Method for evaluating quality of bipolar plate coating

Abstract

The invention provides a bipolar plate coating quality evaluation method, and relates to the technical field of fuel cells, and the evaluation method comprises the following steps: connecting a bipolar plate coated with a to-be-tested coating into a three-electrode system, carrying out a first impedance test on the bipolar plate, and carrying out a second impedance test on the bipolar plate; and sequentially carrying out polarization treatment and relaxation treatment on the bipolar plate after the first impedance test, carrying out second impedance test on the bipolar plate after the relaxation treatment, and carrying out calculation according to test results of the first impedance test and the second impedance test to determine whether the quality of the to-be-tested coating is qualified or not. According to the method for evaluating the quality of the bipolar plate coating, the evaluation time is short, the quality of the bipolar plate coating can be accurately evaluated, the service life of the coating can be judged, and the method has good practicability.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a method for evaluating the quality of bipolar plate coatings. Background Technology

[0002] PEMFC(Proton Exchange Membrane Fuel Cell ， Proton exchange membrane fuel cells (PEMFCs) are characterized by high efficiency, cleanliness, and reliability. In particular, their application in new energy vehicles gives cars the advantages of long driving range and short refueling time, making them comparable to gasoline vehicles.

[0003] Bipolar plates are one of the core components of PEMFCs, playing a crucial role in reactant gas separation and transport, current collection and conduction, and battery support. Currently, PEMFC bipolar plates can be classified into three main categories based on their materials: graphite bipolar plates, metal bipolar plates, and composite bipolar plates.

[0004] Metal bipolar plates possess advantages such as small size, high electrical conductivity, good airtightness, high mechanical strength, excellent processing performance, and low cost, making them considered the best choice for fuel cell vehicles, especially in terms of volumetric power density. However, the corrosion resistance and contact resistance of metal bipolar plates in actual operating environments are not ideal.

[0005] The main substrates of metal bipolar plates include aluminum, nickel, titanium, and stainless steel. Corrosion of metal bipolar plates has the following two main effects on PEMFCs:

[0006] 1. Corrosion and dissolution of metal ions can lead to catalyst poisoning, which in turn reduces the conductivity of the proton exchange membrane.

[0007] 2. The passivation film formed by corrosion increases the contact resistance between the metal bipolar plate and the diffusion layer, thus affecting the overall performance output of the battery. The formation of the passivation film can improve the corrosion resistance of the metal bipolar plate, but at the same time, the formation of the passivation film will lead to an increase in contact resistance. Therefore, the corrosion resistance and conductivity of the metal bipolar plate are contradictory.

[0008] In existing technologies, surface modification is one of the main approaches to improving the corrosion resistance and conductivity of metal bipolar plates. However, both domestically and internationally, the evaluation method for bipolar plate coatings generally involves maintaining a constant potential (0.84V@SHE) for 24 consecutive hours or a constant potential (1.6V@SHE) for 10 hours, followed by potentiodynamic testing of the coating's self-corrosion potential and self-corrosion current.

[0009] The current testing method has the following drawbacks:

[0010] 1. The testing time is relatively long, with the cumulative testing time for a single product requiring approximately 36 to 38 hours.

[0011] 2. Although it can be used to evaluate the quality of bipolar plate coatings, it cannot be used to evaluate the service life of the coatings. Summary of the Invention

[0012] In view of this, the present invention aims to provide a method for evaluating the quality of bipolar plate coatings, which has a short testing time and can be used to assess the service life of the coating.

[0013] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0014] A method for evaluating the quality of bipolar plate coatings, comprising:

[0015] A bipolar plate coated with the coating to be tested is connected to a three-electrode system, and the bipolar plate is subjected to the first impedance test.

[0016] The bipolar plate after the first impedance test is subjected to polarization treatment and relaxation treatment in sequence, and the bipolar plate is subjected to a second impedance test after the relaxation treatment.

[0017] The quality of the coating under test is determined by calculation based on the results of the first and second impedance tests.

[0018] Furthermore, the step of connecting the bipolar plate coated with the test coating to a three-electrode system and performing a first impedance test on the bipolar plate includes:

[0019] The bipolar plate coated with the test coating is connected to the three-electrode system, and the three-electrode system is connected to an electrochemical workstation.

[0020] The first impedance was obtained by performing a first impedance test on the bipolar plate using the electrochemical workstation.

[0021] Furthermore, the step of connecting the bipolar plate coated with the test coating to a three-electrode system, and connecting the three-electrode system to an electrochemical workstation, includes:

[0022] The bipolar plate coated with the coating to be tested is used as the working electrode and installed in an electrolytic cell containing a reference electrode, a counter electrode, and an electrolyte.

[0023] The electrolytic cell is placed in a grounded Faraday cage, the working electrode and the counter electrode are connected to a power source, and the working electrode, the reference electrode and the counter electrode are connected to the electrochemical workstation.

[0024] Furthermore, the reference electrode is a silver chloride electrode, and the counter electrode is a graphite electrode or a platinum electrode.

[0025] Furthermore, the electrolyte used is one that can accelerate the corrosion of the coating under test.

[0026] Furthermore, the first impedance test performed on the bipolar plate using the electrochemical workstation to obtain the first impedance includes:

[0027] The open-circuit potential of the bipolar plate was tested using the electrochemical workstation.

[0028] After the open-circuit potential of the bipolar plate stabilizes, the first impedance is obtained by performing an impedance test on the bipolar plate using the electrochemical workstation.

[0029] Furthermore, the polarization process includes:

[0030] A preset potential is applied to the bipolar plate for a preset time to polarize the bipolar plate at the cathode or the anode.

[0031] Furthermore, the preset potential is between 1V and -1V vs. SHE, and the preset time is between 20min and 60min.

[0032] Furthermore, the relaxation process includes relaxing the bipolar plate in an open-circuit state for a preset time; and / or,

[0033] The second impedance test includes:

[0034] The open-circuit potential of the bipolar plate was tested using an electrochemical workstation;

[0035] After the open-circuit potential of the bipolar plate stabilizes, the electrochemical workstation is used to perform an impedance test on the bipolar plate to obtain a second impedance.

[0036] Furthermore, the polarization process, the relaxation process, and the second impedance test cycle after the relaxation process are performed a preset number of times;

[0037] The calculation based on the test results of the first impedance test and the second impedance test to determine whether the quality of the coating under test is qualified includes:

[0038] The quality of the coating under test is determined to be qualified when the calculated result is less than the preset result, based on the test results of the first impedance test and the second impedance test.

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] The bipolar plate coating quality evaluation method of the present invention polarizes the bipolar plate, which can accelerate the corrosion of the coating and shorten the evaluation time. After polarization is completed, the bipolar plate is allowed to relax for a period of time to restore its equilibrium state before a second impedance test is performed, which helps to improve the accuracy of the test.

[0041] This evaluation method involves performing two impedance tests sequentially. If the impedance data from the two tests are similar, it indicates that the coating exhibits good stability and corrosion resistance under polarization conditions. Conversely, a significant difference in impedance data suggests defects in the coating or poor adhesion between the coating and the substrate. This method assesses the coating quality of the bipolar plate based on the impedance results of the two tests, providing a relatively accurate evaluation and determining the coating's lifespan. This method offers advantages such as ease of operation, accurate and reliable results, and time savings, reducing operation time by more than 3.5 hours compared to existing methods.

[0042] Furthermore, placing the electrolytic cell of the three-electrode system within a grounded Faraday cage eliminates interference from external electromagnetic fields, thus improving test accuracy. A Faraday cage is a closed structure made of a conductive material (such as metal). When grounded, it forms an electrostatic shield that blocks the influence of external electric fields on the internal test environment, ensuring the accuracy and reliability of the electrochemical test. A bipolar plate is used as the working electrode and connected to the electrolytic cell containing a reference electrode and a counter electrode. The reference electrode provides a stable potential reference, while the counter electrode transmits current. During the electrochemical test, the reference electrode provides a stable potential reference point for measuring the potential changes of the working electrode.

[0043] The reference electrode is a silver chloride electrode, which has a stable potential and good reproducibility, and is suitable for various electrolyte solutions and testing conditions. The counter electrode (also called the auxiliary electrode) is mainly used to transfer current and can form a complete electrochemical circuit together with the working electrode (i.e., the bipolar plate being measured). A graphite electrode is used for the counter electrode, which has good conductivity and chemical stability, is suitable for various electrolyte solutions, and is relatively inexpensive and easy to process and manufacture. Alternatively, a platinum electrode can be used as the counter electrode, as it has excellent catalytic performance and chemical stability, and is suitable for various electrochemical testing conditions. The platinum electrode has a wide potential range, allowing for stable electrochemical testing over a broad potential range. The selection of the reference and counter electrodes ensures the accuracy and reliability of the test results.

[0044] Furthermore, selecting an electrolyte that accelerates the corrosion of the coating under test for electrochemical testing can significantly shorten the testing time and save on testing costs. Moreover, before performing the first impedance test on the bipolar plate, measuring its open-circuit potential and allowing it to stabilize helps assess the bipolar plate's corrosion tendency, determine its passivation state, and ensure the stability of the test system, thereby improving the accuracy and reliability of the impedance test.

[0045] During the polarization process of the bipolar plate, a preset potential is applied to the bipolar plate within a preset time. This helps to stably and rapidly corrode the coating of the bipolar plate. The preset potential and preset time are limited because the preset voltage affects the safety of the test; a suitable preset potential helps prevent electric shock, short circuits, or other safety issues. The preset time directly affects the electrochemical reaction process of the coating on the bipolar plate surface. Too short a preset time may not fully reflect the electrochemical performance of the coating, while too long a preset time may lead to severe corrosion or passivation of the coating. Therefore, limiting the preset time to 20-60 minutes helps ensure the accuracy and reliability of the test results.

[0046] During the second impedance test, the open-circuit potential is the potential of the bipolar plate (working electrode) under open-circuit conditions (i.e., when no current flows). It reflects the electrochemical equilibrium state between the electrode and the electrolyte solution. By monitoring the change in open-circuit potential, it can be determined whether the bipolar plate has returned to a stable state, thus determining when to conduct the next impedance test. Performing the second impedance test after the open-circuit potential has stabilized helps ensure the accuracy and reliability of the test.

[0047] By performing a preset number of cycles of polarization treatment, relaxation treatment, and a second impedance test after relaxation treatment, this method performs an impedance test after each cycle, which can effectively evaluate whether the coating quality of the bipolar plate is qualified. This method has the advantages of high accuracy and good repeatability. Attached Figure Description

[0048] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0049] Figure 1 This is an exemplary flowchart of a bipolar plate coating quality evaluation method according to an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the three-electrode system described in an embodiment of the present invention;

[0051] Figure 3 This is a timing current curve obtained during bipolar plate testing in an embodiment of the present invention.

[0052] Explanation of reference numerals in the attached figures:

[0053] 1. Counter electrode; 2. Temperature sensor; 3. Reference electrode; 4. Working electrode; 5. Faraday cage. Detailed Implementation

[0054] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0055] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0056] Furthermore, in the description of this invention, unless otherwise explicitly defined, the terms "installation," "connection," "linking," and "connector" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention in light of the specific circumstances.

[0057] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0058] The performance evaluation method for surface-modified coatings on metal bipolar plates is a test of the surface modification effect. The reasonable selection of the performance evaluation method and the standardization of operation will directly affect the further research of modification methods and the application of surface modification materials. It is also an important means to ensure the quality of bipolar plates and improve product quality.

[0059] For the reasons mentioned above, in order to accurately evaluate the actual use of the coating and lay a reliable testing foundation for the development of fuel cells and new materials, this embodiment mentions a method for evaluating the quality of bipolar plate coatings. This method is mainly based on electrochemical methods to polarize the bipolar plate and combining the tested impedance value of the bipolar plate to evaluate the coating quality on the bipolar plate.

[0060] An exemplary flowchart of the bipolar plate coating quality evaluation method of this embodiment is shown below. Figure 1 As shown, the method mainly includes the following steps:

[0061] S101. Connect the bipolar plate coated with the coating to be tested to the three-electrode system and perform the first impedance test on the bipolar plate.

[0062] S102. After the first impedance test, the bipolar plate is subjected to polarization treatment and relaxation treatment in sequence, and after the relaxation treatment, the bipolar plate is subjected to a second impedance test.

[0063] In this step, polarizing the bipolar plate can accelerate the corrosion of the coating, resulting in a shorter time for the evaluation method. Relaxation refers to the process of gradually returning to the equilibrium state from a certain state during a gradual physical process. After polarization, let the bipolar plate relax for a period of time to restore its equilibrium state, and then conduct the second electrochemical impedance test, which is beneficial to improving the accuracy of the test.

[0064] S103. Calculate based on the test results of the first impedance test and the second impedance test to determine whether the quality of the待测 coating is qualified. In this evaluation method, if the impedance data differences between the two tests are small, it indicates that the coating has good stability and corrosion resistance under polarization conditions. If the impedance data differences between the two tests are large, it indicates that there are defects in the coating or the bonding force between the coating and the substrate is poor.

[0065] Specifically, calculate based on the test result of the first impedance test and the test result of the second impedance test to obtain a calculation result. When the calculation result is less than the preset result, determine that the quality of the待测 coating is qualified.

[0066] The specific calculation method is to calculate the difference between the first impedance test result and the second impedance test result, and the calculation result is called the actual impedance difference. More specifically, based on the test results of multiple tests, set a standard preset impedance difference. When the actual impedance difference between the two tests is less than the standard preset impedance difference, determine that the coating quality of the bipolar plate is qualified, otherwise it is unqualified. Here, the preset impedance difference is the aforementioned preset result.

[0067] This method evaluates the coating quality of the bipolar plate based on the impedance results of the two tests, and the evaluation result is relatively accurate, and can relatively accurately judge the service life of the coating. This method has the advantages of simple operation, accurate and reliable results, etc.

[0068] In the evaluation method of this embodiment, the impedance of the first test and the impedances of subsequent second tests can all be obtained from the electrochemical impedance spectrum (Electrochemical Impedance Spectroscopy, EIS) measured by the electrochemical workstation. When performing each impedance test, record the test time.

[0069] In addition to directly judging whether the coating quality of the bipolar plate is qualified based on the impedance difference between the two tests, it is also possible to calculate the difference between the impedance of the first test and the impedance value of the last second test as the measured impedance difference, divide the measured impedance difference by the time difference between the two tests, and use this as the corrosion rate of the bipolar plate coating. Compare the measured corrosion rate with the preset corrosion rate. When the measured corrosion rate is less than the preset corrosion rate, determine that the coating quality of the bipolar plate is qualified, otherwise it is unqualified.

[0070] The measured corrosion rate is the result calculated based on the results of the first impedance test and the second impedance test, while the preset corrosion rate is the aforementioned preset result.

[0071] Specifically, step S101 above includes:

[0072] S1011. Connect the bipolar plate coated with the test coating to the three-electrode system, and connect the three-electrode system to the electrochemical workstation.

[0073] S1012. The first impedance test of the bipolar plate is performed using an electrochemical workstation to obtain the first impedance.

[0074] As a preferred embodiment, step S1011 above includes,

[0075] S10111, Press Figure 2 The structure shown uses a bipolar plate coated with the coating to be tested as the working electrode 4, which is installed in an electrolytic cell containing a reference electrode 3, a counter electrode 1, and an electrolyte.

[0076] S10112. Place the electrolytic cell in the grounded Faraday cage 5, connect the working electrode 4 and the counter electrode 1 to the power supply respectively, and connect the working electrode 4, the reference electrode 3 and the counter electrode 1 to the electrochemical workstation respectively.

[0077] In step S10111 above, the reference electrode 3 is used to provide a stable potential reference, the counter electrode 1 is used to transmit current, and the working electrode 4 is placed at the bottom of the electrolytic cell. In order to improve the accuracy of the evaluation results, as a preferred embodiment, in the electrolytic cell mentioned in step S10111 above, the reference electrode 3 is a silver chloride electrode, and the counter electrode 1 is a graphite electrode or a platinum electrode.

[0078] It should be noted that in electrochemical testing, reference electrode 3 is used to provide a stable potential reference point for measuring the potential change of working electrode 4. Reference electrode 3 is a silver chloride electrode, which has a stable potential and good reproducibility, and is suitable for various electrolyte solutions and testing conditions.

[0079] The counter electrode 1 (also known as the auxiliary electrode or counting electrode) is mainly used to transfer current and can form a complete electrochemical circuit together with the working electrode 4 (i.e., the bipolar plate being measured). In this method, the counter electrode 1 is a graphite electrode, which has good conductivity and chemical stability, is suitable for a variety of electrolyte solutions, and is relatively inexpensive and easy to process and manufacture.

[0080] The counter electrode 1 is a platinum electrode, which possesses excellent catalytic performance and chemical stability, making it suitable for various electrochemical testing conditions. The platinum electrode has a wide potential range, enabling stable electrochemical testing over a broad potential spectrum. The selection of reference electrode 3 and counter electrode 1 as described above ensures the accuracy and reliability of the test results.

[0081] Meanwhile, as a preferred embodiment, the electrolyte in the electrolytic cell is an electrolyte that can accelerate the corrosion of the coating under test, which can significantly shorten the testing time and save testing costs. In this embodiment, the preferred embodiment uses NaCl solution as the electrolyte, which is a neutral electrolyte, making the testing process safer and effectively accelerating the corrosion of the bipolar plate coating, thus saving testing time.

[0082] It should be noted that the electrolyte plays a role in transferring ions in the three-electrode system, which is the basis for the electrochemical reaction to take place. The properties of the electrolyte directly affect the rate, efficiency and stability of the electrochemical reaction.

[0083] In a preferred embodiment, the concentration of the NaCl solution is 3% to 4%, for example, it can be 3%, 3.5%, 4%, etc. It should be understood that, in addition to NaCl solution, acidic electrolytes such as sulfuric acid (H2SO4) and hydrochloric acid (HCl) can also be used, or alkaline electrolytes such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) can be used.

[0084] It should be noted that in this embodiment, a temperature sensor 2 is also inserted into the electrolyte in the electrolytic cell to facilitate monitoring the electrolyte temperature. Since the electrolyte temperature has a certain impact on the evaluation results of this evaluation method, preferably, the electrolyte temperature can be controlled by a temperature control device. In a preferred embodiment, the electrolyte temperature is controlled between 20°C and 30°C, such as 20°C, 25°C, or 30°C, to improve the accuracy of the test results.

[0085] In step S10112, the working electrode 4 and the counter electrode 1 are connected to the positive and negative terminals of the power supply, respectively, while the working electrode 4, the reference electrode 3, and the counter electrode 1 are connected to the electrochemical workstation, and the connection method refers to the prior art.

[0086] To obtain more accurate test results, as a preferred implementation method, the following method is still referred to. Figure 2As shown in step S10112 above, the reason for placing the electrolytic cell in the grounded Faraday cage 5 is that the Faraday cage 5 is a closed structure made of conductive material (metallic material, such as copper or aluminum). When it is grounded, it can form an electrostatic shielding layer. This shielding layer can block the influence of external electric fields on the internal test environment, thereby ensuring the accuracy and reliability of electrochemical testing. In the evaluation method of this embodiment, placing the electrolytic cell of the three-electrode system in the grounded Faraday cage 5 can eliminate the interference of external electromagnetic fields and help improve the accuracy of the test.

[0087] Specifically, step S1012 above includes:

[0088] S10121. Test the open-circuit potential of the bipolar plate using an electrochemical workstation;

[0089] It should be noted that the electrochemical workstation mentioned in this embodiment is preferably a Gamry electrochemical workstation.

[0090] S10122. After the open-circuit potential of the bipolar plate has stabilized, the impedance of the bipolar plate is tested using an electrochemical workstation to obtain the first impedance.

[0091] It should be noted that, in the above method, before performing the first impedance test on the bipolar plate, the open-circuit potential of the bipolar plate is tested until the open-circuit potential remains stable. This helps to assess the corrosion tendency of the bipolar plate, determine the passivation state, and ensure the stability of the test system, thereby improving the accuracy and reliability of the impedance test.

[0092] As a preferred embodiment, the aforementioned polarization process includes: applying a preset potential to the bipolar plate for a preset time to polarize the bipolar plate at the cathode or the anode.

[0093] In a preferred embodiment, the preset potential applied to the bipolar plate is a constant potential, which helps to stably and rapidly etch the coating of the bipolar plate, while the degree and duration of polarization should be determined according to the specific coating and testing requirements.

[0094] It should be noted that in this step, the preset potential range applied is preferably between 1V and -1V vs. SHE. It should be understood that the applied potential can be a constant potential or fluctuate according to a certain regular curve. When applying a constant potential, the applied potential can be, for example, 1V, 0.5V, -0.5V, -1V, etc.

[0095] Meanwhile, as a preferred embodiment, the aforementioned preset time is 20 min to 60 min, such as 20 min, 30 min, 40 min, 50 min, or 60 min. The reason for limiting the preset time is that the preset time is actually the time during which polarization occurs. The length of the polarization time directly affects the electrochemical reaction process of the coating on the surface of the bipolar plate. Too short a preset time may not be able to fully reflect the electrochemical performance of the coating, while too long a preset time may lead to severe corrosion or passivation of the coating. Therefore, limiting the preset time to 20 min to 60 min helps to ensure the accuracy and reliability of the test results.

[0096] In a preferred embodiment, in step S102 above, the relaxation process includes relaxing the bipolar plate in an open-circuit state for a preset time.

[0097] Here, the relaxation time of the bipolar plate is at least 2 hours. For example, during the test of the open-circuit potential of the bipolar plate, if the potential is found to stabilize within 3 hours, the next stage of testing can begin. As for determining whether the potential is stable, for example, the change in potential within a preset time can be calculated. If the change in potential within the preset time is less than the set value, the potential can be determined to be stable, for example, no change in potential within 5 minutes.

[0098] In a preferred embodiment, the second impedance test in step S102 above includes:

[0099] The open-circuit potential of the bipolar plate was tested using an electrochemical workstation.

[0100] After the open-circuit potential of the bipolar plate stabilizes, an impedance test is performed on the bipolar plate using an electrochemical workstation to obtain the second impedance.

[0101] Preferably, before performing the second impedance test on the bipolar plate, the open-circuit potential of the bipolar plate is measured in real time during the relaxation process until the open-circuit potential remains stable. It should be noted that the reason for measuring the open-circuit potential of the bipolar plate in real time is to help determine when the open-circuit potential can stabilize. The open-circuit potential is the potential of the bipolar plate (working electrode 4) under open-circuit conditions (i.e., when no current flows), which can reflect the electrochemical equilibrium state between the electrode and the electrolyte solution.

[0102] Therefore, by monitoring the change in open circuit potential, it is possible to determine whether the bipolar plate has returned to a stable state, thereby determining when to conduct the next impedance test. Conducting the second impedance test after the open circuit potential has stabilized helps to ensure the accuracy and reliability of the test.

[0103] As a preferred embodiment, the polarization treatment and relaxation treatment, as well as the second impedance test after the relaxation treatment, are repeated a preset number of times. The aforementioned step S103 specifically includes calculating, based on the test results of the first impedance test and the test results of the last second impedance test, whether the quality of the coating to be tested is qualified. The specific calculation method is still as described above and will not be repeated here.

[0104] It should be understood that by repeatedly performing the bipolar plate polarization, relaxation treatment, and second impedance test after relaxation treatment, this evaluation method, which involves performing an impedance test after each cycle, can effectively assess whether the coating quality of the bipolar plate is up to standard. This evaluation method has advantages such as high accuracy and good repeatability, and has broad application prospects in the field of electrochemical testing.

[0105] In a preferred embodiment, the preset number of times for the polarization treatment, relaxation treatment, and the second impedance test cycle after relaxation treatment is 2. It should be understood that the preset number of times can be other than 2, such as 1, 3, 4, etc.

[0106] Next, the coating quality of the bipolar plate will be evaluated using the evaluation method described above.

[0107] On bipolar plates with nickel as the substrate, Pt (platinum) or Au (gold) is generally coated, and the coating thickness is generally 50nm to 200nm. In this test, three types of bipolar plates were selected: a platinum bipolar plate with a coating thickness of about 100nm, a platinum bipolar plate with a coating thickness of about 150nm, and a gold bipolar plate with a coating thickness of about 50nm. The quality of the three types of bipolar plates was evaluated in turn.

[0108] Connect the bipolar plate to the three-electrode system. Also, connect the regulated power supply and the Gamry electrochemical workstation. Use a 3.5% NaCl solution as the electrolyte. Use a silver chloride electrode as the reference electrode 3 (3) and a graphite electrode as the counter electrode 1 (1).

[0109] First, the open-circuit potential of the bipolar plate in the three-electrode system is tested. After the potential stabilizes, the EIS of the first test sample is measured, which is the EIS of the test sample in its initial state.

[0110] Next, constant potential polarization is performed. In this embodiment, the potential polarization is specifically cathodic polarization, with an applied polarization potential of 0.84V vs. SHE for a duration of 30 minutes. Figure 3 In the figure, the horizontal axis represents time and the vertical axis represents current density. It can be observed that the current density gradually decreases with increasing time, indicating that continuous constant potential polarization has an impact on the coating.

[0111] After polarizing each sample, allow it to relax for 2 hours while simultaneously measuring its open-circuit potential. After 2 hours, the potential stabilizes. The EIS of the second test sample is then measured, which is the EIS of the polarized sample. Then, steps S102 and S103 are repeated once.

[0112] Test results show that the low-frequency impedance modulus decreases slightly with increasing cycle number, indicating that cathodic polarization leads to the formation of an electric double layer on the coating surface, which reduces conductivity. Comparison of the high-frequency impedance of samples before and after polarization reveals an increasing trend in high-frequency impedance, suggesting that the polarization-altered surface state of the bipolar plate coating can form a stable electric double layer structure, thereby reducing corrosion current.

[0113] Subsequently, calculations were performed using the method described above in this embodiment, and the final calculated corrosion rates were 0.0149 mΩ / h, 0.0157 mΩ / h, and 0.288 mΩ / h, respectively.

[0114] After performing electrochemical impedance spectroscopy analysis on the bipolar plates of the fuel cells that have been in operation on the vehicle for a certain period of time, and performing electrochemical impedance spectroscopy analysis on multiple samples according to the method described in this embodiment, the reference value for corrosion rate was determined by comparison. For example, it can be 0.05 mΩ / h. The corrosion rates measured for the three types of bipolar plates are all lower than the reference value for corrosion rate, which proves that the quality of the three types of samples is qualified.

[0115] It should be understood that the reference value for corrosion rate can be determined based on actual test results, and no specific limitation is made in this embodiment. According to the evaluation method for bipolar plate coating quality in this embodiment, the test results show little difference from the performance of the bipolar plate on the fuel cell stack or the entire vehicle, and can be used to accurately assess the quality of the bipolar plate coating.

[0116] It should be noted that the aforementioned preset corrosion rate was obtained by comparing the bipolar plates of the fuel cell on the vehicle with EIS analysis after working for a certain period of time. Therefore, the evaluation method for the bipolar plate coating quality according to this embodiment can establish test conditions based on the relationship between offline testing and vehicle performance. It is more practical than national standards or DOE standards and can accurately determine the service life of the coated bipolar plates in different items.

[0117] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for evaluating the quality of bipolar plate coatings, characterized in that, The method includes: A bipolar plate coated with the coating to be tested is connected to a three-electrode system, and the bipolar plate is subjected to the first impedance test. The bipolar plate after the first impedance test is subjected to polarization treatment and relaxation treatment in sequence, and the bipolar plate is subjected to a second impedance test after the relaxation treatment. The quality of the coating under test is determined by calculation based on the results of the first and second impedance tests.

2. The method for evaluating the quality of bipolar plate coatings according to claim 1, characterized in that, The step of connecting a bipolar plate coated with the test coating to a three-electrode system and performing a first impedance test on the bipolar plate includes: The bipolar plate coated with the test coating is connected to the three-electrode system, and the three-electrode system is connected to an electrochemical workstation. The first impedance was obtained by performing a first impedance test on the bipolar plate using the electrochemical workstation.

3. The method for evaluating the quality of bipolar plate coatings according to claim 2, characterized in that, The step of connecting the bipolar plate coated with the test coating to a three-electrode system and connecting the three-electrode system to an electrochemical workstation includes: The bipolar plate coated with the coating to be tested is used as the working electrode (4) and installed in an electrolytic cell having a reference electrode (3), a counter electrode (1) and an electrolyte. The electrolytic cell is placed in a grounded Faraday cage (5), the working electrode (4) and the counter electrode (1) are connected to the power supply respectively, and the working electrode (4), the reference electrode (3) and the counter electrode (1) are connected to the electrochemical workstation respectively.

4. The method for evaluating the quality of bipolar plate coatings according to claim 3, characterized in that: The reference electrode (3) is a silver chloride electrode, and the counter electrode (1) is a graphite electrode or a platinum electrode.

5. The method for evaluating the quality of bipolar plate coatings according to claim 3, characterized in that: The electrolyte used is one that can accelerate the corrosion of the coating under test.

6. The method for evaluating the quality of bipolar plate coatings according to claim 2, characterized in that, The first impedance test of the bipolar plate performed using the electrochemical workstation to obtain the first impedance includes: The open-circuit potential of the bipolar plate was tested using the electrochemical workstation. After the open-circuit potential of the bipolar plate stabilizes, the first impedance is obtained by performing an impedance test on the bipolar plate using the electrochemical workstation.

7. The method for evaluating the quality of bipolar plate coatings according to claim 1, characterized in that, The polarization process includes: A preset potential is applied to the bipolar plate for a preset time to polarize the bipolar plate at the cathode or the anode.

8. The method for evaluating the quality of bipolar plate coatings according to claim 7, characterized in that: The preset potential is between 1V and -1V vs. SHE, and the preset time is between 20min and 60min.

9. The method for evaluating the quality of bipolar plate coatings according to claim 1, characterized in that: The relaxation process includes relaxing the bipolar plate in an open-circuit state for a preset time. And / or, The second impedance test includes: The open-circuit potential of the bipolar plate was tested using an electrochemical workstation; After the open-circuit potential of the bipolar plate stabilizes, the electrochemical workstation is used to perform an impedance test on the bipolar plate to obtain a second impedance.

10. The method for evaluating the quality of bipolar plate coatings according to any one of claims 1-9, characterized in that: The polarization process, the relaxation process, and the second impedance test cycle after the relaxation process are performed a preset number of times. The calculation based on the test results of the first impedance test and the second impedance test to determine whether the quality of the coating under test is qualified includes: The quality of the coating under test is determined to be qualified when the calculated result is less than the preset result, based on the test results of the first impedance test and the second impedance test.

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