A method of activating a fuel cell stack

Abstract

The application provides an activation method of a fuel cell stack, which comprises the following steps: (1) operating the fuel cell stack under target conditions; (2) reducing the load of the fuel cell stack until the load is 0, and cooling the stack and purging the stack at the same time until the inlet humidity of the stack reaches an over-humidification state; (3) loading the fuel cell stack under the over-humidification state and continuously operating the stack so that the stack is fully wetted; (4) reducing the load, and cooling the stack and purging the stack at the same time until the temperature of the stack returns to the temperature of the stack before the cooling of the stack in step (2); and (5) detecting the performance of the stack under the target conditions, if the performance of the stack meets the standard, the activation is completed, if the performance of the stack does not meet the standard, steps (1)-(4) are repeated until the performance of the stack meets the standard. The activation method provided by the application can fully wet the proton exchange membrane and the polymer electrolyte ionomer, and the activation time is shortened.

Description

Technical Field

[0001] This invention belongs to the field of battery activation technology and relates to an activation method for a fuel cell stack. Background Technology

[0002] A fuel cell stack is assembled by connecting multiple individual cells in series, adding current collectors and end plates at both ends, and then bolting or binding them together. After the fuel cell stack is assembled, it needs to undergo activation treatment to reach its optimal state for vehicle use. After activation treatment, the performance of the stack will gradually improve and eventually reach equilibrium, which means the activation process is over. The activation process and mechanism of fuel cell stacks are very complex. Currently, it is widely believed that the activation process includes the establishment of the following processes: humidification of the proton exchange membrane; establishment of transport channels for matter (including electrons, protons, gases, and water); optimization of the electrode structure; and improvement of catalyst activity and utilization (mainly cathode Pt).

[0003] Generally, after the fuel cell stack is assembled, the electrodes in the stack need to be activated under given conditions. The activation process and mechanism of proton exchange membrane fuel cell stacks are very complex, involving six processes simultaneously: humidification of the proton exchange membrane, establishment of electron transport channels, establishment of proton transport channels, establishment of gas transport channels, establishment of water transport channels, and optimization of the electrode structure. Currently, the activation of automotive proton exchange membrane fuel cell stacks requires a considerable amount of time, typically 12–48 hours. Commonly used fuel cell stack activation methods include three main processes: 1. Constant current natural activation; 2. Constant current forced activation; 3. Variable current forced activation. Currently, constant current natural activation and forced constant current activation use lower current densities, cell temperatures, and gas pressures, and require longer activation times, ranging from 24 to 48 hours. Furthermore, prolonged activation consumes large amounts of hydrogen and requires additional humidification equipment, increasing costs and hindering continuous mass production. Even though improved converter-forced activation can shorten the activation time of fuel cell stacks to 5-12 hours, the current activation time still cannot meet the needs of mass production of fuel cell stacks. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide an activation method for fuel cell stacks. By rapidly reducing the temperature of the stack coolant to achieve an over-humidified state in the stack's air intake, and then performing constant current activation, the proton exchange membrane in the membrane electrode assembly and the polymer electrolyte ionomer in the catalyst layer can be fully wetted, thereby significantly shortening the activation time.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] This invention provides a method for activating a fuel cell stack, the activation method comprising:

[0007] (1) The fuel cell stack is operated under target conditions;

[0008] (2) Reduce the load on the fuel cell stack until it is reduced to 0. While cooling the fuel cell stack coolant, purge the fuel cell stack until the intake air humidity of the fuel cell stack reaches an over-humidified state.

[0009] (3) Load the fuel cell stack under an over-humidified state and continue to operate it so that the fuel cell stack is fully wetted;

[0010] (4) Reduce the load on the fuel cell stack, heat up the fuel cell coolant while purging the fuel cell stack until the fuel cell stack temperature returns to the temperature before the coolant was cooled in step (2).

[0011] (5) Test the performance of the fuel cell under the target conditions. If the performance of the fuel cell meets the standard, the activation ends. If the performance of the fuel cell does not meet the standard, repeat steps (1) to (4) until the performance of the fuel cell meets the standard.

[0012] This invention lowers the temperature of the fuel cell stack coolant, allowing the intake air to reach a high humidity level (over-humidification), followed by constant current activation. This ensures sufficient wetting of the proton exchange membrane in the membrane electrode assembly (MEA) and the polymeric electrolyte ionomers in the catalyst layer. Using this activation method, the electrical output performance of the MEA is fully activated, resulting in higher output performance. The entire activation process takes only about 3.5 hours, meeting current mass production requirements. Furthermore, by adding the fuel cell stack's rated operating conditions to the activation process, the system can continuously monitor the battery's performance at its rated power point, constantly assess whether the stack performance meets standards, and determine whether activation should be terminated at any time without requiring intermediate performance tests. This allows for rapid assessment of whether the fuel cell stack meets production requirements.

[0013] It should be noted that the over-humidification state referred to in this invention means that the relative humidity exceeds 100%. By loading the humidity of the fuel cell stack to more than 100%, the proton exchange membrane can be fully wetted as soon as possible, thereby establishing a transport channel between substances (including electrons, protons, gases, and water) and improving the activity and utilization rate of the catalyst layer.

[0014] As a preferred technical solution of the present invention, in step (1), the operation process includes: loading the fuel cell stack to the rated current density and continuously operating it at the rated current density in a constant current discharge mode.

[0015] As a preferred technical solution of the present invention, the continuous running time is 5 to 15 minutes, for example, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] As a preferred technical solution of the present invention, in step (2), the humidity of the over-humidified state is 101% to 200%, for example, it can be 101%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190% or 200%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] As a preferred technical solution of the present invention, step (2) includes the following purging process:

[0018] (2.1) First, the H2 / N2 purging mode is adopted: hydrogen is used to purge the anode of the fuel cell stack, and nitrogen is used to purge the cathode of the fuel cell stack until the minimum voltage of the fuel cell stack is <0.2V;

[0019] (2.2) Switch to N2 / N2 purging mode: Purge the anode and cathode of the fuel cell stack with nitrogen gas for 1 to 5 minutes, for example, 1.0 min, 1.5 min, 2.0 min, 2.5 min, 3.0 min, 3.5 min, 4.0 min, 4.5 min or 5.0 min, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] (2.3) Switch to N2 / air purging mode: purge the anode of the fuel cell with nitrogen and purge the cathode of the fuel cell with air until the intake air humidity of the fuel cell reaches an over-humidified state;

[0021] (2.4) Switch back to N2 / N2 purging mode: Purge the anode and cathode of the fuel cell stack with nitrogen gas for 1 to 5 minutes, for example, 1.0 min, 1.5 min, 2.0 min, 2.5 min, 3.0 min, 3.5 min, 4.0 min, 4.5 min or 5.0 min, but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] During the cooling process of the fuel cell stack coolant, the cathode catalyst and the anode catalyst can be oxidized and reduced simultaneously by sequentially passing through the H2 / N2 purging mode and the N2 / air purging mode, thereby restoring the activity of the catalyst.

[0023] As a preferred technical solution of the present invention, in step (3), the continuous operation process includes: loading the fuel cell stack to a preset current density and continuously operating in a constant current discharge mode at the preset current density.

[0024] As a preferred embodiment of the present invention, the preset current density is 1-2 A / cm². 2 For example, it could be 1.0 A / cm 2 1.1A / cm 2 1.2A / cm 2 1.3A / cm 2 1.4A / cm 2 1.5A / cm 2 1.6A / cm 2 1.7A / cm 2 1.8A / cm 2 1.9A / cm 2 Or 2.0A / cm 2 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0025] As a preferred technical solution of the present invention, in step (3), the continuous running time is 5 to 15 minutes, for example, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes or 15 minutes, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] As a preferred technical solution of the present invention, the purging process used in step (4) is the same as the purging process in step (3).

[0027] As a preferred technical solution of the present invention, in step (5), the detection of the fuel cell stack performance includes detecting the voltage and output power of the fuel cell stack. When the detected voltage is greater than or equal to the preset voltage, or the detected output power is greater than or equal to the preset power, it indicates that the performance of the fuel cell stack meets the standard.

[0028] However, this does not apply to all values ​​listed; other unlisted values ​​within this range also apply.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) The present invention reduces the temperature of the fuel cell coolant, so that the fuel cell intake air reaches a high humidity over-humidification state, and then performs constant current activation, so that the proton exchange membrane in the membrane electrode and the polymer electrolyte ionomer in the catalyst layer can be fully wetted.

[0031] (2) By using the activation method provided by the present invention to activate the stack, the electrical output performance of the membrane electrode can be fully activated, exhibiting higher output performance;

[0032] (3) The activation method provided by the present invention can be completed in about 3.5 hours, which can meet the current demand for batch production of fuel cell stacks;

[0033] (4) The present invention adds the rated operating conditions of the battery stack to the activation conditions, which can detect the performance of the battery at the rated power point at all times, determine whether the performance of the battery stack meets the standard at all times, and determine whether to terminate the activation at any time without having to perform performance tests in the middle to determine whether the activation is complete, thereby quickly determining whether the battery stack meets the requirements for offline use. Attached Figure Description

[0034] Figure 1 A flowchart of an activation performance test provided for a specific embodiment of the present invention;

[0035] Figure 2 The diagram shows the activation performance test results provided in a specific embodiment of the present invention;

[0036] Figure 3 This is a repeatability test chart of activation effect provided for a specific embodiment of the present invention. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0038] In one specific embodiment, the present invention provides an activation method for a fuel cell stack, the activation method being as follows: Figure 1 As shown, it includes:

[0039] (1) Load the fuel cell stack to the rated current density and run it continuously at the rated current density in constant current discharge mode for 5 to 15 minutes.

[0040] By adding the rated operating conditions of the battery stack to the activation conditions, the performance of the battery at the rated power point can be monitored at any time, and the performance of the battery stack can be judged at any time. The activation can be terminated at any time without the need to perform performance tests in the middle to determine whether the activation is complete, thus quickly determining whether the battery stack meets the requirements for use after the end of the production line.

[0041] (2) Reduce the load on the fuel cell stack until it is reduced to 0. While cooling the fuel cell stack coolant, purge the fuel cell stack until the intake air humidity of the fuel cell stack reaches an over-humidified state. The humidity of the over-humidified state is 101-200%.

[0042] By lowering the temperature of the fuel cell coolant, the fuel cell intake air reaches a high humidity overhumidification state, and then constant current activation is performed, so that the proton exchange membrane in the membrane electrode and the polymer electrolyte ionomer in the catalyst layer can be fully wetted.

[0043] The purging process specifically includes the following steps:

[0044] (2.1) First, the H2 / N2 purging mode is adopted: hydrogen is used to purge the anode of the fuel cell stack, and nitrogen is used to purge the cathode of the fuel cell stack until the minimum voltage of the fuel cell stack is <0.2V;

[0045] (2.2) Switch to N2 / N2 purging mode: purge the anode and cathode of the fuel cell stack with nitrogen gas for 1 to 5 minutes;

[0046] (2.3) Switch to N2 / air purging mode: purge the anode of the fuel cell with nitrogen and purge the cathode of the fuel cell with air until the intake air humidity of the fuel cell reaches an over-humidified state;

[0047] (2.4) Switch back to N2 / N2 purging mode: purge the anode and cathode of the fuel cell stack with nitrogen gas for 1 to 5 minutes;

[0048] During the cooling process of the fuel cell stack coolant, the H2 / N2 purging mode and the N2 / air purging mode are passed in sequence, which can simultaneously perform oxidation and reduction on the cathode catalyst and the anode catalyst, thereby restoring the activity of the catalyst.

[0049] (3) Under overhumidified conditions, the fuel cell stack is loaded to a current density of 1-2 A / cm². 2 Run continuously for 5 to 15 minutes to ensure the fuel cell stack is fully wetted;

[0050] (4) Reduce the load on the fuel cell stack. While heating the fuel cell coolant, purge the fuel cell stack until the stack temperature returns to the temperature before the coolant was cooled in step (2). The purging process is the same as the purging process in step (3).

[0051] (5) Detect the voltage and output power of the fuel cell under the target conditions. When the detected voltage is greater than or equal to the preset voltage, or the detected output power is greater than or equal to the preset power, it indicates that the performance of the fuel cell meets the standard and the activation ends. If the performance of the fuel cell does not meet the standard, repeat steps (1) to (4) until the performance of the fuel cell meets the standard.

[0052] The activation method provided by this invention can be used to activate the fuel cell stack, which can fully activate the electrical output performance of the membrane electrode and exhibit higher output performance. The entire activation process only takes about 3.5 hours, which can meet the current demand for mass production of fuel cell stacks.

[0053] Application examples

[0054] This invention provides a method for activating a fuel cell stack, the activation method specifically comprising:

[0055] (1) Load the fuel cell stack to the rated current density and run it continuously for 10 minutes in constant current discharge mode at the rated current density;

[0056] (2) Reduce the load on the fuel cell stack until it reaches 0, and simultaneously cool the fuel cell stack coolant and purge the fuel cell stack until the intake air humidity reaches an over-humidified state, where the humidity is 200%. The purging process specifically includes the following steps:

[0057] (2.1) First, the H2 / N2 purging mode is adopted: hydrogen is used to purge the anode of the fuel cell stack, and nitrogen is used to purge the cathode of the fuel cell stack until the minimum voltage of the fuel cell stack is <0.2V;

[0058] (2.2) Switch to N2 / N2 purging mode: purge the anode and cathode of the fuel cell stack with nitrogen gas for 5 minutes;

[0059] (2.3) Switch to N2 / air purging mode: purge the anode of the fuel cell with nitrogen and purge the cathode of the fuel cell with air until the intake air humidity of the fuel cell reaches an over-humidified state;

[0060] (2.4) Switch back to N2 / N2 purging mode: purge the anode and cathode of the fuel cell stack with nitrogen gas for 5 minutes;

[0061] (3) Under overhumidified conditions, the fuel cell stack is loaded to a current density of 1.5 A / cm². 2 Run continuously for 10 minutes to ensure the fuel cell stack is fully wetted;

[0062] (4) Reduce the load on the fuel cell stack. While heating the fuel cell coolant, purge the fuel cell stack until the stack temperature returns to the temperature before the coolant was cooled in step (2). The purging process is the same as the purging process in step (3).

[0063] (5) Detect the voltage and output power of the fuel cell under the target conditions. When the detected voltage is greater than or equal to the preset voltage, or the detected output power is greater than or equal to the preset power, it indicates that the performance of the fuel cell meets the standard and the activation ends. If the performance of the fuel cell does not meet the standard, repeat steps (1) to (4) until the performance of the fuel cell meets the standard.

[0064] Throughout the activation process, the performance of the fuel cell stack can be continuously monitored to determine whether it meets the standards or reaches saturation, and the activation can be terminated at any time without the need for intermediate performance tests to determine whether activation is complete. During the entire activation process, the current and average voltage of the fuel cell stack are monitored as follows: Figure 2 As shown, by Figure 2 It can be seen that the activation of the fuel cell stack was completed in about three and a half hours.

[0065] To verify the reproducibility of the activation method provided by this invention, samples A and B were subjected to the activation method provided by this invention, as follows: Figure 3 As shown, the current-voltage diagrams of the activated fuel cell stacks remain basically consistent, indicating that the activation method provided by this invention can achieve batch activation of fuel cell stacks.

[0066] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method of activating a fuel cell stack, characterized by, The activation method comprises: (1) running the fuel cell stack under target conditions; (2) reducing the load of the stack until it is reduced to 0, while cooling the stack coolant and purging the stack until the inlet humidity of the stack reaches an over-humidification state; (3) loading the stack under the over-humidification state and continuously running so that the stack is fully wetted; (4) reducing the load of the stack, while heating the stack coolant and purging the stack until the temperature of the stack returns to the temperature of the stack before the cooling of the coolant in step (2); (5) detecting the performance of the stack under the target conditions, if the performance of the stack meets the standard, the activation is completed, if the performance of the stack does not meet the standard, steps (1)-(4) are repeated until the performance of the stack meets the standard; In step (2), the humidity of the over-humidification state is 101-200%.

2. The activation method of claim 1, wherein, In step (1), the running process comprises: loading the stack to the rated current density, and continuously running at the rated current density in the constant current discharge mode.

3. The method of activation of claim 2, wherein, The time of the continuous running is 5-15 min.

4. The activation method of claim 1, wherein, In step (2), the purging process comprises: (2.1) first using the H2 / N2 purging mode: purging the anode of the stack with hydrogen and purging the cathode of the stack with nitrogen until the minimum voltage of the stack is <0.2V; (2.2) switching to the N2 / N2 purging mode: purging the anode and the cathode of the stack with nitrogen for 1-5 min; (2.3) switching to the N2 / air purging mode: purging the anode of the stack with nitrogen and purging the cathode of the stack with air until the inlet humidity of the stack reaches the over-humidification state; (2.4) switching to the N2 / N2 purging mode again: purging the anode and the cathode of the stack with nitrogen for 1-5 min.

5. The activation method of claim 1, wherein, In step (3), the process of the continuous running comprises: loading the stack to a preset current density, and continuously running at the preset current density in the constant current discharge mode.

6. The activation method of claim 5, wherein, The preset current density is 1-2 A / cm 2 .

7. The activation method of claim 6, wherein, In step (3), the time of the continuous running is 5-15 min.

8. The activation method of claim 1, wherein, The purging process used in step (4) is the same as that in step (3).

9. The activation method of claim 1, wherein, In step (5), the detection of the performance of the stack comprises detecting the voltage and the output power of the stack, when the detected voltage ≥ a preset voltage, or the detected output power ≥ a preset power, it indicates that the performance of the stack meets the standard.

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