A system and method for restoring performance during fuel cell operation

Abstract

The present invention discloses a system and method for recovering performance during operation of a fuel cell, and belongs to the technical field of proton exchange membrane fuel cells. The present invention includes a fuel cell, wherein a cathode tail exhaust interface is provided on the fuel cell, wherein the cathode tail exhaust interface is connected to a second three-way valve in sequence through a water divider, a first three-way valve and a back pressure valve, wherein one side of the first three-way valve is connected to the second three-way valve through a normally closed solenoid valve, wherein the normally closed solenoid valve is electrically connected to a voltage inspection device in sequence through a pulse controller and an ECU controller, and the voltage inspection device is connected to the fuel cell. The present invention enables the fuel cell to quickly recover the performance degradation caused by reversible attenuation during operation, realizes long-term high-efficiency operation of the fuel cell, and can significantly enhance the durability of the fuel cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of proton exchange membrane fuel cells, and in particular relates to a system and method for recovering the performance of a fuel cell during operation. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) are one of the most promising energy conversion devices due to their high efficiency, high power density, and environmental friendliness. PEMFCs can significantly reduce carbon emissions while producing clean electricity. However, poor durability is one of the main obstacles that limits the commercialization of PEMFCs.

[0003] As the operation time of proton exchange membrane fuel cells increases, their performance will continue to decline. There are many mechanisms that lead to battery performance degradation, such as the growth, agglomeration, and dissolution of Pt catalysts; pinholes and cracks caused by mechanical stress caused by free radical attacks on PEM and changes in humidity / heat during operation; catalyst separation caused by corrosion of carbon carriers, failure of the three-phase reaction interface, and collapse of mass transfer channels. The attenuation mechanisms of these materials are irreversible. However, there are also some mechanisms that cause reversible attenuation of battery performance, such as the formation of an oxide film on the surface of the Pt catalyst; pollutants (such as H2S, SO2, NO x and CO, etc.) to poison the catalyst; impurities (such as membrane / ionomer degradation products, metal cations Na + , Fe 3+ The reversible attenuation mechanism can be timely restored through some specific operation strategies, thus alleviating the attenuation of the battery, extending the battery life and enhancing the durability.

[0004] After searching the existing technical literature, it was found that some existing performance recovery methods for fuel cells have problems such as cumbersome operation, low recovery efficiency, and poor economy. In addition, most of the existing recovery technologies that use the cathode "oxygen starvation" principle require interrupting the normal operation of the battery. In practical applications, frequent start / stop will cause serious degradation of battery performance. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method and system for restoring the performance of a fuel cell during operation, so as to overcome the defects of the prior art proton exchange membrane fuel cell performance recovery method, such as cumbersome operation, low recovery efficiency and interruption of battery operation.

[0006] The present invention provides a performance recovery system during fuel cell operation, comprising a fuel cell, wherein a cathode tail exhaust interface is provided on the fuel cell, wherein the cathode tail exhaust interface is connected to a second three-way valve in sequence through a water divider, a first three-way valve and a back pressure valve, wherein one side of the first three-way valve is connected to the second three-way valve through a normally closed solenoid valve, wherein the normally closed solenoid valve is electrically connected to a voltage patrol device in sequence through a pulse controller and an ECU controller, and the voltage patrol device is connected to the fuel cell.

[0007] The present invention also provides a recovery method using the above system, comprising the following steps:

[0008] Step 1: Adjust the operating temperature of the fuel cell to 25-60°C, adjust the back pressure of the cathode and anode of the fuel cell to the same value, both 0.5-2 bar, adjust the stoichiometric ratio of the cathode to 1-2.5, and adjust the load value to 800-2500 mA cm -2 ;

[0009] Step 2, when the voltage of the fuel cell is stable, the pulse controller discharges the cathode tail gas in a pulsed manner; the pulsed discharge of the cathode tail gas is to artificially force a gas shortage and create oxygen starvation;

[0010] Step 3, during the exhaust gas discharge, the voltage inspection device monitors the voltage of the fuel cell; if the voltage of the fuel cell is lower than the safe value, the ECU controller can control the pulse controller to reduce the pulse width and extend the cycle interval to protect the battery and avoid damage to the fuel cell component materials;

[0011] Step 4, stopping the pulsed exhaust gas discharge, testing the battery performance, and then repeating steps 2 and 3 until the battery performance remains unchanged;

[0012] Step 5, the recovery operation ends and the fuel cell is adjusted to normal operating parameters.

[0013] In step 1 of the above method, based on the operation of the fuel cell, only the four parameters need to be adjusted, and the other parameters can be kept consistent with those during the operation of the fuel cell.

[0014] During the entire battery operation phase (before, after and during the recovery operation), exhaust gas is discharged normally. During the recovery phase, pulse exhaust is performed on the branch line in addition to the normal exhaust of the battery. After the recovery operation is completed, pulse exhaust is stopped and the battery is exhausted as usual.

[0015] Furthermore, the relative humidity in step 1 is over-humidification.

[0016] Furthermore, in step 2, the pulse width is 0.01 to 3 s, and the pulse cycle interval is 2 to 40 s.

[0017] Furthermore, the duration of the pulsed emission of the exhaust gas in step 2 is 10 to 60 minutes.

[0018] Furthermore, when the tail gas is discharged in a pulsed manner in step 2, the back pressure on the cathode side is 10 to 60 kPa lower than the back pressure on the anode side.

[0019] Furthermore, in step 3, the voltage safety value of the fuel cell is 0.1 to 0.25V.

[0020] The technical solution provided by the present invention has the following advantages:

[0021] (1) The recovery method provided in the present application significantly restores the performance of the fuel cell. The cathode tail gas is discharged by pulse in step 2 to artificially force the gas shortage, and the gas shortage is increased in combination with step 1 to increase the load value and reduce the cathode stoichiometric ratio. The two together create "oxygen starvation" and cause a hydrogen evolution reaction. The cathode potential drops due to the gas shortage, and the back pressure on the cathode and anode sides increased in step 1. During the pulse exhaust, the hydrogen on the anode side penetrates into the cathode side under the action of the pressure difference. The three work together to accelerate the reduction of platinum oxide, and the performance recovery efficiency is higher and the recovery effect is better. In addition, the decrease in cathode potential due to gas shortage will remove some impurities or pollutants (such as SO4 2- ) is desorbed from the surface of the platinum catalyst. The operating temperature of the fuel cell is lowered by step 1, and the relative humidity of the feed gas is increased to over-humidification. The desorbed impurities or pollutants will be discharged from the battery along with the water carried by the cathode feed gas and the product water, resulting in an accelerated ORR reaction kinetic rate and a more complete performance recovery. At the same time, the hydrophilic oxygen-containing groups produced by the oxidation of the carbon support cause the hydrophobicity of the mass transfer channel to decrease, and will also be reduced in the presence of low cathode potential and hydrogen, making the mass transfer smoother. Finally, during the pulsed discharge of the cathode exhaust gas, the liquid water that originally accumulated in the flow channel to block the mass transfer channel or occupy the catalyst surface will be discharged, reducing the mass transfer resistance, so that the battery also shows significant performance recovery under large load values.

[0022] (2) The recovery method provided in the present application can be used for recovery during the operation of the fuel cell. Compared with existing recovery technologies, this method does not require interruption of battery operation, thus avoiding irreversible performance loss caused by frequent start / stop of the battery. Compared with existing technologies that use the "oxygen starvation" principle to restore fuel cell performance, this method can simultaneously generate multiple reduction modes, with higher recovery efficiency and more significant effects. In addition, the recovery method can recover performance degradation caused by multiple reversible attenuations, and has a wide range of applicability. The method of the present application provides an efficient, practical and economical performance recovery strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1FIG. 1 is a schematic diagram of the structure of a system in one embodiment of the present invention.

[0024] Figure 2 The figure is a flow chart of a method in one embodiment of the present invention.

[0025] Figure 3 This is a comparison diagram of the polarization curves of the fuel cell after activation, attenuation and recovery of Example 1 of the present invention.

[0026] Figure 4 This is a comparison chart of the EIS of the fuel cell after activation, attenuation and recovery of Example 1 of the present invention.

[0027] In the figure, 1. fuel cell; 2. cathode tail exhaust interface; 3. water distributor; 4. first three-way valve; 5. back pressure valve; 6. second three-way valve; 7. normally closed solenoid valve; 8. pulse controller; 9. voltage inspection device; 10. ECU controller. DETAILED DESCRIPTION

[0028] In order to make the technical personnel in the field of this invention understand the scheme and advantages of the present invention more clearly, the technical scheme in the embodiment of the present invention is described in detail below in conjunction with the drawings in the examples of the present invention. The specific embodiments described here are only used to explain the present invention and do not limit the present invention or its application.

[0029] refer to Figure 1 A fuel cell performance recovery system during operation includes a fuel cell 1. The fuel cell 1 is provided with a cathode tail exhaust interface 2. The cathode tail exhaust interface 2 is connected to a second three-way valve 6 through a water divider 3, a first three-way valve 4 and a back pressure valve 5 in sequence. One side of the first three-way valve 4 is connected to the second three-way valve 6 through a normally closed solenoid valve 7. The normally closed solenoid valve 7 is electrically connected to a voltage inspection device 9 through a pulse controller 8 and an ECU controller 10 in sequence. The voltage inspection device 9 is connected to the fuel cell 1.

[0030] refer to Figure 2 A method for restoring performance of a fuel cell during operation is provided, comprising the following steps:

[0031] Step 1: Adjust the operating temperature of the fuel cell 1 to 25-60°C, adjust the back pressure of the cathode and anode of the fuel cell 1 to the same value, both 0.5-2 bar, adjust the stoichiometric ratio of the cathode to 1-2.5, and adjust the load value to 800-2500 mA cm -2 ;

[0032] Step 2: When the voltage of the fuel cell 1 is stable, the pulse controller 8 discharges the cathode tail gas in a pulsed manner to artificially create oxygen starvation.

[0033] Step 3, during the exhaust gas discharge, the voltage inspection device 9 monitors the voltage of the fuel cell 1; if the voltage of the fuel cell 1 is lower than the safe value, the ECU controller 10 can control the pulse controller 8 to reduce the pulse width and extend the cycle interval to protect the battery;

[0034] Step 4, stop the pulse exhaust gas emission, test the battery performance, and then repeat steps 2 and 3 until the battery performance remains unchanged;

[0035] Step 5: The recovery operation is completed and the fuel cell 1 is adjusted to normal operating parameters.

[0036] In a specific embodiment, the relative humidity in step 1 is over-humidified.

[0037] In a specific embodiment, in step 2, the pulse width is 0.01 to 3 s, and the pulse cycle interval is 2 to 40 s.

[0038] In a specific embodiment, the duration of the pulsed exhaust gas emission in step 2 is 10 to 60 minutes.

[0039] In a specific embodiment, when the exhaust gas is discharged in a pulsed manner in step 2, the back pressure on the cathode side is 10 to 60 kPa lower than the back pressure on the anode side.

[0040] In a specific embodiment, the voltage safety value of the fuel cell 1 in step 3 is 0.1-0.25V.

[0041] In the following embodiments, a proton exchange membrane fuel cell single cell is used to implement the method of the present invention, and polarization curve and EIS characterization tests are performed on the single cell.

[0042] Example 1

[0043] Step 1: During the operation of the battery, the operating temperature of the fuel cell 1 is adjusted to 50°C, the back pressure on both sides of the cathode and the anode is adjusted to 1.5 bar, the cathode stoichiometric ratio is adjusted to 2, the relative humidity of the reaction gas is 120%, and the load value is adjusted to 1400 mA cm -2 , then run at constant current for 20 min;

[0044] Step 2, when the battery voltage reaches stability, set the pulse width to 0.03s and the pulse cycle interval to 15s on the pulse controller 8, and then pulse-emit cathode tail gas for 30 minutes, artificially forcing gas shortage to create "oxygen starvation".

[0045] Step 3: During the pulse emission of cathode tail gas, the voltage inspection device 9 continuously monitors the battery voltage. If the battery voltage is lower than 0.15V, the ECU controller 10 will reduce the pulse width and extend the cycle interval to protect the battery;

[0046] Step 4, after the pulse emission of cathode tail gas reaches a second predetermined time, the battery performance is tested, and then steps 2 and 3 are repeated until the battery performance no longer increases;

[0047] Step 5: The recovery operation is completed, the fuel cell operating parameters are called back, and external work continues.

[0048] Figure 1 This is a schematic diagram of the performance recovery system structure of this embodiment 1. The cathode tail exhaust during the operation of the fuel cell device 1 is discharged through the cathode tail exhaust interface 2. The cathode tail exhaust passes through the water divider 3 and is discharged in two ways under the action of the first three-way valve 4. One way passes through the back pressure valve 5, and then passes through the second three-way valve 6 to be discharged into the atmosphere, and the other way passes through the normally closed solenoid valve 7, and then passes through the second three-way valve 6 to be discharged into the atmosphere. After setting the pulse width and pulse cycle interval, the pulse controller 8 controls the operation of the normally closed solenoid valve 7. During the pulse discharge of the cathode tail gas, the voltage patrol device 9 detects the voltage value of the single cell, and its voltage signal can be transmitted to the ECU controller 10. If the voltage value is detected to be lower than 0.1V, the ECU controller 10 will issue an instruction to the pulse controller 8 to reduce the pulse width and extend the cycle interval to protect the battery.

[0049] Figure 3 This is a graph showing the performance recovery of the fuel cell in Example 1. It can be seen that after 72 hours of accelerated stress test (AST), the single cell has severe performance degradation. However, under the pulse recovery conditions of Example 1, the single cell has significant performance recovery in the full power density region.

[0050] Figure 4 The fuel cell in Example 1 is 1A·cm -2 From the EIS graphs measured below, it can be seen that after each 24h accelerated stress test, both the charge transfer impedance and the mass transfer impedance increased significantly. This phenomenon corresponds to Figure 3 In the embodiment 1, the battery performance decayed after every 24h accelerated stress test. Under the pulse recovery conditions of Example 1, the charge transfer impedance and mass transfer were significantly reduced, which explains the reason for the recovery of battery performance.

[0051] It can be seen from this example that pulse recovery restores the activity of the platinum catalyst and the mass transfer capacity of the battery. It has been proven that the present invention can significantly restore the performance degradation caused by reversible attenuation during the operation of the fuel cell, increase the output power of the fuel cell, and enhance the durability of the fuel cell.

[0052] Example 2

[0053] Step 1: During the battery operation, the operating temperature of the battery was adjusted to 50°C, the back pressure on both sides of the cathode and the anode was adjusted to 1 bar, the cathode stoichiometric ratio was adjusted to 2, the relative humidity of the reaction gas was adjusted to 120%, and the load value was adjusted to 1600 mA cm -2 , then run at constant current for 20 min;

[0054] Step 2, when the battery voltage reaches stability, set the pulse width to 0.02s and the pulse cycle interval to 12s on the pulse controller 8, and then pulse-emit cathode tail gas for 40 minutes, artificially forcing gas shortage to create "oxygen starvation".

[0055] Step 3: During the pulse emission of cathode tail gas, the voltage inspection device 9 continuously monitors the battery voltage. If the battery voltage is lower than 0.15V, the ECU controller 10 will reduce the pulse width and extend the cycle interval to protect the battery;

[0056] Step 4, after the pulse emission of cathode tail gas reaches a second predetermined time, the battery performance is tested, and then steps 2 and 3 are repeated until the battery performance no longer increases;

[0057] Step 5: The recovery operation is completed, the fuel cell operating parameters are called back, and external work continues.

[0058] The effect of this embodiment is the same as that of embodiment 1.

[0059] Example 3

[0060] Step 1: During the battery operation, the operating temperature of the battery was adjusted to 50°C, the back pressure on both sides of the cathode and the anode was adjusted to 1.5 bar, the cathode stoichiometric ratio was adjusted to 2, the relative humidity of the reaction gas was 120%, and the load value was adjusted to 1200 mA cm -2 , then run at constant current for 20 min;

[0061] Step 2: When the battery voltage reaches stability, set the pulse width to 0.05s and the pulse cycle interval to 18s on the pulse controller, then pulse-emit cathode exhaust gas for 25 minutes, artificially forcing gas shortage to create "oxygen starvation".

[0062] Step 3: During the pulse emission of cathode tail gas, the voltage inspection device 9 continuously monitors the battery voltage. If the battery voltage is lower than 0.15V, the ECU controller 10 will reduce the pulse width and extend the cycle interval to protect the battery;

[0063] Step 4, after the pulse emission of cathode tail gas reaches a second predetermined time, the battery performance is tested, and then steps 2 and 3 are repeated until the battery performance no longer increases;

[0064] Step 5: The recovery operation is completed, the fuel cell operating parameters are called back, and external work continues.

[0065] The effect of this embodiment is the same as that of embodiment 1.

[0066] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A fuel cell performance recovery system during operation, characterized in that: The invention comprises a fuel cell (1), wherein the fuel cell (1) is provided with a cathode tail exhaust interface (2), wherein the cathode tail exhaust interface (2) is connected to a second three-way valve (6) in sequence through a water distributor (3), a first three-way valve (4) and a back pressure valve (5), wherein one side of the first three-way valve (4) is connected to the second three-way valve (6) through a normally closed electromagnetic valve (7), wherein the normally closed electromagnetic valve (7) is electrically connected to a voltage inspection device (9) in sequence through a pulse controller (8) and an ECU controller (10), and wherein the voltage inspection device (9) is connected to the fuel cell (1); The method of using the system comprises the following steps: Step 1, adjusting the operating temperature of the fuel cell (1) to 25-60° C., adjusting the back pressure of the cathode and anode of the fuel cell (1) to the same value, both 0.5-2 bar, adjusting the stoichiometric ratio of the cathode to 1-2.5, and adjusting the load value to 800-2500 mA cm -2 , the relative humidity of the feed gas is over-humidified; Step 2, when the voltage of the fuel cell (1) is stabilized, the pulse controller (8) discharges the tail gas of the cathode in a pulsed manner; Step 3, during the exhaust gas discharge, the voltage inspection device (9) monitors the voltage of the fuel cell (1); if the voltage of the fuel cell (1) is lower than a safe value, the ECU controller (10) can control the pulse controller (8) to reduce the pulse width and extend the cycle interval to protect the battery; Step 4, stopping the pulsed exhaust gas discharge, testing the battery performance, and then repeating steps 2 and 3 until the battery performance remains unchanged; Step 5, the recovery operation is completed and the fuel cell (1) is adjusted to normal operating parameters.

2. A fuel cell performance recovery system during operation according to claim 1, characterized in that: The pulse width in step 2 is 0.01 to 3 s, and the pulse cycle interval is 2 to 40 s.

3. A fuel cell performance recovery system during operation according to claim 1, characterized in that: The duration of the pulsed exhaust gas emission in step 2 is 10 to 60 minutes.

4. A fuel cell performance recovery system during operation according to claim 1, characterized in that: When the tail gas is discharged in pulse mode in step 2, the back pressure on the cathode side is 10-60 kPa lower than the back pressure on the anode side.

5. A fuel cell performance recovery system during operation according to claim 1, characterized in that: The voltage safety value of the fuel cell (1) in step 3 is 0.1 to 0.25V.

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