Offline Pretreatment System, Method for Accelerating Activation of Fuel Cell Stack, and Stack Activation Method

Abstract

The present invention discloses a system and method for accelerating the off-line pre-treatment of fuel cell stack activation and a fuel cell stack activation method, belonging to the fuel cell detection technology. The off-line pre-treatment system and method provided by the present invention reduce the time for the fuel cell stack to occupy the test bench and shorten the activation time of the fuel cell stack. First, place the high-power fuel cell stack that has been stacked in an incubator at 50-150°C, and then introduce steam or saturated or supersaturated moist gas at 50-150°C into the cathode and anode cavities of the fuel cell stack, and maintain for 15-240 minutes, and monitor the change of the internal resistance or impedance of the fuel cell stack. When the internal resistance or impedance of the fuel cell stack reaches a predetermined threshold or standard, move the fuel cell stack to the fuel cell test bench for variable load activation.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen fuel cells, and particularly relates to application scenarios such as vehicles, ships, ports, locomotives, aviation, airports, etc. Specifically, it relates to a system, method and stack activation method for accelerating the off-line pre-treatment of fuel cell stack activation. Background Art

[0002] In the technical field of fuel cells, stack activation is a primary condition in the R & D and production processes. The single cells (including bipolar plate assemblies and membrane electrode assemblies) in high-power stacks may be composed of hundreds or even thousands of groups in series. If a few single cells are not fully activated, the consistency between the single cells of the stack becomes poor, which will directly affect the power generation performance of the entire stack. Therefore, only a stack with sufficient activation has the possibility to meet the stack design and reach the optimal working state. Thus, the activation process is the core and necessary process for the stack to leave the factory. Currently, after integration, the activation of the stack is mainly carried out on a test bench, that is, by introducing hydrogen and air and using an electronic load to draw current under established working conditions. For example, in the existing patent application CN110783589A, the voltage is linearly reduced at a constant rate through the test bench, and continuous high-frequency variable voltage is used for forced activation, but most of the time on the test bench needs to exceed 60 minutes. This method is called on-line activation. However, on-line activation not only occupies valuable test benches (generally, test benches are expensive, and there are only one or two in many fuel cell manufacturers, which cannot meet the huge test data), making on-line activation easily become a bottleneck in the production process, but also on-line activation consumes a large amount of manpower and hydrogen. Therefore, it is extremely urgent to develop an off-line pre-treatment method.

[0003] Compared with on-line activation, the off-line pre-treatment method has the following advantages:

[0004] 1. Resource and time efficiency: Activation on a test bench requires a large amount of time, manpower and material resources. Off-line pre-treatment can reduce the time of the stack on the test bench, save a large amount of resources, and reduce the production cost of the stack.

[0005] 2. Large-scale production: The commercial application of fuel cell technology requires large-scale production, and the traditional activation method on a test bench is not efficient enough in this regard. Off-line pre-treatment can be realized on the factory production line and is more suitable for large-scale production requirements.

[0006] 3. Process optimization: Off-line pre-treatment can provide more flexibility and control, which helps to optimize the activation process of battery components. Through off-line pre-treatment, the activation conditions can be better adjusted to further improve the battery performance and stability.

[0007] 4. Consistency and repeatability: During the offline pretreatment process, the activation conditions can be better controlled to ensure consistency and repeatability among battery components. This helps to ensure that each battery produced has consistent performance and stability.

[0008] Methods similar to offline pretreatment have been used to shorten the activation time of membrane electrode assemblies (MEA) or electrodes. These methods are limited to single or multi-piece MEAs and have not been applied to high-power fuel cell stacks. They are referred to as MEA preconditioning techniques in the literature. These strategies include steaming the MEA in water, soaking the MEA in water or an aqueous methanol solution, or even soaking it in a dilute sulfuric acid aqueous solution at high temperature. In addition, some studies have shown that treating the electrode or catalyst coated membrane (CCM) with acetic acid can improve performance. Some researchers have also adopted the method of circulating methanol between the anode and cathode. However, all of the above methods have some common problems and disadvantages:

[0009] 1. Component deformation: Some preconditioning techniques, such as soaking treatment, may cause changes in the shape of the MEA component, making the membrane electrode soft, which may affect the performance and stability of the battery. Moreover, during the subsequent automated stacking process, it is difficult to transfer the overly soft membrane electrode with a manipulator and complete the positioning during the stacking process.

[0010] 2. Membrane electrode contamination: Soaking in water, an aqueous methanol solution, or a dilute sulfuric acid aqueous solution may introduce contaminants that pollute the catalyst or other key components of the battery, thereby reducing the efficiency and lifespan of the battery.

[0011] 3. Production cost: The preconditioning liquids such as sulfuric acid, methanol, and acetic acid required for large-scale production will increase the production cost, especially for industrial production, which will be a significant expense.

[0012] 4. Production efficiency: Using organic solvents or acids will add an additional cleaning process, reducing the production efficiency.

[0013] Furthermore, patent application 202410107302.2, "An Offline Activation Device and Activation Method for a Membrane Electrode", describes a method for offline activation of MEA, that is, inserting the membrane electrode into a fixture in a cavity filled with humid hydrogen (25 - 85 °C, relative humidity 20 - 300%) and activating it under constant potential or constant voltage. However, each MEA in this patent application is independent of other MEAs in the cavity. After activation, the effectiveness of activation is verified in the form of a single-cell tooling and is not integrated into a stack. Assembling the humid MEAs into a stack is not conducive to the large-scale production process.

[0014] Based on the problems and disadvantages of the above-mentioned prior art, the purpose of the present invention is to provide an improved method and device for MEA pretreatment, aiming to shorten the activation time, improve the battery performance, reduce the cost and improve the production efficiency at the same time. Summary of the Invention

[0015] Object of the Invention: In order to shorten the occupation of the test bench by the activation operation of the fuel cell stack before leaving the factory and to shorten the activation time, the first object of the present invention is to provide an off-line pretreatment system for accelerating the activation of the fuel cell stack, the second object is to provide a method for accelerating the off-line pretreatment of the fuel cell stack activation, and further the third object of the present invention is to provide a method for activating the fuel cell stack.

[0016] To achieve the above object of the invention, the following technical solutions are adopted in the present invention.

[0017] A method for accelerating the off-line pretreatment of fuel cell stack activation, which is used for the off-line treatment of the fuel cell before being installed on the test bench to accelerate the activation speed of the fuel cell stack and shorten the occupation time of the test bench. The method includes placing the stacked fuel cell stack in a thermostat at 50 - 150 °C, then introducing steam or mixed gas flow at 50 - 150 °C into the cathode and anode cavities of the fuel cell stack and maintaining for 15 - 240 minutes, monitoring the change of the internal resistance or impedance of the fuel cell stack, and when the internal resistance or impedance of the fuel cell stack reaches a predetermined threshold or standard, moving the fuel cell stack to the fuel cell stack test bench for variable load activation;

[0018] The steam is generated by a steam generator, and the mixed gas flow is humidified by deionized water, including using saturated or supersaturated gas as the pretreatment medium gas, and the molar percentage of water vapor in the mixed gas flow is controlled at 10 - 99%, and the steam flow rate is supplied at 1 - 100 ml / min according to each single cell, including calculating and adjusting according to the temperature and meeting the requirements of 50 - 150 °C;

[0019] The pretreatment medium gas includes one or more of air, hydrogen, nitrogen, argon, ammonia, helium and other gas mixtures.

[0020] Further, the mixed gas flow is formed by introducing the pretreatment medium gas into a humidifier filled with deionized water to form a saturated or supersaturated water gas flow, and the resistivity of the deionized water is controlled ≥ 18 MΩ·cm and the temperature is between 25 - 150 °C during the operation of the humidifier.

[0021] Further, the method includes calculating the completion degree of the fuel cell stack pretreatment based on the change of the internal resistance or impedance of the fuel cell stack with time; for the fuel cell stack composed of membrane electrode assemblies with different internal resistances or impedances, electrochemical activation is carried out on the fuel cell stack test bench, and the internal resistance or impedance of the fuel cell stack that reaches the activation factory standard earliest is selected as the pretreatment standard.

[0022] Furthermore, the water vapor or water vapor mixture is mixed in a high-temperature steam generator by bubbling or spraying to form a mixed airflow, and the mixed airflow is simultaneously connected to the cathode and anode cavities of the fuel cell stack, and the pressure of the mixed airflow is controlled to be between 0 and 3 atmospheric pressure gauge by the pressure valve and the back pressure valve of the tail exhaust of the fuel cell stack.

[0023] An offline pretreatment system for accelerating the activation of a fuel cell stack, used to implement the above-mentioned offline pretreatment method for accelerating the activation of a fuel cell stack, comprising:

[0024] A thermostat, used for heat preservation of the fuel cell stack, and the thermostat is connected to an internal resistance meter to monitor the internal resistance of the fuel cell stack, which is used to estimate the completion degree of the fuel cell stack pretreatment, and also includes a back pressure valve connected to the tail exhaust of the fuel cell stack to control the pretreatment operating pressure;

[0025] The mixed air flow generating device includes a high-pressure air source, a pressure reducing valve, a steam generator, and a water vapor separator. The high-pressure air source is pressure-regulated by the pressure reducing valve and then enters the steam generator to form a mixed air flow, which is then passed through the water vapor separator to achieve a mixed air flow temperature of 50-150°C and a water vapor mole percentage of 10-99%.

[0026] In the above system, the steam-water separator is used to reduce the amount of liquid water entering the fuel cell stack, so that water vapor can better penetrate the hydrophobic interface of the membrane electrode.

[0027] In the above system, the constant temperature box includes a water bath, an oil bath, a sand bath or a blast oven.

[0028] Furthermore, the pretreatment system operates at a gauge pressure higher than 0 atmospheric pressure, and by adding a circulating water pump, the liquid water collected by the steam-water separator is returned to the steam generator to improve the utilization rate of deionized water.

[0029] In addition, the system includes an ion resin bed for removing various ions from the fuel cell stack and completing the cleaning of the fuel cell stack before leaving the factory.

[0030] Based on the above-mentioned method for accelerating the activation of fuel cell stacks, the fuel cell stack activation method is realized by first pre-treating the stacked fuel cell stack offline, then connecting the stack to the test bench, blowing away excess moisture, and then performing air starvation activation after high temperature and high humidity activation. When the current density is 1.8A / cm 2 When the average single-chip voltage is greater than 0.65V, activation is considered complete, and polarization curve testing is performed to ensure that the product meets factory standards.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following significant effects:

[0032] (1) The present invention has wide applications, is simple and easy to install, has low costs, and complements automated stacking, thereby improving production efficiency.

[0033] (2) The present invention only uses water vapor or water vapor-containing gas for treatment, does not involve organic solvents and acids, and increases the service life of the equipment.

[0034] (3) The present invention does not require additional cleaning processes for the stack and MEA, improving the efficiency of pretreatment.

[0035] (4) The present invention can monitor the hydration of the proton membrane in real time, adjust the pretreatment time according to the detection results, and make the whole process more flexible.

[0036] (5) The present invention can adjust the pipeline connection and steam flow rate to pretreat multiple stacks simultaneously, and can be directly connected to the test bench for verification after treatment, improving the factory efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic structural diagram of the system of the present invention;

[0038] Figure 2 is a schematic flow diagram of the offline pretreatment method of the present invention;

[0039] Figure 3 is a schematic flow diagram of the fuel cell stack activation method of the present invention;

[0040] Figure 4 is the relationship between the activation time and the average voltage in Examples 1-3;

[0041] Figure 5 is the average voltage condition of starvation activation of Examples 1-3 on the test bench;

[0042] Figure 6 is the relationship between the current density and the average voltage during the activation process of Examples 1-3. DETAILED DESCRIPTION OF THE INVENTION

[0043] To describe in detail the technical solutions provided by the present invention, the following further introduces with reference to the embodiments.

[0044] Example 1 (comparative case)

[0045] S1. Install the battery stack to be activated on the test platform, connect the gas pipeline, cooling water pipeline and electronic load. Purge the cathode and anode of the battery stack with N2. Start the electronic load to enable the test platform to communicate with the electronic load. Set the preheating temperature of the water tank on the test platform, turn on the water pump, and preheat the battery stack to be activated;

[0046] S2. High-temperature and high-humidity activation: After the preheating is completed, select the metering ratio mode, introduce hydrogen and air into the anode (a) and cathode (c) respectively, turn on the circulating water, set the stack operating parameters, connect the electronic load and pull the load to a constant current of 2.4 A / cm2 for 5 - 10 min;

[0047] S3. Air starvation activation: Lower the electronic load to 1.8 A / cm2. If the average single-cell voltage has reached the factory standard of 0.65 V after stabilization, stop the activation process. If the average single-cell voltage is lower than 0.65 V, continue with air starvation activation, that is, quickly reduce the cathode metering ratio to 0.5 and then quickly restore it. Repeat this process 5 - 10 times;

[0048] S4. Operate stably at 1.8 A / cm2 for 5 - 10 min, observe the increase in the average voltage. If the average single-cell voltage reaches 0.65 V, stop the activation process; otherwise, repeat S3 - 4;

[0049] S5. After completing S2 - S4, gradually reduce the load and wait for the temperature of the water tank to decrease;

[0050] S6. Test the polarization curve according to the polarization condition.

[0051] Example 2

[0052] First, place the high-power stack (≥100 single cells) that has been stacked in an incubator at 50 - 150 °C, then introduce steam at 50 - 150 °C into the cathode and anode cavities of the stack and maintain it for 15 - 240 minutes, monitoring the change in the internal resistance or impedance of the stack. When the internal resistance or impedance of the stack reaches a predetermined threshold or standard, move the stack to the stack test bench for variable-load activation.

[0053] The difference from Example 1 is that steam pretreatment is increased by 60 min, and then activation is carried out according to S1 - S6.

[0054] Example 3

[0055] First, perform pretreatment using a method for accelerating the off-line pretreatment of fuel cell stack activation. Specifically, it includes the following process:

[0056] Pretreatment steam temperature: The incubator is a water bath, oil bath, sand bath, or forced-air oven, preferably a water bath. The steam is generated by a steam generator and introduced into the cathode and anode cavities of the stack. The power of the steam generator is calculated according to a steam flow rate of 1 - 100 ml / min per single cell and the steam temperature.

[0057] Pretreatment Mixed Gas Composition: When using saturated or supersaturated gas as the pretreatment medium, the molar percentage of water in the gas is 10 - 99%. The gas used to form saturated or supersaturated gas is a mixed gas of one or more gases among air, hydrogen, nitrogen, argon, ammonia, and helium. The gas is passed into a humidifier filled with deionized water (resistivity ≥ 18 MΩ·cm at 25 °C) to form a saturated or supersaturated water airflow. The structure of the humidifier is similar to that of the humidifier in the large fuel cell stack test bench, and the mixed airflow is formed by bubbling, spraying, or a high-temperature steam generator, and the mixed airflow is connected to the cathode and anode cavities of the fuel cell stack simultaneously. The temperature of the mixed airflow is maintained at 50 - 150 °C, and the molar percentage of water vapor is 10 - 99%.

[0058] Pretreatment Standard: The change of the internal resistance or impedance of the fuel cell stack over time can be used to estimate the completion degree of the fuel cell stack pretreatment. To determine the completion degree of the pretreatment, the fuel cell stacks composed of membrane electrode assemblies with different internal resistances or impedances are electrochemically activated on the fuel cell stack test bench. Select the internal resistance or impedance of the fuel cell stack that first reaches the activation factory standard (for example, the average single-cell voltage is 0.65 V at a current density of 1.8 A / cm2) as the pretreatment standard.

[0059] Pretreatment Pressure: Before the high-pressure gas enters the humidifier, it needs to be decompressed to the pretreatment operating pressure by a pressure reducing valve. The pretreatment operating pressure is controlled by the back pressure valve at the tail exhaust of the fuel cell stack. The pretreatment operating pressure is 0 - 3 gauge atmospheric pressure, preferably 0 gauge atmospheric pressure;

[0060] Pretreatment Steam-Water Separator: Before the steam or mixed gas enters the fuel cell stack, a steam-water separator is set up to reduce the liquid water entering the fuel cell stack interior, so that the water vapor can better penetrate the hydrophobic interface of the membrane electrode;

[0061] Pretreatment Circulating Water Pump: If the pretreatment equipment operates at a pressure above 0 gauge atmospheric pressure, a circulating water pump needs to be added to return the liquid water collected by the steam-water separator to the steam generator to improve the utilization rate of deionized water; Preferably, the entire pretreatment equipment contains a deionized resin bed to continuously remove various ions from the fuel cell stack and complete the cleaning step before the fuel cell stack leaves the factory.

[0062] The difference from Example 1 is that steam pretreatment is increased by 240 min, and then activation is carried out according to S1 - S6.

[0063] Table 1. Data of Examples 1 - 3

[0064]

[0065] Further combination Figure 1-6According to Table 1, the present invention first provides an offline preprocessing system and method, aiming to improve the production efficiency of the stack, especially applicable to the stacking of automated production lines; reduce the activation time of the stack on the test bench through the offline preprocessing method, and improve the equipment utilization efficiency of activation; and establish a preprocessing standard by monitoring the change of the internal resistance of the stack during the preprocessing process, so as to judge and control the preprocessing process, thereby realizing the rapid activation of the fuel cell.

Claims

1. An offline pretreatment system for accelerating the activation of a fuel cell stack, characterized in that, Comprising: An incubator for heat preservation of the fuel cell stack. The incubator is connected to an internal resistance meter to monitor the internal resistance of the fuel cell stack, for calculating the completion degree of the pre-treatment of the fuel cell stack. It also includes a back pressure valve connected to the tail exhaust of the fuel cell stack to control the operating pressure during pre-treatment. A mixed gas flow generating device, including a high-pressure gas source, a pressure reducing valve, a steam generator, and a water vapor separator. The high-pressure gas source is regulated by the pressure reducing valve and then enters the steam generator to form a mixed gas flow, and then passes through the water vapor separator to achieve a temperature of the mixed gas flow between 50 - 150°C and a water vapor mole percentage of 10 - 99%. The water vapor separator is used to reduce the liquid water entering the fuel cell stack, enabling the water vapor to better penetrate the hydrophobic interface of the membrane electrode. The water vapor flow is generated by the steam generator and simultaneously introduced into the cathode and anode cavities of the fuel cell stack. The water vapor mixture is mixed in the high-temperature steam generator in a bubbling or spraying manner to form a mixed gas flow, and the mixed gas flow is simultaneously connected to the cathode and anode cavities of the fuel cell stack. The pressure of the water vapor flow or the mixed gas flow is controlled to be between 0 - 3 gauge atmospheric pressures through a pressure regulating valve and the back pressure valve at the tail exhaust of the fuel cell stack. The system also controls the resistivity of deionized water ≥18 MΩ·cm and the temperature between 25 - 150°C through a humidifier. When the pre-treatment system operates at a pressure above 0 gauge atmospheric pressure, it includes adding a circulation water pump to return the liquid water collected by the water vapor separator back to the steam generator to improve the utilization rate of deionized water. The system places the fuel cell stack after stacking treatment in an incubator at 50 - 150°C, then introduces a water vapor flow or a mixed gas flow at 50 - 150°C into the cathode and anode cavities of the fuel cell stack, and maintains it for 15 - 240 minutes. Monitor the change in the internal resistance or impedance of the fuel cell stack. When the internal resistance or impedance of the fuel cell stack reaches a predetermined threshold or standard, move the fuel cell stack to the fuel cell test bench for variable load activation. The mixed gas flow is formed by passing a pre-treatment medium gas through a humidifier filled with deionized water to form a saturated or supersaturated water flow. The water vapor mole percentage in the mixed gas flow is controlled between 10 - 99%, and the steam flow rate is supplied at 1 - 100 ml / min per single cell in each group, including calculation and adjustment according to temperature and meeting the requirements of 50 - 150°C. The pre-treatment medium gas includes a mixed gas of one or more gases among air, hydrogen, nitrogen, argon, ammonia, and helium. Connect the battery stack to the test bench, purge the excess moisture, and perform air starvation activation after high-temperature and high-humidity activation. When the average single-cell voltage is greater than 0.65V at a current density of 1.8A / cm 2 it is considered that the activation is completed, and a polarization curve test is carried out to meet the factory standards.

2. The offline preprocessing system for accelerating the activation of a fuel cell stack according to claim 1, wherein, The system calculates the completion degree of the pre-treatment of the fuel cell stack based on the change in the internal resistance or impedance of the fuel cell stack over time. For fuel cell stacks composed of membrane electrodes with different internal resistances or impedances, electrochemical activation is carried out on the fuel cell test bench, and the internal resistance or impedance of the fuel cell stack that earliest reaches the activation factory standard is selected as the pre-treatment standard.

3. The offline preprocessing system for accelerating the activation of a fuel cell stack according to claim 1, wherein, The incubator includes a water bath, an oil bath, a sand bath, or a forced air oven.

4. The offline pretreatment system for accelerating the activation of a fuel cell stack according to claim 1, wherein, The system also includes an ion resin bed, which is used to remove various ions from the fuel cell stack and simultaneously complete the cleaning of the fuel cell stack before leaving the factory.

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