Fuel cell low-temperature shutdown purging method, device and system

Abstract

The invention discloses a fuel cell low-temperature shutdown purging method, device and system.The purging method comprises the following steps that whether the temperature of an electric pile cooling liquid outlet meets the low-temperature purging condition or not is judged, and the purging process is as follows: step (1), the fuel cell is set to run under the condition of 0.15-0.18 standard current density; dry hydrogen and air are respectively introduced into an anode and a cathode of the battery during the period; (2) operating the fuel cell under the condition that the standard current density is 0.15-0.18; (3) operating the fuel cell under the condition that the standard current density is 0.10-0.12; step (4), operating the fuel cell under the condition that the standard current density is 0.05-0.08; (5) operating the fuel cell under the condition that the standard current density is 0.03-0.04; and step (6), loading 0.03 to 0.04 standard current density. The method can effectively reduce the initial water content of the stack, improve the cold start success rate of the stack, improve the durability of the stack and slow down performance degradation.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to a fuel cell low-temperature shutdown purge method, device and system. Background Art

[0002] With the rapid development of hydrogen energy, proton exchange membrane fuel cells (PEMFC) have been widely applied and promoted, but the low-temperature cold start problem of PEMFC has not yet been completely solved. The low-temperature purge process is closely related to the cold start process. Whether the cold start of PEMFC can be successful depends largely on whether the low-temperature purge process makes the membrane electrode water content reach a suitable value. If the initial water content before the low-temperature start is too much, ice will form during the low-temperature start process to hinder the reaction and cause the stack to fail to start. Gas purge during the shutdown process can effectively reduce the initial water content of the stack.

[0003] At present, the low-current load purge method in the air blast purge is usually adopted. The core requirement of the purge is that there is no high potential during the purge process and the purge is complete. However, the purge method currently used usually causes the stack to be at a high potential for a long time, which will cause carbon corrosion and affect the durability of the stack. Therefore, it is necessary to propose an accurate shutdown purge strategy to meet the requirements of low-temperature cold start for the initial water content of the stack and reduce the time when the stack is at a high potential, thereby improving the durability of the stack.

[0004] Therefore, in view of the above technical problems, it is necessary to provide a fuel cell low-temperature shutdown purge method, device and system.

[0005] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0006] The object of the present invention is to provide a fuel cell low temperature shutdown purge method, device and system.

[0007] In order to achieve the above object, a technical solution provided by a specific embodiment of the present invention is as follows:

[0008] A fuel cell low temperature shutdown purge method comprises the following steps:

[0009] The outlet temperature of the stack coolant determines whether it meets the low-temperature purge conditions. If it does not meet the low-temperature purge conditions, it enters the heating process; if it meets the low-temperature purge conditions, it gradually reduces the load to the idle operating point, and then enters the stack purge process. The purge process is as follows:

[0010] Step (1), the fuel cell is set to operate under the condition of 0.15-0.18 standard current density, during which dry hydrogen and air are respectively introduced into the anode and cathode of the battery, and the gas flow rate of the anode and cathode corresponds to the gas flow rate under the standard current density of 1.2-1.4, the outlet temperature of the stack coolant is controlled to be maintained at 60-65°C, and the purge time is set to 10-20 seconds;

[0011] Step (2), the fuel cell is set to operate under the condition of 0.15-0.18 standard current density, the gas flow rate of the anode and cathode corresponds to the gas flow rate under 0.8-1.0 standard current density, and the purge time is set to 10-20 seconds;

[0012] Step (3), the fuel cell is set to operate under the condition of 0.10-0.12 standard current density, the gas flow rate of the anode and cathode corresponds to the gas flow rate under 0.8-1.0 standard current density, and the purge time is set to 10-20 seconds;

[0013] Step (4), the fuel cell is set to operate under the condition of 0.05-0.08 standard current density, the gas flow rate of the anode and cathode corresponds to the gas flow rate under 0.5-0.8 standard current density, and the purge time is set to 10-20 seconds;

[0014] Step (5), the fuel cell is set to operate under the condition of 0.03-0.04 standard current density, the gas flow rate of the anode and cathode corresponds to the gas flow rate under 0.5-0.8 standard current density, and the purge time is set to 5-10 seconds;

[0015] Step (6), with a load of 0.03-0.04 standard current density, the gas flow rate is set to a flow rate of 0.05-0.3 standard current density, the air supply is turned off, the residual oxygen remaining in the cathode is consumed, and when the average voltage is less than 0.15-0.35V, the load current is turned off and the hydrogen supply is turned off;

[0016] Among them, at least any one of steps (1) to (6) satisfies: the pressure of the gas at the anode and cathode is 30-40 kPa and 35-45 kPa respectively. The standard current density refers to the current density of the stack when it is running at the rated current density of 1A / cm 2 .

[0017] In one or more embodiments of the present invention, the low-temperature purge condition is: when the stack is loaded to a standard current density of 1, it is determined whether the stack coolant outlet temperature is greater than or equal to 60-70°C. If so, the stack enters the heating process to continue normal loading, otherwise, the load is gradually reduced to the idle operating point, and the stack purge process is entered after the load reduction is completed. The purpose of this solution is to determine whether the current working condition is a low-temperature environment in winter based on the coolant outlet temperature. When it is less than this temperature, it means that it is in a low-temperature environment and low-temperature purge is required.

[0018] In one or more embodiments of the present invention, the hydrogen and / or air in steps (1) to (6) are preheated.

[0019] In one or more embodiments of the present invention, the preheated hydrogen and / or air has a temperature ranging from 25°C to 65°C.

[0020] In one or more embodiments of the present invention, the idle operating point is: the current density of the fuel cell stack operation is reduced to 0.4-0.5 standard current density.

[0021] In one or more embodiments of the present invention, the stack enters the stack purge process after running at the idle operating point for 120-240 seconds.

[0022] In one or more embodiments of the present invention, the following conditions are satisfied in steps (1) to (6): the pressure of the gas at the anode is the same and the pressure of the gas at the cathode is the same.

[0023] In one or more embodiments of the present invention, after the air supply is turned off in step (6), the time for the average voltage of the fuel cell to drop from the purge voltage to the average voltage <0.15-0.35V is 5 to 20 seconds.

[0024] In one or more embodiments of the present invention, the purge device implements a fuel cell low temperature shutdown purge method.

[0025] In one or more embodiments of the present invention, a purge system includes a main body and a plurality of purge devices disposed in the main body.

[0026] Compared with the prior art, the fuel cell low-temperature shutdown purge method, device and system of the present invention can effectively reduce the initial water content of the fuel cell stack and improve the success rate of cold start of the fuel cell stack; it can reduce the time that the fuel cell stack is at a high potential and improve the durability of the fuel cell stack; after the purge is completed, using an auxiliary load to discharge and consume the oxygen in the cathode can effectively slow down the performance degradation of the fuel cell after frequent start and stop. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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 only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 This is a graph showing the change of the high-frequency impedance of the proton exchange membrane over time during the purge and water removal process in Example 1 of the present invention;

[0029] Figure 2 The average voltage of the battery stack changes with time during the purge and water removal process in Example 1 of the present invention;

[0030] Figure 3 These are cross-sectional photos of the catalyst layer taken using a scanning electron microscope before and after the low-temperature purge test in Example 1 of the present invention, wherein the left photo is before the test and the right photo is after the test;

[0031] Figure 4 The surface photos of the cathode catalyst layer taken by scanning electron microscope before and after the low-temperature purge test in Example 1 of the present invention, wherein the left photo is before the test and the right photo is after the test;

[0032] Figure 5 The surface photos of the anode catalyst layer taken by scanning electron microscope before and after the low-temperature purge test in Example 1 of the present invention, wherein the left photo is before the test and the right photo is after the test;

[0033] Figure 6 It is the purge gas flow rate corresponding to different electrical densities in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with 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.

[0035] A method for a fuel cell comprising the following steps:

[0036] The purge condition identification module determines whether the low-temperature purge condition is met according to the outlet temperature of the fuel cell stack coolant. If the low-temperature purge condition is not met, the module enters the heating process. If the low-temperature purge condition is met, the module gradually reduces the load to the idle operating point and then enters the stack purge process.

[0037] Step (1), the fuel cell is set to operate under the condition of 0.15-0.18 standard current density, during which dry hydrogen and air are respectively introduced into the anode and cathode of the battery, the flow rate of the cathode and cathode gases corresponds to the gas flow rate at the standard current density of 1.2-1.4, the pressures of the cathode and cathode gases are 40 and 45 kPa respectively, the outlet temperature of the stack coolant is controlled to be maintained at 60-65°C, and the purge time is set to 10-20 seconds;

[0038] Step (2), the fuel cell is set to operate under the condition of 0.15-0.18 standard current density, the flow rate of the anode and cathode gases corresponds to the gas flow rate under 0.8-1.0 standard current density, and the purge time is set to 10-20 seconds;

[0039] Step (3), the fuel cell is set to operate under the condition of 0.10-0.12 standard current density, the flow rate of the anode and cathode gases corresponds to the gas flow rate under 0.8-1.0 standard current density, and the purge time is set to 10-20 seconds;

[0040] Step (4), the fuel cell is set to operate under the condition of 0.05-0.08 standard current density, the flow rate of the anode and cathode gases corresponds to the gas flow rate under 0.5-0.8 standard current density, and the purge time is set to 10-20 seconds;

[0041] Step (5), the fuel cell is set to operate under the condition of 0.03-0.04 standard current density, the flow rate of the cathode and anode gases corresponds to the gas flow rate under 0.5-0.8 standard current density, and the purge time is set to 5-10 seconds;

[0042] Step (6), load 0.03-0.04 standard current density, set the gas flow rate to 0.05-0.3 standard current density. Turn off the air supply to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.15-0.35V, turn off the load current and the hydrogen supply.

[0043] As a preferred solution, the low-temperature purge condition is determined in step (1) by determining whether the outlet temperature of the stack coolant is greater than or equal to 60-70°C when the stack is loaded to 1 standard current density. If so, the temperature is raised to continue normal loading. Otherwise, the load is gradually reduced to the idle operating point of 0.5 standard current density. After the load reduction is completed, the stack purge process is entered.

[0044] As a preferred embodiment, the operating conditions of different current densities in steps (1) to (6) are based on the optimal operating conditions table obtained from sensitivity experiments, and the selection of conditions for the sensitivity experiment includes anode and cathode gas pressures, coolant pressures, cathode and cathode gas flow rates, coolant flow rates, cathode and cathode gas temperatures, coolant temperatures, cathode and cathode gas stoichiometric ratios, cathode and cathode gas humidity, etc. at different current densities.

[0045] As a preferred solution, in step (6), the time for the average voltage of the fuel cell to drop from the purge voltage to an average voltage of <0.15-0.35V is between 5 and 20 seconds, i.e., the time interval from when the air is turned off to when the voltage drops to an average voltage of <0.15-0.35V.

[0046] As a preferred solution, an AC impedance meter is used to monitor the water content in the stack to calculate the internal resistance of the stack, including the wet internal resistance of the stack when idling, the internal resistance during the stack purge process, and the internal resistance after waiting for water balance in the proton exchange membrane.

[0047] As a preferred solution, after the stack is purged, the maximum resistance during the purging process is 5-15 times the wet internal resistance, and the internal resistance after waiting for water equilibrium in the proton exchange membrane, that is, 0.1-1h after the purging is completed, is 2-5 times the wet internal resistance.

[0048] Example 1

[0049] The active area of ​​500 sections is 350cm 2When the stack (water-cooled fuel cell stack, the same below) is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, meeting the low-temperature purge conditions, and gradually reducing the load to the idle operating point of 0.5 standard current density. After running for 120 seconds, the stack purge process is entered. The fuel cell is set to operate at a standard current density of 0.15. During this period, dry, unheated hydrogen and air are introduced into the anode and cathode of the battery respectively. The flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 1.2. The pressures of the anode and cathode gases are 40 and 45 kPa respectively (the same gas supply pressure is used in the following stages, the same below). At the same time, the stack coolant outlet temperature is controlled to be maintained at 65°C, and the purge time is set to 10 seconds; then the fuel cell is set to operate at a standard current density of 0.15, the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 0.8, and the purge time is set to 20 seconds; the fuel cell is set to operate at a standard current density of 0.15, the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 0.8, and the purge time is set to 20 seconds. The fuel cell is set to operate at a standard current density of 0.10, and the flow of the cathode and cathode gases corresponds to the gas flow at a standard current density of 0.8, and the purge time is set to 10 seconds; the fuel cell is set to operate at a standard current density of 0.05, and the flow of the cathode and cathode gases corresponds to the gas flow at a standard current density of 0.5, and the purge time is set to 15 seconds; the fuel cell is set to operate at a standard current density of 0.03, and the flow of the cathode and cathode gases corresponds to the gas flow at a standard current density of 0.5, and the purge time is set to 5 seconds; under a load of a standard current density of 0.03, the gas flow is set to a flow of a standard current density of 0.05. Then, the air supply is turned off to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.2V, the load current is turned off and the hydrogen supply is turned off.

[0050] During the purge period, AC impedance is used to monitor the water content in the stack and calculate the internal resistance of the stack, including the wet internal resistance of the stack at idle speed, the internal resistance during the purge process, and the internal resistance after waiting for the water balance in the proton exchange membrane. After the stack is purged, the maximum resistance reached during the purge process is 15 times the wet internal resistance. After waiting for the water balance in the proton exchange membrane, that is, after waiting for 10 minutes after the purge, the internal resistance no longer changes and is 3.2 times the wet internal resistance.

[0051] After purging, the stack can be successfully cold started at -20 degrees Celsius. The purged stack was tested for 10 freeze / thaw cycles at -40-60 degrees Celsius. Figure 3 As shown in the figure, the cross-section photo of the catalyst layer taken by scanning electron microscope after the test shows that there is no separation between the catalyst layer and the proton exchange membrane. Figure 4 and 5 As shown in the figure, the surface cracks of the cathode catalyst layer change very little, while the anode catalyst layer is relatively thin, and the repeated changes in water content cause the MEA to expand and contract continuously, causing a slight increase in surface cracks. Figure 2As shown, the method of this embodiment controls the load current to accurately control the battery voltage during the discharge process, which can prevent the battery voltage from dropping too quickly, resulting in uneven voltage distribution and battery reverse polarity, and can also prevent the battery stack from being at a high potential for a long time.

[0052] Example 2

[0053] The active area of ​​300 nodes is 300cm 2 When the stack is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, meeting the low-temperature purge conditions, and the load is gradually reduced to the idle operating point of 0.5 standard current density. After running for 120 seconds, the stack purge process begins. The fuel cell is set to operate at a standard current density of 0.15. During this period, dry, unheated hydrogen and air are introduced into the anode and cathode of the battery respectively. The flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 1.2. The pressures of the anode and cathode gases are 40 and 45 kPa respectively (the same gas supply pressure is used in the following stages, the same below). At the same time, the stack coolant outlet temperature is controlled to be maintained at 65°C, and the purge time is set to 20 seconds; then the fuel cell is set to operate at a standard current density of 0.15, the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 0.8, and the purge time is set to 10 seconds; the fuel cell is set to The fuel cell is set to operate at a standard current density of 0.10, the flow of the cathode and cathode gases corresponds to the gas flow at a standard current density of 0.8, and the purge time is set to 20 seconds; the fuel cell is set to operate at a standard current density of 0.05, the flow of the cathode and cathode gases corresponds to the gas flow at a standard current density of 0.5, and the purge time is set to 20 seconds; the fuel cell is set to operate at a standard current density of 0.03, the flow of the cathode and cathode gases corresponds to the gas flow at a standard current density of 0.5, and the purge time is set to 10 seconds; under a load of a standard current density of 0.03, the gas flow is set to a flow of a standard current density of 0.05. Then the air supply is turned off to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.2V, the load current is turned off and the hydrogen supply is turned off.

[0054] After the stack is purged, the maximum resistance reached during the purge process is 12 times the wet state internal resistance. After waiting for the water balance in the proton exchange membrane, the internal resistance will not change after 10 minutes, and will be 2.5 times the wet state internal resistance. After the purge, the stack will not freeze at minus 20 degrees Celsius and can be successfully cold-started.

[0055] Example 3

[0056] The active area of ​​300 nodes is 300cm 2When the stack is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, meeting the low-temperature purge conditions, and the load is gradually reduced to the idle operating point of 0.5 standard current density. After running for 120 seconds, the stack purge process is entered. The fuel cell is set to operate at a standard current density of 0.15. During this period, hydrogen and air dried and heated to 25°C are introduced into the anode and cathode of the battery respectively. The flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 1.2. The pressures of the anode and cathode gases are 40 and 45 kPa respectively. At the same time, the stack coolant outlet temperature is controlled to be maintained at 65°C, and the purge time is set to 20 seconds; then the fuel cell is set to operate at a standard current density of 0.15, and the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 0.8, and the purge time is set to 10 seconds; the fuel cell is set to operate at a standard current density of 0.10. The fuel cell is operated under the condition of 0.05 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.5 standard current density, and the purge time is set to 20 seconds; the fuel cell is operated under the condition of 0.03 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.5 standard current density, and the purge time is set to 10 seconds; under the load of 0.03 standard current density, the gas flow is set to the flow of 0.05 standard current density. Then turn off the air supply to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.2V, turn off the load current and the hydrogen supply.

[0057] After the stack is purged, the maximum resistance reached during the purge process is 13 times the wet state internal resistance. After waiting for the water balance in the proton exchange membrane, the internal resistance will not change after 10 minutes, which is 2.5 times the wet state internal resistance. After the purge, the stack will not freeze at minus 20 degrees Celsius and can be successfully cold-started.

[0058] Example 4

[0059] The active area of ​​300 nodes is 300cm 2When the stack is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, meeting the low-temperature purge conditions, and the load is gradually reduced to the idle operating point of 0.5 standard current density. After running for 120 seconds, the stack purge process begins. The fuel cell is set to operate at a standard current density of 0.15. During this period, hydrogen and air dried and heated to 65°C are introduced into the anode and cathode of the battery respectively. The flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 1.2. The pressures of the anode and cathode gases are 40 and 45 kPa respectively. At the same time, the stack coolant outlet temperature is controlled to be maintained at 65°C, and the purge time is set to 20 seconds; then the fuel cell is set to operate at a standard current density of 0.15, and the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 0.8, and the purge time is set to 10 seconds; the fuel cell is set to operate at a standard current density of 0.10. The fuel cell is operated under the condition of 0.05 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.5 standard current density, and the purge time is set to 20 seconds; the fuel cell is operated under the condition of 0.03 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.5 standard current density, and the purge time is set to 10 seconds; under the load of 0.03 standard current density, the gas flow is set to the flow of 0.05 standard current density. Then turn off the air supply to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.2V, turn off the load current and the hydrogen supply.

[0060] After the stack is purged, the maximum resistance reached during the purge process is 15 times the wet state internal resistance. After waiting for the water balance in the proton exchange membrane, the internal resistance will not change after 10 minutes, which is 3.0 times the wet state internal resistance. After purging, the stack will not freeze at minus 20 degrees Celsius and can be successfully cold-started.

[0061] Example 5

[0062] The active area of ​​300 nodes is 300cm 2When the stack is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, meeting the low-temperature purge conditions, and the load is gradually reduced to the idle operating point of 0.5 standard current density. After running for 120 seconds, the stack purge process begins. The fuel cell is set to operate at a standard current density of 0.15. During this period, hydrogen and air dried and heated to 45°C are introduced into the anode and cathode of the battery respectively. The flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 1.2. The pressures of the anode and cathode gases are 40 and 45 kPa respectively. At the same time, the stack coolant outlet temperature is controlled to be maintained at 65°C, and the purge time is set to 20 seconds; then the fuel cell is set to operate at a standard current density of 0.15, and the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 0.8, and the purge time is set to 10 seconds; the fuel cell is set to operate at a standard current density of 0.10. The fuel cell is operated under the condition of 0.05 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.5 standard current density, and the purge time is set to 20 seconds; the fuel cell is operated under the condition of 0.03 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.5 standard current density, and the purge time is set to 10 seconds; under the load of 0.03 standard current density, the gas flow is set to the flow of 0.05 standard current density. Then turn off the air supply to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.2V, turn off the load current and the hydrogen supply.

[0063] After the stack is purged, the maximum resistance reached during the purge process is 14 times the wet state internal resistance. After waiting for the water balance in the proton exchange membrane, the internal resistance will not change after 10 minutes, which is 2.8 times the wet state internal resistance. After the purge, the stack will not freeze at minus 20 degrees Celsius and can be successfully cold-started.

[0064] Example 6

[0065] The active area of ​​300 nodes is 300cm 2When the stack is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, meeting the low-temperature purge conditions, and the load is gradually reduced to the idle operating point of 0.4 standard current density. After running for 240 seconds, the stack purge process is entered. The fuel cell is set to operate at a standard current density of 0.18. During this period, dry, unheated hydrogen and air are respectively introduced into the anode and cathode of the battery. The flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 1.4. The pressures of the anode and cathode gases are 35 and 35 kPa, respectively. At the same time, the stack coolant outlet temperature is controlled to be maintained at 60°C, and the purge time is set to 10 seconds; then the fuel cell is set to operate at a standard current density of 0.16, the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 0.9, and the purge time is set to 20 seconds; the fuel cell is set to operate at a standard current density of 0.11. The fuel cell is operated under the condition of 0.06 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.7 standard current density, and the purge time is set to 10 seconds; the fuel cell is operated under the condition of 0.035 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.7 standard current density, and the purge time is set to 7 seconds; under the load of 0.035 standard current density, the gas flow is set to 0.15 standard current density. Then turn off the air supply to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.15V, turn off the load current and the hydrogen supply.

[0066] After the stack is purged, the maximum resistance reached during the purge process is 15 times the wet state internal resistance. After waiting for the water balance in the proton exchange membrane, the internal resistance will not change after 10 minutes, which is 3.1 times the wet state internal resistance. After the purge, the stack will not freeze at minus 20 degrees Celsius and can be successfully cold-started.

[0067] Example 7

[0068] The active area of ​​300 nodes is 300cm 2When the stack is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, meeting the low-temperature purge conditions, and the load is gradually reduced to the idle operating point of 0.45 standard current density. After running for 200 seconds, the stack purge process is entered. The fuel cell is set to operate at a standard current density of 0.16. During this period, dry, unheated hydrogen and air are respectively introduced into the anode and cathode of the battery. The flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 1.3. The pressures of the anode and cathode gases are 30 and 40 kPa, respectively. At the same time, the stack coolant outlet temperature is controlled to be maintained at 63°C, and the purge time is set to 15 seconds; then the fuel cell is set to operate at a standard current density of 0.18, and the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 1.0, and the purge time is set to 15 seconds; the fuel cell is set to operate at a standard current density of 0.12. The fuel cell is operated under the condition of 0.08 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.8 standard current density, and the purge time is set to 15 seconds; the fuel cell is operated under the condition of 0.04 standard current density, the flow of cathode and anode gas corresponds to the gas flow at 0.8 standard current density, and the purge time is set to 5 seconds; under the condition of 0.04 standard current density, the gas flow is set to 0.03 standard current density. Then turn off the air supply to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.35V, turn off the load current and the hydrogen supply.

[0069] After the stack is purged, the maximum resistance reached during the purge process is 14 times the wet state internal resistance. After waiting for the water balance in the proton exchange membrane, the internal resistance will not change after 10 minutes, which is 2.7 times the wet state internal resistance. After the purge, the stack will not freeze at minus 20 degrees Celsius and can be successfully cold-started.

[0070] Example 8

[0071] The active area of ​​300 nodes is 300cm 2When the stack is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, meeting the low-temperature purge conditions, and the load is gradually reduced to the idle operating point of 0.45 standard current density. After running for 200 seconds, the stack purge process is entered. The fuel cell is set to operate at a standard current density of 0.16. During this period, dry, unheated hydrogen and air are introduced into the anode and cathode of the battery respectively. The flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 1.3. The pressures of the anode and cathode gases are 40 and 40 kPa respectively. At the same time, the stack coolant outlet temperature is controlled to be maintained at 63°C, and the purge time is set to 15 seconds; then the fuel cell is set to operate at a standard current density of 0.15, and the flow rates of the anode and cathode gases are set to the gas flow rates at a standard current density of 0.8. The pressures of the anode and cathode gases are 40 and 40 kPa respectively, and the purge time is set to 10 seconds; the fuel cell is set to operate at a standard current density of 0.10, and the flow rates of the anode and cathode gases correspond to the gas flow rates at a standard current density of 0.8. The gas flow rate under the current density, the pressure of the cathode and anode gas is 30 and 35 kPa respectively, and the purge time is set to 20 seconds; the fuel cell is set to operate under the condition of 0.05 standard current density, the flow rate of the cathode and anode gas corresponds to the gas flow rate under 0.5 standard current density, the pressure of the cathode and anode gas is 30 and 35 kPa respectively, and the purge time is set to 20 seconds; the fuel cell is set to operate under the condition of 0.03 standard current density, the flow rate of the cathode and anode gas corresponds to the gas flow rate under 0.5 standard current density, the pressure of the cathode and anode gas is 35 and 45 kPa respectively, and the purge time is set to 10 seconds; under the load of 0.03 standard current density, the gas flow rate is set to the flow rate of 0.05 standard current density, and the pressure of the cathode and anode gas is 35 and 45 kPa respectively. Then turn off the air supply to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.2V, turn off the load current and turn off the hydrogen supply.

[0072] After the stack is purged, the maximum resistance reached during the purge process is 12 times the wet state internal resistance. After waiting for the water balance in the proton exchange membrane, the internal resistance will not change after 10 minutes, which is 2.6 times the wet state internal resistance. After the purge, the stack will not freeze at minus 20 degrees Celsius and can be successfully cold-started.

[0073] Comparative Example 1

[0074] The active area of ​​500 sections is 350cm 2When the stack is loaded to 1 standard current density, the stack coolant outlet temperature is 55°C, which meets the low-temperature purge conditions. The load is gradually reduced to the idle operating point of 0.5 standard current density, and the stack purge process is entered after running for 120 seconds. The fuel cell is set to operate at a standard current density of 0.15. During this period, dry, unheated hydrogen and air are introduced into the anode and cathode of the battery respectively. The flow rate of the cathode and cathode gases corresponds to the gas flow rate at a standard current density of 1.2. The pressures of the cathode and cathode gases are 40 and 45 kPa respectively. At the same time, the stack coolant outlet temperature is controlled to be maintained at 65°C, and the purge time is set to 2 minutes; then the load is reduced to 0.03 standard current density, and the gas flow rate is set to 0.05 standard current density. Then turn off the air supply to consume the residual oxygen remaining in the cathode. When the average voltage is less than 0.2V, turn off the load current and the hydrogen supply.

[0075] After the stack is purged, the maximum resistance reached during the purge process is only 8 times the wet internal resistance. After waiting for the water balance in the proton exchange membrane, the internal resistance will no longer change after 10 minutes of waiting, and it will be 2 times the wet internal resistance. The results show that this constant flow purge method cannot achieve the ideal purge effect, which in turn affects the low temperature start-up performance of the fuel cell stack. If this method is used for purge, in order to achieve the ideal internal resistance value, at least 5 minutes of purge time is required, which will consume more electricity and gas.

[0076] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0077] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A fuel cell low temperature shutdown purging method, comprising the following steps: The outlet temperature of the stack coolant determines whether it meets the low-temperature purge conditions. If it does not meet the low-temperature purge conditions, it enters the heating process; if it meets the low-temperature purge conditions, it gradually reduces the load to the idle operating point, and then enters the stack purge process. The purge process is as follows: Step (1), the fuel cell is set to operate under the condition of 0.15-0.18 standard current density, during which dry hydrogen and air are respectively introduced into the anode and cathode of the battery, and the gas flow rate of the anode and cathode corresponds to the gas flow rate under the standard current density of 1.2-1.4, the outlet temperature of the stack coolant is controlled to be maintained at 60-65°C, and the purge time is set to 10-20 seconds; Step (2), the fuel cell is set to operate under the condition of 0.15-0.18 standard current density, the gas flow rate of the anode and cathode corresponds to the gas flow rate under 0.8-1.0 standard current density, and the purge time is set to 10-20 seconds; Step (3), the fuel cell is set to operate under the condition of 0.10-0.12 standard current density, the gas flow rate of the anode and cathode corresponds to the gas flow rate under 0.8-1.0 standard current density, and the purge time is set to 10-20 seconds; Step (4), the fuel cell is set to operate under the condition of 0.05-0.08 standard current density, the gas flow rate of the anode and cathode corresponds to the gas flow rate under 0.5-0.8 standard current density, and the purge time is set to 10-20 seconds; Step (5), the fuel cell is set to operate under the condition of 0.03-0.04 standard current density, the gas flow rate of the anode and cathode corresponds to the gas flow rate under 0.5-0.8 standard current density, and the purge time is set to 5-10 seconds; Step (6), with a load of 0.03-0.04 standard current density, the gas flow rate is set to a flow rate of 0.05-0.3 standard current density, the air supply of the fuel cell is turned off, and the residual oxygen remaining in the cathode is consumed. When the average voltage is less than 0.15-0.35V, the load current is turned off and the hydrogen supply is turned off; in, At least any one of steps (1) to (6) satisfies the following conditions: the pressures of the gases at the anode and cathode are 30-40 kPa and 35-45 kPa, respectively.

2. The fuel cell low temperature shutdown purging method according to claim 1, characterized in that: The low-temperature purge condition is: when the stack is loaded to a standard current density of 1, determine whether the stack coolant outlet temperature is greater than or equal to 60-70°C. If so, enter the heating process to continue normal loading; otherwise, gradually reduce the load to the idle operating point, and enter the stack purge process after the load reduction is completed.

3. The fuel cell low temperature shutdown purging method according to claim 1, characterized in that: In steps (1) to (6), the hydrogen and / or air are preheated.

4. The fuel cell low temperature shutdown purging method according to claim 3, characterized in that: The preheated hydrogen and / or air has a temperature in the range of 25-65°C.

5. The fuel cell low temperature shutdown purge method according to claim 1, characterized in that: The idle operating point is: the current density of the fuel cell stack is reduced to 0.4-0.5 standard current density.

6. The fuel cell low temperature shutdown purging method according to claim 1, characterized in that: The stack runs at the idle operating point for 120-240 seconds before entering the stack purge process.

7. The fuel cell low temperature shutdown purge method according to claim 1, characterized in that: In steps (1) to (6), the following conditions are satisfied: the pressure of the gas at the anode is the same and the pressure of the gas at the cathode is the same.

8. The fuel cell low temperature shutdown purging method according to claim 1, characterized in that: After the air supply is turned off in step (6), the time for the average voltage of the fuel cell to drop from the purge voltage to an average voltage of <0.15-0.35V is 5 to 20 seconds.

9. A purge device for implementing the fuel cell low temperature shutdown purge method according to any one of claims 1 to 8.

10. A purge system, comprising a main body and a plurality of purge devices according to claim 9 arranged in the main body.

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