An accelerated testing method for the durability of metal bipolar plates in proton exchange membrane fuel cells

Abstract

The present invention provides a proton exchange membrane fuel cell metal bipolar plate durability accelerated test method, including: S1, building a metal bipolar plate durability accelerated test system; S2, selecting the working conditions of the metal bipolar plate durability accelerated test according to the actual working conditions corresponding to the use of the proton exchange membrane fuel cell; S3, using a preset fixed durability test time as the termination index of the metal bipolar plate durability test; S4, testing the performance assessment items of the metal bipolar plate to be tested at fixed time intervals until the test termination index is reached; S5, drawing a relationship curve between the test time and the bipolar plate performance change according to the obtained performance assessment results of the metal bipolar plate to be tested, and qualitatively analyzing and evaluating the durability of the metal bipolar plate. The present invention uses a dynamic potential working condition to perform durability testing, which provides an important theoretical basis for the design and development of metal bipolar plates and material selection.

Description

Technical Field

[0001] The present invention relates to a proton exchange membrane fuel cell, and in particular to a proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method. Background Art

[0002] In recent years, with the continuous development of industry, energy depletion and environmental pollution have become increasingly prominent. Hydrogen energy and fuel cell technology are recognized as one of the effective solutions. Among them, proton exchange membrane fuel cells (PEMFCs) have the advantages of low operating temperature, zero emissions, high specific power and high energy conversion rate, and have broad prospects in the fields of automotive power supply, portable devices and aviation.

[0003] PEMFCs are mainly composed of bipolar plates, membrane electrode assemblies, end plates and seals. As the core multifunctional component of PEMFCs, bipolar plates play the role of uniformly distributing gas, draining water, conducting heat and electricity. Their mass accounts for 60% of the entire fuel cell and their cost accounts for 15% to 20%. Their performance and cost will directly affect the service life and commercialization process of the battery. An ideal bipolar plate should have high electrical and thermal conductivity, corrosion resistance, mechanical strength, air tightness and hydrophobicity, as well as low cost and easy processing.

[0004] Traditional graphite plates are gradually being replaced by metal bipolar plates with strong machinability, excellent electrical and thermal conductivity, and good mechanical properties due to their large size, high manufacturing cost, and poor mechanical properties. However, in the acidic, high potential, wet and hot cycle, and air environment of the battery, metal bipolar plates are prone to corrosion. The metal ions formed during the corrosion process will cause the ion transfer efficiency of the proton exchange membrane to decrease. At the same time, the passivation film formed on the surface of the metal bipolar plate will increase the interfacial contact resistance (ICR), thereby causing the performance of the fuel cell to decrease. Therefore, the durability of the bipolar plate is still a bottleneck that hinders its further commercial application in PEMFCs.

[0005] In order to improve the service life of bipolar plates, we should first establish a systematic and reliable method for rapid testing and evaluation of bipolar plate durability, and test and analyze the material system and structure of existing metal bipolar plates, so as to provide an important theoretical basis for the design, development and material selection of new high-durability metal bipolar plates.

[0006] The Chinese patent application number CN202010068832.2 discloses a constant potential accelerated test and evaluation method for the durability of fuel cell metal bipolar plates. This invention uses an accelerated corrosion test method to test the durability of fuel cell metal bipolar plates, which can quickly and conveniently evaluate the actual service life of newly developed metal bipolar plates and reduce the high R&D costs generated by in-situ testing.

[0007] When the accelerated test method used in the above patent is implemented, air is introduced into the corrosion tank, the accelerating potential adopts a 1.5V constant potential electrochemical test method, the circulating water temperature is 90°C, the corrosion solution in the corrosion tank is a pH=1, and the concentration of 200ppm F ion solution, the test time is not limited, and the test is terminated when the termination conditions are met.

[0008] The design of this condition is obviously different from the actual operating conditions of the battery, and cannot truly reflect the potential environment of the metal bipolar plate during the actual operation of the battery. The potential of the actual operation of the battery is maintained at 0.6-0.85V most of the time, and rarely reaches a high potential of 1.5V. In addition, the potential of the battery stack is a dynamic process that is constantly changing during actual operation. Based on the constant potential working conditions assumed in this patent, the test results cannot accurately reflect the actual service life of the bipolar plate, nor can they truly reflect the changes in the metal bipolar plate during the in-situ test. Summary of the invention

[0009] According to the above-mentioned technical problem that the test results under constant potential conditions cannot accurately reflect the actual service life of the bipolar plate, nor can they truly reflect the change process of the metal bipolar plate during the in-situ test, a proton exchange membrane fuel cell metal bipolar plate durability accelerated test method is provided. The present invention mainly utilizes an electrochemical workstation to simulate the actual operation process of the fuel cell in a three-electrode system, and uses a dynamic potential condition to perform a durability test on it, providing an important theoretical basis for the design and development of metal bipolar plates and material selection.

[0010] The technical means adopted by the present invention are as follows:

[0011] A proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method, comprising:

[0012] S1. Build a metal bipolar plate durability accelerated test system;

[0013] S2. Selecting the working conditions for the metal bipolar plate durability accelerated test according to the actual working conditions corresponding to the use of the proton exchange membrane fuel cell, including selecting the main working condition interval or the full working condition interval that has an impact on the durability of the metal bipolar plate in actual application, and compiling the corresponding potential-time working conditions as the dynamic potential working conditions for the metal bipolar plate durability test, wherein the main working condition interval is selected according to the preset metal bipolar plate durability change amplitude threshold;

[0014] S3, using a preset fixed durability test time as a termination indicator for the metal bipolar plate durability test;

[0015] S4, using the metal bipolar plate to be tested as the working electrode of the metal bipolar plate durability accelerated test system, performing a durability test according to the dynamic potential working condition, and testing the performance assessment items of the metal bipolar plate to be tested at fixed time intervals until the termination index of the test is reached;

[0016] S5. Draw a curve of the relationship between the test time and the performance change of the bipolar plate based on the performance assessment results of the metal bipolar plate to be tested. By comparing the corresponding test time and the performance change curves of the bipolar plate obtained under the same time durability test conditions for different materials, the durability of the metal bipolar plate is qualitatively analyzed and evaluated.

[0017] Furthermore, the metal bipolar plate durability accelerated test system includes an electrolytic cell, an electrochemical workstation, a host computer, a super constant temperature water tank, a gas cylinder, and auxiliary wires;

[0018] The electrolytic cell comprises an inner cavity and an outer cavity, wherein the inner cavity is used to contain electrolyte, and a working electrode and a counter electrode are respectively arranged on the side walls thereof, and three openings communicating with the atmosphere are arranged above the inner cavity, which are respectively used to insert an air guide tube, a reference electrode and serve as an air outlet;

[0019] The electrolyte is connected to the electrochemical workstation through the working electrode, the counter electrode and the reference electrode;

[0020] The outer cavity is connected to the super constant temperature water tank through a hose.

[0021] Furthermore, the counter electrode is made of a platinum mesh, and the reference electrode is made of a saturated calomel electrode or a hydrogen electrode.

[0022] Furthermore, the actual operating conditions include the International Electrotechnical Commission standard vehicle fuel cell stack durability bench test cycle conditions, the U.S. Department of Energy vehicle fuel cell stack durability bench test cycle conditions, Chinese urban bus cycle conditions and new European driving conditions.

[0023] Furthermore, the preset fixed durability test time is 20h, 40h, 60h or 100h.

[0024] Furthermore, when measuring the durability of the cavity plate of the metal bipolar plate, the cavity plate side is placed inward to contact the electrolyte, and air is introduced into the air duct.

[0025] Furthermore, when measuring the durability of the hydrogen cavity plate of the metal bipolar plate, the hydrogen cavity plate side is placed inward to contact the electrolyte, hydrogen is introduced into the air guide pipe, and a hydrogen tail exhaust pipe is added.

[0026] Furthermore, step S4 further includes:

[0027] Before the test, start the circulating water pump connected to the super constant temperature water tank, wait until the temperature reaches the set value before testing, and continuously introduce hydrogen or air into the electrolytic cell through the air duct to maintain a saturated gas atmosphere in the electrolyte.

[0028] Furthermore, the performance evaluation results of the metal bipolar plate to be tested include the corrosion current, AC impedance, contact resistance, surface roughness, hydrophilicity, hydrophobicity, microscopic morphology of the coating, element composition and ion concentration in the solution of the metal bipolar plate.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. The present invention is based on actual vehicle operating conditions or battery life test conditions, compiles corresponding dynamic potential conditions, conducts durability tests on fuel cell metal bipolar plates in a three-electrode system, and focuses on the influence of the coupling effect between rapidly changing potentials on the durability of the bipolar plates. It has high effectiveness, can quickly and accurately evaluate the life of metal bipolar plates in the early stage of research and development, and reduce the research and development cost of in-situ testing.

[0031] 2. The present invention is applicable to metal bipolar plates of any material, and can more truly and accurately reflect the performance change law of metal bipolar plates during durability testing. It has a higher equivalence with in-situ testing and can provide important theoretical support for the selection of metal bipolar plate materials and suppliers.

[0032] Based on the above reasons, the present invention can be widely promoted in the fields of proton exchange membrane fuel cell bipolar plate detection and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0034] Figure 1 The figure is a flow chart of the accelerated testing method for the durability of metal bipolar plates of the present invention.

[0035] Figure 2 It is a schematic diagram of the structure of the metal bipolar plate durability accelerated testing system of the present invention.

[0036] Figure 3 It is a schematic diagram of the dynamic potential working condition of the accelerated durability test of the metal bipolar plate of the present invention.

[0037] Figure 4 The corrosion current test results during the accelerated durability test of metal bipolar plates.

[0038] Figure 5 Schematic diagram of the change of corrosion current with test time during the accelerated durability test of metal bipolar plates.

[0039] Figure 6 Schematic diagram of the electrochemical impedance spectroscopy (EIS) test results during the accelerated durability test of metal bipolar plates.

[0040] Figure 7 This is the electrode reaction equivalent circuit fitting diagram.

[0041] Figure 8 This is a schematic diagram of the change in bipolar plate polarization impedance with durability test time obtained through software fitting.

[0042] Fig. 9 Schematic diagram of the change of contact resistance with test time during the accelerated durability test of metal bipolar plates.

[0043] In the figure: 1. electrolytic cell; 2. working electrode; 3. counter electrode; 4. reference electrode; 5. gas guide tube; 6. electrochemical workstation; 7. host computer; 8. super constant temperature water tank; 9. constant temperature water inlet pipe; 10. constant temperature water inlet pipe; 11. constant temperature water cavity outside the electrolytic cell; 12. gas source. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0045] The present invention provides a proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method, the steps comprising:

[0046] (1) Design of metal bipolar plate durability accelerated test system. Figure 2As shown, the accelerated test system includes an electrolytic cell, an electrochemical workstation, a host computer, a super constant temperature water tank, a gas cylinder, and some auxiliary plastic tubes and electrical conductors. The electrolytic cell is made of glass material and is divided into two parts: an inner cavity and an outer cavity. The inner cavity is filled with electrolyte and has three openings connected to the atmosphere, two of which can be used to insert a gas tube and a reference electrode, and the third opening is used as an outlet. The electrolyte is connected to the electrochemical workstation through a three-electrode system for electrochemical testing. The outer cavity is connected to the super constant temperature water tank through a plastic hose. During the electrochemical test, circulating water is used to ensure the constant temperature of the electrolyte. The electrochemical workstation uses the BioLogic HCP-803 electrochemical workstation, which is used to apply potential and data acquisition to the bipolar plate to be tested, and maintain communication and data synchronization with the host computer. The EC-Lab operating software of the host computer can be used to write test conditions and test conditions and observe the changes of voltage, current, etc. over time in real time.

[0047] (2) Selection of accelerated test conditions for metal bipolar plate durability. According to the International Electrotechnical Commission (IEC) standard automotive fuel cell stack durability bench test cycle conditions, select the medium and low current conditions that affect the durability of the metal bipolar plate, and compile the corresponding medium and high potential-time conditions as the dynamic potential conditions for the metal bipolar plate durability test conditions. The main condition interval is selected according to the preset metal bipolar plate durability change amplitude threshold. Figure 3 As shown, a large cycle is composed of four small dynamic potential cycles plus two short high potential cycles, simulating the potential changes of the bipolar plates in the battery during in-situ testing, such as load changes, idling, and start-stop processes.

[0048] (3) Selection of durability index of metal bipolar plate: The preset fixed durability test time can be 20h, 40h, 60h, or 100h, etc., as long as the performance of the metal bipolar plate can be significantly changed. The durability test time selected in this embodiment is 60h.

[0049] (4) Preparation of electrolyte. First, use 0.1ppm HF and 98% concentrated sulfuric acid to prepare a solution with pH=0. Specifically, use a 1000mL glass beaker, add 800-900mL of deionized water, use a measuring cylinder to measure 27mL of concentrated sulfuric acid and 20mL of HF, slowly add them to the beaker, and stir with a glass rod to mix evenly, then transfer to a 1000mL volumetric flask to make up the volume, shake evenly, and use solution 1; then, use solution 1 to prepare a solution with pH=3. Specifically, add 900mL of deionized water to a 1000mL volumetric flask, use a measuring cylinder to measure and add 1mL of solution 1, then add 20mL of 5ppm HF, continue to add deionized water to 1000mL, shake evenly, and use solution 2, which is the electrolyte.

[0050] (5) Preparation and assembly of electrodes. A piece of SS312L gold-plated metal bipolar plate was selected and cut into a sample of 10 mm x 8 mm for testing. The sample to be tested was fixed in the electrolytic cell with an electrode fixture, with the cavity plate facing inward and in contact with the electrolyte as the working electrode, the platinum mesh as the counter electrode, and the hydrogen electrode as the reference electrode.

[0051] (6) Electrochemical test. Saturated air is continuously introduced into the electrolyte through the air duct, the super water bath is started, the temperature is set to 80°C, the circulating water pump is started, and when the temperature reaches the set value, the host computer and EC-Lab software are turned on. The chromoamperometry (CA) program is used to compile the dynamic potential working condition according to the working condition selected in step (2) to conduct a durability test of the metal bipolar plate. The test time is 60 hours, and the performance assessment items of the metal bipolar plate are tested every 20 hours before, during, and after the test until the dynamic potential operation time reaches the index time, and the test is stopped.

[0052] (7) Establish a relationship curve between durability test time and bipolar plate performance change. In this embodiment, the potential setting range of the corrosion current test is -2.5V to 2.5V, the test is carried out at a potential of 0.84V (vsNHE), the test time is 30min, and the test results are as follows: Figure 4 , Figure 5 As shown in Figure 2, with the increase of durability test time, the corrosion current of the metal bipolar plate increases significantly; the frequency range of the electrochemical impedance spectroscopy (EIS) test is 10mHz~200000Hz, and the test potential is 0.84V (vsNHE). The results are as follows: Figure 6 As shown in the figure. Since the impedance spectrum of the metal bipolar plate does not show two distinct semicircular rings, it means that only one step reaction occurs on the surface of the metal plate, so the simulation equivalent circuit diagram selected is LR1 (CdR2), as shown in the figure. Figure 7 As shown, L represents the inductive reactance of the electrode, which is mainly generated by external connection lines, loads and measuring instruments; R1 represents the solution resistance; Cd represents the double-layer capacitive reactance, which is mainly generated by the double-layer formed on the electrode surface; R2 represents the difficulty of charge transfer to the electrolyte through the two reaction interfaces. It can be seen that with the increase of durability test time, the polarization resistance of the metal bipolar plate gradually increases, such as Figure 8 As shown; the contact resistance test results of the metal bipolar plate are shown in Fig. 9 As shown, the test pressure is 0.6Mpa and the current is 5A. As the durability running time of the metal bipolar plate increases, its contact resistance increases linearly, but the increase is small, indicating that the 60h durability test process of the metal bipolar plate has little effect on its contact resistance.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A proton exchange membrane fuel cell metal bipolar plate durability accelerated test method, characterized in that: include: S1. Build a metal bipolar plate durability accelerated test system; S2. Selecting the working conditions for the metal bipolar plate durability accelerated test according to the actual working conditions corresponding to the use of the proton exchange membrane fuel cell, including selecting the main working condition interval or the full working condition interval that has an impact on the durability of the metal bipolar plate in actual application, and compiling the corresponding potential-time working conditions as the dynamic potential working conditions for the metal bipolar plate durability test, wherein the main working condition interval is selected according to the preset metal bipolar plate durability change amplitude threshold; S3, using a preset fixed durability test time as a termination indicator for the metal bipolar plate durability test; S4, using the metal bipolar plate to be tested as the working electrode of the metal bipolar plate durability accelerated test system, performing a durability test according to the dynamic potential working condition, performing a durability test on the fuel cell metal bipolar plate in a three-electrode system, and testing the performance assessment items of the metal bipolar plate to be tested at fixed time intervals until the termination index of the test is reached; S5. Draw a curve of the relationship between the test time and the performance change of the bipolar plate based on the performance assessment results of the metal bipolar plate to be tested. By comparing the corresponding test time and bipolar plate performance change curves obtained for different materials under the same time durability test conditions, conduct a qualitative analysis and evaluation on the durability of the metal bipolar plate, and examine the influence of the coupling effect between rapidly changing potentials on the durability of the bipolar plate. The performance assessment results of the metal bipolar plate to be tested include the corrosion current, AC impedance and polarization resistance of the metal bipolar plate.

2. The proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method according to claim 1, characterized in that: The metal bipolar plate durability accelerated test system includes an electrolytic cell, an electrochemical workstation, a host computer, a super constant temperature water tank, a gas cylinder and auxiliary wires; The electrolytic cell comprises an inner cavity and an outer cavity, wherein the inner cavity is used to contain electrolyte, and a working electrode and a counter electrode are respectively arranged on the side walls thereof, and three openings communicating with the atmosphere are arranged above the inner cavity, which are respectively used to insert an air guide tube, a reference electrode and serve as an air outlet; The electrolyte is connected to the electrochemical workstation through the working electrode, the counter electrode and the reference electrode; The outer cavity is connected to the super constant temperature water tank through a hose.

3. The proton exchange membrane fuel cell metal bipolar plate durability accelerated test method according to claim 2, characterized in that: The counter electrode is made of a platinum mesh, and the reference electrode is made of a saturated calomel electrode or a hydrogen electrode.

4. The proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method according to claim 1, characterized in that: The actual operating conditions include the International Electrotechnical Commission standard vehicle fuel cell stack durability bench test cycle conditions, the U.S. Department of Energy vehicle fuel cell stack durability bench test cycle conditions, Chinese urban bus cycle conditions and new European driving conditions.

5. The proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method according to claim 1, characterized in that: The preset fixed durability test time is 20 h, 40 h, 60 h or 100 h.

6. The proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method according to claim 1, characterized in that: When measuring the durability of the cavity plate of the metal bipolar plate, the cavity plate side is placed inward in contact with the electrolyte and air is introduced into the air duct.

7. The proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method according to claim 1, characterized in that: When measuring the durability of the hydrogen cavity plate of the metal bipolar plate, the hydrogen cavity plate side is placed inward to contact the electrolyte, hydrogen is introduced into the air duct, and a hydrogen tail exhaust pipe is added.

8. The proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method according to claim 1, characterized in that: Step S4 also includes: Before the test, start the circulating water pump connected to the super constant temperature water tank, wait until the temperature reaches the set value before testing, and continuously introduce hydrogen or air into the electrolytic cell through the air duct to maintain a saturated gas atmosphere in the electrolyte.

9. The proton exchange membrane fuel cell metal bipolar plate durability accelerated testing method according to claim 1, characterized in that: The performance evaluation results of the metal bipolar plate to be tested also include the contact resistance, surface roughness, hydrophilicity, microscopic morphology of the coating, elemental composition and ion concentration in the solution of the metal bipolar plate.

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