An analysis method of a fuel cell catalyst layer structure

Abstract

The application discloses a kind of analysis methods of fuel cell catalytic layer structure, comprising the following steps: S1, preparation test cell, under the condition of setting, the complex impedance data of full frequency band is collected, and Nyquist diagram is obtained;S2, establish the mapping relationship of the key features of different frequency bands of Nyquist diagram and catalytic layer structure, determine the structural characteristics of catalytic layer according to measured Nyquist diagram;S3, construct equivalent circuit model, with the measured Nyquist diagram is fitted, and the structural characteristics of catalytic layer are quantified by fitting parameter.The method of the application associates the full frequency band complex impedance data with the structural characteristics of catalytic layer by systematic steps, and realizes quantitative analysis by combining equivalent circuit fitting, establishes the clear mapping relationship between structure and atlas, can comprehensively and accurately identify the key features such as thickness direction ionomer distribution of catalytic layer, carbon skeleton agglomeration, hydrogen cross penetration, and provides a standardized and quantifiable technical path for catalytic layer structure analysis.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cells, in particular to a method for analyzing the structure of a fuel cell catalyst layer. BACKGROUND

[0002] The catalyst layer is the core area of proton transport and charge conversion in a fuel cell, and its microstructure (such as ionomer distribution and carbon skeleton morphology) directly affects the proton migration path and resistance characteristics. Therefore, accurate analysis of the catalyst layer structure is crucial for optimizing the performance of fuel cells.

[0003] Currently, the methods for measuring the internal resistance and catalyst layer structure of a fuel cell mainly include the current interruption method and the electrochemical impedance spectroscopy (EIS). The current interruption method can quickly obtain data by interrupting the current at a constant operating current and calculating the polarization resistance based on the voltage jump. However, this method can only measure the polarization resistance and cannot separate the reaction resistance and capacitance components. Moreover, it is easily affected by the inductance of the load cable and voltage noise, limiting its measurement accuracy.

[0004] The electrochemical impedance spectroscopy (EIS) can separate the polarization resistance, reaction resistance, and capacitance components by measuring the phase shift between voltage and current. This method has higher measurement accuracy and better anti-interference ability. However, there are still many key issues in the analysis of catalyst layer structure using this method: (1) The impedance spectrum is complex, and there is no clear mapping relationship between different frequency bands and specific structural characteristics of the catalyst layer (such as ionomer distribution position and proportion), which makes the Nyquist plot rely more on empirical interpretation and cannot quantify the distribution proportion of ionomers on the membrane side and the gas diffusion layer (GDL) side; (2) It is difficult to decouple the effects of the catalyst layer thickness direction (Z direction) and the in-plane direction (XY direction) structure on the spectrum, limiting the quantitative reconstruction of the microstructure; (3) The in-plane non-uniformity is often masked by the ambiguous characteristics of the 45° and 90° transition bands in the Nyquist plot. Without a standardized identification method, it is easy to be misjudged as a general electrode response, which cannot provide a basis for production process evaluation. SUMMARY

[0005] To overcome the shortcomings of the prior art, the present application aims to develop a catalyst layer structure analysis method based on electrochemical impedance spectroscopy, which can quantitatively analyze the microstructure and distribution of the catalyst layer and provide a basis for fuel cell process optimization and performance improvement.

[0006] To achieve the above-mentioned purpose, a method for analyzing the structure of a fuel cell catalyst layer includes the following steps:

[0007] S1, preparing a test cell, applying an alternating current disturbance voltage under a set condition, collecting complex impedance data in the full frequency band, and obtaining a Nyquist plot;

[0008] S2, mapping relationship between key features of different frequency bands of Nyquist diagram and structure of catalytic layer, 45° line of first frequency band of 1kHz to 100Hz deviates from corresponding thickness direction of catalytic layer ionomer distribution, 90° line of second frequency band of 100Hz to 10Hz deviates from corresponding carbon skeleton agglomeration of catalytic layer, arc of third frequency band of 10Hz to 1Hz corresponds to hydrogen cross permeation, and the structure characteristics of the catalytic layer are determined according to the measured Nyquist diagram;

[0009] S3, constructing an equivalent circuit model, fitting with the measured Nyquist diagram, and quantifying the structure characteristics of the catalytic layer through the fitting parameters.

[0010] The method of the application associates full-band complex impedance data with the structure characteristics of the catalytic layer through systematic steps, and realizes quantitative analysis by combining equivalent circuit fitting, establishes a clear mapping relationship between structure and atlas, and can comprehensively and accurately identify key features such as ionomer distribution in the thickness direction of the catalytic layer, carbon skeleton agglomeration, and hydrogen cross permeation, providing a standardized and quantifiable technical path for catalytic layer structure analysis.

[0011] Further, in the step S2, the impedance phase angle of the first frequency band is calculated by the formula θ=arctan(|Z'' / Z'|), wherein θ is the impedance phase angle, Z'' is the imaginary part of the impedance, Z' is the real part of the impedance, and arctan() is the inverse tangent function; when θ=45°, it is determined that the ionomer is uniformly distributed in the thickness direction of the catalytic layer, when θ>45°, it is determined that the ionomer is concentrated on the proton exchange membrane side in the thickness direction of the catalytic layer, and when θ<45°, it is determined that the ionomer is concentrated on the gas diffusion layer side in the thickness direction of the catalytic layer. This step realizes the quantitative determination of the ionomer distribution in the thickness direction of the catalytic layer, solves the problem that the traditional method cannot distinguish whether the ionomer is concentrated on the proton exchange membrane or the gas diffusion layer side, and can clearly determine the symmetry and distribution difference of the proton conduction path, providing accurate structural basis for optimizing ionomer distribution and reducing proton transport resistance.

[0012] Further, in the step S2, when the second frequency band deviates from the 90° line or appears bending, it is determined that the catalytic layer has carbon skeleton agglomeration. This step clearly corresponds the deviation or bending of the second frequency band 90° line to the carbon skeleton agglomeration, and can accurately identify the structure degradation characteristics such as reduction of three-phase interface and reduction of charge transfer efficiency caused by carbon carrier aggregation in the catalytic layer, solving the problem that the traditional method is difficult to intuitively judge the uniformity of carbon skeleton distribution.

[0013] Further, in the step S2, when the third frequency band appears an arc structure, it is determined that the catalytic layer has hydrogen cross permeation. This step determines the hydrogen cross permeation phenomenon through the arc structure of the third frequency band, and can intuitively identify the problem of hydrogen entering the cathode to cause side reactions through the proton exchange membrane, solving the limitation that the traditional method is difficult to quantize the influence of cross permeation side reactions.

[0014] Further, in the step S3, Z-view software is used for modeling and fitting. The software interface is intuitive, the parameter extraction efficiency is high, and the fitting result is clear. The advantages of the software improve the convenience and accuracy of the equivalent circuit model and Nyquist diagram fitting.

[0015] Further, in the step S3, the equivalent circuit model of the first frequency band is composed of a proton resistance. The equivalent circuit model can accurately represent the impedance characteristics of the membrane resistance corresponding to the first frequency band and the proton resistance distribution in the thickness direction of the catalyst layer, and excludes irrelevant interference factors, thereby providing a targeted circuit model basis for analyzing the thickness direction of the catalyst layer.

[0016] Further, in the step S3, the equivalent circuit model of the second frequency band is extended on the basis of the equivalent circuit model of the first frequency band: a plurality of parallel R-CPE units are added, and the R-CPE unit is composed of a proton resistance and a constant phase element in series. The equivalent circuit model can effectively represent the structural non-uniformity in the XY direction of the catalyst layer and the impedance characteristics caused by the carbon skeleton aggregation. Through the parallel structure of multiple units, the proton resistance and charge accumulation characteristics of different regions are reflected, and the multi-dimensional quantification of the complex structure characteristics of the second frequency band is realized.

[0017] Further, in the step S3, the equivalent circuit model of the third frequency band is extended on the basis of the equivalent circuit model of the second frequency band: a polarization resistance is added in parallel with the constant phase element in the R-CPE unit. The equivalent circuit model can accurately capture the polarization impedance characteristics caused by the hydrogen cross-penetration side reaction, and the impedance characteristics of the slow polarization process of cross-penetration are included in the model, thereby providing reliable circuit model support for quantitatively evaluating the cross-penetration degree.

[0018] Further, in the equivalent circuit model, the impedance calculation formula of the constant phase element is as follows:

[0019]

[0020] In the formula, Z is the impedance of the constant phase element, Y0 is the admittance parameter of the constant phase element, j is the imaginary unit, ω is the angular frequency, and α is the dispersion coefficient.

[0021] By defining the impedance calculation formula of the constant phase element and including the dispersion coefficient α as a quantitative index in the equivalent circuit model, the quantitative characterization of the catalyst layer structure is realized.

[0022] Further, in the step S1, the setting conditions include: inert gas is introduced into the cathode side of the test battery, the test temperature is 60-80℃, and the relative humidity is 10%-20%. The introduction of inert gas into the cathode side of the test battery can isolate oxygen and eliminate the interference of electrochemical reaction, so that the impedance signal only reflects the physical structure of the catalyst layer; the test temperature is close to the actual working state, which ensures the proton conduction activity of the ionomer; and the low humidity condition can increase the proton resistance, enhance the structural signal and suppress the inductive interference.

[0023] Further, in the step S1, the setting conditions include: the bias voltage is 0.2-1V, and the amplitude of the alternating disturbance voltage is not more than 10% of the bias voltage. The bias voltage makes the electrode in a non-reaction state, separates the structure and reaction signals, and the limited amplitude of the alternating disturbance voltage can ensure the linear response of the system and reduce nonlinear distortion. These conditions work together to ensure that the impedance data can accurately represent the structural characteristics of the catalyst layer.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] (1) Establishing the mapping relationship between Nyquist diagram and catalyst layer structure: for the first time, the microstructure characteristics of the catalyst layer in the thickness direction (Z direction) and the in-plane direction (XY direction) are systematically associated with the responses of Nyquist diagram in different frequency bands, and the quantitative mapping relationship between physical structure and frequency spectrum characteristics is established, which provides a standardized and quantifiable technical path for catalyst layer structure analysis and direct quantitative basis for process optimization and formula improvement.

[0026] (2) Quantitatively judging the distribution state of proton resistance and supporting structural optimization decision: with the help of spectral angle analysis and equivalent circuit fitting, it can be determined whether the ionomer is concentrated on the proton exchange membrane side or the gas diffusion layer side, and the symmetry and asymmetry thereof are quantitatively characterized, which provides a quantitative basis for catalyst layer preparation process optimization.

[0027] (3) Identifying in-plane non-uniformity and cross-penetration complex phenomena: the characteristic changes in the Nyquist diagram can identify in-plane ionomer distribution, hydrogen cross-penetration and other structural or interface problems, which provides intuitive and visual basis for failure mechanism analysis and quality control.

[0028] (4) Good adaptability and anti-interference ability: the strategies of introducing inert gas into the cathode, setting bias voltage and low humidity condition can effectively eliminate the influence of active reaction interference and water management factors, so that the test results more truly reflect the structural characteristics of the catalyst layer, improve the accuracy and repeatability of the test, and are suitable for various membrane electrode systems and working conditions.

[0029] (5) The method is easy to implement and has popularization and application value: the analysis method can be implemented by relying on a conventional electrochemical workstation, and fitting and judgment can be completed by cooperating with analysis software such as Z-view, without special hardware or consumables, and the method has good portability and engineering potential, and is suitable for dual needs of research experiments and industrial detection. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a mapping relationship diagram of a Nyquist graph and a catalytic layer structure in the specific embodiment of the application.

[0031] Figure 2 It is a Nyquist graph measured in example 1 of the application.

[0032] Figure 3 It is a Nyquist graph measured in example 2 of the application.

[0033] Figure 4 It is a Nyquist graph measured in example 3 of the application. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned purposes, features and advantages of the application more obvious and easy to understand, the specific embodiments of the application will be described in detail below with reference to the drawings. It should be noted that the following embodiments are only used to illustrate the implementation method and typical parameters of the application, and are not used to limit the parameter range described in the application, and reasonable changes derived therefrom are still within the protection scope of the claims of the application.

[0035] The specific embodiment of the application provides an analysis method of a catalytic layer structure of a fuel cell, which quantitatively analyzes the microstructure and distribution of the catalytic layer by constructing a mapping between a physical structure and a Nyquist graph feature, and combining specific measurement conditions and equivalent circuit modeling.

[0036] The analysis method comprises the following steps:

[0037] Step S1: obtaining a Nyquist graph of a test cell.

[0038] The specific process is as follows: a test cell is prepared, an alternating current disturbance voltage is applied under a set condition, complex impedance data of a full frequency band are collected, and a Nyquist graph is obtained. In this step, the phase offset of voltage and current is determined by using the alternating current impedance method, and the absolute value of the resistance value and its components can be obtained, so that various resistances can be separated, and various information can be obtained.

[0039] In specific embodiments, in order to analyze the structure of the catalytic layer, inert gas is introduced into the cathode side, such as N2, Ar, etc. A bias voltage is applied in an environment where no electrode reaction occurs. According to the frequency characteristics, the catalytic layer is analyzed. The main purpose of introducing inert gas into the cathode side is to avoid the occurrence of cathode electrode reaction. Specifically, when inert gas is introduced, no oxygen reduction reaction occurs on the cathode of the fuel cell, so no current is generated, and the electrochemical impedance signal measured can accurately reflect the charge transfer characteristics, electrical conductivity, and ion conductivity of the catalytic layer, without interference from the oxygen reduction reaction.

[0040] In specific embodiments, the test temperature is set to 60-80°C, and the relative humidity is set to 10%-20%. Testing under lower humidity conditions can improve the proton resistance of the catalytic layer, making the structure-related impedance component more prominent in the Nyquist plot, thereby effectively suppressing the relative interference of the inductance term. This condition is particularly suitable for high-area single cells and low equivalent weight (EW) ionomer systems, and helps to improve the accuracy of structure fitting and parameter extraction.

[0041] In specific embodiments, a bias voltage is applied, typically set to 0.2-1V, which is beneficial for placing the electrode in a non-reactive state and separating the structure and reaction signals. The amplitude of the alternating current disturbance voltage does not exceed 10% of the bias voltage, ensuring linear response of the system and reducing nonlinear distortion.

[0042] Step S2: Establish the mapping relationship between the key features of different frequency bands in the Nyquist plot and the structure of the catalytic layer. This step establishes a clear mapping relationship between the structure and the atlas, which can comprehensively and accurately identify key features such as ionomer distribution in the thickness direction of the catalytic layer, carbon skeleton aggregation, and hydrogen cross-penetration.

[0043] In combination with Figure 1 As shown in the figure, the relationship between the high-frequency, medium-frequency, and low-frequency responses in the Nyquist plot and the structure of the catalytic layer is as follows:

[0044] (A) The first frequency band (1 kHz to 100 Hz) corresponds to (a) the ionomer distribution in the thickness direction of the catalytic layer.

[0045] In the Nyquist plot, the real part (horizontal axis) represents resistance, and the imaginary part (vertical axis) represents reactance. The degree of deviation of the first frequency band from the 45° line corresponds to the ionomer distribution in the thickness direction of the catalytic layer. The impedance phase angle is calculated by the formula θ = arctan(|Z'' / Z'|), where θ is the impedance phase angle, Z'' is the imaginary part of the impedance, and Z' is the real part of the impedance. The specific mapping relationship is as follows:

[0046] When θ = 45°, it shows that the real part and the imaginary part of impedance grow at the same speed, which means that the impedance encountered by the current through the proton exchange membrane side is equal to the impedance encountered by the current through the gas diffusion layer side. The corresponding structural characteristics are that the ionomer is uniformly distributed in the thickness direction of the catalyst layer, and the conduction path is symmetrical.

[0047] When θ > 45°, it shows that the real part becomes smaller and the imaginary part becomes larger, which is because the proton resistance on the proton exchange membrane side is small and the conductivity is good, and the protons can quickly move to the electrode interface, and the charges are more likely to accumulate to form a capacitor. The corresponding structural characteristics are that the ionomer is concentrated on the proton exchange membrane side and fails to effectively penetrate to the gas diffusion layer side.

[0048] When θ < 45°, it shows that the real part becomes larger and the imaginary part becomes smaller, which is because the proton resistance on the proton exchange membrane side is large and the conductivity is poor, and the charge accumulation is insufficient. The corresponding structural characteristics are that the ionomer is distributed closer to the gas diffusion layer side, and the proton channel on the proton exchange membrane side is insufficient.

[0049] (B) The second frequency band (100 Hz to 10 Hz) corresponds to (b) the agglomeration of the carbon skeleton of the catalyst layer.

[0050] The electron channel formed by the carbon carrier can be equivalent to a resistance element, and the ionomer covering its surface forms a proton conduction path and exhibits a capacitor behavior at the electrode / electrolyte interface. The interface capacitor is often equivalent to a pure capacitor or a constant phase element (CPE), reflecting the charge accumulation ability and the integrity of the reaction interface.

[0051] When the proton resistance and the constant phase element are connected in series, it appears as a straight line perpendicular to the horizontal axis (90°) in the Nyquist diagram, but when the carbon carrier aggregates, the ionomer penetration is limited, resulting in a decrease in the three-phase interface, a weakening of the interface capacitor, and an ineffective accumulation of charges. Therefore, the response of the second frequency band is no longer an ideal capacitor behavior. At this time, the interface reaction is restricted by both the electron conduction path and the capacitor, and the impedance response exhibits a non-ideal behavior composed of a resistance and a capacitor in series. This series structure causes the frequency region in the Nyquist diagram to deviate from the vertical upward characteristic close to 90° and to present a certain degree of deviation and bending, reflecting the structural degradation characteristics of the decrease in the three-phase interface density and the decrease in the charge transfer efficiency in the catalyst layer.

[0052] (C) The third frequency band (10 Hz to 1 Hz) corresponds to (c) hydrogen cross-penetration.

[0053] In the fuel cell, the impedance response in the low frequency region usually corresponds to the slower electrochemical behavior dominated by the polarization process. When hydrogen crossover occurs, part of the hydrogen is not completely oxidized at the anode, but passes through the proton exchange membrane into the cathode to react with oxygen to generate water. This side reaction introduces a new polarization process, which is slow and has obvious hysteresis, so it appears as a third frequency band arc structure in the Nyquist plot, representing the additional effect of the cross-penetration side reaction on the overall impedance of the system. Therefore, the presence of the third frequency band arc can be used as a basis for judging whether the hydrogen penetration is severe or not.

[0054] Step S3: Constructing an equivalent circuit model.

[0055] The equivalent circuit model is fitted with the measured Nyquist plot by software, and the structure characteristics of the catalyst layer are quantified by the fitting parameters, providing a standardized and quantifiable technical path for catalyst layer structure analysis.

[0056] In specific embodiments, Z-view software is used for modeling and fitting, which has the advantages of intuitive interface, high parameter extraction efficiency, clear fitting results, etc., facilitating quick judgment of fitting goodness and assisting structure analysis. The equivalent circuit models corresponding to different frequency bands are as follows:

[0057] The equivalent circuit model of the first frequency band is composed of a proton resistance. The change in proton resistance caused by uneven distribution of ionomer can be simulated by an equivalent circuit element, a constant phase element. This equivalent circuit model can accurately represent the impedance characteristics of the proton resistance distribution in the thickness direction of the catalyst layer corresponding to the first frequency band, excluding irrelevant interference factors and providing a targeted circuit model basis for analyzing the ionomer distribution in the thickness direction of the catalyst layer.

[0058] The equivalent circuit model of the second frequency band is extended based on the equivalent circuit model of the first frequency band: multiple parallel R-CPE units are added, and the R-CPE unit is composed of a proton resistance and a constant phase element in series. This equivalent circuit model can effectively represent the structural non-uniformity in the in-plane direction (XY direction) of the catalyst layer and the impedance characteristics caused by carbon skeleton aggregation. Through the multi-unit parallel structure, the proton resistance and charge accumulation characteristics of different regions are reflected, achieving multi-dimensional quantification of the complex structure characteristics of the second frequency band.

[0059] The equivalent circuit model of the third frequency band is extended based on the equivalent circuit model of the second frequency band: a polarization resistance is added in parallel with the constant phase element in the R-CPE unit. This equivalent circuit model can accurately capture the polarization impedance characteristics brought by the hydrogen cross-penetration side reaction.

[0060] In the above steps, the theoretical impedance curve of the equivalent circuit model is fitted with the measured Nyquist diagram by Z-view software, and after the fitting is completed, the software outputs the specific parameter values of each element in the model.

[0061] In the above equivalent circuit model, the impedance calculation formula of the constant phase element is as follows:

[0062]

[0063] In the formula, Z is the impedance of the constant phase element, Y0 is the admittance parameter of the constant phase element, j is the imaginary unit, ω is the angular frequency, and α is the dispersion coefficient.

[0064] By explicitly defining the impedance calculation formula of the constant phase element, the dispersion coefficient α is taken into the equivalent circuit model as a quantitative index, and the quantitative characterization of the catalyst layer structure is realized.

[0065] The above analysis method can be implemented relying on a conventional electrochemical workstation, and the fitting and judgment can be completed by cooperating with analysis software such as Z-view, without special hardware or consumables, and has good portability and engineering potential.

[0066] The technical solutions and effects of the present application are illustrated by specific embodiments as follows.

[0067] Example 1

[0068] In this embodiment, the structure of the fuel cell catalyst layer is analyzed, and the specific steps are as follows:

[0069] (1) The test platform is a standard test cell with a circular 13cm 2 electrode area, cooperating with a suitable gas flow path and humidification system. During assembly, the sealing integrity and consistent contact should be ensured to avoid impedance deviation caused by non-structural factors.

[0070] (2) Set the impedance test conditions to eliminate the interference of active electrode reactions and only extract the structural characteristic parameters. Test temperature: 80℃; gas humidification conditions: anode / cathode dew point is 40℃; bias voltage: 0.5V; AC disturbance voltage amplitude: ±50mV; frequency scanning range: 50kHz to 0.1Hz.

[0071] (3) Use an electrochemical workstation with frequency response analysis function to apply a small signal AC disturbance to the cell, collect the current / voltage response, and obtain the Nyquist diagram as shown in Figure 2 .

[0072] (4) According to the mapping relationship between the key characteristics of different frequency bands in the Nyquist diagram and the structure of the catalyst layer, the structure of the catalyst layer is analyzed. Among them, the impedance phase angle of the first frequency band is 38°, and the corresponding structural feature is that the ionomer is distributed closer to the gas diffusion layer side; the second frequency band deviates from 90°, and it is determined that the catalyst layer exists carbon skeleton aggregation; the third frequency band appears a circular arc structure, and it is determined that the catalyst layer exists hydrogen cross-permeation.

[0073] (5) Using Z-view software, the measured Nyquist diagram data is fitted to the equivalent circuit model.

[0074] Select the basic model based on the characteristics of the first frequency band: take the proton resistance as the core structure of the first frequency band, and the proton resistance is commonly used to simulate the constant phase element CPE1. After importing the Nyquist diagram data, the software automatically iterates and fits to obtain the dispersion coefficient α1=0.42 of CPE1. Among them, the value of α1 is less than 0.5, which is consistent with the phase angle of 38° (<45°) of the first frequency band in step (4), quantitatively reflecting that the ionomer is distributed closer to the gas diffusion layer side.

[0075] Expand the model according to the characteristics of the second frequency band: based on the first frequency band model, add two parallel R-CPE units (both are proton resistance and constant phase element in series). The fitting result shows that the dispersion coefficient α2=0.65 (deviation 1) of CPE2, indicating that the 90° line deviation of the second frequency band is caused by carbon skeleton aggregation. The carbon skeleton aggregation limits the ionomer permeation, leading to the increase of the difference of proton resistance in different regions and the decrease of charge accumulation ability.

[0076] Further optimize the model according to the circular arc characteristics of the third frequency band: in the R-CPE unit of the above second frequency band model, add a polarization resistance R c =1.2Ω・cm 2 in parallel with CPE2. The fitting result shows that the polarization resistance parameter corresponding to the circular arc of the third frequency band is significant, and the value of R c is positively correlated with the radian of the circular arc, quantitatively representing the polarization strength of the hydrogen cross-permeation side reaction.

[0077] Example 2

[0078] This example verifies the recognition ability of the equivalent circuit model to the in-plane (XY direction) structure non-uniformity of the catalyst layer, and the specific steps are as follows:

[0079] (1) Select two groups of comparison samples, one group is a uniform catalyst layer sample without in-plane distribution (prepared by optimizing the spraying process to ensure that the ionomer and carbon skeleton are uniformly distributed in the plane), and the other group is a non-uniform catalyst layer sample with in-plane distribution (prepared by controlling the difference in spraying rate to simulate local uneven ionomer coating).

[0080] (2) Set the impedance test conditions: test temperature 80℃, anode / cathode dew point 40℃, bias voltage 0.5V, AC perturbation voltage amplitude ±50mV, frequency scanning range 50kHz to 0.1Hz, N2 is introduced on the cathode side to eliminate the interference of active reaction.

[0081] (3) Use the electrochemical workstation with FRA function to collect the Nyquist plots of the two groups of samples, the results are shown in Figure 3 , (I) is the Nyquist plot of the sample without in-plane distribution, (II) is the Nyquist plot of the sample with in-plane distribution, and the boundary characteristics of 45° line and 90° line are observed.

[0082] (4) Use Z-view software to construct an equivalent circuit model, on the basis of the first frequency band film resistance R mem and CPE in series, add 3 parallel R-CPE units, each R-CPE unit is composed of proton resistance R i and constant phase element CPE in series, and fit the impedance data of the two groups of samples.

[0083] (5) Analysis results: in the Nyquist plot of the sample without in-plane distribution, the boundary of 45° line and 90° line is clear, the difference of the parameters of the three R-CPE units obtained by fitting is small, and the difference of the dispersion coefficients of the three constant phase elements is less than 0.05, indicating that the proton resistance and charge accumulation characteristics of each region in the plane are consistent; in the Nyquist plot of the sample with in-plane distribution, the boundary of 45° line and 90° line is blurred, the difference of the parameters of the three R-CPE units obtained by fitting is significant, and the dispersion coefficient difference α of the three constant phase elements fluctuates more than 0.1, reflecting the difference between the distribution of ionomer and the dispersion of carbon skeleton in different regions in the plane.

[0084] Example 3

[0085] This example verifies the influence of inductance component on impedance spectrum and the inhibition effect of low humidification condition on inductance interference.

[0086] (1) Select two groups of the same MEA samples (low EW ionomer system, catalyst layer thickness 5μm) to ensure that the catalyst layer structures of the two groups of samples are consistent.

[0087] (2) Set two groups of test conditions, no inductance interference group: test temperature 80℃, anode / cathode dew point 40℃, bias voltage 0.5V, AC perturbation voltage amplitude ±50mV, frequency scanning range 50kHz to 0.1Hz, N2 is introduced on the cathode side; inductance interference group: anode / cathode dew point 60℃, the rest of the conditions are consistent with the no inductance group.

[0088] (3) Use the electrochemical workstation with FRA function to collect the Nyquist plots of the two groups of samples, the results are shown in Figure 4As shown, the focus is on the characteristics near the high frequency end.

[0089] (4) Result analysis: the high frequency end of the inductance interference group deviates from the real axis and shows a clear upward bending trend, which is the imaginary part offset caused by the inductive reactance. This phenomenon will affect the accurate identification of the membrane resistance, and part of the catalytic layer proton resistance may be miscounted into the membrane resistance. In addition, the phase shift caused by the inductive reactance will also increase the angle of the line segment in the impedance spectrum, which is originally about 45°, causing misjudgment of the proton resistance distribution in the thickness direction of the catalytic layer, seriously interfering with the judgment and analysis of the in-plane structure distribution. By moderately reducing the humidification condition and increasing the catalytic layer proton resistance value, the structure-related impedance component is more significant in the Nyquist diagram, thereby effectively suppressing the relative interference of the inductance term.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not limited thereto; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. An analysis method of a structure of a catalytic layer of a fuel cell, characterized by, The method comprises the following steps: S1, preparing a test battery, applying an alternating current disturbance voltage under a set condition, collecting complex impedance data of a full frequency band, and obtaining a Nyquist plot; S2, establishing a mapping relationship between key features of different frequency bands of the Nyquist plot and a catalyst layer structure, a first frequency band of 1 kHz to 100 Hz deviating from a 45° line corresponding to a thickness direction ionomer distribution of the catalyst layer, a second frequency band of 100 Hz to 10 Hz deviating from a 90° line corresponding to carbon skeleton agglomeration of the catalyst layer, a third frequency band of 10 Hz to 1 Hz corresponding to hydrogen cross-permeation, and determining a structural feature of the catalyst layer according to the measured Nyquist plot; S3, constructing an equivalent circuit model, fitting the measured Nyquist plot, and quantifying the structural feature of the catalyst layer through fitting parameters, the equivalent circuit model of the first frequency band being composed of a proton resistance, the equivalent circuit model of the second frequency band being extended on the basis of the equivalent circuit model of the first frequency band by adding a plurality of parallel R-CPE units composed of a proton resistance and a constant phase element in series, and the equivalent circuit model of the third frequency band being extended on the basis of the equivalent circuit model of the second frequency band by adding a polarization resistance in parallel with the constant phase element in the R-CPE unit.

2. The method of analyzing a catalytic layer structure of a fuel cell according to claim 1, characterized by, In the step S2, the impedance phase angle of the first frequency band is calculated by the formula θ=arctan(|Z'' / Z'|), wherein θ is the impedance phase angle, Z'' is the imaginary part of the impedance, and Z' is the real part of the impedance; when θ=45°, it is determined that the ionomer is uniformly distributed in the thickness direction of the catalyst layer, when θ>45°, it is determined that the ionomer is concentrated on the proton exchange membrane side in the thickness direction of the catalyst layer, and when θ<45°, it is determined that the ionomer is concentrated on the gas diffusion layer side in the thickness direction of the catalyst layer.

3. The method of claim 1, wherein the method is a method of analyzing a structure of a catalytic layer of a fuel cell. In the step S2, when the second frequency band deviates from the 90° line or appears bending, it is determined that the catalyst layer has carbon skeleton agglomeration.

4. The method of analyzing a catalytic layer structure of a fuel cell according to claim 1, characterized by, In the step S2, when the third frequency band appears a circular arc structure, it is determined that the catalyst layer has hydrogen cross-permeation.

5. The method of analyzing a catalytic layer structure of a fuel cell according to claim 1, characterized by, In the step S3, Z-view software is used for modeling and fitting.

6. The method of analyzing a catalytic layer structure of a fuel cell according to any one of claims 1 to 5, characterized in that, In the step S1, the set conditions include: inert gas is introduced into the cathode side of the test battery, the test temperature is 60-80℃, and the relative humidity is 10%-20%.

7. The method of analyzing a catalytic layer structure of a fuel cell according to claim 6, characterized by, In the step S1, the set conditions include: the bias voltage is 0.2-1V, and the amplitude of the alternating current disturbance voltage does not exceed 10% of the bias voltage.

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