reduced gas / electron shielding function required for the MEA may increase due to scratches caused by contamination of foreign matter at the interface of the MEA with the gas diffusion electrode. They reduce the performance of the fuel cell and can be determined by inspection of the MEA for electric leaks and gas leaks (hereinafter also referred to as “leaks”). Conventionally, a method is known in which a DC voltage is applied to an MEA and a leak generated in the MEA is inspected from a steady current value detected from the MEA (see, for example, Patent Document 1).

  In the inspection method described in Patent Document 1 below, if there is damage that penetrates the electrolyte membrane due to foreign matter mixed in the electrolyte membrane, it can be detected as a leak, but the foreign matter does not penetrate the electrolyte membrane. For example, if the electrolyte membrane is only damaged (damage) (an electrolyte membrane with a reduced remaining film thickness), it cannot be detected as a leak, and a defective product may flow out.

JP 2013-054925 A

  In order to solve the problem that it is difficult to detect such an electrolyte membrane with a reduced remaining film thickness, a method for inspecting an electrolyte membrane with a reduced remaining film thickness with a withstand voltage (hereinafter referred to as “withstand voltage test”) is also available. Conceivable. This withstand voltage test method is a method of detecting an electrolyte membrane whose remaining film thickness has decreased by sweeping a voltage across the electrolyte membrane and detecting a current that temporarily flows after the electrolyte membrane has broken down.

  However, in the method of inspecting with the withstand voltage, a time difference (time lag) occurs between the time when the electrolyte membrane breaks down and the current rises. Therefore, when the electrolyte membrane breaks down just before the withstand voltage test end voltage (upper limit voltage) The current that flows when the dielectric breakdown occurs cannot be detected, and there is a risk that a defective product will flow out. Considering the time difference from when the electrolyte membrane breaks down until the current rises, it can be held for a certain time at the test end voltage until the current at the time of breakdown can be detected. Since the electrolyte membrane was dissolved by the generated Joule heat, it was not possible to take a method of holding and detecting for a certain period of time. Thus, in the withstand voltage test, a defective product may flow out without being detected as defective, and there still remains a problem to be improved with respect to detecting an electrolyte membrane having a reduced remaining film thickness.

  The present invention has been made in view of such problems, and its purpose is to determine whether an electrolyte membrane that is not detected as defective in a withstand voltage test is defective or not, and to prevent outflow of defective products. An object of the present invention is to provide a method for inspecting an electrolyte membrane for a fuel cell.

  In order to solve the above problems, an inspection method for an electrolyte membrane for a fuel cell according to the present invention is an inspection method for an electrolyte membrane for a fuel cell, wherein a voltage is applied to a membrane electrode assembly up to a first voltage value, When the current flowing through the membrane electrode assembly is less than or equal to the first predetermined value, the step of determining that the withstand voltage test is acceptable, and the acceptable product determined to be acceptable in the withstand voltage inspection, the first voltage A step of holding for a predetermined time at a constant voltage lower than the value, a leakage current value of the electrolyte membrane included in the membrane electrode assembly is measured, and a second predetermined value in which the leakage current value is lower than the first predetermined value A step of determining a failure when exceeding the constant voltage, and maintaining the constant voltage so that the amount of heat generated by the application of the constant voltage is less than the amount of heat of dissolution of the electrolyte membrane in the predetermined time. To do.

  In the method for inspecting a fuel cell electrolyte membrane according to the present invention, first, when the current flowing through the membrane electrode assembly is not more than a first predetermined value by the withstand voltage test, it is determined that the withstand voltage test has passed. Then, for a passed product determined to pass the withstand voltage test, a second voltage is maintained at a constant voltage lower than the first voltage value for a predetermined time, and a leakage current value leaking from the electrolyte membrane is lower than the first predetermined value. When it exceeds a predetermined value, it is determined to be defective. As a result, even in the case of an acceptable product that is not detected as defective by the withstand voltage test (for example, an electrolyte membrane broken at the end voltage of the withstand voltage test), it can be determined whether or not it is defective. Can be prevented. In addition, since the constant voltage is maintained for a predetermined time so as to be less than the amount of heat of dissolution of the electrolyte membrane, it is possible to prevent the electrolyte membrane from being dissolved. Furthermore, in order to determine whether or not the current threshold value is a second predetermined value lower than the first predetermined value in the withstand voltage test, it also detects an electrolyte membrane having a small breakdown that is not detected in the withstand voltage test. be able to. Note that the first voltage value is preferably a voltage (withstand voltage value that can be shipped as a product) that can cause dielectric breakdown of the electrolyte membrane in which the thickness of the electrolyte membrane is thin.

  According to the present invention, there is provided a method for inspecting an electrolyte membrane for a fuel cell that can determine whether or not an electrolyte membrane that is not detected as defective in a withstand voltage test is defective, and can prevent outflow of defective products. Can do.

It is a flowchart which shows the flow of the test | inspection method of the electrolyte membrane for fuel cells in embodiment of this invention. It is a schematic diagram which shows the structure of a withstand voltage test | inspection apparatus. It is a graph for demonstrating the electric current value which flows into the membrane electrode assembly in a withstand voltage test | inspection. It is a figure for demonstrating the presence or absence of melt | dissolution of the electrolyte membrane in a withstand voltage test | inspection. It is a flowchart which shows the flow of the test | inspection method in a comparative example.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The present invention is illustrated by the following preferred embodiments, but can be modified in many ways without departing from the scope of the present invention, and other embodiments other than this embodiment can be utilized. . Accordingly, all modifications within the scope of the present invention are included in the claims.

  A method for inspecting an electrolyte membrane for a fuel cell as an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a flowchart showing a flow of an inspection method for an electrolyte membrane for a fuel cell.

  As shown in FIG. 1, the fuel cell electrolyte membrane inspection method includes the steps of “withstand voltage inspection” (step S100) and “constant voltage measurement for determination” (step S110). As is clear from the figure, the “constant voltage measurement for determination” is performed on the electrolyte membrane for a fuel cell that is determined to be acceptable (OK) in the “withstand voltage test”.

  In the following, first, the configuration of the withstand voltage inspection apparatus 10 used for the “withstand voltage inspection” (step S100) will be described, followed by the description of the withstand voltage inspection method, and then “constant voltage measurement for determination”. (Step S110) will be described.

(Withstand voltage inspection device)
First, the configuration of the withstand voltage inspection apparatus 10 used when performing the withstand voltage inspection in step S100 will be described. FIG. 2 is a schematic diagram showing the configuration of the withstand voltage inspection device 10.

  The withstand voltage test apparatus 10 shown in FIG. 2 is an apparatus that inspects the withstand voltage of the membrane electrode assembly MEA by applying a voltage to the membrane electrode assembly MEA used in the fuel cell while sweeping a voltage in a predetermined voltage region. The membrane electrode assembly MEA is a part of the constituent elements of a single cell including a pair of separators (not shown) that sandwich the membrane electrode assembly MEA. The fuel cell has a fuel cell stack structure in which a plurality of the single cells are stacked. As the fuel cell, for example, a polymer electrolyte fuel cell that is relatively small and excellent in power generation efficiency is used.

  The withstand voltage inspection device 10 includes a measurement control unit 20, an anode 23, and a cathode 24. The anode 23 and the cathode 24 are electrically connected to the measurement control unit 20. The measurement control unit 20 applies a voltage between the anode 23 and the cathode 24 and measures the current flowing between the electrodes. The measurement control unit 20 can sweep the voltage applied between the electrodes in a preset voltage region. Further, the measurement control unit 20 measures the current flowing through the membrane electrode assembly MEA by sweeping the voltage.

  Between the anode 23 and the cathode 24, a membrane electrode assembly MEA, which is an inspection target of a withstand voltage inspection, is installed. As shown in the figure, the membrane electrode assembly MEA includes an electrolyte membrane 42 (an electrolyte membrane for fuel cells). A catalyst electrode 43 as an anode is formed on one surface of the electrolyte membrane 42. On the other surface of the electrolyte membrane 42, a catalyst electrode 44 as a cathode is formed. A gas diffusion layer 45 and a gas diffusion layer 46 are formed on the outer surfaces of the catalyst electrode 43 and the catalyst electrode 44, respectively.

  The electrolyte membrane 42 is a proton conductive ion exchange membrane formed of a solid polymer material such as a fluorine resin, and exhibits good electrical conductivity in a wet state.

  The catalyst electrode 43 and the catalyst electrode 44 are formed as a catalyst layer by applying a catalyst ink containing a catalyst for promoting an electrochemical reaction on the electrolyte membrane 42 and drying it for a predetermined time. As the catalyst ink, for example, a mixture of platinum-supported carbon as a catalyst-supported carbon, an ionomer, and a predetermined solvent is used.

  The gas diffusion layer 45 and the gas diffusion layer 46 are configured by members having gas permeability and conductivity. Providing the gas diffusion layers 45 and 46 can improve the gas supply efficiency to the catalyst electrodes 43 and 44 when functioning as a fuel cell.

(Withstand voltage inspection)
Next, “withstand voltage inspection” (step S100) using the withstand voltage inspection apparatus 10 shown in FIG. 2 will be described. FIG. 3 is a graph showing a current value flowing through the membrane electrode assembly MEA in the “withstand voltage test”.

  A graph F1 shown in FIG. 3 is a current measured by the withstand voltage test apparatus 10 when a predetermined voltage is applied to the membrane electrode assembly MEA. In the withstand voltage inspection, a voltage is applied to the membrane electrode assembly MEA while sweeping a voltage in a predetermined voltage region, and a current value flowing through the membrane electrode assembly MEA is measured. In the withstand voltage test in the present embodiment, the test is performed over an applied voltage of 0 V to a test end voltage. As is clear from the figure, since the current value shown in the graph F1 is smaller than the current threshold from the applied voltage 0 V to the test end voltage, the membrane electrode assembly MEA is determined to pass the withstand voltage test. Thus, when a voltage is applied to the membrane electrode assembly MEA up to the test end voltage (first voltage value) and the current flowing through the membrane electrode assembly MEA is equal to or less than the current threshold value (first predetermined value). It is determined that the withstand voltage test has passed. The test end voltage (first voltage value) in the withstand voltage test is set to 3.3 V, for example, and the current threshold value (first predetermined value) is set to 350 A, for example. A value can be selected.

  As described above, in the “withstand voltage test” (step S100), a voltage is applied to the membrane electrode assembly in a predetermined voltage region, and the value of the current flowing through the membrane electrode assembly is measured to determine a defective product. The defective product is determined to be defective (NG) if the value of the current flowing through the membrane electrode assembly is equal to or greater than the first predetermined value, and is determined to be acceptable (OK) if it is equal to or smaller than the first predetermined value. To do.

  By the way, even if it is a membrane electrode assembly MEA determined to be an acceptable product (OK) by the withstand voltage test, a defective product may be included. This is because the withstand voltage test is completed before the current threshold value (first predetermined value) is exceeded in the membrane electrode assembly MEA that has undergone dielectric breakdown immediately before the test end voltage (first voltage value). It is because it is not determined. In other words, since there is a time lag from when the electrolyte membrane 42 (see FIG. 2) breaks down until the current rises, if the electrolyte membrane 42 breaks down at the test end voltage (first voltage value), the current that flows during the breakdown There is a possibility that defective products may flow out without detecting a current equal to or greater than a threshold value (first predetermined value).

  Considering such a time lag, it is conceivable to hold the voltage at the test end voltage (first voltage value) until the current flowing at the time of dielectric breakdown can be detected. However, it has been found that when the voltage is held at the test end voltage (first voltage value) until the current flowing at the time of dielectric breakdown can be detected, the electrolyte membrane 42 is dissolved by the generated Joule heat.

  Therefore, in the present embodiment, in order to determine a defective product (NG) included in a product that has been determined to be a pass product (OK) by a withstand voltage test without dissolving the electrolyte membrane 42, the amount of heat of dissolution of the electrolyte membrane 42 is less. Whether or not it is defective is determined. Hereinafter, the relationship between the amount of heat of dissolution of the electrolyte membrane 42 and the test time of the withstand voltage test will be described with reference to FIG.

  FIG. 4 is a diagram for explaining the result of verification of the amount of heat of dissolution of the electrolyte membrane 42. More specifically, FIG. 4A shows the relationship between the test time (seconds) and the voltage (V) when the tests were conducted in each of the tests P1, P2, P3, P4, P5, and P6 in the withstand voltage test. It is a graph to represent. FIG. 4B shows the test time (seconds), current amount (C), calorific value (kJ), and electrolyte membrane 42 in each test P1, P2, P3, P4, P5, and P6 of the withstand voltage test. It is a table | surface showing the relationship with the presence or absence of melt | dissolution (film presence or absence).

  As shown in FIG. 4A and FIG. 4B, the test time in the withstand voltage test is not less than a predetermined time, in other words, the amount of heat generated by the predetermined amount of current is not less than the amount of heat of dissolution of the electrolyte membrane 42. If so, it was verified that the electrolyte membrane 42 was dissolved (tests P1 and P2 in FIG. 4B).

  On the other hand, it was verified that the test time in the withstand voltage test is less than the predetermined time, in other words, that the amount of heat generated by the predetermined amount of current is less than the amount of heat of dissolution of the electrolyte membrane 42, the electrolyte membrane 42 does not melt. (Tests P3, P4, P5, and P6 in FIG. 4B). For example, in the test P4 shown in FIG. 4A and FIG. 4B, the applied voltage 3V to 3.V is 1 second in the voltage region of the applied voltage 0V to 2V, 1.9 seconds in the voltage region of the applied voltage 2V to 3V. Although it was performed for 0.1 second in a voltage region of 3 V, it was verified that dissolution of the electrolyte membrane 42 did not occur.

(Constant voltage measurement for judgment)
Next, “constant voltage measurement for determination” (step S110 in FIG. 1) will be described. In consideration of the amount of heat of dissolution of the electrolyte membrane 42 shown in FIG. 4, “constant voltage measurement for determination” is performed on the acceptable product determined to be acceptable in the “voltage resistance test”. In other words, in “constant voltage measurement for determination”, the amount of heat generated by a predetermined amount of current (the amount of heat generated by applying a constant voltage) is within the range of less than the amount of heat of dissolution of the electrolyte membrane 42 and passed after the withstand voltage test Judge whether the product is defective or not.

  Specifically, as “constant voltage measurement for determination”, a constant voltage (eg, 1.4 V or more) lower than the test end voltage in the withstand voltage test is applied to the electrolyte membrane 42 for a predetermined time (eg, 0.3 seconds). And when the leakage current value leaking from the electrolyte membrane 42 within the predetermined time exceeds the second predetermined value, it is determined as defective. If the leakage current value is less than or equal to the second predetermined value, it is determined that the product is acceptable (OK) before shipment, and if the leakage current value is greater than or equal to the second predetermined value, the product is determined to be defective (NG) (see FIG. 1). Step S110). In this embodiment, the second predetermined value is set to 1A. However, the second predetermined value may be various values as long as it is lower than the first predetermined value (for example, 350A). It is possible to set.

  In the above-described “constant voltage measurement for determination”, the leakage current after applying a voltage of 1.4 V to the membrane electrode assembly MEA (withstand voltage OK work) determined to be a pass product in the withstand voltage test is 0. .Measured for 3 seconds to determine whether or not it was defective. As a result, the membrane electrode assembly MEA having a leakage current value of 1 A or more can be detected even if it is a pass product after the withstand voltage test (step S100 (OK) in FIG. 1). It was verified that the determination of

  As described above, in the present embodiment, “constant voltage measurement for determination” (step S110 in FIG. 1) is performed on an acceptable product after a withstand voltage test. In “constant voltage measurement for determination”, the leakage current value of the electrolyte membrane 42 is measured by holding for a predetermined time at a constant voltage lower than the test end voltage (first voltage value) in the withstand voltage test. Is determined to be defective when the value exceeds the second predetermined value. When the leak current value is equal to or greater than the second predetermined value, it is determined as a defective product (NG), and when the leak current value is equal to or less than the second predetermined value, the product is determined as acceptable (OK). In the predetermined time for holding the constant voltage, the constant voltage is applied so that the amount of heat generated by the predetermined amount of current (application of the constant voltage) is less than the amount of heat of dissolution of the electrolyte membrane.

  In this way, by performing “constant voltage measurement for determination” after the withstand voltage test, the electrolyte membrane that has undergone dielectric breakdown immediately before the test end voltage or at the end value of the withstand voltage test (first voltage value) in the withstand voltage test. 42 can be reliably detected. As a result, since it is possible to determine a defect even if it is not detected as a defect in the withstand voltage test, it is possible to prevent a defective product from flowing into the market. In addition, in the “constant voltage measurement for determination”, it is determined whether or not a defective product is based on a second threshold value (for example, 1 A) lower than a current threshold value (for example, 350 A) in the withstand voltage test. It is also possible to detect an electrolyte membrane having a small breakdown that is not detected in the withstand voltage test.

  By the way, instead of performing “constant voltage measurement for determination” with respect to an acceptable product after withstand voltage inspection, it is also conceivable to perform precise current inspection measurement (see FIG. 5). This precise current inspection measurement is a method in which a direct current voltage is applied to the membrane electrode assembly MEA and a leak generated in the membrane electrode assembly MEA is inspected from a steady current value detected from the membrane electrode assembly MEA. However, after the withstand voltage test, since charges are accumulated in the membrane electrode assembly MEA, it is possible to determine whether or not it is defective based on the steady current value measured by such a precise current test measurement. Can not. Although it is conceivable to measure the steady current value after discharging the charge accumulated in the membrane electrode assembly MEA after the withstand voltage test, it takes several minutes to discharge the charge, so the inspection time becomes longer, It becomes impossible to work in the tact.

  As described above, in the method of performing the precision current inspection measurement after the withstand voltage inspection shown in FIG. 5 as a comparative example, it is difficult to achieve both the defect detection for the acceptable product after the withstand voltage inspection and the inspection within the tact.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. In other words, those specific examples that have been appropriately modified by those skilled in the art are also included in the scope of the present invention as long as they have the characteristics of the present invention. The elements included in each of the specific examples described above and their arrangement, materials, conditions, and the like are not limited to those illustrated, but can be changed as appropriate.

10: Withstand voltage test device 42: Electrolyte membrane 43, 44: Catalyst electrode 45, 46: Gas diffusion layer S100: Withstand voltage test S110: Constant voltage measurement for determination MEA: Membrane electrode assembly

Claims (1)

An inspection method for an electrolyte membrane for a fuel cell,
Applying a voltage to the membrane electrode assembly up to a first voltage value, and determining that the withstand voltage test has passed when the current flowing through the membrane electrode assembly is equal to or less than a first predetermined value;
A step of holding for a predetermined time at a constant voltage lower than the first voltage value for the acceptable product determined to be acceptable in the withstand voltage test,
Measuring a leakage current value of an electrolyte membrane included in the membrane electrode assembly, and determining a failure when the leakage current value exceeds a second predetermined value lower than the first predetermined value. ,
The method for inspecting an electrolyte membrane for a fuel cell, wherein the constant voltage is maintained so that the amount of heat generated by applying the constant voltage is less than the amount of heat of dissolution of the electrolyte membrane during the predetermined time.

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