JP2010262896A - Evaluation method of fuel cell, manufacturing method of fuel cell, and evaluation device of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quantitatively evaluate summed resistance including an interface resistance between an electrolyte membrane and an electrode. <P>SOLUTION: A fuel cell equipped with a membrane-electrode assembly in which a first electrode is arranged at one face of the electrolyte membrane and a second electrode is arranged at the other face, is prepared. An evaluation method of the fuel cell includes a pre-evaluation process to introduce inert gas into the first electrode, a measuring process to measure an alternate-current impedance in a state in which the inert gas is introduced while varying frequency, of the membrane-electrode assembly, a first calculation process to obtain alternate-current impedance characteristics about a prescribed frequency range based on the alternate-current impedance for each frequency measured by the measurement process, and a second calculation process to obtain the prescribed summed resistance at least including a resistance of the electrolyte membrane and the interface resistance between the electrolyte membrane and the first electrode by fitting a prescribed alternate-current impedance to an equivalent circuit equipped with Warburg impedance. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for evaluating a fuel cell or a technique for manufacturing a fuel cell.

  Conventionally, a fuel cell is known. The fuel cell includes a membrane electrode assembly in which electrodes are disposed on both surfaces of an electrolyte membrane. By supplying an oxidizing gas (for example, air) containing oxygen to one electrode and supplying a fuel gas (for example, hydrogen) to the other electrode, the hydrogen and oxygen are reacted electrochemically and directly. Electrical energy can be extracted.

  An AC impedance method has been proposed as a method for inspecting and evaluating fuel cells (see Patent Document 1 below).

Japanese Patent Laying-Open No. 2005-071882

  However, in the conventional technique, it is impossible to quantitatively evaluate the state of the fuel cell only by determining whether the fuel cell is good or bad. In particular, there has been a problem that the combined resistance including the interface resistance between the electrolyte membrane and the electrode cannot be quantitatively evaluated.

  The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to quantitatively evaluate a combined resistance including an interface resistance between an electrolyte membrane and an electrode.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A fuel cell evaluation method, comprising a membrane electrode assembly in which a first electrode is disposed on one surface of an electrolyte membrane and a second electrode is disposed on the other surface of the electrolyte membrane. Preparation of a battery, and a pre-evaluation process for introducing an inert gas into the first electrode, and a measurement for measuring the AC impedance of the membrane electrode assembly while changing the frequency in a state where the inert gas is introduced And a first calculation step for obtaining an AC impedance characteristic for a predetermined frequency range based on the AC impedance for each frequency measured in the measurement step, and fitting the AC impedance characteristic to an equivalent circuit having a Warburg impedance A predetermined total resistance including at least the resistance of the electrolyte membrane and the interface resistance between the electrolyte membrane and the first electrode. Evaluation method for a fuel cell and a second calculation step of calculating.

  According to the evaluation method of the fuel cell having the above-described configuration, the AC impedance characteristic for a predetermined frequency range is obtained based on the measured AC impedance for each frequency, and the AC impedance characteristic is fitted to an equivalent circuit having a Warburg impedance. Thus, a predetermined total resistance including at least the resistance of the electrolyte membrane and the interface resistance between the electrolyte membrane and the first electrode can be obtained. Therefore, the total resistance including the interface resistance can be quantitatively evaluated.

Application Example 2 The fuel cell evaluation method according to Application Example 1, wherein the equivalent circuit includes a combined resistance component representing the combined resistance and a correction resistance component.

  According to the fuel cell evaluation method described in Application Example 2, the evaluation can be easily performed by obtaining the combined resistance component from the equivalent circuit.

[Application Example 3] In the fuel cell evaluation method according to Application Example 1 or 2, the first calculation step includes a plotting step of inserting AC impedance at each frequency measured in the measurement step into a complex plane; A fuel cell evaluation method comprising: obtaining a complex impedance plot curve from each plot point obtained by the plotting step; and selecting the predetermined frequency range in the complex impedance plot curve as the AC impedance characteristic.

  According to the fuel cell evaluation method described in Application Example 3, it is possible to easily obtain the AC impedance characteristic for a predetermined frequency range.

Application Example 4 In the fuel cell evaluation method according to Application Example 3, the complex impedance plot curve includes a first line segment having an angle with respect to a real part axis of the complex plane being equal to or less than a predetermined threshold, At least a second line segment that is at a lower frequency than the line segment 1 and has an angle with respect to the real part axis of the complex plane that is equal to or greater than a predetermined threshold value, and the selecting step includes a lower limit of the predetermined frequency range A method for evaluating a fuel cell, comprising the step of performing the selection as a frequency for a turning point between the first line segment and the second line segment.

  According to the fuel cell evaluation method described in Application Example 4, the frequency range in which it is difficult to analyze using the Warburg impedance provided in the equivalent circuit can be excluded from the frequency range in which the fitting is performed. Therefore, the total resistance can be measured with high accuracy.

Application Example 5 In the fuel cell evaluation method according to Application Example 3 or 4, in the selection step, the upper limit of the predetermined frequency range is set, and the imaginary part value of the complex plane is a predetermined positive value. A method for evaluating a fuel cell, comprising the step of performing the selection as the frequency of the fuel cell.

  According to the fuel cell evaluation method described in Application Example 5, it is possible to increase the measurement accuracy in a high frequency region where the frequency is higher.

[Application Example 6] A method of manufacturing a fuel cell, wherein a preparation step of preparing an electrolyte membrane, a first electrode, and a second electrode, and a predetermined step using the electrolyte membrane, the first electrode, and the second electrode A membrane electrode assembly manufacturing process for manufacturing a membrane electrode assembly under manufacturing conditions, a fuel cell manufacturing process for manufacturing a fuel cell by stacking a gas diffusion layer and a separator on the manufactured membrane electrode assembly, and the manufacturing A measurement step of measuring the alternating current impedance of the membrane electrode assembly while changing the frequency in a state where an inert gas is introduced into the first electrode of the membrane electrode assembly provided in the fuel cell, and the measurement step By obtaining AC impedance characteristics based on the measured AC impedance for each frequency, and fitting the AC impedance characteristics to an equivalent circuit, the resistance of the electrolyte membrane And a calculation step for obtaining a predetermined total resistance including at least an interface resistance between the electrolyte membrane and the first electrode, and determining the manufacturing condition based on the total resistance determined by the calculation step, A fuel cell manufacturing method comprising a feedback step of feeding back manufacturing conditions to a membrane electrode assembly manufacturing step.

  According to the fuel cell manufacturing method described in the above configuration, the total resistance including the interface resistance between the electrolyte membrane and the first electrode is obtained by the measurement step and the calculation step, and the obtained sum is obtained. The manufacturing condition of the membrane electrode assembly is corrected by the resistance. Therefore, since the manufacturing conditions of the membrane electrode assembly can be determined so that the interface resistance is appropriate, the fuel cell can be manufactured while ensuring the quality stability of the fuel cell.

[Application Example 7] In the method of manufacturing a fuel cell according to Application Example 6, in the membrane electrode assembly manufacturing process, a laminate in which the first electrode and the second electrode are arranged on both surfaces of the electrolyte membrane is hot pressed. A method of manufacturing a fuel cell, wherein the manufacturing condition is a condition for the temperature and pressure of the hot press.

  According to the method for manufacturing a fuel cell described in Application Example 7, the conditions regarding temperature and pressure when hot pressing the first electrode and the second electrode on the electrolyte membrane can be appropriately determined.

Application Example 8 In the method of manufacturing a fuel cell according to Application Example 7, the calculation step includes a step of performing the fitting using an AC impedance characteristic for a predetermined frequency range, and the equivalent circuit includes a Warburg A method for manufacturing a fuel cell, comprising an impedance.

  According to the fuel cell manufacturing method described in Application Example 8, as in the fuel cell evaluation method described in Application Example 1, the total resistance including the interface resistance can be quantitatively evaluated. Quality stability can be further secured.

Application Example 9 A fuel cell evaluation apparatus for evaluating a fuel cell including a membrane electrode assembly in which a first electrode is disposed on one surface of an electrolyte membrane and a second electrode is disposed on the other surface of the electrolyte membrane. In the state where an inert gas is introduced into the first electrode, a measurement unit that measures the AC impedance of the membrane electrode assembly while changing the frequency, and an AC for each frequency measured by the measurement unit. A first arithmetic unit that obtains an AC impedance characteristic for a predetermined frequency range based on the impedance; and fitting the AC impedance characteristic to an equivalent circuit having a Warburg impedance, thereby providing resistance of the electrolyte membrane and the electrolyte membrane And a second arithmetic unit for obtaining a predetermined total resistance including at least an interface resistance between the first electrode and the first electrode. .

  According to the fuel cell evaluation apparatus configured as described above, the combined resistance including the interface resistance can be quantitatively evaluated in the same manner as the fuel cell evaluation method described in Application Example 1.

  In addition, the manufacturing method of the said fuel cell can also be implement | achieved with the aspect as an apparatus invention. Further, an aspect as a computer program for executing the fuel cell evaluation method and the fuel cell manufacturing method, an aspect as a recording medium in which such a computer program is recorded, and a carrier including the computer program in a carrier wave It can also be realized in various forms such as an embodied data signal.

  Further, when the present invention is configured as a computer program or a recording medium on which the program is recorded, the program may be configured as an entire program for controlling the operation of an apparatus that executes each step of the present invention. Only the part that executes each step may be configured.

It is explanatory drawing which shows schematic structure of the fuel cell evaluation apparatus 10 as 1st Example of this invention with the fuel cell ND. It is explanatory drawing showing schematic structure of the fuel cell CL. 3 is a flowchart showing a fuel cell evaluation process executed by the fuel cell evaluation device 10. It is explanatory drawing which shows the cyclic voltammogram of the fuel cell ND. 5 is a graph showing a complex impedance plot curve V. It is explanatory drawing which shows the circuit structure of the equivalent circuit E1. It is a flowchart which shows the manufacturing method of the fuel cell CL in 1st Example. It is explanatory drawing which shows the mode of the connection of the fuel cell evaluation apparatus 10 and fuel cell CL which are used in 2nd Example. It is a figure about the table | surface TL which shows the relationship between MEA-ized conditions (temperature pressure) and total resistance. It is a flowchart which shows the fuel cell evaluation process performed in the fuel cell evaluation apparatus used with the manufacturing method of 3rd Example. It is explanatory drawing which shows the circuit structure of the equivalent circuit E2 used in 3rd Example.

  Hereinafter, embodiments of the present invention will be described based on examples.

A. First embodiment:
A1. Hardware configuration of fuel cell evaluation system:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell evaluation apparatus 10 as a first embodiment of the present invention together with a fuel cell ND. As shown in the figure, a fuel cell evaluation device (hereinafter also simply referred to as “evaluation device”) 10 is connected to a fuel cell ND by two sets of wires 20 and 30.

  The evaluation device 10 sends an alternating current to the fuel cell ND via the first wiring 20 and measures the alternating current impedance of the fuel cell ND via the second wiring 30. From the result of the measurement, the evaluation device 10 An internal state of a fuel cell CL described later is evaluated.

  The evaluation device 10 includes a CPU 12, a ROM 14, a RAM 16, an input / output control unit 18, a display unit 19, and the like. CPU12 implement | achieves each function as the measurement part 12a, the 1st calculating part 12b, and the 2nd calculating part 12c by performing the process according to the program previously memorize | stored in ROM14. By realizing these functions, the internal state of the fuel cell CL described above is evaluated. The evaluation result is displayed on the display unit 19 via the input / output control unit 18. In addition, it is good also as a structure which replaces with the display by the display part 19 and alert | reports an evaluation result by another methods, such as an audio | voice.

  The fuel cell ND is a polymer electrolyte fuel cell, and generates power using an oxidizing gas (for example, air) and a fuel gas (for example, hydrogen). The fuel cell ND includes a plurality of fuel cells CL, two end plates EP, and two terminals TM. The fuel cell CL is sandwiched between two end plates EP with the terminal TM interposed therebetween. That is, the fuel cell ND has a layered structure in which a plurality of fuel cells CL are stacked. The fuel cell ND has a structure in which each tension plate (not shown) is coupled to each end plate EP by bolts (not shown) to fasten the fuel cells CL with a predetermined force in the stacking direction. It has become. In the fuel cell ND, an insulator may be provided between the terminal TM and the end plate EP to ensure insulation.

  FIG. 2 is an explanatory diagram showing a schematic configuration of the fuel battery cell CL. The fuel cell CL includes a membrane electrode assembly (hereinafter referred to as MEA (Membrane Electrode Assembly)) 50, gas diffusion layers 60 and 70, separators 80 and 90, and a seal member 110.

  The MEA 50 includes an electrolyte membrane 51, a cathode 52 disposed on one surface of the electrolyte membrane 51, and an anode 53 disposed on the other surface of the electrolyte membrane 51. The cathode 52 corresponds to the “first electrode” in Application Example 1, and the anode 53 corresponds to the “second electrode” in Application Example 1.

  The electrolyte membrane 51 is a proton conductive ion exchange membrane formed of a fluorine-based resin that is a solid polymer material, and exhibits good proton conductivity in a wet state. The electrolyte membrane 51 is not limited to the fluorine resin, and may be composed of, for example, a hydrocarbon resin.

  The cathode 52 and the anode 53 are composed of a carrier (for example, carbon) supporting a catalyst metal (for example, platinum (Pt)) and an electrolyte (for example, a fluorine resin). In addition, the electrolyte contained in the cathode 52 and the anode 53 is not limited to the fluorine-based resin, and may be composed of, for example, a hydrocarbon-based resin.

  The gas diffusion layer 60 is disposed on one surface of the MEA 50, and the gas diffusion layer 70 is disposed on the other surface of the MEA 50. Each of the gas diffusion layers 60 and 705 is a carbon porous member having conductivity, and is formed of, for example, carbon cloth or carbon paper.

  A direction in which the members are stacked in the fuel cell CL is also referred to as a stacking direction. The stacking direction is the same direction as the thickness direction of each member of the fuel cell CL.

  The separators 80 and 90 can be formed of a gas-impermeable conductive member, for example, dense carbon that has been made to be gas-impermeable by compressing carbon, or a press-molded metal plate. The separator 80 has an uneven shape in which convex portions 82a and concave portions 82b are alternately formed on one side. In the separator 80, the convex portion 82 a presses the gas diffusion layer 60 (the cathode 52 or the electrolyte membrane 51), and the concave portion 82 b is between the gas diffusion layer 60 and the gas diffusion layer 60 (cathode 52). An in-cell flow path 82 is formed to supply and discharge oxidizing gas. The separator 90 has an uneven shape in which convex portions 92a and concave portions 92b are alternately formed on one surface. In the separator 90, the convex portion 92 a presses the gas diffusion layer 70 (the anode 53 or the electrolyte membrane 51), and the concave portion 92 b is between the gas diffusion layer 70 and the fuel gas with respect to the gas diffusion layer 70 (anode 53). In-cell flow path 92 is formed to supply and discharge the gas.

  Each separator 80, 90 includes holes 103 to 106 at positions corresponding to each other near the outer periphery thereof. When the separators 80 and 90 are stacked together with the MEA 50 and the gas diffusion layers 60 and 70 to assemble the fuel cell ND, the holes provided in the corresponding positions of the stacked separators 80 and 90 overlap each other, A flow path penetrating the inside of the fuel cell ND is formed in the stacking direction. Specifically, the hole 103 forms an oxidizing gas supply manifold, the hole 104 forms an oxidizing gas discharge manifold, the hole 105 forms a fuel gas supply manifold, and the hole 106 is a fuel. A gas exhaust manifold is formed. The oxidizing gas supply manifold is a channel for introducing oxidizing gas into the in-cell channel 82, and the oxidizing gas discharge manifold is a channel for discharging oxidizing gas from the in-cell channel 82. The fuel gas supply manifold is a flow path for introducing fuel gas into the in-cell flow path 92, and the fuel gas discharge manifold is a flow path for discharging fuel gas from the in-cell flow path 92.

  In the fuel cell CL, the seal member 110 is disposed around the in-cell flow path 82, the in-cell flow path 92, and the respective manifolds, and the in-cell flow path 82, the in-cell flow path 92, and the respective manifolds. Ensure gas seal.

  The evaluation device 10 is connected to the terminal TM via the first wiring 20 and is a fuel cell (hereinafter referred to as an inspection target fuel cell) whose internal state is to be evaluated (inspected) via the second wiring 30. (Also referred to as a cell) is connected to a separator 80 and a separator 90 of CL. CPU12 of the evaluation apparatus 10 performs the fuel cell evaluation process shown below. The fuel cell evaluation process is a process routine described by a program stored in the ROM 14.

A2. Software configuration of fuel cell evaluation system:
FIG. 3 is a flowchart showing a fuel cell evaluation process executed by the evaluation apparatus 10. This fuel cell evaluation process is a process for evaluating (inspecting) an internal state (total resistance described later) in the fuel cell CL to be inspected.

  Prior to executing the fuel cell evaluation process, the fuel cell ND is subjected to the following process (pre-evaluation step). That is, in the fuel cell ND, hydrogen as an active gas is introduced from the fuel gas supply manifold, nitrogen (or argon or the like) as an inert gas is introduced from the oxidizing gas supply manifold, and each manifold is sealed. As a result, in the fuel cell CL to be inspected, the anode 53 is sealed with hydrogen and the cathode 52 is sealed with nitrogen. The hydrogen and nitrogen introduced into the fuel cell ND use a low-humidity gas whose relative humidity is in the range of 0.1 to 60%. In this case, the relative humidity of hydrogen and nitrogen is particularly preferably in the range of 10 to 20%. Further, the fuel cell evaluation process is performed in a high temperature state where the temperature of the fuel cell ND is about 90 ° C.

  As shown in FIG. 3, when the processing is started, the CPU 12 of the evaluation apparatus 10 first causes an alternating current to flow through the fuel cell ND while changing the frequency at a predetermined interval, and inspects the target fuel cell CL at each frequency. Specifically, the AC impedance of the MEA 50 of the fuel cell CL to be inspected and the joined body of the gas diffusion layers 60 and 70 is detected (measured) (step S110).

  FIG. 4 is an explanatory diagram showing a cyclic voltammogram of the fuel cell ND. The vertical axis represents the current value [A], and the horizontal axis represents the voltage [V]. The cyclic voltammogram is shown as a current-voltage curve. A region indicated by a one-dot chain line in the figure is an electric double layer region (about 0.3 to 0.5 V). In the process of step S110, a voltage in the electric double layer region (about 0.3 to 0.5 V) shown in FIG. 4 is applied, and an alternating current is supplied with a current value in the electric double layer region.

  Returning to FIG. 3, after execution of step S110, the CPU 12 calculates a complex impedance plot curve V for the fuel cell CL to be inspected based on the AC impedance detected in step S110 (step S120). The complex impedance plot curve is sometimes simply referred to as “complex impedance plot”, and is also referred to as “Cole-Cole plot”. The complex impedance plot curve V is as follows.

  FIG. 5 is a graph showing a complex impedance plot curve V. In FIG. 5, the vertical axis represents the imaginary part value Z2 of the AC impedance, and is hereinafter also referred to as “imaginary part axis”, and the horizontal axis represents the real part value Z1 of the AC impedance. Also called “partial axis”. The complex impedance plot curve V includes (plots) the AC impedance at each frequency detected in step S110 on a plane formed by the imaginary part axis and the real part axis (hereinafter also referred to as “complex plane”). , A curve (approximate curve) created based on the inserted points (plot points).

  In the drawing, the complex impedance plot curve V is shown by a solid line. Squares in the figure are plot points. In the complex impedance plot curve V, the lower left side has a higher frequency.

  Returning to FIG. 3, after executing step S120, the CPU 12 performs a process of selecting a predetermined frequency range from the complex impedance plot curve V calculated in step S120 (step S130).

  The complex impedance plot curve V can be roughly divided into three line segments L1, L2, and L3 from its shape. The line segment L1 is a portion in the high-frequency region, and the slope of the tangent line (the amount of change in the imaginary part value Z2 with respect to the real part value Z1) θ is a value considerably larger than 45 degrees (for example, 60 degrees or more). The line segment L2 is a portion in the middle frequency region (the region on the low frequency side following the high frequency region), and the tangent slope θ is an angle of 45 degrees or around 45 degrees. Here, the vicinity of 45 degrees is 45 degrees and 5 degrees, for example. The line segment L3 is a low frequency region (a region on the low frequency side following the intermediate frequency region), and the slope θ of the tangent line is considerably larger than 45 degrees (for example, 80 degrees or more).

  The boundary between the line segment L1 in the high frequency region and the line segment L2 in the medium frequency region is near the zero cross point Pa where the zero level in the imaginary part axis Z2 is crossed. The boundary between the line segment L2 in the middle frequency range and the line segment L3 in the low frequency range is a point where the slope θ of the tangent line exceeds a predetermined threshold value (for example, 45 degrees 5 degrees) toward the low frequency side, that is, a transition. This is a point Pb.

  In this embodiment, the predetermined frequency range selected in step S130 is set between the frequency at the predetermined point Pc and the frequency at the turning point Pb. The predetermined point Pc is a point at which the imaginary part value Z2 becomes a predetermined positive value (a value greater than 0). The predetermined positive value is, for example, 0.18. The CPU 12 obtains a turning point Pb where the slope θ of the tangent exceeds a predetermined threshold by following the complex impedance plot curve V obtained in step S120, and sets the frequency of the turning point Pb to the lower limit of the predetermined frequency range. In addition, the predetermined point Pc at which the imaginary part value Z2 becomes the predetermined positive value in the complex impedance plot curve V is obtained, and the frequency of the predetermined point Pc is set as the upper limit of the predetermined frequency range.

  In this embodiment, as described above, the CPU obtains the upper and lower limits of the predetermined frequency range by calculation. However, instead of this, a predetermined frequency range, for example, 10 kHz to 100 Hz may be used. Good. The upper limit of 10 kHz is determined in advance by experiment and is a value at which the predetermined point Pc is likely to be taken. The lower limit of 100 Hz is determined in advance by experiment, and is a value at which the turning point Pb is likely to be taken. These illustrated numerical values need not be limited to these.

  Returning to FIG. 3, after executing step S130, the CPU 12 fits the portion Vs (FIG. 5) in the predetermined frequency range selected in step S130 in the complex impedance plot curve V to an equivalent circuit prepared in advance. Then, a process of calculating a combined resistance mainly including the resistance of the electrolyte membrane 51 (hereinafter also referred to as “membrane resistance”) is performed (step S140).

  FIG. 6 is an explanatory diagram showing a circuit configuration of the equivalent circuit E1. The equivalent circuit E1 has been found by the inventors of the present invention. As shown in the figure, the equivalent circuit E1 includes a film resistance equal component Rm, a Warburg impedance Zw, and a correction resistance component Rh as circuit parameters.

  The component Rm such as membrane resistance includes the resistance of the electrolyte membrane 51, the bulk resistance (hereinafter simply referred to as “material bulk resistance”) of the material (gas diffusion layer 60 on the cathode 52 side), the electrolyte membrane 51, the cathode 52, and the like. Represents the sum total of the interface resistance (hereinafter simply referred to as “interface resistance”). Since the resistance of the electrolyte membrane 51 is the largest among the above three, the sum of the above three is referred to as “membrane resistance equal component”. The component Rm such as membrane resistance corresponds to the “total resistance component” in Application Example 1.

  In the case of a fuel cell using the same electrolyte membrane or gas diffusion layer, the resistance of the electrolyte membrane 51 and the material bulk resistance are the same value. There is a possibility that only the interfacial resistance among the above three will show different values. The interface resistance is originally a small value, but according to the conventional technique, there is a possibility that the interface resistance is largely estimated. For this reason, in this embodiment, by providing an evaluation apparatus capable of detecting the component Rm such as membrane resistance with high accuracy, the interface resistance is highly accurate under the condition that the resistance of the electrolyte membrane and the material bulk resistance do not vary. I am planning to evaluate it.

  The Warburg impedance Zw is an expansion type in this embodiment, and can be expressed by the following functional expression (1).

Zw = R × ctnh [(T × I × ω) ^ p] / (T × I × ω) ^ p (1)
Here, R is a resistance, T is a period, and ω is an angular frequency. p is an arbitrary constant and takes a value of 0 to 1, for example. When p takes a value of 0.5, the complex impedance plot curve V has an inclination of 45 degrees.

  The correction resistance component Rh is a resistance component for correction that is set in a pseudo manner based on the performance of the evaluation device 10, and more specifically includes a pseudo reactance component Lg and a pseudo resistance component Rg.

  As shown in FIG. 7, the equivalent circuit E1 has a configuration in which the above-described correction resistance component Rh, film resistance etc. component Rm, and Warburg impedance Zw are connected in series. The equivalent circuit E1 having this configuration is stored in the ROM 14 in the form of a functional equation or the like.

  Specifically, in step S140, Zw obtained from the above equation (1) by changing each value of the correction resistance component Rh, the membrane resistance equal component Rm, and the Warburg impedance Zw is the predetermined frequency range selected in step S130. By calculating the value of the component Rm such as the membrane resistance when it is most approximated to the complex impedance plot curve V, the combined resistance mainly including the membrane resistance is calculated. As described above, the total resistance is the sum of the resistance of the electrolyte membrane 51, the material bulk resistance, and the interface resistance.

  The meaning of the predetermined frequency range at the time of selection in step S130 will be further described using the equivalent circuit E1.

  The line segment L2 in the middle frequency range in the complex impedance plot curve V shown in FIG. 5 is greatly affected by the Warburg impedance Zw (FIG. 6). A region between the predetermined point Pc and the zero cross point Pa in the high frequency line segment L1 of the complex impedance plot curve V is greatly affected by the correction resistance component Rh (FIG. 6). The turning point Pb between the line segment L2 in the middle frequency range and the line segment L3 in the low frequency range is set as the lower limit of the predetermined frequency range, but this is analyzed by the Warburg impedance when moving to the lower frequency side. It is because it becomes difficult to do.

  On the other hand, the upper limit of the predetermined frequency range is a predetermined point Pc at which the imaginary part value Z2 becomes a predetermined positive value, which can be analyzed by the correction resistance component Rh when the frequency shifts further to the high frequency side. This is because it becomes difficult. In the evaluation device 10, a large amount of current flows when the resistance value decreases. It is difficult to apply alternating current at a high frequency, resulting in insufficient accuracy. This is corrected by the pseudo-reactance component Lg included in the correction resistance component Rh. However, if a higher frequency is required, the pseudo-reactance component Lg may not be completely corrected. This limit frequency is the predetermined point Pc.

  Returning to FIG. 3, as described above, the combined resistance as the component Rm of membrane resistance is calculated by the processing up to step S <b> 140. Thereafter, the CPU 12 evaluates whether the interface resistance is too large by determining whether the calculated total resistance does not exceed a predetermined threshold, and the evaluation result is obtained via the input / output control unit 18. The information is displayed on the display unit 19 (step S150). As described above, when the fuel cell evaluation process is performed under the condition that the resistance of the electrolyte membrane and the material bulk resistance do not change, the change of the component Rm such as the membrane resistance is caused by the change of the interface resistance. Therefore, the interface resistance can be evaluated.

  For example, the evaluation result is displayed as “OK” when the total resistance is equal to or less than a predetermined threshold, and is displayed as “NG” when the total resistance exceeds the predetermined threshold. Furthermore, in this embodiment, the value of the total resistance is displayed on the display unit 19 in addition to the evaluation result. Needless to say, the total resistance value may not be displayed, and only the evaluation result “OK” or “NG” may be displayed. In another embodiment, the value of the combined resistance may be displayed as the evaluation result instead of the process of step S150. After execution of step S150, the fuel cell evaluation process is terminated.

  In the fuel cell evaluation process, the process of step S110 is the function of the measurement unit 12a, the processes of steps S120 and S130 are the function of the first calculation unit 12b, and the process of step S140 is the function of the second calculation unit 12c. Each corresponds.

A3. effect:
According to the fuel cell evaluation apparatus 10 of the first embodiment, an AC impedance for each frequency is measured, a complex impedance plot curve V for a predetermined frequency range is obtained based on each AC impedance, and an equivalent with Warburg impedance is provided. By fitting the complex impedance plot curve V for the predetermined frequency range to the circuit E1, a predetermined total resistance including at least the resistance of the electrolyte membrane 51 and the interface resistance between the electrolyte membrane 51 and the cathode 52 is obtained. be able to. Therefore, the total resistance including the interface resistance can be quantitatively evaluated without disassembling the fuel cell ND.

  In particular, in the present embodiment, the equivalent circuit E1 includes the film resistance equal component Rm, the Warburg impedance Zw, and the correction resistance component Rh as circuit parameters, so that the combined resistance is easily and accurately measured. be able to.

A4. Modification of the first embodiment:
In the first embodiment, the complex impedance plot curve is obtained based on the measured AC impedance at each frequency, and then a predetermined frequency range is selected from the complex impedance plot curve. Alternatively, a complex impedance plot curve for a predetermined frequency range may be obtained immediately from the measured AC impedance at each frequency.

  Furthermore, the range measured in the measurement process can be limited to a predetermined frequency range from the beginning, and a curve created based on the measurement result can be an AC impedance characteristic for the predetermined frequency range. Here, the “predetermined frequency range” has a configuration in which a range between the frequency of the turning point Pb and the frequency of the turning point Pb is obtained in advance by experiment and the value is adopted. With this configuration, the same effects as in the first embodiment can be obtained.

  In the first embodiment, the predetermined frequency range selected in step S130, that is, the predetermined frequency range for fitting is set between the predetermined point Pc and the turning point Pb. However, the present invention is not limited to this. For example, the lower limit of the predetermined frequency range may be configured to shift to the lower frequency side than the turning point Pb, or may be configured to shift to the higher frequency side. The upper limit of the predetermined frequency range is the predetermined point Pc. The value of the imaginary part value Z2 for specifying the predetermined point Pc (the above-mentioned “predetermined positive value”) is appropriately different as long as it is a positive value. It can also be a value.

B. Second embodiment:
Next, a second embodiment of the present invention will be described. 2nd Example is an Example which shows the manufacturing method of a fuel cell. The fuel cell to be manufactured is the fuel cell CL (FIG. 2) detailed in the first embodiment. That is, the manufacturing method of the fuel cell of the present invention is applied as a manufacturing method of one fuel cell CL. The manufacturing method of the fuel cell CL is performed by a predetermined operator. The ambient temperature is 23 ° C.

  FIG. 7 is a flowchart showing a method for manufacturing the fuel cell CL in the present embodiment. As shown in the figure, an operator firstly makes an electrolyte (for example, fluorine resin), a solvent (for example, water, alcohol, etc.), a catalyst-supported carrier (for example, platinum-supported carbon), and Teflon (registered trademark). The base material is prepared (step S210). Next, the operator mixes the electrolyte, the solvent, and the catalyst-carrying carrier to create a catalyst ink (step S220).

  Subsequently, the operator coats the catalyst ink on the substrate by a decal method to form a layered ink (step S230). Subsequently, the worker manufactures the cathode 52 by flowing hot air over the layered ink with a hot air generator (not shown) and drying it (step S240). Thereafter, the operator prepares the anode 53 and the electrolyte membrane 51 (step S250), and manufactures the MEA 50 by sandwiching the electrolyte membrane 51 between the manufactured cathode 52 and anode 53 (MEA conversion: step S260). .

  The MEA is performed by hot pressing using a hot press machine in a state where the cathode 52 and the anode 53 are disposed on both surfaces of the electrolyte membrane 51. The conditions for hot pressing are 120 ° C. and 3 MPa. The conditions regarding the temperature and pressure of this hot press are hereinafter referred to as “MEA conditions”.

  Subsequently, the worker manufactures the fuel cell CL using the manufactured MEA 50 (step S270). Specifically, the gas diffusion layers 60 and 70, the separators 80 and 90, and the seal member 110 are prepared, the seal member 110 is arranged around the MEA 50 manufactured in step S260, and the separators 80 and 90 sandwich them. Thus, the fuel cell CL is manufactured.

  Thereafter, the operator introduces nitrogen (or argon or the like) as an inert gas into the cathode 52 of the manufactured fuel battery cell CL, and introduces hydrogen as the active gas into the anode 53 (step S280). As the hydrogen and nitrogen introduced into the fuel battery cell CL, the same low-humidified gas as in the first embodiment is used. In this embodiment, the temperature of hydrogen and nitrogen introduced into the fuel cell CL is about 23 ° C. Next, the worker uses the fuel cell evaluation device 10 detailed in the first embodiment to evaluate the fuel cell CL (step S290).

  FIG. 8 is an explanatory diagram showing a state of connection between the fuel cell evaluation device 10 used in the second embodiment and the fuel cell CL. As illustrated, the evaluation apparatus 10 is connected to the fuel cell CL manufactured in step S270 via the first and second wirings 220 and 230. In this way, the fuel cell evaluation device 10 evaluates (inspects) the fuel cell CL.

  Returning to FIG. 7, the operator determines whether it is “OK” or “NG” by looking at the evaluation result “OK” or “NG” displayed on the display unit 19 of the evaluation apparatus 10 (step S300). Here, if it is determined as “OK”, the fuel cell CL manufactured in step S270 is of high quality, and therefore the fuel cell CL is assumed to be completed. This completes the fuel cell manufacturing method.

  On the other hand, when it is determined in step S300 that the evaluation result is “NG”, the worker discards the fuel cell CL manufactured in step S270 (step S310) and performs the evaluation in step S290. Based on the value of the combined resistance displayed on the evaluation device 10, the MEA condition (temperature, pressure) is corrected (step S320).

  FIG. 9 is a diagram for Table TL showing the relationship between the MEA conditions (temperature, pressure) and the combined resistance. As shown in the drawing, in Table TL, the combined resistance with respect to the MEA condition (temperature, pressure) is shown. This table TL is created from an experiment in which the value of the combined resistance is obtained by changing the MEA conditions (temperature, pressure) in various ways. From this Table TL, it can be seen that the combined resistance and thus the interfacial resistance change depending on the temperature and pressure during hot pressing. In addition, although only 5 patterns are described in the illustrated table TL, it is preferable that more patterns are described.

  The operator looks at the table TL illustrated in FIG. 9, derives the temperature and pressure corresponding to the value of the combined resistance displayed on the evaluation apparatus 10, and corrects the MEA conversion condition to the temperature and pressure (step S <b> 320). . Here, the correction of the MEA conversion condition is specifically to change the temperature and pressure settings of the hot press machine used in the MEA conversion process in step S260 to the temperature and pressure derived from the above table TL. is there.

  After execution of step S320, the operator returns to the process of the first step S210 and repeatedly executes the processes after step S210. In this repetition, the MEA process in step S260 is executed under the MEA conditions (temperature, pressure) corrected in the process in step S310. That is, the operator obtains the temperature and pressure based on the value of the combined resistance displayed on the evaluation device 10, and feeds back the obtained temperature and pressure to the MEA process in step S206.

  Therefore, according to the second embodiment, the manufacturing conditions of the MEA 50, that is, the MEA conditions can be determined so that the interface resistance between the electrolyte membrane and the cathode is appropriate. There is an effect that the fuel cell CL can be manufactured while being secured. Conventionally, since the fuel cell is evaluated and the evaluation result is not fed back to the MEA, the temperature and pressure of the MEA are set excessively high in order to reduce the interface resistance. On the other hand, in the second embodiment, it is only necessary to apply necessary and sufficient temperature and pressure, so that the increase in cost due to excess energy is prevented and the physical load on the electrolyte membrane and electrode is reduced to improve the performance of the fuel cell. There is also an effect that it can be achieved.

  Further, in the second embodiment, the total resistance including the interface resistance between the electrolyte membrane 51 and the cathode 52 can be obtained quantitatively using the same fuel cell evaluation apparatus 10 as in the first embodiment. The quality stability of the fuel cell CL can be further ensured.

  In the second embodiment, the configuration is such that both the temperature and pressure of the hot press are corrected in step S320. However, in place of this, either one may be corrected. Also with this configuration, it is possible to appropriately adjust the interface resistance as compared with the conventional example.

C. Third embodiment:
Next, a third embodiment of the present invention will be described. 3rd Example is an Example which shows the fuel cell manufacturing method similar to 2nd Example, and the fuel cell evaluation apparatus to be used differs compared with 2nd Example.

  FIG. 10 is a flowchart showing a fuel cell evaluation process executed in the fuel cell evaluation apparatus used in the manufacturing method of the third embodiment. As shown in the figure, the CPU of the fuel cell evaluation apparatus executes the same steps S110 and S120 as in the first embodiment when the process is started. As a result, the same complex impedance plot curve V as that in the first embodiment is calculated. In the first embodiment, a predetermined frequency range is then selected from the complex impedance plot curve V. In the third embodiment, however, the complex impedance plot curve V is directly fitted to the equivalent circuit without selecting the frequency range. Thus, a process for calculating the total resistance is performed (step S430). The equivalent circuit has a circuit configuration different from the equivalent circuit E1 (FIG. 6) used in the first embodiment.

  FIG. 11 is an explanatory diagram showing a circuit configuration of an equivalent circuit E2 used in the third embodiment. The equivalent circuit E2 is an equivalent circuit found by the inventor of the present invention. As illustrated, the equivalent circuit E2 includes, as circuit parameters, a membrane resistance component Rm, a plurality of ion conduction resistance components Ri, a plurality of CPE (Constant phase element) components 340, a plurality of reaction resistance components Ra, And a correction resistance component Rh. The film resistance etc. component Rm and the correction resistance component Rh are the same as those in the first embodiment.

  The ion conduction resistance component Ri represents the ion conduction resistance of the electrolyte in the cathode 52. The CPE component 340 represents resistance generated at the interface between the electrolyte and the carrier in the cathode 52. The reaction resistance component Ra is generated when the leak gas reacts with the catalyst of the cathode 52 in the MEA 50 when hydrogen (active gas) from the anode 53 passes through the electrolyte membrane 51 and moves to the cathode 52. Represents reaction resistance.

The capacitive reactance Lc of the CPE component 340 can be obtained by the following equation (2).
Lc = 1 / {C (jω) ^P } (2)
C: Capacitance ω: Frequency P: Arbitrary constant (for example, 0.8 to 0.9)

  In the equivalent circuit E2, the CPE component 340 and the reaction resistance component Ra are connected in parallel. Hereinafter, a parallel circuit composed of the CPE component 340 and the reaction resistance component Ra is also referred to as a CPE parallel circuit. The equivalent circuit E2 includes a correction resistance component Rh, a membrane resistance equal component Rm, and an ion conduction resistance component Ri connected in series, and one end of one CPE parallel circuit is connected to the membrane resistance equal component Rm and ion conduction. A ladder-like structure in which one end of another CPE parallel circuit is connected between adjacent ion conduction resistance components Ri, and the other end of each CPE parallel circuit is connected to the line K. Circuit.

  In the equivalent circuit E2 configured as described above, the complex impedance plot curve V is fitted as it is without selecting a predetermined frequency range from the complex impedance plot curve V, so that the membrane resistance equal component Rm and the like can be started. Each component to be obtained can be obtained. In particular, it is possible to quantitatively determine each component including the component Rm such as membrane resistance.

  Returning to FIG. 10, after the execution of step S430, based on the film resistance equal component Rm obtained in step S430, the evaluation result of the interfacial resistance and the value of the combined resistance are displayed on the display unit as in the first embodiment. It is displayed (step S150). Thereafter, the fuel cell evaluation process is terminated.

  Using the evaluation result obtained by the fuel cell evaluation process and the value of the interface resistance, the fuel cell CL is manufactured in the same manner as in the second embodiment.

  Therefore, according to the third embodiment, as in the second embodiment, the manufacturing conditions of the MEA 50 can be determined so that the interface resistance is appropriate. CL can be manufactured. In the third embodiment, since the total resistance including the interface resistance between the electrolyte membrane 51 and the cathode 52 can be obtained quantitatively using the fuel cell evaluation apparatus using the equivalent circuit E2, the fuel cell The quality stability of the cell CL can be further ensured.

  In the second embodiment and the third embodiment, the fuel cell manufacturing method is performed by a worker who is a person. Instead of this, a configuration in which the work by the worker is automated by an automation device. It is good. According to this configuration, an appropriate fuel cell can be created more easily.

D. Variation:
It should be noted that elements other than those described in the independent claims among the constituent elements in the first to third embodiments and the modifications described above are additional elements and can be omitted as appropriate. The present invention is not limited to the above-described embodiments and modifications, and can be carried out in various modes without departing from the scope of the invention. For example, the following modifications are possible. is there.

D1. Modification 1:
In each of the embodiments described above, the evaluation apparatus 10 performs the electrolyte in the fuel cell evaluation process in a state where hydrogen as an active gas is introduced into the anode 53 of the fuel cell ND and nitrogen as an inert gas is introduced into the cathode 52. Although the total resistance including the interface resistance between the membrane 51 and the cathode 52 is obtained, the present invention is not limited to this. For example, nitrogen is introduced into the anode 53 of the fuel cell ND and hydrogen is introduced into the cathode 52, so that the evaluation apparatus 10 obtains the combined resistance including the interface resistance between the electrolyte membrane 51 and the anode 53 in the fuel cell evaluation process. It may be. In this way, the state of the anode 53 can be estimated in the MEA 50.

D2. Modification 2:
In the fuel cell evaluation apparatus of each of the above embodiments, in the fuel cell evaluation process, hydrogen and nitrogen introduced into the fuel cell ND may use a gas having a relative humidity higher than 60%. Even in this case, at least part of the effects of the above-described embodiment can be achieved.

D3. Modification 3:
The fuel cell ND in which the fuel cell evaluation device of each of the embodiments performs the fuel cell evaluation process is a solid polymer fuel cell, but the present invention is not limited to this, and the solid oxide fuel cell is not limited thereto. Various types of fuel cells such as an electrolyte type and a molten carbonate electrolyte type may be used.

10 ... Fuel cell evaluation device 12 ... CPU
12a ... Measurement unit 12b ... First calculation unit 12c ... Second calculation unit 14 ... ROM
16 ... RAM
DESCRIPTION OF SYMBOLS 18 ... Input / output control part 19 ... Display part 20 ... 1st wiring 30 ... 2nd wiring 50 ... MEA
DESCRIPTION OF SYMBOLS 51 ... Electrolyte membrane 52 ... Cathode 53 ... Anode 60 ... Gas diffusion layer 70 ... Gas diffusion layer 80 ... Separator 82 ... In-cell flow path 82a ... Convex part 82b ... Concave part 90 ... Separator 92 ... In-cell flow path 92a ... Convex part 92b ... Recessed parts 103 to 106 ... Hole part 110 ... Seal member V ... Complex impedance plot curve E1 ... Equivalent circuit Rm ... Membrane resistance component Zw ... Warburg impedance Rh ... Correction resistance component Lg ... Pseudo-reactance component Rg ... Pseudo-resistance component Pa ... Zero cross Point Pb ... Turning point Pc ... Predetermined point E2 ... Equivalent circuit ND ... Fuel cell CL ... Fuel cell TM ... Terminal EP ... End plate

Claims (9)

A fuel cell evaluation method comprising:
A fuel cell including a membrane electrode assembly in which a first electrode is disposed on one surface of an electrolyte membrane and a second electrode is disposed on the other surface of the electrolyte membrane is prepared, and an inert gas is supplied to the first electrode. Pre-evaluation process to be introduced,
In the state where the inert gas is introduced, the measurement step of measuring the AC impedance of the membrane electrode assembly while changing the frequency,
A first calculation step for obtaining an AC impedance characteristic for a predetermined frequency range based on the AC impedance for each frequency measured in the measurement step;
By fitting the AC impedance characteristic to an equivalent circuit having Warburg impedance, a second total resistance that includes at least the resistance of the electrolyte membrane and the interface resistance between the electrolyte membrane and the first electrode is obtained. A method for evaluating a fuel cell comprising: The fuel cell evaluation method according to claim 1,
The equivalent circuit is
A method for evaluating a fuel cell, comprising: a combined resistance component representing the combined resistance; and a correction resistance component. In the fuel cell evaluation method according to claim 1 or 2,
The first calculation step includes:
A plotting step for inserting AC impedance at each frequency measured in the measuring step into a complex plane;
A plot curve calculation step for obtaining a complex impedance plot curve from each plot point obtained by the plot step;
And a selecting step of selecting the predetermined frequency range in the complex impedance plot curve as the AC impedance characteristic. In the fuel cell evaluation method according to claim 3,
The complex impedance plot curve is
A first line segment whose angle with respect to the real part axis of the complex plane is equal to or less than a predetermined threshold value, and a lower frequency side than the first line segment and an angle with respect to the real part axis of the complex plane is equal to or greater than a predetermined threshold value And at least a second line segment,
The selection process includes
A method for evaluating a fuel cell, comprising: selecting the lower limit of the predetermined frequency range as a frequency for a turning point between the first line segment and the second line segment. In the evaluation method of the fuel cell according to claim 3 or 4,
The selection process includes
A method for evaluating a fuel cell, comprising: selecting the upper limit of the predetermined frequency range as a frequency for a point at which an imaginary part value of the complex plane becomes a predetermined positive value. A fuel cell manufacturing method comprising:
A preparation step of preparing an electrolyte membrane, a first electrode, and a second electrode;
A membrane electrode assembly manufacturing process for manufacturing a membrane electrode assembly under predetermined manufacturing conditions using the electrolyte membrane, the first electrode, and the second electrode;
A fuel cell manufacturing process for manufacturing a fuel cell by laminating a gas diffusion layer and a separator on the manufactured membrane electrode assembly; and
A measurement step of measuring the alternating current impedance of the membrane electrode assembly while changing the frequency with an inert gas introduced into the first electrode of the membrane electrode assembly provided in the manufactured fuel cell;
By obtaining AC impedance characteristics based on the AC impedance for each frequency measured in the measurement step, and fitting the AC impedance characteristics to an equivalent circuit, the resistance of the electrolyte membrane, the electrolyte membrane, and the first electrode, A calculation step for obtaining a predetermined total resistance including at least an interfacial resistance between:
A fuel cell manufacturing method comprising: a feedback step of obtaining the manufacturing condition based on the combined resistance obtained by the calculation step and feeding back the obtained manufacturing condition to the membrane electrode assembly manufacturing step. In the manufacturing method of the fuel cell according to claim 6,
The membrane electrode assembly manufacturing process includes:
Hot pressing a laminate in which the first electrode and the second electrode are arranged on both surfaces of the electrolyte membrane,
The manufacturing conditions are as follows:
A method for producing a fuel cell, which is a condition for the temperature and pressure of the hot press. In the manufacturing method of the fuel cell according to claim 7,
The calculation step includes
A step of performing the fitting using an AC impedance characteristic for a predetermined frequency range;
The equivalent circuit is
A method for manufacturing a fuel cell, comprising a Warburg impedance. A fuel cell evaluation apparatus for evaluating a fuel cell including a membrane electrode assembly in which a first electrode is disposed on one surface of an electrolyte membrane and a second electrode is disposed on the other surface of the electrolyte membrane,
A measurement unit that measures the AC impedance of the membrane electrode assembly while changing the frequency with an inert gas introduced into the first electrode,
A first calculation unit for obtaining an AC impedance characteristic for a predetermined frequency range based on the AC impedance for each frequency measured by the measurement unit;
By fitting the AC impedance characteristic to an equivalent circuit having Warburg impedance, a second total resistance that includes at least the resistance of the electrolyte membrane and the interface resistance between the electrolyte membrane and the first electrode is obtained. A fuel cell evaluation apparatus comprising:

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