Test method for evaluating corrosion resistance of metal bipolar plate coating of fuel cell

Abstract

The invention discloses a test method for evaluating corrosion resistance of a metal bipolar plate coating of a fuel cell, and belongs to the field of new energy material evaluation method testing. The invention provides a test method for evaluating the corrosion resistance of a metal bipolar plate coating, especially a bipolar plate coated with a carbon coating, by adopting a high-temperature accelerated corrosion test and combining a constant-potential corrosion test and electrochemical impedance. According to the method for testing the corrosion resistance of the fuel cell metal bipolar plate coating, the influence of shedding of a carbon-plated coating and formation of a metal oxide passivation film on the corrosion resistance of the electrode plate is comprehensively considered, the method is simple and convenient to operate, the performance of different metal coatings is evaluated through an electrochemical method, and the corrosion resistance of the electrode plate is tested. Comprising coating compactness and binding force strength, and the coating is rapidly screened.

Description

Technical Field

[0001] The invention belongs to the field of new energy material evaluation method testing, and in particular relates to a testing method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating. Background Art

[0002] Proton exchange membrane fuel cells are a clean and efficient energy device that can directly convert hydrogen energy into electrical energy. They have the advantages of fast startup, high conversion efficiency, high power density, and low-temperature operation. They can be widely used in transportation, backup power supplies, space equipment, and other fields. The bipolar plate is the core component of the proton exchange membrane fuel cell, and plays the role of supporting the membrane electrode, distributing the reaction gas, collecting current, and discharging the generated water in the stack. Among them, metal bipolar plates have the characteristics of ultra-thin materials, high mechanical strength, and suitable for batch forming. Due to their material characteristics, metal bipolar plates will undergo surface passivation during use, resulting in increased contact resistance, and are prone to corrosion, which will contaminate the membrane electrode and reduce its output performance. Therefore, it is necessary to coat a thin film on the surface to reduce its contact resistance and slow down the formation of the passivation film in order to extend the service life of the bipolar plate.

[0003] Amorphous carbon coating has the advantages of good conductivity and strong corrosion resistance. It has attracted the attention of academia and industry in recent years. However, in actual operation, there are still problems such as coating corrosion and shedding, and decreased conductivity. Therefore, it is necessary to evaluate its corrosion resistance in actual use.

[0004] The patent application with publication number CN117589664A discloses a system and method for testing the corrosion resistance of bipolar plates of proton exchange membrane fuel cells. The system includes: a heating device; a test cell, the test cell has a hollow accommodation space for containing test solutions and test samples, the top of the test cell is fixed with a reference electrode, a counter electrode, a temperature sensor and a condenser, and the other end of the condenser is connected to a gas collecting bottle; the side openings of the test cell are respectively connected to a liquid level tube and a peristaltic pump, the other end of the liquid level tube is connected to a gas collecting bottle, and the other end of the peristaltic pump is connected to a solution tank.

[0005] The patent application with publication number CN114018797A provides a method for testing the corrosion resistance of a fuel cell metal bipolar plate coating, comprising the following steps: (1) encapsulating the metal bipolar plate to be tested in an electrochemical corrosion test cell and adding a corrosion solution; (2) using a three-electrode measurement system to control polarization potential characteristic parameters, and the corrosion process of the metal bipolar plate coating of the fuel cell under simulated actual operating conditions; (3) analyzing and characterizing the coating of the metal bipolar plate, and finally evaluating the corrosion resistance of the coating based on the analysis results of contact resistance, ion release concentration, and film loss area after corrosion of the coating.

[0006] High-temperature accelerated corrosion resistance test is one of the commonly used methods to evaluate the corrosion resistance of metal bipolar plates, and can accurately evaluate the corrosion resistance of different metal bipolar plates. For metal bipolar plate coatings, after undergoing harsh durability tests, the coating will fall off on its surface. The formation and decomposition process of the transition layer metal oxide plating film has different electrochemical properties at different stages. The speed of coating shedding is closely related to the density and bonding strength of the coating. Most of the existing evaluation methods test the initial and final states of the plate coating, and lack corresponding monitoring tests on the processes of plate coating shedding and metal oxide plating film formation. Therefore, they cannot accurately reflect the speed of different coating shedding rates. Summary of the invention

[0007] The present invention adopts high temperature accelerated corrosion test, combined with constant potential corrosion test and electrochemical impedance, to provide a test method for evaluating the corrosion resistance of metal bipolar plate coatings, especially carbon-coated bipolar plates;

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0009] A test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating, the metal bipolar plate comprising a substrate, a metal transition layer and an amorphous carbon functional layer, comprising the following steps:

[0010] (1) Encapsulating the metal bipolar plate to be tested in an electrochemical corrosion test cell and adding a corrosion solution;

[0011] (2) subjecting the corrosion solution to oxygen bubbling treatment, and obtaining a treated sample by controlling the temperature of the corrosion solution to the operating temperature of the fuel cell cathode;

[0012] (3) The initial electrochemical properties of the treated samples were tested using a three-electrode system, including polarization curve test and constant potential electrochemical impedance spectroscopy test;

[0013] (4) subjecting the treated samples to a high voltage constant potential, and then conducting a polarization curve test and a constant potential electrochemical impedance test, recording the changes in corrosion current and electrochemical impedance in the polarization curve test, and dividing the test process into a coating shedding stage and a metal oxide passivation film formation stage according to the change trend of the corrosion current;

[0014] (5) The two stages divided in step (4) are subjected to high voltage constant potential action successively. After each stage, the sample is subjected to polarization curve test and constant potential electrochemical impedance test to evaluate the corrosion resistance of the fuel cell metal bipolar plate coating.

[0015] Metal-coated carbon bipolar plates are mainly composed of a substrate, a transition layer and a functional layer. Among them, the substrate is usually stainless steel, but direct use will precipitate metal ions and contaminate the membrane electrode, so a functional layer needs to be plated on its surface. Due to the high cost of gold plating, research focuses more on carbon-plated coatings. However, the carbon layer directly plated on the substrate is easy to fall off, so a transition layer is often added between the substrate and the carbon-plated functional layer.

[0016] In practical applications, metal-coated carbon bipolar plates face challenges such as acidic environment, the presence of F ions and high voltage. Under these conditions, the functional layers (such as aC and TiCx) are prone to fall off, and then a metal oxide (such as TiOx) passivation film is formed on the transition layer (such as Ti).

[0017] During this process, the electrochemical properties of the bipolar plate change significantly:

[0018] In the early stage of carbon coating peeling, with the formation of metal oxide passivation film, the corrosion current gradually increases, and the impedance also increases accordingly.

[0019] When the carbon coating is completely removed, the metal oxide will continue to decompose and precipitate under the continuous action of high voltage. At this time, the corrosion current will decrease, while the impedance will increase again.

[0020] In summary, the performance change of metal-coated carbon bipolar plates under complex usage environments is a dynamic process involving coating shedding, metal oxide formation and decomposition, and its corrosion current and impedance will change significantly accordingly.

[0021] The purpose of testing the initial electrochemical performance is to compare it with the polarization curve test and impedance data of the metal bipolar plate to be tested in step (4) to evaluate its corrosion resistance.

[0022] As a preferred embodiment, in step (1), the metal bipolar plate to be tested is cut into samples of a predetermined size, wherein the predetermined size is 2-4 cm×2-4 cm; after the corrosive solution is added, the contact area between the sample and the corrosive solution is a circle with a diameter of 1 cm.

[0023] Preferably, in step (1), the corrosive solution is an aqueous H2SO4 solution with a pH of 1-5, wherein the mass concentration of NaF is 0.1-10 ppm. NaF is highly corrosive to the carbon coating and can accelerate the corrosion of the carbon coating.

[0024] Preferably, in step (2), the oxygen bubbling treatment time is 30-60 minutes, and the temperature of the corrosion solution is regulated to 30-85° C. by circulating water.

[0025] Preferably, in step (3), the three-electrode system comprises a working electrode composed of the sample, a counter electrode composed of a platinum mesh, and a reference electrode composed of Ag / AgCl;

[0026] The voltage range of the polarization curve test is -0.5V to 1.4V, and the scanning rate is 2mV / s; the potential of the constant potential electrochemical impedance test is 0.6V, and the frequency is 10kHz to 0.01Hz.

[0027] Preferably, before the three-electrode system test in step (4), an open circuit test is performed on the treated sample for at least 30 minutes to remove impurities on the coating surface.

[0028] Preferably, in step (4), the working voltage of the high voltage constant potential test is 1.0-1.4 V vs. the reference electrode, and the test time is at least 2 h, so that the coating is completely removed and the metal oxide plating film is formed.

[0029] Preferably, the coating shedding stage is characterized by an increase in corrosion current with time and the appearance of an obvious inflection point; the metal oxide passivation film formation stage is characterized by a gradual decrease in corrosion current and a tendency toward stability.

[0030] Preferably, in step (5), the high voltage constant potential action time is reset according to the inflection point appearing in the polarization curve test; in the embodiment of the present invention, as an example, under the action of high potential, as time changes, the corrosion current of the carbon-plated coating increases first and then decreases, indicating that its corrosion process is a process of coating shedding and metal oxide plating film formation, and the inflection time is 2600s;

[0031] First, a high voltage constant potential effect is applied during the coating shedding stage, and after that, a polarization curve test and a constant potential electrochemical impedance test are performed. Then, a high voltage constant potential effect is applied during the metal oxide passivation film formation stage, and after that, a polarization curve test and a constant potential electrochemical impedance test are performed.

[0032] In the embodiment of the present invention, the coating shedding stage (stage 1) and the metal oxide passivation film formation stage (stage 2) are completed together under the action of constant potential, and then the changes in corrosion current and impedance before and after the experiment are tested; then the same sample is used to first conduct the stage 1 experiment, and then test its corrosion current and impedance, and then conduct the stage 2 experiment to test the corrosion current and impedance; the purpose of this is to distinguish the plate performance when the carbon coating is completely shed (after stage 1), and the plate performance after the metal oxide passivation film is precipitated and stabilized (after stage 2). If the test is not distinguished, there will only be data after the carbon coating is completely shed and the metal oxide passivation film is precipitated and stabilized, so the difference in the performance of different carbon functional layers cannot be accurately evaluated.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The corrosion resistance testing method of the fuel cell metal bipolar plate coating of the present invention comprehensively considers the effects of the shedding of the carbon coating and the formation of the metal oxide passivation film on the corrosion resistance of the plate. The method is simple to operate and uses electrochemical methods to evaluate the performance of different metal coatings, including the density of the coating and the strength of the bonding force, to quickly screen the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a high voltage constant potential time and current spectrum of Example 1 of the present invention;

[0036] Figure 2 This is a graph showing the change in corrosion current density before and after high voltage constant potential in Example 1 of the present invention;

[0037] Figure 3 This is a graph of electrochemical impedance changes before and after high voltage constant potential in Example 1 of the present invention;

[0038] Figure 4 This is the corrosion current density and impedance test spectrum after one stage under the action of segmented high voltage constant potential in Example 1 of the present invention;

[0039] Figure 5 This is the corrosion current density and impedance test spectrum after 2 stages under the action of segmented high voltage constant potential in Example 1 of the present invention. DETAILED DESCRIPTION

[0040] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0041] Example 1

[0042] (1) Cut the metal bipolar plate to be tested with a carbon coating (purchased from Shanghai Jie Hydrogen Technology Co., Ltd.) into two samples of 2 cm*2 cm size; first, encapsulate one sample in an electrochemical corrosion cell (commercially purchased), fill it with a prepared pH=3 sulfuric acid aqueous corrosion solution containing 0.1 ppm NaF, and completely immerse the sample coating, that is, expose an area of ​​a circle with a diameter of 1 cm to contact the corrosion solution, to ensure that the corrosion area of ​​each plate is consistent;

[0043] (2) The corrosion solution was bubbled with oxygen for 30 minutes, and then heated by circulating water in a high-temperature water bath to maintain the corrosion solution at 80°C; the sample was electrochemically tested using a three-electrode system (a working electrode composed of the sample, a counter electrode composed of a platinum mesh, and an Ag / AgCl reference electrode);

[0044] (3) First, an open circuit test is performed for 30 minutes to remove impurities on the coating surface, and then the polarization curve and constant potential electrochemical impedance are tested in the initial state. The voltage range of the polarization curve is -0.5 to 1.4V, the scan rate is 2mv / s, the impedance test potential is 0.6V, and the frequency is 10KHz to 0.01Hz; then a high voltage constant potential test is performed, the voltage is 1.4V, and the action time is 2h; after the test, the polarization curve and constant potential electrochemical impedance test are performed;

[0045] (4) Then, another sample is selected and assembled according to the above steps (1) to (2). The initial performance is tested in the same manner as step (3). The corrosion current change in the high voltage constant potential experiment in step (3) is compared with the inflection point of the curve, and the constant potential time is divided into two stages. The inflection point is used as the dividing point, and the high voltage constant potential action time of the two stages is reset. After each stage, the polarization curve and constant potential electrochemical impedance test are performed.

[0046] Example 1 The coating is composed of stainless steel as a substrate, titanium as a transition layer, and a functional layer of amorphous carbon. The contact resistance of the stainless steel is reduced by the amorphous carbon in the functional layer. Under the constant potential process, the corrosive solution contacts the titanium transition layer through the gaps in the coating, pitting occurs to form a metal oxide plating film, which is then continuously decomposed and precipitated, resulting in the shedding of the carbon functional layer. It can be seen from the test results that Figure 1 In the figure, under the action of high potential, the corrosion current of the carbon coating increases first and then decreases with the change of time, indicating that its corrosion process is a process of coating shedding and metal oxide plating film formation, and the inflection point time is 2600s;

[0047] Depend on Figure 2 and Figure 3 After the constant potential test, the corrosion current and impedance of the coating changed significantly. From the Tafel curve, it can be seen that the corrosion potential of the coating shifted to the left, and the corrosion current density increased from 0.17μA / cm 2 Increased to 0.404μA / cm 2 , indicating that the corrosion resistance of the coating is weakened; the impedance test shows that after constant potential, the charge transfer impedance of the coating is significantly reduced;

[0048] For phased testing, Figure 4 Compared with the initial coating performance, after 2600s of stage 1 constant potential test, its corrosion potential shifted to the left and the corrosion current increased; however, in its impedance test, the charge transfer impedance increased significantly, indicating that the formation of metal oxide passivation film can improve the corrosion resistance of the coating, but affect the contact resistance of the coating; Figure 5In the test, after the constant potential test in stage 2, the corrosion current increased slightly, but the charge transfer impedance decreased significantly. This shows that the metal oxide passivation film is continuously decomposed and precipitated under the action of high potential, which leads to a decrease in its charge transfer impedance and a decrease in the corrosion resistance of the coating.

Claims

1. A test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating, wherein the metal bipolar plate comprises a substrate, a metal transition layer and an amorphous carbon functional layer, characterized in that: The following steps are involved: (1) Encapsulating the metal bipolar plate to be tested in an electrochemical corrosion test cell and adding a corrosion solution; (2) subjecting the corrosion solution to oxygen bubbling treatment, and obtaining a treated sample by controlling the temperature of the corrosion solution to the operating temperature of the fuel cell cathode; (3) The initial electrochemical properties of the treated samples were tested using a three-electrode system, including polarization curve test and constant potential electrochemical impedance spectroscopy test; (4) subjecting the treated samples to a high voltage constant potential, and then conducting a polarization curve test and a constant potential electrochemical impedance test, recording the changes in corrosion current and electrochemical impedance in the polarization curve test, and dividing the test process into a coating shedding stage and a metal oxide passivation film formation stage according to the change trend of the corrosion current; (5) The two stages divided in step (4) are subjected to high voltage constant potential action successively. After each stage, the sample is subjected to polarization curve test and constant potential electrochemical impedance test to evaluate the corrosion resistance of the fuel cell metal bipolar plate coating.

2. The test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating according to claim 1, characterized in that: In step (1), the metal bipolar plate to be tested is cut into samples of a predetermined size, wherein the predetermined size is 2 to 4 cm×2 to 4 cm; After the corrosion solution is added, the contact area between the sample and the corrosion solution is a circle with a diameter of 1 cm.

3. The test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating according to claim 1, characterized in that: In step (1), the corrosion solution is a H2SO4 aqueous solution with a pH of 1-5, wherein the mass concentration of NaF is 0.1-10 ppm.

4. The test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating according to claim 1, characterized in that: In step (2), the oxygen bubbling treatment time is 30-60 minutes, and the temperature of the corrosion solution is adjusted to 30-85° C. by circulating water.

5. The test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating according to claim 1, characterized in that: In step (3), the three-electrode system comprises a working electrode composed of the sample, a counter electrode composed of a platinum mesh, and a reference electrode composed of Ag / AgCl; The voltage range of the polarization curve test is -0.5V to 1.4V, and the scanning rate is 2mV / s; the potential of the constant potential electrochemical impedance test is 0.6V, and the frequency is 10kHz to 0.01Hz.

6. The test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating according to claim 1, characterized in that: Before the three-electrode system test in step (4), an open circuit test is also performed on the treated sample, and the test time is at least 30 minutes.

7. The test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating according to claim 1, characterized in that: In step (4), the working voltage of the high voltage constant potential test is 1.0-1.4 V vs. the reference electrode, and the test time is at least 2 h.

8. The test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating according to claim 7, characterized in that: The coating shedding stage is characterized by an increase in corrosion current with time and the appearance of an obvious inflection point; the metal oxide passivation film formation stage is characterized by a gradual decrease in corrosion current and a tendency toward stability.

9. The test method for evaluating the corrosion resistance of a fuel cell metal bipolar plate coating according to claim 8, characterized in that: In step (5), the high voltage constant potential action time is reset according to the inflection point appearing in the polarization curve test; First, a high voltage constant potential effect is applied during the coating shedding stage, and after that, a polarization curve test and a constant potential electrochemical impedance test are performed. Then, a high voltage constant potential effect is applied during the metal oxide passivation film formation stage, and after that, a polarization curve test and a constant potential electrochemical impedance test are performed.

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