Shutdown strategy method and system of fuel cell stack and cell

Abstract

The invention discloses a shutdown strategy method and system for a fuel cell stack and a cell, and the method comprises the following steps: (1) reducing the current density of the stack to a limited state before shutdown, and adjusting the operation condition of the stack to be matched with the current density; (2) after the average voltage of the galvanic pile monomers is stable, reducing the current density of the galvanic pile to 0.02 A / cm < 2 >, and switching cathode gas into dry nitrogen in the same flow state on the premise of keeping other operation conditions unchanged; (3) continuously monitoring the voltage of each monomer in the galvanic pile, and reducing the current density of the galvanic pile to 0.01 A / cm < 2 > when the voltage of one monomer is smaller than a first limited voltage; and (4) when the voltage of one monomer is smaller than the second limited voltage, reducing the current density of the galvanic pile to 0A / cm < 2 >, and shutting down the galvanic pile. By optimizing the shutdown strategy, the adverse effect of high potential on the membrane electrode is effectively avoided, and the service life of the membrane electrode is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cells, and in particular relates to a shutdown strategy method, system and battery for a fuel cell stack. Background Art

[0002] The membrane electrode is the core of the proton exchange membrane fuel cell, and it involves multi-scale heat and mass transfer processes. During the operation of the fuel cell stack, the rated operating voltage of a single membrane electrode is approximately between 0.6 and 0.7V. However, during the testing and operation of the fuel cell stack, the membrane electrode will inevitably experience a high potential (single cell voltage> 0.85V) range. Being at a high potential for a long time will directly affect the efficiency and life of the membrane electrode.

[0003] Theoretically, the presence of high potential will accelerate the chemical degradation of the proton exchange membrane. Under high potential, the chemical groups in the proton exchange membrane (such as the -SO3H group in the perfluorosulfonic acid membrane) are more vulnerable to attack by free radicals (such as ·OH), which will cause the main chain of the proton exchange membrane to break and reduce the proton conductivity of the membrane. High potential will also cause the catalyst to oxidize or dissolve. Taking platinum (Pt) catalyst as an example, under high potential, the atoms on the surface of Pt will be oxidized into species such as Pt-O or Pt-OH. These species will occupy the active sites of the catalyst, thereby reducing the catalytic activity of the catalyst for oxygen reduction reactions. At the same time, high potential may also cause the dissolution of Pt, especially in an acidic environment, where Pt will dissolve as Pt 2+ The Pt in the catalyst layer is dissolved in the electrolyte in the form of Pt, which reduces the effective Pt content in the catalyst layer. High potential may also destroy the microstructure of the gas diffusion layer, which may cause corrosion or damage to the carbon fiber and change its porosity and pore size distribution. The reduction in porosity will increase the resistance to gas transmission, so that the gas cannot reach the catalyst layer in time for reaction, thereby reducing the power output of the battery.

[0004] High potential usually occurs during the startup and shutdown of the fuel cell stack, where the membrane electrode can quickly jump over the high potential interval due to the fast current response after startup. However, during the shutdown process, the current mainstream method is usually to directly purge with nitrogen after disconnecting the load or to use a small current discharge method to reduce the cell voltage to about 0.2V, which greatly prolongs the duration of the high potential during the shutdown process. In addition, the method of a small current discharge will also cause the voltage to repeat, and after the load is turned off, the voltage will tend to rise again. In the long run, the life of the membrane electrode will be seriously affected, and the performance may be severely degraded within a few hundred hours or even less, which cannot meet the needs of actual applications.

[0005] Therefore, in view of the above technical problems, it is necessary to provide a shutdown strategy method, system and battery for a fuel cell stack.

[0006] 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

[0007] The object of the present invention is to provide a shutdown strategy method, system and battery for a fuel cell stack.

[0008] In order to achieve the above object, a technical solution provided by a specific embodiment of the present invention is as follows:

[0009] Shutdown strategy method for fuel cell stack, including

[0010] (1) Reduce the current density of the fuel cell stack (the fuel cell stack is composed of a plurality of monomers) to a defined state before shutdown, and adjust the operating conditions of the fuel cell stack to match the current density;

[0011] (2) After the average voltage of the battery stack is stable, reduce the current density of the battery stack to 0.02A / cm 2 , while maintaining other operating conditions unchanged, switch the cathode gas to dry nitrogen at the same flow rate;

[0012] (3) Continuously monitor the voltage of each cell in the stack. When the voltage of one cell is lower than the first voltage limit, reduce the stack current density to 0.01A / cm 2 ;

[0013] (4) When the voltage of one of the cells is less than the second voltage limit, the stack current density is reduced to 0 A / cm 2 And shut down.

[0014] In one or more embodiments of the present invention, the load reduction in steps (1) and / or (3) and / or (4) satisfies: the current density reduction rate of the battery stack does not exceed 0.2A / cm 2 .

[0015] In one or more embodiments of the present invention, the operating conditions are at least selected from: cathode gas flow, anode gas flow, cathode inlet pressure, anode inlet pressure, cathode inlet temperature, anode inlet temperature, cathode inlet relative humidity, anode inlet relative humidity, circulating water inlet temperature and circulating water inlet and outlet temperature difference.

[0016] In one or more embodiments of the present invention, the current density in the defined state before shutdown satisfies: 0.1-0.2A / cm 2 .

[0017] In one or more embodiments of the present invention, the temperature of the dry nitrogen in step (2) is 30-50°C.

[0018] In one or more embodiments of the present invention, the first voltage limit in step (3) satisfies: 0.3-0.5V.

[0019] In one or more embodiments of the present invention, the second voltage limit in step (4) satisfies 0.05-0.3V.

[0020] In one or more embodiments of the present invention, the temperature of the circulating water entering the stack after the stack current density is reduced in step (2) should be between 30 and 50°C.

[0021] In one or more embodiments of the present invention, the shutdown system runs the aforementioned shutdown strategy method for the fuel cell stack.

[0022] In one or more embodiments of the present invention, a fuel cell includes a main body having a fuel cell stack and a shutdown system as described above for controlling connection to the main body.

[0023] Compared with the prior art, the shutdown strategy method, system and battery of the fuel cell stack of the present invention, by optimizing the shutdown strategy, effectively avoids the duration of high potential during the operation of the fuel cell stack, reduces its adverse effects on the membrane electrode, and generates a hydrogen pump effect during the shutdown process to help remove oxides on the catalyst surface, thereby increasing the service life of the membrane electrode.

[0024] Specifically, the technical solution of the present invention has the following advantages over the prior art:

[0025] (1) The method of the present invention avoids the phenomenon that the voltage rises to a high potential again in a single small current discharge method by discharging with a small current twice, thereby reducing the duration of the high potential during the shutdown process and improving the durability of the membrane electrode.

[0026] (2) The method described in the present invention uses anode humidified hydrogen and cathode dry nitrogen combined with two small current discharges to produce a hydrogen pump effect during the shutdown process, so that some hydrogen is produced on the cathode side to create a reducing environment. Combined with the low potential on the cathode side at this time, the surface oxide of the cathode catalyst is quickly removed, greatly improving the service life of the membrane electrode. 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 1is a current-average voltage curve of the fuel cell stack shutdown process in Example 1 of the present invention;

[0029] Figure 2 The current-average voltage curve of the fuel cell stack shutdown process in Example 2 of the present invention;

[0030] Figure 3 The current-average voltage curve of the fuel cell stack shutdown process in Example 3 of the present invention;

[0031] Figure 4 This is the current-average voltage curve during the shutdown of the fuel cell stack in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0032] 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.

[0033] In order to solve the above technical problems, the present invention provides a shutdown strategy for a fuel cell stack. Anode wet hydrogen and cathode dry nitrogen are used to reduce the cell voltage to below 0.4V through a primary discharge, and then reduce the cell voltage to below 0.15V through a secondary discharge, so as to control the duration of high potential during the shutdown process, and generate a hydrogen pump effect during the shutdown process to help remove oxides on the catalyst surface, thereby improving the durability of the membrane electrode.

[0034] The purpose of the present invention is to provide a shutdown strategy for a fuel cell stack, comprising the following steps:

[0035] (1) Before the shutdown process, reduce the current value of the battery stack to 0.05-0.25A / cm 2 The corresponding current is adjusted to 0.05~0.25A / cm 2 Corresponding working conditions;

[0036] (2) After the average voltage of the battery stack is stable, reduce the current of the battery stack to 0.015-0.025A / cm 2 Corresponding current, the gas flow rate on the anode side is maintained at 0.05~0.25A / cm 2 The cathode side gas is switched to dry nitrogen and maintained at 0.05-0.25A / cm 2 Corresponding to the cathode gas flow rate, the other conditions remain unchanged;

[0037] (3) When the minimum cell voltage is detected to be less than 0.3-0.5V, the stack current is reduced to 0.005-0.015A / cm 2 Corresponding to the current, the other conditions remain unchanged;

[0038] (4) When the minimum cell voltage is detected to be less than 0.05-0.3V, the stack current is reduced to 0A and the system is shut down.

[0039] In one embodiment of the present invention, in step (1), the current reduction rate does not exceed 0.2A / cm 2 Corresponding current per second, if the membrane electrode active area is 300cm 2 , the load reduction rate should not exceed 60A / s; 0.05~0.25A / cm 2 The corresponding operating conditions include cathode and cathode gas flow rates, cathode and cathode inlet pressures, cathode and cathode inlet temperatures, cathode and cathode inlet relative humidity, circulating water inlet temperature, and circulating water inlet and outlet temperature differences. Specifically, the cathode gas stoichiometric ratio is 3-5, the anode gas stoichiometric ratio is 2-4, the cathode inlet pressure is 20-40 kPa, the anode gas inlet pressure is 30-50 kPa, the cathode gas inlet temperature is 30-50°C, the anode gas inlet temperature is 30-50°C, the cathode gas relative humidity is 30-50%, the anode gas relative humidity is 30-50%, the circulating water inlet temperature is 30-50°C, and the circulating water inlet and outlet temperature difference is 3-5°C. More preferably, the current value should be reduced to 0.1-0.2 A / cm 2 Corresponding current.

[0040] In one embodiment of the present invention, in step (2), the current load reduction rate does not exceed 20A / s; the gas on the anode side is pure hydrogen and humidified hydrogen. More preferably, the hydrogen inlet temperature should be between 30 and 50°C, and the relative humidity of hydrogen should be between 30 and 50%; after the cathode side gas is switched to dry nitrogen, it does not need to pass through the humidification tank to ensure that it remains dry nitrogen before entering; more preferably, the dry nitrogen inlet temperature should be between 30 and 50°C; the other conditions remain unchanged, including the anode and cathode gas flow rate, the anode and cathode inlet pressure, the anode and cathode inlet temperature, the anode and cathode inlet relative humidity, the circulating water inlet temperature and the circulating water inlet and outlet temperature difference. More preferably, the circulating water inlet temperature should be between 30 and 50°C.

[0041] In one embodiment of the present invention, in step (3), when the minimum cell voltage is monitored to be less than 0.3-0.5V, more preferably, the minimum cell voltage should be between 0.35-0.45V; the current load reduction rate does not exceed 20A / s; and the other conditions remain unchanged, including the anode and cathode gas flow rates, the anode and cathode inlet pressures, the anode and cathode inlet temperatures, the anode and cathode inlet relative humidity, the circulating water inlet temperature, and the circulating water inlet and outlet temperature differences.

[0042] In one embodiment of the present invention, in step (4), when the minimum cell voltage is monitored to be less than 0.05-0.3V, more preferably, the minimum cell voltage should be 0.1-0.2V; the current load reduction rate does not exceed 20A / s; the shutdown includes shutting down all electronic loads, anode and cathode gas flow rates, anode and cathode inlet pressures, anode and cathode inlet temperatures, anode and cathode inlet relative humidity, circulating water inlet temperature, and circulating water inlet and outlet temperature differences.

[0043] Example 1

[0044] A shutdown strategy for a fuel cell stack specifically comprises the following steps:

[0045] A short stack of 20 fuel cells was selected for the test, with a membrane electrode active area of ​​300 cm 2 Before the test, the short stack was subjected to air tightness test and activation test. After the activation was completed, the short stack was loaded to 300A and operated stably for 30 minutes, and then discharged with a small current.

[0046] (1) Reduce the short stack load from 300A to 0.1A / cm 2 The corresponding current is 30A, and the load reduction rate is 20A / s. After the current stabilizes, the conditions are adjusted to the operating conditions corresponding to 30A. The specific operating conditions are shown in Table 1.

[0047] (2) After the average voltage stabilizes, the current is reduced from 30 A to 6 A at a rate of 20 A / s. The gas flow rate on the anode side remains at 15 L / min, and the gas on the cathode side is switched to 30 °C dry nitrogen, and the dry nitrogen flow rate is set to 50 L / min. The circulating water inlet temperature is 30 °C, and the other conditions remain unchanged.

[0048] (3) When the minimum cell voltage is detected to be less than 0.3 V, the current is reduced to 3 A at a rate of 20 A / s, and the other conditions remain unchanged;

[0049] (4) When the minimum cell voltage is detected to be less than 0.15V, the current is reduced to 0A and the machine is shut down.

[0050] The current-average voltage curve during low current discharge is as follows Figure 1 As shown in the figure, the early stage of average voltage stability is the 90s process after the short stack 30A constant current operation, and the average voltage is stable at 0.837V. After the short stack starts to reduce the load, the average voltage first rises and then decreases. During this period, the average voltage is greater than 0.85V for about 12s. When the lowest single cell voltage is monitored to be less than 0.3V, the current is further reduced to 3A. At this time, the average voltage begins to rise, but it does not exceed 0.85V and then continues to decline. When the lowest single cell voltage is monitored to be less than 0.15V, the current is reduced to 0A and shut down. At this time, the average voltage rises slightly and gradually decreases to close to 0V.

[0051] It can be seen from the above that during the shutdown process, two small current discharges greatly shortened the duration of the high potential, and the high potential only existed for about 12 seconds.

[0052] Example 2

[0053] A shutdown strategy for a fuel cell stack specifically comprises the following steps:

[0054] A short stack of 20 fuel cells was selected for the test, with a membrane electrode active area of ​​380cm 2 Before the test, the short stack was subjected to air tightness test and activation test. After the activation was completed, the short stack was loaded to 380A and operated stably for 20 minutes, and then discharged with a small current.

[0055] (1) Reduce the short stack load from 380A to 0.2A / cm 2 The corresponding current is 76A, and the load reduction rate is 20A / s. After the current stabilizes, the conditions are adjusted to the operating conditions corresponding to 76A. The specific operating conditions are shown in Table 2.

[0056] (2) After the average voltage stabilizes, the current is reduced from 76A to 7.6A at a rate of 20A / s. The gas flow rate on the anode side remains at 20L / min, and the gas on the cathode side is switched to 50°C dry nitrogen, and the dry nitrogen flow rate is set to 80L / min. The circulating water inlet temperature is 40°C, and the other conditions remain unchanged.

[0057] (3) When the minimum cell voltage is detected to be less than 0.4 V, the current is reduced to 3.8 A at a rate of 20 A / s, and the other conditions remain unchanged;

[0058] (4) When the minimum cell voltage is detected to be less than 0.3V, the current is reduced to 0A and the machine is shut down.

[0059] The current-average voltage curve during low current discharge is as follows Figure 2 As shown in the figure, the early stage of average voltage stability is the 60s process after the short stack 76A constant current operation, and the average voltage is stable at 0.820V. After the short stack starts to reduce the load, the average voltage first rises and then decreases. During this period, the average voltage is greater than 0.85V for about 14s. When the lowest single cell voltage is monitored to be less than 0.4V, the current is further reduced to 5A. At this time, the average voltage begins to rise, but it does not exceed 0.85V and then continues to decline. When the lowest single cell voltage is monitored to be less than 0.3V, the current is reduced to 0A and shut down. At this time, the average voltage rises slightly and gradually decreases to close to 0V.

[0060] It can be seen from the above that during the shutdown process, two small current discharges greatly shortened the duration of the high potential, and the high potential only existed for about 14 seconds.

[0061] Example 3

[0062] A shutdown strategy for a fuel cell stack specifically comprises the following steps:

[0063] A short stack of 20 fuel cells was selected for the test, with a membrane electrode active area of ​​300 cm 2 Before the test, the short stack was subjected to air tightness test and activation test. After the activation was completed, the short stack was loaded to 300A and operated stably for 30 minutes, and then discharged with a small current.

[0064] (1) Reduce the short stack load from 300A to 0.15A / cm 2 The corresponding current is 45A, and the load reduction rate is 20A / s. After the current stabilizes, the conditions are adjusted to the operating conditions corresponding to 45A. The specific operating conditions are shown in Table 3.

[0065] (2) After the average voltage stabilizes, the current is reduced from 45A to 6A at a rate of 20A / s. The gas flow rate on the anode side remains at 18L / min, and the gas on the cathode side is switched to 35°C dry nitrogen, and the dry nitrogen flow rate is set to 75L / min. The circulating water inlet temperature is 50°C, and the other conditions remain unchanged.

[0066] (3) When the minimum cell voltage is detected to be less than 0.5 V, the current is reduced to 3 A at a rate of 20 A / s, and the other conditions remain unchanged;

[0067] (4) When the minimum cell voltage is detected to be less than 0.05V, the current is reduced to 0A and the machine is shut down.

[0068] The current-average voltage curve during low current discharge is as follows Figure 3 As shown in the figure, the early stage of average voltage stability is the 50s process after the short stack 45A constant current operation, and the average voltage is stable at 0.835V. After the short stack starts to reduce the load, the average voltage first rises and then decreases. During this period, the average voltage is greater than 0.85V for about 16s. When the lowest single cell voltage is monitored to be less than 0.35V, the current is further reduced to 3A. At this time, the average voltage begins to rise, but it does not exceed 0.85V and then continues to decline. When the lowest single cell voltage is monitored to be less than 0.15V, the current is reduced to 0A and shut down. At this time, the average voltage rises slightly and gradually decreases to close to 0V.

[0069] It can be seen from the above that during the shutdown process, two small current discharges greatly shortened the duration of the high potential, and the high potential only existed for about 16 seconds.

[0070] Comparative Example 1

[0071] The process is basically the same as Example 1, except that step (3) is not performed.

[0072] The current-average voltage curve during low current discharge is as follows Figure 3 As shown, the early average voltage stable stage is the 90s process after the short stack 300A constant current operation, the average voltage is stable at 0.836V, after the short stack starts to reduce the load, the average voltage first rises and then decreases, during which the average voltage is greater than 0.85V for about 12s. When the lowest single cell voltage is monitored to be less than 0.15V, the current is reduced to 0 and shut down. At this time, the average voltage is observed to rise rapidly, exceeding 0.85V in a short time and maintaining for 35s. Therefore, the high potential cumulative time during the shutdown process is 47s, which is 3.92 times that of Example 1.

[0073] Table 1 shows the corresponding operating conditions at 30A current point in Example 1;

[0074] <![CDATA[Current density A / cm 2 > 0.1 Anode gas flow rate L / min 15 Cathode gas flow rate L / min 50 Anode inlet pressure kPa 40 Cathode inlet pressure kPa 30 Anode inlet temperature ℃ 40 Cathode inlet temperature ℃ 40 Anode gas relative humidity % 40 Cathode inlet relative humidity % 40 Circulating water inlet temperature℃ 40 Temperature difference of circulating water in and out of the reactor ℃ 3

[0075] Table 2 shows the corresponding working conditions at 76A current point in Example 2

[0076]

[0077]

[0078] Table 3 shows the corresponding operating conditions at 45A current point in Example 3

[0079] <![CDATA[Current density A / cm 2 > 0.15 Anode gas flow rate L / min 18 Cathode gas flow rate L / min 75 Anode inlet pressure kPa 50 Cathode inlet pressure kPa 40 Anode inlet temperature ℃ 35 Cathode inlet temperature ℃ 35 Anode gas relative humidity % 35 Cathode inlet relative humidity % 35 Circulating water inlet temperature℃ 35 Temperature difference of circulating water in and out of the reactor ℃ 3

[0080] 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.

[0081] 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 shutdown strategy method for a fuel cell stack, comprising: (1) reducing the current density of the fuel cell stack to a limited state before shutdown, and adjusting the operating conditions of the fuel cell stack to match the current density; (2) After the average voltage of the battery stack is stable, reduce the current density of the battery stack to 0.02A / cm 2 , Under the premise of maintaining other operating conditions unchanged, switch the cathode gas to dry nitrogen at the same flow rate; (3) Continuously monitor the voltage of each cell in the stack. When the voltage of one cell is lower than the first voltage limit, reduce the stack current density to 0.01A / cm 2 ; (4) When the voltage of one of the cells is less than the second voltage limit, the stack current density is reduced to 0 A / cm 2 And shut down.

2. The shutdown strategy method for a fuel cell stack according to claim 1, characterized in that: The load reduction in steps (1) and / or (3) and / or (4) satisfies: the current density reduction rate of the battery stack does not exceed 0.2A / cm 2 .

3. The shutdown strategy method for a fuel cell stack according to claim 1, characterized in that: The operating conditions are at least selected from: cathode gas flow, anode gas flow, cathode inlet pressure, anode inlet pressure, cathode inlet temperature, anode inlet temperature, cathode inlet relative humidity, anode inlet relative humidity, circulating water inlet temperature and circulating water inlet and outlet temperature difference.

4. The shutdown strategy method for a fuel cell stack according to claim 1, characterized in that: The current density of the limited state before shutdown meets the following requirements: 0.1-0.2A / cm 2 .

5. The shutdown strategy method for a fuel cell stack according to claim 1, characterized in that: The temperature of the dry nitrogen in step (2) is 30-50°C.

6. The shutdown strategy method for a fuel cell stack according to claim 1, characterized in that: In step (3), the first voltage limit satisfies: 0.3-0.5V.

7. The shutdown strategy method for a fuel cell stack according to claim 1, characterized in that: In step (4), the second voltage limit satisfies 0.05-0.3V.

8. The shutdown strategy method for a fuel cell stack according to claim 1, characterized in that: After the stack current density is reduced in step (2), the temperature of the circulating water entering the stack should be between 30 and 50°C.

9. A shutdown system that runs the shutdown strategy method for a fuel cell stack according to any one of claims 1 to 8.

10. A fuel cell comprising a main body having a fuel cell stack and a shutdown system according to claim 9 provided for controlling the connection of the main body.

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