A method for detecting micro-leakage of a fuel cell bipolar plate

Abstract

The present application relates to a kind of fuel cell bipolar plate micro leakage detection method, comprising: preparing test fuel cell stack;Using nitrogen to the cooling cavity of fuel cell stack, fuel cavity and oxidation cavity inlet are purged;Impedance of each single cell is measured using fuel cell impedance test system;Cooling liquid is introduced into the cooling liquid cavity of fuel cell stack, and pressure maintaining is carried out;During pressure maintaining, the impedance of each single cell is measured again, and interval sampling is carried out to the end of pressure maintaining;After draining the liquid in cooling cavity, using nitrogen to the cooling cavity of fuel cell stack, fuel cavity and oxidation cavity inlet are purged;The impedance of each single cell is measured again;The electronic transfer resistance R ct of each single cell impedance test result is analyzed to determine whether there is leakage in current single cell.Compared with prior art, the present application can detect leakage in batch for whole stack bipolar plate without disassembling stack and contaminating cavity, and has the advantages of convenient operation method, fast detection speed, high identification rate and micro leakage detection.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a method for detecting microleakage in fuel cell bipolar plates. Background Technology

[0002] A fuel cell is a device that directly converts the chemical energy of fuel and oxidant into electrical energy. It boasts advantages such as high energy conversion efficiency, fast response speed, clean operation, and low noise, and is currently widely used in transportation, stationary power plants, aerospace, and other fields. A proton exchange membrane fuel cell mainly consists of components such as bipolar plates, membrane electrode assemblies (MEAs), and a sealing structure. The bipolar plates play a crucial role in the fuel cell stack, supporting the MEAs, transmitting fuel gas, conducting current, and dissipating reaction heat.

[0003] Currently, bipolar plate failure is mainly caused by bipolar plate leakage. The main causes of leakage include: leak points on the plate, problems in the bonding or welding process of the single plate leading to external leakage, and failure of the sealing structure between the bipolar plate and the membrane electrode assembly (MEA). In low-temperature applications, fuel cells require ethylene glycol-based antifreeze instead of deionized water as the coolant to prevent freezing. However, defects in the graphite plate manufacturing process can create micropores in the bipolar plate, leading to antifreeze leakage during use. This can easily contaminate the MEA, causing low temperatures during battery operation and affecting battery performance. Therefore, leak testing of the bipolar plates before the fuel cell stack leaves the factory is essential.

[0004] Traditional bipolar plate leak detection methods primarily rely on gas detection, which involves introducing a detection gas into the bipolar plate's cavity and observing for leaks by checking for bubble leakage or pressure changes. Alternatively, methods like CN109167088A utilize electrochemical reactions, introducing a detection gas into the bipolar plate and detecting the generation of voltage through an electrochemical reaction. However, after operation, liquid deionized water or antifreeze fills the microcracks or pores in the bipolar plate. Due to the adhesion forces at the solid-liquid interface between the coolant and the bipolar plate, the detection gas struggles to penetrate these microcracks or pores, making it difficult for conventional gas detection methods to detect even minor leaks. Therefore, liquid leak detection can also be employed. For example, Chinese patent CN112414629A proposes introducing a fluorescent agent liquid into the bipolar plate's water cavity, then observing the appearance of the fluorescent agent liquid in the flow channels after pressure maintenance to detect leaks.

[0005] However, in the aforementioned detection methods, CN109167088A primarily involves introducing fuel gas into the water cavity of the bipolar plate and oxidant gas into the anode / cathode flow field. Since the gas cavity and water cavity of the bipolar plate are isolated from each other, this aeration method will not produce voltage in a single cell under normal circumstances. If a voltage is generated in a single cell, it indicates that the bipolar plate of that cell has experienced cross-leakage. However, this method cannot effectively screen bipolar plates with microporous defects. CN112414629A primarily involves introducing a coolant containing a fluorescent agent into the water cavity of the bipolar plate, followed by static pressure holding. After a period of time, the bipolar plate is disassembled and placed under a UV lamp; the area showing a fluorescent reaction is the dew point area of ​​the bipolar plate. The advantage of this method is that it can identify bipolar plates with micro-leakage, but it is very easy to contaminate the membrane electrode, so it can only be applied to failure analysis and cannot be used in production. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art by providing a method for detecting micro-leakage in fuel cell bipolar plates. This method is simple to operate and can reliably detect whether leakage has occurred in the bipolar plates without causing damage or contamination to the bipolar plates and membrane electrodes.

[0007] The objective of this invention can be achieved through the following technical solution: a method for detecting micro-leakage in a fuel cell bipolar plate, comprising the following steps:

[0008] S1: Prepare to test the fuel cell stack by connecting the gas supply system, coolant supply system, and fuel cell impedance system to the fuel cell stack respectively.

[0009] S2: Nitrogen gas is used to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack through the gas supply system to ensure thorough drying;

[0010] S3: Measure the impedance of each individual cell using a fuel cell impedance testing system;

[0011] S4: Coolant is introduced into the coolant chamber of the fuel cell stack through the coolant supply system and pressure is maintained;

[0012] S5: During the pressure holding period, the impedance of each individual cell is measured again using the fuel cell impedance testing system, and samples are taken at intervals until the pressure holding period ends;

[0013] S6: After draining the liquid from the cooling chamber, use nitrogen to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack and allow them to dry thoroughly.

[0014] S7: Measure the impedance of each individual cell using a fuel cell impedance testing system;

[0015] S8: Electron transfer resistance R in the impedance test results of each single cellct An analysis was conducted to determine if there was a leak in the current single cell.

[0016] Further, step S1 specifically involves connecting the gas supply system to the corresponding pipelines of the fuel chamber and oxidation chamber of the fuel cell stack; connecting the coolant supply system to the corresponding pipelines of the coolant chamber of the fuel cell stack; and connecting the fuel cell impedance testing system to the fuel cell stack voltage monitoring system.

[0017] Furthermore, the coolant in the coolant supply system is specifically deionized water.

[0018] Furthermore, in step S2, the flow rate of nitrogen is 50-100 mL / min, and the purging time is 10-30 min.

[0019] Furthermore, in steps S3, S5, and S7, the impedance test range is 10. -1 ~10 5 Hz.

[0020] Furthermore, in step S4, the holding pressure of the coolant is 10-200 kPa.

[0021] Furthermore, in step S5, the sampling interval is 5-10 minutes, and the pressure holding time is 1-2 hours.

[0022] Furthermore, in step S6, the flow rate of nitrogen is 50-100 mL / min, and the purging time is 10-60 min.

[0023] Furthermore, step S8 specifically involves analyzing the radius of the circle in the Nyquist plot of the impedance spectrum to determine whether there is leakage in the current single cell.

[0024] Furthermore, in step S8, if R is maintained during the water cavity pressure holding period ct The value of R measured in steps S3 and S7 before and after pressure holding shows a decreasing trend. ct If the change is less than or equal to the set threshold, it indicates that there is a leak in that single cell.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) By testing the change trend of single-piece impedance during the pressure holding process, the present invention can locate the micro-leaking bipolar plate in the case of the whole stack without disassembling the stack for leak detection, which has the advantages of saving time, effort and convenient operation.

[0027] (2) The present invention is tested on a test bench containing an impedance testing system. Once there are microcracks or pores in the bipolar plate, water leakage will cause the surface state of the plate to change, which will then appear in the impedance spectrum. The micro-leaking bipolar plate can be identified by the trend of the transfer impedance in the spectrum. It has the characteristics of sensitive response and ability to detect micro-leaks. Moreover, the equipment is simple and does not require additional tooling fixtures.

[0028] (3) The present invention uses water for pressure holding test. Even if water leaks, it will not damage the bipolar plate and membrane electrode. Moreover, the water that permeates into the gas cavity of the plate can be dried by nitrogen. Compared with the polluting fluorescent antifreeze for pressure holding test, the detection method of the present invention is pollution-free. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the method flow of the present invention;

[0030] Figure 2 This is a schematic diagram of the application system of the present invention;

[0031] Figure 3 This is a typical Nyquist plot in impedance spectroscopy;

[0032] Figure 4 This is a schematic diagram comparing the microleakage detection results of the bipolar plate in Example 1;

[0033] Figure 5a This is a schematic diagram of the EIS test results of the normal electrode plate in Example 2;

[0034] Figure 5b This is a schematic diagram of the EIS test results of the micro-leak plate in Example 2. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0036] like Figure 1 As shown, a method for detecting microleakage in a fuel cell bipolar plate includes the following steps:

[0037] S1: Prepare to test the fuel cell stack by connecting the gas supply system, coolant supply system, and fuel cell impedance system to the fuel cell stack respectively.

[0038] S2: Nitrogen gas is used to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack through the gas supply system to ensure thorough drying;

[0039] S3: Measure the impedance of each individual cell using a fuel cell impedance testing system;

[0040] S4: Coolant is introduced into the coolant chamber of the fuel cell stack through the coolant supply system and pressure is maintained;

[0041] S5: During the pressure holding period, the impedance of each individual cell is measured again using the fuel cell impedance testing system, and samples are taken at intervals until the pressure holding period ends;

[0042] S6: After draining the liquid from the cooling chamber, use nitrogen to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack and allow them to dry thoroughly.

[0043] S7: Measure the impedance of each individual cell using a fuel cell impedance testing system;

[0044] S8: Electron transfer resistance R in the impedance test results of each single cell ct An analysis was conducted to determine if there was a leak in the current single cell.

[0045] The application of the above technical solution in practice mainly includes:

[0046] First, prepare for testing the fuel cell stack. Connect the gas supply system to the corresponding pipelines of the fuel chamber and oxidation chamber of the fuel cell stack, connect the coolant supply system to the corresponding pipelines of the coolant chamber of the fuel cell stack, and connect the fuel cell impedance testing system to the fuel cell stack voltage monitoring system. Figure 2 As shown;

[0047] 2. Use nitrogen to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack and allow them to dry thoroughly;

[0048] 3. The impedance of each individual cell was measured using a fuel cell impedance testing system;

[0049] 4. Introduce coolant into the coolant chamber of the fuel cell stack and maintain pressure;

[0050] 5. During the pressure holding period, the impedance of each individual cell is measured again using a fuel cell impedance testing system, and samples are taken at intervals until the pressure holding period ends;

[0051] 6. After draining the liquid from the cooling chamber, use nitrogen to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack and allow them to dry thoroughly.

[0052] 7. The impedance of each individual cell was measured using a fuel cell impedance testing system;

[0053] 8. Electron transfer resistance R in the impedance test results of each single cell ct Analysis was conducted, and if R... ct The value shows a decreasing trend, while before and after pressure holding, R in S3 and S7... ct If there is no obvious change, it indicates that there is a leak in that single cell.

[0054] In step S1, the coolant in the coolant supply system is deionized water.

[0055] In step S2, the flow rate of nitrogen is 50-100 mL / min, and the purging time is 10-30 min;

[0056] In steps S3, S5, and S7, the impedance test range is 10. -1 -10 5 Hz;

[0057] In step S4, the holding pressure of the coolant is 10-200 kPa;

[0058] In step S5, the sampling interval is 5-10 min, and the pressure holding time is 1-2 h;

[0059] In step S6, the flow rate of nitrogen is 50-100 mL / min, and the purging time is 10-60 min;

[0060] The working principle of this technical solution is that if there is a crack in the coolant chamber of the bipolar plate, under the action of capillary force, pressure, and concentration difference, the coolant will penetrate through the crack to the vicinity of the membrane electrode, causing a change in the surface state of the single cell. Consequently, the impedance of the single cell changes, and the electron transfer resistance R in the impedance spectrum changes accordingly. ct It will become smaller (i.e.) Figure 3 The radius of the circle in the Nyquist plot decreases, therefore, by observing R... ct The changing trend can be used to determine whether there is micro-leakage in the bipolar plate.

[0061] Example 1

[0062] The specific process of applying the above technical solution in this embodiment is as follows:

[0063] A method for leak detection of bipolar plates in fuel cells, the specific steps of which are as follows:

[0064] S1: Prepare to test the fuel cell stack. Connect the gas supply system to the corresponding pipelines of the fuel chamber and oxidation chamber of the fuel cell stack, connect the coolant supply system to the corresponding pipelines of the coolant chamber of the fuel cell stack, and connect the fuel cell impedance testing system to the fuel cell stack voltage monitoring system. The coolant in the coolant supply system is deionized water.

[0065] S2: Use nitrogen to purge the inlets of the cooling chamber, fuel chamber and oxidation chamber of the fuel cell stack and dry them thoroughly. The flow rate of nitrogen is 80 mL / min and the purging time is 20 min.

[0066] S3: The impedance of each individual cell is measured using a fuel cell impedance testing system, with an impedance testing range of 10. -1 -10 5 Hz;

[0067] S4: Coolant is introduced into the coolant chamber of the fuel cell stack and pressure is maintained at 100 kPa.

[0068] S5: During the pressure holding period, the impedance of each individual cell is measured again using a fuel cell impedance testing system, with sampling intermittently until the end of the pressure holding period. The impedance test range is 10. -1 -10 5 Hz, with a sampling interval of 5 min and a holding time of 2 h;

[0069] S6: After draining the liquid from the cooling chamber, use nitrogen to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack to ensure thorough drying. The nitrogen flow rate is 100 mL / min and the purging time is 40 min.

[0070] S7: The impedance of each individual cell is measured using a fuel cell impedance testing system, with an impedance testing range of 10. -1 -10 5 Hz;

[0071] S8: Electron transfer resistance R in the impedance test results of each single cell ct Analysis was conducted, and if R... ct The value shows a decreasing trend, while before and after pressure holding, R in S3 and S7... ct If there is no obvious change, it indicates that there is a leak in that single cell.

[0072] like Figure 4 The image shows the impedance spectrum changes of a microleaking bipolar plate during the water cavity pressure holding period. ct The trend of decreasing radius indicates that there is leakage in the bipolar plate of this segment.

[0073] Example 2

[0074] In this embodiment, the coolant in the cooling chamber is replaced with ethylene glycol-based antifreeze instead of deionized water; otherwise, it is the same as in Embodiment 1. EIS (Enhanced Ionization System) of the micro-leaking bipolar plate. Figure 5b The electron transfer impedance of the bipolar plate shows a clear decreasing trend, while the electron transfer impedance of the normal bipolar plate ( Figure 5a The result remains almost unchanged, proving the effectiveness of the testing method proposed in this invention.

[0075] Example 3

[0076] In this embodiment, the coolant in the cooling chamber is controlled at a constant temperature of 10°C, and the rest is the same as in Embodiment 1.

[0077] In summary, this technical solution involves filling the water chamber of the bipolar plate in the test stack with an appropriate amount of water and maintaining pressure. By detecting the AC impedance of a single cell, if the charge transfer impedance in the impedance test results shows a significant decreasing trend, it indicates that the bipolar plate of that single cell is leaking. This technical solution, through pressure maintenance, can accelerate the rate of liquid leakage and amplify even minute defects in the bipolar plate. By detecting the AC impedance of a single cell, if the charge transfer impedance in the impedance test results shows a significant decreasing trend, it indicates that the bipolar plate of that single cell is leaking. This method allows for batch leak detection of the entire stack of bipolar plates without dismantling the stack or contaminating the chamber. It has the advantages of convenient operation, fast detection speed, high identification rate, and the ability to detect micro-leaks.

[0078] This technical solution is time-saving, labor-saving, easy to operate, and highly efficient in testing: the entire fuel cell stack can be tested, and the leakage of the bipolar plates can be located without disassembling the stack.

[0079] It is highly responsive and can detect micro-leakage: Due to the enhanced water permeability under pressure, once the bipolar plate leaks, the surface state of the plate changes and the impedance spectrum changes accordingly, which can detect micro-cracks and micro-pores on the bipolar plate.

[0080] The testing equipment is simple: no complex tooling or testing equipment is required, only an impedance testing system is needed;

[0081] The detection method is pollution-free: the detection will not cause damage or pollution to the bipolar plates and membrane electrodes, and the water that permeates into the gas chamber of the plates can be dried by fuel nitrogen.

Claims

1. A method for detecting microleakage in fuel cell bipolar plates, characterized in that, Includes the following steps: S1: Prepare to test the fuel cell stack by connecting the gas supply system, coolant supply system, and fuel cell impedance system to the fuel cell stack respectively; S2: Nitrogen gas is used to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack through the gas supply system to ensure thorough drying; S3: Measure the impedance of each individual cell using a fuel cell impedance testing system; S4: Coolant is introduced into the coolant chamber of the fuel cell stack through the coolant supply system and pressure is maintained. The coolant in the coolant supply system is deionized water. S5: During the pressure holding period, the impedance of each individual cell is measured again using the fuel cell impedance testing system, and samples are taken at intervals until the pressure holding period ends; S6: After draining the liquid from the cooling chamber, use nitrogen to purge the inlets of the cooling chamber, fuel chamber, and oxidation chamber of the fuel cell stack and allow them to dry thoroughly. S7: Measure the impedance of each individual cell using a fuel cell impedance testing system; S8: Electron transfer resistance R in the impedance test results of each single cell ct An analysis will be conducted to determine if there is a leak in the current single cell; Step S8 specifically involves analyzing the radius of the circle in the Nyquist plot of the impedance spectrum to determine whether there is leakage in the current single cell. In step S8, if R is during the water chamber pressure holding period ct The value of R measured in steps S3 and S7 before and after pressure holding shows a decreasing trend. ct If the change is less than or equal to the set threshold, it indicates that the single cell is leaking.

2. The method for detecting microleakage in a fuel cell bipolar plate according to claim 1, characterized in that, Specifically, step S1 involves connecting the gas supply system to the corresponding pipelines of the fuel chamber and oxidation chamber of the fuel cell stack; connecting the coolant supply system to the corresponding pipelines of the coolant chamber of the fuel cell stack; and connecting the fuel cell impedance testing system to the fuel cell stack voltage monitoring system.

3. The method for detecting microleakage in a fuel cell bipolar plate according to claim 1, characterized in that, In step S2, the nitrogen flow rate is 50-100 mL / min and the purging time is 10-30 min.

4. The method for detecting microleakage in a fuel cell bipolar plate according to claim 1, characterized in that, In steps S3, S5, and S7, the impedance test range is 10. -1 ~10 5 Hz.

5. The method for detecting microleakage in a fuel cell bipolar plate according to claim 1, characterized in that, In step S4, the holding pressure of the coolant is 10-200 kPa.

6. The method for detecting microleakage in a fuel cell bipolar plate according to claim 1, characterized in that, In step S5, the sampling interval is 5-10 min, and the pressure holding time is 1-2 h.

7. The method for detecting microleakage in a fuel cell bipolar plate according to claim 1, characterized in that, In step S6, the flow rate of nitrogen is 50-100 mL / min, and the purging time is 10-60 min.

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